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FEATURES
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LT6604-5 Dual Very Low Noise, Differential Amplifier and 5MHz Lowpass Filter DESCRIPTION
The LT(R)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. 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.
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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, 800 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 x 7mm x 0.75mm QFN Package
APPLICATIONS
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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
TYPICAL APPLICATION
3V 25 LT6604-5 806 V+A 3V 50 50 18pF LTC22xx DUAL ADC
Channel to Channel Gain Matching
50 TYPICAL UNITS TA = 25C GAIN = 1 20 f = 5MHz IN NUMBER OF UNITS 15
-
+INA VMIDA VOCMA -INA
+
- +
-OUTA +OUTA V+B
+
AIN DOUT
0.01F
+
806
- +
-
-
806
3V 50 50 18pF
10
+INB VMIDB VOCMB -INB
- +
V-
-OUTB +OUTB
+
AIN DOUT
5
0.01F
+
806
-
-
0 -0.20
66045 TA01
-0.10 0 0.10 GAIN MATCH (dB)
0.20
66045 TA01b
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LT6604-5 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW 34 VMIDA 33 NC 32 V- 31 V-
Total Supply Voltage .................................................11V Operating Temperature Range (Note 6).... -40C to 85C Specified Temperature Range (Note 7) .... -40C to 85C Junction Temperature ........................................... 150C Storage Temperature Range................... -65C to 150C Input Voltage +IN, -IN, VOCM, VMID (Note 8) ..............................VS Input Current +IN, -IN, VOCM, VMID (Note 8) ........................10mA
NC 1 +INA 2 NC 3 -INA 4 NC 5 VOCMA 6 V- 7 VMIDB 8 NC 9 +INB 10 NC 11 -INB 12 NC 13 VOCMB 14 NC 15 NC 16 V+B 17 35
30 NC 29 -OUTA 28 NC 27 +OUTA 26 NC 25 V+A 24 V- 23 NC 22 NC 21 -OUTB 20 NC 19 +OUTB 18 NC
UFF PACKAGE 34-LEAD (4mm 7mm) PLASTIC QFN TJMAX = 150C, JA = 43C/W, JC = 4C/W EXPOSED PAD (PIN 35) IS V-, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT6604CUFF-5#PBF LT6604IUFF-5#PBF TAPE AND REEL LT6604CUFF-5#TRPBF LT6604IUFF-5#TRPBF PART MARKING* 66045 66045 PACKAGE DESCRIPTION 34-Lead (4mm x 7mm) Plastic QFN 34-Lead (4mm x 7mm) Plastic QFN SPECIFIED TEMPERATURE RANGE 0C to 70C -40C to 85C
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/
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Unless otherwise specified VS = 5V (V+ = 5V, V- = 0V), RIN = 806, and RLOAD = 1k.
PARAMETER Filter Gain Either Channel, VS = 3V CONDITIONS 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
ELECTRICAL CHARACTERISTICS
MIN -0.5 -0.15 -0.4 -0.7 -1.1
TYP 0 0 -0.1 -0.1 -0.2 -28 -44
MAX 0.5 0.1 0.3 0.6 0.8 -25
UNITS dB dB dB dB dB dB dB
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LT6604-5 ELECTRICAL CHARACTERISTICS
PARAMETER Matching of Filter Gain, VS = 3V CONDITIONS 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) VIN = 2VP-P, fIN = 2.5MHz VIN = 2VP-P, fIN = 4MHz 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) 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) VIN = 2VP-P, fIN = 2.5MHz VIN = 2VP-P, fIN = 4MHz VIN = 2VP-P, fIN = DC to 260kHz VOUT = 2VP-P, fIN = DC to 260kHz VS = 3V VS = 5V VS = 5V fIN = 260kHz, VIN = 2VP-P Noise BW = 10kHz to 5MHz, RIN = 806 VIN = 2VP-P, fIN = 1MHz, RL = 800 2nd Harmonic 3rd Harmonic VIN = 2VP-P, fIN = 5MHz, RL = 800 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-
l l l l l l l l l l l l l l l l l l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Unless otherwise specified VS = 5V (V+ = 5V, V- = 0V), RIN = 806, and RLOAD = 1k.
