LTC6404 600MHz, Low Noise, High Precision Fully Differential Input/Output Amplifier/Driver FEATURES
n n n
DESCRIPTION
The LTC®6404 is a family of AC precision, very low noise, low distortion, fully differential input/output amplifiers optimized for 3V, single supply operation. The LTC6404-1 is unity-gain stable. The LTC6404-2 is designed for closed-loop gains greater than or equal to 2V/V. The LTC6404-4 is designed for closed-loop gains greater than or equal to 4V/V. The LTC6404 closed-loop bandwidth extends from DC to 600MHz. In addition to the normal unfiltered outputs (OUT+ and OUT–), the LTC6404 has a built-in 88.5MHz differential single-pole lowpass filter and an additional pair of filtered outputs (OUTF+, OUTF–). An input referred voltage noise of 1.5nV/√Hz make the LTC6404 able to drive state-of-the-art 16-/18-bit ADCs while operating on the same supply voltage, saving system cost and power. The LTC6404 is characterized, and maintains its performance for supplies as low as 2.7V and can operate on supplies up to 5.25V. It draws only 27.3mA, and has a hardware shutdown feature which reduces current consumption to 250μA. The LTC6404 family is available in a compact 3mm × 3mm 16-pin leadless QFN package and operates over a –40°C to 125°C temperature range.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
n n n n n n n n n
Fully Differential Input and Output Low Noise: 1.5nV/√Hz RTI Very Low Distortion: LTC6404-1 (2VP-P , 10MHz): –91dBc LTC6404-2 (2VP-P , 10MHz): –96dBc LTC6404-4 (2VP-P , 10MHz): –101dBc Closed-Loop –3dB Bandwidth: 600MHz Slew Rate: 1200V/μs (LTC6404-4) Adjustable Output Common Mode Voltage Rail-to-Rail Output Swing Input Range Extends to Ground Large Output Current: 85mA (Typ) DC Voltage Offset < 2mV (Max) Low Power Shutdown Tiny 3mm × 3mm × 0.75mm 16-Pin QFN Package
APPLICATIONS
n n n n
Differential Input A/D Converter Driver Single-Ended to Differential Conversion/Amplification Common Mode Level Translation Low Voltage, Low Noise, Signal Processing
TYPICAL APPLICATION
Single-Ended Input to Differential Output with Common Mode Level Shifting
0.5VP-P 0V VS
LTC6404-4 Distortion vs Frequency
–40 –50 –60 HD2, HD3 (dBc) VCM = VOCM = MID-SUPPLY VS = 3V VOUT = 2VP-P RI = 100Ω, RF = 402Ω DIFFERENTIAL INPUT SINGLE-ENDED INPUT
50Ω
100Ω 71.5Ω
402Ω 3V 0.1μF 1VP-P
–70 –80 –90 HD2 –100 –110 –120 –130 0.1 HD3 HD2
SIGNAL GENERATOR 1.5VDC 0.1μF 130Ω
+
VOCM
1.5VDC
–
402Ω 1VP-P
6404 TA01
1.5VDC
HD3 1 10 FREQUENCY (MHz) 100
64044 G16
6404f
1
LTC6404 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW OUTF– 12 V– 17 11 V+ 10 V+ 9 5 NC 6 IN– 7 OUT+ 8 OUTF+ V– OUT– IN+ NC SHDN V+ V– VOCM 1 2 3 4
Total Supply Voltage (V+ to V–) ................................5.5V Input Voltage: IN+, IN–, VOCM, SHDN (Note 2) ...................... V+ to V– Input Current: IN+, IN–, VOCM, SHDN (Note 2) ........................±10mA Output Short-Circuit Duration (Note 3) ............ Indefinite Output Current (Continuous): (OUTF+, OUTF–) DC + ACRMS ...........................±40mA Operating Temperature Range (Note 4).. –40°C to 125°C Specified Temperature Range (Note 5) .. –40°C to 125°C Junction Temperature ........................................... 150°C Storage Temperature Range................... –65°C to 150°C
16 15 14 13
UD PACKAGE 16-LEAD (3mm 3mm) PLASTIC QFN TJMAX = 150°C, θJA = 68°C/W, θJC = 4.2°C/W EXPOSED PAD (PIN 17) IS V–, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC6404CUD-1#PBF LTC6404IUD-1#PBF LTC6404HUD-1#PBF LTC6404CUD-2#PBF LTC6404IUD-2#PBF LTC6404HUD-2#PBF LTC6404CUD-4#PBF LTC6404IUD-4#PBF LTC6404HUD-4#PBF TAPE AND REEL LTC6404CUD-1#TRPBF LTC6404IUD-1#TRPBF LTC6404HUD-1#TRPBF LTC6404CUD-2#TRPBF LTC6404IUD-2#TRPBF LTC6404HUD-2#TRPBF LTC6404CUD-4#TRPBF LTC6404IUD-4#TRPBF LTC6404HUD-4#TRPBF PART MARKING* LCLW LCLW LCLW LCLX LCLX LCLX LCLY LCLY LCLY PACKAGE DESCRIPTION 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN 16-Lead (3mm × 3mm) Plastic QFN SPECIFIED TEMPERATURE RANGE 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C 0°C to 70°C –40°C to 85°C –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
6404f
2
LTC6404 LTC6404 DC ELECTRICAL CHARACTERISTICS +The l d–enotes the specifications which apply over
the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RL = OPEN, RBAL = 100k (See Figure 1). For the LTC6404-1: RI = 100Ω, RF = 100Ω. For the LTC6404-2: RI = 100Ω, RF = 200Ω. For the LTC6404-4: RI = 100Ω, RF = 402Ω, unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined (VIN+ + VIN–)/2. VOUTDIFF is defined (VOUT+ – VOUT–). VINDIFF = (VINP – VINM)
PARAMETER Differential Offset Voltage (Input Referred) ΔVOSDIFF/ΔT Differential Offset Voltage Drift (Input Referred) Input Bias Current (Note 6) IB Input Bias Current Drift (Note 6) ΔIB/ΔT IOS RIN CIN en in enVOCM Input Offset Current (Note 6) Input Resistance Input Capacitance Differential Input Referred Noise Voltage Density Input Noise Current Density Input Referred Common Mode Noise Voltage Density SYMBOL VOSDIFF CONDITIONS VS = 2.7V to 5.25V VS = 2.7V to 5.25V VS = 2.7V to 5.25V VS = 2.7V to 5.25V VS = 2.7V to 5.25V Common Mode Differential Mode f = 1MHz f = 1MHz f = 1MHz, Referred to VOCM Pin LTC6404-1 LTC6404-2 LTC6404-4 VS = 3V VS = 5V VS = 3V, ΔVCM = 0.75V VS = 5V, ΔVCM = 1.25V VS = 5V, ΔVOCM = 1V VS = 2.7V to 5.25V VS = 2.7V to 5.25V LTC6404-1 LTC6404-2 LTC6404-4 VS = 5V, ΔVOCM = 1V LTC6404-1 LTC6404-2 LTC6404-4 VS = 5V, ΔVOCM = 1V LTC6404-1 LTC6404-2 LTC6404-4 ΔVOUTDIFF = 2V, Single-Ended Input LTC6404-1 LTC6404-2 LTC6404-4 ΔVOUTDIFF = 2V, Differential Input LTC6404-1 LTC6404-2 LTC6404-4 VS = 2.7V to 5.25V LTC6404-1 LTC6404-2 LTC6404-4
l
MIN
l l l
TYP ±0.5 1 –23 0.01 ±1 1000 3 1 1.5 3 9 10.5 27
MAX ±2 0 ±10
UNITS mV μV/°C μA μA/°C μA kΩ kΩ pF nV/√Hz pA/√Hz nV/√Hz nV/√Hz nV/√Hz V V dB dB dB dB
–60
VICMR (Note 7) CMRRI (Note 8) CMRRIO (Note 8) PSRR (Note 9) PSRRCM (Note 9)
Input Signal Common Mode Range Input Common Mode Rejection Ratio (Input Referred) ΔVICM/ΔVOSDIFF Output Common Mode Rejection Ratio (Input Referred) ΔVOCM/ΔVOSDIFF Differential Power Supply Rejection (ΔVS/ΔVOSDIFF) Output Common Mode Power Supply Rejection (ΔVS/ΔVOSCM) Common Mode Gain (ΔVOUTCM/ΔVOCM)
l l
0 0 60 60 66 60 94
1.6 3.6
l l l l l l l l l l l l l l l l l l
50 50 40
63 63 51 1 1 0.99
dB dB dB V/V V/V V/V 0.1 0.1 –0.4 –40 –40 –40 –40 –40 –40 ±25 ±50 ±100 % % % dB dB dB dB dB dB mV mV mV
