LTC6401-26 1.6GHz Low Noise, Low Distortion Differential ADC Driver for DC-140MHz FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION 1.6GHz –3dB Bandwidth Fixed Gain of 20V/V (26dB) –85dBc IMD3 at 70MHz (Equivalent OIP3 = 46.5dBm) –72dBc IMD3 at 140MHz (Equivalent OIP3 = 40dBm) 1nV/√⎯H⎯z Internal Op Amp Noise 1.5nV/√⎯H⎯z Total Input Referred Noise 6.8dB Noise Figure Differential Inputs and Outputs 50Ω Input Impedance 2.85V to 3.5V Supply Voltage 45mA Supply Current (135mW) 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 The LTC®6401-26 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 LTC6401-26 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 LTC6401-26 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6401-26 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 Equivalent OIP3 vs Frequency Single-Ended to Differential ADC Driver at 140MHz IF 3.3V 60 3.3V DIFFERENTIAL INPUT (NOTE 7) 50 1000pF 33pF V+ 0.1μF VIN 150Ω 0.1μF +OUT L1 24nH LTC6401-26 LTC6401-26 –IN 37.4Ω 10Ω 15Ω +IN V– COILCRAFT 0603CS 1.25V 10Ω 33pF VDD LTC2208 33pF 15Ω –OUT OCM VVOCM AIN+ AIN– 100Ω 40 30 20 10 VCM LTC2208 130Msps 16-BIT ADC NO RL RL = 200Ω 0 0 640126 TA01a 0.1μF OUTPUT IP3 (dBm) 0.1μF 50 100 150 FREQUENCY (MHz) 200 640126 TA01b 640126f 1 LTC6401-26 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 –OUT 7 8 +OUT 6 10 V+ 9 V– +OUTF 5 –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 SPECIFIED TEMPERATURE RANGE LTC6401CUD-26#PBF LTC6401CUD-26#TRPBF LCDG 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC6401IUD-26#PBF LTC6401IUD-26#TRPBF LCDG 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) LTC6401-8 8 2.5 400 45 LTC6401-20 20 10 200 50 LTC6401-26 26 20 50 45 LTC6400-20 20 10 200 90 LTC6400-26 26 20 50 85 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 14dB will follow. 640126f 2 LTC6401-26 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, ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX 26 27 UNITS Input/Output Characteristic (+IN, –IN, +OUT, –OUT, +OUTF, –OUTF) GDIFF Gain VIN = ±50mV Differential ● TCGAIN Gain Temperature Drift VIN = ±50mV Differential ● 0.003 VSWINGMIN Output Swing Low Each Output, VIN = ±200mV Differential ● 0.09 VSWINGMAX Output Swing High Each Output, VIN = ±200mV Differential ● 2.3 2.43 V 4.3 4.7 VP-P 25 0.15 VOUTDIFFMAX Maximum Differential Output Swing 1dB Compressed ● IOUT Output Current Drive Each Output, VIN = ±200mV, VOUT > 2VP-P ● 10 VOS Input Offset Voltage Differential ● –2.5 TCVOS Input Offset Voltage Drift Differential ● IVRMIN Input Common Mode Voltage Range, MIN IVRMAX Input Common Mode Voltage Range, MAX RINDIFF Input Resistance (+IN, –IN) Differential CINDIFF Input Capacitance (+IN, –IN) Differential, Includes Parasitic ROUTDIFF Output Resistance (+OUT, –OUT) Differential ● 18 25 32 ROUTFDIFF Filtered Output Resistance (+OUTF, –OUTF) Differential ● 85 100 115 COUTFDIFF Filtered Output Capacitance (+OUTF, –OUTF) Differential, Includes Parasitic CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V to1.4V 2.5 1 42.5 50 mV μV/°C 1 V 57.5 Ω V 50 1 ● V mA 1.6 ● dB dB/°C pF Ω Ω 2.7 pF 75 