LTC6400-26 1.9GHz Low Noise, Low Distortion Differential ADC Driver for DC-300MHz FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION The LTC®6400-26 is a high-speed differential amplifier targeted at processing signals from DC to 300MHz. The part has been specifically designed to drive 12-, 14- and 16-bit ADCs with low noise and low distortion, but can also be used as a general-purpose broadband gain block. 1.9GHz –3dB Bandwidth Fixed Gain of 20V/V (26dB) –94dBc IMD3 at 70MHz (Equivalent OIP3 = 51dBm) –71dBc IMD3 at 300MHz (Equivalent OIP3 = 39.5dBm) 1nV/√Hz Internal Op Amp Noise 1.5nV/√Hz Total Input Referred Noise 6.8dB Noise Figure Differential Inputs and Outputs 50Ω Input Impedance 2.85V to 3.5V Supply Voltage 85mA Supply Current (255mW) 1V to 1.6V Output Common Mode, Adjustable DC- or AC-Coupled Operation Max Differential Output Swing 4.7VP-P Small 16-Lead 3mm × 3mm × 0.75mm QFN Package The LTC6400-26 is easy to use, with minimal support circuitry required. The output common mode voltage is set using an external pin, independent of the inputs, which eliminates the need of transformers or AC-coupling capacitors in many applications. The gain is internally fixed at 26dB (20V/V). The LTC6400-26 saves space and power compared to alternative solutions using IF gain blocks and transformers. The LTC6400-26 is packaged in a compact 16-lead 3mm × 3mm QFN package and operates over the –40°C to 85°C temperature range. APPLICATIONS ■ ■ ■ ■ ■ 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 Single-Ended to Differential ADC Driver at 140MHz IF Equivalent OIP3 vs Frequency 3.3V 60 3.3V DIFFERENTIAL INPUT (NOTE 7) 50 1000pF 33pF V+ 0.1μF 150W 0.1μF +OUT LTC6400-26 –IN 37.4Ω 10Ω 15Ω +IN VIN 24nH –OUT VOCM V– 1.25V 0.1μF 10Ω 33pF VDD LTC2208 33pF 15Ω COILCRAFT 0603CS AIN+ AIN– VCM 40 30 20 10 LTC2208 130Msps 16-BIT ADC 0 640026 TA01a 100Ω OUTPUT IP3 (dBm) 0.1μF NO RL RL = 200Ω 0 50 100 150 200 FREQUENCY (MHz) 250 300 640026 TA01b 640026fa 1 LTC6400-26 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) 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 +IN +IN –IN –IN TOP VIEW 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 s 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 LTC6400CUD-26#PBF LTC6400IUD-26#PBF PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LTC6400CUD-26#TRPBF LCCX 16-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC6400IUD-26#TRPBF LCCX 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 LTC6400-26 26 20 50 85 LTC6401-8 8 2.5 400 45 LTC6401-20 20 10 200 50 LTC6401-26 26 20 50 45 In addition to the LTC6400 family of amplifiers, a lower power LTC6401 family is available. The LTC6401 is pin compatible to the LTC6400, and has the same low noise performance. The lower power consumption of the LTC6401 comes at the expense of slightly higher non-linearity, especially at input frequencies above 140MHz. Please refer to the separate LTC6401 data sheets for complete details. Other gain versions from 8dB to 14dB will follow. 640026fa 2 LTC6400-26 DC ELECTRICAL CHARACTERISTICS + The ● –denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. V = 3V, V = 0V, +IN = –IN = VOCM = 1.25V, ENABLE= 0V, No RL unless otherwise noted. 