Amplifiers – Modulator-demodulator-type amplifier
Patent
1994-09-20
1996-04-16
Mullins, James B.
Amplifiers
Modulator-demodulator-type amplifier
330107, 330260, 330294, H03F 1134, H03F 338
Patent
active
055086632
ABSTRACT:
In a pulse width modulation amplifier use for audio devices, an input side of an operational amplifier of a pulse width modulation amplifier is used as an alternating current amplifier by grounding its negative terminal through a series circuit formed with a resistor and a capacitor. The direct current gain of the operational amplifier becomes 1, and the offset voltage decreases to the inherent offset voltage of the operational amplifier. The operational amplifier has no direct current coupling with next amplifying stage and hence, the offset voltage is not increased after leaving the operational amplifier. Also, the pulse width modulation amplifier includes negative feedback circuits connecting a final output stage to the input of the operational amplifier including a low-pass filter, each low-pass filter having a grounded capacitor, wherein the negative feedback signal is transmitted through another capacitor to the input of the operational amplifier to provide an alternating current coupling to reduce the influence of the carrier and its higher harmonics and other noises leaked to the operational amplifier through the feedback circuit.
REFERENCES:
patent: 4673889 (1987-06-01), Cini et al.
patent: 4987381 (1991-01-01), Butler
Sierra, "Active RC Filters Without Inductors", IBM Technical Disclosure Bulletin, vol. 15, No. 6, Nov. 1972 pp. 1788, 1789.
Matsushita Electric - Industrial Co., Ltd.
Mullins James B.
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