dB 1 V/V Output Common Mode 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 ● 3 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 0.5 μA 1.4 3 μA ⎯E⎯N⎯A⎯B⎯L⎯E Pin ● 2.4 V Power Supply VS Operating Supply Range IS Supply Current ISHDN Shutdown Supply Current PSRR Power Supply Rejection Ratio (Differential Outputs) ● 2.85 3 3.5 V ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, Both Inputs and Outputs Floating ⎯E⎯N⎯A⎯B⎯L⎯E = 3V, Both Inputs and Outputs Floating ● 35 45 60 mA 0.8 3 mA 2.85V to 3.5V ● ● 60 95.5 dB 640126f 3 LTC6401-26 AC ELECTRICAL CHARACTERISTICS ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER –3dBBW 0.5dBBW Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, CONDITIONS MIN TYP MAX UNITS –3dB Bandwidth 200mVP-P,OUT (Note 6) 1.2 1.6 GHz Bandwidth for 0.5dB Flatness 200mVP-P,OUT (Note 6) 0.5 GHz 0.1dBBW Bandwidth for 0.1dB Flatness 200mVP-P,OUT (Note 6) 0.22 GHz 1/f 1/f Noise Corner 16 kHz 3300 V/μs SR Slew Rate Differential VOUT = 2V Step (Note 6) tS1% 1% Settling Time VOUT = 2VP-P (Note 6) 3 ns tOVDR Overdrive Recovery Time VOUT = 1.9VP-P (Note 6) 19 ns tON Turn-On Time +OUT, –OUT Within 10% of Final Values 93 ns tOFF Turn-Off Time ICC Falls to 10% of Nominal 140 ns –3dBBWVOCM VOCM Pin Small Signal –3dB BW 0.1VP-P at VOCM, Measured Single-Ended at Output (Note 6) 14.7 MHz VOUT = 2VP-P , RL = 200Ω –95/–81 dBc VOUT = 2VP-P , No RL –93/–96 dBc 10MHz Input Signal HD2,10M/HD3,10M Second/Third Order Harmonic Distortion Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) VOUT = 2VP-P Composite, RL = 200Ω –80 dBc VOUT = 2VP-P Composite, No RL –97 dBc OIP3,10M Equivalent Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) VOUT = 2VP-P Composite, No RL (Note 7) 52.5 dBm P1dB,10M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.3 dBm NF10M Noise Figure RL = 375Ω (Note 5) 6.8 dB eIN,10M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.5 nV/√⎯H⎯z eON,10M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 30 nV/√⎯H⎯z IMD3,10M 70MHz Input Signal HD2,70M/HD3,70M Second/Third Order Harmonic Distortion VOUT = 2VP-P , RL = 200Ω –83/–66 dBc VOUT = 2VP-P , No RL –86/–81 dBc Third-Order Intermodulation (f1 = 69.5MHz f2 = 70.5MHz) VOUT = 2VP-P Composite, RL = 200Ω –74 dBc VOUT = 2VP-P Composite, No RL –85 dBc OIP3,70M Equivalent Third-Order Output Intercept Point (f1 = 69.5MHz f2 = 70.5MHz) VOUT = 2VP-P Composite, No RL (Note 7) 46.5 dBm P1dB,70M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.2 dBm NF70M Noise Figure RL = 375Ω (Note 5) 6.7 dB eIN,70M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.44 nV/√⎯H⎯z eON,70M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 28.8 nV/√⎯H⎯z IMD3,70M 640126f 4 LTC6401-26 AC ELECTRICAL CHARACTERISTICS ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, PARAMETER CONDITIONS MIN TYP MAX UNITS HD2,140M/ HD3,140M Second/Third Order Harmonic Distortion VOUT = 2VP-P , RL = 200Ω –81/–54 dBc VOUT = 2VP-P , No RL –85/–69 dBc IMD3,140M Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) VOUT = 2VP-P Composite, RL = 200Ω –64 dBc VOUT = 2VP-P Composite, No RL –72 dBc OIP3,140M Equivalent