Realization of allpass filters using operational transresistance amplifier (OTRA)

A new voltage-mode allpass filter configuration is proposed. The presented circuit uses a single operational transresistance amplifier (OTRA) and can realize both first- and second-order allpass filtering functions. The proposed circuit is insensitive to parasitic input capacitances and input resistances due to internally grounded input terminals of the OTRA. It provides an alternative solution to the realization of phase equalizer; quadrature oscillator and high-Q bandpass filter for analog signal processing applications. The theoretical results are verified with PSPICE simulations using a CMOS realization of the OTRA. The feasibility of the proposed allpass filter is illustrated by the design of a quadrature oscillator.