# Introduction onventional analog circuits use the ratio of resistances to set the transfer function of filter circuits. The values of RC product determine the frequency responses of these circuits [1][2]. A switchedcapacitor can replace a resistor [2]. MOSFET technology can be used for designing switchedcapacitor circuits [3]. The filter circuits using Switched-Capacitor allow very sophisticated, accurate and tunable analog circuits to be manufactured. Many of the circuits proposed the working of only one type of operation [5][6][7][8][9][10]. The Switched-Capacitor concept can be used to realize wide variety of universal filter that have the advantage of compactness and tenability [5]. Switched capacitor techniques have been developed so that both digital and analog functions can be integrated on a single silicon chip. Switched-Capacitor filters have the advantage of better accuracy in most cases. Typical center frequency accuracies are normally on the order of Author ?: School of Physics, SRTM University, Nanded, Maharashtra, India. e-mail: almogammer80@gmail.com Author ?: Principal, Indira Gandhi (SR) College, CIDCO, Nanded, Maharashtra, India. e-mail: shindegn@yahoo.co.in about 0.2% foremost Switched-Capacitor ICs, and worst-case numbers range from 0.4% to 1.5% (assuming, of Course, that an accurate clock is provided) [6]. This Paper of Electronically Tunable Third-Order Switched-Capacitor Filter with Feedforward Signal to minimize Overshoot has been studied for different values of circuit merit factor Q and f 0 =15 KHz . # II. # Basic Switching Operation The essence of the Switched-Capacitor is the use of Capacitors and analog Switches to perform the same function as resistors. This replacement of resistor, analog with op. amp based integrator, and then forms an active filter. Furthermore, the use of the Switched-Capacitor will be seen to give frequency tenability to active filters. Filter using Switched-Capacitor technique overcome a major obstacle of filter on a chip fabrication?the implementation of resistors by simulating resistors with high speed Switched-Capacitors using MOSFETs. The switching function of the MOSFET produces a discrete response rather than a continuous response from the filter [14]. The operation of switched-capacitor can be explained with the help of following circuit diagram. Therefore, when S 2 closes with S 1 open, then S 1 closes with S 2 open a charge q is transferred from V 2 to V 1 with ??? = ?? (?? ? ?? ) If this switching process is repeated N times in time (t), then the amount of charge transferred per unit time is given by # ??? ??? = ?? 1 (?? 2 ? ?? 1 ) ?? ??? L.H.S. is current and number of cycles per unit time is switching frequency. ? ?? = ?? 1 (?? 2 ? ?? 1 ) ð??"ð??" ?????? ? (?? 2 ? ?? 1 ) ?? = 1 ?? 1 ð??"ð??" ?????? = ?? Thus the switched-capacitor is equivalent a resistor. # III. # Proposed Circuit Configuration The proposed circuit configuration for Electronically Tunable Third-Order Switched-Capacitor Filter with Feedforward Signal to minimize Overshoot is shown in Figure 2. The circuit consists of three op-amps (µA 741) with wide identical gain bandwidth product Switched-Capacitor. Switched-Capacitor can replace resistors, which was proposed earlier [2]. The input sinusoidal voltage is applied to the inverting terminal of the first op-amp through switched capacitor (SC). The non-inverting terminal is grounded. SC is used in the feedback circuit. The output of the first op-amp is supplied as non-inverting input of the second op-amp. The feedforward input signal is given to the inverting terminal of the second op-amp. SC is used as feedback. The output of the second op-amp is supplied as noninverting input of the third op-amp. The inverting terminal is grounded. SC is used as feedback. Low-pass function is observed at the output of the third op-amp. The output of the second op-amp gives Band-pass function. The High-pass function is seen at the inverting input of the first op-amp. # Circuit Analysis and Design Equations Op-amp (µA 741) is an internally compensated op-amp, which represented by "Single pole model", ( ) ( ) 0 0 0 / A s A S ? ? = +(1) Where, ( ) 0 0 / / , A s A S GB S ? = =(2) Where, 0 S ? >> ?? ???? = ? ???? 1 ???? 2 ???? 3 ?? 4 ?? 1 ?? 3 +?? 2 ?? 2 +?? 3 ??+?? 4 The voltage transfer function for band-pass filter: ?? ???? = ? ?????? 1 ???? 2 ?? 4 ?? 1 ?? 3 +?? 2 ?? 2 +?? 3 ??+?? 4 The voltage transfer function for high-pass filter: ?? ???? = ?? 3 ?? 4 ?? 1 ?? 3 +?? 2 ?? 2 +?? 3 ??+?? 4 Where ?? 1 = ?? 1 + ?? 2 + ?? 3 + ?? 4 ?? 2 = ???? 1 ?? 1 + ???? 2 ?? 2 ?? 3 = ???? 1 ???? 2 ?? 2 + ???? 2 ???? 3 ?? 3 ?? 