CFOA-based state-variable biquad and its high-frequency compensation

Abstract

Abstract:A four-Current feedback operational amplifier (CFOA)-based state variable biquad is described which permits the accommodation of or compensation for the z-pin parasitic impedances of the CFOAsand offers a number of advantages over previously known CFOA-based biquad configurations. The workability of the circuit has been confirmed by SPICE simulation results based on commercially available AD844 type CFOAs.

Symbolic formulation method for mixed-mode analog circuits using nullors

“…The proposed formulation method is very suitable for opamp [7], current conveyors [2], CFOA [10], and in general for mixed-mode circuits at the integrated circuit level [11]. Moreover, the nullor also is quite useful in the synthesis of analog circuits [12], where the non-ideal performance analysis including the parasitic elements can be done by applying the proposed NA-formulation method.…”

“…The solution generates the exact transfer functions of the low-pass (LP), bandpass (BP) and high-pass (HP) filter responses given by (5), (6) and (7), respectively, where D(s) is given by (8). (9), (10) and (11), and D(s) is written in (12). The cut-off (LP and HP) or center frequency (BP) is approximated by (13).…”

New Universal Biquads Employing CFOAs

“…Due to these advantages, CFOAs are being regarded as attractive alternative building blocks for realizing filters, and a number of CFOA-based multifunction filters have been proposed in the literature so far [5]- [17]. Filters employing grounded capacitors (GCs) such as those in [5] and [11]- [17] are desirable from the viewpoint of integrated circuit (IC) implementation [18].…”

“…Filters employing grounded capacitors (GCs) such as those in [5] and [11]- [17] are desirable from the viewpoint of integrated circuit (IC) implementation [18]. Among the previously known CFOA-based biquads, those in [6]- [10] (MISO)-type biquads that suffer from one or more of the following drawbacks: 1) nonavailability of tunability of all the three filter parameters [namely gain , BW, and resonant frequency ]; 2) employment of one or both floating capacitors in some responses; and 3) undesirable capacitive input impedance in several cases.…”

“…On the other hand, the circuits from [5] and [11]- [17], which realize fixed-topology single-input-multiple-output (SIMO)-type biquads (with which this brief is concerned), also suffer from one or more of the following drawbacks: 1) availability of only three responses as against five desired (as in [5], [12], [16], and [17]); 2) nonavailability of tunability of all the three filter parameters (as in [5] and [11]- [16]); and/or 3) requirement of a relatively larger number (five to ten) of CFOAs (as in [11], [14], and [15]). …”