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FEATURES
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LT1568 Very Low Noise, High Frequency Active RC, Filter Building Block DESCRIPTIO
The LT(R)1568 is an easy-to-use, active-RC filter building block with rail-to-rail inputs and outputs. The internal capacitors of the IC and the GBW product of the internal low noise op amps are trimmed such that consistent and repeatable filter responses can be achieved. With a single resistor value, the LT1568 provides a pair of matched 2-pole Butterworth lowpass filters with unity gain suitable for I/Q channels. By using unequal-valued external resistors, the two 2-pole sections can create different frequency responses or gains. In addition, the two stages may be cascaded to create a single 4-pole filter with a programmable response. Capable of cutoff frequencies up to 10MHz, the LT1568 is ideal for antialiasing or channel filtering in high speed data communications systems. The LT1568 can also be used as a bandpass filter. The LT1568 features very low noise, supporting signal-tonoise ratios of over 90dB. It also provides single-ended to differential signal conversion for directly driving high speed A/D converters. The LT1568 has a shutdown mode that reduces supply current to approximately 0.5mA on a 5V supply. The LT1568 is available in a narrow 16-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Up to 10MHz Center Frequency on a Single 3V Supply Easy to Use--A Single Resistor Value Sets Lowpass Cutoff Frequency (200kHz C 5MHz), Unequal Resistor Values Extend Cutoff Frequency Up to 10MHz Extremely Flexible--Different Resistor Values Allow Lowpass Transfer Functions with or Without Gain (Butterworth, Chebyshev or Custom) SNR = 92dB (C = 2MHz, 2VP-P) THD = -84dB (C = 2MHz, 1VP-P) Internal Capacitors Trimmed to 0.75% Single 4-Pole Lowpass Filter or Matched Pair of 2-Pole Lowpass Filters Can be Connected as a Bandpass Filter Single-Ended or Differential Output Operates from Single 3V (2.7V Min) to 5V Supply Rail-to-Rail Input and Output Voltages
APPLICATIO S
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Replaces Discrete RC Active Filters and LC Filter Modules Antialiasing/Reconstruction Filters Dual or I-and-Q Channels (Two Matched 2nd Order Filters in One Package) Single-Ended to Differential Conversion Video Signal Processing
TYPICAL APPLICATIO
3V 0.1F 1 511 VINA VOUTA VOUTA 511 511 2 3 4 5 6 0.1F 7 8
Amplitude and Phase Matched Dual Butterworth 2.5MHz Lowpass Filter with Differential Output. Single 3V Supply Operation
16 V+ LT1568 15 INVA INVB 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V- V+
Amplitude Response
3 0 -3
511
511
GAIN (dB)
-6
VINB VOUTB 511 VOUTB THE PROPRIETARY ARCHITECTURE ALLOWS FOR A SIMPLE RESISTOR CALCULATION: 10MHz R = 128 * ; C = CUTOFF FREQUENCY
C
-9 -12 -15 -18 -21 -24 -27 100k 1M FREQUENCY (Hz) 10M
1568 TA02
1568 TA01
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LT1568
ABSOLUTE
(Note 1)
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RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW V+ INVA SA OUTA OUTA GNDA NC V- 1 2 3 4 5 6 7 8 16 V + 15 INVB 14 SB 13 OUTB 12 OUTB 11 GNDB 10 EN 9 V-
Total Supply Voltage (V + to V -) ........................... 11.6V Input Voltage on INVA, INVB, GNDA and GNDB Pins ....................................................... V + to V - Input Current on INVA, INVB, GNDA and GNDB Pins (Note 2) ........................................... 10mA Output Short-Circuit Duration on OUTA, OUTB, OUTA and OUTB Pins ............................................... Indefinite Maximum Continuous Output Current (Note 3) DC ............................................................... 100mA Specified Temperature Range (Note 9) LT1568C ............................................ - 40C to 85C LT1568I ............................................. - 40C to 85C Junction Temperature .......................................... 150C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT1568CGN LT1568IGN
GN PART MARKING 1568 1568I
GN PACKAGE 16-LEAD PLASTIC SSOP
TJMAX = 150C, JA = 135C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL VS IS PARAMETER Total Supply Voltage Supply Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400, connected to midsupply, RFIL = R11 = R21 = R31 = R12 = R22 = R32, unless otherwise noted (see Block Diagram).