Third-Order Output Intercept Point(f1 = 139.5MHz f2 = 140.5MHz) VOUT = 2VP-P Composite, No RL (Note 7) 40 dBm P1dB,140M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.4 dBm NF140M Noise Figure RL = 375Ω (Note 5) 6.5 dB eN,140M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.43 nV/√⎯H⎯z eON,140M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 28.6 IMD3,130M/150M Third-Order Intermodulation (f1 = 130MHz f2 = 150MHz) Measure at 170MHz VOUT = 2VP-P Composite, RL = 375Ω –70 140MHz Input Signal 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 nV/√⎯H⎯z –62 dBc 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. RL = 87.5Ω per output. Note 7: Since the LTC6401-26 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 LTC6401-26 with amplifiers that require 50Ω output load, the 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. 640126f 5 LTC6401-26 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response Gain 0.1dB Flatness 30 1.0 TEST CIRCUIT B 0.8 25 GAIN FLATNESS (dB) 0.6 GAIN (dB) 20 15 10 0.4 0.2 0 –0.2 –0.4 –0.6 5 –0.8 TEST CIRCUIT B 0 10 –1.0 100 1000 FREQUENCY (MHz) 3000 100 FREQUENCY (MHz) 10 Input and Output Reflection and Reverse Isoloation vs Frequency S21 Phase and Group Delay vs Frequency TEST CIRCUIT B 0.8 0 S11 –10 –50 –100 0.4 PHASE 0.2 –150 S PARAMETERS (dB) 0.6 GROUP DELAY GROUP DELAY (ns) PHASE (DEGREE) 3000 640126 G02 640126 G01 0 1000 –20 S22 –30 S12 –40 –50 –60 –200 0 200 600 400 FREQUENCY (MHz) 0 1000 800 TEST CIRCUIT B –70 10 100 1000 FREQUENCY (MHz) 640126 G04 640126 G03 Input and Output Impedance vs Frequency PSRR and CMRR vs Frequency 150 120 50 100 120 40 90 30 60 20 30 10 0 10 100 FREQUENCY (MHz) 0 1000 640126 G05 PSRR, CMRR (dB) ZIN MAG ZOUT MAG ZIN PHASE ZOUT PHASE 60 PHASE (DEGREE) IMPEDANCE MAGNITUDE (Ω) 180 3000 PSRR 80 CMRR 60 40 20 0 1 10 100 FREQUENCY (MHz) 1000 640126 G06 640126f 6 LTC6401-26 TYPICAL PERFORMANCE CHARACTERISTICS Small Signal Transient Response 2.0 8 1.5 EN 7 1.0 NOISE FIGURE 6 0.5 5 10 1.35 OUTPUT VOLTAGE (V) 9 INPUT REFERRED NOISE VOLTAGE (nV/√Hz) NOISE FIGURE (dB) Noise Figure and Input Referred Noise Voltage vs Frequency +OUT 1.30 1.25 –OUT 1.20 1.15 0 1000 100 FREQUENCY (MHz) RL = 87.5Ω PER OUTPUT TEST CIRCUIT B 2 0 6 4 TIME (ns) 8 640126 G07 640126 G08 Overdriven Transient Response Large Signal Transient Response 2.5 2.5 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B –OUT +OUT OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) RL = 87.5Ω PER OUTPUT 2.0 2.0 1.5 1.0 –OUT 1.5 1.0 +OUT 0.5 0.5 0 0 4 0 12 8 TIME (ns) 16 20 TEST CIRCUIT B 50 0 150 100 TIME (ns) 200 1% Settling Time for 2V Output Step Harmonic Distortion vs Frequency –40 5 HARMONIC DISTORTION (dBc) 4 3 SETTLING (%) 2 1 0 –1 –2 –3 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B –4 0 1 3 2 TIME (ns) 250 640126 G10 640126 G09 –5 10 4 5 640126 G11 DIFFERENTIAL INPUT VOUT = 2VP-P –50 –60 –70 –80 –90 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω –100 –110 0 50 150 100 FREQUENCY (MHz) 200 640126 G12 640126f 7 LTC6401-26 TYPICAL PERFORMANCE CHARACTERISTICS Third Order Intermodulation Distortion