LTC6400-20 1.8GHz Low Noise, Low Distortion Differential ADC Driver for 300MHz IF FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION 1.8GHz –3dB Bandwidth Fixed Gain of 10V/V (20dB) –94dBc IMD3 at 70MHz (Equivalent OIP3 = 51dBm) –65dBc IMD3 at 300MHz (Equivalent OIP3 = 36.5dBm) 1nV/√Hz Internal Op Amp Noise 2.1nV/√Hz Total Input Noise 6.2dB Noise Figure Differential Inputs and Outputs 200Ω Input Impedance 2.85V to 3.5V Supply Voltage 90mA Supply Current (270mW) 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®6400-20 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 LTC6400-20 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 LTC6400-20 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6400-20 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 Equivalent Output IP3 vs Frequency Single-Ended to Differential ADC Driver 60 3.3V 1.25V 50 0.1μF 1000pF V+ 0.1μF INPUT VOCM 10Ω +IN 66.5Ω 0.1μF 29Ω +OUT +OUTF LTC6400-20 –OUTF –OUT –IN – V ENABLE 20dB GAIN AIN+ VCM VDD LTC2208 AIN– OUTPUT IP3 (dBm) 0.1μF (NOTE 7) 40 30 20 10 10Ω LTC2208 130Msps 16-Bit ADC 640020 TA01a 0 0 50 100 150 200 FREQUENCY (MHz) 250 300 640020 TA01b 640020f 1 LTC6400-20 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 Lead Temperature (Soldering, 10 sec) .................. 300°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 = 125°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 LTC6400CUD-20#PBF LTC6400IUD-20#PBF LTC6400CUD-20#TRPBF LCCS 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC6400IUD-20#TRPBF LCCS 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) IS (mA) LTC6400-20 20 10 200 90 LTC6401-20 20 10 200 50 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 26dB will follow. 640020f 2 LTC6400-20 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 20 20.6 UNITS Input/Output Characteristic GDIFF Gain VIN = ±100mV Differential ● TCGAIN Gain Temperature Drift VIN = ±100mV Differential ● –1.5 VSWINGMIN Output Swing Low Each Output, VIN = ±600mV Differential ● 80 VSWINGMAX Output Swing High Each Output, VIN = ±600mV Differential ● 19.4 2.35 VOUTDIFFMAX Maximum Differential Output Swing 1dB Compressed ● IOUT Output Current Drive Each Output ● 20 VOSDIFF Input Differential Offset Voltage ● –2 TCVOSDIFF Input Differential Offset Voltage Drift TMIN to TMAX 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 ● 150 V 4.4 VP-P mA 2 1.2 ROUTDIFF Output Resistance (+OUT, –OUT) Differential ROUTFDIFF Filtered Output Resistance (+OUTF, –OUTF) Differential ● COUTFDIFF Filtered Output Capacitance (+OUTF, –OUTF) Differential, Includes Parasitic CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V~1.4V ● V V 200 230 1 ● mV μV/°C 1 170 mV 2.46 1.6 ● dB mdB/°C Ω pF 18 25 32 Ω 85 100 115 Ω 45 2.7 pF 65 dB 1 V/V Output Common Mode Voltage Control GCM Common Mode Gain VOCMMIN Output Common Mode Range, MIN VOCMMAX Output Common Mode Range, MAX VOSCM Common Mode Offset Voltage TCVOSCM Common Mode Offset Voltage Drift IVOCM VOCM = 1V to 1.6V 1 1.1 ● ● 1.6 1.5 VOCM = 1.1V to 1.5V ● –15 TMIN to TMAX ● 16 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 ● 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 VS Operating Supply Range ● 2.85 3 3.5 V ● 75 90 105 mA 1 3 mA IS Supply Current ⎯E⎯N⎯A⎯B⎯L⎯E = 0.8V ISHDN Shutdown