CONDITIONS
q
MIN 2.7
q q q q q q q q q q q q q q
TYP 24 26 28 0.3 0.5 1.0
MAX 11 35 36 38 1.0 1.3 2.5
UNITS V mA mA mA mA mA mA V V V V
VS = 3V VS = 5V VS = 5V VS = 3V, VEN = 2.4V VS = 5V, VEN = 4.4V VS = 5V, VEN = 4.4V VS = 3V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 128, RL = 400 VS = 5V, RFIL = 1.28k, RL = 1k VS = 3V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 128, RL = 400 VS = 5V, RFIL = 1.28k, RL = 1k VS = 3V VS = 5V VS = 5V VS = 3V VS = 5V VS = 5V
Shutdown Supply Current
Output Voltage Swing High (OUTA, OUTA, OUTB, OUTB Pins)
2.75 4.60 4.50 4.60
2.85 4.80 4.65 4.75 0.05 0.07 0.20 80 0.12 0.15 0.40 -4.7 1.5 2.5 4.5 7.0 4.5 2.0
Output Voltage Swing Low (OUTA, OUTA, OUTB, OUTB Pins)
IOUT
Maximum Output Current Op Amp Input Offset Voltage
q q q q q q
-2.5 -2.5 -2.0 -2 -10 -12
-0.5 0.2 1.2 2.5 0.6 -4.0
Inverter Output Offset Voltage
2
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V V V V mA mV mV mV mV mV mV
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LT1568
ELECTRICAL CHARACTERISTICS
SYMBOL IB PARAMETER Op Amp Input Bias Current
The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400, connected to midsupply, RFIL = R11 = R21 = R31 = R12 = R22 = R32, unless otherwise noted (see Block Diagram).
CONDITIONS VS = 3V VS = 5V VS = 5V Frequency = DC Frequency = 2MHz Frequency = 10MHz Frequency = DC Frequency = 2MHz Frequency = 10MHz
q q q
MIN
TYP 0.5 0.4 -0.2 55
MAX 2 2 2 0.2
UNITS A A A MHz dB dB dB DEG DEG DEG V/s V V V
Inverter Bandwidth (Note 4) Inverter Gain (Sections A and B, Note 5)
q
-0.2
0.01 0.01 0.27 180 179 176 53
Inverter Phase Shift (Sections A and B, Note 5) SR VCM Slew Rate (OUTA, OUTB, OUTA, OUTB) Pins Common Mode Input Voltage Range (GNDA and GNDB Pins, Note 6) Single Supply GND Reference Voltage VIL VIH tDIS tEN EN Input Logic Low Level EN Input Logic High Level EN Input Pull-Up Resistor Disable (Shutdown) Time Enable (Start-Up) Time
VS = 3V VS = 5V VS = 5V, GNDA Tied to GNDB VS = 3V, 5V or 5V VS = 3V, 5V or 5V EN Pin Steps from 0V to V+ EN Pin Steps from V+ to 0V
q q
1 to 1.9 -3.4 to 2.7 2.5 V + - 2.1 V+ - 0.6 30 40 20 100
V V k s s
FILTER ELECTRICAL CHARACTERISTICS
Specifications are for the output (OUTA or OUTB) of a single 2nd order section (A or B) with respect to VGND = VGNDA = VGNDB, gain = -1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, (see Block Diagram). The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400, unless otherwise noted.
SYMBOL ADC VOS(OUT) PARAMETER DC Gain DC Offset Voltage (VOUTA - VGNDA) or (VOUTB - VGNDB) DC Offset Voltage Mismatch (VOUTA - VGNDA) - (VOUTB - VGNDB) Cutoff Frequency Range (Note 7) Cutoff Frequency Temperature Coefficient VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, VS = 5V, VS = 5V CONDITIONS
q q q q q q
MIN -1.01 -5 -10 -12 -8 -10 0.2
TYP -1 2.6 0.6 -4.0 4 4
MAX -0.99 15 10 4 8 10 10
UNITS V/V mV mV mV mV mV MHz ppm/C
VOS(OUT)
Transfer Function Characteristics for Each Section (A or B) to Single-Ended Output (OUTA or OUTB) fC TC
q q
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LT1568
FILTER ELECTRICAL CHARACTERISTICS
Specifications are for the output (OUTA or OUTB) of a single 2nd order section (A or B) with respect to VGND = VGNDA = VGNDB, gain = -1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, (see Block Diagram). The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400 connected to midsupply, unless otherwise noted.
SYMBOL PARAMETER Filter Gain, fC = 1MHz, VS = 5V, RFIL = 1.28k (Measured with Respect to DC Gain) CONDITIONS Test Frequency = 300kHz (0.3 * fC) Test Frequency = 750kHz (0.75 * fC) Test Frequency = 1MHz (1 * fC) Test Frequency = 2MHz (2 * fC) Test Frequency = 4MHz (4 * fC) Test Frequency = 1MHz (0.1 * fC) Test Frequency = 7.5MHz (0.75 * fC) Test Frequency = 10MHz (1 * fC) Test Frequency = 20MHz (2 * fC) Test Frequency = 40MHz (4 * fC) fC = 1MHz, fIN = fC fC = 10MHz, fIN = fC fC = 1MHz, RFIL = 1.28k, BW = 2MHz fC = 10MHz, RFIL = 128, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128, fIN = 2MHz, VIN = 1VP-P
q q q q q q q q q q
MIN -0.05 -1.45 -3.60 -13.7 -0.1 -1.5 -3.5 -14.2 -0.25 -0.30
TYP 0.05 -1.20 -3.20 -13.2 -25.0 0.02 -1.0 -3.0 -13.2 -27.5 0.02 0.02 18 34 - 84 - 69
MAX 0.25 -0.85 -2.80 -12.5 0.25 -0.50 -2.40 -12.2 0.25 0.30
UNITS dB dB dB dB dB dB dB dB dB dB dB dB VRMS VRMS dB dB
Filter Gain, fC = 10MHz, VS = 5V, RFIL = 128 (Measured with Respect to DC Gain)
Filter Gain Mismatch (VOUTA - VOUTB) Wideband Output Noise THD Total Harmonic Distortion
Specifications are for the OUTA or OUTB of a single 2nd order section (A or B) with respect to VGND = VGNDA = VGNDB, gain = 1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, (see Block Diagram) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400 connected to midsupply, unless otherwise noted.