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 ● 0.0038 VSWINGMIN Output Swing Low Each Output, VIN = ±200mV Differential ● 90 VSWINGMAX Output Swing High Each Output, VIN = ±200mV Differential ● 2.35 2.48 V 4.38 4.7 VP-P 25 160 VOUTDIFFMAX Maximum Differential Output Swing 1dB Compressed ● IOUT Output Current Drive Each Output, VIN = ±200mV, VOUT > 2VP-P ● 20 VOS Input Offset Voltage Differential ● –2 TCVOS Input Offset Voltage Drift Differential ● IVRMIN Input Common Mode Voltage Range, MIN IVRMAX Input Common Mode Voltage Range, MAX RINDIFF Input Resistance (+IN, –IN) Differential CINDIFF Input Capacitance Differential, Includes Parasitics 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 Parasitics CMRR Common Mode Rejection Ratio Input Common Mode Voltage 1.1V to 1.4V 2 1 42.5 50 mV μV/°C 1 V 57.5 Ω V 50 1 ● mV 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 ENABLE Input Low Voltage ● VIH ENABLE Input High Voltage IIL ENABLE Input Low Current ENABLE = 0.8V ● IIH ENABLE Input High Current ENABLE = 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 3 μA ENABLE Pin ● 2.4 V 1.4 Power Supply VS Operating Supply Range ● 2.85 3 3.5 V IS Supply Current ENABLE = 0.8V ● 70 85 102 mA ISHDN Shutdown Supply Current ENABLE = 2.4V Both Inputs and Outputs Floating ● 0.8 3 mA PSRR Power Supply Rejection Ratio (Differential Outputs) 2.85V to 3.5V ● 65 96 dB 640026fa 3 LTC6400-26 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 1.9 GHz 0.5dBBW Bandwidth for 0.5dB Flatness 200mVP-P,OUT (Note 6) 0.53 GHz 0.1dBBW Bandwidth for 0.1dB Flatness 200mVP-P,OUT (Note 6) 0.28 GHz 1/f 1/f Noise Corner 13.9 kHz SR Slew Rate Differential VOUT = 2V Step (Note 6) 6670 V/μs tS1% 1% Settling Time VOUT = 2VP-P (Note 6) 2 ns tOVDR Overdrive Recovery Time VOUT = 1.9VP-P (Note 6) 16 ns tON Turn-On Time +OUT, –OUT Within 10% of Final Values 120 ns tOFF Turn-Off Time ICC Falls to 10% of Nominal 166 ns –3dBBWVOCM VOCM Pin Small Signal –3dB BW 0.1VP-P at VOCM, Measured Single-Ended at Output (Note 6) 14.7 MHz 2VP-P,OUT, RL = 200Ω –99/–90 dBc 2VP-P,OUT, No RL –98/–99 dBc –91 dBc 10MHz Input Signal HD2,10M/HD3,10M Second/Third Order Harmonic Distortion IMD3,10M Third-Order Intermodulation (f1 = 9.5MHz f2 = 10.5MHz) 2VP-P,OUT Composite, RL = 200Ω 2VP-P,OUT Composite, No RL –93 dBc OIP3,10M Equivalent Third-Order Output Intercept Point (f1 = 9.5MHz f2 = 10.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 50.5 dBm P1dB,10M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.8 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/√Hz eON,10M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 30 nV/√Hz 70MHz Input Signal HD2,70M/HD3,70M Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω –87/–81 dBc 2VP-P,OUT, No RL –87/–94 dBc IMD3,70M Third-Order Intermodulation (f1 = 69.5MHz f2 = 70.5MHz) 2VP-P,OUT Composite, RL = 200Ω –85 dBc 2VP-P,OUT Composite, No RL –94 dBc OIP3,70M Equivalent 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) 18.2 dBm NF70M Noise Figure RL = 375Ω (Note 5) 6.7 dB eIN,70M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.4 nV/√Hz eON,70M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 28 nV/√Hz HD2,140M/ HD3,140M Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω –83/–72 dBc 2VP-P,OUT, No RL –81/–83 dBc IMD3,140M Third-Order Intermodulation (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT Composite, RL = 200Ω –80 dBc 2VP-P,OUT Composite, No RL –88 dBc Equivalent Third-Order Output Intercept Point (f1 = 139.5MHz f2 = 140.