LTC6401IUD-20#TRPBF

LTC6401-20 1.3GHz Low Noise, Low Distortion Differential ADC Driver for 140MHz IF FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION 1.3GHz –3dB Bandwidth Fixed Gain of 10V/V (20dB) –93dBc IMD3 at 70MHz (Equivalent OIP3 = 50.5dBm) –74dBc IMD3 at 140MHz (Equivalent OIP3 = 41dBm) 1nV/√⎯H⎯z Internal Op Amp Noise 2.1nV/√⎯H⎯z Total Input Noise 6.2dB Noise Figure Differential Inputs and Outputs 200Ω Input Impedance 2.85V to 3.5V Supply Voltage 50mA Supply Current (150mW) 1V to 1.6V Output Common Mode Voltage, Adjustable DC- or AC-Coupled Operation Max Differential Output Swing 4.4VP-P Small 16-Lead 3mm × 3mm × 0.75mm QFN Package The LTC®6401-20 is a high-speed differential amplifier targeted at processing signals from DC to 140MHz. 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 LTC6401-20 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 for transformers or AC-coupling capacitors in many applications. The gain is internally fixed at 20dB (10V/V). The LTC6401-20 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6401-20 is packaged in a compact 16-lead 3mm × 3mm QFN package and operates over the –40°C to 85°C temperature range. APPLICATIONS ■ ■ ■ ■ ■ , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 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 3.3V Equivalent Output IP3 vs Frequency 70 1.25V 0.1μF + 1000pF (NOTE 7) 60 0.1μF 0.1μF INPUT VOCM 10Ω +IN 66.5Ω 0.1μF 29Ω +OUT +OUTF LTC6401-20 –OUTF –OUT –IN V– ENABLE 20dB GAIN AIN+ VCM VDD LTC2208 AIN– OUTPUT IP3 (dBm) 3.3V V+ 50 40 30 20 10Ω LTC2208 130Msps 16-Bit ADC 10 0 640120 TA01a 0 50 100 150 FREQUENCY (MHz) 200 640120 TA01b 640120f 1 LTC6401-20 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) +IN +IN –IN –IN TOP VIEW 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 16 15 14 13 12 V– V+ 1 VOCM 2 11 ENABLE 17 5 6 7 8 –OUT +OUTF +OUT 10 V+ 9 V– –OUTF V+ 3 V– 4 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 TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC6401CUD-20#PBF LTC6401CUD-20#TRPBF LCDB 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC6401IUD-20#PBF LTC6401IUD-20#TRPBF LCDB 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°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/ LTC6400 AND LTC6401 SELECTOR GUIDE PART NUMBER Please check each datasheet for complete details. GAIN (dB) GAIN (V/V) ZIN (DIFFERENTIAL) (Ω) ICC (mA) LTC6400-20 20 10 200 90 LTC6401-20 20 10 200 50 In addition to the LTC6401 family of amplifiers, a lower distortion LTC6400 family is available. The LTC6400 is pin compatible to the LTC6401, and has the same low noise performance. The low distortion of the LTC6400 comes at the expense of higher power consumption. Please refer to the separate LTC6400 data sheets for complete details. Other gain versions from 8dB to 26dB will follow. 