LTC6400IUD-26-TRPBF

LTC6400-26 1.9GHz Low Noise, Low Distortion Differential ADC Driver for DC-300MHz FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LTC®6400-26 is a high-speed differential amplifier targeted at processing signals from DC to 300MHz. The part has been specifically designed to drive 12-, 14- and 16-bit ADCs with low noise and low distortion, but can also be used as a general-purpose broadband gain block. The LTC6400-26 is easy to use, with minimal support circuitry required. The output common mode voltage is set using an external pin, independent of the inputs, which eliminates the need of transformers or AC-coupling capacitors in many applications. The gain is internally fixed at 26dB (20V/V). The LTC6400-26 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6400-26 is packaged in a compact 16-lead 3mm × 3mm QFN package and operates over the –40°C to 85°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. 1.9GHz –3dB Bandwidth Fixed Gain of 20V/V (26dB) –94dBc IMD3 at 70MHz (Equivalent OIP3 = 51dBm) –71dBc IMD3 at 300MHz (Equivalent OIP3 = 39.5dBm) 1nV/√Hz Internal Op Amp Noise 1.5nV/√Hz Total Input Referred Noise 6.8dB Noise Figure Differential Inputs and Outputs 50Ω Input Impedance 2.85V to 3.5V Supply Voltage 85mA Supply Current (255mW) 1V to 1.6V Output Common Mode, Adjustable DC- or AC-Coupled Operation Max Differential Output Swing 4.7VP-P Small 16-Lead 3mm × 3mm × 0.75mm QFN Package APPLICATIONS ■ ■ ■ ■ ■ Differential ADC Driver Differential Driver/Receiver Single Ended to Differential Conversion IF Sampling Receivers SAW Filter Interfacing TYPICAL APPLICATION Single-Ended to Differential ADC Driver at 140MHz IF 3.3V 3.3V 60 50 0.1μF 1000pF V+ 0.1μF VIN 150W 0.1μF +IN +OUT 24nH 15Ω COILCRAFT 0603CS 1.25V 0.1μF 100Ω 33pF 33pF 10Ω AIN– 15Ω 10Ω AIN+ VDD LTC2208 VCM 33pF OUTPUT IP3 (dBm) 40 30 20 10 0 640026 TA01a Equivalent OIP3 vs Frequency DIFFERENTIAL INPUT (NOTE 7) LTC6400-26 –IN –OUT VOCM 37.4Ω V– LTC2208 130Msps 16-BIT ADC NO RL RL = 200Ω 0 50 100 150 200 FREQUENCY (MHz) 250 300 640026 TA01b 640026fa 1 LTC6400-26 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW –IN –IN +IN 7 +OUTF +IN 12 V– 17 11 ENABLE 10 V+ 9 V– 8 +OUT 16 15 14 13 V+ 1 VOCM 2 V+ 3 V– 4 5 –OUT 6 –OUTF Supply Voltage (V+ – V–)..........................................3.6V Input Current (Note 2)..........................................±10mA Operating Temperature Range (Note 3) ............................................... –40°C to 85°C Specified Temperature Range (Note 4) ............................................... –40°C to 85°C Storage Temperature Range................... –65°C to 150°C Maximum Junction Temperature........................... 150°C 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 LTC6400CUD-26#PBF LTC6400IUD-26#PBF TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION 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 LTC6400CUD-26#TRPBF LCCX LTC6400IUD-26#TRPBF LCCX 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/ LTC6400 AND LTC6401 SELECTOR GUIDE PART NUMBER LTC6400-20 LTC6400-26 LTC6401-8 LTC6401-20 LTC6401-26 GAIN (dB) 20 26 8 20 26 GAIN (V/V) 10 20 2.5 10 20 Please check each datasheet for complete details. ZIN (DIFFERENTIAL) (Ω) 200 50 400 200 50 IS (mA) 90 85 45 50 45 In addition to the LTC6400 family of amplifiers, a lower power LTC6401 family is available. The LTC6401 is pin compatible to the LTC6400, and has the same low noise performance. The lower power consumption of the LTC6401 comes at the expense of slightly higher non-linearity, especially at input frequencies above 140MHz. Please refer to the separate LTC6401 data sheets for complete details. Other gain versions from 8dB to 14dB will follow. 