FEATURES Guaranteed Filter Speciication or ±.7V and ±5V Supply Operates Up to khz Low Power and 88dB Dynamic Range at ±.5V Supply Center Frequency Q Product Up to.mhz Guaranteed Oset Voltages Guaranteed Clock-to-Center Frequency Accuracy Over Temperature:.% or LTCA.8% or LTC Guaranteed Q Accuracy Over Temperature Low Temperature Coeicient o Q and Center Frequency Low Crosstalk, 7dB Clock Inputs TTL and CMOS Compatible APPLICATIO S U Single 5V Supply Medium Frequency Filters Very High Q and High Dynamic Range Bandpass, Notch Filters Tracking Filters Telecom Filters LTC Universal Dual Filter Building Block DESCRIPTIO U The LTC consists o two high perormance, switched capacitor ilters. Each ilter, together with to 5 resistors, can produce various nd order ilter unctions such as lowpass, bandpass, highpass notch and allpass. The center requency o these unctions can be tuned by an external clock or by an external clock and resistor ratio. Up to th order ull biquadratic unctions can be achieved by cascading the two ilter blocks. Any o the classical ilter conigurations (like Butterworth, Chebyshev, Bessel, Cauer) can be ormed. The LTC operates with either a single or dual supply rom ±.7V to ±8V. When used with low supply (i.e. single 5V supply), the ilter typically consumes mw and can operate with center requencies up to khz. With ±5V supply, the requency range extends to khz and very high Q values can also be obtained. The LTC is manuactured by using Linear Technology s enhanced LTCMOS silicon gate process. Because o this, low osets, high dynamic range, high center requency Q product and excellent temperature stability are obtained. The LTC is pinout compatible with MF., LTC and LT are registered trademarks o Linear Technology Corporation. LTCMOS trademark o Linear Technology Corporation. TYPICAL APPLICATIO U Single 5V, Gain o th Order Bandpass Filter.k 7 Amplitude Response OUTPUT k 9 k 5 mv(rms).k k 5V 5 7 8 LTC 8 7 5 k 5V k k.µf GAIN (db) 9 5 5 75 5 5 75 INPUT FREQUENCY (Hz) CLOCK IN 7.5kHz LTC TA LTC TA b
LTC ABSOLUTE AXI U RATI GS (Note ) W W W Supply Voltage... 8V Power Dissipation... 5mW Operating Temperature Range LTCAC/LTCC... C T A 85 C LTCAM/LTCM... 55 C T A 5 C Storage Temperature Range... 5 C to 5 C Lead Temperature (Soldering, sec)... C U U U W PACKAGE/ORDER I FOR ATIO A A N/AP/HP A INV A SA 5 V A 7 V D 8 LSh 9 CLKA TOP VIEW 9 8 7 5 N PACKAGE SW PACKAGE -LEAD PDIP -LEAD PLASTIC SO WIDE T JMAX = C, θ JA = C/W (N) T JMAX = 5 C, θ JA = 8 C/W (SW) J PACKAGE -LEAD CERDIP T JMAX = 5 C, θ JA = 7 C/W B B N/AP/HP B INV B SB AGND V A V D 5//HOLD CLKB OBSOLETE PACKAGE Consider the N and SW Package or Alternate Source ORDER PART NUMBER LTCACN LTCCN LTCCSW LTCACJ LTCMJ LTCAMJ LTCCJ Consult LTC Marketing or parts speciied with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes speciications which apply over the ull operating temperature range, otherwise speciications are at. (Complete Filter) V s = ±5V, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Center Frequency Range Q khz, Mode, Figure. to k Hz (See Applications Inormation) Q.MHz, Mode, Figure. to k Hz Clock-to-Center Frequency Ratio LTCA Mode, 5:, = 5kHz, Q = 5 ±.% LTC Mode, 5:, = 5kHz, Q = 5 ±.8% LTCA Mode, :, = 5kHz, Q = ±.% LTC Mode, :, = 5kHz, Q = ±.8% Q Accuracy LTCA Mode, 5: or :, = 5kHz, Q= ±.5 % LTC Mode, 5: or :, = 5kHz, Q= ±.5 5 % Temperature Coeicient Mode, < 5kHz ppm/ c Q Temperature Coeicient Mode, < 5kHz, Q = ppm/ c DC Oset V OS 5 mv V OS = 5kHz, 5:, = High mv V OS = 5kHz, :, = High 8 mv V OS = 5kHz, 5:, = Low mv V OS = 5kHz, :, = Low mv V OS = 5kHz, 5:, = Low mv V OS = 5kHz, :, = Low mv DC Lowpass Gain Accuracy Mode, R = = 5k ±. % Gain Accuracy at Mode, Q =, = 5kHz ±. % Clock Feedthrough MHz mv (P-P) Max Clock Frequency.5 MHz Power Supply Current 5 8 ma ma Crosstalk 7 db b
