Selective Filters and Sinusoidal Oscillators Using CFA Transimpedance Pole

Abstract

Using a single current feedback amplifier (CFA) device, two new variable frequency sinusoidal RC oscillators are presented. The transadmittance pole of the device (AD-844) has been utilized in the design for generating sine wave signals covering a range of 1 MHz ≤ f 0 ≤ 31 MHz. Under open-loop conditions, both circuits exhibit resonance characteristics at moderate Q-values (1 ≤ Q ≤ 9). These responses have been experimentally verified with hardware circuit implementation and PSPICE macromodel simulation.

Single-CFA first-order allpass filter

“…The second order filter uses a single-ended DVCCTA element based lossless inductor L, shunted to C as the Y-admittance in Fig. 1(a); it had been configured with CFAs wherein the devices had been tested a-priori for their nodal relations and parasitic behavior so that the overall filters are built with matched properties [15,22,25]. …”

“…At relatively lower frequencies a magnitude error may also be postulated as o % ð1 À j" i jÞ, o % ð1 À j" v jÞ and o % ð1 À j" jÞ albeit these errors are quite low [18,25]. It has been reported that the pole frequencies (!…”

Third order lowpass Butterworth filters using unity gain current amplifiers

“…We next Table I. Details of realizability design examined the effect of the device parasitic capacitances appearing internally at the z-node of CDBA (C z1 ) and at CFA (C z2 ), and also at the y-node (C y ) of the CFA [11,14,15]. Associated with these small capacitors (C z1,2 ∼ 3 pF to 6 pF), there are shunt internal resistances (r y ∼ 3 MΩ and r z ∼ 6 MΩ) which were neglected since we followed the design such that (R/r y,z ) 1.…”

“…Recently some such filters using voltage buffers and current amplifiers are reported [3]. With the availability of CDBA [4] and CFA [5,6] type active building blocks, there is renewed interest on analog function circuits using these devices [7,8,9,10,11,12,13,14]. These elements are essentially unity-gain current amplifiers with the provision of additional voltage follower feature.…”

“…The literature describes several advantageous properties [3,6,15] of these elements. Albeit some second order filters [7,8,9,10,11,12,13,14] are now available, a third order Butterworth filter design scheme using these devices had not yet been reported. We therefore present some new realizations of these filters wherein a CDBA based dominant pole-pair forming stage is coupled to a CFA based single-pole stage.…”