LTC6400-8 2.2GHz Low Noise, Low Distortion Differential ADC Driver for DC-300MHz FEATURES DESCRIPTION n The LTC®6400-8 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. n n n n n n n n n n n n n 2.2GHz –3dB Bandwidth Fixed Gain of 2.5V/V (8dB) –99dBc IMD3 at 70MHz (Equivalent OIP3 = 53.4dBm) –61dBc IMD3 at 300MHz (Equivalent OIP3 = 34.8dBm) 1nV/√Hz Internal Op Amp Noise 7.6dB Noise Figure Differential Inputs and Outputs 400Ω Input Impedance 2.85V to 3.5V Supply Voltage 85mA Supply Current (255mW) 1V to 1.6V Output Common Mode, Adjustable DC- or AC-Coupled Operation Max Differential Output Swing 4.8VP-P Small 16-Lead 3mm × 3mm × 0.75mm QFN Package APPLICATIONS n n n n n The LTC6400-8 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 8dB (2.5V/V). The LTC6400-8 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6400-8 is packaged in a compact 16-lead 3mm × 3mm QFN package and operates over the –40°C to 85°C temperature range. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Differential ADC Driver Differential Driver/Receiver Single Ended to Differential Conversion IF Sampling Receivers SAW Filter Interfacing TYPICAL APPLICATION 3.3V 3.3V Equivalent Output IP3 vs Frequency 70 C1 1000pF CF2 33pF C3 0.1μF V+ +IN VIN R1 59.0Ω C4 0.1μF +OUT LTC6400-8 –IN R2 27.4Ω RS3 10Ω RS1 15Ω –OUT VOCM V– L1 RS2 24nH 15Ω COILCRAFT 0603CS 1.25V CF1 33pF RS4 10Ω CF3 33pF AIN+ VDD LTC2208 AIN– VCM LTC2208 130Msps 16-Bit ADC R3 100Ω 50 40 30 20 10 64008 TA01a C5 0.1μF (NOTE 7) 60 OUTPUT IP3 (dBm) C2 0.1μF 0 0 50 100 150 200 FREQUENCY (MHz) 250 300 64008 TA01b 64008f 1 LTC6400-8 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) +IN +IN –IN –IN TOP VIEW Supply Voltage (VCC – VEE) ......................................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 V+ 1 12 V– VOCM 2 10 V+ 9 V– 7 8 +OUT 6 +OUTF 5 –OUT 4 –OUTF V– 11 ENABLE 17 V+ 3 UD PACKAGE 16-LEAD (3mm s 3mm) PLASTIC QFN TJMAX = 150°C, θJA = 68°C/W, θJC = 7.5°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 LTC6400CUD-8#PBF LTC6400CUD-8#TRPBF LCCQ 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC6400IUD-8#PBF LTC6400IUD-8#TRPBF LCCQ 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 LTC6401-14 14 5 200 45 LTC6401-20 20 10 200 50 LTC6401-26 26 20 50 45 LTC6400-8 8 2.5 400 85 LTC6400-14 14 5 200 85 LTC6400-20 20 10 200 90 LTC6400-26 26 20 50 85 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. 64008f 2 LTC6400-8 DC ELECTRICAL CHARACTERISTICS + The l –denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, +IN = –IN = VOCM = 1.25V, ENABLE = 0V, No RL unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX 8 8.5 UNITS Input/Output Characteristic GDIFF Gain VIN = ±400mV Differential l TCGAIN Gain Temperature Drift VIN = ±400mV Differential l –0.13 VSWINGMIN Output Swing Low Each Output, VIN = ±1.6V Differential l 74 VSWINGMAX Output Swing High Each Output, VIN = ±1.6V Differential l 7.5 2.3 VOUTDIFFMAX Maximum Differential Output Swing 1dB Compressed l IOUT Output Current Drive VOUT > 2VP-P,DIFF l 20 VOS Input Offset Voltage Differential l –5 TCVOS Input Offset Voltage Drift Differential l 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 170 V 4.8 VP-P mA 5 2 ROUTDIFF Output Resistance (+OUT, –OUT) Differential ROUTFDIFF Filtered Output Resistance (+OUTF, –OUTF) Differential l COUTFDIFF Filtered