SYMBOL ADC VOS(OUT) VOS(OUT) PARAMETER DC Gain DC Offset Voltage (VOUTA - VGNDA) or (VOUTB - VGNDB) DC Offset Voltage Mismatch (VOUTA - VGNDA) - (VOUTB - VGNDB) Cutoff Frequency Range (Note 7) Cutoff Frequency Temperature Coefficient Filter Gain, fC = 1MHz, VS = 5V, RFIL = 1.28k (Measured with Respect to DC Gain) Test Frequency = 300kHz (0.3 * fC) Test Frequency = 750kHz (0.75 * fC) Test Frequency = 1MHz (1 * fC) Test Frequency = 2MHz (2 * fC) Test Frequency = 4MHz (4 * fC) VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, VS = 5V, VS = 5V CONDITIONS
q q q q q
MIN 0.99 -9 -10 -8 -10 0.2
TYP 1 -2 -1 2 2
MAX 1.01 5 10 8 10 10
UNITS V/V mV mV mV mV MHz ppm/C dB dB dB dB dB
Transfer Function Characteristics for Each Section (A or B) to Single-Ended Output (OUTA or OUTB) fC TC
q q q q q q
1 -0.10 -1.40 -3.50 -13.7 0.15 -1.00 -3.10 -13.0 -25.0 0.40 -0.65 -2.60 -12.5
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LT1568
FILTER ELECTRICAL CHARACTERISTICS
Specifications are for the OUTA or OUTB of a single 2nd order section (A or B) with respect to VGND = VGNDA = VGNDB, gain = 1, RFIL = R11 = R21 = R31 = R12 = R22 = R32, (see Block Diagram) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typcial values are at TA = 25C. VS = single 5V, EN pin to logic "low," RL = 400 connected to midsupply, unless otherwise noted.
SYMBOL PARAMETER Filter Gain, fC = 10MHz, VS = 5V, RFIL = 128 (Measured with Respect to DC Gain) CONDITIONS Test Frequency = 1MHz (0.1 * fC) Test Frequency = 7.5MHz (0.75 * fC) Test Frequency = 10MHz (1 * fC) Test Frequency = 20MHz (2 * fC) Test Frequency = 40MHz (4 * fC) fC = 1MHz, fIN = fC fC = 10MHz, fIN = fC fC = 1MHz, RFIL = 1.28k, BW = 2MHz fC = 10MHz, RFIL = 128, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128, fIN = 2MHz, VIN = 1VP-P
q q q q q q
MIN -0.3 -1.2 -3.1 -12.2 -0.4 -0.5
TYP 0.15 -0.50 -2.30 -11.2 -19.1 0.02 0.02 22 60 - 84 - 75
MAX 0.5 0.0 -1.5 -10.2 0.4 0.5
UNITS dB dB dB dB dB dB dB VRMS VRMS dB dB
Filter Gain Mismatch (VOUTA - VOUTB) Wideband Output Noise THD Total Harmonic Distortion
Specifications are for the differential output (OUTA - OUTA or OUTB - OUTB) of a single 2nd order section (A or B), gain = -2, RFIL = R11 = R21 = R31 = R12 = R22 = R32. All voltages are with respect to VGND = VGNDA = VGNDB. The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RLDIFF = 800 connected at midsupply, unless otherwise noted.
