Final Electrical Specifications LTC1565-31 650kHz Continuous Time, Linear Phase Lowpass Filter March 2000 U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO 7th Order, 650kHz Linear Phase Filter in an SO-8 Differential Inputs and Outputs Operates on a Single 5V or a ±5V Supply Low Offset: 5mV Typical 75dB THD and SNR 78dB SNR Shutdown Mode Requires No External Components Requires No External Clock Signal U APPLICATIO S ■ ■ ■ ■ ■ ■ CDMA Base Stations Data Communications Antialiasing Filters Smoothing or Reconstruction Filters Matched Filter Pairs Replacement for LC Filters The LTC®1565-31 is a 7th order, continuous time, linear phase lowpass filter. The selectivity of the LTC1565-31, combined with its linear phase and dynamic range, make it suitable for filtering in data communications or data acquisition systems. The filter attenuation is 37dB at 2× fCUTOFF and at least 72dB for frequencies above 3× fCUTOFF. Unlike comparable LC filters, the LTC1565-31 achieves this selectivity with a linear phase response in the passband. With 5% accuracy of the cutoff frequency, the LTC1565-31 can be used in applications requiring pairs of matched filters, such as transceiver I and Q channels. Furthermore, the differential inputs and outputs provide a simple interface for these wireless systems. With a single 5V supply and a 2VP-P input, the LTC1565-31 features an impressive spurious free dynamic range of 75dB. The maximum signal-to-noise ratio is 78dB and it is achieved with a 2.5VP-P input signal. The LTC1565-31 features a shutdown mode where power supply current is reduced to less than 10µA. 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 650kHz Lowpass Filter 2 +IN –IN +OUT –OUT VOUT+ 7 VOUT– 6 5V LTC1565-31 3 0.1µF 4 GND V– V+ SHDN 5V 0.1µF 5 ATTENUATION (dB) VIN– 8 GAIN 1.8 –20 1.6 GROUP DELAY –40 1.4 –60 1.2 –80 1.0 DELAY (µs) VIN+ 1 0 2.0 15645-31 TA01 –100 104 105 106 FREQUENCY (Hz) 0.8 107 1565-31 TA02 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. 1 LTC1565-31 W U U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) Total Supply Voltage ............................................... 11V Power Dissipation ............................................. 500mW Operating Temperature Range LTC1565-31CS8 ..................................... 0°C to 70°C LTC1565-31IS8 ................................. – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER TOP VIEW +IN 1 8 +OUT –IN 2 7 –OUT GND 3 6 V+ V– 4 5 SHDN LTC1565-31CS8 LTC1565-31IS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 156531 56531I TJMAX = 150°C, θJA = 80°C/ W (NOTE 5) Consult factory for Military grade parts. 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 open unless otherwise specified. PARAMETER CONDITIONS MIN Operating Supply Voltage TYP 4.75 Filter Gain VIN = 1VP-P, fIN = 25kHz fIN = 200kHz (Gain Relative to 25kHz) fIN = 300kHz (Gain Relative to 25kHz) fIN = 500kHz (Gain Relative to 25kHz) fIN = 650kHz (Gain Relative to 25kHz) fIN = 900kHz (Gain Relative to 25kHz) fIN = 1.3MHz (Gain Relative to 25kHz) fIN = 2.3MHz (Gain Relative to 25kHz) Filter Phase VIN = 1VP-P, fIN = 25kHz fIN = 200kHz fIN = 300kHz fIN = 500kHz fIN = 600kHz fIN = 650kHz fIN = 900kHz ● ● ● ● ● ● ● – 0.3 – 0.2 – 0.7 – 2.2 –4 ● – 162 ● 34 ● 1.97 0 0 –0.4 –1.6 –3 –11 –36 –72 –13 –101 –150 113 60 36 – 92 UNITS 11 V 0.3 0.1 – 0.1 – 1.0 –2 –7 – 31 dB dB dB dB dB dB dB dB – 138 85 Deg Deg Deg Deg Deg Deg Deg Phase Linearity Ratio of 600kHz Phase/300kHz Phase Wideband Noise Noise BW = DC to 2 • fCUTOFF 115 µVRMS THD fIN = 100kHz, 1VP-P (Note 2) 85 dB Filter Differential DC Swing Maximum Difference Between Pins 7 and 8 VS = 5V VS = ±5V Filter DC Common Mode Range (Note 4) Common Mode, VIN = 1.5V to 3.5V Differential Input Capacitance 2 VS = 5V VS = ±5V (Note 6) ±1.7 ±2.3 2.03 ±1.9 ±2.5 V + – 1.5 V – + 0.8 0.1 Input Offset Current Output DC Offset (Note 3) ±1.4 ±2.2 Upper Lower Input Bias Current Input Resistance ● ● 2 MAX 0.3 VP VP V V 0.6 µA 25 nA >50 >50 MΩ MΩ 2 pF ±5 ±5 ±12 ±12 mV mV LTC1565-31 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 open unless otherwise specified. PARAMETER CONDITIONS Output DC Offset Drift VS = 5V VS = ±5V MIN Ground Voltage (Pin 3) in Single Supply Applications VS = 5V SHDN Pin Logic Thresholds VS = 5V, Minimum Logical “1” VS = 5V, Maximum Logical “0” 4.2 3.3 V V VS = ±5V, Minimum Logical “1” VS = ±5V, Maximum