LT6604-5 Dual Very Low Noise, Differential Amplifier and 5MHz Lowpass Filter DESCRIPTION FEATURES n n n n n n n Dual Differential Amplifier with 5MHz Lowpass Filters 4th Order Filters Approximates Chebyshev Response Guaranteed Phase and Gain Matching Resistor-Programmable Differential Gain >82dB Signal-to-Noise (3V Supply, 2VP-P Output) Low Distortion (1MHz, 2VP-P Output, 800Ω Load) HD2: 93dBc HD3: 96dBc Specified for Operation with 3V, 5V and ±5V Supplies Fully Differential Inputs and Outputs Adjustable Output Common Mode Voltage Small 4mm × 7mm × 0.75mm QFN Package The LT®6604-5 consists of two matched, fully differential amplifiers, each with a 4th order, 5MHz lowpass filter. The fixed frequency lowpass filter approximates a Chebyshev response. By integrating a filter and a differential amplifier, distortion and noise are made exceptionally low. At unity gain, the measured in-band signal-to-noise ratio is an impressive 82dB. At higher gains, the input referred noise decreases, allowing the part to process smaller input differential signals without significantly degrading the signal-to-noise ratio. Gain and phase are well matched between the two channels. Gain for each channel is independently programmed using two external resistors. The LT6604-5 enables level shifting by providing an adjustable output common mode voltage, making it ideal for directly interfacing to ADCs. The LT6604-5 is fully specified for 3V operation. The differential design enables outstanding performance at a 2VP-P signal level for a single 3V supply. APPLICATIONS n n n n n n n Dual Differential ADC Driver and Filter Single-Ended to Differential Converter Matched, Dual, Differential Gain or Filter Stage Common Mode Translation of Differential Signals High Speed ADC Antialiasing and DAC Smoothing in Wireless Infrastructure or Networking Applications High Speed Test and Measurement Equipment Medical Imaging See the back page of this datasheet for a complete list of related single and dual differential amplifiers with integrated 2.5MHz to 20MHz lowpass filters. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Channel to Channel Gain Matching 3V 25 – 806Ω +INA VMIDA 0.01μF + V+A + – VOCMA –INA – + 806Ω – 806Ω 0.01μF 806Ω +OUTA V+B +INB VMIDB + –OUTA + – VOCMB –INB – + –OUTB +OUTB LTC22xx 3V 50Ω 50Ω + 18pF AIN DOUT – 3V 50Ω 50Ω + 18pF AIN 50 TYPICAL UNITS TA = 25°C GAIN = 1 20 f = 5MHz IN DUAL ADC NUMBER OF UNITS LT6604-5 15 10 5 DOUT – 0 V– –0.20 66045 TA01 –0.10 0 0.10 GAIN MATCH (dB) 0.20 66045 TA01b 66045f 1 LT6604-5 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) 31 V– 32 V– 33 NC TOP VIEW 34 VMIDA Total Supply Voltage .................................................11V Operating Temperature Range (Note 6).... –40°C to 85°C Specified Temperature Range (Note 7) .... –40°C to 85°C Junction Temperature ........................................... 150°C Storage Temperature Range................... –65°C to 150°C Input Voltage +IN, –IN, VOCM, VMID (Note 8) ..............................±VS Input Current +IN, –IN, VOCM, VMID (Note 8) ........................±10mA 30 NC NC 1 29 –OUTA +INA 2 28 NC NC 3 27 +OUTA –INA 4 26 NC NC 5 25 V+A VOCMA 6 V– 7 24 V– 35 VMIDB 8 23 NC NC 9 22 NC +INB 10 21 –OUTB NC 11 20 NC –INB 12 19 +OUTB NC 13 V+B 17 NC 16 NC 15 VOCMB 14 18 NC UFF PACKAGE 34-LEAD (4mm s 7mm) PLASTIC QFN TJMAX = 150°C, θJA = 43°C/W, θJC = 4°C/W EXPOSED PAD (PIN 35) IS V–, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE LT6604CUFF-5#PBF LT6604CUFF-5#TRPBF 66045 34-Lead (4mm × 7mm) Plastic QFN 0°C to 70°C LT6604IUFF-5#PBF LT6604IUFF-5#TRPBF 66045 34-Lead (4mm × 7mm) 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/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k. PARAMETER CONDITIONS MIN TYP MAX UNITS Filter Gain Either Channel, VS = 3V VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz) –0.5 –0.15 –0.4 –0.7 –1.1 0 0 –0.1 –0.1 –0.2 –28 –44 0.5 0.1 0.3 0.6 0.8 –25 dB dB dB dB dB dB dB l l l l l l 66045f 2 LT6604-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k. PARAMETER CONDITIONS Matching of Filter Gain, VS = 3V VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz) Matching of Filter Phase, VS = 3V TYP MAX l l l l l l 0.05 0.005 0.01 0.03 0.05 0.15 0.1 