vs Frequency –60 –70 –80 –90 –100 –110 0 50 –70 –80 –90 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω –110 200 150 100 FREQUENCY (MHz) 0 50 –80 –90 –100 NO RL RL = 200Ω –110 0 DIFFERENTIAL INPUT (NOTE 7) OUTPUT IP3 (dBm) 50 18.0 17.5 17.0 40 30 20 16.5 10 16.0 0 100 150 FREQUENCY (MHz) NO RL RL = 200Ω 0 200 50 100 150 FREQUENCY (MHz) Turn-On Time Turn-Off Time 3.0 ICC 3.0 50 2.5 50 40 2.0 40 1.0 20 +OUT 10 0.5 0 100 300 200 TIME (ns) 400 60 ENABLE –OUT 1.5 1.0 30 20 +OUT 10 0.5 ICC ENABLE 0 RL = 87.5Ω PER OUTPUT ICC (mA) VOLTAGE (V) 60 30 1.5 –0.5 –100 3.5 ICC (mA) –OUT 70 70 VOLTAGE (V) RL = 87.5Ω PER OUTPUT 2.0 200 640126 G17 640126 G16 2.5 200 640126 G15 60 DIFFERENTIAL INPUT RL = 375Ω 18.5 TEST CIRCUIT A (NOTE 7) 3.5 150 100 FREQUENCY (MHz) 50 Equivalent Output Third Order Intercept Point vs Frequency 19.0 OUTPUT 1dB COMPRESSION POINT (dBm) –70 640126 G14 Output 1dB Compression Point vs Frequency 50 –60 200 150 100 FREQUENCY (MHz) 640126 G13 0 SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –50 –60 –100 NO RL RL = 200Ω –40 SINGLE-ENDED INPUT VOUT = 2VP-P –50 HARMONIC DISTORTION (dBc) –50 THIRD ORDER IMD (dBc) –40 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE THIRD ORDER IMD (dBc) –40 Third Order Intermodulation Distortion vs Frequency Harmonic Distortion vs Frequency 0 0 –10 500 –0.5 –100 640126 G18 0 0 100 300 200 TIME (ns) 400 –10 500 640126 G19 640126f 8 LTC6401-26 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. ⎯E⎯N⎯A⎯B⎯L⎯E (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 V– 12 V– V+ ENABLE 11 10 9 BIAS CONTROL +IN 13 RF 500Ω RG 25Ω +OUT 8 RFILT 50Ω +IN 14 IN+ +OUTF 7 OUT– CFILT 2.7pF RFILT 50Ω –IN 15 –IN 16 ROUT 12.5Ω IN– OUT+ RF 500Ω RG 25Ω –OUTF 6 ROUT 12.5Ω –OUT 5 2k COMMON MODE CONTROL 5.3pF 1 V+ 2 3 VOCM V+ 4 640126 BD V– 640126f 9 LTC6401-26 APPLICATIONS INFORMATION • Operation from DC to 1.6GHz –3dB bandwidth • Fixed gain of 20V/V (26dB) • Differential input impedance 50Ω • Differential output impedance 25Ω • Differential impedance of output filter 100Ω The LTC6401-26 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. Referring to Figure 3, LTC6401-26 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. LTC6401-26 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 LTC6401-26 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 LTC6401-26 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. 25Ω The differential input impedance of the LTC6401-26 is 50Ω. The interface between the input of LTC6401-26 and 50Ω source is straightforward. One way is to directly connect 12.5Ω 13 +IN +OUT 8 50Ω IN+ + – VIN OUT– +OUTF 7 14 +IN 50Ω 15 –IN 25Ω IN– 500Ω 25Ω 2.7pF –OUTF 6 OUT+ 12.5Ω –OUT 5 16 –IN 640126 F01 Figure 1. Input Termination for Differential 50Ω Input Impedance LTC6401-26 50Ω 500Ω 25Ω 12.5Ω 13 +IN +OUT 8 50Ω + – VIN 1:1 IN+ OUT– IN– OUT+ +OUTF 7 14 +IN 50Ω 15 –IN 25Ω Input Impedance and Matching 500Ω 25Ω • The LTC6401-26 is a low noise and low distortion fully differential op amp/ADC driver with: 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. Alternatively, one could apply a narrowband impedance