640026fa 2 LTC6400-26 DC ELECTRICAL CHARACTERISTICS + The ● –denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, +IN = –IN = VOCM = 1.25V, ENABLE= 0V, No RL unless otherwise noted. PARAMETER Gain Gain Temperature Drift Output Swing Low Output Swing High Maximum Differential Output Swing Output Current Drive Input Offset Voltage Input Offset Voltage Drift Input Common Mode Voltage Range, MIN Input Common Mode Voltage Range, MAX Input Resistance (+IN, –IN) Input Capacitance Output Resistance (+OUT, –OUT) Filtered Output Resistance (+OUTF, –OUTF) Filtered Output Capacitance (+OUTF, –OUTF) Common Mode Rejection Ratio Differential Differential, Includes Parasitics Differential Differential Differential, Includes Parasitics Input Common Mode Voltage 1.1V to 1.4V VOCM = 1V to 1.6V ● ● ● ● ● SYMBOL GDIFF TCGAIN VSWINGMIN VSWINGMAX VOUTDIFFMAX IOUT VOS TCVOS IVRMIN IVRMAX RINDIFF CINDIFF ROUTDIFF ROUTFDIFF COUTFDIFF CMRR CONDITIONS VIN = ±50mV Differential VIN = ±50mV Differential Each Output, VIN = ±200mV Differential Each Output, VIN = ±200mV Differential 1dB Compressed Each Output, VIN = ±200mV, VOUT > 2VP-P Differential Differential ● ● ● ● ● ● ● ● MIN 25 TYP 26 0.0038 90 MAX 27 160 UNITS dB dB/°C mV V VP-P mA Input/Output Characteristic (+IN, –IN, +OUT, –OUT, +OUTF, –OUTF) 2.35 4.38 20 –2 2.48 4.7 2 1 1 mV μV/°C V V Ω pF Ω Ω pF dB 1.6 42.5 18 85 50 50 1 25 100 2.7 75 32 115 57.5 Output Common Mode Control GCM VOCMMIN VOCMMAX VOSCM TCVOSCM IVOCM ENABLE Pin VIL VIH IIL IIH Power Supply VS IS ISHDN PSRR Operating Supply Range Supply Current Shutdown Supply Current Power Supply Rejection Ratio (Differential Outputs) ENABLE = 0.8V ENABLE = 2.4V Both Inputs and Outputs Floating 2.85V to 3.5V ● ● ● ● Common Mode Gain Output Common Mode Range, MIN Output Common Mode Range, MAX 1 1 1.1 1.6 1.5 –15 3 5 15 0.8 2.4 0.5 1.4 2.85 70 3 85 0.8 65 96 3 3.5 102 3 15 V/V V V V V mV μV/°C μA V V μA μA V mA mA dB ● Common Mode Offset Voltage Common Mode Offset Voltage Drift VOCM Input Current ENABLE Input Low Voltage ENABLE Input High Voltage ENABLE Input Low Current ENABLE Input High Current VOCM = 1.1V to 1.5V ● ● ● ● ● ENABLE = 0.8V ENABLE = 2.4V ● ● 640026fa 3 LTC6400-26 AC ELECTRICAL CHARACTERISTICS ENABLE = 0V, No RL unless otherwise noted. SYMBOL –3dBBW 0.5dBBW 0.1dBBW 1/f SR tS1% tOVDR tON tOFF –3dBBWVOCM 10MHz Input Signal HD2,10M/HD3,10M Second/Third Order Harmonic Distortion IMD3,10M OIP3,10M Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) Equivalent Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) 1dB Compression Point Noise Figure Input Referred Voltage Noise Density Output Referred Voltage Noise Density 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL 2VP-P,OUT Composite, No RL (Note 7) RL = 375Ω (Notes 5, 7) RL = 375Ω (Note 5) Includes Resistors (Short Inputs) Includes Resistors (Short Inputs) 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL IMD3,70M OIP3,70M Third-Order Intermodulation (f1 = 69.5MHz f2 = 70.5MHz) Equivalent Third-Order Output Intercept Point (f1 = 69.5MHz f2 = 70.5MHz) 1dB Compression Point Noise Figure Input Referred Voltage Noise Density Output Referred Voltage Noise Density Second/Third Order Harmonic Distortion Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) Equivalent Third-Order Output Intercept Point (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL 2VP-P,OUT Composite, No RL (Note 7) RL = 375Ω (Notes 5, 7) RL = 375Ω (Note 5) Includes Resistors (Short Inputs) Includes Resistors (Short Inputs) 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL 2VP-P,OUT Composite, No RL (Note 7) –99/–90 –98/–99 –91 –93 50.5 dBc dBc dBc dBc dBm PARAMETER –3dB Bandwidth Bandwidth for 0.5dB Flatness Bandwidth for 0.1dB Flatness 1/f Noise Corner Slew Rate 1% Settling Time Overdrive Recovery Time Turn-On Time Turn-Off Time VOCM Pin Small Signal –3dB BW Differential VOUT = 2V Step (Note 6) VOUT = 2VP-P (Note 6) VOUT = 1.9VP-P (Note 6) +OUT, –OUT Within 10% of Final Values ICC Falls to 