0.7 0.1 0.2 0.5 0.6 1.8 2.8 dB dB dB dB dB dB dB VIN = 2VP-P, fIN = 2.5MHz VIN = 2VP-P, fIN = 4MHz l l 0.2 0.5 2 3 deg deg Filter Gain Either Channel, VS = 5V VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz) l l l l l l 0 0 –0.1 –0.1 –0.2 –28 –44 0.5 0.1 0.3 0.6 0.8 –25 dB dB dB dB dB dB dB Matching of Filter Gain, VS = 5V VIN = 2VP-P, fIN = DC to 260kHz VIN = 2VP-P, fIN = 500kHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 2.5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 4MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 5MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 15MHz (Gain Relative to 260kHz) VIN = 2VP-P, fIN = 25MHz (Gain Relative to 260kHz) l l l l l l 0.05 0.005 0.01 0.03 0.05 0.15 0.1 0.7 0.1 0.2 0.5 0.6 1.8 2.8 dB dB dB dB dB dB dB Matching of Filter Phase, VS = 5V VIN = 2VP-P, fIN = 2.5MHz VIN = 2VP-P, fIN = 4MHz l l 0.2 0.5 2 3 deg deg Filter Gain Either Channel, VS = ±5V VIN = 2VP-P, fIN = DC to 260kHz –0.6 –0.1 0.4 dB Filter Gain, RIN = 229Ω VOUT = 2VP-P, fIN = DC to 260kHz VS = 3V VS = 5V VS = ±5V 10.4 10.3 10.1 10.9 10.8 10.7 11.5 11.4 11.3 Filter Gain Temperature Coefficient (Note 2) fIN = 260kHz, VIN = 2VP-P 780 ppm/°C Noise Distortion (Note 4) Noise BW = 10kHz to 5MHz, RIN = 806Ω VIN = 2VP-P, fIN = 1MHz, RL = 800Ω 2nd Harmonic 3rd Harmonic VIN = 2VP-P, fIN = 5MHz, RL = 800Ω 2nd Harmonic 3rd Harmonic VIN = 2VP-P, fIN = 1MHz Measured Between OUT+ and OUT–, VOCM Shorted to VMID VS = 5V VS = 3V Average of IN+ and IN– 45 μVRMS 93 96 dBc dBc 66 73 –117 dBc dBc dB 4.8 4.8 –30 VP-P_DIFF VP-P_DIFF μA Channel Separation (Note 9) Differential Output Swing Input Bias Current MIN l l l –0.5 –0.15 –0.4 –0.7 –1.1 3.85 3.85 –70 UNITS dB dB dB 66045f 3 LT6604-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Unless otherwise specified VS = 5V (V+ = 5V, V– = 0V), RIN = 806Ω, and RLOAD = 1k. PARAMETER CONDITIONS Input Referred Differential Offset RIN = 806Ω VS = 3V VS = 5V VS = ±5V RIN = 229Ω VS = 3V VS = 5V VS = ±5V Differential Offset Drift Input Common Mode Voltage (Note 3) Output Common Mode Voltage (Note 5) Output Common Mode Offset (with Respect to VOCM) Common Mode Rejection Ratio Voltage at VMID VMID Input Resistance VOCM Bias Current Power Supply Current (Per Channel) MIN Differential Input = 500mVP-P, RIN = 229Ω VS = 3V VS = 5V VS = ±5V Differential Output = 2VP-P, VMID at Mid Supply VS = 3V VS = 5V VS = ±5V VS = 3V VS = 5V VS = ±5V VS = 5V VS = 3V VOCM = VMID = VS/2 VS = 5V VS = 3V VS = 3V, VS = 5V VS = 3V, VS = 5V VS = ±5V 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: This is the temperature coefficient of the internal feedback resistors assuming a temperature independent external resistor (RIN). Note 3: The input common mode voltage is the average of the voltages applied to the external resistors (RIN). Specification guaranteed for RIN ≥ 229Ω. Note 4: Distortion is measured differentially using a differential stimulus. The input common mode voltage, the voltage at VOCM, and the voltage at VMID are equal to one half of the total power supply voltage. Note 5: Output common mode voltage is the average of the +OUT and –OUT voltages. The output common mode voltage is equal to VOCM. Note 6: The LT6604C-5 is guaranteed functional over the operating temperature range –40°C to 85°C. TYP MAX UNITS l l l 5 10 8 25 30 35 mV mV mV l l l 5 5 5 10 13 16 20 mV mV mV μV/°C l l l 0 0 –2.5 1.5 3 1 V V V l l l l l l 1 1.5 –1 –25 –30 –55 1.5 3 2 50 45 35 l 2.45 l 4.3 7.7 V V V mV mV mV dB V V kΩ l –15 –10 31 34 38 μA μA mA mA mA l l 5 5 –5 61 2.51 1.5 5.5 –3 –3 28 30 2.56 Note 7: The LT6604C-5 is guaranteed to meet 0°C to 70°C specifications and is designed, characterized and expected to meet the extended temperature limits, but is not tested at –40°C to 85°C. The LT6604I-5 is guaranteed to meet specified performance from –40°C to 85°C. Note 8: Input pins (+IN, –IN, VOCM and VMID) are protected by steering diodes to either supply. If the inputs should exceed either supply voltage, the input current should be limited to less than 10mA. In addition, the inputs +IN, –IN are protected by a pair of back-to-back diodes. If the differential input voltage exceeds 1.4V, the input current should be limited to less than 10mA Note 9: Channel separation (the inverse of crosstalk) is measured by driving a signal into one input while terminating the other input. Channel separation is the ratio of the resulting output signal at the driven channel to the output at the channel that is not driven. 