A Low-Power Low-Voltage Second-Order High-Pass Butterworth Leapfrog Filter

A low-power bipolar continuous-time low-frequency high-pass second-order Butterworth filter that works in the current domain and operates from a single 1.3-V battery is presented. The filter contains two adjustable integrators. These integrators are realized by means of a capacitance and an adjustable transconductance amplifier with an indirect output. The complete filter, including all capacitances needed, can be integrated in a standard full-custom IC process. A semi-custom realization is shown. The filter demonstrates operation with battery voltages down to IV with less than 16 μW power consumption and a dynamic range of 50 dB. Its cutoff frequency can be varied exponentially with a control current from 100 Hz - 1 kHz.