640120f 2 LTC6401-20 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, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX 19.4 20 20.6 UNITS Input/Output Characteristic GDIFF Gain VIN = ±100mV Differential ● GTEMP Gain Temperature Drift VIN = ±100mV Differential ● 1 VSWINGMIN Output Swing Low Each Output, VIN = ±400mV Differential ● 90 VSWINGMAX Output Swing High Each Output, VIN = ±400mV Differential ● 2.3 VOUTDIFFMAX Maximum Differential Output Swing 1dB Compressed IOUT Output Current Drive Single-Ended ● 10 VOS Input Offset Voltage Differential ● –2 TCVOS Input Offset Voltage Drift Differential ● IVRMIN Input Common Mode Voltage Range, MIN IVRMAX Input Common Mode Voltage Range, MAX RINDIFF Input Resistance Differential CINDIFF Input Capacitance Differential, Includes Parasitic 170 V 4.4 VP-P mA 2 1.4 ROUTDIFF Output Resistance Differential ROUTFDIFF Filtered Output Resistance Differential ● COUTFDIFF Filtered Output Capacitance Differential, Includes Parasitic CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V to 1.4V ● V V 200 230 1 ● mV μV/°C 1 170 mV 2.44 1.6 ● dB mdB/°C Ω pF 18 25 32 Ω 85 100 115 Ω 45 2.7 pF 66 dB 1 V/V Output Common Mode Voltage Control GCM Common Mode Gain VOCM = 1V to 1.6V VOCMMIN Output Common Mode Range, MIN VOCMMAX Output Common Mode Range, MAX VOSCM Common Mode Offset Voltage TCVOSCM Common Mode Offset Voltage Drift ● 6 IVOCM VOCM Input Current ● 5 VIL ⎯E⎯N⎯A⎯B⎯L⎯E Input Low Voltage ● VIH ⎯E⎯N⎯A⎯B⎯L⎯E Input High Voltage ● IIL ⎯E⎯N⎯A⎯B⎯L⎯E Input Low Current ⎯E⎯N⎯A⎯B⎯L⎯E = 0.8V ● IIH ⎯E⎯N⎯A⎯B⎯L⎯E Input High Current ⎯E⎯N⎯A⎯B⎯L⎯E = 2.4V ● 1 1.1 ● VOCM = 1.1V to 1.5V ● 1.6 1.5 ● –15 V V V V 15 mV μV/°C 15 μA 0.8 V ⎯E⎯N⎯A⎯B⎯L⎯E Pin 2.4 V ±0.5 μA 1.2 3 μA Power Supply ● 2.85 3 3.5 V ⎯E⎯N⎯A⎯B⎯L⎯E = 0.8V ● 38 50 62 mA Shutdown Supply Current ⎯E⎯N⎯A⎯B⎯L⎯E = 2.4V ● 1 3 mA Power Supply Rejection Ratio (Differential Outputs) 2.85V to 3.5V ● 55 84 VS Operating Supply Range IS Supply Current ISHDN PSRR dB 640120f 3 LTC6401-20 AC ELECTRICAL CHARACTERISTICS Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN floating, VOCM = 1.25V, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS –3dBBW –3dB Bandwidth 200mVP-P,OUT (Note 6) 1.25 GHz 0.1dBBW Bandwidth for 0.1dB Flatness 200mVP-P,OUT (Note 6) 130 MHz 0.5dBBW Bandwidth for 0.5dB Flatness 200mVP-P,OUT (Note 6) 250 MHz 1/f 1/f Noise Corner 12.5 kHz SR Slew Rate Differential (Note 6) 4500 V/μs tS1% 1% Settling Time 2VP-P,OUT (Note 6) 2 ns tOVDR Output Overdrive Recovery Time 1.9VP-P,OUT (Note 6) 7 ns tON Turn-On Time +OUT, –OUT Within 10% of Final Values 78 ns tOFF Turn-Off Time ICC Falls to 10% of Nominal 146 ns –3dBBWCM Common Mode Small Signal –3dB BW 0.1VP-P at VOCM, Measured Single-Ended at Output (Note 6) 15 MHz Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 400Ω –122/–92 dBc 2VP-P,OUT, No RL –110/–103 dBc 2VP-P,OUTFILT, No RL –113/–102 dBc 2VP-P,OUT Composite, RL = 400Ω –96 dBc 2VP-P,OUT Composite, No RL –108 dBc 2VP-P,OUTFILT Composite, No RL –105 dBc 58 dBm dBm 10MHz Input Signal HD2,10M /HD3,10M IMD3,10M Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) OIP3,10M Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) 2VP-P,OUT Composite, No RL (Note 7) P1dB,10M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.3 NF10M Noise Figure RL = 375Ω (Note 5) 6.2 dB eIN,10M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√⎯H⎯z eON,10M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21 nV/√⎯H⎯z 70MHz Input Signal HD2,70M /HD3,70M IMD3,70M Second/Third Order Harmonic Distortion