GCM
Common Mode Gain Error
–0.6 –0.6 –1.6
–0.125 –0.25 –1 –60 –60 –53 –66 –66 –66 ±10 ±20 ±40
BAL
Output Balance (ΔVOUTCM/ΔVOUTDIFF)
VOSCM
Common Mode Offset Voltage (VOUTCM – VOCM)
6404f
3
LTC6404 LTC6404 DC ELECTRICAL CHARACTERISTICS +The l d–enotes the specifications which apply over
the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RL = OPEN, RBAL = 100k (See Figure 1). For the LTC6404-1: RI = 100Ω, RF = 100Ω. For the LTC6404-2: RI = 100Ω, RF = 200Ω. For the LTC6404-4: RI = 100Ω, RF = 402Ω, unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined (VIN+ + VIN–)/2. VOUTDIFF is defined (VOUT+ – VOUT–). VINDIFF = (VINP – VINM)
PARAMETER Common Mode Offset Voltage Drift CONDITIONS VS = 2.7V to 5.25V LTC6404-1 LTC6404-2 LTC6404-4 VS = 3V LTC6404-1 LTC6404-2 LTC6404-4 VS = 5V LTC6404-1 LTC6404-2 LTC6404-4 LTC6404-1 LTC6404-2 LTC6404-4 VS = 3V VS = 3V, IL = 0mA VS = 3V, IL = 5mA VS = 3V, IL = 20mA VS = 5V, IL = 0mA VS = 5V, IL = 5mA VS = 5V, IL = 20mA VS = 3V, IL = 0mA VS = 3V, IL = –5mA VS = 3V, IL = –20mA VS = 5V, IL = 0mA VS = 5V, IL = –5mA VS = 5V, IL = –20mA VS = 2.7V VS = 3V VS = 5V VS = 3V VS = 2.7V, VSHDN = VS – 0.6V VS = 3V, VSHDN = VS – 0.6V VS = 5V, VSHDN = VS – 0.6V VS = 2.7V, VSHDN = VS – 0.6V VS = 3V, VSHDN = VS – 0.6V VS = 5V, VSHDN = VS – 0.6V VS = 2.7V, VSHDN = VS – 0.6V VS = 3V, VSHDN = VS – 0.6V VS = 5V, VSHDN = VS – 0.6V VS = 2.7V, VSHDN = VS – 2.1V VS = 3V, VSHDN = VS – 2.1V VS = 5V, VSHDN = VS – 2.1V VS = 2.7V, VSHDN = VS – 2.1V VS = 3V, VSHDN = VS – 2.1V VS = 5V, VSHDN = VS – 2.1V VS = 2.7V, VSHDN = VS – 2.1V VS = 3V, VSHDN = VS – 2.1V VS = 5V, VSHDN = VS – 2.1V MIN TYP ±10 ±20 ±20
l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
SYMBOL ΔVOSCM/ΔT
MAX
UNITS μV/°C μV/°C μV/°C
VOUTCMR (Note 7)
Output Signal Common Mode Range (Voltage Range for the VOCM Pin)
1.1 1.1 1.1 1.1 1.1 1.1 15 8 4 1.45
2 2 1.7 4 4 3.7 32 20 10 1.55 550 600 750 700 750 1000 230 260 350 320 350 550
V V V V V V kΩ kΩ kΩ V mV mV mV mV mV mV mV mV mV mV mV mV mA mA mA dB V mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA mA
6404f
RINVOCM
Input Resistance, VOCM Pin
23.5 14 7 1.5 325 360 480 460 500 650 120 140 200 175 200 285 ±60 ±65 ±85 90 27.2 27.3 27.8 29.7 29.8 30.4 30.0 30.2 31.0 0.22 0.25 0.35 0.22 0.25 0.35 0.28 0.30 0.50
VMID VOUT
Voltage at the VOCM Pin Output Voltage High, Either Output Pin (Note 10)
Output Voltage Low, Either Output Pin (Note 10)
ISC
Output Short-Circuit Current, Either Output Pin (Note 11) Large-Signal Voltage Gain Supply Voltage Range Supply Current (LTC6404-1)
±35 ±40 ±55 2.7
AVOL VS IS
Supply Current (LTC6404-2)
Supply Current (LTC6404-4)
ISHDN
Supply Current in Shutdown (LTC6404-1)
Supply Current in Shutdown (LTC6404-2)
Supply Current in Shutdown (LTC6404-4)
5.25 35.5 35.5 36.5 38.5 38.5 39.5 39 39 40 1 1 2 1 1 2 1.2 1.2 2.4
4
LTC6404 LTC6404 DC ELECTRICAL CHARACTERISTICS +The l d–enotes the specifications which apply over
the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RL = OPEN, RBAL = 100k (See Figure 1). For the LTC6404-1: RI = 100Ω, RF = 100Ω. For the LTC6404-2: RI = 100Ω, RF = 200Ω. For the LTC6404-4: RI = 100Ω, RF = 402Ω, unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined (VIN+ + VIN–)/2. VOUTDIFF is defined (VOUT+ – VOUT–). VINDIFF = (VINP – VINM)
SYMBOL VIL VIH RSHDN tON tOFF PARAMETER SHDN Input Logic Low SHDN Input Logic High SHDN Pin Input Impedance Turn-On Time Turn-Off Time CONDITIONS VS = 2.7V to 5V VS = 2.7V to 5V VS = 5V, VSHDN = 2.9V to 0V VS = 3V, VSHDN = 0.5V to 3V VS = 3V, VSHDN = 3V to 0.5V MIN
l l l
TYP
MAX V+ – 2.1 94
V+ – 0.6 38
66 750 300
UNITS V V kΩ ns ns
LTC6404-1 AC ELECTRICAL CHARACTERISTICS
SYMBOL SR GBW f3dB HDSEIN PARAMETER Slew Rate Gain-Bandwidth Product –3dB Frequency (See Figure 2) 10MHz Distortion
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 3V, V– = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RI = 100Ω, RF = 100Ω, RL = 200Ω (See Figure 2) unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined as (VIN+ + VIN–)/2. VOUTDIFF is defined as (VOUT+ – VOUT–). VINDIFF = (VINP – VINM).
CONDITIONS VS = 3V to 5V VS = 3V to 5V, RI = 100Ω, RF = 499Ω, fTEST = 500MHz VS = 3V to 5V VS = 3V, VOUTDIFF = 2VP-P Single-Ended Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P Differential Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P MIN TYP 450 500 600 MAX UNITS V/μs MHz MHz
l
300
–88 –91
dBc dBc
HDDIFFIN
10MHz Distortion
IMD10M OIP310M tS
Third-Order IMD at 10MHz f1 = 9.5MHz, f2 = 10.5MHz OIP3 at 10MHz (Note 12) Settling Time 2V Step at Output Noise Figure, RS = 50Ω Differential Filter 3dB Bandwidth (Note 13)
–102 –91 –93 50 10 13 17 13.4 88.5
dBc dBc dBc dBm ns ns ns dB MHz
NF f3dBFILTER
1% Settling 0.1% Settling 0.01% Settling f = 10MHz
6404f
5
LTC6404 LTC6404-2 AC ELECTRICAL CHARACTERISTICS
SYMBOL SR GBW f3dB HDSEIN PARAMETER Slew Rate Gain-Bandwidth Product –3dB Frequency (See Figure 2) 10MHz Distortion
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 3V, V– = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RI = 100Ω, RF = 200Ω, RL = 200Ω (See Figure 2) unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined as (VIN+ + VIN–)/2. VOUTDIFF is defined as (VOUT+ – VOUT–). VINDIFF = (VINP – VINM).
CONDITIONS VS = 3V to 5V VS = 3V to 5V, RI = 100Ω, RF = 499Ω, fTEST = 500MHz VS = 3V to 5V VS = 3V, VOUTDIFF = 2VP-P Single-Ended Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P Differential Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P MIN TYP 700 900 600 MAX UNITS V/μs MHz MHz
l
300
–95 –96
dBc dBc
HDDIFFIN
10MHz Distortion
IMD10M OIP310M tS
Third-Order IMD at 10MHz f1 = 9.5MHz, f2 = 10.5MHz OIP3 at 10MHz (Note 12) Settling Time 2V Step at Output Noise Figure, RS = 50Ω Differential Filter 3dB Bandwidth (Note 13)
–98 –99 –100 53 9 12 15 10 88.5
dBc dBc dBc dBm ns ns ns dB MHz
NF f3dBFILTER
1% Settling 0.1% Settling 0.01% Settling f = 10MHz
LTC6404-4 AC ELECTRICAL CHARACTERISTICS
SYMBOL SR GBW f3dB HDSEIN PARAMETER Slew Rate Gain-Bandwidth Product –3dB Frequency (See Figure 2) 10MHz Distortion
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V+ = 3V, V– = 0V, VCM = VOCM = VICM = Mid-Supply, VSHDN = OPEN, RI = 100Ω, RF = 402Ω, RL = 200Ω (See Figure 2) unless otherwise noted. VS is defined (V+ – V–). VOUTCM = (VOUT+ + VOUT–)/2. VICM is defined as (VIN+ + VIN–)/2. VOUTDIFF is defined as (VOUT+ – VOUT–). VINDIFF = (VINP – VINM).