Supply Current ⎯E⎯N⎯A⎯B⎯L⎯E = 2.4V ● Power Supply Rejection Ratio (Differential Outputs) V+ = 2.85V to 3.5V ● PSRR 55 86 dB 640020f 3 LTC6400-20 AC ELECTRICAL CHARACTERISTICS ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, SYMBOL PARAMETER CONDITIONS –3dBBW –3dB Bandwidth 200mVP-P,OUT (Note 6) MIN 1.84 TYP MAX UNITS GHz 0.1dBBW Bandwidth for 0.1dB Flatness 200mVP-P,OUT (Note 6) 0.3 GHz 0.5dBBW Bandwidth for 0.5dB Flatness 200mVP-P,OUT (Note 6) 0.7 GHz 1/f 1/f Noise Corner 10.5 kHz SR Slew Rate Differential (Note 6) 4.5 V/ns tS1% 1% Settling Time 2VP-P,OUT (Note 6) 0.8 ns tOVDR Overdrive Recovery Time 1.9VP-P,OUT (Note 6) 4 ns tON Turn-On Time +OUT, –OUT Within 10% of Final Values 82 ns tOFF Turn-Off Time ICC Falls to 10% of Nominal 190 ns –3dBBWVOCM VOCM Pin 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 –97/–93 dBc 2VP-P,OUT, No RL –98/–97 dBc 2VP-P,OUTFILT, No RL –100/–98 dBc 2VP-P,OUT Composite, RL = 400Ω –95 dBc 2VP-P,OUT Composite, No RL –99 dBc 10MHz Input Signal HD2,10M /HD3,10M IMD3,10M Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) 2VP-P,OUTFILT Composite, No RL –100 dBc OIP3,10M Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 53.8 dBm P1dB,10M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18 dBm NF10M Noise Figure RL = 375Ω (Note 5) 6.2 dB eIN,10M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.2 nV/√Hz eON,10M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.7 nV/√Hz 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 –86/–85 dBc 2VP-P,OUT, No RL –88/–87 dBc 2VP-P,OUTFILT, No RL –86/–88 dBc 2VP-P,OUT Composite, RL = 400Ω –93 dBc 2VP-P,OUT Composite, No RL –94 dBc 2VP-P,OUTFILT Composite, No RL –93 dBc OIP3,70M Third-Order Output Intercept Point (f1 = 69.5MHz f2 = 70.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 51 dBm P1dB,70M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18 dBm NF70M Noise Figure RL = 375Ω (Note 5) 6.2 dB eIN,70M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√Hz eON,70M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21 nV/√Hz 640020f 4 LTC6400-20 AC ELECTRICAL CHARACTERISTICS ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, CONDITIONS MIN TYP MAX UNITS 140MHz Input Signal HD2,140M /HD3,140M Second/Third Order Harmonic Distortion IMD3,140M Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) OIP3,140M Third-Order Output Intercept Point (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT, RL = 400Ω –74/–74 dBc 2VP-P,OUT, No RL –73/–83 dBc 2VP-P,OUTFILT, No RL –77/–76 dBc 2VP-P,OUT Composite, RL = 400Ω –93 dBc 2VP-P,OUT Composite, No RL –87 dBc 2VP-P,OUTFILT Composite, No RL –89 dBc 2VP-P,OUT Composite, No RL (Notes 7) 47.7 dBm P1dB,140M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18.4 dBm NF140M Noise Figure RL = 375Ω (Note 5) 6.5 dB eIN,140M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 2.1 nV/√Hz eON,140M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.5 nV/√Hz 240MHz Input Signal HD2,240M /HD3,240M Second-Order Harmonic Distortion IMD3,240M Third-Order Intermodulation (f1 = 239.5MHz f2 = 240.5MHz) 2VP-P,OUT, RL = 400Ω –66/–58 dBc 2VP-P,OUT, No RL –65/–63 dBc 2VP-P,OUTFILT, No RL –65/–58 dBc 2VP-P,OUT Composite, RL = 400Ω –71 dBc 2VP-P,OUT Composite, No RL –74 dBc 2VP-P,OUTFILT Composite, No RL –67 