Third-Order Intermodulation (f1 = 69.5MHz f2 = 70.5MHz) 2VP-P,OUT, RL = 400Ω –91/–80 dBc 2VP-P,OUT, No RL –95/–88 dBc 2VP-P,OUTFILT, No RL –95/–88 dBc 2VP-P,OUT Composite, RL = 400Ω –88 dBc 2VP-P,OUT Composite, No RL –93 dBc 2VP-P,OUTFILT Composite, No RL –92 dBc 2VP-P,OUT Composite, No RL (Note 7) 50.5 dBm OIP3,70M Third-Order Output Intercept Point (f1 = 69.5MHz f2 = 70.5MHz) P1dB,70M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.3 dBm NF70M Noise Figure RL = 375Ω (Note 5) 6.1 dB eIN,70M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√⎯H⎯z eON,70M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21 nV/√⎯H⎯z 140MHz Input Signal HD2,140M /HD3,140M Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 400Ω –80/–57 dBc 2VP-P,OUT, No RL –81/–60 dBc 2VP-P,OUTFILT, No RL –80/–65 dBc 640120f 4 LTC6401-20 AC ELECTRICAL CHARACTERISTICS Specifications are at TA = 25°C. V+ = 3V, V– = 0V, +IN and –IN floating, VOCM = 1.25V, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER CONDITIONS IMD3,140M Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) MIN TYP MAX UNITS 2VP-P,OUT Composite, RL = 400Ω –71 dBc 2VP-P,OUT Composite, No RL –74 dBc 2VP-P,OUTFILT Composite, No RL –72 dBc 2VP-P,OUT Composite, No RL (Note 7) 41 dBm OIP3,140M Third-Order Output Intercept Point (f1 = 139.5MHz f2 = 140.5MHz) P1dB,140M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18 dBm NF140M Noise Figure RL = 375Ω (Note 5) 6.4 dB eIN,140M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√⎯H⎯z eON,140M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 22 nV/√⎯H⎯z IMD3,130M/150M Third-Order Intermodulation (f1 = 130MHz f2 = 150MHz) Measure at 170MHz –69 dBc 2VP-P,OUT Composite, RL = 375Ω (Note 5) 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 LTC6401C and LTC6401I are guaranteed functional over the operating temperature range of –40°C to 85°C. Note 4: The LTC6401C 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 –61 temperatures. The LTC6401I 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. Note 7: Since the LTC6401-20 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 LTC6401-20 with amplifiers that require 50Ω output load, the LTC6401-20 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 the actual RL. TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response 25 S21 Phase and Group Delay vs Frequency Gain 0.1dB Flatness 1.0 TEST CIRCUIT B 100 TEST CIRCUIT B 1.5 TEST CIRCUIT B 0.8 15 10 5 0.4 PHASE (DEGREE) NORMALIZED GAIN (dB) 0.6 0.2 0 –0.2 –0.4 –0.6 0 1.2 –100 0.9 –200 0.6 0.3 –300 PHASE GROUP DELAY –0.8 0 –1.0 10 100 1000 FREQUENCY (MHz) 3000 640120 G01 –400 10 100 FREQUENCY (MHz) 1000 640120 G02 GROUP DELAY (ns) GAIN (dB) 20 0 200 400 600 FREQUENCY (MHz) 800 0 1000 640120 G03 640120f 5 LTC6401-20 TYPICAL PERFORMANCE CHARACTERISTICS 0 Input and Output Impedance vs Frequency TEST CIRCUIT B 225 IMPEDANCE MAGNITUDE (Ω) S11 –30 S22 –40 –50 S12 –60 ZIN 200 100 80 90 60 80 40 175 ZOUT 150 125 20 0 ZIN –20 100 PHASE IMPEDANCE MAGNITUDE 75 –40 50 –60 –70 25 –80 –80 0 100 1000 FREQUENCY (MHz) 3000 ZOUT 640120 G04 2 eIN 0 1000 1.35 OUTPUT VOLTAGE (V) NOISE FIGURE INPUT REFERRED NOISE VOLTAGE (nV/√Hz) 4 100 FREQUENCY (MHz) 