LTC ELECTRICAL CHARACTERISTICS The denotes speciications which apply over the ull operating temperature range, otherwise speciications are at. (Complete Filter) V S = ±.7V. PARAMETER CONDITIONS MIN TYP MAX UNITS Center Frequency Range Q khz. to k Hz Clock-to-Center Frequency Ratio LTCA Mode, 5:, = 5kHz, Q = 5 ±.5% LTC Mode, 5:, = 5kHz, Q = 5 ±.8% LTCA Mode, :, = 5kHz, Q = ±.5% LTC Mode, :, = 5kHz, Q = ±.8% Q Accuracy LTCA Mode, 5: or :, =.5kHz, Q = ± % LTC Mode, 5: or :, =.5kHz, Q = ± % Max Clock Frequency 5 khz Power Supply Current.5 ma The denotes speciications which apply over the ull operating temperature range, otherwise speciications are at. (Internal Op Amps). PARAMETER CONDITIONS MIN TYP MAX UNITS Supply Voltage Range ±.7 ±8 V Voltage Swings LTCA ± ± V LTC,R L = 5k (Pins,,9,) ±.8 ± V LTC, LTCA R L =.5k (Pins,8) ±. ± V Output Short-Circuit Current Source 5 ma Sink ma Op Amp GBW Product MHz Op Amp Slew Rate 7 V/µs Op Amp DC Open Loop Gain R L = k, 85 db Note : Absolute Maximum Ratings are those values beyond which the lie o a device may be impaired. BLOCK DIAGRA W V D VA N/AP/HP A SA A A 8 7 5 INVA AGND 5 CLK A LEVEL SHIFT NON-OVERLAP CLOCK S A 5//HOLD LEVEL SHIFT 9 CLK B TO AGND LEVEL SHIFT CONTROL NON-OVERLAP CLOCK S AB INV B 7 S B 8 9 V D VA N/AP/HP B SB B B LTC BD b
LTC TYPICAL PERFOR A CE CHARACTERISTICS UW Graph. Mode : ( / ) Deviation vs Q Graph. Mode : ( / ) Deviation vs Q Graph. Mode : Q Error vs Clock Frequency % DEVIATION ( / ). CLK = 5kHz..8.... = 5 (TEST POINT) % DEVIATION ( / )......5. = 5kHz CLK = (TEST POINT) DEVIATION FROM IDEAL Q (%) V S = ±.5V 5 5 V S = ±.5V = : 5 5 = 5:. IDEAL Q. IDEAL Q....8.....8. (MHz) LT TPC LT TPC LTC TPC Graph. Mode : Q Error vs Clock Frequency Graph 5. Mode : Measured Q vs and Temperature Graph. Mode : ( / ) vs and Q DEVIATION FROM IDEAL Q (%) V S = ±7.5V = : = 5: 5 5 DEVIATION FROM IDEAL Q (%) Q = = : = 5: 85 C 5 C 5 C 85 C 55 C 55 C DEVIATION FROM : (%).8.... = : Q = Q =....8.....8. (MHz)....8.....8 (MHz).....8... (MHz) LTC TPC LTC TPC5 LTC TPC DEVIATION FROM 5: (%).8..... Graph 7. Mode : ( / ) vs and Q = 5: Q = Q =....8... (MHz) DEVIATION FROM : (%)..8..... Graph 8. Mode : ( / ) vs and Temperature Q = = : 5 C 85 C 55 C...8.....8 (MHz) DEVIATION FROM 5: (%)..8..... Graph 9. Mode : ( / ) vs and Temperature Q = 5 C = 5: 85 C 55 C...8.....8 (MHz) LTC TPC9 LTC TPC7 LTC TPC8 b
LTC TYPICAL PERFOR A CE CHARACTERISTICS UW DEVIATION FROM : (%)..8.... Graph. Mode : ( / ) vs and Q V S = ±.5V = : Q = Q = 5 7 (MHz) DEVIATION FROM 5: (%).8..... Graph. Mode : ( / ) vs and Q V S = ±.5V = 5: Q = Q = 5 7 (MHz) DEVIATION FROM : (%).8... Graph. Mode : ( / ) vs and Temperature V S = ±.5V Q = = : 5 C 85 C....8 (khz) 55 C.. DEVIATION FROM 5: (%)..8.... Graph. Mode : ( / ) vs and Temperature 85 C 5 C 55 C....8 (khz) LTC TPC V S = ±.5V Q = = 5:.. LTC TPC NOTCH DEPTH (db) 8 Graph. Mode : Notch Depth vs Clock Frequency Q = : Q = : Q = 5: = V RMS LTC TPC....8.... (MHz) LTC TPC DEVIATION OF WITH RESPECT TO O Q = MEASUREMENT (%)......5 LTC TPC Graph 5. Mode : Deviation o ( / ) with Respect to Q = Measurement. PIN AT : (A) (B) = 5: O = R 5 O = R = : IDEAL Q LTC TPC5 DEVIATION FROM IDEAL Q (%) Graph. Mode : Q Error vs Clock Frequency V S = ±.5V 5 = : 5 V S = ±.5V 5 5 = 5: Q ERROR (%) Graph 7. Mode ( = R): Q Error vs Clock Frequency V S = ±7.5V = : 5 5 = 5: DEVIATION FROM IDEAL Q (%) Graph 8. Mode ( = R): Measured Q vs and Temperature 5 C Q = = : = 5: 5 C 85 C 85 C 55 C 55 C....8.....8. (MHz) LTC TPC....8.....8. (MHz) LTC TPC7....8.....8 (MHz) LTC TPC8 b 5
LTC TYPICAL PERFOR A CE CHARACTERISTICS UW Graph 9. Mode ( = R): ( / ) vs and Q Graph. Mode ( = R): ( / ) vs and Q Graph. Mode ( = R): ( / ) vs and Temperature DEVIATION FROM : (%).8.... V S = ± 5V = : Q = Q =, Q =, DEVIATION FROM 5: (%).8.... V S = ± 5V = 5: Q = Q = DEVIATION FROM: (%)..8... V S = ± 5V Q = = : 85 C 5 C 55 C.....8... (MHz).....8... (MHz).....8.....8 (MHz) LTC TPC9 LTC TPC LTC TPC DEVIATION FROM 5: (%)..8... Graph. Mode ( = R): ( / ) vs and Temperature. Q = = : 5 C 85 C 55 C...8....8 (MHz) LTC TPC DEVIATION FROM : (%).8..... Graph. Mode ( = R): ( / ) vs and Temperature V S = ±.5V Q = = : 5 C 85 C....8 (MHz) 55 C.. LTC TPC DEVIATION FROM 5: (%)..8... Graph. Mode ( = R): ( / ) vs and Temperature 85 C 5 C....8 (MHz) 55 C V S = ±.5V Q = = :. LTC TPC DEVIATION FROM IDEAL Q (%) Graph 5. Mode c (R5 = ), Mode ( = R) Q Error vs Clock Frequency 7.7 = 5.7 MODE = R Q = MODE = R Q = Q = Q = SUPPLY CURRENT (ma) 8 8 Graph.Supply Current vs Supply Voltage MHz T A = 55 C....8... (MHz) ± ± ± ± ±5 ± ±7 ±8 ±9 ± ± SUPPLY VOLTAGE (±V) LTC TPC5 LTC TPC b
