Cascadable allpass and notch filters employing single operational transresistance amplifier

A new voltage-mode filter configuration is proposed. The presented topology uses single operational transresistance amplifier (OTRA) and can realize first-order allpass, second-order allpass and notch filtering functions. The proposed circuits are insensitive to parasitic capacitances and resistances due to internally grounded input terminals of OTRA. Low output impedance of the configuration enables the circuits to be cascaded without additional buffers. The theoretical results are verified with PSPICE simulations using a CMOS realization of OTRA. Experimental work is also carried out. The feasibility of the proposed first-order allpass filter is illustrated on the design of a quadrature oscillator.