Differential Type Class-AB Second-Order Log-Domain Notch Filter

In this paper, a new current-mode second-order differential type Class-AB log-domain notch filter is proposed. It is systematically designed using state-space synthesis method. The filter circuit is current-mode, Class-AB and differential type. In the circuit, the input and the output values, and dominant variables are all currents. Input and output currents are also differential signals. Only transistors and grounded capacitors are required to realize the filter circuit. Three cases of the second-order notch filter were obtained. The regular notch was obtained when omega_n=omega₀, the low-pass notch was obtained when omega_n>omega₀, and the high-pass notch was obtained when omega_n>omega₀. The center frequency, the notch frequency, the quality factor, and gain of the filter can be electronically tuned by changing external currents. Time and frequency-domain simulations are performed using PSPICE program for the filter to verify the theory and to show the performance of it. For this purpose, the filter is simulated by using idealized bipolar junction transistor models and AT&T CBIC-R (NR200N-2X NPN), (PR200N-2X PNP) type transistors.