PIN DESCRIPTION AND APPLICATIONS INFORMATIO U W U U U U U Power Supplies The V A and V D (pins 7 and 8) and the V A and V D (Pins and ) are, respectively, the analog and digital positive and negative supply pins. For most cases, Pins 7 and 8 should be tied together and bypassed by a.µf disc ceramic capacitor. The same holds or Pins and. I the LTC operates in a high digital noise environment, the supply pins can be bypassed separately. Pins 7 and 8 are internally connected through the IC substrate and should be biased rom the same DC source. Pins and should also be biased rom the same DC source. The LTC is designed to operate with ±.5V supply (or single 5V) and with ±5V to ±8V supplies. The minimum supply, where the ilter operates reliably, is ±.7V. With low supply operation, the maximum input clock requency is about 5kHz. Beyond this, the device exhibits excessive Q enhancement and center requency errors. Clock Input Pins and Level Shit The level shit (LSh) Pin 9 is used to accommodate T L or CMOS clock levels. With dual supplies equal or higher to ±.5V, Pin 9 should be connected to ground (same potential as the AGND pin). Under these conditions the clock levels can be T L or CMOS. With single supply operation, the negative supply pins and the LSh pin should be tied to the system ground. The AGND, Pin 5, should be biased at / supplies, as shown in the Single 5V Gain o th Order Bandpass Filter circuit. Again, under these conditions, the clock levels can be T L or CMOS. The input clock pins (,) share the same level shit pin. The clock logic threshold level over temperature is typically.5v ±.V above the LSh pin potential. The duty cycle o the input clock should be close to 5%. For clock requencies below MHz, the ( / ) ratio is independent rom the clock input levels and rom its rise and all times. Fast rising clock edges, however, improve the ilter DC osets. For clock requencies above MHz, T L level clocks are recommended. 5//Hold (Pin ) By tying Pin to (V A and V D), the ilter operates in the 5: mode. With ±5V supplies, Pin can be typically V below the positive supply without aecting the 5: LTC operation o the device. By tying Pin to / supplies (which should be the AGND potential), the LTC operates in the : mode. The / supply bias o Pin can vary around the / supply potential without aecting the : ilter operation. This is shown in Table. When Pin is shorted to the negative supply pin, the ilter operation is stopped and the bandpass and lowpass outputs act as a S/H circuit holding the last sample. The hold step is mv and the droop rate is 5µV/second! Table TOTAL POWER SUPPLY VOLTAGE RANGE OF PIN FOR : OPERATION 5V.5 ±.5V V 5V ± V 5V 7.5V ±.5V S A, S B (Pins 5 and ) These are voltage signal input pins and, i used, they should be driven with a source impedance below 5kΩ. The S A, S B pins can be used to alter the CLK to center requency ratio ( / ) o the ilter (see Modes b, c, a, b) or to eedorward the input signal or allpass ilter conigurations (see Modes and 5). When these pins are not used, they should be tied to the AGND pin. (Pin ) When is high, the S input o the ilter s voltage summer (see Block Diagram) is tied to the lowpass output. This rees the S pin to realize various modes o operation or improved applications lexibility. When the pin is connected to the negative supply, the S input switches to ground and internally becomes inactive. This improves the ilter noise perormance and typically lowers the value o the oset V OS. AGND (Pln 5) This should be connected to the system ground or dual supply operation. When the LTC operates with a single positive supply, the analog ground pin should be tied to / supply and bypassed with a.µf capacitor, as shown in the application, Single 5V, Gain o th Order Bandpass Filter. The positive inputs o all the b 7