Logical “0” 2.75 2.50 V V 5 9 µA µA ● SHDN Pin Pull-Up Current VS = 5V VS = ±5V Power Supply Current VS = 5V VS = ±5V ● ● Power Supply Current in Shutdown Mode Shutdown. Includes SHDN Pull-Up 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 and Pin 2 connected to Pin 3. Note 4: A 250mVP-P, 100kHz differential signal is applied to Pins 1 and 2. The DC voltages at Pins 1 and 2 are equal. This is the “common mode TYP MAX 2.49 4 10 2.51 UNITS µV/°C µV/°C – 400 – 400 2.52 V 24 25 31 33 mA mA 8 20 16 40 µA µA voltage.” The “common mode range” is the range of common mode voltages for which the 250mVP-P differential output has better than 65dB 2nd or 3rd harmonic distortion. Note 5: 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 2 oz copper on both sides. Note 6: Output DC offset measurements are performed by automatic test equipment approximately 0.5 seconds after application of power. U U U PIN FUNCTIONS +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 1.0V/V. The input range is described in the Applications Information section. The impedance seen at Pin 3 is 2.5kΩ in normal mode. In shutdown, the pin is internally biased to the same levels as normal mode. The impedance in shutdown mode is typically 500kΩ but varies with supply voltage and temperature. GND (Pin 3): Ground. The ground pin is the reference voltage for the filter and is internally biased to one-half the total power supply voltage of the filter, maximizing the dynamic range of the filter. 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. 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. The maximum voltage difference between the ground pin (Pin 3) and the positive supply pin (Pin 6) should not exceed 5.5V. 3 LTC1565-31 U U U PIN FUNCTIONS SHDN (Pin 5): Shutdown. When the Pin 5 voltage is low, the LTC1565-31 goes into the current saving shutdown mode. Pin 5 has a 4µA pull-up current. Leaving Pin 5 open will place the LTC1565-31 in its normal operating mode. – OUT, + OUT (Pins 7, 8): Output Pins. Pins 7 and 8 are the filter differential output. Each pin can drive 1kΩ or 300pF loads. The common mode voltage at the output pins is the same as the voltage at Pin 3. W BLOCK DIAGRA +IN 1 + 8 +OUT – R + R – – 7th ORDER LINEAR PHASE FILTER NETWORK OUTPUT BUFFER OUTPUT BUFFER 7 –OUT –IN 2 + INPUT BUFFERS WITH COMMON MODE TRANSLATION CIRCUIT V+ ~1M SHUTDOWN SWITCH 5k 6 V+ GND 3 5k ~1M SHUTDOWN SWITCH V+ V– V– 4 4µA SHUTDOWN 5 1565-31 BD 4 SHDN LTC1565-31 U U W U APPLICATIONS INFORMATION Interfacing to the LTC1565-31 Input Common Mode and Differential Voltage Range 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 the biasing network if AC coupled (Figures 1 and 2). The output common mode voltage is equal to the voltage of Pin 3, the GND pin. The GND pin is biased to one-half of the supply voltage by an internal resistive divider (see Block Diagram). To alter the common mode output voltage, Pin 3 can be driven with an external voltage source or resistor network. If external resistors are used, it is important to note that the internal 5k resistors can vary ±20% (their ratio only varies ±2%). The output can also be AC coupled. The range of voltage each input can support while operating in its linear region is typically 0.8V to 3.5V 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. Figures 3 and 4 show the THD of the filter versus common mode input voltage with a 2VP-P differential input signal. 1 2 + – VIN+ + – +IN –IN VIN– –OUT 4 V– THD (dB) –50 –70 –80 –90 VOUT+ 7 VOUT– SHDN 6 –30 0.1µF 5 –40 THD (dB) V + + VIN– VIN (COMMON MODE) = IN 2 V + + VOUT– V+ = VOUT (COMMON MODE) = OUT 2 2 Figure 1 –60 –80 2 + – –50 –70 0.1µF VIN+ VIN– 0.1µF 100k +IN +OUT –IN –OUT 100k 1µF 8 VOUT+ 7 VOUT– 5V LTC1565-31 3 4 GND V– V + SHDN 5 AC COUPLED INPUT VIN (COMMON MODE) = VOUT (COMMON MODE) Figure 2 V+ 2 VIN = 2VP-P VS = ±5V fIN = 100kHz 0.5 3.0 1.0 2.0 2.5 1.5 INPUT COMMON MODE VOLTAGE (V) 3.5 1565-31 F04 Figure 4. THD vs Common Mode Input Voltage 6 0.1µF 15645-31 F02 = 5 Figure 3. THD vs Common Mode Input Voltage DC COUPLED INPUT 1 VIN = 2VP-P VS = ±5V fIN = 100kHz 1565-31 F03 15645-31 F01 + – –60 5V V+ GND –40 –5 –4 –3 –2 –1 0 1 2 3 4 INPUT COMMON MODE VOLTAGE (V) 8 LTC1565-31 3 0.1µF +OUT –30 Figure 5 shows the THD and S/N ratio versus differential input voltage level for both a single 5V supply 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, where