Output Capacitance (+OUTF, –OUTF) Differential, Includes Parasitic CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V~1.7V l V V 400 460 1 l mV μV/°C 1 340 mV 2.48 1.8 l dB mdB/°C Ω pF 18 25 32 Ω 85 100 115 Ω 39 2.7 pF 55 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 l 6 IVOCM VOCM Input Current l 4.5 VIL ENABLE Input Low Voltage l VIH ENABLE Input High Voltage l IIL ENABLE Input Low Current ENABLE = 0.8V l IIH ENABLE Input High Current ENABLE = 2.4V l 1 1.1 l VOCM = 1.1V to 1.5V l 1.6 1.5 l –15 V V V V 15 mV μV/°C 15 μA 0.8 V ENABLE Pin 2.4 V 0.5 μA 1.3 4 μA 3 3.5 V 85 95 mA 0.9 3 mA Power Supply VS Operating Supply Range l 2.85 70 IS Supply Current ENABLE = 0.8V, Input and Output Floating l ISHDN Shutdown Supply Current ENABLE = 2.4V, Input and Output Floating l PSRR Power Supply Rejection Ratio (Differential Outputs) V+ = 2.85V to 3.5V l 50 68 dB 64008f 3 LTC6400-8 AC ELECTRICAL CHARACTERISTICS ENABLE = 0V, No RL unless otherwise noted. Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS –3dBBW –3dB Bandwidth 200mVP-P,OUT (Note 6) 1.2 2.2 GHz 0.5dBBW Bandwidth for 0.5dB Flatness 200mVP-P,OUT (Note 6) 0.43 GHz 0.1dBBW Bandwidth for 0.1dB Flatness 200mVP-P,OUT (Note 6) 1/f 1/f Noise Corner SR Slew Rate VOUT = 2V Step (Note 6) tS1% 1% Settling Time VOUT = 2VP-P (Note 6) 0.2 GHz 16.5 kHz 3810 V/μs 1.8 ns tOVDR Overdrive Recovery Time VOUT = 1.9VP-P (Note 6) 18 ns tON Turn-On Time Differential Output Reaches 90% of Steady State Value 10 ns tOFF Turn-Off Time Differential Output Drops to 10% of Original Value 12 ns –3dBBWVOCM VOCM Pin Small Signal –3dB BW 0.1VP-P at VOCM, Measured Single-Ended at Output (Note 6) 14 MHz –118/–98 dBc –120/–109 dBc dBc 10MHz Input Signal HD2,10M/HD3,10M Second/Third Order Harmonic Distortion VOUT = 2VP-P, RL = 200Ω VOUT = 2VP-P, No RL IMD3,10M Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) VOUT = 2VP-P Composite, RL = 200Ω –99 VOUT = 2VP-P Composite, No RL –112 dBc OIP3,10M Equivalent Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) VOUT = 2VP-P Composite, No RL (Note 7) 60 dBm P1dB,10M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18.2 dBm NF10M Noise Figure RS = 400Ω, RL = 375Ω 7.6 dB eIN,10M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 3.7 nV/√Hz eON,10M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 9.3 nV/√Hz 70MHz Input Signal HD2,70M/HD3,70M Second/Third Order Harmonic Distortion VOUT = 2VP-P, RL = 200Ω VOUT = 2VP-P, No RL –97/–85 dBc –100/–98 dBc Third-Order Intermodulation (f1 = 69.5MHz f2 = 70.5MHz) VOUT = 2VP-P Composite, RL = 200Ω –90 dBc VOUT = 2VP-P Composite, No RL –99 dBc OIP3,70M Equivalent Third-Order Output Intercept Point (f1 = 69.5MHz f2 = 70.5MHz) VOUT = 2VP-P Composite, No RL (Note 7) 53.4 dBm P1dB,70M 1dB Compression Point RL = 375Ω (Notes 5, 7) 19.2 dBm NF70M Noise Figure RS = 400Ω, RL = 375Ω 7.6 dB eIN,70M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 3.7 nV/√Hz eON,70M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 9.3 nV/√Hz IMD3,70M 140MHz Input Signal HD2,140M/ HD3,140M Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω 2VP-P,OUT, No RL IMD3,140M Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT Composite, RL = 200Ω –79 dBc 2VP-P,OUT Composite, No RL –84 dBc Third-Order Output Intercept Point (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT Composite, No RL (Notes 7) 45.8 dBm OIP3,140M –86/–71 dBc –91/–81 dBc 64008f 4 LTC6400-8 AC ELECTRICAL CHARACTERISTICS ENABLE = 0V, No RL unless otherwise noted. Specifications are at TA = 25°C. V+ = 3V, V– = 0V, VOCM = 1.25V, SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS P1dB,140M 1dB Compression Point RL = 375Ω (Notes 5, 7) 19.2 dBm NF140M Noise Figure RS = 400Ω, RL = 375Ω 7.7 dB eIN,140M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 3.7 nV/√Hz eON,140M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 9.3 nV/√Hz HD2,240M/ HD3,240M Second-Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω –71/–53 dBc 2VP-P,OUT, No RL –73/–59 dBc IMD3,240M Third-Order Intermodulation (f1 = 239.5MHz f2 = 240.5MHz) 2VP-P,OUT Composite, RL = 200Ω –64 dBc 2VP-P,OUT Composite, No RL –68 dBc 240MHz Input Signal OIP3,240M Third-Order Output Intercept Point (f1 = 239.5MHz f2 = 240.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 37.8 dBm P1dB,240M 1dB Compression Point RL = 375Ω (Notes 5, 7) 18.2 dBm NF240M Noise Figure RS = 400Ω, RL = 375Ω 8.1 dB eN, 240M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 3.7 nV/√Hz eON,240M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 9.6 nV/√Hz 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 = 200Ω –67/–46 dBc 2VP-P,OUT, No RL –69/–50 dBc 2VP-P,OUT Composite, RL = 200Ω –57 dBc 2VP-P,OUT Composite, No RL –61 dBc 2VP-P,OUT Composite, No RL (Note 7) 34.8 dBm P1dB,300M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.6 dBm NF300M Noise Figure RS = 400Ω, RL = 375Ω 8.5 dB eN,300M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 3.8 nV/√Hz eON,300M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 10 nV/√Hz IMD3,280M/320M Third-Order Intermodulation (f1 = 280MHz f2 = 320MHz) Measured at 360MHz 2VP-P,OUT Composite, RL = 375Ω –59 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 –53 dBc performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LTC6400I is guaranteed to meet specified performance from –40°C to 85°C. Note 5: Input and output baluns used. See Test Circuit A. Note 6: Measured using Test Circuit B. RL = 87.5Ω per output. Note 7: Since the LTC6400-8 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 LTC6400-8 with amplifiers that require 50Ω output load, the LTC6400-8 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. 64008f 5 LTC6400-8 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response 1.0 TEST CIRCUIT B 10 0.6 6 4 2 –50 0.4 0.2 0 –0.2 –0.4 0 –0.6 –2 –0.8 100 1000 FREQUENCY (MHz) 10 3000 100 1000 FREQUENCY (MHz) Input and Output Reflection and Reverse Isolation vs Frequency 500 TEST CIRCUIT B IMPEDANCE MAGNITUDE (Ω) –30 S22 –50 S12 400 ZIN 300 0 200 –20 ZIN 150 ZOUT 10 3000 9.0 4.0 8.5 3.5 EN 3.0 2.5 NOISE FIGURE 7.0 2.0 6.5 1.5 6.0 1.0 5.5 0.5 100 150 200 FREQUENCY (MHz) 250 0 300 64008 G07 1.35 OUTPUT VOLTAGE (V) NOISE FIGURE (dB) 4.5 INPUT REFERRED NOISE VOLTAGE (nV/√Hz) 9.5 50 50 CMRR 40 30 20 10 –100 1000 0 1 10 100 FREQUENCY (MHz) 1000 64008 G06 Small Signal Transient Response 8.0 0 1000 64008 G05 5.0 NF TEST: RS = 400Ω 800 60 –80 100 FREQUENCY (MHz) 400 600 FREQUENCY (MHz) PSRR –60 Noise Figure and Input Referred Noise Voltage vs Frequency 0 –40 100 64008 G04 5.0 70 20 0 7.5 80 250 –80 10.0 80 40 ZOUT 50 100 1000 FREQUENCY (MHz) 100 60 350 –70 10 200 64008 G03 PHASE (DEGREES) S