Silent start class-D amplifier

摘要

A Class-D amplifier includes a pre-amplifier having an input configured to receive an amplifier reference voltage signal which is ramped at start-up at a fast rate. An integrator has a first input configured to receive an input signal from the pre-amplifier and a second input configured to receive an integrator reference voltage signal which is ramped at start-up at a slower rate. A modulator has an input coupled to an output of the integrator. The modulator generates a pulse width modulated output signal. Operation of the Class-D amplifier is controlled at start-up by applying a slow ramped signal as the integrator reference voltage signal and a fast ramped signal as the amplifier reference voltage so that the pulse width modulated output signal exhibits an increasing change in duty cycle in response to an increasing voltage of the integrator reference voltage signal, and no “pop” is introduced at start-up.

主权项

1. A Class-D amplifier circuit, comprising:
a pre-amplifier circuit having a first input configured to receive a signal and a second input configured to receive an amplifier reference voltage signal, said pre-amplifier circuit configured to generate an input signal in response to the received signal; an integrator having a first input configured to receive said input signal and a second input configured to receive an integrator reference voltage signal; a first ramp generator configured to generate an integrator ramp signal at amplifier start-up, said integrator ramp signal applied as the integrator reference voltage signal to the second input of the integrator; a second ramp generator configured to generate an amplifier ramp signal at amplifier start-up, said amplifier ramp signal applied as the amplifier reference voltage signal to the second input of the pre-amplifier circuit; a modulator circuit having an input coupled to an output of the integrator; a transistor bridge circuit configured to be driven in response to a modulation signal output from the modulator circuit; and a feedback loop coupling an output of the transistor bridge to the first input of the integrator.