dBc 41 dBm dBm OIP3,240M Third-Order Output Intercept Point (f1 = 239.5MHz f2 = 240.5MHz) 2VP-P,OUT Composite, No RL (Note 7) P1dB,240M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.9 NF240M Noise Figure RL = 375Ω (Note 5) 7.1 dB eN, 240M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.9 nV/√Hz eON,240M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 21.7 nV/√Hz 640020f 5 LTC6400-20 AC ELECTRICAL CHARACTERISTICS ⎯E⎯N⎯A⎯B⎯L⎯E = 0V, No RL unless otherwise noted. SYMBOL PARAMETER Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, CONDITIONS MIN TYP MAX UNITS 300MHz Input Signal HD2,300M /HD3,300M Second-Order Harmonic Distortion IMD3,300M Third-Order Intermodulation (f1 = 299.5MHz f2 = 300.5MHz) OIP3,300M Third-Order Output Intercept Point (f1 = 299.5MHz f2 = 300.5MHz) 2VP-P,OUT, RL = 400Ω –61/–53 dBc 2VP-P,OUT, No RL –60/–55 dBc 2VP-P,OUTFILT, No RL –63/–46 dBc 2VP-P,OUT Composite, RL = 400Ω –64 dBc 2VP-P,OUT Composite, No RL –65 dBc 2VP-P,OUTFILT Composite, No RL –58 dBc 2VP-P,OUT Composite, No RL (Note 7) 36.6 dBm P1dB,300M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.5 dBm NF300M Noise Figure RL = 375Ω (Note 5) 7.5 dB eN,300M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.8 nV/√Hz eON,300M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 22 nV/√Hz IMD3,280M/320M Third-Order Intermodulation (f1 = 280MHz f2 = 320MHz) Measure at 360MHz –70 dBc 2VP-P,OUT Composite, RL = 375Ω 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 and LTC6400I are 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 –64 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. Note 7: Since the LTC6400-20 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 LTC6400-20 with amplifiers that require 50Ω output load, the LTC6400-20 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 actual RL. 640020f 6 LTC6400-20 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response 25 S21 Phase and Group Delay vs Frequency Gain 0.1dB Flatness 1.0 TEST CIRCUIT B 0 TEST CIRCUIT B 1.2 TEST CIRCUIT B 0.8 15 10 5 0.4 PHASE (DEGREE) GAIN FLATNESS (dB) 0.6 0.2 0 –0.2 –0.4 –0.6 –100 0.9 –200 0.6 –300 0.3 PHASE GROUP DELAY –0.8 0 –1.0 100 1000 FREQUENCY (MHz) 3000 10 100 1000 FREQUENCY (MHz) 640020 G01 50 IMPEDANCE MAGNITUDE (Ω) –30 S22 –50 S12 100 90 ZIN 200 30 ZOUT 150 10 ZIN 100 –10 PHASE IMPEDANCE MAGNITUDE 50 80 100 1000 FREQUENCY (MHz) 3000 1 10 100 FREQUENCY (MHz) 640020 G04 2 EN 0 1000 640020 G07 1.35 30 0 1 10 100 FREQUENCY (MHz) 1000 640020 G06 Large Signal Transient Response 2.5 RL = 87.5Ω PER OUTPUT RL = 87.5Ω PER OUTPUT 2.0 OUTPUT VOLTAGE (V) NOISE FIGURE (dB) NOISE FIGURE INPUT REFERRED NOISE VOLTAGE (nV/√Hz) 4 100 FREQUENCY (MHz) CMRR 40 Small Signal Transient Response 6 10 50 640020 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 –50 1000 1.30 OUTPUT VOLTAGE (V) 10 60 10 ZOUT 0 PSRR 70 20 –30 –70 –80 0 1000 800 640020 G03 PHASE (DEGREES) S PARAMETERS (dB) S11 –60 400 600 FREQUENCY (MHz) PSRR and CMRR vs Frequency 250 TEST CIRCUIT B –40 200 Input and Output Impedance vs Frequency –10 –20 0 640020 G02 Input and Output Reflection and Reverse Isolation vs Frequency 0 3000 PSRR, CMRR (dB) 10 –400 GROUP DELAY (ns) GAIN (dB) 20 +OUT 1.25 1.20 –OUT +OUT 1.5 1.0 –OUT 0.5 0 1.15 0 2 4 6 TIME (ns) 8 10 640020 G08 0 