30 20 10 0 1 10 100 FREQUENCY (MHz) Large Signal Transient Response RL = 87.5Ω PER OUTPUT RL = 87.5Ω PER OUTPUT 2.0 1.30 +OUT 1.25 1.20 –OUT 5 1.0 –OUT 0.5 1.15 0 +OUT 1.5 10 TIME (ns) 0 20 15 0 5 10 TIME (ns) 640120 G08 20 640120 G09 5 RL = 87.5Ω PER OUTPUT –OUT 15 1% Settling Time for 2V Output Step Overdrive Transient Response 2.5 1000 640120 G06 2.5 640120 G07 RL = 87.5Ω PER OUTPUT 4 2.0 3 2 SETTLING (%) OUTPUT VOLTAGE (V) CMRR 40 Small Signal Transient Response 6 10 50 640120 G05 Noise Figure and Input Referred Noise Voltage vs Frequency 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 60 –100 1000 10 100 FREQUENCY (MHz) 1 PSRR 70 OUTPUT VOLTAGE (V) 10 NOISE FIGURE (dB) 100 IMPEDANCE PHASE (DEGREE) S PARAMETERS (dB) –10 –20 PSRR and CMRR vs Frequency 250 PSRR, CMRR (dB) Input and Output Reflection and Reverse Isolation vs Frequency 1.5 1.0 1 0 –1 –2 –3 0.5 –4 +OUT –5 0 0 50 100 TIME (ns) 150 200 640120 G10 0 1 2 3 TIME (ns) 4 5 6 640120 G11 640120f 6 LTC6401-20 TYPICAL PERFORMANCE CHARACTERISTICS Harmonic Distortion (Unfiltered) vs Frequency –60 –70 –80 –90 –100 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL –110 –120 0 50 100 150 FREQUENCY (MHz) –40 DIFFERENTIAL INPUT = 2VP-P V –50 OUT NO RL –60 –70 –80 –90 –100 –110 0 50 100 150 FREQUENCY (MHz) –90 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL 50 100 150 FREQUENCY (MHz) 200 100 150 FREQUENCY (MHz) –60 –70 –80 –90 –100 –120 50 100 150 FREQUENCY (MHz) –60 –70 –80 –90 –100 –110 HD2 HD3 0 UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL –50 –110 SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –120 0 200 50 100 150 FREQUENCY (MHz) Equivalent Output 1dB Compression Point vs Frequency –40 20 DIFFERENTIAL INPUT VOUT = 2VP-P at 100MHz –50 RL = 400Ω –60 HD3 –70 –80 HD2 –90 –100 1.5 1.1 1.2 1.3 1.4 OUTPUT COMMON MODE VOLTAGE (V) 640120 G18 200 640120 G17 640120 G16 Harmonic Distortion vs Output Common Mode Voltage (Unfiltered Outputs) 200 Third Order Intermodulation Distortion vs Frequency –40 640120 G15 1.0 50 640120 G14 SINGLE-ENDED INPUT = 2VP-P V –50 OUT NO RL OUTPUT 1dB COMPRESSION (dBm) 0 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE 0 THIRD ORDER IMD (dBc) –80 HARMONIC DISTORTION (dBc) –70 DISTORTION (dBc) HARMONIC DISTORTION (dBc) –60 –120 –100 –120 –40 –110 –90 Harmonic Distortion (Filtered) vs Frequency SINGLE-ENDED INPUT VOUT = 2VP-P –100 –80 640120 G13 Harmonic Distortion (Unfiltered) vs Frequency –50 –70 200 640120 G12 –40 –60 –110 HD2 HD3 –120 200 UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL –50 THIRD ORDER IMD (dBc) HARMONIC DISTORTION (dBc) –50 Third Order Intermodulation Distortion vs Frequency –40 DIFFERENTIAL INPUT VOUT = 2VP-P HARMONIC DISTORTION (dBc) –40 Harmonic Distortion (Filtered) vs Frequency 19 DIFFERENTIAL INPUT RL = 400Ω (NOTE 7) 18 17 16 15 50 80 110 140 FREQUENCY (MHz) 170 200 640020 G19 640120f 7 LTC6401-20 TYPICAL PERFORMANCE CHARACTERISTICS Equivalent Output Third Order Intercept vs Frequency UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL 60 Turn-Off Time RL = 87.5Ω PER OUTPUT 3.0 ICC VOLTAGE (V) 40 30 20 2.0 10 0 0 50 100 150 FREQUENCY (MHz) 200 640120 G20 60 3.0 50 2.5 40 –OUT 30 1.5 