MIN TYP 0.05 0.005 0.01 0.03 0.05 0.15 0.1 0.2 0.5 -0.5 -0.15 -0.4 -0.7 -1.1 0 0 -0.1 -0.1 -0.2 -28 -44 0.05 0.005 0.01 0.03 0.05 0.15 0.1 0.2 0.5 -0.6 10.4 10.3 10.1 -0.1 10.9 10.8 10.7 780 45 93 96 66 73 -117
l l l
MAX 0.7 0.1 0.2 0.5 0.6 1.8 2.8 2 3 0.5 0.1 0.3 0.6 0.8 -25 0.7 0.1 0.2 0.5 0.6 1.8 2.8 2 3 0.4 11.5 11.4 11.3
UNITS dB dB dB dB dB dB dB deg deg dB dB dB dB dB dB dB dB dB dB dB dB dB dB deg deg dB dB dB dB ppm/C VRMS dBc dBc dBc dBc dB VP-P_DIFF VP-P_DIFF A
Matching of Filter Phase, VS = 3V Filter Gain Either Channel, VS = 5V
Matching of Filter Gain, VS = 5V
Matching of Filter Phase, VS = 5V Filter Gain Either Channel, VS = 5V Filter Gain, RIN = 229
Filter Gain Temperature Coefficient (Note 2) Noise Distortion (Note 4)
Channel Separation (Note 9) Differential Output Swing
Input Bias Current
3.85 3.85 -70
4.8 4.8 -30
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LT6604-5 ELECTRICAL CHARACTERISTICS
PARAMETER Input Referred Differential Offset CONDITIONS RIN = 806 VS = 3V VS = 5V VS = 5V RIN = 229 VS = 3V VS = 5V VS = 5V Differential Input = 500mVP-P, RIN = 229 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
l l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. Unless otherwise specified VS = 5V (V+ = 5V, V- = 0V), RIN = 806, and RLOAD = 1k.
MIN TYP 5 10 8 5 5 5 10 0 0 -2.5 1 1.5 -1 -25 -30 -55 2.45 4.3 -15 -10 MAX 25 30 35 13 16 20 UNITS mV mV mV mV mV mV V/C V V V V V V mV mV mV dB V V k A A mA mA mA
Differential Offset Drift Input Common Mode Voltage (Note 3)
l l l l l l l l l l l l
1.5 3 1 1.5 3 2 50 45 35 2.56 7.7
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)
5 5 -5 61 2.51 1.5 5.5 -3 -3 28 30
l l
31 34 38
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 229. 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 -40C to 85C.
Note 7: The LT6604C-5 is guaranteed to meet 0C to 70C specifications and is designed, characterized and expected to meet the extended temperature limits, but is not tested at -40C to 85C. The LT6604I-5 is guaranteed to meet specified performance from -40C to 85C. 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.
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LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
10 0 -10 -20 GAIN (dB) GAIN (dB) -30 -40 -50 -60 -70 -80 0.1 1 10 FREQUENCY (MHz) 100
66045 G01
Passband Gain and Group Delay
VS = 5V GAIN = 1 TA = 25C 1 0 -1 -2 -3 -4 -5 -6 -7 -8 GAIN = 1 TA = 25C -9 012 DELAY GAIN 120 110 100 90 DELAY (ns) GAIN (dB) 80 70 60 50 40 30 34567 FREQUENCY (MHz) 8 9 20 10 13 12 11 10 9 8 7 6 5
Passband Gain and Group Delay
120 GAIN 110 100 90 DELAY 80 70 60 50 40 30 20 8 9 10 DELAY (ns)
4 GAIN = 4 TA = 25C 3 01234567 FREQUENCY (MHz)
66045 G02
66045 G03
Output Impedance vs Frequency
100 VS = 5V GAIN = 1 TA = 25C 90 80 70 CMRR (dB)
Common Mode Rejection Ratio
VS = 5V GAIN = 1 VIN = 1VP-P TA = 25C PSRR (dB) 80 70 60 50 40 30 20 40 10 0.1 1 10 FREQUENCY (MHz) 100
66045 G05
Power Supply Rejection Ratio
OUTPUT IMPEDANCE ()
10
60 50
1
0.1 0.1 1 10 FREQUENCY (MHz) 100
66045 G04
30 0.01
0 0.01
VS = 3V VIN = 200mVP-P TA = 25C V+ TO DIFFOUT 0.1 1 10 FREQUENCY (MHz) 100
66045 G06
Distortion vs Frequency
-50 -60 DISTORTION (dBc) -70 -80 -90 DIFFERENTIAL INPUT, 2ND HARMONIC DIFFERENTIAL INPUT, 3RD HARMONIC SINGLE-ENDED INPUT, 2ND HARMONIC SINGLE-ENDED INPUT, 3RD HARMONIC -50 -60 DISTORTION (dBc) -70 -80 -90
