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| Final Electrical Specifications LTC1562-2 Very Low Noise, Low Distortion Active RC Quad Universal Filter December 1998 FEATURES s s DESCRIPTION The LTC(R)1562-2 is a low noise, low distortion continuous time filter with rail-to-rail inputs and outputs, optimized for a center frequency (fO) of 20kHz to 300kHz. It contains four independent 2nd order filter blocks, which can be cascaded in any combination, such as one 8th order or two 4th order filters. Each block's response is programmed with three external resistors for center frequency, Q and gain, using simple design formulas. Each 2nd order block provides lowpass and bandpass outputs. Highpass response is available if an external capacitor replaces one of the resistors. Allpass and elliptic responses can also be realized. The LTC1562-2 is designed for applications where dynamic range is important. For example, by cascading 2nd order sections in pairs, the user can configure the IC as a dual 4th order Butterworth lowpass filter with over 90dB signal-tonoise ratio from a single 5V power supply. Low level signals can exploit the built-in gain capability of the LTC1562-2. Varying the gain of a section can achieve a dynamic range as high as 114dB with a 5V supply. Other cutoff frequency ranges can be provided upon request. Please contact LTC Marketing. , LTC and LT are registered trademarks of Linear Technology Corporation. s s s s s s s s s s Continuous Time--No Clock Four 2nd Order Filter Sections, 20kHz to 300kHz Center Frequency Butterworth, Chebyshev, Elliptic or Equiripple Delay Response Lowpass, Bandpass, Highpass Responses 99dB Typical S/N, 5V Supply (Q = 1) 93dB Typical S/N, Single 5V Supply (Q = 1) Rail-to-Rail Input and Output Voltages DC Accurate to 3mV (Typ) 0.5% Typical Center Frequency Accuracy "Zero-Power" Shutdown Mode Single or Dual Supply, 5V to 10V Total Resistor-Programmable fO, Q, Gain APPLICATIONS s s s s s s High Resolution Systems (14 Bits to 18 Bits) Antialiasing/Reconstruction Filters Data Communications, Equalizers Dual or I-and-Q Channels (Two Matched 4th Order Filters in One Package) Linear Phase Filtering Replacing LC Filter Modules TYPICAL APPLICATION Dual 4th Order 200kHz Butterworth Lowpass Filter RIN2 7.87k RIN1 7.87k VIN1 RQ1 4.22k R21 7.87k 5V 0.1F R23 7.87k RQ3 4.22k RIN3 7.87k VIN2 *V - ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM 1 2 3 5 6 8 9 10 20 19 18 RQ2 10.2k GAIN (dB) 10 VOUT1 0 -10 -20 -30 -40 -50 -60 -70 -80 50k 100k FREQUENCY (Hz) 1562-2 TA02 INV B V1 B V2 B INV C V1 C V2 C R22 7.87k - 5V* 0.1F R24 7.87k RQ4 10.2k 16 V+ LTC1562-2 V - 15 SHDN AGND 13 V2 A V2 D 12 V1 A V1 D 11 INV A INV D RIN4 7.87k 1562-2 TA01 VOUT2 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 U U Amplitude Response 1M 1.5M 1 LTC1562-2 ABSOLUTE MAXIMUM RATINGS (Note 1) PACKAGE/ORDER INFORMATION TOP VIEW INV B V1 B V2 B V -* V+ SHDN V -* V2 A V1 A INV A 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 INV C V1 C V2 C V -* V- AGND V -* V2 D V1 D INV D Total Supply Voltage (V + to V -) .............................. 11V Maximum Input Voltage at Any Pin ....................(V - - 0.3V) V (V + + 0.3V) Storage Temperature Range ................. - 65C to 150C Operating Temperature Range LTC1562C-2 ............................................ 