1.0 20 +OUT 10 0.5 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE (NOTE 7) 3.5 –0.5 –100 0 100 200 300 TIME (ns) 400 50 40 2.0 –OUT 1.5 30 +OUT 1.0 20 10 0.5 0 0 –10 500 –0.5 –100 640120 G21 60 ENABLE ENABLE 0 70 RL = 87.5Ω PER OUTPUT ICC 0 100 200 300 TIME (ns) SUPPLY CURRENT (mA) 2.5 50 70 SUPPLY CURRENT (mA) OUTPUT IP3 (dBm) Turn-On Time 3.5 VOLTAGE (V) 70 0 400 –10 500 640120 G22 640120f 8 LTC6401-20 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. A 0.1μF external bypass capacitor is recommended. V– (Pins 4, 9, 12, 17): Negative Power Supply. All four pins must be connected to the same voltage/ground. –OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins have 12.5Ω series resistors. –OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins have 50Ω series resistors and a 1.7pF shunt capacitance. ⎯E⎯N⎯A⎯B⎯L⎯E (Pin 11): This pin is a logic input referenced to V–. If low, the part is enabled. If high, the part is disabled and draws approximately 1mA supply current. +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 the same voltage/ground as pins 4, 9, 12. BLOCK DIAGRAM V– 12 V– V+ ENABLE 11 10 9 BIAS CONTROL +IN 13 ROUT 12.5Ω +OUT 8 RFILT 50Ω +IN 14 IN+ +OUTF 7 OUT– CFILT 1.7pF RFILT 50Ω –IN 15 –IN 16 RF 1000Ω RG 100Ω IN– OUT+ RF 1000Ω RG 100Ω –OUTF 6 ROUT 12.5Ω –OUT 5 2k COMMON MODE CONTROL 5.3pF 1 V+ 2 3 VOCM V+ 4 640120 BD V– 640120f 9 LTC6401-20 APPLICATIONS INFORMATION Circuit Operation The LTC6401-20 is a low noise and low distortion fully differential op amp/ADC driver with: • Operation from DC to 1.3GHz –3dB bandwidth impedance • Fixed gain of 10V/V (20dB) • Differential input impedance 200Ω • Differential output impedance 25Ω • Differential impedance of output filter 100Ω The LTC6401-20 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 100Ω/1000Ω 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. the differential inputs may need to be terminated to a lower value impedance, e.g. 50Ω, in order to provide an impedance match to the source. Several choices are available. One approach is to use a differential shunt resistor (Figure 1). Another approach is to employ a wideband transformer (Figure 2). Both methods provide a wideband match. The termination resistor or 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 LTC640120 for frequency selection and/or noise reduction. Referring to Figure 3, LTC6401-20 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 LTC6401-20 25Ω 1000Ω 100Ω 12.5Ω 13 +IN 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. + – VIN Input Impedance and Matching The differential input impedance of the LTC6401-20 is 200Ω. If a 200Ω source impedance is unavailable, then IN+ OUT– IN– OUT+ 14 +IN 66.5Ω +OUTF 7 50Ω 15 –IN 25Ω The LTC6401-20 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 LTC6401-20 provides an output common mode voltage set by VOCM, which allows driving an ADC directly without external components such as a transformer or AC coupling capacitors. The input signal can be either single-ended or differential with only minor differences in distortion performance. +OUT 8 50Ω 1000Ω 100Ω 1.7pF –OUTF 6 12.5Ω –OUT 5 16 –IN 640120 F01 Figure 1. Input Termination