66045f 4 LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS Frequency Response Passband Gain and Group Delay VS = 5V GAIN = 1 TA = 25°C 0 110 12 –1 100 11 100 –2 90 10 90 –3 80 GAIN –30 –40 DELAY –4 70 120 GAIN 9 110 80 DELAY 8 70 –5 60 7 60 –6 50 6 50 –60 –7 40 5 40 –70 –8 GAIN = 1 TA = 25°C –9 0 1 2 30 4 GAIN = 4 TA = 25°C 3 0 1 2 3 4 5 6 7 FREQUENCY (MHz) 30 –50 –80 0.1 1 10 FREQUENCY (MHz) 100 3 4 5 6 7 FREQUENCY (MHz) 8 66045 G01 VS = 5V GAIN = 1 TA = 25°C 80 1 VS = 5V GAIN = 1 VIN = 1VP-P TA = 25°C 70 60 PSRR (dB) 50 60 40 30 20 40 30 0.01 100 0.1 1 10 FREQUENCY (MHz) Distortion vs Frequency –80 –90 –110 VS = 3V, VIN = 2VP-P RL = 800Ω, TA = 25°C, GAIN = 1 0.1 1 FREQUENCY (MHz) –70 –80 –90 –110 10 66045 G07 100 1 FREQUENCY (MHz) –60 3RD HARMONIC, 5MHz INPUT –70 2ND HARMONIC, 5MHz INPUT –80 3RD HARMONIC, 1MHz INPUT –90 –100 VS = p5V, VIN = 2VP-P RL = 800Ω, TA = 25°C, GAIN = 1 0.1 VS = 3V, RL = 800Ω TA = 25°C, GAIN = 1 –50 –100 –100 1 10 FREQUENCY (MHz) Distortion vs Signal Level –40 DIFFERENTIAL INPUT, 2ND HARMONIC DIFFERENTIAL INPUT, 3RD HARMONIC SINGLE-ENDED INPUT, 2ND HARMONIC SINGLE-ENDED INPUT, 3RD HARMONIC –60 DISTORTION (dBc) DISTORTION (dBc) –70 0.1 66045 G06 Distortion vs Frequency –50 DIFFERENTIAL INPUT, 2ND HARMONIC DIFFERENTIAL INPUT, 3RD HARMONIC SINGLE-ENDED INPUT, 2ND HARMONIC SINGLE-ENDED INPUT, 3RD HARMONIC –60 0 0.01 100 66045 G05 66045 G04 –50 VS = 3V VIN = 200mVP-P TA = 25°C V+ TO DIFFOUT 10 DISTORTION (dBc) 1 10 FREQUENCY (MHz) 10 Power Supply Rejection Ratio 50 0.1 9 80 70 10 0.1 20 8 66045 G03 Common Mode Rejection Ratio 90 CMRR (dB) OUTPUT IMPEDANCE (Ω) 20 10 66045 G02 Output Impedance vs Frequency 100 9 DELAY (ns) GAIN (dB) –20 DELAY (ns) 13 0 –10 GAIN (dB) Passband Gain and Group Delay 120 1 GAIN (dB) 10 2ND HARMONIC, 1MHz INPUT –110 10 66045 G08 0 1 2 3 INPUT LEVEL (VP-P) 4 5 66045 G09 66045f 5 LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS Distortion vs Input Common Mode Voltage –40 –40 DISTORTION (dBc) –50 –60 2ND HARMONIC 5MHz INPUT –70 3RD HARMONIC 1MHz INPUT –80 2ND HARMONIC 1MHz INPUT –90 –100 VS = p5V RL = 800Ω, TA = 25°C, GAIN = 1 –110 0 1 2 3 5 4 INPUT LEVEL (VP-P) 66045 G10 –60 –70 –80 –90 –100 GAIN = 1, VMID = VS/2 2VP-P 1MHz INPUT RL = 800Ω, TA = 25°C –110 –1 0 1 2 3 –3 –2 INPUT COMMON MODE VOLTAGE RELATIVE TO VMID (V) 66045 G11 2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V –50 –60 –70 –80 –90 –100 GAIN = 4, VMID = VS/2 2VP-P 1MHz INPUT RL = 800Ω, TA = 25°C –110 –1 0 1 2 3 –3 –2 INPUT COMMON MODE VOLTAGE RELATIVE TO VMID (V) 66045 G12 Transient Response, Differential Gain = 1, Single-Ended Input, Differential Output Single Channel Supply Current vs Total Supply Voltage 36 OUT– 200mV/DIV 34 SUPPLY CURRENT (mA) –40 2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V –50 DISTORTION COMPONENT (dBc) 3RD HARMONIC 5MHz INPUT Distortion vs Input Common Mode Voltage DISTORTION COMPONENT (dBc) Distortion vs Signal Level TA = 85°C 32 30 OUT+ 200mV/DIV TA = 25°C 28 26 TA = –40°C 24 IN– 500mV/DIV IN+ 22 20 6 10 4 8 TOTAL SUPPLY VOLTAGE (V) 2 100ns/DIV 12 66045 G14 66045 G13 Distortion vs Output Common Mode Voltage Distortion vs Temperature 1dB PASSBAND GAIN COMPRESSION POINTS OUTPUT LEVEL (dBV) 0 –40 1MHz TA = 25°C 1MHz TA = 85°C DISTORTION COMPONENT (dBc) 20 3RD HARMONIC TA = 85°C –20 3RD HARMONIC TA = 25°C –40 –60 –80 2ND HARMONIC TA = 85°C –100 0 1 4 3 5 2 1MHz INPUT LEVEL (VP-P) 6 2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V 2ND HARMONIC, VS = p5V 3RD HARMONIC, VS = p5V –70 –80 –90 –100 2ND HARMONIC TA = 25°C –120 GAIN = 4 VMID = VS/2 –50 T = 25°C A 0.5VP-P 1MHz INPUT R –60 L = 800Ω 7 66045 G15 –110 –1.5 –1.0 –0.5 0 0.5 1.0 1.5 2.0 VOLTAGE VOCM TO VMID (V) 2.5 66045 G16 66045f 6 LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS Channel Separation vs Frequency (Note 9) Input Referred Noise 35 80 70 30 60 25 50 20 40 15 30 10 20 5 10 INTEGRATED NOISE (μV) NOISE DENSITY (nV/√Hz) 40 –10 90 INTEGRATED NOISE, GAIN = 1X INTEGRATED