match at the inputs of the LTC6401-26 for frequency selection and/or noise reduction. • Circuit Operation 16 –IN M/A-COM MABA-007159-000000 500Ω 2.7pF –OUTF 6 12.5Ω –OUT 5 640126 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a Balun 640126f 10 LTC6401-26 APPLICATIONS INFORMATION RS 50Ω 500Ω 25Ω 12.5Ω 13 +IN VIN + – LTC6401-26 0.1μF +OUT 8 50Ω RT 150Ω IN+ OUT– +OUTF 7 14 +IN 0.1μF 50Ω 15 –IN 0.1μF IN– 2.7pF –OUTF 6 OUT+ 500Ω 25Ω 12.5Ω 16 –IN –OUT 5 37.4Ω 640126 F03 Figure 3. Input Termination for Single-Ended 50Ω Input Impedance The LTC6401-26 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 LTC6401-26 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 LTC6401-26 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. The internal low pass filter outputs at +OUTF/–OUTF have a –3dB bandwidth of 590MHz. External capacitors 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 16nH inductor create a bandpass filter with 165MHz center frequency, –3dB frequencies at 138MHz and 200MHz. Output Common Mode Adjustment The LTC6401-26’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 voltage disturbance. The VOCM pin should be tied to a DC bias voltage with a 0.1μF bypass capacitor. When interfacing with 3V 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 LTC6401-26 has been specifically designed to interface directly with high speed A/D converters. Figure 7 shows the LTC6401-26 with 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 LTC6401-26 1/2 RS 500Ω 25Ω 13 +IN LTC6401-26 1/2 RL 12.5Ω +OUT 8 500Ω 25Ω 13 +IN +OUT 8 50Ω IN+ + – VIN OUT– 15 –IN 1/2 RS IN– 25Ω 16 –IN IN+ VOUT 50Ω 500Ω OUT– 50Ω 15 –IN 1/2 RL 12.5Ω –OUT 5 640126 F04 Figure 4. Calculate Differential Gain +OUTF 7 14 +IN 2.7pF –OUTF 6 OUT+ 8pF 50Ω +OUTF 7 14 +IN 12.5Ω IN– 25Ω 16 –IN –OUTF 6 OUT+ 500Ω 2.7pF FILTERED OUTPUT 12pF (87.5MHz) 8pF 12.5Ω –OUT 5 640126 F05 Figure 5. LTC6401-26 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 640126f 11 LTC6401-26 APPLICATIONS INFORMATION –40 SINGLE-ENDED INPUT FS = 122.8Msps –50 DRIVER V OUT = 2VP-P COMPOSITE –60 13 +IN 10Ω IMD3 (dBc) LTC6401-26 12.5Ω 500Ω 25Ω 39pF 4.99Ω +OUT 8 50Ω IN+ OUT– +OUTF 7 14 +IN 50Ω IN– 25Ω OUT+ –80 –90 16nH 15 –IN –70 39pF LTC2208 1.7pF –100 –OUTF 6 500Ω 12.5Ω 10Ω –OUT 5 16 –IN –110 4.99Ω 0 39pF 640126 F06 50 150 100 FREQUENCY (MHz) 200 640126 F08 Figure 6. LTC6401-26 with 165MHz Output Bandpass Filter Figure 8. IMD3 for the Combination of LTC6401-26 and LTC2208 of the LTC6401-26 is connected to VCM of the LTC2208 at 1.25V. Alternatively, a single-ended input signal can be converted to a differential signal via a balun and fed to the input of the LTC6401-26. Figure 8 summarizes the IMD3 performance of the whole system as shown in Figure 7. 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. 