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 48 dBm 140MHz Input Signal OIP3,140M 640026fa 4 LTC6400-26 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) 18.7 NF140M Noise Figure RL = 375Ω (Note 5) 6.6 dB eN,140M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.4 nV/√Hz eON,140M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 28 nV/√Hz dBm 240MHz Input Signal 2VP-P,OUT, RL = 200Ω –70/–59 dBc 2VP-P,OUT, No RL –75/–71 dBc 2VP-P,OUT Composite, RL = 200Ω –70 dBc 2VP-P,OUT Composite, No RL –76 dBc 2VP-P,OUT Composite, No RL (Note 7) 42 dBm RL = 375Ω (Notes 5, 7) 18.1 dBm RL = 375Ω (Note 5) 6.9 dB Includes Resistors (Short Inputs) 1.4 nV/√Hz Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 28 nV/√Hz HD2,300M/ HD3,300M Second/Third Order Harmonic Distortion 2VP-P,OUT, RL = 200Ω –66/–54 dBc 2VP-P,OUT, No RL –76/–62 dBc IMD3,300M Third Order Intermodulation (f1 = 299.5MHz f2 = 300.5MHz) 2VP-P,OUT Composite, RL = 200Ω –66 dBc 2VP-P,OUT Composite, No RL –71 dBc OIP3,300M Equivalent Third Order Output Intercept Point (f1 = 299.5MHz f2 = 300.5MHz) 2VP-P,OUT Composite, No RL (Note 7) 39.5 dBm P1dB,300M 1dB Compression Point RL = 375Ω (Notes 5, 7) 17.7 dBm NF300M Noise Figure RL = 375Ω (Note 5) 7.6 dB HD2,240M/ HD3,240M Second/Third Order Harmonic Distortion IMD3,240M Third Order Intermodulation (f1 = 239.5MHz f2 = 240.5MHz) OIP3,240M Third Order Output Intercept Point (f1 = 239.5MHz f2 = 240.5MHz) P1dB,240M 1dB Compression Point NF240M Noise Figure eN,240M Input Referred Voltage Noise Density eON,240M 300MHz Input Signal eN,300M Input Referred Voltage Noise Density Includes Resistors (Short Inputs) 1.5 nV/√Hz eON,300M Output Referred Voltage Noise Density Includes Resistors (Short Inputs) 30 nV/√Hz IMD3,280M/320M Third Order Intermodulation (f1 = 280MHz f2 = 320MHz) Measured at 360MHz 2VP-P,OUT Composite, RL = 375Ω –68 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Input pins (+IN, –IN) are protected by steering diodes to either supply. If the inputs go beyond either supply rail, the input current should be limited to less than 10mA. Note 3: The LTC6400C is guaranteed functional over the operating temperature range of –40°C to 85°C. Note 4: The LTC6400C is guaranteed to meet specified performance from 0°C to 70°C. It is designed, characterized and expected to meet specified –62 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 LTC6400-26 is a feedback amplifier with low output impedance, a resistive load is not required when driving an AD converter. Therefore, typical output power is very small. In order to compare the LTC6400-26 with amplifiers that require 50Ω output load, the LTC6400-26 output voltage swing driving a given RL is converted to OIP3 and P1dB as if it were driving a 50Ω load. Using this modified convention, 2VP-P is by definition equal to 10dBm, regardless of actual RL. 640026fa 5 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response Gain 0.1dB Flatness 30 1.0 0.8 25 GAIN FLATNESS (dB) 0.6 GAIN (dB) 20 15 10 0.2 0 –0.2 –0.4 –0.6 5 0 0.4 –0.8 TEST CIRCUIT B 100 1000 FREQUENCY (MHz) 10 –1.0 3000 10 100 FREQUENCY (MHz) 640026 G01 640026 G02 Input and Output Reflection and Reverse Isoloation vs Frequency S21 Phase and Group Delay vs Frequency 0 1000 2000 TEST CIRCUIT B 0 0.8 GROUP DELAY 0.6 –100 0.4 PHASE –150 GROUP DELAY (ns) PHASE (DEGREE) –50 S PARAMETERS (dB) –10 –20 S22 –30 –40 S11 –50 –60 0.2 S12 –70 –200 0 200 600 400 FREQUENCY (MHz) 800 –80 0 1000 10 100 1000 FREQUENCY (MHz) 640026 G04 640026 G03 Input and Output Impedance vs Frequency ZIN MAG ZOUT MAG ZIN PHASE ZOUT PHASE 90 80 45 70 35 60 30 50 25 40 20 30 15 20 10 10 5 0 10 100 FREQUENCY (MHz) 100 40 0 1000 640026 G05 PHASE (DEGREE) IMPEDANCE MAGNITUDE (Ω) PSRR and CMRR vs Frequency 120 50 PSRR, CMRR (dB) 100 3000 80 PSRR 60 CMRR 40 20 0 1 10 100 FREQUENCY (MHz) 1000 640026 G06 640026fa 6 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Small Signal Transient Response 2.5 9 2.0 EN 8 1.5 7 1.0 NOISE FIGURE 6 5 10 0.5 1.35 OUTPUT VOLTAGE (V) 10 INPUT REFERRED NOISE VOLTAGE (nV/√Hz) NOISE FIGURE (dB) Noise Figure and Input Referred Noise Voltage vs Frequency 0 1000 100 FREQUENCY (MHz) RL = 87.5W PER OUTPUT TEST CIRCUIT B –OUT 1.30 1.25 +OUT 1.20 1.15 2 0 6 4 TIME (ns) 8 640026 G07 640026 G08 Large Signal Transient Response 2.5 Overdriven Transient Response 2.5 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B 1.5 +OUT 0.5 0 RL = 87.5Ω PER OUTPUT +OUT 2.0 –OUT OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 2.0 1.0 1.5 1.0 0.5 0 4 12 8 TIME (ns) 16 0 20 –OUT TEST CIRCUIT B 0 50 150 100 TIME (ns) 640026 G09 HARMONIC DISTORTION (dBc) 3 SETTLING (%) 2 1 0 –1 –2 –3 DIFFERENTIAL INPUT VOUT = 2VP-P –50 –60 –70 –80 –90 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω –100 –4 –5 –110 0 1 3 2 TIME (ns) 250 Harmonic Distortion vs Frequency –40 RL = 87.5Ω PER OUTPUT TEST CIRCUIT B 4 200 640026 G10 1% Settling Time for 2V Output Step 5 10 4 5 640026 G11 0 50 200 150 100 FREQUENCY (MHz) 250 300 640026 G12 640026fa 7 LTC6400-26 TYPICAL PERFORMANCE CHARACTERISTICS Third Order Intermodulation Distortion vs Frequency HARMONIC DISTORTION (dBc) –50 THIRD ORDER IMD (dBc) –40 DIFFERENTIAL INPUT VOUT = 2VP-P COMPOSITE –60 –70 –80 –90 –100 –110 0 50 200 150 100 FREQUENCY (MHz) 250 –50 –70 –80 –90 –110 300 HD2 NO RL HD2 RL = 200Ω HD3 NO RL HD3 RL = 200Ω 0 50 200 150 100 FREQUENCY (MHz) 250 640026 G13 –70 –80 –90 –100 300 –110 NO RL RL = 200Ω 0 OUTPUT IP3 (dBm) 17 16 DIFFERENTIAL INPUT (NOTE 7) 40 30 20 10 250 100 150 200 FREQUENCY (MHz) 0 300 NO RL RL = 200Ω 0 50 250 100 150 200 FREQUENCY (MHz) 640026 G16 640026 G17 Turn-On Time Turn-Off Time 140 3.5 3.0 120 3.0 120 100 100 2.5 2.0 –OUT 80 2.0 60 1.5 40 +OUT 0.5 20 ENABLE 0 –0.5 –100 0 0 100 300 200 TIME (ns) 400 500 640026 G18 –20 VOLTAGE (V) ICC 140 ENABLE 80 –OUT 60 1.5 1.0 40 +OUT 0.5 20 ICC 0 –0.5 –100 ICC (mA) 2.5 ICC (mA) VOLTAGE (V) 300 3.5 1.0 300 50 18 50 250 640026 G15 60 DIFFERENTIAL INPUT RL = 3757 TEST CIRCUIT A 19 (NOTE 7) 0 200 150 100 FREQUENCY (MHz) 50 Equivalent Output Third Order Intercept Point vs Frequency 20 OUTPUT 1dB COMPRESSION POINT (dBm) –60 640026 G14 Output 1dB Compression Point vs Frequency 15 SINGLE-ENDED INPUT VOUT = 2VP-P COMPOSITE –50 –60 –100 NO RL RL = 200Ω –40 SINGLE-ENDED INPUT VOUT = 2VP-P THIRD ORDER IMD (dBc) –40 Third Order Intermodulation Distortion vs Frequency Harmonic Distortion vs Frequency 0 100 300 200 TIME (ns) 0 400 –20 500 640026 G19 640026fa 8 LTC6400-26 PIN FUNCTIONS V+ (Pins 1, 3, 10): Positive Power Supply (Normally tied to 3V or 3.3V). All three pins must be tied to the same voltage. Bypass each pin with 1000pF and 0.1μF capacitors as close to the pins as possible. VOCM (Pin 2): This pin sets the output common mode voltage. An 0.1μF external bypass capacitor is recommended. V– (Pins 4, 9, 12, 17): Negative Power Supply. All four pins must be connected to same voltage/ground. –OUT, +OUT (Pins 5, 8): Unfiltered Outputs. These pins have series 12.5Ω resistors ROUT. –OUTF, +OUTF (Pins 6, 7): Filtered Outputs. These pins have 50Ω series resistors and a 2.7pF shunt capacitor. ENABLE (Pin 11): This pin is a logic input referenced to VEE. If low, the part is enabled. If high, the part is disabled and draws very low standby current while the internal op amp has high output impedance. +IN (Pins 13, 14): Positive Input. Pins 13 and 14 are internally shorted together. –IN (Pins 15, 16): Negative Input. Pins 15 and 16 are internally shorted together. Exposed Pad (Pin 17): V–. The Exposed Pad must be connected to same voltage/ground as pins 4, 9, 12. BLOCK DIAGRAM 12 V– 11 ENABLE 10 V+ 9 V– BIAS CONTROL +IN 13 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 640026 BD V– 640026fa 9 LTC6400-26 APPLICATIONS INFORMATION • Operation from DC to 1.9GHz –3dB bandwidth • Fixed gain of 20V/V (26dB) • Differential input impedance 50Ω • Differential output impedance 25Ω • Differential impedance of output filter 100Ω The LTC6400-26 is composed of a fully differential amplifier with on chip feedback and output common mode voltage control circuitry. Differential gain and input impedance are set by 25Ω/500Ω resistors in the feedback network. Small output resistors of 12.5Ω improve the circuit stability over various load conditions. They also provide a possible external filtering option, which is often desirable when the load is an ADC. Filter resistors of 50Ω are available for additional filtering. Lowpass/bandpass filters are easily implemented with just a couple of external components. Moreover, they offer single-ended 50Ω matching in wideband applications and no external resistor is needed. The LTC6400-26 is very flexible in terms of I/O coupling. It can be AC- or DC-coupled at the inputs, the outputs or both. Due to the internal connection between input and output, users are advised to keep input common mode voltage between 1V and 1.6V for proper operation. If the inputs are AC-coupled, the input common mode voltage is automatically biased close to VOCM and thus no external circuitry is needed for bias. The LTC6400-26 provides an output common mode voltage set by VOCM, which allows driving ADC directly without external components such as transformer or AC coupling capacitors. The input signal can be either single-ended or differential with only minor difference in distortion performance. Referring to Figure 3, LTC6400-26 can be easily configured for single-ended input and differential output without a balun. The signal is fed to one of the inputs through a matching network while the other input is connected to the same matching network and a source resistor. Because the return ratios of the two feedback paths are equal, the two outputs have the same gain and thus symmetrical swing. In general, the single-ended input impedance and termination resistor RT are determined by the combination of RS, RG and RF. For example, when RS is 50Ω, it is found that the single-ended input impedance is 75Ω and RT is 150Ω in order to match to a 50Ω source impedance. LTC6400-26 25Ω The differential input impedance of the LTC6400-26 is 50Ω. The interface between the input of LTC6400-26 and 50Ω source is straightforward. One way is to directly connect 12.5Ω 13 +IN +OUT 8 50Ω + – VIN IN+ OUT– IN– OUT+ +OUTF 7 14 +IN 50Ω 15 –IN 25Ω 500Ω 25Ω 2.7pF –OUTF 6 12.5Ω 16 –IN –OUT 5 640026 F01 Figure 1. Input Termination for Differential 50Ω Input Impedance LTC6400-26 500Ω 25Ω 50Ω 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 LTC6400-26 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. The transformer must be placed close to the input pins in order to minimize the reflection due to input mismatch. Alternatively, one could apply a narrowband impedance match at the inputs of the LTC6400-26 for frequency selection and/or noise reduction. • Circuit Operation 16 –IN MACOM MABA-007159-000000 500Ω 2.7pF –OUTF 6 12.5Ω –OUT 5 640026 F02 Figure 2. Input Termination for Differential 50Ω Input Impedance Using a Balun 640026fa 10 LTC6400-26 APPLICATIONS INFORMATION RS 50Ω VIN + – LTC6400-26 0.1μF 500Ω 25Ω 12.5Ω 13 +IN RT 150Ω +OUT 8 50Ω IN+ OUT– +OUTF 7 14 +IN 50Ω 15 –IN 0.1μF IN– 2.7pF –OUTF 6 OUT+ 500Ω 25Ω 12.5Ω 16 –IN –OUT 5 37.4Ω 640026 F03 The internal low pass filter outputs at +OUTF/–OUTF have a –3dB bandwidth of 590MHz. External capacitor can reduce the low pass filter bandwidth as shown in Figure 5. A bandpass filter is easily implemented