Offset cancelling circuit

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Wiegerink, Remco J. ; Seevinck, Evert ; de Jager, Wim (1989)
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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 eliminated
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    2E0+.O0O0- Wim de Jager \\'I\ born in DocLuni The Xcrhcr I,uid\. o n March 12. 1930 From 1056 to 1959 he \\'I\ educ'ited at the €ITS for Elcctroiiic\ iii kill\er\uiii. The \etherland\. reiei\in_pthe HcitroiiIC\ Tcihniii~indrplniiia in 1929 From l Y 5 Y to 1967 he s e n d i n the Ro\.iI From 1962 t o 1966 tic \\a\ aith aiiipcn f'ibrieken i n EindIio\cn and e ;Cc.therland\. uhcre tic \rorkcd on the dc\ign of tc\t and niea~itrenientin\trun Since 1966 lic h,i\ heen a member oi the

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