Realization of second-order differential type class-AB log-domain universal filter without changing circuit configuration

In this paper, a new current-mode second-order differential type class-AB log-domain universal filter is proposed. The design is based on the state-space synthesis method. It has simple differential type class-AB structure and using minimum components. The proposed filter has one input and five outputs and can simultaneously realize lowpass (LP), highpass (HP), bandpass (BP), notch (N), and allpass (AP) responses without any changes in the circuit topology. The natural frequency, and the quality factor of the filter can be electronically tuned by changing external currents. Only NPN transistors and grounded capacitors were used, and operated with single power supply of 2 V. PSPICE simulations are given to confirm the theoretical analysis.