CONDITIONS VS = 3V to 5V VS = 3V to 5V, RI = 100Ω, RF = 499Ω, fTEST = 500MHz VS = 3V to 5V VS = 3V, VOUTDIFF = 2VP-P Single-Ended Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P Differential Input 2nd Harmonic 3rd Harmonic VS = 3V, VOUTDIFF = 2VP-P MIN TYP 1200 1700 530 MAX UNITS V/μs MHz MHz
l
300
–97 –98
dBc dBc
HDDIFFIN
10MHz Distortion
IMD10M OIP310M tS
Third-Order IMD at 10MHz f1 = 9.5MHz, f2 = 10.5MHz OIP3 at 10MHz (Note 12) Settling Time 2V Step at Output Noise Figure, RS = 50Ω Differential Filter 3dB Bandwidth (Note 13)
–100 –101 –101 54 8 11 14 8 88.5
dBc dBc dBc dBm ns ns ns dB MHz
NF f3dBFILTER
1% Settling 0.1% Settling 0.01% Settling f = 10MHz
6404f
6
LTC6404 ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The inputs IN+, IN– are protected by a pair of back-to-back diodes. If the differential input voltage exceeds 1.4V, the input current should be limited to less than 10mA. Input pins (IN+, IN–, VOCM and SHDN) are also protected by steering diodes to either supply. If the inputs should exceed either supply voltage, the input current should be limited to less than 10mA. Note 3: A heat sink may be required to keep the junction temperature below the absolute maximum rating when the output is shorted indefinitely. Long-term application of output currents in excess of the absolute maximum ratings may impair the life of the device. Note 4: The LTC6404C/LTC6404I are guaranteed functional over the operating temperature range –40°C to 85°C. The LTC6404H is guaranteed functional over the operating temperature range –40°C to 125°C. Note 5: The LTC6404C is guaranteed to meet specified performance from 0°C to 70°C. The LTC6404C is designed, characterized, and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LTC6404I is guaranteed to meet specified performance from –40°C to 85°C. The LTC6404H is guaranteed to meet specified performance from –40°C to 125°C. Note 6: Input bias current is defined as the average of the input currents flowing into Pin 6 and Pin 15 (IN– and IN+). Input offset current is defined as the difference of the input currents flowing into Pin 15 and Pin 6 (IOS = IB+ – IB–) Note 7: Input common mode range is tested using the test circuit of Figure 1 by measuring the differential gain with a ±1V differential output with VICM = mid-supply, and with VICM at the input common mode range limits listed in the Electrical Characteristics table, verifying the differential gain has not deviated from the mid-supply common mode input case by more than 1%, and the common mode offset (VOSCM) has not deviated from the zero bias common mode offset by more than ±15mV (LTC6404-1), ±20mV (LTC6404-2) or ±40mV (LTC6404-4). The voltage range for the output common mode range is tested using the test circuit of Figure 1 by applying a voltage on the VOCM pin and testing at both mid-supply and at the Electrical Characteristics table limits to verify that the the common mode offset (VOSCM) has not deviated by more than ±15mV (LTC6404-1), ±20mV (LTC6404-2) or ±40mV (LTC6404-4). Note 8: Input CMRR is defined as the ratio of the change in the input common mode voltage at the pins IN+ or IN– to the change in differential input referred voltage offset. Output CMRR is defined as the ratio of the change in the voltage at the VOCM pin to the change in differential input referred voltage offset. These specifications are strongly dependent on feedback ratio matching between the two outputs and their respective inputs, and is difficult to measure actual amplifier performance. (See “The Effects of Resistor Pair Mismatch” in the Applications Information section of this data sheet. For a better indicator of actual amplifier performance independent of feedback component matching, refer to the PSRR specification. Note 9: Differential power supply rejection (PSRR) is defined as the ratio of the change in supply voltage to the change in differential input referred voltage offset. Common mode power supply rejection (PSRRCM) is defined as the ratio of the change in supply voltage to the change in the common mode offset, VOUTCM – VOCM. Note 10: This parameter is pulse tested. Output swings are measured as differences between the output and the respective power supply rail. Note 11: This parameter is pulse tested. Extended operation with the output shorted may cause junction temperatures to exceed the 125°C limit and is not recommended. See Note 3 for more details. Note 12: Since the LTC6404 is a voltage feedback amplifier with low output impedance, a resistive load is not required when driving an ADC. Therefore, typical output power is very small. In order to compare the LTC6404 with amplifiers that require 50Ω output loads, output swing of the LTC6404 driving an ADC is converted into an “effective” OIP3 as if the LTC6404 were driving a 50Ω load. Note 13: The capacitors used to set the filter pole might have up to ±15% variation. The resistors used to set the filter pole might have up to ±12% variation.
6404f
7
LTC6404 LTC6404-1 TYPICAL PERFORMANCE CHARACTERISTICS
Active Supply Current vs Temperature
30 29 28 ICC (mA) 27 26 25 24 –75 –50 –25 VS = 5V ICC (mA) VS = 3V VS = 2.7V 0.3 VS = 3V 0.2 VS = 2.7V 0.1 VCM = VOCM = MID-SUPPLY 0.5
Shutdown Supply Current vs Temperature
1.0 VCM = VOCM = MID-SUPPLY 0.8 0.6 VS = 5V VOSDIFF (mV) 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8
Differential Voltage Offset (Input Referred) vs Temperature
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
0.4
0 25 50 75 100 125 150 TEMPERATURE (°C)
64041 G01
0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
64041 G02
–1.0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
64041 G03
Common Mode Voltage Offset vs Temperature
10 8 6 4 VOSCM (mV) ICC (mA) 2 0 –2 –4 –6 –8 –10 –75 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C)
64041 G04
Active Supply Current vs Supply Voltage and Temperature
30 VCM = VOCM = MID-SUPPLY + 25 SHDN = V 20 15 10 5 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 0 1 3 2 VSUPPLY (V) 4 5
64041 G05
SHDN Supply Current vs Supply Voltage and Temperature
0.5 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
0.4
ICC (mA)
0.3
0.2
0.1 VCM = VOCM = MID-SUPPLY SHDN = V– 0 1 2 3 VSUPPLY (V) 4 5
64041 G06
0
SHDN Pin Current vs SHDN Pin Voltage and Temperature
0 –5 SHDN PIN CURRENT (μA) –10 ICC (mA) –15 –20 –25 –30 0 0.5 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 1.5 2.5 1.0 2.0 SHDN PIN VOLTAGE (V) 3.0 VCM = VOCM = MID-SUPPLY VS = 3V 30 25 20 15 10 5 0
Supply Current vs SHDN Pin Voltage and Temperature
VCM = VOCM = MID-SUPPLY VS = 3V 5
Small-Signal Frequency Response
VS = 3V VS = 5V CF = 0pF
0
CF = 1.8pF
TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 0 0.5 1.0 1.5 2.0 2.5 SHDN PIN VOLTAGE (V) 3.0
GAIN (dB)
64041 G08
–5
–10 –15 UNFILTERED OUTPUTS VCM = VOCM = MID-SUPPLY TA = 25°C RF = RI = 100Ω, CF IN PARALLEL WITH RF –20 10 100 1000 FREQUENCY (MHz)
64041 G09
64041 G07
6404f
8
LTC6404 LTC6404-1 TYPICAL PERFORMANCE CHARACTERISTICS
Small-Signal Frequency Response vs Gain Setting Resistor Values and Supply Voltage
5 0 –5 GAIN (dB) –10 –15 –20 VS = 3V VS = 5V RF = RI = 100Ω GAIN (dB) GAIN (dB) RF = RI = 200Ω RF = RI = 499Ω 0 –5 CLOAD = 5pF CLOAD = 0pF 0 TA = 25°C –5 TA = 90°C –10 UNFILTERED OUTPUTS –15 VCM = VOCM = MID-SUPPLY RF = RI = 100Ω VS = 3V AND VS = 5V –20 10 100 FREQUENCY (MHz) 10 CLOAD = 10pF 5
Small-Signal Frequency Response vs CLOAD
10 5
Small-Signal Frequency Response vs Temperature
TA = –45°C