10% of Nominal 0.1VP-P at VOCM, Measured Single-Ended at Output (Note 6) Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, MIN 1.2 TYP 1.9 0.53 0.28 13.9 6670 2 16 120 166 14.7 MAX UNITS GHz GHz GHz kHz V/μs ns ns ns ns MHz CONDITIONS 200mVP-P,OUT (Note 6) 200mVP-P,OUT (Note 6) 200mVP-P,OUT (Note 6) P1dB,10M NF10M eIN,10M eON,10M 70MHz Input Signal 17.8 6.8 1.5 30 –87/–81 –87/–94 –85 –94 51 dBm dB nV/√Hz nV/√Hz dBc dBc dBc dBc dBm HD2,70M/HD3,70M Second/Third Order Harmonic Distortion P1dB,70M NF70M eIN,70M eON,70M 140MHz Input Signal HD2,140M/ HD3,140M IMD3,140M OIP3,140M 18.2 6.7 1.4 28 –83/–72 –81/–83 –80 –88 48 dBm dB nV/√Hz nV/√Hz dBc dBc dBc dBc dBm 640026fa 4 LTC6400-26 AC ELECTRICAL CHARACTERISTICS ENABLE = 0V, No RL unless otherwise noted. SYMBOL P1dB,140M NF140M eN,140M eON,140M 240MHz Input Signal HD2,240M/ HD3,240M IMD3,240M OIP3,240M P1dB,240M NF240M eN,240M eON,240M 300MHz Input Signal HD2,300M/ HD3,300M IMD3,300M OIP3,300M Second/Third Order Harmonic Distortion Third Order Intermodulation (f1 = 299.5MHz f2 = 300.5MHz) Equivalent Third Order Output Intercept Point (f1 = 299.5MHz f2 = 300.5MHz) 1dB Compression Point Noise Figure Input Referred Voltage Noise Density Output Referred Voltage Noise Density Third Order Intermodulation (f1 = 280MHz f2 = 320MHz) Measured at 360MHz 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL 2VP-P,OUT Composite, No RL (Note 7) RL = 375Ω (Notes 5, 7) RL = 375Ω (Note 5) Includes Resistors (Short Inputs) Includes Resistors (Short Inputs) 2VP-P,OUT Composite, RL = 375Ω –66/–54 –76/–62 –66 –71 39.5 dBc dBc dBc dBc dBm Second/Third Order Harmonic Distortion Third Order Intermodulation (f1 = 239.5MHz f2 = 240.5MHz) Third Order Output Intercept Point (f1 = 239.5MHz f2 = 240.5MHz) 1dB Compression Point Noise Figure Input Referred Voltage Noise Density Output Referred Voltage Noise Density 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL 2VP-P,OUT Composite, No RL (Note 7) RL = 375Ω (Notes 5, 7) RL = 375Ω (Note 5) Includes Resistors (Short Inputs) Includes Resistors (Short Inputs) –70/–59 –75/–71 –70 –76 42 18.1 6.9 1.4 28 dBc dBc dBc dBc dBm dBm dB nV/√Hz nV/√Hz PARAMETER 1dB Compression Point Noise Figure Input Referred Voltage Noise Density Output Referred Voltage Noise Density Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, MIN TYP 18.7 6.6 1.4 28 MAX UNITS dBm dB nV/√Hz nV/√Hz CONDITIONS RL = 375Ω (Notes 5, 7) RL = 375Ω (Note 5) Includes Resistors (Short Inputs) Includes Resistors (Short Inputs) P1dB,300M NF300M eN,300M eON,300M IMD3,280M/320M 17.7 7.6 1.5 30 –68 –62 dBm dB nV/√Hz nV/√Hz dBc 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: Input pins (+IN, –IN) are protected by steering diodes to either supply. If the inputs go beyond either supply rail, the input current should be limited to less than 10mA. Note 3: The LTC6400C is guaranteed functional over the operating temperature range of –40°C to 85°C. Note 4: The LTC6400C is guaranteed to meet specified performance from 0°C to 70°C. It 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 LTC6400I is guaranteed to meet specified performance from –40°C to 85°C. Note 5: Input and output baluns used. See Test Circuit A. Note 6: Measured using Test Circuit B. RL = 87.5Ω per output. Note 7: Since the LTC6400-26 is a feedback amplifier with low output impedance, a resistive load is not required when driving an AD converter. Therefore, typical output power is very small. In order to compare the LTC6400-26 with amplifiers that require 50Ω output load, the LTC6400-26 output voltage swing driving a given RL is converted to OIP3 and P1dB as if it were driving a 50Ω load. Using this modified convention, 2VP-P is by definition equal to 10dBm, regardless of actual RL. 640026fa 5 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response 30 25 GAIN FLATNESS (dB) TEST CIRCUIT B 10 