for Differential 50Ω Input Impedance Using Shunt Resistor LTC6401-20 25Ω 1000Ω 100Ω 12.5Ω 13 +IN +OUT 8 50Ω 1:4 + – VIN • • IN+ OUT– IN– OUT+ +OUTF 7 14 +IN 50Ω 15 –IN 25Ω 100Ω 16 –IN 1000Ω 1.7pF –OUTF 6 12.5Ω –OUT 5 640120 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a 1:4 Balun 640120f 10 LTC6401-20 APPLICATIONS INFORMATION RS 50Ω 1000Ω 100Ω 12.5Ω 13 +IN VIN + – LTC6401-20 0.1μF +OUT 8 50Ω RT 66.5Ω IN+ OUT– +OUTF 7 14 +IN 0.1μF 50Ω 15 –IN RS 50Ω RT 66.5Ω 0.1μF IN– 100Ω input Smith Chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. Output Match and Filter 1.7pF –OUTF 6 OUT+ 1000Ω 12.5Ω –OUT 5 16 –IN 640120 F03 Figure 3. Input Termination for Single-Ended 50Ω Input Impedance 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 200Ω and RT is 66.5Ω in order to match to a 50Ω source impedance. The LTC6401-20 is unconditionally stable. However, the overall differential gain is affected by both source impedance and load impedance as shown in Figure 4: The LTC6401-20 can drive an ADC directly without external output impedance matching. Alternatively, the differential output impedance of 25Ω can be matched to higher value impedance, e.g. 50Ω, by series resistors or an LC network. 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. LTC6401-20 13 +IN +OUT 8 IN+ 13 +IN + – VIN Figure 5. LTC6401-20 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 15 –IN 1/2 RS IN– 100Ω 16 –IN 1000Ω 100Ω 1000Ω OUT– 16nH 50Ω 15 –IN IN– 100Ω 1/2 RL –OUT 5 4.99Ω +OUTF 7 14 +IN 1.7pF 12.5Ω 39pF 10Ω 50Ω –OUTF 6 OUT+ LTC6401-20 12.5Ω +OUT 8 VOUT 50Ω 8.2pF 12.5Ω –OUT 5 IN+ +OUTF 7 14 +IN 1000Ω 640120 F05 50Ω OUT– FILTERED OUTPUT 12pF (87.5MHz) –OUTF 6 OUT+ 13 +IN +OUT 8 1.7pF 16 –IN 1/2 RL 12.5Ω IN– 100Ω LTC6401-20 IN+ +OUTF 7 50Ω The noise performance of the LTC6401-20 also depends upon the source impedance and termination. For example, an input 1:4 balun transformer in Figure 2 improves SNR by adding 6dB of gain at the inputs. A trade-off between gain and noise is obvious when constant noise figure circle and constant gain circle are plotted within the same 1000Ω 8.2pF OUT– 14 +IN 15 –IN 100Ω 12.5Ω 50Ω V RL 2000 A V = OUT = • VIN RS + 200 25 + RL 1/2 RS 1000Ω 100Ω 16 –IN OUT+ 1000Ω 1.7pF LTC2208 39pF –OUTF 6 12.5Ω 10Ω –OUT 5 640120 F06 4.99Ω 39pF 640120 F04 Figure 4. Calculate Differential Gain Figure 6. LTC6401-20 Application Circuit for Bandpass Filtering (Three External Capacitors, One External Inductor) 640120f 11 LTC6401-20 APPLICATIONS INFORMATION Output Common Mode Adjustment 1.25V 0.1μF The LTC6401-20’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 around 300MHz, allowing fast common mode rejection at the outputs of the LTC6401-20. The VOCM pin should be tied to a DC bias voltage where a 0.1μF bypass capacitor is recommended. When interfacing with A/D converters such as the LT22xx families, the VOCM can be normally connected to the VCM pin of the ADC. Driving A/D Converters The LTC6401-20 has been specifically designed to interface directly with high speed A/D converters. In Figure 7, an example schematic shows the LTC6401-20 with a single-ended input driving the LTC2208, which is a 16-bit, 130Msps ADC. Two external 10Ω resistors help eliminate potential resonance associated with stray capacitance of PCB traces and bond wire inductance of either the ADC input or the driver output. VOCM of the LTC6401-20 is connected to VCM of the LTC2208 at 1.25V. Alternatively, a single-ended input signal can be converted to differential signal via a balun and fed to the input of the LTC6401-20. The balun also converts input impedance to match 50Ω source impedance. 