LTC APPLICATIO S I FOR ATIO internal op amps, as well as the reerence point o all the internal switches are connected to the AGND pin. Because o this, a clean ground is recommended. / Ratio The / reerence o : or 5: is derived rom the ilter center requency measured in mode, with a Q = and. The clock requencies are, respectively, 5kHz/5kHz or the :/5: measurement. All the curves shown in the Typical Perormance Characteristics section are normalized to the above reerences. Graphs and in the Typical Perormance Characteristics show the ( / ) variation versus values o ideal Q. The LTC is a sampled data ilter and it only approximates continuous time ilters. In this data sheet, the LTC is treated in the requency domain because this approximation is good enough or most ilter applications. The LTC deviates rom its ideal continuous ilter model when the ( / ) ratio decreases and when the Q s are low. Since low Q ilters are not selective, the requency domain approximation is well justiied. In Graph 5 the LTC is connected in mode and its ( / ) ratio is adjusted to : and 5:. Under these conditions, the ilter is over-sampled and the ( / ) curves are nearly independent o the Q values. In mode, the ( / ) ratio typically deviates rom the tested one in mode by ±.%. x Q Product Ratio This is a igure o merit o general purpose active ilter building blocks. The x Q product o the LTC depends on the clock requency, the power supply voltages, the junction temperature and the mode o operation. At 5 C ambient temperature or ±5V supplies, and or clock requencies below MHz, in mode and its derivatives, the x Q product is mainly limited by the desired and Q accuracy. For instance,rom Graph at 5: and or below 8kHz, a predictable ideal Q o can be obtained. Under this condition, a respectable x Q product o.mhz is achieved. The khz center requency will be about.% o rom the tested value at 5kHz clock (see Graph ). For the same clock requency o 8kHz and or the same Q value o, the x Q product can be urther increased i the 8 U W U U clock-to-center requency is lowered below 5:. In mode c with R = and R =, the ( / ) ratio is 5/. The x Q product can now be increased to 9MHz since, with the same clock requency and same Q value, the ilter can handle a center requency o khz x. For clock requencies above MHz, the x Q product is limited by the clock requency itsel. From Graph at ±7.5V supply, 5: and.mhz clock, a Q o 5 has about 8% error; the measured 8kHz center requency was skewed by.8% with respect to the guaranteed value at 5kHz clock. Under these conditions, the x Q product is only khz but the ilter can handle higher input signal requencies than the 8kHz clock requency, very high Q case described above. Mode, Figure, and the modes o operation where R is inite, are slower than the basic mode. This is shown in Graph and 7. The resistor R places the input op amp inside the resonant loop. The inite GBW o this op amp creates an additional phase shit and enhances the Q value at high clock requencies. Graph was drawn with a small capacitor, C C, placed across R and as such, at V S = ±5V, the (/πrc C ) = MHz. With V S = ±.5V the (/ πrc C ) should be equal to.mhz. This allows the Q curve to be slightly latter over a wider range o clock requencies. I, at ±5V supply, the clock is below 9kHz (or khz or V S = ±.5V), this capacitor, C C, is not needed. For Graph 5, the clock-to-center requency ratios are altered to 7.7: and 5.5:. This is done by using mode c with R5 =, Figure 7, or mode with = R = kω. The mode c, where the input op amp is outside the main loop, is much aster. Mode, however, is more versatile. At 5:, and or the mode c can be tuned or center requencies up to khz. Output Noise The wideband RMS noise o the LTC outputs is nearly independent rom the clock requency, provided that the clock itsel does not become part o the noise. The LTC noise slightly decreases with ±.5V supply. The noise at the and outputs increases or high Q s. Table shows typical values o wideband RMS noise. The numbers in parentheses are the noise measurement in mode with the pin shorted to V as shown in Figure 5. b
LTC APPLICATIO S I FOR ATIO Table. Wideband RMS Noise U W U U NOTCH/HP V S (µv RMS ) (µv RMS ) (µv RMS ) CONDITIONS ±5V 5: 9 () 5 () 75 (5) Mode, R = = ±5V : 7 (55) 8 (58) 9 (88) Q = ±.5V 5: () () 8 () ±.5V : 8 () 5 () (55) ±5V 5: (8) 5 (5) 8 (55) Mode, Q = ±5V : 5 () () (8) R = or out ±.5V 5: (5) (8) (87) R = or out ±.5V. (7) 5 (5) 5 (9) ±5V 5: 57 57 Mode, R = = = R ±5V : 7 7 8 Q = ±.5V 5: ±.5V. 5 5 5 ±5V 5: 5 Mode, = R, Q = ±5V : 7 85 = R or out ±.5V 5: 88 R = R or and HP out ±.5V : 5 5 Short-Circuit Currents Short circuits to ground, positive or negative power supply are allowed as long as the power supplies do not exceed ±5V and the ambient temperature stays below 85 C. Above ±5V and at elevated temperatures, continuous short circuits to the negative power supply will cause excessive currents to