A Compact Electronically Controllable Biquad Filter Synthesizing from Parallel Passive RLC Configuration

This paper describes a synthesis of versatile voltage-mode biquad filter. The presented multifunction filtering topology has one output node and four input nodes for applying input signal. The principle to synthesize the presented versatile second order filter is based on the parallel connection of the passive RLC circuit. The proposed filtering structure is very compact employing single active elements, voltage differencing differential difference amplifiers (VDDDA), two passive resistors and a couple of passive capacitors. In the offered circuit, five voltage-mode biquadratic filtering functions, band pass (BP), low pass (LP), high pass (HP), notch and all pass (AP) filter with unit voltage gain. These filtering functions are given by selecting the voltage signal to appropriate input voltage nodes. The tuning feature of the angular frequency (ω0) is done electronically by respective bias current. Additionally, the quality factor (Q) is tuned without affecting the ω0 by changing value of resistor. The proposed circuit is designed and supported by Pspice simulation. The implementation of VDDDA is realized from off-the-shelf available ICs, LM13700 and AD830. Several simulation results are obtained and confirmed the design and theorical analysis.