SYMBOL ADC VOS(OUT) PARAMETER DC Gain DC Offset Voltage (OUTA - OUTA) or (OUTB - OUTB) DC Offset Voltage Mismatch (OUTA - OUTA) - (OUTB - OUTB) VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 5V, fC = 1MHz, RFIL = 1.28k VS = 3V, VS = 5V, VS = 5V Test Frequency = 300kHz (0.3 * fC) Test Frequency = 750kHz (0.75 * fC) Test Frequency = 1MHz (1 * fC) Test Frequency = 2MHz (2 * fC) Test Frequency = 4MHz (4 * fC) Test Frequency = 1MHz (0.1 * fC) Test Frequency = 7.5MHz (0.75 * fC) Test Frequency = 10MHz (1 * fC) Test Frequency = 20MHz (2 * fC) Test Frequency = 40MHz (4 * fC) CONDITIONS
q q q q q q q
MIN -4 -12 -20 -8 -12 -15 0.2
TYP -2 6 2 -5 2 -2 2
MAX 16 15 10 8 12 15 10
UNITS V/V mV mV mV mV mV mV MHz ppm/C dB dB dB dB dB dB dB dB dB dB
VOS(OUT)
Transfer Function Characteristics for Each Section (A or B) to Differential Output (OUTA - OUTA or OUTB - OUTB) fC TC Cutoff Frequency Range (Note 7) Cutoff Frequency Temperature Coefficient Filter Gain, fC = 1MHz, VS = 5V, RFIL = 1.28k (Note 8) (Measured with Respect to DC Gain)
q q q q q q q q q q
1 -0.05 -1.40 -3.60 -13.7 -0.20 -1.30 -3.30 -13.1 0.10 -1.10 -3.20 -13.1 -25.0 0.1 -0.8 -2.6 -12.1 -24.3 0.25 -0.80 -2.70 -12.5 0.30 -0.20 -1.90 -11.1
Filter Gain, fC = 10MHz, VS = 5V, RFL = 128 (Note 8) (Measured with Respect to DC Gain)
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LT1568
FILTER ELECTRICAL CHARACTERISTICS
Specifications are for the differential output (OUTA - OUTA or OUTB - OUTB) of a single 2nd order section (A or B), gain = -2, RFIL = R11 = R21 = R31 = R12 = R22 = R32. All voltages are with respect to VGND = VGNDA = VGNDB. The q denotes the specifications which apply over the full operating temperature range, otherwise specifications and typical values are at TA = 25C. VS = single 5V, EN pin to logic "low," RLDIFF = 800 connected to midsupply, unless otherwise noted.
SYMBOL PARAMETER Filter Gain Mismatch (VOUTA - VOUTA) - (VOUTB - VOUTB) Wideband Output Noise THD Total Harmonic Distortion CONDITIONS fC = 1MHz, fIN = fC fC = 10MHz, fIN = fC fC = 1MHz, RFIL = 1.28k, BW = 2MHz fC = 10MHz, RFIL = 128, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128, fIN = 2MHz, VIN = 1VP-P Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The inputs of each op amp are protected by back-to-back diodes. If either differential input voltage exceeds 1.4V, the input current should be limited to less than 10mA. Note 3: A heat sink may be required to keep the junction temperature below the absolute maximum rating when the output is shorted indefinitely. Note 4: The inverter bandwidth is measured with the SA or SB output floating, and is defined as the frequency at which the phase shift from OUTA (OUTB) to OUTA (OUTB) drops from 180 to 135. Note 5: Measured with the SA or SB output connected in the filter application circuit as shown in the Block Diagram. Note 6: The common mode input voltage range is measured by shorting the filter input to the common mode reference (GNDA or GNDB) and applying a DC input voltage to search for the common mode voltage range that creates a 2mV (VS = 3V) or 5mV (VS = 5V) change in the (OUTA or OUTB) voltage (measured with respect to GNDA or GNDB).
q q
MIN -0.3 -0.4
TYP 0.10 0.15 36 88 - 84 - 69
MAX 0.3 0.4
UNITS dB dB VRMS VRMS dB dB
Note 7: The minimum cutoff frequency of the LT1568 is arbitrarily listed as 200kHz. The limit is arrived at by setting the maximum resistor value limit at 6.4k. Due to input bias current, the output DC offset through a single section can be as high as 25mV with resistors this large. The LT1568 can be used with even larger resistors if the large offset voltages can be tolerated. For cutoff frequencies below 200kHz, refer to the LTC1563-2, LTC1563-3. Note 8: With equal-sized resistors, the differential DC gain through either a single section or cascaded sections is 6dB. Note 9: The LT1568C is guaranteed to meet specified performance from 0C to 70C. The LT1568C is designed, characterized and expected to meet specified performance from -40C to 85C but is not tested or QA sampled at these temperatures. The LT1568I is guaranteed to meet specified performance from -40C to 85C.