low. Under these conditions, the device will get damaged i the short-circuit current is allowed to exceed 8mA. DEFINITION OF FILTER FUNCTIONS U U U U Each building block o the LTC, together with an external clock and a ew resistors, closely approximates nd order ilter unctions. These are tabulated below in the requency domain.. Bandpass unction: available at the bandpass output Pins (9). (Figure.) Q = Quality actor o the complex pole pair. It is the ratio o to the db bandwidth o the nd order bandpass unction. The Q is always measured at the ilter output.. Lowpass unction: available at the output Pins (). (Figure.) G(s) = H O sω o /Q s (sω o /Q) ω o G(s) = H O ω o s s(ω o /Q) ω o H O = Gain at ω = ω o = ω/π; is the center requency o the complex pole pair. At this requency, the phase shit between input and output is 8. H O DC gain o the output. b 9
LTC DEFINITION OF FILTER FUNCTIONS U U U U. Highpass unction: available only in mode at the ouput Pins (8). (Figure.) s G(s) = H OHP s s(ω o /Q) ω o H OHP = gain o the HP output or. Notch unction: available at Pins (8) or several modes o operation. s G(s) = (H ON ) ω o s (sω o /Q) ω o H ON = gain o the notch output or H ON = gain o the notch output or n = ω n /π; n is the requency o the notch occurrence. 5. Allpass unction: available at Pins (8) or mode, a. [s G(s) = H s(ω o /Q) ω o ] OAP s s(ω o /Q) ω o H OAP = gain o the allpass output or << For allpass unctions, the center requency and the Q o the numerator complex zero pair is the same as the denominator. Under these conditions, the magnitude response is a straight line. In mode 5, the center requency z, o the numerator complex zero pair, is dierent than. For high numerator Q s, the magnitude response will have a notch at z. HIGHPASS OUTPUT GAIN (V/V) H O.77 H O BANDPASS OUTPUT Q = ; = H L L H (LOG SCALE) ( ( ( Q ( L H L = Q ( ) ) H = Q ( TLC DFF GAIN (V/V) H OP H O.77 H O LOWPASS OUTPUT Figure Figure Figure P C = Q ( ( Q P = H OP = H O ( C (LOG SCALE) Q Q Q TLC DFF ( GAIN (V/V) H OP H OHP.77 H OHP C P (LOG SCALE) C = Q ( ( Q P = H OP = H OHP Q Q ( Q ( TLC DFF ODES OF OPERATIO U W Table. Modes o Operation: st Order Functions MODE PIN (9) PIN (8) C Z a HP b 7 AP (5) (5) (5) (5) b
LTC ODES OF OPERATIO U W Table. Modes o Operation: nd Order Functions MODE PIN () PIN (9) PIN (8) n Notch (5) a (5) b Notch c Notch (5) R R5 R R (5) R5 R (5) R R5 R R (5) R5 R Notch (5) R (5) a Notch b Notch HP a Notch R (5) R R5 R R (5) R R5 R (5) (5) R R R (5) R5 R (5) (5) R R5 R R h R I AP (5) a AP 5 CZ (5) R (5) R R (5) R R (7) N SA (8) 5 () (9) () (7) SA (8) 5 () (9) () 5 / LTC TLC MOO 5 / LTC TLC MOO V = CLK ; n = ; H O = ; H O = ; H ON = ; Q = (5) R R R V = CLK ; Q = ; H O = ; H O = (NON-INVERTING) H O = (5) Figure. Mode : nd Order Filter Providing Notch, Bandpass, Lowpass Figure 5. Mode a: nd Order Filter Providing Bandpass, Lowpass b
LTC ODES OF OPERATIO U W R R5 R R5 R (7) N SA 5 () (9) () R (7) N SA 5 (8) () (9) () 5 / LTC TLC MOO 5 / LTC TLC MOO V = CLK R ; n = ; Q = (5) R5 R R R5 R ( ) /R H N ( ) = H N = ; H = ; H = ; R5 < 5kΩ R R/(R5 R) R Figure. Mode b: nd Order Filter Providing Notch, Bandpass, Lowpass V = CLK R R ; n = ; Q = ; (5) R5 R R5 R ( ) /R H N ( ) = H N = ; H = ; H = ; R5 < 5kΩ R R R/(R5 R) Figure 7. Mode c: nd Order Filter Providing Notch, Bandpass, Lowpass R R R R5 R (7) N SA (8) 5 () (9) () R (7) N SA (8) 5 () (9) () 5 / LTC TLC MOO5 5 / LTC TLC MOO V = CLK ; n = CLK ; Q = ; H = /R (5) R (5) R ( R) ( ) /R H CLK = /R ; H N ( ) = ; H N = = /R ( R) Figure 8. Mode : nd Order Filter Providing Notch, Bandpass, Lowpass V = CLK R ; n = CLK R ; Q = (5) R R5 R (5) R5 R ( ) R/(R5 R) H CLK N ( ) = ; H R N = /R (/R) [R/(R5 R)] H = /R ; H = /R (/R) [R/(R5 R)] Figure 9. Mode a: nd Order Filter Providing Notch, Bandpass, Lowpass R R R5 R b
LTC ODES OF OPERATIO U W R R R (7) R R5 N SA (8) 5 () (9) () R (7) N SA (8) 5 () (9) () V 5 / LTC = CLK R ; n = CLK R ; Q = (5) R R5 R (5) R5 R ( ) TLC MOO7 R R/(R5 R) H CLK N ( ) = ; H R N = /R (/R) [R/(R5 R)] /R H = /R ; H = (/R) [R/(R5 R)] R R5 R V 5 / LTC TLC MOO8 = CLK ; Q = ; H HP = /R; H = /R; H = R/R (5) R R Figure. Mode : nd Order Filter Providing Highpass, Bandpass, Lowpass Figure. Mode b: nd Order Filter Providing Notch, Bandpass, Lowpass R R (7) HP SA (8) 5 () (9) () R g V 5 / LTC R h R I EXTERNAL OP AMP NOTCH = CLK ; n = CLK R h ; H HP = /R; H = /R, H = R/R (5) R (5) R I ( ) ( ) R g R R g R g R H g N ( ) = ; H N = ; H N ( = ) = Q H H HP ; Q = R I R R h R R I R h Figure. Mode a: nd Order Filter Providing Highpass, Bandpass, Lowpass, Notch R TLC MOO9 b