0.1μF IF IN VOCM 10Ω +IN +OUT +OUTF LTC6401-20 –OUTF –IN –OUT 66.5Ω 29Ω AIN+ VCM LTC2208 AIN– 10Ω ENABLE 20dB GAIN LTC2208 130Msps 16-Bit ADC 640120 F07 Figure 7. Single-Ended Input to LTC6401-20 and LTC2208 Test Circuits Due to the fully-differential design of the LTC6401 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 LTC6401 family. The schematic and silkscreen are shown below. This circuit includes input and output transformers (baluns) for single-ended-to-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 LTC6401 with a 375Ω differential load, optimizing distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 1.3GHz to approximately 1.1GHz. 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. 640120f 12 LTC6401-20 APPLICATIONS INFORMATION Top Silkscreen 640120f 13 LTC6401-20 TYPICAL APPLICATION Demo Circuit 987B Schematic (Test Circuit A) VCC ENABLE 1 3 DIS 2 JP1 13 T1 (2) 4 R4 (2) C21 0.1μF 2 3 R3 (2) C2 0.1μF 14 R24 (1) SL1 (2) +IN +OUT +IN +OUTF 8 R10 86.6Ω 7 R8 (1) 6 R7 (1) LTC6401-20 15 C1 0.1μF 16 R1 0Ω –IN –OUTF –IN –OUT V+ VOCM 1 VCC C10 0.1μF VCC 9 V– 2 V+ 5 R14 (1) C4 0.1μF SL2 (2) 4 C9 1000pF R12 0Ω 1 5 R11 (1) C22 0.1μF R13 0Ω C3 0.1μF R9 86.6Ω V– 3 4 T2 3 TCM 4-19 1:4 2 • R5 0dB (1) 1 • • 5 10 V+ C18 0.1μF • J2 –IN R6 0Ω C17 1000pF R16 0Ω 12 11 V– ENABLE R2 (1) J1 +IN VCC J4 +OUT SL3 (2) J5 –OUT VCC C12 1000pF C13 0.1μF R19 1.5k TP5 VOCM 5 T3 TCM 4-19 1:4 2 C23 0.1μF C19 0.1μF R21 (1) C24 0.1μF 3 3 C5 0.1μF C20 0.1μF R22 (1) C6 0.1μF T4 TCM 4-19 1:4 4 R18 0Ω 5 R26 0Ω 2 1 • 4 1 • R25 0Ω • R17 0Ω • J6 TEST IN C7 0.1μF R20 1k J7 TEST OUT VCC TP2 VCC 2.85V TO 3.5V TP3 GND C14 4.7μF NOTE: UNLESS OTHERWISE SPECIFIED. (1) DO NOT STUFF. C15 1μF (2) VERSION -G IC R3 R4 LTC6401CUD-20 OPEN OPEN SL = SIGNAL LEVEL T1 SL1 SL2 SL3 MINI-CIRCUITS TCM4-19 (1:4) 6dB 20dB 14dB 640120 TA03 640120f 14 LTC6401-20 TYPICAL APPLICATION Test Circuit B, 4-Port Analysis V+ 1000pF 0.1μF V– 11 V– V+ ENABLE 12 10 9 BIAS CONTROL RF 1000Ω RG 100Ω +IN 13 PORT 1 (50Ω) ROUT 12.5Ω RFILT 50Ω 0.1μF 1/2 AGILENT E5O71A +IN 14 200Ω IN+ PORT 3 (50Ω) +OUTF IN– CFILT 1.7pF 1/2 AGILENT E5O71A –OUTF 6 OUT+ RF 1000Ω RG 100Ω –IN 16 0.1μF 7 OUT– RFILT 50Ω –IN 15 PORT 2 (50Ω) +OUT 37.4Ω 8 ROUT 12.5Ω –OUT 37.4Ω PORT 4 (50Ω) 5 0.1μF 0.1μF COMMON MODE CONTROL 1 1000pF 2 V+ 3 VOCM 0.1μF VOCM V+ 4 640120 TA02 V– V+ 0.1μF PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) BOTTOM VIEW—EXPOSED PAD 3.00 ± 0.10 (4 SIDES) 0.70 ±0.05 PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) 16 2 PACKAGE OUTLINE (UD16) QFN 0904 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 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 640120f 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 LTC6401-20 