Distortion vs Frequency
DIFFERENTIAL INPUT, 2ND HARMONIC DIFFERENTIAL INPUT, 3RD HARMONIC SINGLE-ENDED INPUT, 2ND HARMONIC SINGLE-ENDED INPUT, 3RD HARMONIC -40 -50 DISTORTION (dBc)
Distortion vs Signal Level
VS = 3V, RL = 800 TA = 25C, GAIN = 1
-60 3RD HARMONIC, 5MHz INPUT -70 -80 -90 2ND HARMONIC, 5MHz INPUT 3RD HARMONIC, 1MHz INPUT
-100 -110 VS = 3V, VIN = 2VP-P RL = 800, TA = 25C, GAIN = 1 0.1 1 FREQUENCY (MHz) 10
66045 G07
-100 -110 VS = 5V, VIN = 2VP-P RL = 800, TA = 25C, GAIN = 1 0.1 1 FREQUENCY (MHz) 10
66045 G08
-100 -110 0 1
2ND HARMONIC, 1MHz INPUT 2 3 INPUT LEVEL (VP-P) 4 5
66045 G09
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LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS
Distortion vs Signal Level
-40 DISTORTION COMPONENT (dBc) -50 DISTORTION (dBc) -60 -70 -80 -90 -100 -110 0 3RD HARMONIC 1MHz INPUT 2ND HARMONIC 1MHz INPUT VS = 5V RL = 800, TA = 25C, GAIN = 1 1 2 3 4 5
66045 G10
Distortion vs Input Common Mode Voltage
-40 DISTORTION COMPONENT (dBc) -50 -60 -70 -80 -90 2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V -40 -50 -60 -70 -80 -90
Distortion vs Input Common Mode Voltage
2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V
3RD HARMONIC 5MHz INPUT 2ND HARMONIC 5MHz INPUT
INPUT LEVEL (VP-P)
-100 GAIN = 1, VMID = VS/2 2VP-P 1MHz INPUT RL = 800, TA = 25C -110 -1 0 1 2 3 -3 -2 INPUT COMMON MODE VOLTAGE RELATIVE TO VMID (V) 66045 G11
-100 GAIN = 4, VMID = VS/2 2VP-P 1MHz INPUT RL = 800, TA = 25C -110 -1 0 1 2 3 -3 -2 INPUT COMMON MODE VOLTAGE RELATIVE TO VMID (V) 66045 G12
Single Channel Supply Current vs Total Supply Voltage
36 34 SUPPLY CURRENT (mA) 32 30 28 26 24 22 20 2 6 10 4 8 TOTAL SUPPLY VOLTAGE (V) 12
66045 G13
Transient Response, Differential Gain = 1, Single-Ended Input, Differential Output
OUT- 200mV/DIV
TA = 85C OUT+ 200mV/DIV
TA = 25C
TA = -40C
IN- 500mV/DIV IN+ 100ns/DIV
66045 G14
Distortion vs Temperature
20 0 OUTPUT LEVEL (dBV) -20 -40 -60 -80 2ND HARMONIC TA = 85C 2ND HARMONIC TA = 25C 0 1 4 3 5 2 1MHz INPUT LEVEL (VP-P) 6 7 1dB PASSBAND GAIN COMPRESSION POINTS 1MHz TA = 25C DISTORTION COMPONENT (dBc) 1MHz TA = 85C 3RD HARMONIC TA = 85C 3RD HARMONIC TA = 25C -40
Distortion vs Output Common Mode Voltage
GAIN = 4 VMID = VS/2 -50 T = 25C A 0.5VP-P 1MHz INPUT RL = 800 -60 -70 -80 -90 2ND HARMONIC, VS = 3V 3RD HARMONIC, VS = 3V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V 2ND HARMONIC, VS = 5V 3RD HARMONIC, VS = 5V
-100 -120
-100 -110 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 VOLTAGE VOCM TO VMID (V)
2.5
66045 G15
66045 G16
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LT6604-5 TYPICAL PERFORMANCE CHARACTERISTICS
Input Referred Noise
45 40 NOISE DENSITY (nV/Hz) 35 30 25 20 15 10 5 0 0.01 0.1 1 10 FREQUENCY (MHz) INTEGRATED NOISE, GAIN = 1X INTEGRATED NOISE, GAIN = 4X NOISE DENSITY, GAIN = 1X NOISE DENSITY, GAIN = 4X 90 80 70 60 50 40 30 20 10 0 100
66045 G17
Channel Separation vs Frequency (Note 9)
-10 VIN = 2VP-P VS = 5V -30 RL = 800 AT EACH OUTPUT GAIN = 1 -50 -70 -90
CHANNEL SEPARATION (dB)
INTEGRATED NOISE (V)
-110 -130 100k
1M 10M FREQUENCY (Hz)
100M
66045 G18
