LTC1566-1 Low Noise 2.3MHz Continuous Time Lowpass Filter U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®1566-1 is a 7th order continuous time lowpass filter with 12dB of passband gain. The selectivity, linearity and dynamic range makes the LTC1566-1 suitable for filtering in data communications or data acquisition systems. The filter attenuation is 40dB at 1.5 × fCUTOFF and at least 60dB for frequencies above 10MHz. 7th Order, 2.3MHz Lowpass Filter in an SO-8 62µVRMS Input Referred Noise Operates on a Single 5V or a ±5V Supply Differential Inputs and Outputs Low Offset (3mV typical, 10mVMAX) Adjustable Output Common Mode Voltage 40dB Attenuation at 1.5 × fCUTOFF Requires No External Components The LTC1566-1 has an input referred noise of 62µVRMS in a 2MHz bandwidth. In receiver applications where the signal levels are small, the filter features 71dB of spurious free dynamic range. U APPLICATIO S ■ ■ ■ ■ ■ ■ With 5% accuracy of the cutoff frequency, the LTC1566-1 can be used in applications requiring pairs of matched filters, such as transceiver I and Q channels. WCDMA Basestations Communication Filters Antialiasing Filters Smoothing or Reconstruction Filters Matched Filter Pairs Replacement for LC Filters The differential inputs and outputs provide a simple interface for wireless systems. The high impedance inputs are easily coupled to differential demodulators or D/A converters. The output DC common mode voltage and output DC offset voltage are adjustable so the signal path can be optimized for driving an A/D converter or differential modulator. Other cutoff frequencies and single-ended I/O can be provided upon request. Please contact LTC Marketing. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO Frequency Response 20 Single 5V Supply, Differential 2.3MHz Lowpass Filter IN + 2 3 10k 8 LTC1566-1 VIN – OUT + 0.1µF 4 IN – GND + VOUT OUT – V+ 7 – 6 5V 10k V– GAIN (dB) 1 VODC 0.1µF 5 900 0 800 –10 700 –20 600 500 –40 400 –50 300 –60 200 –70 100 –80 1566-1 TA01 DELAY –30 0.1 1.0 10 FREQUENCY (MHz) DELAY (ns) + 1000 GAIN 10 0 100 1566-1 G01 sn15661 1566-1fs 1 LTC1566-1 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER TOP VIEW Total Supply Voltage ................................................ 11V Power Dissipation .............................................. 500mW Operating Temperature Range LTC1566-1CS .......................................... 0°C to 70°C LTC1566-1IS ...................................... – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C IN + 1 8 OUT + IN – 2 7 OUT – LTC1566-1CS8 LTC1566-1IS8 6 V+ GND 3 V– 4 5 VODC S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 80°C/W (Note 4) 15661 15661I Consult factory for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V (V+ = 5V, V– = 0V), RLOAD = 10k from each output to AC ground, Pin 5 connected to Pin 3, Pin 3 biased to mid supply, unless otherwise specified. PARAMETER CONDITIONS Filter Gain, VS = 5V VIN = 0.25VP-P Filter Phase, VS = ±5V VIN = 0.25VP-P Phase Linearity, VS = ±5V Filter Gain, VS = ±5V VIN = 0.25VP-P MIN TYP MAX UNITS fIN = 20kHz to 100kHz ● 11.8 12.1 12.3 dB fIN = 1.8MHz (Gain Relative to 100kHz) fIN = 2MHz (Gain Relative to 100kHz) fIN = 2.3MHz (Gain Relative to 100kHz) fIN = 3MHz (Gain Relative to 100kHz) fIN = 5MHz (Gain Relative to 100kHz) fIN = 10MHz (Gain Relative to 100kHz) ● ● ● ● –0.35 –0.85 –7.5 0 – 0.1 –3 – 22 – 42 – 62 0.5 0.5 –0.95 –17 dB dB dB dB dB dB fIN = 900kHz ● –160 –150 –135 deg fIN = 1.8MHz ● –320 –285 –265 deg Ratio of phases: 1.8MHz/900kHz ● 1.9 1.95 2 fIN = 20kHz to 100kHz ● 11.9 12.1 12.3 dB fIN = 900kHz (Gain Relative to 100kHz) fIN = 1.8MHz (Gain Relative to 100kHz) fIN = 2MHz (Gain Relative to 100kHz) fIN = 2.3MHz (Gain Relative to 100kHz) fIN = 3MHz (Gain Relative to 100kHz) fIN = 5MHz (Gain Relative to 100kHz) fIN = 10MHz (Gain Relative to 100kHz) ● ● ● ● ● –0.2 –0.3 –0.55 –6 0 0.1 0.1 –2 – 20 – 61 –61 0.2 0.7 0.75 –0.3 –16 dB dB dB dB dB dB dB Input Referred Wideband Noise Noise BW = 50kHz to 2MHz 62 µVRMS THD fIN = 100kHz, VOUT = 2VP-P (Note 2) 80 dB Filter Differential DC Swing Maximum Difference Between Pins 7 and Pin 8 with Pin 5, Pin 3 Biased to Mid Supply ±1.7 ±2.9 VP VP VS = 5V VS = ±5V Input Bias Current ● 300 600 nA nA Common Mode, VIN = 1.5V to 3.5V 70 MΩ Differential 140 MΩ Input Capacitance Output DC Offset (Notes 3, 5) ±1.3 ±2.7 ±10 Input Offset Current Input Resistance ● ● 2 VS = 5V VS = ±5V ±3 ±3 pF ±10 ±10 mV mV sn15661 1566-1fs 2 LTC1566-1 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V (V+ = 5V, V– = 0V), RLOAD = 10k from each output to AC ground, and Pin 5 connected to Pin 3 unless otherwise specified PARAMETER CONDITIONS MIN Output DC Offset Drift TYP VS = 5V VS = ±5V VS = 5V, VS = ±2.5V Output DC Common Mode Voltage MAX UNITS µV/°C µV/°C –160 –160 –80 Power Supply Current VS = 5V VS = ±5V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Input and output voltages expressed as peak-to-peak numbers are assumed to be fully differential. Note 3: Output DC offset is measured between Pin 8 and Pin 7 with Pin 1, Pin 2 and Pin 5 connected to Pin 3. Pin 3 biased to mid supply. mV 24 25 ● ● 31 33 mA mA Note 4: Thermal resistance varies depending upon the amount of PC board metal attached to the device. θJA is specified for a 3.8 square inch test board covered with 2oz copper on both sides. Note 5: Output DC offset measurements are performed by automatic test equipment approximately 0.5 seconds after application of power. U W TYPICAL PERFOR A CE CHARACTERISTICS Passband Gain vs Frequency and Temperature Passband Gain and Delay vs Frequency 12.4 1 TA = 25°C 12.4 GAIN ±5V 12.0 12.0 Stopband Gain vs Frequency –10 TA = 85°C TA = –40°C TA = 25°C TA = 25°C –20 ±5V GAIN 5V 10.8 11.6 GAIN (dB) DELAY 11.2 GAIN (dB) 11.6 DELAY (µs) 11.2 10.4 10k 0 5M 100k 1M FREQUENCY (Hz) 100k 1M FREQUENCY (Hz) TA = –40, 85°C 40 0 20 –60 –40 –80 3 4 5 6 7 8 FREQUENCY (MHz) 9 10 1566-1 G05 5 6 7 8 FREQUENCY (MHz) 10 1dB COMPRESSION –20 –40 –60 OIP3 = 38dBm OIP2 = 74dBm –100 –25 9 0 450k 1.55M 2M 2.45M 3.55M NOISE FLOOR 1.1M –60 –50 4 500kHz Distortion vs Input Level, VS = 5V 20 –20 VOUT (dBm) GAIN (dB) –20 TA = 25°C 3 1566-1 G04 450k/2M Intermodulation, VS = 5V VS = 5V –40 5M 1566-1 G03 Stopband Gain vs Frequency and Temperature –30 –40 –60 10.4 10k 1566-1 G02 –10 –30 –50 10.8 VOUT (dBm) GAIN (dB) 5V 0 –15 –10 –5 VX (dBm) VIN = VX COS(2π • 450kHz) + VX COS (2π • 2MHz) –20 500kHz 1MHz 1.5MHz NOISE FLOOR –80 –100 –25 –20 –15 –10 –5 VIN (dbm) 0 5 10 1566-1 G07 1566-1 G06 sn15661 1566-1fs 3 LTC1566-1 U W TYPICAL PERFOR A CE CHARACTERISTICS Common Mode Rejection Ratio Supply Current vs Temperature 90 23 VIN = 1VP-P VS = 5V TA = 25°C VIN = 0.2VP-P VS = 5V TA = 25°C 60 22 PSRR (dB) 70 CMRR (dB) SUPPLY CURRENT (mA) 80 VS = ±5V Power Supply Rejection Ratio 70 60 50 40 50 VS = 5V 30 40 21 –50 –30 –10 10 30 50 70 90 TEMPERATURE (°C) 30 20 1k 10k 100k 1M FREQUENCY (Hz) 1566-1 G08 10M 1566-1 G09 1k 10k 100k 1M FREQUENCY (Hz) 10M 1566-1 G10 U U U