100 1000 FREQUENCY (MHz) 3000 20 GAIN (dB) 15 10 5 0 1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 10 100 FREQUENCY (MHz) 1000 2000 640026 G02 Gain 0.1dB Flatness 640026 G01 S21 Phase and Group Delay vs Frequency 0 TEST CIRCUIT B 0.8 0 –10 S PARAMETERS (dB) –50 PHASE (DEGREE) GROUP DELAY 0.6 GROUP DELAY (ns) –20 Input and Output Reflection and Reverse Isoloation vs Frequency S22 –30 –40 S11 –50 –60 –70 S12 –100 0.4 –150 PHASE 0.2 –200 0 200 600 400 FREQUENCY (MHz) 800 0 1000 640026 G03 –80 10 100 1000 FREQUENCY (MHz) 3000 640026 G04 Input and Output Impedance vs Frequency 100 90 IMPEDANCE MAGNITUDE (Ω) 80 70 60 50 40 30 20 10 0 10 100 FREQUENCY (MHz) ZIN MAG ZOUT MAG ZIN PHASE ZOUT PHASE 50 45 40 PSRR, CMRR (dB) 35 30 25 20 15 10 5 0 1000 640026 G05 PSRR and CMRR vs Frequency 120 100 80 PSRR 60 CMRR 40 20 0 PHASE (DEGREE) 1 10 100 FREQUENCY (MHz) 1000 640026 G06 640026fa 6 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Noise Figure and Input Referred Noise Voltage vs Frequency 10 2.5 INPUT REFERRED NOISE VOLTAGE (nV/√Hz) 1.35 Small Signal Transient Response RL = 87.5W PER OUTPUT TEST CIRCUIT B –OUT 9 NOISE FIGURE (dB) EN 2.0 8 1.5 OUTPUT VOLTAGE (V) 1.30 1.25 7 NOISE FIGURE 1.0 6 0.5 1.20 +OUT 5 10 100 FREQUENCY (MHz) 0 1000 640026 G07 1.15 0 2 6 4 TIME (ns) 8 10 640026 G08 Large Signal Transient Response 2.5 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B OUTPUT VOLTAGE (V) –OUT 1.5 2.5 Overdriven Transient Response RL = 87.5Ω PER OUTPUT +OUT 2.0 OUTPUT VOLTAGE (V) 2.0 1.5 1.0 +OUT 1.0 0.5 0.5 TEST CIRCUIT B 0 50 –OUT 0 0 4 12 8 TIME (ns) 16 20 640026 G09 0 150 100 TIME (ns) 200 250 640026 G10 1% Settling Time for 2V Output Step 5 4 3 2 SETTLING (%) 1 0 –1 –2 –3 –4 –5 0 1 3 2 TIME (ns) 4 5 640026 G11 Harmonic Distortion vs Frequency –40 HARMONIC DISTORTION (dBc) –50 –60 –70 –80 –90 DIFFERENTIAL INPUT VOUT = 2VP-P RL = 87.5Ω PER OUTPUT TEST CIRCUIT B –100 –110 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω 0 50 200 150 100 FREQUENCY (MHz) 250 300 640026 G12 640026fa 7 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Third Order Intermodulation Distortion vs Frequency –40 –50 THIRD ORDER IMD (dBc) –60 –70 –80 –90 NO RL RL = 200Ω 0 50 200 150 100 FREQUENCY (MHz) 250 300 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE HARMONIC DISTORTION (dBc) –40 –50 –60 –70 –80 –90 Harmonic Distortion vs Frequency SINGLE-ENDED INPUT VOUT = 2VP-P THIRD ORDER IMD (dBc) –40 –50 –60 –70 –80 –90 Third Order Intermodulation Distortion vs Frequency SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –100 –110 –100 –110 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω 0 50 200 150 100 FREQUENCY (MHz) 250 300 –100 –110 NO RL RL = 200Ω 0 50 200 150 100 FREQUENCY (MHz) 250 300 640026 G13 640026 G14 640026 G15 Output 1dB Compression Point vs Frequency 20 OUTPUT 1dB COMPRESSION POINT (dBm) DIFFERENTIAL INPUT RL = 375 TEST CIRCUIT A 19 (NOTE 7) OUTPUT IP3 (dBm) 60 50 40 30 20 10 0 Equivalent Output Third Order Intercept Point vs Frequency DIFFERENTIAL INPUT (NOTE 7) 18 17 16 15 NO RL RL = 200Ω 0 50 100 150 200 FREQUENCY (MHz) 250 300 0 50 100 150 200 FREQUENCY (MHz) 250 300 640026 G16 640026 G17 Turn-On Time 3.5 3.0 2.5 VOLTAGE (V) 2.0 1.5 1.0 0.5 ENABLE 0 –0.5 –100 0 100 300 200 TIME (ns) 400 500 0 –20 +OUT ICC –OUT 140 120 100 VOLTAGE (V) 80 60 40 20 ICC (mA) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Turn-Off Time ENABLE 140 120 100 –OUT 80 60 +OUT 40 20 ICC 0 400 –20 500 ICC (mA) –0.5 –100 0 100 300 200 TIME (ns) 640026 G18 640026 G19 640026fa 8 LTC6400-26 PIN FUNCTIONS V+ (Pins 1, 3, 10): Positive Power Supply (Normally tied to 3V or 3.3V). All three pins must be tied to the same voltage. Bypass each pin with 1000pF and 0.1μF capacitors as close to the pins as possible. VOCM (Pin 2): This pin sets the output common mode voltage. An 0.1μF external bypass capacitor