LTC ODES OF OPERATIO U W R R = (7) 5 AP SA (8) 5 () / LTC (9) TLC MOO () R V (7) 5 HP (8) SA 5 () / LTC (9) R R () R5 EXTERNAL OP AMP V ( ) = CLK ; Q = ; H OAP = ; H O = H O = (5) R Figure. Mode : nd Order Filter Providing Allpass, Bandpass, Lowpass = CLK R5 ; Q = ; H AP = ; H HP = ; H = (5) R R ; H = R R R R R Figure. Mode a: nd Order Filter Providing Highpass, Bandpass, Lowpass, Allpass TLC MOO R R V (7) 5 = CLK (5) Q = CZ SA (8) 5 () / LTC ; z = CLK R ; Q = R (5) R TLC MOO Figure 5. Mode 5: nd Order Filter Providing Numerator Complex Zeros, Bandpass, Lowpass (9) R R ; H CLK OZ = ( ) = (R/R) = R (R/) ; H OZ ; R R ( ) (/R) H O = ( ) ; H O = R (/R) () R V (7) 5 N SA (8) 5 () / LTC (9) C = CLK ; H = /R ; H HP = /R (5) Figure. Mode a: st Order Filter Providing Highpass, Lowpass TLC MOO () b
LTC ODES OF OPERATIO U W (7) SA (8) 5 () (9) () R= (7) 5 =R AP SA (8) 5 () / LTC (9) TLC MOO5 () V 5 / LTC C = CLK ; H O = ; H O = (5) TLC MOO H O = x V P = CLK ; z = CLK ; GAIN AT AP OUTPUT = FOR CLK (5) (5) Figure 7. Mode b: st Order Filter Providing Lowpass Figure 8. Mode 7: st Order Filter Providing Allpass, Lowpass COMM E TS ON THE M ODES OF OPERATIO U W U U WW There are basically three modes o operation: mode, mode, mode. In the mode (Figure ), the input ampliier is outside the resonant loop. Because o this, mode and its derivatives (mode a, b, c) are aster than modes and. In mode, or instance, the Q errors are becoming noticeable above MHz clock requency. Mode a (Figure 5), represents the most simple hook-up o the LTC. Mode a is useul when voltage gain at the bandpass output is required. The bandpass voltage gain, however, is equal to the value o Q; i this is acceptable, a second order, clock tunable, resonator can be achieved with only resistors. The ilter center requency directly depends on the external clock requency. For high order ilters, mode a is not practical since it may require several clock requencies to tune the overall ilter response. Mode (Figure ), provides a clock tunable notch; the depth is shown in Graph. Mode is a practical coniguration or second order clock tunable bandpass/ notch ilters. In mode, a bandpass output with a very high Q, together with unity gain, can be obtained without creating problems with the dynamics o the remaining notch and lowpass outputs. Modes b and c (Figures and 7), are similar. They both produce a notch with a requency which is always equal to the ilter building block center requency. The notch and the center requency, however, can be adjusted with an external resistor ratio. The practical clock-to-center requency ratio range is: 5 or 5 ; mode b or 5 or 5 ; mode c o The input impedance o the S pin is clock dependent, and in general R5 should not be larger than 5k. Mode b can be used to increase the clock-to-center requency ratio beyond :. For this mode, a practical limit or the ( / ) ratio is 5:. Beyond this, the ilter will exhibit large output osets. Mode c is the astest mode o operation: In the 5: mode and with (R5 =, R = ) the clock-to-center requency ratio becomes (5/ ) and center requencies beyond khz can easily be achieved as shown in Graph 5. Figure 9 illustrates how to cascade the two sections o the LTC connected in mode c to obtain a sharp ourth order, db ripple, Chebyshev ilter. Note that the center requency to the BW ratio or this ourth order bandpass ilter is /. By varying the clock requency to sweep the ilter, the center requency o the overall ilter will increase proportionally and so will the BW to maintain the : ratio constant. All the modes o operation yield constant Q s; with any ilter realization the BW s will vary when the ilter is swept. This is shown in Figure 9, where the ilter is swept rom khz to khz center requency. b 5