with only a few components as shown in Figure 6. Three 39pF capacitors and a 16nH inductor create a bandpass filter with 165MHz center frequency, –3dB frequencies at 138MHz and 200MHz. Output Common Mode Adjustment Figure 3. Input Termination for Single-Ended 50Ω Input Impedance The LTC6400-26 is unconditionally stable, i.e. differential stability factor Kf>1 and stability measure B1>0. However, the overall differential gain is affected by both source impedance and load impedance as shown in Figure 4: AV = VOUT RL 1000 = • VIN RS + 50 25 + RL The noise performance of the LTC6400-26 also depends upon the source impedance and termination. A trade-off between gain and noise is obvious when constant noise figure circle and constant gain circle are plotted within the same input Smith Chart, based on which users can choose the optimal source impedance for a given gain and noise requirement. Output Impedance Match and Filter The LTC6400-26 can drive an ADC directly without external output impedance matching. Alternatively, the differential output impedance of 25Ω can be made larger, e.g. 50Ω, by series resistors or LC network. The LTC6400-26’s output common mode voltage is set by the VOCM pin, which is a high impedance input. The output common mode voltage is capable of tracking VOCM in a range from 1V to 1.6V. Bandwidth of VOCM control is typically 15MHz, which is dominated by a low pass filter connected to the VOCM pin and is aimed to reduce common mode noise generation at the outputs. The internal common mode feedback loop has a –3dB bandwidth of 400MHz, allowing fast rejection of any common mode output disturbance. The VOCM pin should be tied to a DC bias voltage with a 0.1μF bypass capacitor. When interfacing with A/D converters such as the LTC22xx families, the VOCM pin can be connected to the VCM pin of the ADC. Driving A/D Converters The LTC6400-26 has been specifically designed to interface directly with high speed A/D converters. Figure 7 shows the LTC6400-26 with a single-ended input driving the LTC2208, which is a 16-bit, 130Msps ADC. Two external 5Ω resistors help eliminate potential resonance associated with bond wires of either the ADC input or the driver output. VOCM of the LTC6400-26 is connected to VCM of the LTC2208 at 1.25V. Alternatively, a single-ended input signal can be LTC6400-26 1/2 RS 500Ω 25Ω 13 +IN LTC6400-26 1/2 RL 12.5Ω +OUT 8 500Ω 25Ω 13 +IN +OUT 8 50Ω IN+ + – VIN OUT– 50Ω 15 –IN 1/2 RS IN– 25Ω 16 –IN 500Ω IN+ VOUT OUT– 50Ω 15 –IN 1/2 RL 12.5Ω –OUT 5 640026 F04 Figure 4. Calculate Differential Gain +OUTF 7 14 +IN 2.7pF –OUTF 6 OUT+ 8.2pF 50Ω +OUTP 7 14 +IN 12.5Ω IN– 25Ω 16 –IN –OUTF 6 OUT+ 500Ω 2.7pF FILTERED OUTPUT 12pF (87.5MHz) 8.2pF 12.5Ω –OUT 5 640026 F05 Figure 5. LTC6400-26 Internal Filter Topology Modified for Low Filter Bandwidth (Three External Capacitors) 640026fa 11 LTC6400-26 APPLICATIONS INFORMATION –40 LTC6400-26 12.5Ω 500Ω 25Ω 13 +IN SINGLE-ENDED INPUT FS = 122.8Msps –50 DRIVER VOUT = 2VP-P COMPOSITE 39pF 10Ω 4.99Ω –60 +OUT 8 50Ω IN+ –70 OUT– +OUTF 7 14 +IN 15 –IN IN– OUT+ 500Ω 25Ω 16nH 1.7pF 50Ω 39pF LTC2208 –80 –90 –OUTF 6 12.5Ω 16 –IN 10Ω –OUT 5 640026 F06 –100 4.99Ω –110 39pF 0 50 200 150 100 FREQUENCY (MHz) 250 300 640026 F08 Figure 6. LTC6400-26 with 165MHz Output Bandpass Filter converted to a differential signal via a balun and fed to the input of the LTC6400-26. Figure 8 summarizes the IMD3 performance of the whole system in Figure 7. Test Circuits Figure 8. IMD3 for the Combination of LTC6400-26 and LTC2208 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. Due to the fully-differential design of the LTC6400 