is recommended. V– (Pins 4, 9, 12, 17): Negative Power Supply. All four pins must be connected to same voltage/ground. –OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins have series 12.5Ω resistors ROUT. –OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins have 50Ω series resistors and a 2.7pF shunt capacitor. ENABLE (Pin 11): This pin is a logic input referenced to VEE. If low, the part is enabled. If high, the part is disabled and draws very low standby current while the internal op amp has high output impedance. +IN (Pins 13, 14): Positive Input. Pins 13 and 14 are internally shorted together. –IN (Pins 15, 16): Negative Input. Pins 15 and 16 are internally shorted together. Exposed Pad (Pin 17): V–. The Exposed Pad must be connected to same voltage/ground as pins 4, 9, 12. BLOCK DIAGRAM 12 V– 11 ENABLE 10 V+ 9 V– BIAS CONTROL +IN 13 +IN 14 –IN 15 –IN 16 RG 25Ω RG 25Ω RF 500Ω ROUT 12.5Ω 8 RFILT 50Ω IN+ OUT– RFILT 50Ω IN– OUT+ RF 500Ω 2k 5.3pF ROUT 12.5Ω 5 COMMON MODE CONTROL CFILT 2.7pF 6 –OUT 7 –OUTF +OUTF +OUT 1 V+ 2 VOCM 3 V+ 4 640026 BD V– 640026fa 9 LTC6400-26 APPLICATIONS INFORMATION Circuit Operation The LTC6400-26 is a low noise and low distortion fully differential op amp/ADC driver with: • Operation from DC to 1.9GHz –3dB bandwidth • Fixed gain of 20V/V (26dB) • Differential input impedance 50Ω • Differential output impedance 25Ω • Differential impedance of output filter 100Ω The LTC6400-26 is composed of a fully differential amplifier with on chip feedback and output common mode voltage control circuitry. Differential gain and input impedance are set by 25Ω/500Ω resistors in the feedback network. Small output resistors of 12.5Ω improve the circuit stability over various load conditions. They also provide a possible external filtering option, which is often desirable when the load is an ADC. Filter resistors of 50Ω are available for additional filtering. Lowpass/bandpass filters are easily implemented with just a couple of external components. Moreover, they offer single-ended 50Ω matching in wideband applications and no external resistor is needed. The LTC6400-26 is very flexible in terms of I/O coupling. It can be AC- or DC-coupled at the inputs, the outputs or both. Due to the internal connection between input and output, users are advised to keep input common mode voltage between 1V and 1.6V for proper operation. If the inputs are AC-coupled, the input common mode voltage is automatically biased close to VOCM and thus no external circuitry is needed for bias. The LTC6400-26 provides an output common mode voltage set by VOCM, which allows driving ADC directly without external components such as transformer or AC coupling capacitors. The input signal can be either single-ended or differential with only minor difference in distortion performance. Input Impedance and Matching The differential input impedance of the LTC6400-26 is 50Ω. The interface between the input of LTC6400-26 and 50Ω source is straightforward. One way is to directly connect them if the source is differential (Figure 1). Another approach is to employ a wideband transformer if the source is single ended (Figure 2). Both methods provide a wideband match. The transformer must be placed close to the input pins in order to minimize the reflection due to input mismatch. Alternatively, one could apply a narrowband impedance match at the inputs of the LTC6400-26 for frequency selection and/or noise reduction. Referring to Figure 3, LTC6400-26 can be easily configured for single-ended input and differential output without a balun. The signal is fed to one of the inputs through a matching network while the other input is connected to the same matching network and a source resistor. Because the return ratios of the two feedback paths are equal, the two outputs have the same gain and thus symmetrical