2 4 6 TIME (ns) 8 10 640020 G09 640020f 7 LTC6400-20 TYPICAL PERFORMANCE CHARACTERISTICS 1% Settling Time for 2V Output Step Overdrive Recovery Time 2.5 5 RL = 87.5Ω PER OUTPUT Harmonic Distortion (Unfiltered) vs Frequency –40 RL = 87.5Ω PER OUTPUT +OUT OUTPUT VOLTAGE (V) 2.0 HARMONIC DISTORTION (dBc) 4 3 SETTLING (%) 2 1.5 1.0 1 0 –1 –2 0.5 –3 –OUT DIFFERENTIAL INPUT VOUT = 2VP-P –50 –60 –70 –80 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL –90 –4 –5 0 50 0 100 TIME (ns) 150 200 –100 0 0.5 1.0 1.5 2.0 TIME (ns) 2.5 640020 G10 –60 –70 –80 –90 –100 HD2 HD3 –100 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE –110 50 100 150 200 FREQUENCY (MHz) 250 –40 HARMONIC DISTORTION (dBc) –90 0 0 300 50 100 150 200 FREQUENCY (MHz) 250 640020 G13 –80 –90 –70 –80 SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –100 50 100 150 200 FREQUENCY (MHz) 250 300 640020 G16 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL –90 0 50 100 150 200 FREQUENCY (MHz) 0 50 100 150 200 FREQUENCY (MHz) 250 300 640020 G15 –40 –90 0 –80 Harmonic Distortion vs Output Common Mode Voltage (Unfiltered Outputs) –60 HD2 HD3 –100 –70 –100 HARMONIC DISTORTION (dBc) –70 –60 300 UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL –50 THIRD ORDER IMD (dBc) HARMONIC DISTORTION (dBc) –40 SINGLE-ENDED INPUT VOUT = 2VP-P –50 NO RL 300 –50 Third Order Intermodulation Distortion vs Frequency –40 250 SINGLE-ENDED INPUT VOUT = 2VP-P 640020 G14 Harmonic Distortion (Filtered) vs Frequency –60 100 150 200 FREQUENCY (MHz) Harmonic Distortion (Unfiltered) vs Frequency UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL –50 THIRD ORDER IMD (dBc) HARMONIC DISTORTION (dBc) –40 DIFFERENTIAL INPUT VOUT = 2VP-P –50 NO RL –80 50 640020 G12 Third Order Intermodulation Distortion vs Frequency –40 –70 0 640020 G11 Harmonic Distortion (Filtered) vs Frequency –60 3.0 250 300 640020 G17 VOUT = 2VP-P at 100MHz RL = 400Ω –50 –60 –70 HD3 –80 –90 HD2 –100 1.0 1.5 1.1 1.2 1.3 1.4 OUTPUT COMMON MODE VOLTAGE (V) 640020 G18 640020f 8 LTC6400-20 TYPICAL PERFORMANCE CHARACTERISTICS Output 1dB Compression Point vs Frequency 19 60 DIFFERENTIAL INPUT RL = 400Ω (NOTE 7) 50 OUTPUT IP3 (dBm) OUTPUT 1dB COMPRESSION (dBm) 20 Output Third Order Intercept vs Frequency 18 17 16 40 DIFFERENTIAL INPUT 30 VOUT = 2VP-P COMPOSITE (NOTE 7) 20 UNFILTERED NO RL UNFILTERED 200Ω RL FILTERED NO RL 10 15 0 50 100 150 200 FREQUENCY (MHz) 250 300 0 50 100 150 200 FREQUENCY (MHz) 640020 G19 300 640020 G20 Turn-On Time Turn-Off Time 3.0 120 3.0 120 100 2.5 100 ICC 2.0 80 –OUT 1.5 60 1.0 40 +OUT 0.5 20 0 RL = 87.5Ω PER OUTPUT –0.5 –100 0 100 200 300 TIME (ns) 2.0 80 –OUT 1.5 60 1.0 40 0.5 +OUT 0 –20 500 –0.5 –100 640020 G21 140 RL = 87.5Ω PER OUTPUT 0 ENABLE 400 VOLTAGE (V) 3.5 20 ICC 0 ENABLE 0 SUPPLY CURRENT (mA) 140 SUPPLY CURRENT (mA) 3.5 2.5 VOLTAGE (V) 250 100 200 300 TIME (ns) 400 –20 500 640020 G22 640020f 9 LTC6400-20 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 (GND). All four pins must be connected to same voltage/ground. –OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins have series resistors, ROUT 12.5Ω. –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 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 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 640020 BD V– 640020f 10 LTC6400-20 APPLICATIONS INFORMATION Circuit Operation The LTC6400 is a low noise and low distortion fully differential op amp/ADC driver with: • Operation from DC to 1.8GHz (–3dB bandwidth) • Fixed gain of 10V/V (20dB) • Differential input impedance 200Ω • Differential output impedance 25Ω • On-Chip 590MHz output filter The LTC6400 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. 