LT1568IGN

FEATURES s s LT1568 Very Low Noise, High Frequency Active RC, Filter Building Block DESCRIPTIO The LT®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. s s s s s s s s s Up to 10MHz Center Frequency on a Single 3V Supply Easy to Use—A Single Resistor Value Sets Lowpass Cutoff Frequency (200kHz ≤ ƒC ≤ 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 (ƒC = 2MHz, 2VP-P) THD = –84dB (ƒC = 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 s s s s s 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 0.1µF 1 511Ω VINA VOUTA VOUTA 511Ω 511Ω 2 3 4 5 6 0.1µF 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 511Ω 511Ω GAIN (dB) –6 VINB VOUTB 511Ω VOUTB THE PROPRIETARY ARCHITECTURE ALLOWS FOR A SIMPLE RESISTOR CALCULATION: 10MHz R = 128Ω • ; ƒC = CUTOFF FREQUENCY ƒ C –9 –12 –15 –18 –21 –24 –27 100k 1M FREQUENCY (Hz) 10M 1568 TA02 1568 TA01 U U U 1568f 1 LT1568 ABSOLUTE (Note 1) AXI U 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 ............................................ – 40°C to 85°C LT1568I ............................................. – 40°C to 85°C Junction Temperature .......................................... 150°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER LT1568CGN LT1568IGN GN PART MARKING 1568 1568I GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 150°C, θJA = 135°C/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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω, 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 = 128Ω, RL = 400Ω VS = ± 5V, RFIL = 1.28k, RL = 1k VS = 3V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 1.28k, RL = 1k VS = 5V, RFIL = 128Ω, RL = 400Ω 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 U V V V V mA mV mV mV mV mV mV 1568f W U U WW W 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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω, connected to midsupply, RFIL = R11 = R21 = R31 = R12 = R22 = R32, unless otherwise noted (see Block Diagram). CONDITIONS V S = 3V V S = 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 µA µA µA MHz dB dB dB DEG DEG DEG V/µs 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 V S = 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 kΩ µs µs 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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω, 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 ±1 1568f 3 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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω 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 = 128Ω, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128Ω, 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 µVRMS µVRMS dB dB Filter Gain, fC = 10MHz, VS = 5V, RFIL = 128Ω (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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω 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 1568f 4 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 = 25°C. VS = single 5V, EN pin to logic “low,” RL = 400Ω connected to midsupply, unless otherwise noted. SYMBOL PARAMETER Filter Gain, fC = 10MHz, VS = 5V, RFIL = 128Ω (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 = 128Ω, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128Ω, 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 µVRMS µVRMS 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 = 25°C. VS = single 5V, EN pin to logic “low,” RLDIFF = 800Ω 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 = 128Ω (Note 8) (Measured with Respect to DC Gain) 1568f 5 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 = 25°C. VS = single 5V, EN pin to logic “low,” RLDIFF = 800Ω 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 = 128Ω, BW = 20MHz fC = 1MHz, RFIL = 1.28k, fIN = 200kHz, VIN = 1VP-P fC = 10MHz, RFIL = 128Ω, 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 µVRMS µVRMS 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 0°C to 70°C. The LT1568C is designed, characterized and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LT1568I is guaranteed to meet specified performance from –40°C to 85°C. 1568f 6 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 = 400Ω 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 RL = 400Ω –45 fIN = 2.5MHz –50 –30 –40 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 RL = 400Ω –50 VIN = 1VP-P –55 Distortion vs Output Voltage Swing VS = ± 5V, fCUTOFF = 5MHz –40 RL = 400Ω –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 = 400Ω 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 1568f 7 LT1568 PI FU CTIO S V+ (Pins 1, 16): The V+ positive supply voltage pins should be tied together and bypassed with a 0.1µF 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 400Ω 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 400Ω 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 0.1µF 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 0.1µF 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 0.1µF capacitor. 