Automatic gain control circuit of audio power amplifier

Abstract

The invention discloses an automatic gain control circuit of an audio power amplifier, which comprises a fully differential operational amplifier and an automatic gain control circuit, wherein the in-phase and anti-phase input ends of the amplifier are provided with divider resistors respectively; feedback resistors are arranged between the in-phase input end and an output end as well as between the in-phase input end and the output end respectively; a biasing circuit is connected the fully differential operational amplifier; the input end of the control circuit is connected with the output end of the fully differential operational amplifier; a reference voltage circuit is connected with the control circuit; and the output end of the control circuit is connected with an adjustable resistor at the input end of the fully differential operational amplifier. In the invention, an output signal is compared with a reference voltage to obtain a digital signal, and the digital signal is used for controlling the front resistance value of the input end of the amplifier, so that a fixed gain can be kept for amplifying an audio signal during inputting of a small signal, closed-loop gain in the circuit is reduced during inputting of a large audio signal, and high linearity and low harmonic distortion of an output audio signal are ensured.

Description

【Technical field】 [0001] The invention relates to an audio frequency power amplifier in the field of large-scale analog integrated circuit design, in particular to an audio frequency power amplifier automatic gain control circuit. 【Background technique】 [0002] figure 1 It is a circuit structure of a traditional power audio amplifier in the prior art. In this circuit structure, the audio signal is amplified by a fully differential operational amplifier. The output of the audio signal changes with the input. When a large audio signal is input (Vi+ and Vi- are relatively large), the audio input signal is amplified by a fully differential operational amplifier, and the output Vo- and Vo+ are also relatively large, resulting in The output peak value of the audio signal is relatively large, and if the signal is modulated and demodulated, the demodulated signal will produce top distortion, resulting in a large amount of harmonic distortion and poor sound quality. [0003] In th...

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Problems solved by technology

[0004] The technical problem to be solved by the present invention is to overcome the defects in the above-mentioned prior art, that is, when a large audio signal is inpu

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