PI FU CTIO S IN+, IN – (Pins 1, 2): Input Pins. Signals can be applied to either or both input pins. The DC gain from differential inputs (Pin 1 to Pin 2) to the differential outputs (Pin 8 to Pin 7) is 4V/V. The input range is described in the Applications Information section. GND (Pin 3): Ground. The ground pin is the reference voltage for the filter. This is a high impedance input, which requires an external biasing network. Biasing GND to one-half the total power supply voltage of the filter maximizes the dynamic range. For single supply operation the ground pin should be bypassed with a quality 0.1µF ceramic capacitor to Pin 4. For dual supply operation, connect Pin 3 to a high quality DC ground. A ground plane should be used. A poor ground will increase noise and distortion. Pin 3 also serves as the DC reference voltage for Pin 7. V –, V + (Pins 4, 6): Power Supply Pins. For a single 5V supply (Pin 4 grounded) a quality 0.1µF ceramic bypass capacitor is required from the positive supply pin (Pin 6) to the negative supply pin (Pin 4). The bypass should be as close as possible to the IC. For dual supply applications (Pin 3 is grounded), bypass Pin 6 to Pin 3 and Pin 4 to Pin 3 with a quality 0.1µF ceramic capacitor. VODC (Pin 5): Output DC Offset. Pin 5 is the DC reference voltage for Pin 8. By applying a DC offset between Pin 3 and Pin 5, a DC offset will be added to the differential signal between Pin 7 and Pin 8. Like the GND pin, the VODC pin is a high impedance which requires no bias current. Care should be taken when biasing Pin 5 since noise between Pin 3 and Pin 5 will appear at the filter output unattenuated. The frequency response of Pin 5 is described in the Applications Information section. OUT – , OUT + (Pins 7, 8): Output Pins. Pins 7 and 8 are the filter differential outputs. Each pin can drive 1kΩ or 300pF loads. The DC reference voltage of Pin 8 is the same as the voltage at Pin 5. The DC reference voltage of Pin 7 is the same as the voltage at Pin 3. sn15661 1566-1fs 4 LTC1566-1 W BLOCK DIAGRA IN + + 1 1× – – R + 2 GND 3 IN V– + OUT + 1× 7 OUT – 6 V+ 5 VODC 7th ORDER FILTER NETWORK WITH 12dB GAIN R – 1× – 8 + – – 1× INPUT AMPLIFIERS WITH COMMON MODE TRANSLATION CIRCUIT + UNITY GAIN OUTPUT BUFFERS WITH DC REFERENCE ADJUSTMENT 4 1566-1 BD U U W U APPLICATIO S I FOR ATIO Interfacing to the LTC1566-1 The difference between the voltages at Pin 1 and Pin 2 is the “differential input voltage.” The average of the voltages at Pin 1 and Pin 2 is the “common mode input voltage.” The difference between the voltages at Pin 7 and Pin 8 is the “differential output voltage.” The average of the voltages at Pin 7 and Pin 8 is the “common mode output voltage.” The input and output common mode voltages are independent. The input common mode voltage is set by the signal source, if DC coupled, or by an external 1 + – 8 OUT + The output common mode voltage is equal to the voltage of Pin 3, the GND pin, whenever Pin 5 is shorted to Pin 3. In configurations where Pin 5, the VODC pin, is not shorted to Pin 3, the output common mode voltage is equal to the average of the voltages at Pin 3 and Pin 5. The operation of Pin 5 is described in the paragraph “Output DC Offset Control”. Pin 3 is a high impedance pin and must be biased externally with an external resistor network or reference voltage. VOUT+ 0.1µF LTC1566-1 VIN+ + – IN + biasing network, if AC coupled (Figures 1 and 2). The output can also be AC coupled. 