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LT1568 TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Temperature
40
-80 -85
35
CROSSTALK (dB)
ICC (mA)
30 VS = 3V
-95 -100 OUTA, OUTB -105 -110
CROSSTALK (dB)
VS = 5V VS = 5V
25
20
-115
15 -40 -25
50 0 25 TEMPERATURE (C)
Distortion vs Frequency VS = 5V, fCUTOFF = 5MHz
-60 -65 RL = 400 VIN = 2VP-P -45
DISTORTION (dB)
-70 2ND -75 -80 3RD -85
DISTORTION (dB)
-60 -65 -70 -75 -80 3RD -85 -90 500k 2ND
DISTORTION (dB)
-90 200k
1M FREQUENCY (Hz)
Distortion vs Output Voltage Swing VS = 5V, fCUTOFF = 5MHz
-40 -30 -40 RL = 400 -45 fIN = 2.5MHz -50
POWER SUPPLY REJECTION (dB)
DISTORTION (dB)
DISTORTION (dB)
-55 -60 -65 -70 -75 -80 -85 -90 0 1 2 3 4 OUTA (VP-P) 5 6
1568 G07
2ND
3RD -80 -90 0 1
UW
75 85
1568 G01
1568 G04
Crosstalk vs Frequency fCUTOFF = 1MHz
-50
VIN = 2VP-P VS = 5V OUTA, OUTB
Crosstalk vs Frequency fCUTOFF = 10MHz
VIN = 2VP-P VS = 5V
-60 -70 -80
-90
OUTA, OUTB -90 OUTA, OUTB
-100 -110 10k
-120 1k 10k 100k 1M FREQUENCY (Hz) 10M
1568 G02
100k
1M 10M FREQUENCY (Hz)
100M
1568 G03
Distortion vs Frequency VS = 5V, fCUTOFF = 10MHz
-40
RL = 400 -50 VIN = 1VP-P -55
Distortion vs Output Voltage Swing VS = 5V, fCUTOFF = 5MHz
RL = 400 -45 fIN = 2.5MHz -50 -55 -60 -65 -70 -75 -80 -85 -90 3RD 2ND
5M
1M FREQUENCY (Hz)
10M
1568 G05
0
1
2
3
4567 OUTA (VP-P)
8
9 10 11
1568 G06
Distortion vs Output Voltage Swing VS = 3V, fCUTOFF = 5MHz
RL = 400 fIN = 2.5MHz
Power Supply Rejection vs Frequency
70 60 50 OUTA, OUTB 40 OUTA, OUTB 30 20 10 0 10k
-50 -60 2ND -70 3RD
2 OUTA (VP-P)
3
4
1568 G08
100k
1M 10M FREQUENCY (Hz)
100M
1568 G09
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LT1568
PI FU CTIO S
V+ (Pins 1, 16): The V+ positive supply voltage pins should be tied together and bypassed with a 0.1F capacitor to an adequate analog ground plane using the shortest possible wiring. INVA, INVB (Pins 2, 15): Inverting Input. Each of the INV pins is an inverting input of an op amp. Note that the INV pins are high impedance, and are susceptible to coupling of unintended signals. External parasitic capacitance on the INV nodes will also affect the frequency response of the filter sections. For these reasons, printed circuit connections to the INV pins must be kept as short as possible. SA, SB (Pins 3, 14): Summing Pins. These pins are a summing junction for input signals. Stray capacitance on the SA or SB pins may cause "small" frequency errors of the frequency response near the cutoff frequency (or center frequency). The three external resistors for each section should be located as close as possible to the SA or SB pin to minimize stray capacitance (one picofarad of stray capacitance may add up to 0.1% frequency error). OUTA, OUTB (Pins 4, 13): Lowpass Output. These pins are the rail-to-rail outputs of op amps. Each output is designed to drive a nominal net load of 400 and 30pF. OUTA, OUTB (Pins 5, 12): These pins are the inverted versions of the OUTA and OUTB outputs respectively. Each output is designed to drive a nominal load of 400 and 30pF. GNDA (Pin 6): GNDA serves as the common mode reference voltage for section A. It should be tied to the analog ground plane in a dual supply system. In a single-supply system, an internal resistor divider can be used to establish a half-supply reference point. In that case, GNDA must be bypassed to V- (Pins 8, 9) by a 0.1F capacitor. NC (Pin 7): This pin is not connected internally and can be connected to ground. V- (Pins 8, 9): The V- negative supply voltage pins should be tied together and bypassed to GND by a 0.1F capacitor in a dual-supply system. In a single-supply system, tie these pins to the ground plane. EN (Pin 10): ENABLE. When the EN input goes high or is open circuited, the LT1568 enters a shutdown state which reduces the supply current to approximately 0.5mA (VS = 5V). The OUTA, OUTB, OUTA and OUTB pins assume high impedance states. GNDA will continue to be biased at half-supply. If an input signal is applied to a complete filter circuit while the LT1568 is in shutdown, some signal will normally flow to the output through passive components around the inactive IC. EN is connected to V+ through an internal pull-up resistor of approximately 40k. This defaults the LT1568 to the shutdown state if the EN pin is left floating. Therefore, the user must connect the EN pin to a voltage equal to or less than (V + - 2.1)V to enable the part for normal operation. (For example, if V+ is 5V, then to enable the part the EN pin voltage should be 2.9V or less.) GNDB (Pin 11): GNDB serves as the common mode reference voltage for section B. It should be tied to the analog ground plane in a dual supply system. In a singlesupply system, GNDB can be tied to GNDA to set the common mode voltage at half-supply. If it is tied to another reference voltage, GNDB should be bypassed to V- (Pins 8, 9) by a 0.1F capacitor.