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 LTC6400-20 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 LTC6400-20 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. value impedance, e.g. 50Ω, in order to provide an impedance match for the source. Several choices are available. One approach is to use a differential shunt resistor (Figure 1). Another approach is to employ a wide band transformer (Figure 2). Both methods provide a wide band impedance 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 LTC6400-20 for frequency selection and/or noise reduction. Referring to Figure 3, LTC6400-20 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 two outputs have the same gain and thus symmetrical LTC6400-20 25Ω The differential input impedance of the LTC6400-20 is 200Ω. If a 200Ω source impedance is unavailable, then the differential inputs may need to be terminated to a lower 12.5Ω 13 +IN +OUT 8 50Ω IN+ + – VIN OUT– 14 +IN 66.5Ω 15 –IN 25Ω +OUTF 7 50Ω IN– 1.7pF –OUTF 6 OUT+ 1000Ω 100Ω 12.5Ω –OUT 5 16 –IN 640020 F01 Figure 1. Input Termination for Differential 50Ω Input Impedance Using Shunt Resistor LTC6400-20 25Ω 1000Ω 100Ω 12.5Ω 13 +IN +OUT 8 50Ω 1:4 + – VIN IN+ • • OUT– +OUTF 7 14 +IN 50Ω 15 –IN Input Impedance and Matching 1000Ω 100Ω 25Ω IN– 100Ω 16 –IN 1000Ω 1.7pF –OUTF 6 OUT+ 12.5Ω –OUT 5 640020 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a 1:4 Balun 640020f 11 LTC6400-20 APPLICATIONS INFORMATION RS 50Ω 1000Ω 100Ω 12.5Ω 13 +IN VIN + – LTC6400-20 0.1μF +OUT 8 50Ω RT 66.5Ω IN+ OUT– +OUTF 7 14 +IN 0.1μF 50Ω 15 –IN RS 50Ω 0.1μF RT 66.5Ω IN– 100Ω 1.7pF –OUTF 6 OUT+ 1000Ω 12.5Ω –OUT 5 16 –IN 640020 F03 Figure 3. Input Termination for Single-Ended 50Ω Input Impedance 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 202Ω and RT is 66.5Ω in order to match to a 50Ω source impedance. The LTC6400-20 is unconditionally stable. However, the overall differential gain is affected by both source impedance and load impedance as shown in Figure 4: AV = VOUT RL 2000 = • VIN RS + 200 25 + RL Output Match and Filter The LTC6400-20 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 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 a 16nH inductor create a bandpass filter with 165MHz center frequency, –3dB frequencies at 138MHz and 200MHz. Output Common Mode Adjustment The 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 LTC6400-20 1000Ω 100Ω 12.5Ω 13 +IN +OUT 8 8.2pF 50Ω The noise performance of the LTC6400-20 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 voltage 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 input Smith Chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. IN+ 1000Ω 100Ω 12.5Ω 50Ω 15 –IN 13 +IN IN– 100Ω + – Figure 5. LTC6400-20 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 100Ω 16 –IN 1000Ω OUT– +OUTF 7 16nH 50Ω 15 –IN IN– 100Ω 1/2 RL –OUT 5 4.99Ω 50Ω 1.7pF 