Indian Journal Engineering & Materials Sciences Vol. April pp. 87-9 Voltage-mode universal biquad with five inputs and two outputs using two current feedback amplifiers Jiun-Wei Horng* Department Electronic Engineering Chung Yuan Christian University Chung-Li Taiwan Received August ; accepted February A voltage-mode universal biquadratic filter using two current-feedback amplifiers (CFAs two capacitors and four resistors is presented. The new circuit has five inputs and two outputs and can realize all the standard filter functions which are lowpass bandpass highpass notch and allpass filters without changing the circuit topology. Some the derived filter types enjoy the advantage having two simultaneous output filter responses. One the derived filter types enjoys the advantage realizing non-inverting lowpass and inverting bandpass signals simultaneously with all the parasitic impedances the CFAs can be absorbed by the outside passive components. Because the output impedance the CFA is very low the output terminals the proposed configuration can be directly connected to the next stage. Keywords: Current-feedback amplifier Universal biquad Active filter The current feedback amplifier (CFA can provide not only constant bandwidth independent closed-loop gain but also high slew-rate capability. The CFA integrated circuit (IC is available like AD8. It is both interesting and practically significant to use the CFA as a basic building block to realize analogue signal processing circuits -. Several realizations voltage-mode universal biquadratic filters with multiinput terminals have been reported in the literatures 5-8. Liu and Wu 5 used two CFAs two capacitors and four resistors to implement such a universal biquad. Each the universal biquadratic filters reported in references 6-8 employs two CFAs two capacitors and three resistors. Horng proposed two universal biquadratic filters 9 by using two CFAs two capacitors and two resistors or one CFA one voltage follower two capacitors and two resistors respectively. Two universal biquads each uses two CFAs two capacitors and two resistors are presented. However these circuits 8- require other active elements for unity gain inverting the input voltage signals in the realization allpass responses. Hou et al. proposed a biquadratic filter with three inputs and one output using two capacitors three resistors and only one CFA. However the output impedance is not small. Moreover it needs a unity *E-mail: jwhorng@cycu.edu.tw gain inverting input for the notch response and the allpass filter signal cannot be obtained from the same circuit configuration. Horng et al. proposed a universal biquadratic filter with four inputs and one output using two capacitors three resistors and only one CFA. However the output impedance is not small and it needs a unity gain inverting input for the allpass response. Other researches 56 presented two voltage-mode biquads each with three inputs using five (or two resistors two capacitors and one CFA. However each these two circuits requires other active components for amplifying the input signals in the filter realizations. Moreover the reported universal biquads 5-7 9-6 can obtain only one filter type in each circuit realization. Nikoloudis and Psychalinos 7 proposed a voltage-mode high input impedance universal biquad by using four CFAs two grounded capacitors and five resistors. However it uses too many active and passive components. Yuce 8 proposed a voltage-mode universal biquad by using one so called specific current feedback operational amplifier (SCFOA two capacitors and three resistors. However the SCFOA is not commercially available and the port relations a SCFOA are equivalent to the port relations two secondgeneration current conveyors (CCIIs. In this paper a new voltage-mode universal biquadratic filter with five inputs and two outputs is