0C to 70C LTC1562I-2 ........................................ - 40C to 85C Lead Temperature (Soldering, 10 sec).................. 300C ORDER PART NUMBER LTC1562CG-2 LTC1562IG-2 G PACKAGE 20-LEAD PLASTIC SSOP *G PACKAGE PINS 4, 7, 14, 17 ARE SUBSTRATE/SHIELD CONNECTIONS AND MUST BE TIED TO V - TJMAX = 150C, JA = 136C/W Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL VS IS PARAMETER Total Supply Voltage Supply Current VS = 5V, outputs unloaded, TA = 25C, SHDN pin to logic "low", unless otherwise noted. AC specs are for a single 2nd order section, RIN = R2 = 10.4k 0.1%, RQ = 9.09k 0.1%, fO = 175kHz. CONDITIONS VS = 2.375V, RL = 5k, CL = 30pF, Outputs at 0V VS = 5V, RL = 5k, CL = 30pF, Outputs at 0V VS = 2.375V, RL = 5k, CL = 30pF, Outputs at 0V VS = 5V, RL = 5k, CL = 30pF, Outputs at 0V Output Voltage Swing, V2 Outputs Output Voltage Swing, V1 Outputs VOS DC Offset Magnitude, V2 Outputs DC AGND Reference Point Center Frequency (f O) Error (Notes 2, 3) HL Lowpass Passband Gain at V2 Output Q Accuracy Wideband Output Noise Input-Referred Noise, Gain = 100 VS = 2.375V, RL = 5k, CL = 30pF VS = 5V, RL = 5k, CL = 30pF VS = 2.375V, RL = 5k, CL = 30pF, f = 250kHz VS = 5V, RL = 5k, CL = 30pF, f = 250kHz VS = 2.375V, Input at AGND Voltage VS = 5V, Input at AGND Voltage VS = Single 5V Supply VS = 5V, V2 Output Has RL = 5k, CL = 30pF VS = 2.375V, fIN = 10kHz, V2 Output Has RL = 5k, CL = 30pF VS = 2.375V, V2 Output Has RL = 5k, CL = 30pF VS = 2.375V, BW = 400kHz, Input AC GND VS = 5V, BW = 400kHz, Input AC GND BW = 400kHz, f O = 200kHz, Q = 1, Input AC GND q q q q q MIN 4.75 TYP 21 22.5 MAX 10.5 23.5 25 28 30 UNITS V mA mA mA mA VP-P VP-P VP-P VP-P 4.2 9.3 8.4 4.6 9.8 4.5 9.7 3 3 2.5 0.5 1.7 + 0.1 17 17 0 + 0.05 +2 39 39 7.3 VRMS VRMS VRMS 2 U W U U WW W mV mV V % dB % LTC1562-2 VS = 5V, outputs unloaded, TA = 25C, SHDN pin to logic "low", unless otherwise noted. AC specs are for a single 2nd order section, RIN = R2 = 10.4k 0.1%, RQ = 9.09k 0.1%, fO = 175kHz. SYMBOL THD PARAMETER Total Harmonic Distortion, V2 Output CONDITIONS fIN = 20kHz, 2.8VP-P, V1 and V2 Outputs Have RL = 5k, CL = 30pF fIN = 20kHz, 9VP-P, V1 and V2 Outputs Have RL = 5k, CL = 30pF Shutdown Supply Current Shutdown-Input Logic Threshold Shutdown-Input Bias Current Shutdown Delay Shutdown Recovery Delay Inverting Input Bias Current, Each Biquad The q denotes specifications that apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. SHDN Pin to 0V SHDN Pin Steps from 0V to V + SHDN Pin Steps from V + to 0V SHDN Pin to V + SHDN Pin to V +, VS = 2.375V MIN TYP - 100 - 82 1.5 1.0 2.5 - 10 20 100 5 Note 2: fO change from 5V to 2.375 supplies is - 0.2% typical, fO temperature coefficient, - 40C to 85C, is 25ppm/C typical. Note 3: This data sheet reflects initial production limits that will be tightened in the final data sheet. - 20 15 MAX UNITS dB dB A A V A s s pA ELECTRICAL CHARACTERISTICS PIN FUNCTIONS Power Supply Pins: The V + and V - pins should be bypassed with 0.1F capacitors to an adequate analog ground or ground plane. These capacitors should be connected as closely as possible to the supply pins. Pins 4, 7, 14 and 17 are internally connected to V - (Pin 16) and should also be tied to the same point as Pin 16 for best shielding. Low noise linear supplies are recommended. Switching supplies are not recommended as