UNFILTERED OUTPUTS –25 VCM = VOCM = MID-SUPPLY TA = 25°C VS = 3V AND VS = 5V –30 10 100 FREQUENCY (MHz)
1000
64041 G10
UNFILTERED OUTPUTS –10 VCM = VOCM = MID-SUPPLY TA = 25°C RF = RI = 100Ω –15 VS = 3V AND VS = 5V RLOAD = 200Ω, (EACH OUTPUT TO GROUND) –20 10 100 FREQUENCY (MHz)
1000
64041 G11
1000
64041 G12
Small-Signal Frequency Response vs Temperature
5 0 –5 GAIN (dB) –10 –15 –20 UNFILTERED DIFFERENTIAL OUTPUT FILTERED DIFFERENTIAL OUTPUT TA = 90°C TA = 25°C TA = –45°C 1.5 TA = 25°C VOUTDIFF (OUT+ – OUT–) (V) 1.0 0.5
Large-Signal Step Response
0.50
Small-Signal Step Response
VOUTDIFF (OUT+ – OUT–) (V)
0.25
VINDIFF
VINDIFF 0 –0.5 –1.0 –1.5 0 3
VOUTDIFF
VOUTDIFF 0
–25 FILTERED OUTPUT V = VOCM = MID-SUPPLY –30 RCM R = 100Ω F= I VS = 3V AND VS = 5V –35 10 100 FREQUENCY (MHz)
–0.25 VCM = VOCM = MID-SUPPLY RF = RI = 100Ω 0 3 9 6 TIME (ns) 12 15
64041 G15
VCM = VOCM = MID-SUPPLY RF = RI = 100Ω 6 9 TIME (ns) 12 15
64041 G14
–0.50
1000
64041 G13
Distortion vs Frequency
–40 –50 –60 HD2, HD3 (dBc) –70 –80 –90 HD2 –100 –110 HD3 –120 0.1 –110 1.0 10 FREQUENCY (MHz) 100
64041 G16
Distortion vs Input Common Mode Voltage
–40 VS = 3V RF = RI = 100Ω –50 V = 2V IN P-P fIN = 10MHz –60 DIFFERENTIAL INPUT SINGLE-ENDED –70 INPUT –80 –90 –100 HD3 HD3 HD2 –100 –110 HD2 –30
Distortion vs Output Amplitude
VCM = VOCM = MID-SUPPLY –40 VS = 3V TA = 25 C C = 0pF –50 F RF = RI = 100 V = FULLY DIFFERENTIAL INPUT –60 IN fIN = 10MHz –70 –80 –90 HD3 HD2
VCM = VOCM = MID-SUPPLY VS = 3V VOUTDIFF = 2VP-P RF = RI = 100Ω HD2, HD3 (dBc) DIFFERENTIAL INPUT SINGLE-ENDED INPUT
HD3 HD2
HD2, HD3 (dBc)
0 0.5 1.0 1.5 2.0 2.5 3.0 DC COMMON MODE INPUT (AT IN+ AND IN– PINS) (V)
64041 G17
0
1
2 3 4 VOUTDIFF (VP-P)
5
6
64041 G18
6404f
9
LTC6404 LTC6404-1 TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Output Amplitude
–30 VCM = VOCM = MID-SUPPLY –40 VS = 3V TA = 25°C RF = RI = 100Ω –50 VIN = SINGLE-ENDED INPUT f = 10MHz –60 IN (dB) –70 –80 HD2 –90 –100 –110 0 1 2 3 VOUTDIFF (VP-P) 4 5
64041 G19
LTC6404-1 Driving LTC2207 16-Bit ADC
0 –20 –40 –60 –80 –100 –120 0 10 20 30 40 FREQUENCY (MHz) 50
64041 G20
LTC6404-1 Driving LTC2207 16-Bit ADC
0 –20 –40 (dB) –60 –80 VCM = VOCM = 1.5V VS = 3V RF = RI = 100Ω VIN = 2VP-P DIFFERENTIAL fSAMPLE = 105Msps 10MHz, 65536 POINT FFT FUNDAMENTAL = –1dBFS HD2 = –90.7dBc HD3 = –86.6dBc HD2 HD9 –120 0 10 20 30 40 FREQUENCY (MHz) 50
64041 G21
HD2, HD3 (dBc)
VCM = VOCM = 1.7V VS = 3.3V RF = RI = 100Ω VIN = 2VP-P DIFFERENTIAL fSAMPLE = 105Msps 10MHz, 4092 POINT FFT FUNDAMENTAL = –1dBFS HD2 = –98.8dBc HD3 = –90.2dBc
HD3 HD7 HD4 HD5
HD3
HD9 HD2
HD3 HD7 HD4
HD5
–100
HD8
Voltage Noise Density vs Frequency
100 VOLTAGE NOISE DENSITY (nV/√Hz) VCM = VOCM = MID-SUPPLY VS = 3V TA = 25°C RF = RI = 100Ω NOISE FIGURE (dB) 100 1000
64041 G22
LTC6404-1 Noise Figure vs Frequency
28 VCM = VOCM = MID-SUPPLY V = 3V 24 T S = 25°C A SEE FIGURE 2 CIRCUIT 20 16 12 8 4 0 10 100 FREQUENCY (MHz) 1000
64041 G23
10
COMMON MODE
DIFFERENTIAL INPUT REFERRED 1 0.01
0.1
1 10 FREQUENCY (MHz)
6404f
10
LTC6404 LTC6404-2 TYPICAL PERFORMANCE CHARACTERISTICS
Active Supply Current vs Temperature
33 32 VS = 5V 31 ICC (mA) ICC (mA) VS = 3V 30 VS = 2.7V 29 28 27 –75 –50 –25 0.1 0.3 VS = 3V 0.2 VS = 2.7V VCM = VOCM = MID-SUPPLY 0.5
Shutdown Supply Current vs Temperature
1.0 VCM = VOCM = MID-SUPPLY 0.8 0.6 VS = 5V VOSDIFF (mV) 0.4 0.2 0
Differential Voltage Offset (Input Referred) vs Temperature
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
0.4
–0.2 –0.4 –0.6 –0.8
0 25 50 75 100 125 150 TEMPERATURE (°C)
64042 G01
0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
64042 G02
–1.0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
64042 G03
Common Mode Voltage Offset (Input Referred) vs Temperature
10 8 6 4 VOSCM (mV) ICC (mA) 2 0 –2 –4 –6 –8 –10 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C)
64042 G03
Active Supply Current vs Supply Voltage and Temperature
40 35 30 ICC (mA) 25 20 15 10 5 0 0 1 2 3 VSUPPLY (V) TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 4 5
64042 G05
SHDN Supply Current vs Supply Voltage and Temperature
0.5 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
VCM = VOCM = MID-SUPPLY SHDN = V+ 0.4
0.3
0.2
0.1 VCM = VOCM = MID-SUPPLY SHDN = V– 0 1 2 3 VSUPPLY (V) 4 5
64042 G06
0
SHDN Pin Current vs SHDN Pin Voltage and Temperature
0 –5 SHDN PIN CURRENT (μA) –10 ICC (mA) –15 –20 –25 –30 0 0.5 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 1.5 2.5 1.0 2.0 SHDN PIN VOLTAGE (V) 3.0 VCM = VOCM = MID-SUPPLY VS = 3V 35 30 25
Supply Current vs SHDN Pin Voltage and Temperature
15 VCM = VOCM = MID-SUPPLY VS = 3V 10 5
Small-Signal Frequency Response
VS = 3V VS = 5V CF = 0pF
CF = 1pF GAIN (dB) TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 0 0.5 1.0 1.5 2.0 2.5 SHDN PIN VOLTAGE (V) 3.0 0 –5 –10 UNFILTERED OUTPUTS VCM = VOCM = MID-SUPPLY –15 TA = 25°C RI = 100Ω, RF = 200Ω, CF IN PARALLEL WITH RF –20 10 100 FREQUENCY (MHz)
20 15 10 5 0
1000
64042 G09
64042 G07
64042 G08
6404f
11
LTC6404 LTC6404-2 TYPICAL PERFORMANCE CHARACTERISTICS
Small-Signal Frequency Response vs Gain Setting Resistor Values
15 10 5 GAIN (dB) GAIN (dB) 0 –5 –10 VS = 3V VS = 5V RI = 200Ω, RF = 402Ω RI = 499Ω, RF = 1k RI = 100Ω, RF = 200Ω 25 20 15 10 5 0 CLOAD = 0pF CLOAD = 10pF 10 CLOAD = 5pF 5 GAIN (dB) 0 TA = 25°C TA = 90°C
Small-Signal Frequency Response vs CLOAD
15
Small-Signal Frequency Response vs Temperature
TA = –45°C
UNFILTERED OUTPUTS –20 VCM = VOCM = MID-SUPPLY TA = 25°C VS = 3V AND VS = 5V –25 10 100 FREQUENCY (MHz)
1000
64042 G10
UNFILTERED OUTPUTS VCM = VOCM = MID-SUPPLY T = 25°C –5 RA = 100Ω, R = 200Ω I F VS = 3V AND VS = 5V –10 R LOAD = 200Ω, (EACH OUTPUT TO GROUND) –15 10 100 FREQUENCY (MHz)
1000
64042 G11
UNFILTERED OUTPUTS –5 VCM = VOCM = MID-SUPPLY TA = 25°C RI = 100Ω, RF = 200Ω –10 VS = 3V AND VS = 5V RLOAD = 200Ω, (EACH OUTPUT TO GROUND) –15 10 100 FREQUENCY (MHz)
1000
64042 G12
Small-Signal Frequency Response vs Temperature
15 10 5 FILTERED GAIN (dB) 0 –5 –10 –15 –20 FILTERED DIFFERENTIAL OUTPUT UNFILTERED DIFFERENTIAL OUTPUT VOUTDIFF (OUT+ – OUT–) (V) TA = 25°C 1.5
Large-Signal Step Response
1.00 VOUTDIFF VOUTDIFF (OUT+ – OUT–) (V) 1.0 0.5 VINDIFF 0 –0.5 –1.0 –1.5 1000
64042 G13
Small-Signal Step Response
0.75 VOUTDIFF 0.50 0.25 0 –0.25 –0.50 –0.75 VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 200Ω –1.00 0 3 9 6 TIME (ns) VINDIFF
TA = 90°C TA = 25°C TA = –45°C
VCM = VOCM = MID-SUPPLY –25 RI = 100Ω, RF = 200Ω VS = 3V –30 10 100 FREQUENCY (MHz)
VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 200Ω 0 3 6 9 TIME (ns) 12 15
64042 G14
12
15
64042 G15
Distortion vs Frequency
–40 –50 –60 HD2, HD3 (dBc) –70 –80 –90 –100 –110 –120 –130 –140 0.1 HD3 HD2 HD3 VCM = VOCM = MID-SUPPLY VS = 3V VOUTDIFF = 2VP-P RF = 100Ω, RI = 200Ω HD2, HD3 (dBc) DIFFERENTIAL INPUT SINGLE-ENDED INPUT HD2 –40
Distortion vs Input Common Mode Voltage
VS = 3V VCM = VOCM = MID-SUPPLY –50 R = 100Ω, R = 200Ω I F VIN = 1VP-P –60 fIN = 10MHz DIFFERENTIAL INPUT SINGLE-ENDED INPUT –70 –80 –90 –100 –110 HD3 HD2 –120 HD2 HD3 –40
Distortion vs Output Amplitude
VS = 3V –50 VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 200Ω –60 VIN = DIFFERENTIAL INPUT fIN = 10MHz HD2, HD3 (dBc) –70 –80 –90 HD3 HD2
–100 –110 0 1 2 3 4 VOUTDIFF (VP-P) 5 6
64042 G18
1 10 FREQUENCY (MHz)
100
64042 G16
0 0.5 1.0 1.5 2.0 2.5 DC COMMON MODE INPUT (AT IN+ AND IN– PINS) (V)
64042 G17
6404f
12
LTC6404 LTC6404-2 TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Output Amplitude