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS High-Speed Differential Amplifiers/Differential Op Amps LT1993-2 800MHz Differential Amplifier/ADC Driver AV = 2V/V, OIP3 = 38dBm at 70MHz LT1993-4 900MHz Differential Amplifier/ADC Driver AV = 4V/V, OIP3 = 40dBm at 70MHz LT1993-10 700MHz Differential Amplifier/ADC Driver AV = 10V/V, OIP3 = 40dBm at 70MHz LT1994 Low Noise, Low Distortion Differential Op Amp 16-Bit SNR and SFDR at 1MHz, Rail-to-Rail Outputs LT5514 Ultralow Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain OIP3 = 47dBm at 100MHz, Gain Control Range 10.5dB to 33dB LT5524 Low Distortion IF Amplifier/ADC Driver with Digitally Controlled Gain OIP3 = 40dBm at 100MHz, Gain Control Range 4.5dB to 37dB LTC6400-20 1.8GHz Low Noise, Low Distortion, Differential ADC Driver AV = 20dB, 90mA Supply Current, IMD3 = –65dBc at 300MHz LT6402-6 300MHz Differential Amplifier/ADC Driver AV = 6dB, Distortion < –80dBc at 25MHz LT6402-12 300MHz Differential Amplifier/ADC Driver AV = 12dB, Distortion < –80dBc at 25MHz LT6402-20 300MHz Differential Amplifier/ADC Driver AV = 20dB, Distortion < –80dBc at 25MHz LTC6406 3GHz Rail-to-Rail Input Differential Op Amp 1.6nV/√Hz Noise, –72dBc Distortion at 50MHz, 18mA LT6411 Low Power Differential ADC Driver/Dual Selectable Gain Amplifier 16mA Supply Current, IMD3 = –83dBc at 70MHz, AV = 1, –1 or 2 High-Speed Single-Ended Output Op Amps LT1812/LT1813/ High Slew Rate Low Cost Single/Dual/Quad Op Amps LT1814 8nV/√Hz Noise, 750V/μs, 3mA Supply Current LT1815/LT1816/ Very High Slew Rate Low Cost Single/Dual/Quad Op Amps LT1817 6nV/√Hz Noise, 1500V/μs, 6.5mA Supply Current LT1818/LT1819 Ultra High Slew Rate Low Cost Single/Dual Op Amps 6nV/√Hz Noise, 2500V/μs, 9mA Supply Current LT6200/LT6201 Rail-to-Rail Input and Output Low Noise Single/Dual Op Amps 0.95nV/√Hz Noise, 165MHz GBW, Distortion = –80dBc at 1MHz LT6202/LT6203/ Rail-to-Rail Input and Output Low Noise Single/Dual/Quad LT6204 Op Amps 1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW LT6230/LT6231/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps LT6232 1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW LT6233/LT6234/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps LT6235 1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW Integrated Filters LTC1562-2 Very Low Noise, 8th Order Filter Building Block Lowpass and Bandpass Filters up to 300kHz LT1568 Very Low Noise, 4th Order Filter Building Block Lowpass and Bandpass Filters up to 10MHz LTC1569-7 Linear Phase, Tunable 10th Order Lowpass Filter Single-Resistor Programmable Cut-Off to 300kHz LT6600-2.5 Very Low Noise Differential 2.5MHz Lowpass Filter SNR = 86dB at 3V Supply, 4th Order Filter LT6600-5 Very Low Noise Differential 5MHz Lowpass Filter SNR = 82dB at 3V Supply, 4th Order Filter LT6600-10 Very Low Noise Differential 10MHz Lowpass Filter SNR = 82dB at 3V Supply, 4th Order Filter LT6600-15 Very Low Noise Differential 15MHz Lowpass Filter SNR = 76dB at 3V Supply, 4th Order Filter LT6600-20 Very Low Noise Differential 20MHz Lowpass Filter SNR = 76dB at 3V Supply, 4th Order Filter 640120f 16 Linear Technology Corporation LT 0907 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007