they will lower the filter dynamic range. Analog Ground (AGND): The AGND pin is the midpoint of a resistive voltage divider, developing a potential halfway between the V + and V - pins, with an equivalent series resistance nominally 7k. This serves as an internal ground reference. Filter performance will reflect the quality of the analog signal ground and an analog ground plane surrounding the package is recommended. The analog ground plane should be connected to any digital ground at a single point. For dual supply operation, the AGND pin should be connected to the ground plane. For single supply operation, the AGND pin should be bypassed to the ground plane with at least a 0.1F capacitor (at least 1F for best AC performance). Shutdown (SHDN): When the SHDN input goes high or is open-circuited, the LTC1562-2 enters a "zero-power" shutdown state and only junction leakage currents flow. The AGND pin and the amplifier outputs (see Figure 1) assume a high impedance state and the amplifiers effectively disappear from the circuit. (If an input signal is applied to a complete filter circuit while the LTC1562-2 is in shutdown, some signal will normally flow to the output through passive components around the inactive op amps.) A small pull-up current source at the SHDN input defaults the LTC1562-2 to the shutdown state if the SHDN pin is left floating. Therefore, the user must connect the SHDN pin to a logic "low" (0V for 5V supplies, V - for 5V total supply) for normal operation of the LTC1562-2. (This convention permits true "zero-power" shutdown since not even the driving logic must deliver current while the part is in shutdown.) U U U 3 LTC1562-2 PIN FUNCTIONS INV A, INV B, INV C, INV D: Each of the INV pins is a virtualground summing point for the corresponding 2nd order section. For each section, all three external components ZIN, R2, RQ connect to the INV pin as shown in Figure 1 and described further in the Applications Information. Note that the INV pins are sensitive internal nodes of the filter and will readily receive any unintended signals that are capacitively coupled into them. Capacitance to 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, less than one inch (2.5cm) total and surrounded by a ground plane. V1 A, V1 B, V1 C, V1 D: Output Pins. Provide a bandpass, highpass or other response depending on external circuitry (see Applications Information section). Each V1 pin also connects to the RQ resistor of the corresponding 2nd order filter section (see Figure 1 and Applications Information). Each output is designed to drive a nominal net load of 4k and 30pF, which includes the loading due to the external RQ. Distortion performance improves when the outputs are loaded as lightly as possible. V2 A, V2 B, V2 C, V2 D: Output Pins. Provide a lowpass, bandpass or other response depending on external circuitry (see Applications Information section). Each V2 pin also connects to the R2 resistor of the corresponding 2nd order filter section (see Figure 1 and Applications Information). Each output is designed to drive a nominal net load of 4k and 30pF, which includes the loading due to the external R2. Distortion performance improves when the outputs are loaded as lightly as possible. 