PARAMETERS (dB) S11 –60 0 PSRR and CMRR vs Frequency PHASE IMPEDANCE MAGNITUDE 450 –40 –200 3000 0.2 GROUP DELAY Input and Output Impedance vs Frequency –10 –20 0.4 64008 G02 64008 G01 0 –100 PSRR, CMRR (dB) 10 0.6 PHASE –150 –1.0 –4 Large Signal Transient Response 2.5 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B RL = 87.5Ω PER OUTPUT TEST CIRCUIT B 2.0 1.30 +OUT 1.25 1.20 1.15 0.8 TEST CIRCUIT B OUTPUT VOLTAGE (V) GAIN (dB) 8 0 TEST CIRCUIT B GROUP DELAY (ns) GAIN FLATNESS (dB) 12 0.8 PHASE (DEGREE) 14 S21 Phase and Group Delay vs Frequency Gain 0.1dB Flatness –OUT 0 2 4 6 TIME (ns) +OUT 1.5 1.0 –OUT 0.5 8 10 64008 G08 0 0 2 4 6 TIME (ns) 8 10 64008 G09 64008f 6 LTC6400-8 TYPICAL PERFORMANCE CHARACTERISTICS 1% Settling Time for 2V Output Step RL = 87.5Ω PER OUTPUT 4 TEST CIRCUIT B –IN 1 4.5 4 4.0 3 3.5 3.0 +IN 2.5 0 +OUT –1 2.0 –2 1.5 –3 1.0 –4 –5 1 0 –1 –2 –3 –5 1 0 2 3 TIME (ns) 4 Third Order Intermodulation Distortion vs Frequency –40 HARMONIC DISTORTION (dBc) 200Ω RL –70 NO RL –80 –90 –100 –110 50 100 150 200 FREQUENCY (MHz) –90 250 300 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL 0 50 150 200 100 FREQUENCY (MHz) 250 –50 –70 –80 –90 –110 HD2 NO RL HD2 200Ω RL HD3 NO RL HD3 200Ω RL 0 50 SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –50 –60 100 150 200 FREQUENCY (MHz) 250 300 –60 200Ω RL –70 NO RL –80 –90 –100 –110 0 50 100 150 200 FREQUENCY (MHz) 250 64008 G14 Equivalent Output 1dB Compression Point vs Frequency 300 64008 G15 Equivalent Output Third Order Intercept Point vs Frequency IMD3 vs VICM and VOCM 70 20 300 Third Order Intermodulation Distortion vs Frequency –40 64008 G13 –85 60 –88 19 OUTPUT IP3 (dBm) OUTPUT 1dB COMPRESSION POINT (dBm) –80 64008 G12 SINGLE-ENDED INPUT VOUT = 2VP-P –100 0 –70 –110 5 18 17 16 15 50 100 150 200 FREQUENCY (MHz) SWEEP VOCM, INPUT AC-COUPLE NO RL 40 200Ω RL 30 –91 SWEEP VICM, VOCM = 1.25V –94 20 –97 DIFFERENTIAL INPUT RL = 375Ω TEST CIRCUIT A (NOTE 7) 0 50 IMD3 (dBc) THIRD ORDER IMD (dBc) –60 –60 Harmonic Distortion vs Frequency DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE –50 –50 64008 G11 64008 G10 –40 DIFFERENTIAL INPUT VOUT = 2VP-P –100 –4 0 20 40 60 80 100 120 140 160 180 200 TIME (ns) 0 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B 2 0.5 –OUT Harmonic Distortion vs Frequency –40 THIRD ORDER IMD (dBc) 2 5 OUTPUT VOLTAGE (V) INPUT VOLTAGE (V) 3 5.0 SETTLING (%) 5 HARMONIC DISTORTION (dBc) Overdrive Recovery Response 10 0 250 300 64008 G16 DIFFERENTIAL INPUT (NOTE 7) 0 50 100 150 200 FREQUENCY (MHz) 250 300 64008 G17 DIFFERENTIAL INPUT, NO RL VOUT = 100MHz, 2VP-P COMPOSITE –100 1.0 1.2 1.4 1.6 COMMON MODE VOLTAGE (V) 1.8 64008 G18 64008f 7 LTC6400-8 TYPICAL PERFORMANCE CHARACTERISTICS Turn-Off Time 3.5 3.0 3.0 2.5 2.5 2.0 +OUT VOLTAGE (V) VOLTAGE (V) Turn-On Time 3.5 1.5 –OUT 1.0 0.5 RL = 87.5Ω PER OUTPUT 2.0 1.5 1.0 +OUT –OUT 0.5 0 RL = 87.5Ω PER OUTPUT –0.5 –20 0 20 40 TIME (ns) 0 ENABLE 60 80 64008 G19 ENABLE –0.5 –20 0 20 40 TIME (ns) 60 80 64008 G20 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 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. ENABLE (Pin 11): This pin is a logic input referenced to VEE. If low, the part is enabled. If high, the part is disabled and draws very low standby current while the internal op amp has high output impedance. +IN (Pins 13, 14): Positive Input. Pins 13 and 14 are internally shorted together. –IN (Pins 15, 16): Negative Input. Pins 15 and 16 are internally shorted together. Exposed Pad (Pin 17): V–. The Exposed Pad must be connected to same voltage/ground as pins 4, 9, 12. 