Offset cancelling circuit

1 June 1989

journal article
Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Journal of Solid-State Circuits

Vol. 24 (3) , 651-658
https://doi.org/10.1109/4.32022

Abstract

A monolithic offset cancelling circuit to reduce the offset voltage at an integrated audio-amplifier output is described. This offset voltage is detected using a low-pass filter with a very large time constant for which only one small on-chip capacitor is needed. The circuit was realized with a bipolar cell-based semicustom array. Measurements have shown that a -3-dB bandwidth below 5 Hz can be realized with a capacitor value of 50 pF. The resulting offset voltage at the audio-amplifier output was 2.5 mV. The offset cancelling circuit increases the wideband noise voltage at the audio-amplifier output by 0.15-MV RMS over the frequency range of 10 Hz to 30 kHz. The use of the offset cancelling circuit eliminates the need for a large external electrolytic capacitor. If an audio amplifier with a single supply voltage is used, a second electrolytic capacitor, needed to obtain a stable reference at half the supply voltage, can be eliminate

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