NOISE, GAIN = 4X NOISE DENSITY, GAIN = 1X NOISE DENSITY, GAIN = 4X CHANNEL SEPARATION (dB) 45 VIN = 2VP-P VS = 5V –30 RL = 800Ω AT EACH OUTPUT GAIN = 1 –50 –70 –90 –110 0 0.01 0.1 1 10 FREQUENCY (MHz) 0 100 –130 100k 1M 10M FREQUENCY (Hz) 100M 66045 G18 66045 G17 PIN FUNCTIONS +INA, –INA (Pins 2, 4): Channel A Input Pins. Signals can be applied to either or both input pins through identical external resistors, RIN. The DC gain from the differential inputs to the differential outputs is 806Ω/RIN. +INB, –INB (Pins 10, 12): Channel B Input Pins. Signals can be applied to either or both input pins through identical external resistors, RIN. The DC gain from differential inputs to the differential outputs is 806Ω/RIN. VOCMA (Pin 6): DC Common Mode Reference Voltage for the 2nd Filter Stage in channel A. Its value programs the common mode voltage of the differential output of the filter. Pin 6 is a high impedance input, which can be driven from an external voltage reference, or Pin 6 can be tied to Pin 34 on the PC board. Pin 6 should be bypassed with a 0.01μF ceramic capacitor unless it is connected to a ground plane. VOCMB (Pin 14): DC Common Mode Reference Voltage for the 2nd Filter Stage in Channel B. Its value programs the common mode voltage of the differential output of the filter. Pin 14 is a high impedance input, which can be driven from an external voltage reference, or Pin 14 can be tied to Pin 8 on the PC board. Pin 14 should be bypassed with a 0.01μF ceramic or greater capacitor unless it is connected to a ground plane. V– (Pins 7, 24, 31, 32, 35): Negative Power Supply Pin (can be ground). V+A, V+B (Pins 25, 17): Positive Power Supply Pins for Channels A and B. For a single 3.3V or 5V supply (V– grounded) a quality 0.1μF ceramic bypass capacitor is required from each positive supply pin (V+A, V+B) to the negative supply pin (V–). The bypass should be as close as possible to the IC. For dual supply applications, bypass the negative supply pins to ground and each of the positive supply pins (V+A, V+B) to ground with a quality 0.1μF ceramic capacitor. VMIDB (Pin 8): The VMIDB pin is internally biased at mid supply, see Block Diagram. For single supply operation the VMIDB pin should be bypassed with a quality 0.01μF ceramic capacitor to V–. For dual supply operation, Pin 8 can be bypassed or connected to a high quality DC ground. A ground plane should be used. A poor ground will increase noise and distortion. Pin 8 sets the output common mode voltage of the 1st stage of the filter in channel B. It has a 5.5kΩ impedance, and it can be overridden with an external low impedance voltage source. +OUTB, –OUTB (Pins 19, 21): Output Pins. Pins 19 and 21 are the filter differential outputs for channel B. With a typical short-circuit current limit greater than ±40mA, each pin can drive a 100Ω and/or 50pF load to AC ground. 66045f 7 LT6604-5 PIN FUNCTIONS +OUTA, – OUTA (Pins 27, 29): Output Pins. Pins 27 and 29 are the filter differential outputs for channel A. With a typical short-circuit current limit greater than ±40mA, each pin can drive a 100Ω and/or 50pF load to AC ground. VMIDA (Pin 34): The VMIDA pin is internally biased at mid supply, see Block Diagram. For single supply operation the VMIDA pin should be bypassed with a quality 0.01μF ceramic capacitor to Pins V–. For dual supply operation, Pin 34 can be bypassed or connected to a high quality DC ground. A ground plane should be used. A poor ground will increase noise and distortion. Pin 34 sets the output common mode voltage of the 1st stage of the filter in channel A. It has a 5.5kΩ impedance, and it can be overridden with an external low impedance voltage source. Exposed Pad (Pin 35): V–. The Exposed Pad must be soldered to PCB. If V– is separate from ground, tie the Exposed Pad to V–. BLOCK DIAGRAM VMIDA V– NC V+A NC RIN NC 11k +INA VIN+A V– LOWPASS FILTER STAGE 806Ω –OUTA 11k 400Ω V– NC OP AMP + –INA VIN–A + – – VOCM VOCM + – RIN NC 400Ω – + 400Ω NC +OUTA NC 400Ω 806Ω VOCMA V– VMIDB V+A V+B V– 11k LOWPASS FILTER STAGE 806Ω NC 11k 400Ω V– NC OP AMP +INB + VIN+B RIN NC 400Ω + – – VOCM NC – –OUTB VOCM + – + 400Ω NC –INB VIN–B +OUTB RIN 400Ω 806Ω NC NC 66045 BD VOCMB NC NC V+B 66045f 8 LT6604-5 APPLICATIONS