64008f 8 LTC6400-8 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 2.7pF RFILT 50Ω –IN 15 –IN 16 RF 500Ω RG 200Ω IN– RF 500Ω RG 200Ω –OUTF 6 OUT+ ROUT 12.5Ω –OUT 5 2k COMMON MODE CONTROL 5.3pF 1 V+ 2 3 VOCM V+ 4 64008 BD V– APPLICATIONS INFORMATION Circuit Operation The LTC6400-8 is a low noise and low distortion fully differential op amp/ADC driver with: • Operation from DC to 2.2GHz –3dB bandwidth • Fixed gain of 2.5V/V (8dB) • Differential input impedance 400Ω • Differential output impedance 25Ω • Differential impedance of output filter 100Ω The LTC6400-8 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 200Ω/500Ω resistors in the feedback network. Small output resistors of 12.5Ω improve the circuit stability over various load conditions. They also provide a possible external filtering option, which is often desirable when the load is an ADC. Filter resistors of 50Ω are available for additional filtering. Lowpass/bandpass filters are easily implemented with just a couple of external components. Moreover, they offer single-ended 50Ω matching in wideband applications and no external resistor is needed. The LTC6400-8 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 1.8V for proper operation. If the inputs are AC-coupled, the input common mode voltage is automatically biased approximately 450mV above VOCM and thus no external circuitry is needed for bias. The LTC6400-8 provides an output common mode voltage set by VOCM, which allows driving ADC directly without external components such as transformer or AC coupling capacitors. The input signal can be either single-ended or differential with only minor difference in distortion performance. Input Impedance and Matching The differential input impedance of the LTC6400-8 is 400Ω. Usually the differential inputs need to be terminated to a lower 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 wideband transformer and shunt resistor (Figure 2). Both methods provide a wideband match. The termination resistor or the transformer must be placed close to the input pins in 64008f 9 LTC6400-8 APPLICATIONS INFORMATION LTC6400-8 500Ω 200Ω 25Ω 13 +IN +OUT 8 + – 50Ω IN+ + – VIN OUT– 14 +IN 57.6Ω +OUTF 7 50Ω 15 –IN 25Ω RS 50Ω 12.5Ω IN– 500Ω 200Ω 2.7pF 0.1μF LTC6400-8 12.5Ω 13 +IN +OUT 8 50Ω 1:4 IN+ • • + – VIN OUT– 14 +IN 402Ω 15 –IN 25Ω MINI CIRCUITS TCM4-19 IN– 200Ω 16 –IN +OUTF 7 50Ω 500Ω IN– OUT+ +OUTF 7 –OUTF 6 500Ω 200Ω 2.7pF 12.5Ω 16 –IN –OUT 5 27.4Ω 64008 F03 Figure 3. Input Termination for Single-Ended 50Ω Input Impedance The LTC6400-8 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: 2.7pF –OUTF 6 OUT+ OUT– 50Ω 15 –IN Figure 1. Input Termination for Differential 50Ω Input Impedance Using Shunt Resistor 500Ω IN+ 0.1μF –OUT 5 200Ω +OUT 8 14 +IN 64008 F01 25Ω 12.5Ω 50Ω RT 59.0Ω 12.5Ω 16 –IN 500Ω 200Ω 13 +IN VIN –OUTF 6 OUT+ LTC6400-8 0.1μF AV = 12.5Ω VOUT RL 1000 = • VIN RS + 400 25 + RL –OUT 5 64008 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a Balun order to minimize the reflection due to input mismatch. Alternatively, one could apply a narrowband impedance match