2 VIN– 3 10k 0.1µF 4 IN – 7 OUT – 6 V+ GND VOUT 5V 5 VODC + – 2 IN – 8 VOUT+ OUT – 7 VOUT– V+ 6 OUT + LTC1566-1 100k VIN+ 0.1µF VIN– IN + 100k 3 0.1µF 10k V– + – – 1 10k 0.1µF 4 GND 5V 0.1µF 10k V– VODC 5 1566-1 F01 DC COUPLED INPUT 1566-1 F02 V + + VIN– VIN (COMMON MODE) = IN AC COUPLED INPUT 2 V VOUT (COMMON MODE) = OUT ++V – OUT = 2 Figure 1 V+ VIN (COMMON MODE) = VOUT (COMMON MODE) = V+ 2 2 Figure 2 sn15661 1566-1fs 5 LTC1566-1 U U W U APPLICATIO S I FOR ATIO Input Common Mode and Differential Voltage Range The range of voltage each input can support while operating in its linear region is typically 0.8V to 3.7V for a single 5V supply and – 4.2V to 3.2V for a ±5V supply. Therefore, the filter can accept a variety of common mode input voltages. Figure 3 shows the total harmonic distortion of the filter versus input common mode voltage with a 2VP-P differential output signal. Figure 4 shows the total harmonic distortion and signal to noise ratio versus differential output voltage level for both a single 5V and a ±5V supply. The common mode voltage of the input signal is one-half the total power supply voltage of the filter. The spurious free dynamic range (SFDR), the level where the THD and S/N ratio are equal, is 72dB. For best performance, the inputs should be driven differentially. For single-ended signals, connect the unused input to Pin 3 or a common mode reference. The filter DC differential swings listed in the “Electrical Characteristics” are measured with input differential voltages of 0.9VP-P and 1.5VP-P for 5V and ±5V supplies respectively. Ideally the corresponding output levels would be 3.6VP-P and 6VP-P. As seen in Figure 4, these levels are above the range of linear operation. Input signals larger than 0.9VP-P/1.5VP-P will result in phase inversion and should be avoided. Output Common Mode and Differential Voltage Range The output is a fully differential signal with a common mode level equal to the voltage at Pin 3 when Pin 5 is shorted to Pin 3. The best performance is achieved using Output DC Offset Control A unique feature of the LTC1566-1 is the ability to introduce a differential offset voltage at the output of the filter. As seen in the “Block Diagram”, if a DC voltage is applied to Pin 5 with respect to Pin 3, the same voltage will be added to the differential voltage seen between Pins 8 and␣ 7. The output DC offset control pin can be used for sideband suppression in differential modulators, calibration of A/D converters, or simple signal summation. Since the voltage summing occurs at the output of the filter, Pin 5 acts as a unfiltered input. The response from Pin 5 to Pin 8 – Pin 7 with Pins 1,2 and 3 grounded is shown in Figure 7. The range of voltages that can be applied to Pin 5 is shown in Figure 6 where THD is plotted versus output offset. Pin 3 is biased to mid supply. Output Drive Pins 7 and 8 can drive a 1kΩ or 300pF load connected to AC ground with a ±0.5V signal (corresponding to a 2VP-P differential signal). For differential loads (loads connected across Pins 7 and 8) the outputs can produce a 2VP-P differential signal across 2kΩ or 150pF. For smaller signal amplitudes the outputs can drive correspondingly larger loads. – 30 –40 – 40 –50 – 50 –60 – 30 VS = 5V VS = ±5V S/N – 50 – 60 – 60 –70 – 70 – 70 –80 – 80 – 80 –90 –5 –4 –3 –2 –1 0 1 2 3 4 5 INPUT COMMON MODE VOLTAGE (V) 1566-1 F03 Figure 3 – 90 0.5 VS = 5V VS = ±5V – 40 THD (dB) VS = 5V VS = ±5V THD, SNR (dB) THD (dB) –30 a common mode voltage that is equal to one-half of the total supply voltage. Figure 5 illustrates the THD versus output common mode voltage for a 0.5VP-P/2.0VP-P differential input/output voltage and a common mode input voltage that is equal to one-half the total supply voltage. 