INFORMATION Interfacing to the LT6604-5 gain; the input signal is DC-coupled. The common mode input voltage is 0.5V, and the differential input voltage is 2VP-P. The common mode output voltage is 1.65V, and the differential output voltage is 2VP-P for frequencies below 5MHz. The common mode output voltage is determined by the voltage at VOCM. Since VOCM is shorted to VMID, the output common mode is the mid supply voltage. In addition, the common mode input voltage can be equal to the mid supply voltage of VMID. Note: The LT6604-5 contains two identical filters. The following applications information only refers to one filter. The two filters are independent except that they share the same negative supply voltage V–. The two filters can be used simultaneously by replicating the example circuits. The referenced pin numbers correspond to the A channel filter. Each LT6604-5 channel requires two equal external resistors, RIN, to set the differential gain to 806Ω/RIN. The inputs to the filter are the voltages VIN+ and VIN– presented to these external components, Figure 1. The difference between VIN+ and VIN– is the differential input voltage. The average of VIN+ and VIN– is the common mode input voltage. Similarly, the voltages VOUT+ and VOUT– appearing at Pins 27 and 29 of the LT6604-5 are the filter outputs. The difference between VOUT+ and VOUT– is the differential output voltage. The average of VOUT+ and VOUT– is the common mode output voltage. Figure 1 illustrates the LT6604-5 operating with a single 3.3V supply and unity passband Figure 2 shows how to AC couple signals into the LT6604-5. In this instance, the input is a single-ended signal. AC-coupling allows the processing of single-ended or differential signals with arbitrary common mode levels. The 0.1μF coupling capacitor and the 806Ω gain setting resistor form a high pass filter, attenuating signals below 2kHz. Larger values of coupling capacitors will proportionally reduce this highpass 3dB frequency. In Figure 3 the LT6604-5 is providing 12dB of gain. The gain resistor has an optional 62pF in parallel to improve the passband flatness near 5MHz. The common mode output voltage is set to 2V. 3.3V 0.1μF V 3 VIN – 806Ω 4 VIN+ 1 0.01μF + VIN 0 t VIN– 3 – 34 2 V 25 6 2 27 1/2 + LT6604-5 VOUT+ – 29 VOUT– + 806Ω 7 2 VOUT+ 1 VOUT– t 0 66045 F01 Figure 1 3.3V 0.1μF V 0.1μF 2 4 – 27 34 1/2 + LT6604-5 6 1 VIN 0 + 0.1μF t VIN 0.01μF 2 + –1 V 25 806Ω – + 806Ω 29 3 VOUT+ 2 VOUT– 1 7 VOUT+ VOUT– 0 66045 F02 t Figure 2 62pF 5V 0.1μF V 3 VIN – 4 – 27 34 1/2 + LT6604-5 6 2 1 0 0.01μF 500mVP-P (DIFF) VIN+ VIN– VIN 2 + + – – + 200Ω t V 25 200Ω 7 2V 29 3 VOUT+ VOUT+ 2 VOUT– 1 0 VOUT– 66045 F03 t 62pF Figure 3 66045f 9 LT6604-5 APPLICATIONS INFORMATION Use Figure 4 to determine the interface between the LT6604-5 and a current output DAC. The gain, or “transimpedance,” is defined as A = VOUT/IIN. To compute the transimpedance, use the following equation: A= 806 • R1 Ω R1 + R2 By setting R1 + R2 = 806Ω, the gain equation reduces to A = R1(Ω). The voltage at the pins of the DAC is determined by R1, R2, the voltage on VMID and the DAC output current. Consider Figure 4 with R1 = 49.9Ω and R2 = 750Ω. The voltage at VMID, for VS = 3.3V, is 1.65V. The voltage at the DAC pins is given by: R1 R1• R2 + IIN R1+ R2 + 806 R1+ R2 = 51mV + IIN 46.8Ω VDAC = VMID • and 787Ω resistors satisfy the two constraints above. The transformer converts the single-ended source into a differential stimulus. Similarly, the output of the LT6604-5 will have lower distortion with larger load resistance yet the analyzer input is typically 50Ω. The 4:1 turns (16:1 impedance) transformer and the two 402Ω resistors of Figure 5, present the output of the LT6604-5 with a 1600Ω differential load, or the equivalent of 800Ω to ground at each output. The impedance seen by the network analyzer input is still 50Ω, reducing reflections in the cabling be2.5V 0.1μF NETWORK ANALYZER SOURCE 50Ω COILCRAFT TTWB-1010 1:1 787Ω 4 51.1Ω – 27 34 1/2 + LT6604-5 6 2 787Ω CURRENT OUTPUT DAC – + 7 29 COILCRAFT TTWB-16A 4:1 402Ω NETWORK ANALYZER INPUT 50Ω 402Ω 0.1μF 66045 F05 3.3V 0.1μF –2.5V – R2 IIN R1 0.01μF 25 4 27 – 34 1/2 + LT6604-5 6 IIN+ 66045 F04 25 R1 2 R2 – + 7 29 Figure 5 VOUT+ tween the transformer and analyzer input. VOUT– VOUT+ – VOUT– IIN+ – IIN– = 806 • R1 R1 + R2 Figure 4 Evaluating the LT6604-5 The low impedance levels and high frequency operation of the LT6604-5 require some attention to the matching networks between the LT6604-5 and other devices. The previous examples assume an ideal (0Ω) source impedance and a large (1k) load resistance. Among practical examples where impedance must be considered is the evaluation of the LT6604-5 with a network analyzer. Figure 5 is a laboratory setup that can be used to characterize the LT6604-5 using single-ended instruments with 50Ω source impedance and 50Ω input impedance. For a unity gain configuration the LT6604-5 requires an 806Ω source resistance yet the network analyzer output is calibrated for a 50Ω load resistance. The 1:1 transformer, 51.1Ω Differential and Common Mode Voltage Ranges The differential amplifiers inside the LT6604-5 contain circuitry to limit the maximum peak-to-peak differential voltage through the filter. This limiting function prevents excessive power dissipation in the internal circuitry and provides output short-circuit protection. The limiting function begins to take effect at output signal levels above 2VP-P and it becomes noticeable above 3.5VP-P. This is illustrated in Figure 6; the LT6604-5 channel was configured with unity passband gain and the input of the filter was driven with a 1MHz signal. Because this voltage limiting takes place well before the output stage of the filter reaches the supply rails, the input/output behavior of the IC shown in Figure 6 is relatively independent of the power supply voltage. The two amplifiers inside the LT6604-5 channel have independent control of their output common mode voltage (see the “Block Diagram” section). The following guidelines will optimize the performance of the filter. 66045f 10 LT6604-5 APPLICATIONS INFORMATION 20 1dB PASSBAND GAIN COMPRESSION POINTS OUTPUT LEVEL (dBV) 0 Common Mode DC Currents 1MHz TA = 25°C In applications like Figure 1 and Figure 3 where the LT6604-5 not only provides lowpass filtering but also level shifts the common mode voltage of the input signal, DC currents will be generated through the DC path between input and output terminals. Minimize these currents to decrease power dissipation and distortion. 1MHz TA = 85°C 3RD HARMONIC TA = 85°C –20 3RD HARMONIC TA = 25°C –40 –60 –80 2ND HARMONIC TA = 85°C –100 2ND HARMONIC TA = 25°C, GAIN = 1 –120 0 1 4 3 5 2 1MHz INPUT LEVEL (VP-P) 6 7 6600 F06 Figure 6. Differential Voltage Range VMID can be allowed to float, but it must be bypassed to an AC ground with a 0.01μF capacitor or some instability may be observed. VMID can be driven from a low impedance source, provided it remains at least 1.5V above V– and at least 1.5V below V+. An internal resistor divider sets the voltage of VMID. While the internal 11k resistors are well matched, their absolute value can vary by ±20%. This should be taken into consideration when connecting an external resistor network to alter the voltage of VMID. VOCM can be shorted to VMID for simplicity. If a different common mode output voltage is required, connect VOCM to a voltage source or resistor network. For 3V and 3.3V supplies the voltage at VOCM must be less than or equal to the mid supply level. For example, voltage (VOCM) ≤ 1.65V on a single 3.3V supply. For power supply voltages higher than 3.3V the voltage at VOCM can be set above mid supply. The voltage on VOCM should not be more than 1V below the voltage on VMID. The voltage on VOCM should not be more than 2V above the voltage on VMID. VOCM is a high impedance input. The LT6604-5 was designed to process a variety of input signals including signals centered on the mid supply voltage and signals that swing between ground and a positive voltage in a single supply system (Figure 1). The allowable range of the input common mode voltage (the average of VIN+ and VIN– in Figure 1) is determined by the power supply level and gain setting (see “Electrical Characteristics”). Consider the application in Figure 3. VMID sets the output common mode voltage of the 1st differential amplifier inside the LT6604-5 (see the “Block Diagram” section) at 2.5V. Since the input