the THD and S/N ratio are equal, is 75dB to 77dB when the differential input voltage level is 2VP-P; that is, for a single 5V supply, the 5 LTC1565-31 U W U U APPLICATIONS INFORMATION –40 THD, SNR (dB) Output Common Mode and Differential Voltage Range THD: VS = 5V THD: VS = ±5V SNR fIN = 100kHz The output is a fully differential signal with a common mode level equal to the voltage at Pin 3. The specifications in the Electrical Characteristics table assume the inputs are driven differentially and the output is observed differentially. However, Pin 8 can be used as a single-ended output by simply floating Pin 7. Pin 7 can be used as an inverting single-ended output by floating Pin 8. Using Pins 7 or 8 as single-ended outputs will decrease the performance. –50 –60 –70 –80 –90 0.5 1.0 3.0 1.5 2.0 2.5 DIFFERENTIAL INPUT (P-P) 3.5 1565-31 F05 Figure 5. Dynamic Range Diff-In, Diff-Out input voltages are Pin 1 = 2.5V DC ±0.5V and Pin 2 = 2.5V DC ±0.5V. Also note Figure 5 shows a 78dB SNR ratio for higher THD levels. As seen in Figures 3 and 4, the spurious free dynamic range can be optimized by setting the input common mode voltage slightly below one-half of the power supply voltage, i.e., 2V for a single 5V supply and – 0.5V to – 1V for a ±5V supply. Figure 6 shows the THD and SNR ratio versus differential input voltage level for both a single 5V supply and a ±5V supply when the common mode input voltage is 2V and – 0.5V respectively. The common mode output voltage can be adjusted by overdriving the voltage present on Pin 3. The best performance is achieved using a common mode output voltage that is equal to mid supply (the default Pin 3 voltage). Figures 7 and 8 illustrate the THD versus output common mode voltage for a 2VP-P differential input voltage and a common mode input voltage that is 0.5V below mid supply. 0 –20 –40 –60 –70 –80 1.5 2.0 2.5 3.5 4.0 3.0 COMMON MODE OUTPUT VOLTAGE (V) 1565-31 F07 Figure 7. THD vs Common Mode Output Voltage THD: VS = 5V THD: VS = ±5V SNR fIN = 100kHz 0 –10 VIN = 2VP-P 100kHz VS = ±5V VIN(CM) = –0.5V –20 –60 –30 THD (dB) THD, SNR (dB) –50 –30 –50 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. –40 VIN = 2VP-P 100kHz VS = 5V VIN(CM) = 2V –10 THD (dB) –30 –70 –40 –50 –80 –60 –90 –80 –70 0.5 3.0 1.5 2.0 2.5 1.0 DIFFERENTIAL INPUT VOLTAGE (VP-P) 3.5 1565-31 F06 Figure 6. THD vs VIN for a Common Mode Input Voltage 0.5V Below Mid Supply 6 –90 –4 –2 0 2 4 COMMON MODE OUTPUT VOLTAGE (V) 1565-31 F08 Figure 8. THD vs Common Mode Output Voltage LTC1565-31 U U W U APPLICATIONS INFORMATION Table 1. Wideband Noise vs Bandwidth, Single 5V Supply Output Drive Pin 7 and Pin 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 from Pin 7 to Pin 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. Noise The wideband noise of the filter is the RMS value of the device’s output noise spectral density. The wideband noise data is used to determine the operating signal-tonoise at a given distortion level. Most of the noise is concentrated in the filter passband and cannot be removed with post filtering (Table 1). Table 2 lists the typical change in wideband noise with supply voltage. U PACKAGE DESCRIPTION BANDWIDTH TOTAL INTEGRATED NOISE DC to fCUTOFF 110µVRMS DC to 2 • fCUTOFF 115µVRMS Table 2. Wideband Noise vs Supply Voltage, fCUTOFF = 650kHz POWER SUPPLY TOTAL INTEGRATED NOISE DC TO 2 • fCUTOFF 5V 115µVRMS ±5V 117µVRMS DC Offset The output DC offset of the LTC1565-31 is trimmed to less than ±5mV. The trimming is done with VS = ±2.5V. The output DC offset will typically change by ±1mV when the power supply varies from 5V to ±5V. 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) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 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 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC SO8 1298 7 LTC1565-31 U TYPICAL APPLICATIO Narrowband Cellular Base Station Receiver 0° LTC1565-31 LPF ADC I RF/IF SECTION 90° LO DSP Q 90° LTC1565-31 LPF ADC 1565-31 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1560-1 1MHz/500kHz Continuous Time, Low Noise, Lowpass Elliptic Filter fCUTOFF = 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 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) 8 Linear Technology Corporation 156531i LT/TP 0300 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 2000