4 = ???? 1 ???? 2 ???? 3 ?? 3 The circuit was designed using coefficient matching technique i.e. by comparing these transfer functions with General Third-order transfer functions [10]. The general Third-order transfer function is given by T(S) = 3 0 2 0 2 0 3 0 1 2 2 3 3 S Q 1 1 S Q 1 1 S S S S ? + ? ? ? ? ? ? ? ? + ? + ? ? ? ? ? ? ? ? + ? + ? + ? + ? + ? (6) By comparing (3), (4), and ( 5) with (6), we get the design equation as This shows that the op-amplifier is an "integrator", Thus Electronically Tunable Third-Order Switched-Capacitor Filter transfer function at three different terminals are given below. The voltage transfer function for low-pass filter: (3) (4) (5) Electronically Tunable Third-Order Switched-Capacitor Filter with Feedforward Signal to minimize Overshoot (GB) and four Capacitors with MOSFET, which form V. ?? 1 + ?? 2 + ?? 3 + ?? 4 = 1 ???? 1 ?? 1 + ???? 2 ?? 2 =W {1+1 /Q} (8) ???? 1 ???? 2 ?? 2 + ???? 2 ???? 3 ?? 3 =W {1+1/Q (9)(7) # Sensitivity The sensitivities of 0 ? and Q in this Electronically Tunable third-order Switched-capacitor Filter are as follows. ?? C 1 ?? 0 = ? 1 3 C 1 ?? C 2 ?? 0 = ? 1 3 C 2 ?? C 3 ?? 0 = ? 1 3 {C 3 ? 1} ?? C 4 ?? 0 ? 1 3 C 4 ?? ???? 1 ?? 0 = ?? ???? 2 ?? 0 = ?? ???? 3 ?? 0 = 1 3 S C 1 Q = ? 1 3 (1 + ??)C 1 S C 2 Q = ?(1 + ??)C 2 ? 1 (?? 2 + ?? 3 ) ? 1 3 ? ?? C 3 ?? = ?(1 + ??) ? 1 (?? 2 + ?? 3 ) ? 1 3 ? 2 3?? 3 ? ?? C 4 ?? = ? 1 3 (1 + ??) C 4 ?? GB 1 ?? = ?(1 + ??) ? ?? 2 ?? 2 + ?? 3 ? 2 3 ? ?? GB 2 ?? = ? 1 3 (1 + ??) ?? GB 3 ?? = ?(1 + ??) ? ?? 3 ?? 2 + ?? 3 ? 2 3 ? VI. # Experimental Set Up The circuit consists of three op-amps (µA 741) with wide identical gain bandwidth product (GB) and different Values of circuit merit factor Q with center frequency f 0 =15 KHz. The general operating range of this filter is 10 Hz to 1.2 MHz The value of GB (GB 1 =GB 2 =GB 3 ) is ( 2?? × (5.6) × 10 5 rad/sec). The table1 shows the capacitor values for different circuit merit factor Q. MOSFETs are driven by two nonoverlapping clocks. The input voltage of 0.5mV is applied. The table1 shows the capacitor values for different circuit merit factor Q. # VII. # Result and Discussion Following observations are noticed for Lowpass, Band-pass and High-pass at corresponding terminals. # a) Low-Pass Response The figure 3 shows the low pass response for different values of circuit merit factor Q. The maximum pass-band gain varies between 91.3dB to 94dB and the gain roll-off per octave varies between 17 to 18dB/octave. But in previous reported configuration maximum pass-band gain varies between 82dB to 87dB. Also, the gain roll-off per octave in stopband varies between 14 to 19dB/octave [14]. The maximum pass-band gain increase with increase in Global Journal of Researches in Engineering ( ) F Volume XIV Issue VII Version I ???? 1 ???? 2 ???? 3 ?? 3 =W(10) 0 3 four Capacitors with MOSFET, which form Switched -Capacitor. The circuit performance is studied for values of circuit merit factor Q but after Q?4 this value gets stabilized at the maximum pass-band gain. The 18dB/octave for third order switched-capacitor filter. The response shows no overshoot for all the values of circuit merit factor Q where as the previous reported configuration shows overshoot with increase in Q (for Q=10, the overshoot is 14 dB) [14]. # b) High-pass response The figure 4 shows the High pass response for different values of circuit merit factor Q. The Gain roll-off in stop-band varies between 17.4dB to 18dB/octave which is close to the ideal value of 18 dB /octave for third order Switched-Capacitor filter .Also, the gain is stabilized for all values of circuit merit factor Q ? 0.4 . But in previous reported Configuration, the Gain roll-off in stop-band varies between 11 to 12dB/octave. Also, the gain can't be stabilized at 0dB for all values of circuit merit factor Q [14]. The peak gain for overshoot is minimizing from 44dB to 5dB due to the feedforward input signal that's given to the second Op-amp in the proposed circuit configuration. The gain gets stabilized almost at 0 dB for all values of Q ? 0.4. The response shows overshoot for all the values of Q ? 