common mode voltage is near 0V, there will be approximately a total of 2.5V drop across the series combination of the internal 806Ω feedback resistor and the external 200Ω input resistor. The resulting 2.5mA common mode DC current in each input path, must be absorbed by the sources VIN+ and VIN–. VOCM sets the common mode output voltage of the 2nd differential amplifier inside the LT6604-5 channel, and therefore sets the common mode output voltage of the filter. Since, in the example of Figure 3, VOCM differs from VMID by 0.5V, an additional 1.25mA (625μA per side) of DC current will flow in the resistors coupling the 1st differential amplifier output stage to the filter output. Thus, a total of 6.25mA is used to translate the common mode voltages. A simple modification to Figure 3 will reduce the DC common mode currents by 36%. If VMID is shorted to VOCM the common mode output voltage of both op amp stages will be 2V and the resulting DC current will be 4mA. Of course, by AC coupling the inputs of Figure 3 and shorting VMID to VOCM, the common mode DC current is eliminated. Noise The noise performance of the LT6604-5 channel can be evaluated with the circuit of Figure 7. Given the low noise output of the LT6604-5 and the 6dB attenuation of the transformer coupling network, it is necessary to measure the noise floor of the spectrum analyzer and subtract the instrument noise from the filter noise measurement. Example: With the IC removed and the 25Ω resistors grounded, Figure 7, measure the total integrated noise 66045f 11 LT6604-5 APPLICATIONS INFORMATION (eO )2 – (eS )2 eIN = A 45 NOISE DENSITY (nV/√Hz) 35 4 34 6 2 RIN 25 50 20 40 15 30 10 20 5 10 0.1 0 100 1 10 FREQUENCY (MHz) 66045 F08 25 – + 1/2 Figure 8. Input Referred Noise 27 COILCRAFT TTWB-1010 25Ω 1:1 LT6604-5 – + 70 60 0 0.01 0.1μF RIN 80 30 2.5V VIN 90 INTEGRATED NOISE, GAIN = 1X INTEGRATED NOISE, GAIN = 4X NOISE DENSITY, GAIN = 1X NOISE DENSITY, GAIN = 4X 40 INTEGRATED NOISE (μV) (eS) of the spectrum analyzer from 10 kHz to 5MHz. With the IC inserted, the signal source (VIN) disconnected, and the input resistors grounded, measure the total integrated noise out of the filter (eO). With the signal source connected, set the frequency to 1MHz and adjust the amplitude until VIN measures 100mVP-P. Measure the output amplitude, VOUT, and compute the passband gain A = VOUT/VIN. Now compute the input referred integrated noise (eIN) as: 29 7 SPECTRUM ANALYZER INPUT 50Ω 25Ω gives a true measure of the S/N achievable in the system. Conversely, if each output is measured individually and the noise power added together, the resulting calculated noise level will be higher than the true differential noise. 66045 F07 Power Dissipation 0.1μF –2.5V Figure 7 Table 1 lists the typical input referred integrated noise for various values of RIN. Table 1. Noise Performance PASSBAND GAIN RIN INPUT REFERRED INTEGRATED NOISE 10kHz TO 5MHz INPUT REFERRED NOISE dBm/Hz 4 200Ω 24μVRMS –149 2 402Ω 38μVRMS –145 1 806Ω 69μVRMS –140 Figure 8 is plot of the noise spectral density as a function of frequency for an LT6604-5 with RIN = 806Ω using the fixture of Figure 7 (the instrument noise has been subtracted from the results). The noise at each output is comprised of a differential component and a common mode component. Using a transformer or combiner to convert the differential outputs to single-ended signal rejects the common mode noise and The LT6604-5 amplifiers combine high speed with large signal currents in a small package. There is a need to ensure that the die’s junction temperature does not exceed 150°C. The LT6604-5 has an exposed pad (pin 35) which is connected to the lower supply (V–). Connecting the pad to a ground plane helps to dissipate the heat generated by the chip. Metal trace and plated through-holes can be used to spread the heat generated by the device to the backside of the PC board. Junction temperature, TJ, is calculated from the ambient temperature, TA, and power dissipation, PD. The power dissipation is the product of supply voltage, VS, and total supply current, IS. Therefore, the junction temperature is given by: TJ = TA + (PD • θJA) = TA + (VS • IS • θJA) where the supply current, IS, is a function of