Log-Domain First-Order Multifunction Current-Mode Filter Design

A new log-domain first-order multifunction filter is proposed in this paper. The proposed filter is systematically derived using the state-space synthesis procedure from a corresponding block diagram. It provides lowpass, highpass, and allpass responses simultaneously for a single input signal. The filter circuit has a very simple structure, since it uses only BJTs and a grounded capacitor. It can be electronically tuned by changing an external current. The filter has a greater bandwidth due to inherently current-mode and log-domain operation. PSPICE simulations are given to confirm the theoretical analysis.