LTC COMM E TS ON THE M ODES OF OPERATIO Modes, a, and b have a notch output which requency, n, can be tuned independently rom the center requency,. For all cases, however, n <. These modes are useul when cascading second order unctions to create an U W U U WW R R V = 5V T L OR CMOS CLK IN R5 LTC 5 7 8 9 A A N A INV A SA V A V D LSh CLK A B B N B INV B SB AGND V A V D 5/ CLK B 9 8 7 5 PRECISE RESISTOR VALUES R = 9.k =.99k = 9.k R5 =.55k R =.9k R5 5V = 5.k = 5.k =.k R5 =.9k R =.9k V OUT R V = 5V LTC CM overall elliptic highpass, bandpass or notch response. The input ampliier and its eedback resistors (/R) are now part o the resonant loop. Because o this, mode and its derivatives are slower than mode s. Figure 9. Cascading the Two Sections o the LTC Connected in Mode c to Obtain a Clock Tunable th Order db Ripple Bandpass Chebyshev Filter with (Center Frequency)/(Ripple Bw) = /. db 5dB db 5dB db 5dB db 5dB db 5dB db 5dB.9kHz 8kHz 9kHz 5Hz khz khz khz khz = khz.khz = 8kHz khz TLC CMOb In mode (Figure ), a single resistor ratio (/R) can tune the center requency below or above the / (or /5) ratio. Mode is a state variable coniguration since it provides a highpass, bandpass, lowpass output through progressive integration; notches are obtained by summing the highpass and lowpass outputs (mode a, Figure ). The notch requency can be tuned below or above the center requency through the resistor ratio (R h /R i ). Because o this, modes and a are the most versatile and useul modes or cascading second order sections to obtain high order elliptic ilters. Figure shows the two sections o an LTC connected in mode a to obtain a clock tunable th order sharp elliptic bandpass ilter. The irst notch is created by summing directly the HP and outputs o the irst section into the inverting input o the second section op amp. The individual Q s are 9. and the ilter maintains its shape and perormance up to khz center requency (Figure ). For this circuit an external op amp is required to obtain the nd notch. The dynamics o Figure are excellent because the amplitude response at each output pin does not exceed db. The gain in the passband depends on the ratio o (R g /R h ) (/R h ) (/R). Any gain value can be obtained by acting on the (R g /R h ) ratio o the external op amp, meanwhile the remaining ratios are adjusted or optimum dynamics o the LTC output nodes. The external op amp o Figure is not always required. In Figure, one section o the LTC in mode a is cascaded with the other section in mode b to obtain a th order, db ripple, elliptic bandreject ilter. This coniguration is interesting because a th order unction with two dierent notches is realized without requiring an external op amp. The clock-to-center requency ratio is adjusted to :; this is done in order to better approximate a linear R,C notch ilter. The amplitude response o the ilter is shown in Figure with up to MHz clock requency. The db bandwidth to the stop bandwidth ratio is 9/. When the ilter is centered at khz, it should theoretically have a db rejection with a 5Hz stop bandwidth. For a more narrow ilter than the above, the unused output o the b
COMM E TS ON THE M ODES OF OPERATIO U W U U WW mode b section (Figure ), has a gain exceeding unity which limits the dynamic range o the overall ilter. For very selective bandpass/bandreject ilters, the mode a LTC approach, as in Figure, yields better dynamic range since the external op amp helps to optimize the dynamics o the output nodes o the LTC. R H R L R G NOTE: R R 7.5V V = 7.5V T L OR CMOS CLOCK IN R = 55.9k R H =.k R = 5k LTC 5 7 8 9 A A HP A INV A SA V A V D LSh CLK A B B HP B INV B SB AGND V A V D 5/ CLK B 9 8 7 5 PRECISE RESISTOR VALUES = 5k = 5k R L =.7k = 5.k R L =.k R H = 5k R 7.5V 7.5V R = 5.7k = 5.8k R G = 7.k FOR CLOCK FREQUENCIES ABOVE 7kHz, A pf CAPACITOR ACROSS R AND A pf CAPACITOR ACROSS R WERE USED TO PREVENT THE PASSBAND RIPPLE FROM ANY ADDITIONAL PEAKING R L R H EXTERNAL OP AMP V OUT LTC CM Figure. Combining Mode with Mode a to Make The th Order Filter o Figure with Improved Dynamics. The Gain at Each Output Node is db or all Input Frequencies. = khz = MHz db db db db db db db db db db 5dB 5dB.5kHz.75kHz khz.5khz.5khz 5kHz 7.5kHz khz.5khz 5kHz TLC CMO Figure. The Filter o Figure, When Swept From a khz to khz Center Frequency. b 7