signal level, load impedance, temperature and common mode voltages. For a given supply voltage, the worst-case power dissipation occurs when the differential input signal is maximum, the common mode currents are maximum (see Applications 66045f 12 LT6604-5 APPLICATIONS INFORMATION Information regarding Common Mode DC Currents), the load impedance is small and the ambient temperature is maximum. To compute the junction temperature, measure the supply current under these worst-case conditions, use 43°C/W as the package thermal resistance, then apply the equation for TJ. For example, using the circuit in Figure 3 with DC differential input voltage of 250mV, a differential output voltage of 1V, 1k load resistance and an ambient temperature of 85°C, the supply current (current into V+) measures 32.2mA per channel. The resulting junction temperature is: TJ = TA + (PD • θJA) = 85 + (5 • 2 • 0.0322 • 43) = 99°C. The thermal resistance can be affected by the amount of copper on the PCB that is connected to V–. The thermal resistance of the circuit can increase if the exposed pad is not connected to a large ground plane with a number of vias. TYPICAL APPLICATIONS Dual, Matched, 5MHz Lowpass Filter 5MHz Phase Distribution (50 Units) 3V 0.1μF 0.01μF IIN 30 4 25 – + 27 34 1/2 LT6604-5 6 2 RIN + – QOUT 29 7 GAIN = VOCM (1V-1.5V) 3V 0.1μF RIN 0.01μF QIN 12 19 – 8 1/2 + LT6604-5 14 10 RIN 17 + – 24 806Ω RIN PERCENTAGE OF UNITS (%) RIN 25 20 15 10 5 IOUT 0 21 –135 –134.5 –134 –133.5 –133 –132.5 –132 –131.5 5MHz PHASE (DEG) 66045 TA02 66045f 13 LT6604-5 TYPICAL APPLICATIONS Dual, Matched, 6th Order, 5MHz Lowpass Filter Single-Ended Input (IIN and QIN) and Differential Output (IOUT and QOUT) V+ 0.1μF IIN 0.1μF V+ 806Ω 1 249Ω V+ 16 V+ LT1568 2 15 INVA INVB 3 14 SA SB 4 13 OUTA OUTB 5 12 OUTA OUTB 6 11 GNDA GNDB 7 10 NC EN 8 – 9 V V– 249Ω QIN 249Ω 4 34 249Ω 249Ω 6 2 249Ω 806Ω 25 – + 27 1/2 LT6604-5 + – IOUT 29 7 0.1μF V– I Q GAIN = OUT OR OUT = 1 IIN QIN 806Ω 0.1μF V+ 0.1μF 12 8 V– 14 10 806Ω 17 – + 19 1/2 LT6604-5 + – 24 QOUT 21 0.1μF 66045 TA03 V– Frequency Response Transient Response 12 GAIN (dB) 20 LOG (IOUT/IIN) OR 20 LOG (QOUT/QIN) 0 OUTPUT (IOUT OR QOUT) 200mV/DIV –12 –24 –36 –48 –60 INPUT (IIN OR QIN) 500mV/DIV –72 –84 –96 –108 0.1 1 10 FREQUENCY (MHz) 40 100ns/DIV 66045 TA04b 66045 TA04a 66045f 14 LT6604-5 PACKAGE DESCRIPTION UFF Package 34-Lead Plastic QFN (4mm × 7mm) (Reference LTC DWG # 05-08-1758 Rev Ø) 0.70 ± 0.05 1.90 ± 0.05 4.50 ± 0.05 PACKAGE OUTLINE 1.83 ± 0.05 3.10 ± 0.05 1.50 REF 1.90 ± 0.05 1.47 ± 0.05 2.64 ± 0.05 1.29 ± 0.05 0.25 ± 0.05 0.50 BSC 6.00 REF 6.10 ± 0.05 7.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 PIN 1 NOTCH R = 0.30 OR 0.25 × 45° CHAMFER R = 0.10 TYP 0.75 ± 0.05 1.50 REF 33 34 0.40 ± 0.10 1 PIN 1 TOP MARK (NOTE 6) 1.90 ± 0.10 2 1.47 ± 0.10 7.00 ± 0.10 6.00 REF 1.83 ± 0.10 1.90 ± 0.10 2.64 ± 0.10 (UFF34) QFN 0807 REV Ø 0.200 REF R = 0.125 TYP 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 0.99 ± 0.10 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 0.20mm 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 66045f 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 LT6604-5 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS Integrated Filters LTC1562-2 Very Low Noise, 8th Order Filter Building Block Lowpass and Bandpass Filters up to 300kHz LTC1565-31 650kHz Linear Phase Lowpass Filter Continuous Time, 7th Order, Differential LTC1566-1 Low Noise, 2.3MHz Lowpass Filter Continuous Time, 7th Order, Differential 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 LTC6601 Low Noise, Fully Differential, Pin Configurable Amplifier/Driver/2nd Order Filter Building Block LTC6602 Dual Adjustable Lowpass Filter for RFID LTC6603 Dual Adjustable Lowpass Filter for Communications LT6604-2.5 Dual Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter SNR = 86dB at 3V Supply, 4th Order Filter LT6604-10 Dual Very Low Noise, Differential Amplifier and 10MHz Lowpass Filter SNR = 82dB at 3V Supply, 4th Order Filter LT6604-15 Dual Very Low Noise, Differential Amplifier and 15MHz Lowpass Filter SNR = 76dB at 3V Supply, 4th Order Filter 66045f 16 Linear Technology Corporation LT 0708 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008