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 806/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 0.01F ceramic capacitor unless it is connected to a ground plane. V- (Pins 7, 24, 31, 32, 35): Negative Power Supply Pin (can be ground). 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 0.01F 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 5.5k impedance, and it can be overridden with an external low impedance voltage source. +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 806/RIN. 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 0.01F ceramic or greater capacitor unless it is connected to a ground plane. 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 0.1F 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 0.1F ceramic capacitor. +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 100 and/or 50pF load to AC ground.
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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 100 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 0.01F 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 5.5k 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 NC +INA VIN+A RIN 806 11k 400 NC V- OP AMP NC NC V+A 11k LOWPASS FILTER STAGE -OUTA V- V- NC
+
-INA VIN-A RIN NC VOCM
400
- +
400
+-
VOCM
-
-+
+OUTA
400 806
NC
VOCMA V- VMIDB
V+B 11k 806 11k 400 V- OP AMP LOWPASS FILTER STAGE
V+A V-
NC
NC +INB VIN+B RIN NC -INB VIN-B RIN 806 NC
NC
+
VOCM
400
- +
400
+-
VOCM
-OUTB
-
-+
NC
+OUTB 400
NC
66045 BD
VOCMB
NC
NC
V+B
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LT6604-5 APPLICATIONS INFORMATION
Interfacing to the LT6604-5 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 806/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 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. 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 0.1F coupling capacitor and the 806 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 V 3 2 1 0 VIN+ VIN VIN- t
+
0.1F
-
V 3 VOUT+ VOUT- 2 1 0
66045 F01
806
VIN
4 34 0.01F 6 2
25
-
27 1/2 + LT6604-5
VOUT+ VOUT- t
+
7
- 29
806
Figure 1
3.3V V 0.1F 2 1 0 -1 VIN
+
0.1F 806 4 - 27 34 1/2 + LT6604-5 6 2 25 3 VOUT+ VOUT- 2 1 0
V
VOUT+ VOUT- t
0.1F t VIN
+
0.01F 806
+
7
-
29
66045 F02
Figure 2
62pF V 3 2 1 0 500mVP-P (DIFF) VIN+ VIN- t 62pF 0.01F VIN
+
5V 0.1F V 3 VOUT+ 2 VOUT- 1 0 VOUT- 25
VIN
-
200
4 - 27 34 1/2 + LT6604-5 6 2
VOUT+
+
7
-
29
200
+ -
2V
66045 F03
t
Figure 3
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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 R1 + R2 and 787 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 50. The 4:1 turns (16:1 impedance) transformer and the two 402 resistors of Figure 5, present the output of the LT6604-5 with a 1600 differential load, or the equivalent of 800 to ground at each output. The impedance seen by the network analyzer input is still 50, reducing reflections in the cabling be2.5V 0.1F NETWORK ANALYZER SOURCE 50 COILCRAFT TTWB-1010 1:1 787 4 51.1 COILCRAFT TTWB-16A 4:1 402 NETWORK ANALYZER INPUT
By setting R1 + R2 = 806, the gain equation reduces to A = R1(). 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 = 49.9 and R2 = 750. The voltage at VMID, for VS = 3.3V, is 1.65V. The voltage at the DAC pins is given by: VDAC = VMID * R1 R1* R2 + IIN R1+ R2 + 806 R1+ R2 = 51mV + IIN 46.8
3.3V 0.1F
25
- 27 34 1/2 + LT6604-5 6
2
50 402
66045 F05
+
7
-
29
787 CURRENT OUTPUT DAC IIN
-
0.1F
-2.5V R2 4 27 - 34 1/2 + LT6604-5 6 2 R2 25
Figure 5
VOUT+
R1 IIN+
66045 F04
0.01F
tween the transformer and analyzer input.