–40 VS = 3V –50 VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 200Ω –60 VIN = SINGLE-ENDED INPUT fIN = 10MHz HD2, HD3 (dBc) –70 (dB) –80 –90 HD2 0 –20 –40 –60 –80 –100 –120 0 1 2 3 4 VOUTDIFF (VP-P) 5 6
64042 G19
LTC6404-2 Driving LTC2207 16-Bit ADC (Single Tone)
VS = 3.3V VOUTDIFF = 2VP-P VCM = VOCM = 1.25V RI = 100 , RF = 200 10.1MHz, 16184 POINT FFT fSAMPLE = 105Msps FUNDAMENTAL = –1dBFS HD2 = –92.4dBc HD3 = –93.02dBc HD2 HD3 HD7 0 –20 –40 (dB) –60
LTC6404-2 Driving LTC2207 16-Bit ADC (Two Tones)
VS = 3.3V VINDIFF = 1VP-P FULLY DIFFERENTIAL VOUTDIFF = 2VP-P VCM = VOCM = 1.25V RI = 100Ω, RF = 200Ω 16184 POINT FFT fSAMPLE = 105Msps TONE1, TONE2 = –7dBFS IM3U IM3U = –106.8dBc IM3L = –107.7dBc
–80 IM3L HD4 HD5 –100 –120
–100 –110 –120 HD3
0
10
20 30 40 FREQUENCY (MHz)
50
64042 G20
0
10
20 30 40 FREQUENCY (MHz)
50
64042 G21
Voltage Noise Density vs Frequency
100 VOLTAGE NOISE DENSITY (nV/√Hz) VS = 3V VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 200Ω TA = 25°C NOISE FIGURE (dB) 28 24 20 16 12 8 4 0
LTC6404-2 Noise Figure vs Frequency
VCM = VOCM = MID-SUPPLY VS = 3V TA = 25°C SEE FIGURE 2 CIRCUIT
COMMON MODE 10
DIFFERENTIAL INPUT REFERRED 1 0.01
0.1
1 10 FREQUENCY (MHz)
100
1000
64042 G22
10
100 FREQUENCY (MHz)
1000
64042 G23
6404f
13
LTC6404 LTC6404-4 TYPICAL PERFORMANCE CHARACTERISTICS
Active Supply Current vs Temperature
33 32 31 ICC (mA) 30 VS = 2.7V 29 0.2 28 27 –75 –50 –25 0.1 0 –75 –50 –25 VS = 5V ICC (mA) VS = 3V VCM = VOCM = MID-SUPPLY 0.7 VCM = VOCM = MID-SUPPLY 0.6 VS = 5V 0.5 VOSDIFF (mV) 0.4 VS = 3V 0.3 VS = 2.7V
Shutdown Supply Current vs Temperature
1.0 0.8 0.6 0.4 0.2 0
Differential Voltage Offset (Input Referred) vs Temperature
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
–0.2 –0.4 –0.6 –0.8
0 25 50 75 100 125 150 TEMPERATURE (°C)
64044 G01
0 25 50 75 100 125 150 TEMPERATURE (°C)
64044 G02
–1.0 –75 –50 –25
0 25 50 75 100 125 150 TEMPERATURE (°C)
64044 G03
Common Mode Voltage Offset (Input Referred) vs Temperature
50 40 30 20 VOSCM (mV) ICC (mA) 10 0 –10 –20 –30 –40 –50 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C)
64044 G04
Active Supply Current vs Supply Voltage and Temperature
40 35 30 25 ICC (mA) 20 15 10 5 0 0 1 3 VSUPPLY (V) 2 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 4 5
64044 G05
SHDN Supply Current vs Supply Voltage and Temperature
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1 VCM = VOCM = MID-SUPPLY SHDN = V+ 2 3 4 5
64044 G06
5 REPRESENTATIVE UNITS VCM = VOCM = MID-SUPPLY VS = 3V
VCM = VOCM = MID-SUPPLY SHDN = V+
TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C
VSUPPLY (V)
SHDN Pin Current vs SHDN Pin Voltage and Temperature
0 –5 SHDN PIN CURRENT (μA) –10 –15 –20 –25 –30 TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 0 0.5 1.0 1.5 2.0 SHDN PIN VOLTAGE (V) 2.5 3.0 20 15 10 5 0 VCM = VOCM = MID-SUPPLY VS = 3V 35 30 25
Supply Current vs SHDN Pin Voltage and Temperature
VCM = VOCM = MID-SUPPLY VS = 3V 20 15 10
Small-Signal Frequency Response
VS = 3V VS = 5V CF = 0pF
CF = 1pF GAIN (dB) ICC (mA) TA = 125°C TA = 105°C TA = 90°C TA = 75°C TA = 50°C TA = 25°C TA = –10°C TA = –45°C TA = –60°C 0 0.5 2.0 1.5 2.5 1.0 SHDN PIN VOLTAGE (V) 3.0 5 0 –5 –10 –15 VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 402Ω, CF IN PARALLEL WITH RF 10 100 FREQUENCY (MHz) 1000
64044 G09
64044 G07
64044 G08
6404f
14
LTC6404 LTC6404-4 TYPICAL PERFORMANCE CHARACTERISTICS
Small-Signal Frequency Response vs Gain Setting Resistor Values
20 RI = 100Ω, RF = 402Ω 15 10 GAIN (dB) GAIN (dB) 5 0 –5 –10 –15 VS = 3V VS = 5V VCM = VOCM = MID-SUPPLY VS = 3V AND VS = 5V 10 100 FREQUENCY (MHz) 1000
64044 G10
Small-Signal Frequency Response vs CLOAD
25 CLOAD = 10pF 20 15 CLOAD = 0pF GAIN (dB) CLOAD = 5pF 15 10 5 0 –5 20
Small-Signal Frequency Response vs Temperature
TA = –45°C TA = 25°C TA = 90°C
RI = 140Ω, RF = 562Ω RI = 200Ω, RF = 800Ω
10 5 0 –5 –10 –15
VS = 3V VS = 5V VCM = VOCM = MID-SUPPLY RI = 100Ω, RF = 402Ω VS = 3V AND VS = 5V 10 100 FREQUENCY (MHz) 1000
64044 G11
VCM = VOCM = MID-SUPPLY –10 R = 100Ω, R = 402Ω I F VS = 3V AND VS = 5V –15 10 100 FREQUENCY (MHz)
1000
64044 G12
Small-Signal Frequency Response vs Temperature
20 15 10 FILTERED GAIN (dB) 5 0 –5 –10 –15 FILTERED DIFFERENTIAL OUTPUT TA = 25°C TA = –45°C TA = 90°C UNFILTERED DIFFERENTIAL OUTPUT AT 25°C VOUTDIFF (OUT+ – OUT–) (V) 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 1000
64044 G13
Large-Signal Step Response
0.75 VOUTDIFF
Small-Signal Step Response
VOUTDIFF VOUTDIFF (OUT+ – OUT–) (V) 0.50 0.25 0
VINDIFF
VINDIFF
–0.25 –0.50 –0.75 0 3 VCM = VOCM = MID-SUPPLY VS = 3V RI = 100Ω, RF = 402Ω 6 9 TIME (ns) 12 15
64044 G15
VCM = VOCM = MID-SUPPLY –20 RI = 100Ω, RF = 402Ω VS = 3V –25 100 10 FREQUENCY (MHz)
–2.5
VCM = VOCM = MID-SUPPLY VS = 3V RI = 100Ω, RF = 402Ω 0 3 9 6 TIME (ns) 12 15
64044 G14
Distortion vs Frequency
–40 –50 –60 HD2, HD3 (dBc) –70 –80 –90 HD2 –100 –110 –120 –130 0.1 HD3 HD3 1 10 FREQUENCY (MHz) 100
64044 G16
Distortion vs Input Common Mode Voltage
–40 –50 –60 HD2, HD3 (dBc) –70 –80 –90 –100 HD2 –110 –120 HD3 HD2 HD3 –100 –110 –120 VCM = VOCM = MID-SUPPLY VS = 3V RI = 100Ω, RF = 402Ω fIN = 10MHz HD2, HD3 (dBc) DIFFERENTIAL INPUT SINGLE-ENDED INPUT –40 –50 –60 –70 –80 –90
Distortion vs Output Amplitude
VCM = VOCM = MID-SUPPLY VS = 3V RI = 100Ω, RF = 402Ω fIN = 10MHz DIFFERENTIAL INPUT SINGLE-ENDED INPUT HD3 HD3 HD2 HD2
VCM = VOCM = MID-SUPPLY VS = 3V VOUT = 2VP-P RI = 100Ω, RF = 402Ω DIFFERENTIAL INPUT SINGLE-ENDED INPUT
HD2
0.5 1.0 2.0 2.5 0 1.5 DC COMMON MODE INPUT (AT IN+ AND IN– PINS) (V)
64044 G17
0
1
2
4 3 VOUTDIFF (VP-P)
5
6
64044 G18
6404f
15
LTC6404 LTC6404-4 TYPICAL PERFORMANCE CHARACTERISTICS
LTC6404-4 Driving LTC2207 16-Bit ADC (Single Tone)
0 –20 AMPLITUDE (dBFS) –40 –60 –80 –100 –120 –140 0 10 20 30 40 50
64044 G19
LTC6404-4 Driving LTC2207 16-Bit ADC (Two Tones)
0 –20 AMPLITUDE (dBFS) –40 –60 –80 IMD3L –100 –120 –140 0 10 20 30 40 50
64044 G20
VS = 3.3V VOUTDIFF = 2VP-P VCM = VOCM = 1.25V RI = 100Ω, RF = 402Ω 10.1MHz, 64k POINT FFT fSAMPLE = 105Msps FUNDAMENTAL = –1dBFS HD2 = –98.9dBc HD3 = –99.6dBc
VS = 3.3V VOUTDIFF = 2VP-P VCM = VOCM = 1.4V RI = 100Ω, RF = 402Ω 64k POINT FFT fSAMPLE = 105Msps 9.5MHz, 10.5MHz = –7dBFS IMD3L = –100.8dBc IMD3U = –102dBc IMD3U
FREQUENCY (MHz)
FREQUENCY (MHz)
Voltage Noise Density vs Frequency
100 VOLTAGE NOISE DENSITY (nV/√Hz) VCM = VOCM = MID-SUPPLY VS = 3V RI = 100Ω, RF = 402Ω TA = 25°C COMMON MODE 10 NOISE FIGURE (dB) 28 24 20 16 12 8 4 0
LTC6404-4 Noise Figure vs Frequency
VCM = VOCM = MID-SUPPLY VS = 3V TA = 25°C SEE FIGURE 2 CIRCUIT
DIFFERENTIAL INPUT REFERRED 1 0.01
0.1
1 10 FREQUENCY (MHz)
100
1000
64044 G21
10
100 FREQUENCY (MHz)
1000
64044 G22
PIN FUNCTIONS
SHDN (Pin 1): When SHDN is floating or directly tied to V+, the LTC6404 is in the normal (active) operating mode. When Pin 1 is pulled a minimum of 2.1V below V+, the LTC6404 enters into a low power shutdown state. See Applications Information for more details. V+, V– (Pins 2, 10, 11 and Pins 3, 9, 12): Power Supply Pins. Three pairs of power supply pins are provided to keep the power supply inductance as low as possible to prevent degradation of amplifier 2nd harmonic performance. See the Layout Considerations section for more detail. VOCM (Pin 4): Output Common Mode Reference Voltage. The voltage on VOCM sets the output common mode voltage level (which is defined as the average of the voltages on the OUT+ and OUT– pins). The VOCM pin is the midpoint of an internal resistive voltage divider between the supplies, developing a (default) mid-supply voltage potential to maximize output signal swing. In general, the VOCM pin can be overdriven by an external voltage reference capable of driving the input impedance presented by the VOCM pin. On the LTC6404-1, the VOCM pin has a input resistance of approximately 23.5k to a mid-supply
