Design of a log-domain differentiator and integrator based universal analog biquadratic filter

A novel implementation of a continuous-time universal analog biquadratic filter is presented. Using a log-domain differentiator and integrator along with a few current mirrors and current copiers, the low pass, high pass, band pass, band elimination (notch) and all pass filter transfer functions are realized. The filter has been designed using a purely current-mode approach. The filter realized is electronically tunable by altering the magnitude of the bias/control current sources. Both the differentiator and the integrator used here have been designed using bipolar junction transistors. The design can be extended and realized with MOSFETs operating in the weak inversion region. The concept has been validated by circuit simulations.