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LT1568
PI FU CTIO S
Dual Supply Power and Ground Connections
ANALOG GROUND PLANE V+ 1 2 3 4 5 6 7 V- 8 16 V+ V+ 15 INVA INVB 14 SA SB LT1568 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V-
0.1F
SINGLE POINT SYSTEM GROUND
BLOCK DIAGRA
V+ CBP1 0.1F
R11 1.27k INA
V+ R31 1 1.27k INVA 2
R21 1.27k
SA 3
A1A
+
A-SIDE DIFFERENTIAL OUTPUTS
OUTA
OUTA
4 C2A C2B -1 V
+
-
OUTA
OUTA
5
5k GNDA NC V- 0.1F V
-
6 7 8 V- 5k
+
-
-
+
UW
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Single Supply Power and Ground Connections
ANALOG GROUND PLANE V+ 1 2 3 4 5 6 0.1F 7 8 16 V+ V+ 15 INVA INVB 14 SA SB LT1568 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V-
0.1F
0.1F
DIGITAL GROUND PLANE (IF ANY)
1568 PF01
SINGLE POINT SYSTEM GROUND
DIGITAL GROUND PLANE (IF ANY)
1568 PF02
A D TEST CIRCUIT
16 15
V+
R32 INVB 1.27k
R12 1.27k INB
C1A
C1B A1B 14 SB R22 1.27k
13
OUTB
OUTB
+
B-SIDE DIFFERENTIAL OUTPUTS
-1
12
OUTB
OUTB
-
GNDB 11 10 9 EN V- TYPICAL CAPACITOR VALUES: C1 = 105.7pF 0.75% C2 = 141.3pF 0.75%
1568BD
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LT1568
APPLICATIO S I FOR ATIO
The LT1568 has been designed to make the implementation of high frequency filtering functions very easy. Internal low noise amplifiers and capacitors are configured in a topology that requires only three external resistors to implement a 2nd order filter stage. The two 2nd order stages can be used independently or cascaded for simple 4th order filter functions. With two stages integrated on the same die, the matching of the independent sections is better than what can be achieved with separate amplifier components. OPERATING WITH SINGLE OR DUAL SUPPLIES Figure 1 shows the recommended connection of an analog ground plane with the LT1568 biased from either symmetrical dual (V) power supplies or a single supply. Connection of the two GND pins is important to properly DC bias the internal amplifiers. The use of a ground plane helps to minimize noise and stray components to preserve signal integrity and maintain frequency response accuracy. When biasing from a dual supply, it is recommended that a Schottky diode clamp (BAT54S) be added as shown. These diodes ensure that improper supply voltages, through either reverse polarity or power-up sequencing, do not damage the LT1568.
Dual Supply Power and Ground Connections
ANALOG GROUND PLANE V+ 1 2 BAT54S 3 4 5 6 7 V- 8 V+ INVA SA V+ INVB 16 15 14 0.1F
SB LT1568 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V-
0.1F
SINGLE POINT SYSTEM GROUND
DIGITAL GROUND PLANE (IF ANY)
1568 F01a
Figure 1. Dual and Single Supply and Ground Plane Connections
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SIMPLE FILTER IMPLEMENTATIONS The basic 2nd order filter block of the LT1568, with three external resistors connected as shown in the Block Diagram, has the following lowpass transfer function: DCGAIN * (2fO ) eOUT =- 2f 2 eIN s2 + O s + (2fO ) Q
2
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where eOUT is either OUTA or OUTB,
DCGAIN =
and
R2 1 , fO = R1 2 R2 * R3 * C1 * C2
Q=
2 * C1 * C2 * R1 * R2 * R3 * fO C1 * R1 * (R2 + R3) + R2 * R3 - C2 * R1 * R2
[
]
The typical values of the internal capacitors are: C1= 105.7pF C2 = 141.3pF These filter functions assume ideal amplifiers.
Single Supply Power and Ground Connections
ANALOG GROUND PLANE V+ 1 2 3 4 5 6 0.1F 7 8 V+ INVA SA V+ INVB 16 15 14 0.1F
SB LT1568 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V-
SINGLE POINT SYSTEM GROUND
DIGITAL GROUND PLANE (IF ANY)
1568 F01b
LT1568
APPLICATIO S I FOR ATIO
The following filter examples are provided to make it easy to design a variety of filter stages. Both 2nd and 4th order filters are shown. For each filer, a table of external resistor values (standard 1% tolerance) is provided. These resistor values have been adjusted to compensate for the finite gain bandwidth product of the LT1568 amplifiers. To implement a filter, simply connect the resistor values shown in the table for the cutoff frequency desired. If the desired cutoff frequency is not shown in the table of values, use interpolation as recommended in the next section. DESIGNING FOR ANY CUTOFF FREQUENCY To implement a lowpass filter with a cutoff frequency not included in the design table, resistor values can be interpolated in the following manner: For a Cutoff Frequency, fC, Less Than 1MHz Start with the resistor values for fC = 1MHz and then scale them up by the ratio of (1MHz/fC).