1.0 3.5 3.0 1.5 2.0 2.5 DIFFERENTIAL OUTPUT (VP-P) 4.0 – 90 –4 0 1 3 2 – 3 – 2 –1 OUTPUT COMMON MODE VOLTAGE (V) 1566-1 F04 Figure 4 4 1566-1 F05 Figure 5 sn15661 1566-1fs 6 LTC1566-1 U U W U APPLICATIO S I FOR ATIO – 30 Noise VS = 5V VS = ± 5V – 40 THD (dB) – 50 – 60 – 70 – 80 – 90 –3 –2 2 –1 0 1 PIN 5 DC VOLTAGE (V) 4 3 The wideband noise of the filter is the RMS value of the output noise power spectral density integrated over a given bandwidth. Since the filter has a DC gain of 4, the wideband noise is divided by 4 when referred to the input. The input referred wideband noise is used to determine the signal-to-noise ratio at a given distortion level and hence the spurious free dynamic range. Most of the noise is concentrated in the filter passband and cannot be removed with post filtering (Table 1). The noise is mostly independent of supply level (Table 2). 1566-1 F06 Figure 6 Table 1. Input Referred Wideband Noise vs Bandwidth, Single 5V Supply VIN = 200mVP-P BANDWIDTH TOTAL INTEGRATED NOISE 50kHz to 2MHz 62µVRMS 50kHz to 4MHz 76µVRMS 0 GAIN PIN 8 – PIN 7 (dB) PIN 5 2.5 Table 2. Input Referred Wideband Noise vs Supply Voltage, 50kHz to 2MHz VS = 5V VS = ± 5V – 2.5 10k 100k 1M FREQUENCY (Hz) BANDWIDTH 10M TOTAL INTEGRATED NOISE VS = 5V 62µVRMS VS = ±5V 63µVRMS 1566-1 F07 Figure 7 U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *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 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 2 3 4 sn15661 1566-1fs 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. 7 LTC1566-1 U TYPICAL APPLICATIO S A Fixture for Evaluation with Single-Ended, Ground Referenced Test Equipment 15V MINICIRCUITS SPLITTER ZSCJ-2-2 1 0° 50Ω Σ° VIN 50Ω 3 S1 CLOSE SWITCH S1 AND APPLY A VOLTAGE –2.5V TO ALTER THE OUTPUT COMMON MODE. 8 5k OUT + + 5k LTC1566-1 2 π° IN + 0.1µF 4 10k IN – 6 V+ GND LT1363 7 5k OUT – VOUT – 2.5V –15V 10k V– 5 VODC 5k 0.1µF 1k CLOSE SWITCH S2 AND APPLY A VOLTAGE TO ADD A DC OFFSET. CHANGE THE POWER SUPPLY VOLTAGES TO ALTER THE INPUT COMMON MODE VOLTAGE. FOR EXAMPLE, VS = 3, –2 MAKES THE EFFECTIVE INPUT COMMON MODE –0.5V BELOW MID SUPPLY. 0.1µF S2 1566-1 TA01a Simple Pulse Shaping Circuit for Single 5V Operation, 5Mbps 2 Level Data 1 5V 5V IN + OUT + 8 LTC1566-1 2k 5Mbps DATA 2 10k 15k 3 2k 10k 0.1µF 4 IN – GND + VOUT OUT – 7 V+ 6 – 5V 300mV/ 0 DIV 0.1µF V– VODC 5 1566-1 TA02a 50ns/DIV 1566-1 TA02b Wideband CDMA Base Station Receiver Block Diagram LTC1566-1 LPF ADC 0° I RF/IF SECTION 0°/90° LO Q DSP 90° LTC1566-1 LPF ADC 1566-1 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1560-1 1MHz/500kHz Continuous Time, Lowpass Elliptic Filter fCUTTOFF = 500kHz or 1MHz LTC1562/LTC1562-2 Universal 8th Order Active RC Filters fCUTOFF(MAX) = 150kHz (LTC1562), fCUTOFF(MAX) = 300kHz (LTC1562-2) LTC1563-2/LTC1563-3 4th Order Active RC Lowpass Filters fCUTOFF(MAX) = 256kHz LTC1565-31 7th Order, Differential Inputs and Outputs 650kHz Continuous Time, Linear Phase Lowpass Filter LTC1569-6/LTC1569-7 Self Clocked, 10th Order Linear Phase Lowpass Filters fCLK/fCUTOFF = 64/1, fCUTOFF(MAX) = 75kHz (LTC1569-6), fCLK/fCUTOFF = 32/1, fCUTOFF(MAX) = 300kHz (LTC1569-7) sn15661 1566-1fs 8 Linear Technology Corporation LT/TP 0101 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 2001