VOUT- VOUT+ - VOUT- IIN+ - IIN- = 806 * R1 R1 + R2
+
7
-
29
R1
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.
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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 (0) 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 50 source impedance and 50 input impedance. For a unity gain configuration the LT6604-5 requires an 806 source resistance yet the network analyzer output is calibrated for a 50 load resistance. The 1:1 transformer, 51.1
10
LT6604-5 APPLICATIONS INFORMATION
20 0 OUTPUT LEVEL (dBV) -20 -40 -60 -80 2ND HARMONIC TA = 85C 2ND HARMONIC TA = 25C, GAIN = 1 0 1 4 3 5 2 1MHz INPUT LEVEL (VP-P) 6 7
6600 F06
1dB PASSBAND GAIN COMPRESSION POINTS
1MHz TA = 25C 1MHz TA = 85C
Common Mode DC Currents 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. 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 806 feedback resistor and the external 200 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 (625A 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 25 resistors grounded, Figure 7, measure the total integrated noise
3RD HARMONIC TA = 85C 3RD HARMONIC TA = 25C
-100 -120
Figure 6. Differential Voltage Range
VMID can be allowed to float, but it must be bypassed to an AC ground with a 0.01F 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").
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11
LT6604-5 APPLICATIONS INFORMATION
(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: (eO )2 - (eS )2 eIN = A
2.5V 0.1F VIN RIN 25 COILCRAFT TTWB-1010 25 1:1 SPECTRUM ANALYZER INPUT 45 40 NOISE DENSITY (nV/Hz) 35 30 25 20 15 10 5 0 0.01 0.1 1 10 FREQUENCY (MHz) INTEGRATED NOISE, GAIN = 1X INTEGRATED NOISE, GAIN = 4X NOISE DENSITY, GAIN = 1X NOISE DENSITY, GAIN = 4X 90 80 70 60 50 40 30 20 10 0 100
66045 F08
INTEGRATED NOISE (V)
Figure 8. Input Referred Noise
4 34 6 2
-+ 1/2 +
7
27
LT6604-5
50 25
66045 F07
-
29
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. Power Dissipation 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 150C. 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 * JA) = TA + (VS * IS * JA) 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
RIN
0.1F -2.5V
Figure 7
Table 1 lists the typical input referred integrated noise for various values of RIN.