swing. In general, the single-ended input impedance and termination resistor RT are determined by the combination of RS, RG and RF. For example, when RS is 50Ω, it is found that the single-ended input impedance is 75Ω and RT is 150Ω in order to match to a 50Ω source impedance. LTC6400-26 25Ω 13 +IN 50Ω IN+ OUT– 50Ω 15 –IN 25Ω 16 –IN 25Ω IN– OUT+ 500Ω 12.5Ω –OUT 5 640026 F01 25Ω 500Ω 12.5Ω +OUT 8 + – VIN 14 +IN +OUTF 7 2.7pF –OUTF 6 Figure 1. Input Termination for Differential 50Ω Input Impedance LTC6400-26 50Ω 13 +IN 50Ω 1:1 14 +IN 50Ω 15 –IN 25Ω MACOM MABA-007159-000000 16 –IN IN– OUT+ 500Ω 12.5Ω –OUT 5 640026 F02 25Ω 500Ω 12.5Ω +OUT 8 IN+ OUT– + – VIN +OUTF 7 2.7pF –OUTF 6 • Figure 2. Input Termination for Differential 50Ω Input Impedance Using a Balun • 640026fa 10 LTC6400-26 APPLICATIONS INFORMATION RS 50Ω VIN 0.1μF 13 +IN 50Ω IN+ 14 +IN 50Ω 15 –IN 0.1μF 16 –IN 37.4Ω 25Ω IN– OUT+ 500Ω 12.5Ω –OUT 5 640026 F03 LTC6400-26 25Ω 500Ω 12.5Ω +OUT 8 OUT– + – RT 150Ω +OUTF 7 2.7pF –OUTF 6 The internal low pass filter outputs at +OUTF/–OUTF have a –3dB bandwidth of 590MHz. External capacitor can reduce the low pass filter bandwidth as shown in Figure 5. A bandpass filter is easily implemented with only a few components as shown in Figure 6. Three 39pF capacitors and a 16nH inductor create a bandpass filter with 165MHz center frequency, –3dB frequencies at 138MHz and 200MHz. Output Common Mode Adjustment Figure 3. Input Termination for Single-Ended 50Ω Input Impedance The LTC6400-26 is unconditionally stable, i.e. differential stability factor Kf>1 and stability measure B1>0. However, the overall differential gain is affected by both source impedance and load impedance as shown in Figure 4: AV = VOUT RL 1000 = • VIN RS + 50 25 + RL The noise performance of the LTC6400-26 also depends upon the source impedance and termination. A trade-off between gain and noise is obvious when constant noise figure circle and constant gain circle are plotted within the same input Smith Chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. Output Impedance Match and Filter The LTC6400-26 can drive an ADC directly without external output impedance matching. Alternatively, the differential output impedance of 25Ω can be made larger, e.g. 50Ω, by series resistors or LC network. LTC6400-26 1/2 RS 13 +IN 50Ω IN+ OUT– 50Ω 15 –IN 1/2 RS 16 –IN 25Ω IN– OUT+ 500Ω 12.5Ω –OUT 5 640026 F04 The LTC6400-26’s output common mode voltage is set by the VOCM pin, which is a high impedance input. The output common mode voltage is capable of tracking VOCM in a range from 1V to 1.6V. Bandwidth of VOCM control is typically 15MHz, which is dominated by a low pass filter connected to the VOCM pin and is aimed to reduce common mode noise generation at the outputs. The internal common mode feedback loop has a –3dB bandwidth of 400MHz, allowing fast rejection of any common mode output disturbance. The VOCM pin should be tied to a DC bias voltage with a 0.1μF bypass capacitor. When interfacing with A/D converters such as the LTC22xx families, the VOCM pin can be connected to the VCM pin of the ADC. Driving A/D Converters The LTC6400-26 has been specifically designed to interface directly with high speed A/D converters. Figure 7 shows the LTC6400-26 with a single-ended input driving the LTC2208, which is a 16-bit, 130Msps ADC. Two external 5Ω resistors help eliminate potential resonance associated with bond wires of either the ADC input or the driver output. VOCM of the LTC6400-26 is connected to VCM of the LTC2208 at 1.25V. Alternatively, a single-ended input signal can be LTC6400-26 25Ω 13 +IN 50Ω IN+ OUT– 50Ω 15 –IN IN– 25Ω 16 –IN OUT+ 500Ω 12.5Ω –OUT 5 640026 F05 25Ω 500Ω 12.5Ω +OUT 8 1/2 RL 500Ω 12.5Ω +OUT 8 8.2pF +OUTF 7 2.7pF –OUTF 6 FILTERED OUTPUT 12pF (87.5MHz) 8.2pF + – VIN 14 +IN +OUTP 7 VOUT 2.7pF –OUTF 6 1/2 RL 14 +IN Figure 4. Calculate