at the inputs of the LTC6400-8 for frequency selection and/or noise reduction. Referring to Figure 3, LTC6400-8 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 322Ω and RT is 59Ω in order to match to a 50Ω source impedance. The noise performance of the LTC6400-8 also depends upon the source impedance and termination. For example, an input 1:4 transformer in Figure 2 improves SNR by adding 6dB 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 input Smith Chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. LTC6400-8 500Ω 200Ω 1/2 RS 12.5Ω 1/2 RL 13 +IN +OUT 8 50Ω IN+ + – VIN OUT– +OUTF 7 14 +IN VOUT 50Ω 15 –IN 1/2 RS IN– 200Ω 2.7pF –OUTF 6 OUT+ 500Ω 1/2 RL 12.5Ω 16 –IN –OUT 5 64008 F04 Figure 4. Calculate Differential Gain 64008f 10 LTC6400-8 APPLICATIONS INFORMATION Output Impedance Match and Filter Output Common Mode Adjustment The LTC6400-8 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 LTC6400-8’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 14MHz, 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 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 LT22xx families, the VOCM pin can be connected to the VCM pin of the ADC. The internal low pass filter outputs at +OUTF/–OUTF have a –3dB bandwidth of 590MHz. External capacitors can reduce the lowpass filter bandwidth as shown in Figure 5. A bandpass filter is easily implemented with LTC6400-8 500Ω 200Ω 12.5Ω 13 +IN +OUT 8 8pF 50Ω IN+ OUT– +OUTF 7 14 +IN 50Ω 15 –IN IN– 200Ω 2.7pF FILTERED OUTPUT 12pF (87.5MHz) –OUTF 6 OUT+ 500Ω 8pF Driving A/D Converters 12.5Ω 16 –IN –OUT 5 64008 F05 Figure 5. LTC6400-8 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 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. 500Ω 200Ω LTC6400-8 12.5Ω 13 +IN The LTC6400-8 has been specifically designed to interface directly with high speed A/D converters. Figure 7 shows the LTC6400-8 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 of the LTC6400-8 is connected to VCM of the LTC2208 at 1.25V. Alternatively, an input single-ended signal can be converted to differential signal via a balun and fed to the input of the LTC6400-8. 39pF 10Ω 4.99Ω 1.25V +OUT 8 0.1μF 50Ω IN+ OUT– +OUTF 7 14 +IN 15 –IN IN– 200Ω 16 –IN 0.1μF 16nH 50Ω OUT+ 500Ω 2.7pF LTC2208 39pF –OUTF 6 12.5Ω 59.0Ω 10Ω –OUT 5 64008 F06 4.99Ω 39pF VOCM 4.99Ω +IN IF IN 27.4Ω 0.1μF +OUT +OUTF LTC6400-8 –OUTF –IN –OUT AIN– VCM LTC2208 AIN+ 4.99Ω ENABLE 8dB GAIN LTC2208 130Msps 16-Bit ADC 64008 F07 Figure 6. LTC6400-8 Modified 165MHz for Bandpass Filtering (Three External Capacitors, One External Inductor) Figure 7. Single-Ended Input to LTC6400-8 and LTC2208 64008f 11 LTC6400-8 APPLICATIONS INFORMATION Figure 8 summarizes the IMD3 performance of the whole system as shown in Figure 7. –40 SINGLE-ENDED INPUT FS = 122.8Msps –50 DRIVER V OUT = 2VP-P COMPOSITE IMD3 (dBc) –60 –70 –80 –90 –100 –110 0 50 100 150 200 FREQUENCY (MHz) 250 300 64008 F08 Figure 8. IMD3 for the Combination of LTC6400-8 and LTC2208 Test Circuits Due to the fully-differential design of the LTC6400 and its usefulness in applications with differing characteristic specifications, two test circuits are used to generate the information in this datasheet. Test Circuit A is DC987B, a two-port demonstration circuit for the LTC6400 family. The silkscreen is shown in Figure 9. This circuit includes input and output transformers (baluns) for single-endedto-differential conversion and impedance transformation, allowing direct hook-up to a 2-port network analyzer. There are also series resistors at the output to present the LTC6400 with a 375Ω differential load, optimizing distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 2.2GHz to approximately 1.46GHz. Figure 9. Top Silkscreen for DC987B. Test Circuit A 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. 