1/4 LTC1562-2 1 sR1C* V2 R2 INV ZIN + - RESPONSE RESPONSE ZIN TYPE AT V1 AT V2 R BANDPASS LOWPASS C HIGHPASS BANDPASS VIN IN EACH CASE, fO = (200kHz) Q = RQ 200kHz R2 fO Figure 1. Equivalent Circuit of a Single 2nd Order Section (Inside Dashed Line) Shown in Typical Connection. Form of ZIN Determines Response Types at the Two Outputs (See Table) 4 + - U U U INV *R1 AND C ARE PRECISION INTERNAL COMPONENTS V1 V2 INV V1 V2 V+ V+ SHUTDOWN SWITCH R 2ND ORDER SECTIONS R SHUTDOWN SWITCH V- INV V1 V2 INV V1 V2 1562-2 F02 C A B V- SHDN V1 1562-2 F01 AGND D C RQ Figure 2.Overall Block Diagram Showing Four 3-Terminal 2nd Order Sections () ( 7958 R2 ) LTC1562-2 APPLICATIONS INFORMATION Functional Description The LTC1562-2 contains four matched, 2nd order, 3-terminal universal continuous-time filter blocks, each with a virtual-ground input node (INV) and two rail-to-rail outputs (V1, V2). In the most basic application, one such block and three external resistors provide 2nd order lowpass and bandpass responses simultaneously (Figure 1, with a resistor for ZIN). The three external resistors program fO, Q and gain. A combination of internal precision components and external resistor R2 sets the center frequency fO of each 2nd order block. The LTC1562-2 is trimmed at manufacture so that fO will be 200kHz 0.5% if the external resistor R2 is exactly 7958. The LTC15622 is a higher frequency, pin compatible variant of the LTC1562, with different internal R and C values and higher speed amplifiers. However, lowpass/bandpass filtering is only one specific application for the 2nd order building blocks in the LTC1562-2. Highpass response results if the external impedance ZIN in Figure 1 becomes a capacitor CIN (whose value sets only gain, not critical frequencies) as described below. Responses with zeroes (e.g, elliptic or notch responses) are available by feedforward connections with multiple 2nd order blocks (see Typical Applicatons). Moreover, the virtual-ground input gives each 2nd order section the built-in capability for analog operations such as gain (preamplification), summing and weighting of multiple inputs, or accepting current or charge signals directly. These Operational FilterTM frequency-selective building blocks are nearly as versatile as operational amplifiers. Setting fO, Q and Gain Standard all-pole transfer functions characterize the response of each 2nd order filter section. The responses from VIN in Figure 1 to the V2 and V1 outputs, with a resistor RIN for ZIN, are, respectively: HLP (s) = s2 + O / Q s + O ( - HL O 2 ) 2 U W U U HBP (s) = - HB O / Q s s2 + O / Q s + O ( ( ) ) 2 The external resistors R2, RIN and RQ set the filter parameters O = 2fO, Q, HL and HB as follows: fO = 7958 = (200kHz R2 2(C) (R1)(R2) 1 2 ) 200kHz or, R2 = 7958 fO R RQ R2 HB = Q Q= HL = RIN RIN (R1)(R2) ( ) Note that R1 (= 7958) and C (= 100pF) are internal to the LTC1562-2 while R2, RIN and RQ are external. The usual design procedure is to first determine R2 from the required fO, then determine RQ to set Q once R2 is known, and finally determine RIN to set gain. The fO range is approximately 20kHz to 300kHz, limited mainly by the magnitudes of the external resistors required. As shown above, R2 varies with the inverse square of fO. This relationship desensitizes fO to R2's tolerance (by a factor of 2 incrementally), but it also implies that R2 has a wider range than fO. (RQ and RIN also