and its usefulness in applications with differing characteristic specifications, two test circuits are used to generate the information in this datasheet. Test Circuit A is DC987B, a two-port demonstration circuit for the LTC6400 family. The silkscreen is shown in Figure 9. This circuit includes input and output transformers (baluns) for single-endedto-differential conversion and impedance transformation, allowing direct hook-up to a 2-port network analyzer. There are also series resistors at the output to present the LTC6400 with a 375Ω differential load, optimizing distortion performance. Due to the input and output transformers, the –3dB bandwidth is reduced from 1.9GHz to 1.67GHz. 1.25V 0.1μF 0.1μF IF IN VOCM 4.99Ω +OUT +OUTF LTC6400-26 –OUTF –OUT –IN +IN 150Ω 37.4Ω 0.1μF AIN+ VCM LTC2208 AIN– 4.99Ω ENABLE 26dB GAIN LTC2208 130Msps 16-Bit ADC 640026 F07 Figure 7. Single-Ended Input to LTC6400-26 and LTC2208 Figure 9. Top Silkscreen of DC987B, Test Circuit A 640026fa 12 LTC6400-26 TYPICAL APPLICATION Demo Circuit 987B Schematic (Test Circuit A) VCC ENABLE 1 3 DIS 2 JP1 VCC C17 1000pF R16 0W 12 V– R2 (1) T1 (2) R5 0dB (1) 1 • • 5 4 R4 (2) 2 3 C21 0.1μF R3 (2) C2 0.1μF 14 R24 (1) SL1 (2) 16 R1 0Ω +IN +OUTF –IN –OUTF –IN –OUT V+ VOCM 1 VCC R10 86.6Ω 7 R8 (1) C10 0.1μF V+ 2 6 5 R14 (1) C4 0.1μF SL2 (2) R7 (1) C3 0.1μF R9 86.6Ω V– 3 4 C9 1000pF T2 TCM 4:19 1:4 4 R12 0Ω 1 6 R11 (1) C22 0.1μF R13 0Ω 3 2 J4 +OUT SL3 (2) J5 –OUT VCC C12 1000pF C13 0.1μF R19 1.5k TP5 VOCM C7 0.1μF R20 1k R17 0Ω 6 T3 TCM 4:19 1:4 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 • • J6 TEST IN +OUT +IN 8 LTC6400-26 15 C1 0.1μF VCC 9 V– • J2 –IN R6 0Ω 10 V+ • J1 +IN 13 11 ENABLE C18 0.1μF 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 -D IC LTC6400CUD-26 SL = SIGNAL LEVEL R3 R4 T1 OPEN OPEN MACOM MABA-007159-000000 SL1 SL2 SL3 0dB 20dB 14dB 640026 TA02 640026fa 13 LTC6400-26 TYPICAL APPLICATIONS Test Circuit B, 4-Port Analysis V+ 0.1μF 1000pF 12 V– 11 ENABLE 10 V+ 9 V– 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 2.7pF 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 2 V+ 3 VOCM 0.1μF 1000pF VOCM V+ 4 640026 TA03 V– V+ 0.1μF Optical Photodiode Receiver 3V 3V 249Ω 100pF 0.1μF 0.1μF 0.1μF LTC6400-26 249Ω 640026 TA04 PD:JDSU ETX 100RFC2 –3dB BW: 1.1GHz RISE TIME: 200ps 640026fa 14 LTC6400-26 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 p 0.05 3.50 p 0.05 1.45 p 0.05 2.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p 0.05 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 640026fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 15 LTC6400-26 RELATED PARTS PART NUMBER 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 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 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 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/ LT1814 High Slew Rate Low Cost Single/Dual/Quad Op Amps 8nV/√Hz Noise, 750V/μs, 3mA Supply Current LT1815/LT1816/ LT1817 Very High Slew Rate Low Cost Single/Dual/Quad Op Amps 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/ LT6204 Rail-to-Rail Input and Output Low Noise Single/Dual/Quad Op Amps 1.9nV/√Hz Noise, 3mA Supply Current, 100MHz GBW LT6230/LT6231/ LT6232 Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps 1.1nV/√Hz Noise, 3.5mA Supply Current, 215MHz GBW LT6233/LT6234/ LT6235 Rail-to-Rail Output Low Noise Single/Dual/Quad Op Amps 1.9nV/√Hz Noise, 1.2mA Supply Current, 60MHz GBW 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 Integrated Filters 640026fa 16 Linear Technology Corporation LT 1108 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008