88 INDIAN J. ENG. MATER. SCI. APRIL presented. The proposed circuit can realize all the standard filter functions from the same circuit configuration. With respect to the biquadratic filters reported in references - the output impedance the proposed circuit is small which makes the circuit cascadable without additional buffer. With respect to the universal biquads in references 8-6 the proposed circuit needs not other active elements for unity gain inverting the input signals or amplifying the input signals in the realizations all filter responses. With respect to the universal biquads reportedin references 5-79-7 one more standard filter response can be obtained from some derived filter types in the proposed circuit. Moreover one the derived filter types in the proposed circuit has the feature realizing non-inverting lowpass and inverting bandpass signals simultaneously with all the parasitic impedances the CFAs can be absorbed by the outside passive components. Comparisons the proposed circuit with those previous works as the following aspects are given in Table. Proposed Circuit The circuit symbol a CFA is shown in Fig.. This circuit is equivalent to a plus-type CCII with a voltage buffer 9. Its characteristic can be expressed as: i v i y x z v i v y x z and v o v z ( The proposed circuit comprises two CFAs two capacitors and four resistors is shown in Fig.. Circuit analysis yields the output voltages as: V V ( sc + G G GV in + ( sc + G G GV in + sc ( sc + G G Vin + GG Vin + scgv in5 s CC + s[ C ( G G + C G ] + ( G G G + G G o GG Vin GGV in scg Vin + ( sc + G G V + sc ( sc + G V in in5 o s CC + s[ C ( G G + C G ] + ( G G G + G G ( ( From Eqs ( and ( we can see the following: If V in V in V in V in5 (grounded V in V in and G G then an inverting bandpass filter is Table Comparisons some multi-inputs biquads Reference Number active devices Number passive components Needs other active devices Low output impedance Kinds filter functions [5] 6 no yes [6] 5 no yes [7] 5 no yes [8] 5 yes yes [9] yes yes [] yes yes [] yes yes [] yes yes [] 5 yes no [] 5 yes no [5] 7 yes yes [6] yes yes [7] 7 no yes Proposed circuit 6 no yes Fig. Circuit symbol current-feedback amplifier Fig. The proposed voltage-mode universal biquadratic filter
HORNG: VOLTAGE-MODE UNIVERSAL BIQUADRATIC FILTER 89 obtained at V o and a non-inverting lowpass filter is obtained at V o. If V in V in V in V in5 (grounded V in V in and G G then a non-inverting bandpass filter is obtained at V o and an inverting lowpass filter is obtained at V o. If V in V in V in V in5 (grounded V in V in and G G then a non-inverting highpass filter is obtained at V o and an inverting bandpass filter is obtained at V o. If V in V in V in V in5 (grounded and V in V in then a non-inverting lowpass filter is obtained at V o. If V in V in V in V in (grounded and V in5 V in then a non-inverting bandpass filter is obtained at V o. If V in V in V in5 (grounded V in V in V in and G G then a non-inverting notch filter is obtained at V o and a non-inverting lowpass filter is obtained at V o. If V in V in5 (grounded V in V in V in V in G G and G G then a non-inverting allpass filter is obtained at V o and a non-inverting lowpass filter is obtained at V o. If V in V in V in5 (grounded V in V in V in and G G then a non-inverting bandpass filter is obtained at V o. If V in V in V in (grounded V in V in5 V in C C and G G then a non-inverting highpass filter is obtained at V o. If V in V in (grounded V in V in V in5 V in C C and G G then a non-inverting notch filter is obtained at V o. If V in V in (grounded V in V in V in5 V in G G and C G C G then a non-inverting allpass filter is obtained at V o. Thus all standard filter functions: highpass bandpass lowpass notch and allpass can be obtained from the proposed circuit. Taking into account the tracking errors CFAs namely v x β(s v y v o γ(s v z and i z α(si x where α(s and β(s represent the frequency transfers the internal current and voltage followers the CFA respectively and γ(s represents the frequency transfer the output voltage follower the CFA. They can be approximated by the first-order lowpass functions. Assuming the circuits are working at frequencies much less than the corner frequencies α(s β(s and γ(s that is β ε and ε ( ε << is the input voltage tracking error γ - ε and ε ( ε << is the output voltage tracking error α ε and ε ( ε << is the current tracking error a CFA. The denominator the output voltage becomes: D( s s CC + s[ C ( G Gα β + CG ] + G ( G G α β + The parameters o and Q can be expressed as: G ( G G α β + ( (5 CC Q C C [ G ( G G α β + ] C ( G G α β + C G (6 The active and passive sensitivities this universal biquadratic filter are: o S C C G α β γ γ G ( G G α β G G α ( Gα β γ γ G β G α G GG Sβ o G G α β ( G Gα β C S Q C C G S Q C