tend to scale with R2.) At high fO these resistors fall below 4k, heavily loading the outputs of the LTC1562-2 and leading to increased THD and other effects. At the other extreme, a lower fO limit of 20kHz reflects an arbitrary upper resistor limit of 1M. The LTC1562-2's MOS input circuitry can accommodate higher resistor values than this, but junction leakage current from the input protection circuitry may cause DC errors. The 2nd order transfer functions HLP(s), HBP(s) and HHP(s) (below) are all inverting so that, for example, at DC the lowpass gain is - HL. If two such sections are cascaded, these phase inversions cancel. Thus, the filter in the application schematic on the first page of this data sheet Operational Filter is a trademark of Linear Technology Corporation. 5 LTC1562-2 APPLICATIONS INFORMATION is a dual DC preserving, noninverting, rail-to-rail lowpass filter, approximating two "straight wires with frequency selectivity." Highpass Option If ZIN in Figure 1 becomes a capacitor of value CIN, then a standard all-pole highpass response becomes available between VIN and the V1 output. HHP (s) = 2 s2 + O / Q s + O ( -HHs 2 ) Here, the passband gain is HH = CIN/C where C is the internal capacitance, 100pF. The expressions for fO and Q remain as above. Two Bandpass Options There are two distinct ways to obtain a bandpass response HBP(s) from the LTC1562-2. When ZIN in Figure 1 is a resistor of value RIN, the V1 output has a bandpass response from VIN. Alternatively, with an input capacitor CIN for ZIN, the V1 output has a highpass response as described above, but simultaneously the V2 output now has a bandpass response, with the same HBP(s) form as above. The bandpass gain parameter becomes HB = (RQ/R1)(CIN/100pF) where again R1 = 7958. fO and Q are controlled by R2 and RQ as always. Relative Signal Swings The signal swings in each 2nd order section must be scaled so that neither output overloads (saturates), even if it is not used as a signal output. (Filter literature often calls this the "dynamics" issue.) For an LTC1562-2 section as in Figure 1, magnitudes of the two outputs V2 and V1, at a frequency = 2f, have the ratio: V2 j ( ) = (200kHz) f V1( j ) 6 U W U U Thus an input frequency above or below 200kHz produces larger output amplitude at V1 or V2, respectively. When an unused output has a larger signal swing than the output of interest, the section's gain or input amplitude must be scaled to avoid overdriving the unused output. The LTC1562-2 can still be used with high performance in such situations as long as this constraint is followed. The following cases are the most convenient because the relative-signal-swing issue does not arise: the unused output's swing is naturally the lower of the two. Lowpass response (resistor input, V2 output) with fO < 200kHz Bandpass response (capacitor input, V2 output) with fO < 200kHz Bandpass response (resistor input, V1 output) with fO > 200kHz Highpass response (capacitor input, V1 output) with fO > 200kHz Low Level or Wide Range Input Signals The LTC1562-2 contains a built-in capability for low noise amplification of low level signals. The Z IN impedance in each 2nd order section controls the block's gain. When set for unity passband gain, a 2nd order section can deliver an output signal 99dB above the noise level. If low