New resistorless and electronically tunable realization of dual-output VM all-pass filter using VDIBA

Abstract

In this paper, a new active element called voltage differencing inverting buffered amplifier (VDIBA) is presented. Using single VDIBA and a capacitor, a new resistorless voltage-mode (VM) first-order all-pass filter (APF) is proposed, which provides both inverting and noninverting outputs at the same configuration simultaneously. The pole frequency of the filter can be electronically controlled by means of bias current of the internal transconductance. No component-matching conditions are required and it has low sensitivity. In addition, the parasitic and loading effects are also investigated. By connecting two newly introduced APFs in open loop a novel secondorder APF is proposed. As another application, the proposed VM APF is connected in cascade to a lossy integrator in a closed loop to design a four-phase quadrature oscillator. The theoretical results are verified by SPICE simulations using TSMC 0.18 lm level-7 CMOS process parameters with ±0.9 V supply voltages. Moreover, the behavior of the proposed VM APF was also experimentally measured using commercially available integrated circuit OPA860 by Texas Instruments.Keywords Analog signal processing Á All-pass filter Á Electronically tunable circuit Á Four-phase quadrature oscillator Á Loading effect Á Resistorless filter Á Voltage-mode Á Voltage differencing inverting buffered amplifier (VDIBA)

Electronically tunable allpass filter: linear VCO design

“…2; error e was seen to be small for the ETAF while the THD-level (upto 7 th harmonic) for both ETAF and QVCO is quite low compared to [10,29,30,32]. Tuning error in Table II is measured upto 3.3 MHz by a new method here by evaluating the phase margin of the loop at gain-crossover frequency.…”

“…A relevant comparative summary to this extent is presented in Table I. It may be seen that albeit electronically tuned QVCOs are also proposed earlier [10,26,27,28,29,30,31,32], but such an oscillator based on electronically tunable AP filters with linear tuning law had not yet been presented, as is seen by the comparative description in Table I below.…”

“…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].…”

“…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 ).…”

“…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.…”