6404f
16
LTC6404 PIN FUNCTIONS
potential. On the LTC6404-2, the VOCM pin has a input resistance of approximately 14k. On the LTC6404-4, the VOCM pin has a input resistance of approximately 7k. The VOCM pin should be bypassed with a high quality ceramic bypass capacitor of at least 0.01μF (unless you are using , split supplies, then connect directly to a low impedance, low noise ground plane) to minimize common mode noise from being converted to differential noise by impedance mismatches both externally and internally to the IC. NC (Pins 5, 16): No Connection. These pins are not connected internally. OUT+, OUT– (Pins 7, 14): Unfiltered Output Pins. Besides driving the feedback network, each pin can drive an additional 50Ω to ground with typical short-circuit current limiting of ±65mA. Each amplifier output is designed to drive a load capacitance of 10pF This basically means . the amplifier can drive 10pF from each output to ground or 5pF differentially. Larger capacitive loads should be decoupled with at least 25Ω resistors in series with each output. For long-term device reliability, it is recommended that the continuous (DC + ACRMS) output current be limited to under 50mA. OUTF+, OUTF– (Pins 8, 13): Filtered Output Pins. These pins have a series 50Ω resistor connected between the filtered and unfiltered outputs and three 12pF capacitors. Both OUTF+ and OUTF– have 12pF to V–, plus an additional 12pF differentially between OUTF+ and OUTF–. This filter creates a differential lowpass frequency response with a –3dB bandwidth of 88.5MHz. For long-term device reliability, it is recommended that the continuous (DC + ACRMS) output current be limited to under 40mA. IN+, IN– (Pins 15, 6): Noninverting and Inverting Input Pins of the Amplifier, Respectively. For best performance, it is highly recommended that stray capacitance be kept to an absolute minimum by keeping printed circuit connections as short as possible, and if necessary, stripping back nearby surrounding ground plane away from these pins. Exposed Pad (Pin 17): Tie the pad to V– (Pins 3, 9, and 12). If split supplies are used, do not tie the pad to ground.
BLOCK DIAGRAM
16 V+ NC V– V+ SHDN 1 V+ 2 V– 3 V– VOCM 4 V+ V– V+ V– 2 • RVOCM 66k V+ 50Ω V– 15 IN+ V+ 14 OUT– V– V+ 12pF V– 12 V– V+ 11 12pF V+ 50Ω 12pF V+ 10 V– V– 9 V– V– 5 IC 2 • RVOCM 47k LTC6404-1 28k LTC6404-2 14k LTC6404-4
6404f
13
OUTF– V+
+
VOCM
2 • RVOCM
–
V– NC
V+
V– V+ 7 OUT+ 8 OUTF+
V+
6
IN–
6404 BD
17
LTC6404 APPLICATIONS INFORMATION
RI VIN+ RF VOUT– VOUTF– 16 NC 15 IN+ 14 OUT– 13 OUTF– LTC6404 12pF V– 12 V– V+ 11 V+ 10 12pF V– V– 9 5 RI NC 6 IN– 7 OUT+ VOUT+ 8 OUTF+ 0.1μF V– 0.1μF 0.1μF RBAL V– 0.1μF VOUTCM V+ 0.1μF RBAL IL
+
VINP
–
SHDN SHDN VSHDN V+ VCM 0.1μF V– 3 1 V+ 2 V– V– VOCM VOCM 4 0.01μF V+ 50Ω
+
VOCM
12pF V+ 50Ω
–
–
VINM
+
VIN–
RF
VOUTF+
IL
6404 F01
Figure 1. DC Test Circuit
0.01μF
RI
VIN+
RF
VOUT– VOUTF–
100Ω
0.01μF
16
NC
15
IN+
14
OUT–
13
SHDN 50Ω MINI-CIRCUITS TCM4-19 SHDN VSHDN V+ 0.1μF V– 3 1 V+ 2 V– V– VOCM VOCM 0.01μF 5 0.01μF RI 4 NC 6 IN– 7 OUT+ 8 V+ 50Ω
OUTF– LTC6404 12pF V– 12 V– V + 11 V+ 10 V– V– 9 OUTF+ 0.01μF
6404 F02
V– 0.1μF 0.1μF
MINI-CIRCUITS TCM4-19
•
•
•
•
+
VIN
+
VOCM
12pF V+ 50Ω 12pF
50Ω V+ 0.1μF 0.1μF V– 0.1μF
–
–
VIN–
RF
VOUT+
VOUTF+
100Ω
Figure 2. AC Test Circuit (–3dB BW testing)
6404f
18
LTC6404 APPLICATIONS INFORMATION
Functional Description The LTC6404 is a small outline, wide band, low noise, and low distortion fully-differential amplifier with accurate output phase balancing. The LTC6404 is optimized to drive low voltage, single-supply, differential input 14-bit to 18-bit analog-to-digital converters (ADCs). The LTC6404’s output is capable of swinging rail-to-rail on supplies as low as 2.7V, which makes the amplifier ideal for converting ground referenced, single-ended signals into DC level-shifted differential signals in preparation for driving low voltage, single-supply, differential input ADCs. Unlike traditional op amps which have a single output, the LTC6404 has two outputs to process signals differentially. This allows for two times the signal swing in low voltage systems when compared to single-ended output amplifiers. The balanced differential nature of the amplifier also provides even-order harmonic distortion cancellation, and less susceptibility to common mode noise (e.g., power supply noise). The LTC6404 can be used as a single-ended input to differential output amplifier, or as a differential input to differential output amplifier. The LTC6404’s output common mode voltage, defined as the average of the two output voltages, is independent of the input common mode voltage, and is adjusted by applying a voltage on the VOCM pin. If the pin is left open, there is an internal resistive voltage divider that develops a potential halfway between the V+ and V– pins. Whenever this pin is not hard tied to a low impedance ground plane, it is recommended that a high quality ceramic capacitor is used to bypass the VOCM pin to a low impedance ground plane (See Layout Considerations in this document). The LTC6404’s internal common mode feedback path forces accurate output phase balancing to reduce even order harmonics, and centers each individual output about the potential set by the VOCM pin. VOUTCM = VOCM = VOUT + + VOUT – 2 on-chip single pole RC passive filter band limits the filtered outputs to a –3dB frequency of 88.5MHz. The user has a choice of using the unfiltered outputs, the filtered outputs, or modifying the filtered outputs to adjust the frequency response by adding additional components. In applications where the full bandwidth of the LTC6404 is desired, the unfiltered outputs (OUT+ and OUT–) should be used. The unfiltered outputs OUT+ and OUT– are designed to drive 10pF to ground (or 5pF differentially). Capacitances greater than 10pF will produce excess peaking, and can be mitigated by placing at least 25Ω in series with each output pin. Input Pin Protection The LTC6404’s input stage is protected against differential input voltages which exceed 1.4V by two pairs of backto-back diodes connected in anti-parallel series between IN+ and IN– (Pins 6 and 15). In addition, the input pins have steering diodes to either power supply. If the input pair is overdriven, the current should be limited to under 10mA to prevent damage to the IC. The LTC6404 also has steering diodes to either power supply on the VOCM and SHDN pins (Pins 4 and 1), and if forced to voltages which exceed either supply, they too, should be current-limited to under 10mA. SHDN Pin If the SHDN pin (Pin 1) is pulled 2.1V below the positive supply, circuitry is activated which powers down the LTC6404. The pin will have the Thevenin equivalent impedance of approximately 66kΩ to V+. If the pin is left unconnected, an internal pull-up resistor of 150k will keep the part in normal active operation. Care should be taken to control leakage currents at this pin to under 1μA to prevent inadvertently putting the LTC6404 into shutdown. In shutdown, all biasing current sources are shut off, and the output pins, OUT+ and OUT–, will each appear as open collectors with a non-linear capacitor in parallel and steering diodes to either supply. Because of the non-linear capacitance, the outputs still have the ability to sink and source small amounts of transient current if driven by significant voltage transients. The inputs (IN+, and IN–) appear as anti-parallel diodes which can conduct