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 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 LTC6401 with a 375Ω differential load, optimizing distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 1.6GHz to 1.37GHz. 1.25V 0.1μF 0.1μF +IN IF IN 150Ω 37.4Ω 0.1μF VOCM 4.99Ω +OUT +OUTF LTC6401-26 –OUTF –OUT –IN AIN– VCM LTC2208 AIN+ 4.99Ω ENABLE 26dB GAIN LTC2208 130Msps 16-Bit ADC 640126 F07 Figure 7. Single-Ended Input to LTC6401-26 and LTC2208 Figure 9. Top Silkscreen for DC987B, Test Circuit A 640126f 12 LTC6401-26 TYPICAL APPLICATION Demo Circuit 987B Schematic (Test Circuit A) VCC ENABLE 1 3 DIS 2 JP1 VCC C17 1000pF R16 0Ω 12 V– R2 (1) 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) LTC6401-26 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 6 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+ J4 +OUT • J2 –IN R6 0Ω • J1 +IN 13 11 ENABLE C18 0.1μF SL3 (2) J5 –OUT VCC C12 1000pF C13 0.1μF R19 1.5k TP5 VOCM 6 T3 TCM 4:19 1:4 • R17 0Ω 4 R21 (1) C24 0.1μF • 2 C23 0.1μF C19 0.1μF 3 3 C5 0.1μF C20 0.1μF R22 (1) C6 0.1μF 2 T4 TCM 4:19 1:4 4 R18 0Ω 6 R26 0Ω • R25 0Ω 1 • J6 TEST IN C7 0.1μF R20 1k 1 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 -H IC LTC6401UD-26 SL = SIGNAL LEVEL R3 R4 OPEN OPEN T1 M/A-COM MABA-007159-000000 SL1 SL2 SL3 0dB 20dB 14dB 640126 TA02 640126f 13 LTC6401-26 TYPICAL APPLICATION Test Circuit B, 4-Port Analysis V+ 0.1μF 1000pF V– 11 V– V+ ENABLE 12 10 9 BIAS CONTROL 24.9Ω PORT 1 (50Ω) RF 500Ω RG 25Ω +IN 13 ROUT 12.5Ω RFILT 50Ω 0.1μF +IN 14 1/2 AGILENT E5O71A IN+ 24.9Ω PORT 3 (50Ω) +OUTF IN– CFILT 1.7pF 1/2 AGILENT E5O71A –OUTF 6 OUT+ RF 500Ω RG 25Ω –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 640126 TA03 V– V+ 0.1μF 640126f 14 LTC6401-26 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ±0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER R = 0.115 TYP 0.75 ± 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 (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 640126f 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 LTC6401-26 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS High-Speed Differential Amplifiers/Differential Op Amps LT®1993-2 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 = 2V/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 LTC6400-26 1.9GHz Low Noise, Low Distortion, Differential ADC Driver AV = 26dB, 85mA Supply Current, IMD3 = –71dBc at 300MHz LTC6401-8 2.2GHz Low Noise, Low Distortion, Differential ADC Driver AV = 8dB, 45mA Supply Current, IMD3 = –80dBc at 140MHz LTC6401-20 1.3GHz Low Noise, Low Distortion, Differential ADC Driver AV = 20dB, 50mA Supply Current, IMD3 = –74dBc at 140MHz 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/√⎯H⎯z 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/√⎯H⎯z Noise, 750V/μs, 3mA Supply Current LT1815/LT1816/ Very High Slew Rate Low Cost Single/Dual/Quad Op Amps LT1817 6nV/√⎯H⎯z 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/√⎯H⎯z 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/√⎯H⎯z Noise, 3mA Supply Current, 100MHz GBW LT6230/LT6231/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps LT6232 1.1nV/√⎯H⎯z Noise, 3.5mA Supply Current, 215MHz GBW LT6233/LT6234/ Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps LT6235 1.9nV/√⎯H⎯z 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 640126f 16 Linear Technology Corporation LT 0108 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008