LTC COMM E TS ON THE M ODES OF OPERATIO U W U U WW R R 5V V = 5V 5 7 8 9 V D LSh CLK A R H R L LTC A B A B HP A N B INV A INV B SA SB AGND V A V A V D 5/ CLK B 9 8 7 5 R R5 V = 5V R V OUT V OUT / (db) = ; CLK MHz T L OR CMOS CLOCK IN R = k R = 8.8k R5 = 5k = 55.75k RESISTOR VALUES = 5k = 5.75k R H = 5k R L = 9.k R =.59k = k R = 5.85k LTC CM 5.7.8.9 =.... INPUT FREQUENCY NORMALIZED TO FILTER CENTER FREQUENCY Figure. Combining Mode with Mode b to Create a th Order BR Elliptic Filter with db Ripple and a Ratio o db to Stop Bandwidth Equal to 9/. TLC CMO5 Figure. Amplitude Response o the Notch Filter o Figure LTC OFFSETS Switched capacitor integrators generally exhibit higher input osets than discrete R, C integrators. These osets are mainly due to the charge injection o the CMOS switches into the integrating capacitors and they are temperature independent. The internal op amp osets also add to the overall oset budget and they are typically a couple o millivolts. Because o this, the DC output osets o switched capacitor ilters are usually higher than the osets o discrete active ilters. (7) V OS (8) () (9) () 5 VOS V OS Figure shows hal o an LTC ilter building block with its equivalent input osets V OS, V OS, V OS. All three are % tested or both sides o the LTC. V OS is generally the larger oset. When the, Pin, o the LTC is shorted to the negative supply (i.e., mode ), the value o the V OS decreases. Additionally, with low, a % to % noise reduction is observed. Mode can still be achieved, i desired, by shorting the S pin to the lowpass output (Figure 5). R (7) N SA (8) 5 () (9) () 5 TLC LO 5 / LTC TLC LO V Figure. Equivalent Input Osets o / LTC Filter Building Block 8 Figure 5. Mode (LN): Same Operation as Mode but Lower V OS Oset and Lower Noise b
LTC LTC OFFSETS Output Osets The DC oset at the ilter bandpass output is always equal to V OS. The DC osets at the remaining two outputs (Notch and ) depend on the mode o operation and external resistor ratios. Table 5 illustrates this. It is important to know the value o the DC output osets, especially when the ilter handles input signals with large Table 5 dynamic range. As a rule o thumb, the output DC osets increase when:. The Q s decrease.. The ratio ( / ) increases beyond :. This is done by decreasing either the (/R) or the R/(R5 R) resistor ratios. V OSN V OS V OS MODE PIN (8) PIN (9) PIN (), V OS [(/Q) H O ] V OS /Q V OS V OSN V OS a V OS [ (/Q)] V OS /Q V OS V OSN V OS b V OS [(/Q) /R] V OS /Q V OS ~ (V OSN V OS ) ( R5/R) c V OS [(/Q) /R] V OS /Q V OS (R5 R) ~(V OSN V OS ) (R5 R), 5 [V OS ( /R / /R) V OS (/)] V OS V OSN V OS [R/( R)] V OS [/( R)] a [V OS ( /R / /R) V OS (/)] b R( k) R( k) V R OS ;k = R( k) R5 R [V OS ( /R / /R) V OS (/)] Rk Rk V R OS ;k = Rk R5 R (R5 R) V OS ~(V OSN V OS ) (R5 R) V OS ~ (V OSN V OS ) ( R5/R), a V OS V OS R V OS R V OS R R R V OS R PACKAGE DESCRIPTIO U N Package -Lead PDIP (Narrow. Inch) (Reerence LTC DWG # 5-8-5)..5 (7. 8.55).8.5 (..8).55 ±.5* (.77 ±.8).* (.) MAX 9 8 7 5. (.58) MIN.5.5 (.75.8).5.5 (..5).5 (.5) TYP.5.5.5.889 8.55.8 ( ) 5 7 8 9 NOTE: INCHES. DIMENSIONS ARE MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED. INCH (.5mm). (.8) MIN.5 (.7) MIN. (.5) BSC.8 ±. (.57 ±.7) N Inormation urnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed or its use. Linear Technology Corporation makes no representation that the interconnection o its circuits as described herein will not inringe on existing patent rights. b 9
LTC PACKAGE DESCRIPTIO U J Package -Lead CERDIP (Narrow. Inch, Hermetic) (Reerence LTC DWG # 5-8-) CORNER LEADS OPTION ( PLCS). (.9) MAX 9 8 7 5.5.5 (..5) FULL LEAD OPTION. BSC (7. BSC)..5 (.58.) HALF LEAD OPTION.. (5.588 7.87).5 (.5) RAD TYP 5 7 8 9.5 (.7) MIN. (5.8) MAX.5. (.8.5).8.8 (..57) 5 NOTE: LEAD DIMENSIONS APPLY TO SOLDER DIP/PLATE OR TIN PLATE LEADS.5 (.75) MIN OBSOLETE PACKAGE.5.5 (..5).. (.5.) SW Package -Lead Plastic Small Outline (Wide. Inch) (Reerence LTC DWG # 5-8-). (.5) BSC J 8. ±.5 TYP N.5 BSC.5 ±.5.9.5 (.598.5) NOTE 9 8 7 5. MIN.5 ±.5 N NOTE.9.9 (.7.) N/ N/ RECOMMENDED SOLDER PAD LAYOUT.5 (.7) RAD MIN.9.99 (7.9 7.595) NOTE..9 5 (.5.77) 8 TYP.9. (..) 5 7 8 9.7.5 (.9.).5.9. (.9.) NOTE (.7) BSC..5 (..7)..9 (.5.8) NOTE: TYP INCHES. DIMENSIONS IN (MILLIMETERS). DRAWING NOT TO SCALE. PIN IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED." (.5mm) Linear Technology Corporation McCarthy Blvd., Milpitas, CA 955-77 (8) -9 FAX: (8) -57 www.linear.com.. (..5) S (WIDE) 5 b LW/TP K REV B PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 988