level inputs require further dynamic range, reducing the value of ZIN boosts the signal gain while reducing the input-referred noise. This feature can increase the SNR for low level signals. Varying or switching ZIN is also an efficient way to effect automatic gain control (AGC). From a system viewpoint, this technique boosts the ratio of maximum signal to minimum noise, for a typical 2nd order lowpass response (Q = 1, fO = 200kHz), to 114dB. LTC1562-2 TYPICAL APPLICATIONS 175kHz 8th Order Elliptic Highpass Filter CIN2 82pF RIN2 20.5k CIN3 47pF VIN 1 RQ1 9.09k R21 7.15k 2 3 5 0.1F R23 11.3k RQ3 59k 6 8 9 10 INV B V1 B V2 B V + INV C V1 C V2 C 20 19 18 RQ2 26.7k R22 10k RIN3 45.3k GAIN (dB) CIN1 220pF 5V LTC1562-2 SHDN V2 A V1 A INV A RIN4 40.2k CIN4 100pF *V - ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM ALL CAPACITORS 5% STANDARD VALUES 1562-2 TA03a GAIN (dB) 256kHz Linear Phase 6th Order Lowpass Filter, Single Supply RFF1 6.19k VIN RIN1 7.5k 1 RQ1 3.24k R21 6.81k 5V 0.1F R23 4.12k RQ3 7.32k 2 3 5 6 8 9 10 RIN3 4.12k INV B V1 B V2 B V + LTC1562-2 SHDN V2 A V1 A INV A RIN4 4.12k CIN4 22pF 5% DELAY (s) *GROUND ALSO AT PINS 4, 7, 14 & 17 ALL RESISTORS 1% METAL FILM U Amplitude Response 10 0 -10 -20 -30 -40 -50 -60 - 5V* 0.1F V - 16 -70 -80 -90 50k 200k FREQUENCY (Hz) 900k 1562-2 TA03b AGND V2 D V1 D INV D 15 13 12 11 R24 4.02k RQ4 3.24k VOUT Amplitude Response 10 0 -10 -20 -30 -40 -50 RB1 1.54k -60 -70 RQ2 4.12k R22 6.19k * INV C V1 C V2 C V- 20 19 18 16 15 13 12 11 VOUT R24 4.12k RQ4 7.32k 1F -80 10k 100k FREQUENCY (Hz) 1M 1562-2 TA04b Group Delay Response 8 7 6 5 4 3 2 1 0 50 100 150 200 250 300 FREQUENCY (kHz) 350 400 AGND V2 D V1 D INV D 1562-2 TA04a 1562-2 TA04c 7 LTC1562-2 TYPICAL APPLICATIONS Dual 5th Order 170kHz Elliptic Highpass Filter, Single 5V Supply CIN2 220pF RIN2 15k CI1 CIN1 100pF 82pF VIN1 RI1 2k 5V 0.1F R23 11.5k CI3 CIN3 100pF 82pF VIN2 RI3 2k RQ3 43.2k 1 RQ1 43.2k R21 11.5k 2 3 5 6 8 9 10 INV B V1 B V2 B V+ INV C V1 C V2 C LTC1562-2 V - AGND V2 D V1 D INV D RIN4 15k CIN4 220pF *GROUND ALSO AT PINS 4, 7, 14 & 17 20 19 18 16 15 13 12 11 VOUT2 1F R24 6.34k RQ4 7.68k RQ2 7.68k R22 6.34k * VOUT1 GAIN (dB) SHDN V2 A V1 A INV A 100kHz 8th Order Bandpass Linear Phase, - 3dB BW = fCENTER/10 10 CIN1 10pF 1 VIN RQ1 78.7k R21 31.6k 5V 0.1F R23 35.7k RQ3 142k 2 3 5 6 8 9 10 CIN3 10pF INV B V1 B V2 B V+ INV C V1 C V2 C LTC1562-2 V - AGND V2 D V1 D INV D RIN4 221k 20 19 18 16 15 13 12 11 VOUT 1562-2 TA6a RQ2 76.8k R22 30.1k - 5V* 0.1F R24 28.7k RQ4 118k AMPLITUDE RESPONSE (dB) SHDN V2 A V1 A INV A *V - ALSO AT PINS 4, 7, 14 & 17 RELATED PARTS PART NUMBER LTC1068 LTC1560-1 LTC1562 DESCRIPTION Quad 2-Pole Switched Capacitor Building Block 5-Pole Elliptic Lowpass, fC = 1MHz/0.5MHz Quad 2-Pole Active RC, 10kHz to 150kHz COMMENTS Clock Tuned No External Components, SO8 Same Pinout as LTC1562-2 8 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com U Amplitude Response 10 0 - 10 - 20 - 30 - 40 - 50 - 60 - 70 - 80 - 90 10k 100k FREQUENCY (Hz) 1M 1562-2 TA05b 1562-2 TA05a Frequency Response RIN2 178k 0 -10 - 20 -30 - 40 - 50 - 60 -70 60k 80k 100k AMPLITUDE RESPONSE 60 GROUP DELAY (s) GROUP DELAY 120k 0 140k 1562-2 TA06b FREQUENCY (Hz) 15622i LT/TP 1298 4K * PRINTED IN USA (c) LINEAR TECHNOLOGY CORPORATION 1998 |
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