Amplifiers – With periodic switching input-output
Patent
1988-09-01
1989-05-23
Mottola, Steven
Amplifiers
With periodic switching input-output
330258, 330259, H03F 345
Patent
active
048334189
ABSTRACT:
An apparatus for nullifying the differential output offset voltage between the outputs of a differential amplifier and for setting the DC levels of the outputs to a known reference voltage includes a circuit which cross-couples the opposing AC output signals to obtain only the DC components of each signal. The apparatus further includes a first operational amplifier to generate a compensation voltage from the DC components of the outputs of the differential amplifier proportional to the amount of offset between the DC components of the outputs of the differential amplifier. The compensation voltage is fed back to the offset control inputs of the differential amplifier to reduce the differential offset voltage to substantially zero volts. The apparatus further includes a dual voltage divider network having a second operational amplifier that supplies a variable reference voltage to one terminal of each leg of the voltage divider network. The outputs of the differential amplifier each provided to a respective other terminal of the dual voltage divider network. The second operational amplifier has a reference voltage on one of its inputs. A signal responsive to the common mode output voltage from the differential amplifier is provided to the other input. The second operational amplifier provides an output voltage that is responsive to the common mode voltage output from the differential amplifier. The output voltage from the second operational amplifier provided to the terminals of the dual voltage divider network varies such that the voltage outputs from the voltage divider network have a common mode voltage substantially equal to the reference voltage.
REFERENCES:
patent: 3845404 (1974-10-01), Trilling
patent: 4363977 (1982-12-01), Tsuda et al.
patent: 4490682 (1984-12-01), Poulo
Quintus John J.
Sheehan Michael S.
Archive Corporation
Mottola Steven
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