6404f
The outputs (OUT+ and OUT–) of the LTC6404 are capable of swinging rail-to-rail. They can source or sink up to approximately 65mA of current. Additional outputs (OUTF+ and OUTF–) are available that provide filtered versions of the OUT+ and OUT– outputs. An
19
LTC6404 APPLICATIONS INFORMATION
if voltage transients at the input exceed 1.4V. The inputs also have steering diodes to either supply. The turn-on and turn-off time between the shutdown and active states is typically less than 1μs. General Amplifier Applications As levels of integration have increased and correspondingly, system supply voltages decreased, there has been a need for ADCs to process signals differentially in order to maintain good signal to noise ratios. These ADCs are typically supplied from a single supply voltage which can be as low as 3V (2.7V min), and will have an optimal common mode input range near mid-supply. The LTC6404 makes interfacing to these ADCs easy, by providing both single-ended to differential conversion as well as common mode level shifting. The front page of this data sheet shows a typical application. Referring to Figure 1, the gain to VOUTDIFF from VINM and VINP is: VOUTDIFF = VOUT + – VOUT – ≈ RF • ( VINP – VINM ) RI of single ended signals to differential output signals to drive differential input ADCs. Effects of Resistor Pair Mismatch In the circuit of Figure 3, it is possible the gain setting resistors will not perfectly match. Assuming infinite open loop gain, the differential output relationship is given by the equation: VOUTDIFF = VOUT + – VOUT – ≅ RF •V + RI INDIFF
Δβ Δβ • VINCM – •V β AVG β AVG OCM where: RI2 ⎞ 1 ⎛ RI1 β AVG = • ⎜ + 2 ⎝ RI1 + RF1 RI2 + RF 2 ⎟ ⎠ RF is the average of RF1, and RF2, and RI is the average of RI1, and RI2. βAVG is defined as the average feedback factor (or gain) from the outputs to their respective inputs: Δβ is defined as the difference in feedback factors: Δβ = RI2 RI1 – RI2 + RF 2 RI1 + RF1
VOUT–
Note from the above equation, the differential output voltage (VOUT+ – VOUT–) is completely independent of input and output common mode voltages, or the voltage at the common mode pin. This makes the LTC6404 ideally suited for pre-amplification, level shifting and conversion
RI2 RF2
+
VINP
VOUTF– 16 NC 15 IN+ 14 OUT– 13 OUTF– LTC6404 V– 12 V– V+ 11 V+ V+ 10 V– V– 9 5 RI1 NC 6 IN– RF1 7 OUT+ 8 OUTF+
6404 F03
–
SHDN SHDN VSHDN V+ 0.1μF V– 3 1 V+ 2 V– V– VOCM VVOCM 4 V+
V– 0.1μF 0.1μF
+
VOCM
V+ 0.1μF 0.1μF V– 0.1μF
–
–
VINM
0.01μF
+
VOUTF+
VOUT+
Figure 3. Basic Differential Amplifier with Feedback Resistor Pair Mismatch
6404f
20
LTC6404 APPLICATIONS INFORMATION
VINCM is defined as the average of the two input voltages VINP, and VINM (also called the source-referred input common mode voltage): 1 VINCM = • ( VINP + VINM ) 2 and VINDIFF is defined as the difference of the input voltages: VINDIFF = VINP – VINM When the feedback ratios mismatch (Δβ), common mode to differential conversion occurs. Setting the differential input to zero (VINDIFF = 0), the degree of common mode to differential conversion is given by the equation: VOUTDIFF = VOUT+ – VOUT – Δβ ≈ ( VINCM – VOCM ) • β AVG VINDIFF = 0 Using the LTC6404-1 in a single supply application on a single 5V supply with 1% resistors, and the input common mode grounded, with the VOCM pin biased at mid-supply, the worst-case DC offset can induce 25mV of apparent offset voltage. With 0.1% resistors, the worst case apparent offset reduces to 2.5mV. Input Impedance and Loading Effects The input impedance looking into the VINP or VINM input of Figure 1 depends on whether the sources VINP and VINM are fully differential. For balanced input sources (VINP = –VINM), the input impedance seen at either input is simply: RINP = RINM = RI For single ended inputs, because of the signal imbalance at the input, the input impedance increases over the balanced differential case. The input impedance looking into either input is: RINP = RINM = RI ⎛ 1 ⎛ RF ⎞ ⎞ ⎜ 1– 2 • ⎜ R + R ⎟ ⎟ ⎝ I F ⎠⎠ ⎝
⏐
In general, the degree of feedback pair mismatch is a source of common mode to differential conversion of both signals and noise. Using 1% resistors or better will mitigate most problems, and will provide about 34dB worst-case of common mode rejection. Using 0.1% resistors will provide about 54dB of common mode rejection. A low impedance ground plane should be used as a reference for both the input signal source, and the VOCM pin. A direct short of VOCM to this ground or bypassing the VOCM with a high quality 0.1μF ceramic capacitor to this ground plane, will further prevent common mode signals from being converted to differential. There may be concern on how feedback ratio mismatch affects distortion. Distortion caused by feedback ratio mismatch using 1% resistors or better is negligible. However, in single supply level shifting applications where there is a voltage difference between the input common mode voltage and the output common mode voltage, resistor mismatch can make the apparent voltage offset of the amplifier appear higher than specified. The apparent input referred offset induced by feedback ratio mismatch is derived from the following equation: VOSDIFF(APPARENT) ≈ (VICM – VOCM) • Δβ
Input signal sources with non-zero output impedances can also cause feedback imbalance between the pair of feedback networks. For the best performance, it is recommended that the source’s output impedance be compensated for. If input impedance matching is required by the source, R1 should be chosen (see Figure 4): R1 = RINM • RS RINM – RS
RINM RS VS R1 RI RF
– +
RI R2 = RS || R1 RF
+ –
R1 CHOSEN SO THAT R1 || RINM = RS R2 CHOSEN TO BALANCE R1 || RS
6404 F04
Figure 4. Optimal Compensation for Signal Source Impedance
6404f
21
LTC6404 APPLICATIONS INFORMATION
According to Figure 4, the input impedance looking into the differential amp (RINM) reflects the single ended source case, thus: RINM = RI ⎛ 1 ⎛ RF ⎞ ⎞ ⎜ 1– 2 • ⎜ R + R ⎟ ⎟ ⎝ I F ⎠⎠ ⎝ With singled ended inputs, there is an input signal component to the input common mode voltage. Applying only VINP (setting VINM to zero), the input common voltage is approximately: VICM = ⎛ RI ⎞ VIN+ + VIN– ≈ VOCM • ⎜ + 2 ⎝ RI + RF ⎟ ⎠ ⎛ RF ⎞ •⎜ ⎝ RF + RI ⎟ ⎠
R2 is chosen to balance R1 || RS: R2 = RI • RS RI + RS
⎛ RF ⎞ VINP VCM • ⎜ + 2 ⎝ RF + RI ⎟ ⎠
Output Common Mode Voltage Range The output common mode voltage is defined as the average of the two outputs: VOUTCM = VOCM = VOUT + + VOUT – 2
Input Common Mode Voltage Range The LTC6404’s input common mode voltage (VICM) is defined as the average of the two input voltages, VIN+, and VIN–. It extends from V– to 1.4V below V+. The operating input common mode range depends on the circuit configuration (gain), VOCM and VCM (Refer to Figure 5). For fully differential input applications, where VINP = –VINM, the common mode input voltage is approximately: VICM = ⎛ RI ⎞ VIN+ + VIN– ≈ VOCM • ⎜ + 2 ⎝ RI + RF ⎟ ⎠
The VOCM pin sets this average by an internal common mode feedback loop which internally forces VOUT+ = –VOUT–. The output common mode range extends from 1.1V above V– to 1V below V+ (see the Electrical Characteristics table for the LTC6404-4 output common mode voltage range). The VOCM pin sits in the middle of a voltage divider which sets the default mid-supply open circuit potential.