8 U U U 1568f LT1568 PI FU CTIO S Dual Supply Power and Ground Connections ANALOG GROUND PLANE V+ 1 2 3 4 5 6 7 V– 0.1µF 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– 0.1µF SINGLE POINT SYSTEM GROUND BLOCK DIAGRA V+ CBP1 0.1µF 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– 0.1µF V – 6 7 8 V– 5k + – – + UW U U U Single Supply Power and Ground Connections ANALOG GROUND PLANE V+ 1 2 3 4 5 6 0.1µF 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– 0.1µF 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 1568f 9 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– 0.1µF 8 V+ INVA SA V+ INVB 16 15 14 0.1µF 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 F01a Figure 1. Dual and Single Supply and Ground Plane Connections 1568f 10 U 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 • (2πfO ) eOUT =– 2πf 2 eIN s2 + O s + (2πfO ) Q 2 W UU where eOUT is either OUTA or OUTB, DCGAIN = and R2 1 , fO = R1 2π R2 • R3 • C1 • C2 Q= 2π • 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 0.1µF 7 8 V+ INVA SA V+ INVB 16 15 14 0.1µF 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). U 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 = 976Ω and R31 825Ω. Scaling for fC = 256kHz: R11 = R21 = 976Ω • (1MHz/256kHz) ≈ 3.83k R31 = 825Ω • (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 = 316Ω and R31 = 274Ω. Scaling for fC = 3.2MHz: R11 = R21 = 316Ω • (3MHz/3.2MHz) ≈ 294Ω R31 = 274Ω • (3MHz/3.2MHz) ≈ 255Ω 1568f W UU 11 LT1568 DUAL 2nd ORDER LOWPASS FILTER DESIG S Dual 2nd Order Lowpass Filter, Dual Supply Operation 5V 0.1µF R11 VIN1 BAT54S VOUTA VOUTA R21 R31 0.1µF R32 R12 VIN2 R22 VOUTB VOUTB VOUTA VOUTA VIN1 R21 R11 R31 1 2 3 4 5 6 7 8 0.1µF –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 = 128Ω • 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 6340Ω 2550Ω 1270Ω 634Ω 422Ω 324Ω 255Ω 210Ω 182Ω 162Ω 143Ω 127Ω 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 12 U Dual 2nd Order Lowpass Filter, Single Supply Operation 2.7V ≤ V + ≤ 10V 1 2 3 4 5 6 0.1µF 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 1µs/DIV 1568 TA08 1568f 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 976Ω 475Ω 316Ω 226Ω 178Ω 143Ω 121Ω R31 825Ω 412Ω 274Ω 205Ω 165Ω 137Ω 118Ω 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 1µs/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 866Ω 422Ω 280Ω 210Ω 165Ω 137Ω 115Ω R31 1180Ω 590Ω 383Ω 287Ω 232Ω 191Ω 162Ω 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 1µs/DIV 1568 TA12 1568 TA11 U 1568f 13 LT1568 4th ORDER LOWPASS FILTER DESIG S 4th Order Lowpass Filter, Dual Supply Operation 5V 0.1µF R11 VIN BAT54S R21 R31 0.1µF 1 2 3 4 5 6 7 8 0.1µF –5V 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 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 523Ω 348Ω 255Ω 205Ω 169Ω 143Ω 124Ω 107Ω 97.6Ω R31 1.58k 787Ω 523Ω 383Ω 309Ω 255Ω 221Ω 196Ω 174Ω 158Ω R12, R22 1.82k 909Ω 590Ω 432Ω 348Ω 280Ω 232Ω 196Ω 169Ω 143Ω R32 887Ω 432Ω 294Ω 215Ω 174Ω 143Ω 124Ω 107Ω 97.6Ω 88.7Ω 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 14 U 4th Order Lowpass Filter, Single Supply Operation V+ 1 R31 2 3 R21 4 5 6 0.1µF 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 1µs/DIV 1568 TA14 1568f 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 1.87k 931Ω 604Ω 453Ω 357Ω 287Ω 243Ω 205Ω 178Ω 154Ω R31 2.05k 1.05k 681Ω 511Ω 402Ω 332Ω 287Ω 249Ω 221Ω 196Ω R12, R22 2.21k 1.10k 698Ω 499Ω 383Ω 309Ω 255Ω 215Ω 182Ω 158Ω R32 634Ω 324Ω 205Ω 154Ω 121Ω 100Ω 86.6Ω 76.8Ω 66.5Ω 61.9Ω 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 715Ω 357Ω 237Ω 174Ω 137Ω 115Ω R31 1.15k 562Ω 374Ω 280Ω 221Ω 187Ω R12, R22 1.91k 432Ω 280Ω 205Ω 162Ω 130Ω R32 324Ω 365Ω 243Ω 187Ω 147Ω 124Ω 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. U Transient Response 4th Order Lowpass Chebyshev, ±0.25dB Passband Ripple, fCUTOFF = 1MHz INPUT 500mV/DIV OUTPUT 200mV/DIV 1µs/DIV 1568 TA16 Transient Response 4th Order Lowpass Bessel, fCUTOFF = 1MHz INPUT 500mV/DIV OUTPUT 200mV/DIV 1µs/DIV 1568 TA18 1568f 15 LT1568 TYPICAL APPLICATIO S 4th Order Bandpass Filter fCENTER = 10MHz, –3dB Passband = fCENTER/5.4 5V CIN1 39pF 5% VIN R21 113Ω 0.1µF 1 R11 93.1Ω 2 3 4 5 6 0.1µF 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 × 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 ® 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 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q U U Amplitude Response 4th Order Bandpass Filter fCENTER = 10MHz 6 0 PIN 13 OUTPUT R12 93.1Ω R22 113Ω CIN2 39pF 5% –6 –12 –18 –24 –30 –36 –42 –48 –54 1 1568 TA19 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 55µVRMS Noise 100kHz to 10MHz, Operates with 3V Supply 86µVRMS Noise 100kHz to 20MHz, Operates with Single 3V Supply 1568f LT/TP 0403 2K • PRINTED IN USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003