Electronically tunable first-order all-pass circuit employing DVCC and OTA

Single-CFA first-order allpass filter

“…Realization of APF had been proposed earlier with various types of active building blocks (ABBs), e.g., voltage op-amp [1,2], current conveyor-CC [3,4], DDA [5], DDCC [6], CDTA [7], CITA [8], DVCC [9,10] VD-DIBA [11], DXCCII [12], VDIBA [13] and DVCCTA [14]. Here we present a simple single CFA circuit topology for first order APF realization using a grounded capacitor.…”

“…Literature study reveals that APFs proposed recently, are based on active building blocks which are either assorted version of two types of devices [7,8,11,12], or are topological variants of a primary device (e.g., OTA or CC/DVCC) conjoined with additional voltage/ current differencing unit [4,5,6,9,10] (VDU/CDU); hence an elaborate set of device-nodal relations with associated realizability constraints. A description of these implementations are listed in Table I.…”

Electronically tunable allpass filter: linear VCO design

“…Albeit most of these designs are passive tuned, only few versions of electronically tunable topologies are also reported recently [10,11,12]. These designs use bias current (I b ) control of trans-conductance (g m ) tuning of OTA type devices for phase variation; this approach requires additional current processing hardware and involvement of thermal voltage (V T ).…”

“…Realization of several variants of AP filters had been reported in the recent past following the appearance of various types of active building blocks, e.g., voltage op-amp [1], current conveyor [2,3], DVCCTA [4], DXCCII [5], DDA [6], CITA [7], DDCC [8], VD-DIBA [9], VDIBA [10], DVCC with OTA [11] and DO-CCC [12]. Albeit most of these designs are passive tuned, only few versions of electronically tunable topologies are also reported recently [10,11,12].…”

“…Here we utilize the relatively new MMCC element [13] coupled with a readily available CFA device as a composite building block for the ETAF design that provides direct variation of the phase by the control voltage (V) of the MMCC element. Such composite building block configuration approach were used in some previous work, viz., DVCC with OTA [11], OTA with unity-gain difference amplifier (UGDA) [9], OTA with inverting voltage buffer VDIBA [10] and MMCC with DVCCTA based synthetic-L [14] and MMCC-CFA based dual-input integrato; in [14] phase tuning is upto 200 KHz and in the latter, range is upto 1.8 MHz. Present work is also of composite MMCC-CFA building block category wherein we obtained better performance with respect to frequencyrange at low THD.…”