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Example: Implement a 2nd order lowpass Chebyshev filter with an fC of 256kHz. From Table 2 the values for fC of 1MHz are R11 = R21 = 976 and R31 825. Scaling for fC = 256kHz: R11 = R21 = 976 * (1MHz/256kHz) 3.83k R31 = 825 * (1MHz/256kHz) 3.24k For a Cutoff Frequency, fC, Between Values Given in a Design Table Start with the resistor values for the cutoff frequency closest to the desired one and scale the values up or down accordingly. Example: Implement a 2nd order lowpass Chebyshev filter with an fC of 3.2MHz. From Table 2 the closest values are for fC of 3MHz and are R11 = R21 = 316 and R31 = 274. Scaling for fC = 3.2MHz: R11 = R21 = 316 * (3MHz/3.2MHz) 294 R31 = 274 * (3MHz/3.2MHz) 255
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LT1568
DUAL 2nd ORDER LOWPASS FILTER DESIG S
Dual 2nd Order Lowpass Filter, Dual Supply Operation
5V 0.1F R11 VIN1 BAT54S VOUTA VOUTA R21 R31 0.1F R32 R12 VIN2 R22 VOUTB VOUTB VOUTA VOUTA VIN1 R21 R11 R31
1 2 3 4 5 6 7 8 0.1F -5V
V+
V+
16 15
INVA INVB LT1568 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN - -9 V V
1568 TA03
R11 = R21 = R31 = R = 128 * fC = fCUTOFF
10MHz fC
Table 1. Resistor Values in Ohms, Dual 2nd Order Butterworth, Gain = 1, R12 = R11, R22 = R21, R32 = R31
fCUTOFF (MHz) 0.2 0.5 1 2 3 4 5 6 7 8 9 10 R11 = R21 = R31 6340 2550 1270 634 422 324 255 210 182 162 143 127
Amplitude Response 2nd Order Butterworth, fCUTOFF = 1MHz
10 0 -10 -20
GAIN (dB)
-30 -40 -50 -60 -70 -80 -90 0.1
INPUT 500mV/DIV OUTPUT 200mV/DIV
1 FREQUENCY (MHz)
10
20
1568 TA07
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Dual 2nd Order Lowpass Filter, Single Supply Operation
2.7V V + 10V
1 2 3 4 5 6 0.1F 7 8
V+
V+
16 R32 R12 VIN2 R22 VOUTB VOUTB
15 INVA INVB LT1568 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN - -9 V V
1568 TA04
Transient Response 2nd Order Butterworth, fCUTOFF = 1MHz
1s/DIV
1568 TA08
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LT1568
DUAL 2nd ORDER LOWPASS FILTER DESIG S
Table 2. Resistor Values in Ohms, Dual 2nd Order Lowpass Chebyshev, 0.25dB Passband Ripple, Gain = 1, R11 = R12, R21 = R22, R31 = R32
fCUTOFF (MHz) 1 2 3 4 5 6 7 R11, R21 976 475 316 226 178 143 121 R31 825 412 274 205 165 137 118
Amplitude Response 2nd Order Lowpass Chebyshev, 0.25dB Passband Ripple, fCUTOFF = 1MHz
10 0 -10 -20
Transient Response 2nd Order Lowpass Chebyshev, 0.25dB Passband Ripple, fCUTOFF = 1MHz
GAIN (dB)
-30 -40 -50 -60 -70 -80 -90 0.1 1 FREQUENCY (MHz) 10 20
INPUT 500mV/DIV OUTPUT 200mV/DIV 1s/DIV
1568 TA10
1568 TA09
Table 3. Resistor Values in Ohms, Dual 2nd Order Lowpass Bessel, Gain = 1
fCUTOFF (MHz) 1 2 3 4 5 6 7 R11, R21 866 422 280 210 165 137 115 R31 1180 590 383 287 232 191 162
Amplitude Response 2nd Order Lowpass Bessel, fCUTOFF = 1MHz
10 0 -10 -20
Transient Response 2nd Order Lowpass Bessel, fCUTOFF = 1MHz
GAIN (dB)
-30 -40 -50 -60 -70 -80 -90 0.1 1 FREQUENCY (MHz) 10 20
INPUT 500mV/DIV OUTPUT 200mV/DIV 1s/DIV
1568 TA12
1568 TA11
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LT1568
4th ORDER LOWPASS FILTER DESIG S
4th Order Lowpass Filter, Dual Supply Operation
5V 0.1F R11 VIN BAT54S R21 R31
0.1F
1 2 3 4 5 6 7 8 0.1F
V+
V+
16 15 R32 R12
VIN
INVA INVB LT1568 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN - -9 V V
1568 TA05
R22 VOUT VOUT
-5V
Table 4. Resistor Values in Ohms, 4th Order Lowpass Butterworth, Gain = 1
fCUTOFF (MHz) 1 2 3 4 5 6 7 8 9 10 R11, R21 1.05k 523 348 255 205 169 143 124 107 97.6 R31 1.58k 787 523 383 309 255 221 196 174 158 R12, R22 1.82k 909 590 432 348 280 232 196 169 143 R32 887 432 294 215 174 143 124 107 97.6 88.7
Amplitude Response 4th Order Lowpass Butterworth Lowpass, fCUTOFF = 1MHz
12 0 -12 -24
GAIN (dB)
-36 -48 -60 -72 -84 -96 -108 0.1