4. The analysis for the responses are summarizes in the table 3. c) Band-pass response The figure 5 shows the Band-pass response for different values of circuit merit factor Q. The maximum pass-band gain varies between 39dB to 62.5dB. Also, the bandwidth varies between 43.2 KHz to 59.2 KHz and Gain roll-off in trailing part varies between 11.6 to 12dB/octave. But in previous reported configuration the maximum pass-band gain varies between 33dB to 73dB.Also, the bandwidth varies between 59.4 KHz to 22 KHz and Gain roll-off in trailing part varies between 8dB/octave to 13dB/octave [14]. The maximum pass-band gain increases with increase in circuit merit factor Q. The bandwidth decreases with increasing in values of circuit merit factor Q but after Q?4 this value gets stabilized at 43.2 KHz. For lower values of circuit merit factor Q, this filter can be used for wide bandwidth and for higher values of circuit merit factor Q it can be used for narrow bandwidth. There is no shift in the central frequency. It is also observed that the pass band distribution of frequency is symmetric for both sides. The gain roll-off/octave in leading and trailing part of the response is same. The circuit works better band pass response for Q ?0.4. # VIII. # Conclusions A realization of Electronically Tunable Third-Order Switched-Capacitor Filter with Feedforward Signal to minimize Overshoot has been proposed. The filter circuit can be used for both narrow as well as for wide bandwidth, so this circuit works for electronically tunable bandwidth. The gain roll-off for this circuit is close to the ideal value. The gain gets stabilized almost at 0 dB for all values of Q ? 0.4.The Low pass filter function works practically only for higher merit factor Q. The circuit the proposed circuit configuration, the peak gain for overshoot is minimizing from 44dB to 5dB due to the feedforward input signal. 1![Figure 1 : Circuit diagram for operation of the switchedcapacitor](image-2.png "Figure 1 :") 1values of QQ?? 1 (µf)?? 2 (µf)?? 3 (nf)?? 4 (µf)0.1286.87.919.2705.30.491.32.519.2906.20.858.71.619.2939.7152.21.419.2946.4432.60.919.2966.5829.30.819.2909.81028.70.7719.2970.5 2Graph (Fig. 3)QMax. Passband Gain (dB)f 0L (kHz)f 0L (kHz) f 0 ?Gain Roll-off in stop band dB/Octave Octave (kHz) starting at (kHz)0?191.3205172150?493.4382317.7900.893.643281860193.8432818604944429186089444291860109444291860 3Graph (Fig. 4)Gain Roll-off inGainQf 0H (kHz)f 0 ? f 0H (kHz)dB/Octavestop band Octave Starting at ( kHz )Stabilization Peak Gain of overshoot (dB) f (dB) S (kHz)0.1 158 14317.42-346000.43722183.5017000.81941850460113218504604132185040381321850405101321850405 4Overshoot observed in dBQ Previous Reported circuit Proposed circuit0.100100538310445 5Gain roll-off values are close to ideal value ofXIV Issue VII Version I( ) F VolumerGlobal Journal of Researches in EngineeringQMax. Passband gain (dB)f 1 (kHz)f 2 (kHz)BW (kHz)dB/ octave Gain Roll-off / octave in stop Octave starting at (kHz) dB/ octave Octave starting at (kHz) band Leading Part Trailing Part0?1390.4 55 54.6 5.80.6122060?4520.8 60 59.26312610.8571.2 52 51.86312401581.3 51 50.7631241 Year 2014 © 2014 Global Journals Inc. (US) © 2014 Global Journals Inc. (US) * Study of active-R second order filter using feedback of non-inverting terminal GNShinde PBPatil Bulletin of Pure and Applied Sciences 21 1 2002 * Analog active filters MGhausi IEEE Transactions on Circuits and Systems 31 1984 * Applications of Switched capacitor circuits in active filters and Instrunental Amplifiers WilliamRGrise 1999 * Active-R biquadratic filter using positive feedforwardsignal GNShinde PBPatil ABKadam PRMirkute BRI'S JAST 5 2002 I and II * MOS switched capacitor sample data filters AvinashKumar SKSaha 1983 * GNShide SRBhagat tunble bandwidth third order switched-capacitor with multiple feedbacks filter for different center frequencies" Engineering 2010 2 * Design of a tunable frequency CMOS fully differential fourth order Chebyshev filter JinguangJiang YaonanWang Microelectronics Journal 37 2006 * Designof current mode square root domain bandpass filter withreduced voltage GJYu CYHuang JJChen BDLiu Analog-Integrated Circuit and Signal Processing 44 2005 * Low universal filter using only current followers as active elements RSenani SSGupta International Journal of Electronics and Communication 60 2006 * Design of a tunable frequency CMOS fully differential fourth order chebyshe filter JGJiang YNWang Microelectronics Journal 37 2006 * Synthesis of transfer functions using the operational amplifier pole Srinivasan Int. J. Electronics 40 1 1976 * Applications of Switched capacitor circuits in active filters and Instrumental Amplifiers WilliamRGrise 1999 3 * Design of a tunable frequency CMOS fully differential fourth order Chebyshev filter JinguangJiang YaonanWang Microelectronics Journal 37 2006 * Feed Forward Third Order Switched Capacitor Filter for different circuit merit factor Q values GNShinde SRBhagat Archives of Applied Science Research 2 1 2010 * A highperformance continuosly Tunable Bandpass Filter YonghyunShim MinaRais-Zaden IEEE Transactions on microwave theory and Technique 60 8 2012