Differential Gain Figure 5. LTC6400-26 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 640026fa 11 LTC6400-26 APPLICATIONS INFORMATION –40 LTC6400-26 12.5Ω +OUT 8 50Ω IN+ 14 +IN 50Ω 15 –IN 25Ω 16 –IN IN– OUT+ 500Ω 12.5Ω –OUT 5 640026 F06 39pF 10Ω 4.99Ω 25Ω 13 +IN 500Ω SINGLE-ENDED INPUT FS = 122.8Msps –50 DRIVER VOUT = 2VP-P COMPOSITE –60 –70 OUT– +OUTF 7 1.7pF –OUTF 6 10Ω 39pF 4.99Ω –100 –110 16nH 39pF LTC2208 –80 –90 0 50 200 150 100 FREQUENCY (MHz) 250 300 640026 F08 Figure 6. LTC6400-26 with 165MHz Output Bandpass Filter Figure 8. IMD3 for the Combination of LTC6400-26 and LTC2208 converted to a differential signal via a balun and fed to the input of the LTC6400-26. Figure 8 summarizes the IMD3 performance of the whole system in Figure 7. Test Circuits Due to the fully-differential design of the LTC6400 and its usefulness in applications with differing characteristic specifications, two test circuits are used to generate the information in this datasheet. Test Circuit A is DC987B, a two-port demonstration circuit for the LTC6400 family. The silkscreen is shown in Figure 9. This circuit includes input and output transformers (baluns) for single-endedto-differential conversion and impedance transformation, allowing direct hook-up to a 2-port network analyzer. There are also series resistors at the output to present the LTC6400 with a 375Ω differential load, optimizing distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 1.9GHz to 1.67GHz. 1.25V 0.1μF Test Circuit B uses a 4-port network analyzer to measure S-parameters and gain/phase response. This removes the effects of the wideband baluns and associated circuitry, for a true picture of the >1GHz S-parameters and AC characteristics. 0.1μF IF IN 150Ω 0.1μF +IN VOCM +OUT +OUTF LTC6400-26 –OUTF –OUT –IN ENABLE 26dB GAIN 4.99Ω AIN+ VCM LTC2208 AIN– 4.99Ω LTC2208 130Msps 16-Bit ADC 640026 F07 37.4Ω Figure 7. Single-Ended Input to LTC6400-26 and LTC2208 Figure 9. Top Silkscreen of DC987B, Test Circuit A 640026fa 12 LTC6400-26 TYPICAL APPLICATION Demo Circuit 987B Schematic (Test Circuit A) VCC ENABLE 1 3 DIS 2 JP1 R16 0W VCC C17 1000pF C18 0.1μF 12 R2 (1) R6 0Ω 5 T1 (2) 1 R4 (2) C2 0.1μF R24 (1) C1 0.1μF 16 R1 0Ω VCC SL1 (2) V– 13 +IN 11 ENABLE 10 V+ V– 9 8 R10 86.6Ω R8 (1) R7 (1) R9 86.6Ω C3 0.1μF C4 0.1μF SL2 (2) T2 TCM 4:19 1:4 R14 (1) 3 2 1 4 R12 0Ω J4 +OUT SL3 (2) J5 –OUT +OUT • • J1 +IN J2 –IN R5 0dB (1) 2 3 R3 (2) C21 0.1μF 14 +IN LTC6400-26 +OUTF 7 • R11 (1) • 4 15 –IN –OUTF 6 6 –IN V+ 1 VOCM 2 V+ 3 –OUT V– 4 5 C22 0.1μF VCC R13 0Ω VCC R19 1.5k R20 1k R17 0Ω T3 TCM 4:19 1:4 C10 0.1μF C9 1000pF C12 1000pF C13 0.1μF TP5 VOCM C7 0.1μF T4 TCM 4:19 1:4 R18 0Ω J6 TEST IN 6 1 2 C19 0.1μF C23 0.1μF C24 0.1μF R25 0Ω 4 3 R21 (1) C5 0.1μF C6 0.1μF 3 R22 (1) C20 0.1μF 2 1 4 J7 TEST OUT • • VCC • 6 R26 0Ω • TP2 VCC 2.85V TO 3.5V TP3 GND C14 4.7μF C15 1μF (2) VERSION -D SL = SIGNAL LEVEL IC LTC6400CUD-26 R3 R4 T1 SL1 0dB SL2 20dB SL3 14dB OPEN OPEN MACOM MABA-007159-000000 NOTE: UNLESS OTHERWISE SPECIFIED. (1) DO NOT STUFF . 640026 TA02 640026fa 13 LTC6400-26 TYPICAL APPLICATIONS Test Circuit B, 4-Port Analysis V+ 1000pF 0.1μF 12 V– 11 ENABLE 10 V+ 9 V– BIAS CONTROL 24.9Ω 0.1μF 1/2 AGILENT E5O71A +IN 14 –IN 15 24.9Ω 0.1μF –IN 16 RG 25Ω IN+ OUT– RFILT 50Ω IN– OUT+ RF 500Ω ROUT 12.5Ω 5 COMMON MODE CONTROL 1 2 VOCM 0.1μF VOCM 0.1μF 3 4 640026 TA03 PORT 1 (50Ω) +IN 13 RG 25Ω RF 500Ω ROUT 12.5Ω 8 RFILT 50Ω 7 CFILT 2.7pF 6 +OUT 37.4Ω +OUTF 0.1μF PORT 3 (50Ω) –OUTF 1/2 AGILENT E5O71A PORT 2 (50Ω) –OUT 37.4Ω 0.1μF PORT 4 (50Ω) V+ V+ V– 1000pF V+ Optical Photodiode Receiver 3V 3V 249Ω 0.1μF 100pF 0.1μF 0.1μF LTC6400-26 249Ω 640026 TA04 PD:JDSU ETX 100RFC2 –3dB BW: 1.1GHz RISE TIME: 200ps 640026fa 14 LTC6400-26 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 0.05 3.50 0.05 2.10 1.45 0.05 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 0.05 BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 15 16 0.40 1 1.45 0.10 (4-SIDES) 2 0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.25 45 CHAMFER 3.