⎛ RF ⎞ VCM • ⎜ ⎝ RF + RI ⎟ ⎠
RI RF VOUTF– 16 NC 15 IN+ 14 OUT– 13 OUTF– LTC6404 V– 12 V– V+ V– 3 V– VOCM VVOCM 4 5 RI NC 6 IN– RF 7 OUT+ 8 OUTF+
6404 F05
+
VINP
VOUT–
–
SHDN SHDN VSHDN V+ 0.1μF V– 1 V+ VCM 2
V– 0.1μF 0.1μF
+
VOCM V+
V+ 11 V+ 10
V+ 0.1μF 0.1μF
–
V– V– 9
V– 0.1μF
–
VINM
0.01μF
+
VOUTF+
VOUT+
Figure 5. Circuit for Common Mode Range
6404f
22
LTC6404 APPLICATIONS INFORMATION
In single supply applications, where the LTC6404 is used to interface to an ADC, the optimal common mode input range to the ADC is often determined by the ADC’s reference. If the ADC makes a reference available for setting the input common mode voltage, it can be directly tied to the VOCM pin, but must be capable of driving the input impedance presented by the VOCM as listed in the Electrical Characteristics Table. This impedance can be assumed to be connected to a mid-supply potential. If an external reference drives the VOCM pin, it should still be bypassed with a high quality 0.01μF or larger capacitor to a low impedance ground plane to filter any thermal noise and to prevent common mode signals on this pin from being inadvertently converted to differential signals. Output Filter Considerations and Use Filtering at the output of the LTC6404 is often desired to provide either anti-aliasing or improved signal to noise ratio. To simplify this filtering, the LTC6404 includes an additional pair of differential outputs (OUTF+ and OUTF–) which incorporate an internal lowpass filter network with a –3dB bandwidth of 88.5MHz (Figure 6). These pins each have a DC output impedance of 50Ω. Internal capacitances are 12pF to V– on each filtered output, plus an additional 12pF capacitor connected differentially between the two filtered outputs. This resistor/capacitor combination creates filtered outputs that look like a series 50Ω resistor with a 36pF capacitor shunting each filtered output to AC ground, providing a –3dB bandwidth of
14 13
88.5MHz, and a noise bandwidth of 139MHz. The filter cutoff frequency is easily modified with just a few external components. To increase the cutoff frequency, simply add 2 equal value resistors, one between OUT+ and OUTF+ and the other between OUT– and OUTF– (Figure 7). These resistors, in parallel with the internal 50Ω resistor, lower the overall resistance and therefore increase filter bandwidth. For example, to double the filter bandwidth, add two external 50Ω resistors to lower the series filter resistance to 25Ω. The 36pF of capacitance remains unchanged, so filter bandwidth doubles. Keep in mind, the series resistance also serves to decouple the outputs from load capacitance. The unfiltered outputs of the LTC6404 are designed to drive 10pF to ground or 5pF differentially, so care should be taken to not lower the effective impedance between OUT+ and OUTF+ or OUT– and OUTF– below 25Ω. To decrease filter bandwidth, add two external capacitors, one from OUTF+ to ground, and the other from OUTF– to ground. A single differential capacitor connected between OUTF+ and OUTF– can also be used, but since it is being driven differentially it will appear at each filtered output as a single-ended capacitance of twice the value. To halve the filter bandwidth, for example, two 36pF capacitors could be added (one from each filtered output to ground). Alternatively, one 18pF capacitor could be added between the filtered outputs, again halving the filter bandwidth. Combinations of capacitors could be used as well; a three
49.9Ω
LTC6404 LTC6404 OUT– OUTF– 12pF V– 12 V– FILTERED OUTPUT (88.5MHz)
14
OUT–
13
OUTF– 12pF V– 12 V– FILTERED OUTPUT (176MHz)
50Ω
50Ω
+
12pF
+
12pF
–
50Ω
– 12pF V V–
–
50Ω
– 12pF V V–
9 9 7 OUT+ 49.9Ω 8 OUTF+
6404 F07
7
OUT+
8
OUTF+
6404 F06
Figure 6. LTC6404 Internal Filter Topology
Figure 7. LTC6404 Filter Topology Modified for 2x Filter Bandwidth (2 External Resistors)
6404f
23
LTC6404 APPLICATIONS INFORMATION
capacitor solution of 12pF from each filtered output to ground plus a 12pF capacitor between the filtered outputs would also halve the filter bandwidth (Figure 8). Noise Considerations The LTC6404’s input referred voltage noise is on the order of 1.5nV/√Hz. Its input referred current noise is on the order of 3pA/√Hz. In addition to the noise generated by the amplifier, the surrounding feedback resistors also contribute noise. A noise model is shown in Figure 9. The output noise generated by both the amplifier and the feedback components is governed by the equation: ⎛ ⎛ RF ⎞ ⎞ 2 ⎜ eni • ⎜ 1+ R ⎟ ⎟ + 2 • (In • RF ) + ⎝ ⎝ I ⎠⎠ ⎛ ⎛ R ⎞⎞ 2 • ⎜ enRI • ⎜ F ⎟ ⎟ + 2 • enRF 2 ⎝ RI ⎠ ⎠ ⎝
2 2
LTC6404
14
OUT–
13
OUTF– 12pF V– 12 V– 12pF
12pF
50Ω
+
12pF
FILTERED OUTPUT (44.25MHz)
–
50Ω
– 12pF V V–
12pF 9
eno =
7
OUT+
8
OUTF+
6404 F08
Figure 8. LTC6404 Filter Topology Modified for 1/2x Filter Bandwidth (3 External Capacitors)
enRI22 RI2 in+2 RF2 enRF22
A plot of this equation, and a plot of the noise generated by the feedback components for the LTC6404 is shown in Figure 10.
16
NC
15
IN+
14
OUT–
13
SHDN SHDN 1 V+ V+ 2 V– V– encm
2
OUTF– LTC6404 V– 12 V– V+ 11 V+ V+ 10 V– V– 9 V– V+ enof2 eno2 V–
V+
+
VOCM
3
V– VOCM
–
4 5 NC in–2 6 IN– 7 OUT+ 8 OUTF+
6404 F09
eni2 enRI12 RI1 RF1 enRF12
Figure 9. Noise Model of the LTC6404
6404f
24
LTC6404 APPLICATIONS INFORMATION
100 TOTAL (AMPLIFIER AND FEEDBACK NETWORK) OUTPUT NOISE 10 nV/√Hz
Layout Considerations Because the LTC6404 is a very high speed amplifier, it is sensitive to both stray capacitance and stray inductance. Three pairs of power supply pins are provided to keep the power supply inductance as low as possible to prevent degradation of amplifier 2nd Harmonic performance. It is critical that close attention be paid to supply bypassing. For single supply applications (Pins 3, 9 and 12 grounded) it is recommended that 3 high quality 0.1μF surface mount ceramic bypass capacitor be placed between pins 2 and 3, between pins 11and 12, and between pins10 and 9 with direct short connections. Pins 3, 9 and 10 should be tied directly to a low impedance ground plane with minimal routing. For dual (split) power supplies, it is recommended that at least two additional high quality, 0.1μF ceramic capacitors are used to bypass pin V+ to ground and V– to ground, again with minimal routing. For driving large loads (400Ω in circuits with RF = RI. Excessive peaking in the frequency response can be mitigated by adding small amounts of feedback capacitance (0.5pF to 2pF) around RF. Always keep in mind the differential nature of the LTC6404, and that it is critical that the load impedances seen by both outputs (stray or intended) should be as balanced and symmetric as possible. This will help preserve the natural balance of the LTC6404, which minimizes the generation of even order harmonics, and preserves the rejection of common mode signals and noise. It is highly recommended that the VOCM pin be either hard tied to a low impedance ground plane (in split supply applications), or bypassed to ground with a high quality ceramic capacitor whose value exceeds 0.01μF This will . help stabilize the common mode feedback loop as well as prevent thermal noise from the internal voltage divider and
6404f
FEEDBACK RESISTOR NETWORK NOISE ALONE 1
0.1 10 100 RF = RI (Ω) 1k 10k
6404 F10
Figure 10. LTC6404-1 Output Spot Noise vs Spot Noise Contributed by Feedback Network Alone
The LTC6404’s input referred voltage noise contributes the equivalent noise of a 140Ω resistor. When the feedback network is comprised of resistors whose values are less than this, the LTC6404’s output noise is voltage noise dominant (See Figure 10.): ⎛ R⎞ eno ≈ eni • ⎜ 1+ F ⎟ ⎝ RI ⎠ Feedback networks consisting of resistors with values greater than about 200Ω will result in output noise which is resistor noise and amplifier current noise dominant. eno ≈ 2 •
(In • RF )2 + ⎜ 1+ RF ⎟ • 4 • k • T • RF ⎝ R⎠
I
⎛
⎞
Lower resistor values (
工商网监
湘ICP备2023018690号