1 FREQUENCY (MHz)
10
20
1568 TA13
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4th Order Lowpass Filter, Single Supply Operation
V+
1 R31 2 3 R21 4 5 6 0.1F 7 8
R11
V+
V+
16 R32 R12
15 INVA INVB LT1568 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN - -9 V V
R22 VOUT VOUT
1568 TA06
Transient Response 4th Order Lowpass Butterworth Lowpass, fCUTOFF = 1MHz
INPUT 500mV/DIV OUTPUT 200mV/DIV
1s/DIV
1568 TA14
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LT1568
4th ORDER LOWPASS FILTER DESIG S
Table 5. Resistor Values in Ohms, 4th Order Lowpass Chebyshev, 0.25dB Passband Ripple, Gain = 1
fCUTOFF (MHz) 1 2 3 4 5 6 7 8 9 10 R11, R21 2.1k 1.05k 681 499 392 316 261 221 187 154 R31 1.82k 909 604 453 365 309 267 232 210 196 R12, R22 2.21k 1.1k 715 511 402 324 267 221 187 158 R32 634 316 205 154 121 100 84.5 71.5 63.4 59
Amplitude Response 4th Order Lowpass Chebyshev, 0.25dB Passband Ripple, fCUTOFF = 1MHz
12 0 -12 -24
GAIN (dB)
-36 -48 -60 -72 -84 -96 -108 0.1
1 FREQUENCY (MHz)
10
20
1568 TA13
Table 6. Resistor Values in Ohms, 4th Order Lowpass Bessel, Gain = 1
fCUTOFF (MHz) 1 2 3 4 5 6 R11, R21 715 357 237 174 137 115 R31 1.15k 562 374 280 221 187 R12, R22 1.91k 432 280 205 162 130 R32 324 365 243 187 147 124
Amplitude Response 4th Order Lowpass Bessel, fCUTOFF = 1MHz
12 0 -12 -24
GAIN (dB)
-36 -48 -60 -72 -84 -96 -108 0.1 1 FREQUENCY (MHz) 10 20
1568 TA17
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.
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Transient Response 4th Order Lowpass Chebyshev, 0.25dB Passband Ripple, fCUTOFF = 1MHz
INPUT 500mV/DIV OUTPUT 200mV/DIV 1s/DIV
1568 TA16
Transient Response 4th Order Lowpass Bessel, fCUTOFF = 1MHz
INPUT 500mV/DIV OUTPUT 200mV/DIV 1s/DIV
1568 TA18
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LT1568
TYPICAL APPLICATIO S
4th Order Bandpass Filter fCENTER = 10MHz, -3dB Passband = fCENTER/5.4
5V CIN1 39pF 5% VIN R21 113 0.1F 1 R11 93.1 2 3 4 5 6 0.1F 7 8 V
+
LT1568 15 INVA INVB 14 SA SB 13 OUTA OUTB 12 OUTA OUTB 11 GNDA GNDB 10 NC EN 9 V- V-
V
+ 16
GAIN (dB)
PACKAGE DESCRIPTIO
.015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .016 - .050 (0.406 - 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 0 - 8 TYP
.053 - .068 (1.351 - 1.727)
.008 - .012 (0.203 - 0.305)
3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
RELATED PARTS
PART NUMBER LTC 1563 LTC1565-31 LTC1566-1 LT1567 LT6600-10 LT6600-20
(R)
DESCRIPTION 4th Order Filter Building Block 7th Order, Fully Differential 650kHz Lowpass Filter 7th Order, Fully Differential 2.3MHz Lowpass Filter Very Low Noise Op Amp and Inverter Fully Differential 10MHz Lowpass Filter Fully Differential 20MHz Lowpass Filter
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
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Amplitude Response 4th Order Bandpass Filter fCENTER = 10MHz
6 0 PIN 13 OUTPUT
R12 93.1
CIN2 39pF 5%
-6 -12 -18 -24 -30 -36 -42 -48 -54 1
1568 TA19
R22 113 VOUT VOUT
10 FREQUENCY (MHz)
40
1568 TA20
GN Package 16-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.189 - .196* (4.801 - 4.978) .004 - .0098 (0.102 - 0.249) 16 15 14 13 12 11 10 9 .009 (0.229) REF
.045 .005
.0250 (0.635) BSC
.229 - .244 (5.817 - 6.198)
.150 - .157** .254 MIN (3.810 - 3.988)
.150 - .165
GN16 (SSOP) 0502
1
23
4
56
7
8
.0165 .0015
.0250 TYP
RECOMMENDED SOLDER PAD LAYOUT
COMMENTS Lowpass or Bandpass Filter Designs, 256Hz to 256kHz SO-8, No External Components SO-8, No External Components 1.4nV/Hz Op Amp, MSOP Package, Differential Outputs 55VRMS Noise 100kHz to 10MHz, Operates with 3V Supply 86VRMS Noise 100kHz to 20MHz, Operates with Single 3V Supply
1568f LT/TP 0403 2K * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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