Electronically tunable allpass filter: linear VCO design

Abstract

A new electronically tunable allpass filter (ETAF) realization using the composite Current Feedback Amplifier (CFA) and Multiplication Mode Current Conveyor (MMCC) building blocks is proposed. First order non-minimum phase function with electronically variable output phase is derived. Extension of the filter to a linear quadrature-VCO design is then implemented. Simulation test responses of all these functions are satisfactorily verified.

Quadrature voltage control oscillator with a linear tuning law

“…Response as in Fig. 1 e of the proposed design physical hardware implementation is verified after configuring the ABB with commercially available CFA (AD‐844) and MMCC (CFA and Multiplier‐AD534/835) devices [13, 18]. The theoretical f o ‐tuning law was tested with PSPICE simulation; lower‐tuning range verified with AD‐534 ( k = 0.1), whereas higher‐tuning range had been tested with AD‐835 ( k = 1) coupled with a resistive voltage divider of 0.1 scale.…”

“…There are a number of electronically tunable (ET) quadrature oscillator (QO) designs using various types of active building blocks (ABBs) in recent literatures [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]; only few of these provide linear tuning law. The QO is found to be a useful tool for various electronic signal processing and measurement applications, namely quadrature mixer, Single Side Band (SSB)-wave generator and for built-in self-test [17] of integrated analogue filters.…”

“…Effects of device non‐idealities had been examined which indicate that ω o ‐sensitivity relative to port mismatch‐ ɛ is low; however, the parasitics tend to affect the higher‐tuning range. The frequency‐roll‐off feature of port transfer ratios becomes dominant at very high‐frequency ranges since the roll‐off poles appear at hundreds of megahertz [13, 30].…”

Voltage-variable inductor based linear voltage controlled quadrature oscillator implementation

“…Albeit quite a number of electronically tunable quadrature oscillators had been reported in recent past [5,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29], only a few have a linear tuning law as listed in Table II. These are mostly tuned by bias current (I b ) of some trans-conductance device, which attracts issues of thermal voltage (V T ) and quiescent dissipation.…”