12.5Ω 39pF 10Ω +OUT 8 IN+ –OUTF 6 OUT+ 1000Ω LTC6400-20 12.5Ω 13 +IN VOUT IN– 8.2pF 12.5Ω –OUT 5 +OUTF 7 50Ω 1/2 RS 1000Ω 14 +IN OUT– 14 +IN 15 –IN –OUTF 6 OUT+ +OUT 8 IN+ FILTERED OUTPUT 12pF (87.5MHz) 640020 F05 50Ω VIN 1.7pF 16 –IN 100Ω 1/2 RL +OUTF 7 14 +IN LTC6400-20 1/2 RS OUT– 16 –IN OUT+ 1000Ω 1.7pF LTC2208 39pF –OUTF 6 12.5Ω 10Ω –OUT 5 640020 F06 4.99Ω 39pF 640020 F04 Figure 4. Calculate Differential Gain Figure 6. LTC6400-20 Internal Filter Topology Modified for Bandpass Filtering (Three External Capacitors, One External Inductor) 640020f 12 LTC6400-20 APPLICATIONS INFORMATION 94 92 90 SFDR (dB) 1.6V. The 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 LTC6400-20. 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 LT22xx families, the VOCM pin can be connected to the VCM pin of the ADC. 88 86 84 82 70 Driving A/D Converters 120 170 220 FREQUENCY (MHz) 270 300 640020 F08 The LTC6400-20 has been specifically designed to interface directly with high speed A/D converters. In Figure 7, an example schematic shows the LTC6400-20 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 wires of either the ADC input or the driver output. VOCM of the LTC6400-20 is connected to VCM of the LTC2208 VCM pin 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 LTC6400-20. The balun also converts input impedance to match 50Ω source impedance. Figure 8. SFDR for the Combination of LTC6400-20 and LTC2208 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 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 Top Silkscreen Figure 8 summarizes the spurious free dynamic range (SFDR) for IMD3 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 1.25V 0.1μF 0.1μF +IN IF IN 66.5Ω 29Ω 0.1μF VOCM 10Ω +OUT +OUTF LTC6400-20 –OUTF –OUT –IN AIN– VCM LTC2208 AIN+ 10Ω ENABLE 20dB GAIN LTC2208 130Msps 16-Bit ADC 640020 F07 Figure 7. Single-Ended Input to LTC6400-20 and LTC2208 640020f 13 LTC6400-20 APPLICATIONS INFORMATION 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 1.8GHz to approximately 1.3GHz. 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 true picture of the >1GHz S-parameters and AC characteristics. TYPICAL APPLICATIONS 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) LTC6400-20 15 C1 0.1μF 16 R1 0Ω –IN –OUTF –IN –OUT V+ VOCM 1 VCC C10 0.1μF VCC 9 V– 2 V+ 6 5 R14 (1) C4 0.1μF 4 C9 1000pF 1 5 R11 (1) R9 86.6Ω C22 0.1μF R13 0Ω J4 +OUT 2 C3 0.1μF V– 3 R12 0Ω T2 SL2 (2) R7 (1) 4 3 • 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 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 -C IC R3 R4 LTC6400CUD-20 OPEN OPEN SL = SIGNAL LEVEL T1 SL1 SL2 SL3 MINI-CIRCUITS TCM4-19 (1:4) 6dB 20dB 14dB 640020 TA03 640020f 14 LTC6400-20 TYPICAL APPLICATIONS 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 640020 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 16 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) 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 640020f 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 LTC6400-20 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 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/√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 640020f 16 Linear Technology Corporation LT 0707 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007