64008f 12 LTC6400-8 TYPICAL APPLICATIONS Demo Circuit 987B Schematic (Test Circuit A) VCC 3 DIS 2 JP1 VCC C17 1000pF R16 0Ω 12 V– R2 (1) 6 T1 (2) 1 2 C21 0.1μF 4 3 R3 (2) C2 0.1μF 14 R24 (1) SL1 (2) +IN 9 V– +OUT +IN +OUTF 8 R10 86.6Ω 7 R8 (1) 6 R7 (1) LTC6400-8 15 C1 0.1μF 16 R1 0Ω –IN –OUTF –IN –OUT V+ VOCM 1 VCC C10 0.1μF VCC 10 V+ V+ 2 5 R14 (1) C4 0.1μF SL2 (2) C3 0.1μF R9 86.6Ω V– 3 4 C9 1000pF 4 R12 0Ω 1 6 R11 (1) C22 0.1μF R13 0Ω 3 2 T2 TCM 4:19 1:4 • R5 0dB (1) R4 (2) • J2 –IN R6 0Ω • J1 +IN 13 11 ENABLE C18 0.1μF • ENABLE 1 J4 +OUT SL3 (2) J5 –OUT VCC C12 1000pF C13 0.1μF R19 1.5k TP5 R17 0Ω 6 T3 TCM 4:19 1:4 • J6 TEST IN C7 0.1μF R20 1k 2 C23 0.1μF C19 0.1μF 4 R21 (1) C24 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 • VOCM 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 -A IC LTC6400CUD-8 SL = SIGNAL LEVEL R3 R4 T1 SL1 SL2 SL3 200Ω MINI-CIRCUITS TCM4-19 (1:4) 6dB 8dB 2dB 64008 TA02 64008f 13 LTC6400-8 TYPICAL APPLICATIONS Test Circuit B, 4-Port Analysis V+ 1000pF V– 0.1μF 11 V– V+ ENABLE 12 10 9 BIAS CONTROL RF 500Ω RG 200Ω +IN 13 PORT 1 (50Ω) ROUT 12.5Ω RFILT 50Ω 0.1μF 1/2 AGILENT E5O71A +IN 14 133Ω IN+ IN– +OUTF CFILT 2.7pF 0.1μF 1/2 AGILENT E5O71A –OUTF 6 OUT+ RF 500Ω RG 200Ω ROUT 12.5Ω –OUT 37.4Ω PORT 4 (50Ω) 5 0.1μF 0.1μF COMMON MODE CONTROL 1 1000pF PORT 3 (50Ω) 7 OUT– RFILT 50Ω –IN 15 –IN 16 PORT 2 (50Ω) +OUT 37.4Ω 8 2 V+ 3 VOCM 0.1μF VOCM V+ 4 64008 TA03 V– V+ 0.1μF 64008f 14 LTC6400-8 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 p0.05 3.50 p 0.05 1.45 p 0.05 2.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 s 45o CHAMFER R = 0.115 TYP 0.75 p 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 p 0.10 1 1.45 p 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 p 0.05 0.50 BSC 64008f 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 LTC6400-8 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 = 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 LTC6400-14 1.9GHz Low Noise, Low Distortion, Differential ADC Driver AV = 14dB, 85mA Supply Current, IMD3 = –66dBc at 300MHz 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 LTC6401-14 2GHz Low Noise, Low Distortion, Differential ADC Driver AV = 14dB, 45mA Supply Current, IMD3 = –81dBc at 140MHz LTC6401-20 1.3GHz Low Noise, Low Distortion, Differential ADC Driver AV = 20dB, 50mA Supply Current, IMD3 = –74dBc at 140MHz LTC6401-26 1.6GHz Low Noise, Low Distortion, Differential ADC Driver AV = 26dB, 45mA Supply Current, IMD3 = –72dBc 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 LTC6404-1 600MHz Low Noise Differential ADC Driver en = 1.5nV/√Hz, Rail-to-Rail Outputs 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 64008f 16 Linear Technology Corporation LT 0708 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 l FAX: (408) 434-0507 l www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008