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.25 0.05 0.50 BSC 640026fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC6400-26 RELATED PARTS PART NUMBER LT®1993-2 LT1993-4 LT1993-10 LT1994 LT5514 LT5524 LTC6400-20 LTC6401-8 LTC6401-20 LTC6401-26 LT6402-6 LT6402-12 LT6402-20 LTC6406 LT6411 DESCRIPTION 800MHz Differential Amplifier/ADC Driver 900MHz Differential Amplifier/ADC Driver 700MHz Differential Amplifier/ADC Driver Low Noise, Low Distortion Differential Op Amp Ultralow Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain Low Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain 1.8GHz Low Noise, Low Distortion, Differential ADC Driver 2.2GHz Low Noise, Low Distortion, Differential ADC Driver 1.3GHz Low Noise, Low Distortion, Differential ADC Driver 1.6GHz Low Noise, Low Distortion, Differential ADC Driver 300MHz Differential Amplifier/ADC Driver 300MHz Differential Amplifier/ADC Driver 300MHz Differential Amplifier/ADC Driver 3GHz Rail-to-Rail Input Differential Op Amp Low Power Differential ADC Driver/Dual Selectable Gain Amplifier High Slew Rate Low Cost Single/Dual/Quad Op Amps Very High Slew Rate Low Cost Single/Dual/Quad Op Amps Ultra High Slew Rate Low Cost Single/Dual Op Amps Rail-to-Rail Input and Output Low Noise Single/Dual Op Amps Rail-to-Rail Input and Output Low Noise Single/Dual/Quad Op Amps Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps COMMENTS AV = 2V/V, OIP3 = 38dBm at 70MHz AV = 4V/V, OIP3 = 40dBm at 70MHz AV = 2V/V, OIP3 = 40dBm at 70MHz 16-Bit SNR and SFDR at 1MHz, Rail-to-Rail Outputs OIP3 = 47dBm at 100MHz, Gain Control Range 10.5dB to 33dB OIP3 = 40dBm at 100MHz, Gain Control Range 4.5dB to 37dB AV = 20dB, 90mA Supply Current, IMD3 = –65dBc at 300MHz AV = 8dB, 45mA Supply Current, IMD3 = –80dBc at 140MHz AV = 20dB, 50mA Supply Current, IMD3 = –74dBc at 140MHz AV = 26dB, 45mA Supply Current, IMD3 = –72dBc at 140MHz AV = 6dB, Distortion < –80dBc at 25MHz AV = 12dB, Distortion < –80dBc at 25MHz AV = 20dB, Distortion < –80dBc at 25MHz 1.6nV/√Hz Noise, –72dBc Distortion at 50MHz, 18mA 16mA Supply Current, IMD3 = –83dBc at 70MHz, AV = 1, –1 or 2 High-Speed Differential Amplifiers/Differential Op Amps High-Speed Single-Ended Output Op Amps LT1812/LT1813/ LT1814 LT1815/LT1816/ LT1817 LT1818/LT1819 LT6200/LT6201 LT6202/LT6203/ LT6204 LT6230/LT6231/ LT6232 LT6233/LT6234/ LT6235 Integrated Filters LTC1562-2 LT1568 LTC1569-7 LT6600-2.5 LT6600-5 LT6600-10 LT6600-15 LT6600-20 Very Low Noise, 8th Order Filter Building Block Very Low Noise, 4th Order Filter Building Block Linear Phase, Tunable 10th Order Lowpass Filter Very Low Noise Differential 2.5MHz Lowpass Filter Very Low Noise Differential 5MHz Lowpass Filter Very Low Noise Differential 10MHz Lowpass Filter Very Low Noise Differential 15MHz Lowpass Filter Very Low Noise Differential 20MHz Lowpass Filter Lowpass and Bandpass Filters up to 300kHz Lowpass and Bandpass Filters up to 10MHz Single-Resistor Programmable Cut-Off to 300kHz SNR = 86dB at 3V Supply, 4th Order Filter SNR = 82dB at 3V Supply, 4th Order Filter SNR = 82dB at 3V Supply, 4th Order Filter SNR = 76dB at 3V Supply, 4th Order Filter SNR = 76dB at 3V Supply, 4th Order Filter 8nV/√Hz Noise, 750V/μs, 3mA Supply Current 6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current 6nV/√Hz Noise, 2500V/μs, 9mA Supply Current 0.95nV/√Hz Noise, 165MHz GBW, Distortion = –80dBc at 1MHz 1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW 1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW 1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW 640026fa 16 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 1108 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008