Tunable allpass filter for low voltage operation

A novel high-performance first-order allpass filter with electronically adjustable filter parameters is presented. The core of the circuit is an inverting unity gain amplifier with electronically adjustable output resistance, which leads to an allpass filter realisation with tunable time constant. The circuit is composed of a simple CMOS cascode circuit and a level shifter, and is also very suitable for low voltage operation, since it employs two active devices between its rails. SPICE simulation and experimental results verifying theoretical analyses are also given.