Table 1. Noise Performance
PASSBAND GAIN 4 2 1 INPUT REFERRED INTEGRATED NOISE 10kHz TO 5MHz 24VRMS 38VRMS 69VRMS INPUT REFERRED NOISE dBm/Hz -149 -145 -140
RIN 200 402 806
Figure 8 is plot of the noise spectral density as a function of frequency for an LT6604-5 with RIN = 806 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
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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 43C/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 85C, the supply current (current into V+) measures 32.2mA per channel. The resulting junction temperature is: TJ = TA + (PD * JA) = 85 + (5 * 2 * 0.0322 * 43) = 99C. 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
3V 0.1F RIN 0.01F IIN 30 25
5MHz Phase Distribution (50 Units)
QOUT
PERCENTAGE OF UNITS (%)
- + 27 34 1/2 LT6604-5 6
2
4
25 20 15 10 5
+-
7
RIN VOCM (1V-1.5V) RIN 0.01F QIN 12
29 GAIN = 806 RIN
3V 0.1F 17
19 - 8 1/2 + LT6604-5 14 10
IOUT 0 -135 -134.5 -134 -133.5 -133 -132.5 -132 -131.5 5MHz PHASE (DEG)
66045 TA02
+-
24
21
RIN
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13
LT6604-5 TYPICAL APPLICATIONS
Dual, Matched, 6th Order, 5MHz Lowpass Filter Single-Ended Input (IIN and QIN) and Differential Output (IOUT and QOUT)
IIN 0.1F V+ 0.1F V+ 806 1 249 QIN 249 249 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- V+ 16 V+ 249 249 4 34 6 2 249 806
-+ +-
7 V-
25
27 IOUT
1/2 LT6604-5 29 0.1F
I Q GAIN = OUT OR OUT = 1 IIN QIN 806 12 8
V+ 0.1F
0.1F V-
-+ +-
24 V-
17
19 QOUT
14 10 806
1/2 LT6604-5 21 0.1F
66045 TA03
Frequency Response
12 0 GAIN (dB) 20 LOG (IOUT/IIN) OR 20 LOG (QOUT/QIN) -12 -24 -36 -48 -60 -72 -84 -96 -108 0.1 1 10 FREQUENCY (MHz) 40
66045 TA04a
Transient Response
OUTPUT (IOUT OR QOUT) 200mV/DIV
INPUT (IIN OR QIN) 500mV/DIV
100ns/DIV
66045 TA04b
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14
LT6604-5 PACKAGE DESCRIPTION
UFF Package 34-Lead Plastic QFN (4mm x 7mm)
(Reference LTC DWG # 05-08-1758 Rev O)
0.70 0.05 1.90 0.05 1.83 0.05 1.47 0.05 1.90 0.05 PACKAGE OUTLINE
4.50 0.05 3.10 0.05 1.50 REF
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 R = 0.10 TYP PIN 1 NOTCH R = 0.30 OR 0.25 x 45 CHAMFER 1.50 REF 33 34 0.40 0.10 1 1.90 0.10 2
4.00 0.10 PIN 1 TOP MARK (NOTE 6)
0.75 0.05
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 O
0.200 REF 0.00 - 0.05
R = 0.125 TYP
0.25 0.05 0.50 BSC BOTTOM VIEW--EXPOSED PAD 0.99 0.10
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
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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 Integrated Filters LTC1562-2 LTC1565-31 LTC1566-1 LT1568 LTC1569-7 LT6600-2.5 LT6600-5 LT6600-10 LT6600-15 LT6600-20 LTC6601 LTC6602 LTC6603 LT6604-2.5 LT6604-10 LT6604-15 Very Low Noise, 8th Order Filter Building Block 650kHz Linear Phase Lowpass Filter Low Noise, 2.3MHz Lowpass Filter Very Low Noise, 4th Order Filter Building Block Linear Phase, Tunable 10th Order Lowpass Filter Very Low Noise Differential 2.5MHz Lowpass Filter Very Low Noise Differential 5MHz Lowpass Filter Very Low Noise Differential 10MHz Lowpass Filter Very Low Noise Differential 15MHz Lowpass Filter Very Low Noise Differential 20MHz Lowpass Filter Low Noise, Fully Differential, Pin Configurable Amplifier/Driver/2nd Order Filter Building Block Dual Adjustable Lowpass Filter for RFID Dual Adjustable Lowpass Filter for Communications Dual Very Low Noise, Differential Amplifier and 2.5MHz Lowpass Filter Dual Very Low Noise, Differential Amplifier and 10MHz Lowpass Filter Dual Very Low Noise, Differential Amplifier and 15MHz Lowpass Filter SNR = 86dB at 3V Supply, 4th Order Filter SNR = 82dB at 3V Supply, 4th Order Filter SNR = 76dB at 3V Supply, 4th Order Filter Lowpass and Bandpass Filters up to 300kHz Continuous Time, 7th Order, Differential Continuous Time, 7th Order, Differential Lowpass and Bandpass Filters up to 10MHz Single-Resistor Programmable Cut-Off to 300kHz SNR = 86dB at 3V Supply, 4th Order Filter SNR = 82dB at 3V Supply, 4th Order Filter SNR = 82dB at 3V Supply, 4th Order Filter SNR = 76dB at 3V Supply, 4th Order Filter SNR = 76dB at 3V Supply, 4th Order Filter COMMENTS
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0708 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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