Differential Type Class-AB Log-Domain Third-Order Universal Filter

A new current-mode third-order differential type class-AB log-domain universal filter is proposed in this study. The design is based on the state-space synthesis method. The proposed filter can realize lowpass (LP), highpass (HP), bandpass (BP), lowpass notch (LPN), highpass notch (HPN), and allpass (AP) responses by changing external currents without any changes in the circuit topology. Butterworth, Chebyshev, and Bessel filter responses of the third-order universal filter are obtained without changing circuit configuration. Also, several different Chebyshev responses can be obtained by changing external currents. The parameters of proposed filter are tunable. Only NPN transistors and grounded capacitors are required to realize filter circuit. PSPICE simulations are given to confirm the theoretical analysis.