9 INDIAN J. ENG. MATER. SCI. APRIL Fig. Non-ideal equivalent circuit the CFA includes the parasitic impedances (a (a (b Fig. Experimental frequency responses Fig. design with V in V in V in V in5 (grounded V in V in C C pf R R k Ω and R R 9 k Ω (a the inverting bandpass filter at V o and (b the non-inverting lowpass filter at V o G ( G G α β C G G α ( G α β γ γ G β C G α β + α (b Fig. 5 Experimental frequency responses Fig. design with V in V in V in5 (grounded V in V in V in C C pf R R k Ω and R R 9 k Ω (a the noninverting notch filter at V o (b the non-inverting lowpass at V o G G C G S Q α β γ γ G G α β C G α β S Q β + G G Gα β + GG C ( G Gα β + CG. ( α α β γ γ The non-ideal equivalent circuit model the CFA is shown in Fig. where R x is the x terminal input resistance R y //(/sc y represents the y terminal parasitic input impedance R p //(/sc p represents the
HORNG: VOLTAGE-MODE UNIVERSAL BIQUADRATIC FILTER 9 parasitic impedance at the compensation terminal z. The typical data sheet values the various parasitic for the bipolar CFAs (such as AD8 are: R x 5 Ω C p 5.5 pf R p M Ω R y M Ω and C y pf. The filter type (a is special interest among the eleven filter types because all parasitic impedances the two CFAs can be absorbed by the outside passive components two standard filter responses can be obtained simultaneously and using only grounded capacitors. Experimental Results Experiments for the circuit in Fig. have been carried out using AD8s from Analog Devices. Figure (a & b represent the experimental frequency responses for the bandpass (V o and lowpass (V o filters respectively design with V in V in V in V in5 (grounded V in V in C C pf R R k Ω and R R 9k Ω. Figure 5 (a & b represent the experimental frequency responses for the notch (V o and lowpass (V o filters respectively design with V in V in V in5 (grounded V in V in V in C C pf R R k Ω and R R 9k Ω. Conclusions In this paper a new voltage-mode universal biquadratic filter with five inputs and two outputs is presented. The new circuit can realize all the standard filter functions which are lowpass bandpass highpass notch and allpass filters without changing the circuit topology. The derived filter types (a (b (c (f and (g enjoy the advantage having two simultaneous output filter responses. The derived filter type (a enjoys the advantage realizing noninverting lowpass and inverting bandpass signals simultaneously with all the parasitic impedances the CFAs can be absorbed by the outside passive components and using grounded capacitors. Because the output impedance the CFA is very low the output terminals the proposed circuit can be directly connected to the next stage. References Shah N A & Malik M A Indian J Eng Mater Sci (5 78. Nandi R Sanyal S K & Bandyopadhyay T K Int J Electron 95 (8. Gupta S S Bhaskar D R & Senani R AEU Int J Electron Commun 6 (9 9. Horng J W Chou P Y & Wu J Y Active Passive Electron Components (communicated. 5 Liu S I & Wu D S IEEE Trans Instrum Meas (995 95. 6 Wu D S Lee H T Hwang Y S & Wu Y P Int J Electron 77 (99 59. 7 Abuelma atti M T & Al-shahrani S M Int J Electron 8 (996 75. 8 Shah N A Rather M F & Iqbal S Z Indian J Pure Appl Phys (5 66. 9 Horng J W IEEE Trans Instrum Meas 9 (. Horng J W Int J Electron 88 ( 5. Shah N A & Rather M F Indian J Pure Appl Phys (6. Tangsrirat W & Surakampontorn M AEU Int J Electron Commun 6 (9 8. Hou C L Huang C C Lan Y S Shaw J J & Chang C M Int J Electron 86 (999 99. Horng J W Chang C K & Chu J M IEICE Trans Fundam Electron Commun Comput Sci E85-A ( 97. 5 Sharma R K & Senani R AEU Int J Electron Commun 57 (. 6 Sagbaş M & Koksal M Frequenz 6 (7 87. 7 Nikoloudis S & Psychalinos C Circuits Syst Signal Process 9 ( 67. 8 Yuce E AEU Int J Electron Commun 6 (. 9 Svoboda J A Mcgory L & Webb S Int J Electron 7 (99 59. Fabre A Proc Inst Electr Eng Pt. G (99 9. Singh A K & Senani R IEEE Trans Circuits Syst-II: Analog Digital Signal Process 8 ( 5. Analog Devices INC Linear products data book (Norwood MA 99.