Circuit and method for reducing noise in class D amplifiers
AssigneeMeyer Sound Laboratories, Incorporated
InventorsPaul Kohut, Peter L. Winship, Peter Kowalcyzk, Steven Metz, Kurt Keown
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Abstract
A circuit for reducing noise in Class D amplifiers has a power stage voltage control means (17, 21, 22) responsive to defined signal conditions of the audio signal input (1). The power stage voltage control means is operative to lower the voltage at the supply voltage input (31) of the amplifier's switching power output stage (30) upon the detection of a defined condition in the audio signal input such that the Class-D amplifier operates at reduced voltage (“idles”) during the defined audio input signal condition.
Claims20
A Class D audio amplifier circuit comprising
- an audio signal input,
- a pulse width modulator (PWM) stage for converting the audio input signal to a series of pulses wherein the width of pulses in the series of pulses is representative of the audio input signal,
- a switching power output stage having a supply voltage input and being switchable between an “on” state and an “off” state in response to the series of pulses produced by said PWM stage for producing a series of amplified power output pulses corresponding to the series of pulses produced by said PWM stage,
- a main voltage supply for providing a voltage at the supply voltage input of said switching power output stage, and wherein the Class D amplifier has a gain determined by said supply voltage input, and
- power output stage voltage control means responsive to defined signal conditions of the audio signal input, said power output stage voltage control means being operative to lower the voltage at the supply voltage input of said switching power output stage, and thereby the gain of the Class D amplifier, upon the detection of a defined condition in the audio signal input and to hold the voltage at the supply voltage input in a lowered voltage condition for a period of time wherein the Class D amplifier operates at reduced voltage (“idles”) during such defined audio signal input condition.
A Class D audio amplifier circuit comprising
- an audio signal input,
- a pulse width modulator (PWM) stage for converting the audio input signal to a series of pulses wherein the width of pulses in the series of pulses is representative of the audio input signal,
- a switching transistor power output stage having a supply voltage input and being switchable between an “on” state and an “off” state in response to the series of pulses produced by said PWM stage for producing a series of amplified power output pulses corresponding to the series of pulses produced by said PWM stage,
- a main voltage supply for providing a voltage at the supply voltage input of said switching power output stage,
- power output stage voltage control means between the main voltage supply of the Class D amplifier circuit and the supply voltage input of said switching transistor power output stage, said power output stage voltage control means being responsive to defined signal conditions of the audio signal input as follows:
- the defined signal conditions include a selected signal threshold level, Loff,
- the power output stage voltage control means treats the audio signal input as being in an idle state after a period of time after the audio input signal falls below Loff,
- the period of time after the audio input signal falls below Loff before which the audio signal is treated as being in the idle state is selected to preserve natural pauses in the audio content of the audio signal input, and
- upon detection of the idle state signal condition in the audio signal input the power output stage voltage control means causes the voltage at the supply voltage input of said switching power output stage to be reduced, and
- an output filter stage for converting the series of amplified power output pulses to an amplified analog audio signal for driving a loudspeaker.
A method of reducing noise in a Class D amplifier having an audio signal input having a signal level, a pulse width modulator (PWM) stage for converting the audio input signal to a series of pulses wherein the width of pulses in the series of pulses is representative of the audio input signal, a switching power output stage having a supply voltage input and being switchable between an “on” state and an “off” state in response to the series of pulses produced by said PWM stage for producing a series of amplified power output pulses corresponding to the series of pulses produced by said PWM stage, and a main voltage supply for providing a voltage at the supply voltage input of said switching power output stage, said method comprising
- establishing when an idle state of the audio signal input exists based on the signal level of the audio signal input,
- detecting the level of the audio signal input of the Class D amplifier to determine when an idle state of the audio signal input exists,
- reducing the voltage at the supply voltage input of the switching power output stage of the Class D amplifier upon the detection of the idle state of the audio signal input.
Dependencies are inferred from the claim text.