Power supply rejection for pulse width modulated amplifiers and automatic gain control
View Patent ↗A circuit according to the present invention improves the power supply rejection ratio for a pulse width modulated digital amplifier and can be used as a compressor and/or limiter. The circuit preferably operates by using voltage level translation to vary the amplitude of a triangle wave in response to changes in power supply voltage prior to input of the wave into a comparator of the PWM device. Because the circuit operates to improve power supply rejection, little or no distortion is introduced into the signal when used as a compressor and/or limiter. Additionally, the circuit is optionally implemented in a Class D amplifier, and provides a lower cost of implementation than conventional designs in such implementations.
1. A device for providing improved power supply rejection of a pulse width modulated digital amplifier, comprising:
a buffering mechanism that buffers divided reference voltages;
an oscillator which outputs a first waveform, wherein the first waveform can be combined with the divided reference voltages;
a circuit that performs a voltage level translation, wherein the voltage level translation outputs a second waveform having a similar frequency to the first waveform, wherein the second waveform has an amplitude that varies between the divided reference voltages; and,
an integrator that converts the second waveform into a triangle waveform that can be used with the pulse width modulated digital amplifier.
2. The device of claim 1 , wherein the pulse width modulated digital amplifier is a Class D amplifier.
3. The device of claim 1 , wherein the buffering mechanism is an operational amplifier.
4. The device of claim 1 , wherein the buffering mechanism ensures an accurate low impedance voltage.
5. The device of claim 1 , wherein the second waveform is a square waveform.
6. The device of claim 1 , wherein the oscillator is a fixed oscillator.
7. The device of claim 1 , wherein the first waveform has a 50% duty cycle.
8. The device of claim 1 , wherein the divided reference voltages can include ground.
9. A device useful as a compressor or limiter with a Class D amplifier, comprising:
means for rectifying an audio input signal;
means for DC amplifying the audio input signal;
means for injecting the audio input signal into a circuit for providing improved power supply rejection, the circuit comprising:
a buffering mechanism that buffers divided reference voltages;
an oscillator which outputs a first waveform, wherein the first waveform can be combined with the divided reference voltages;
a subcircuit that performs a voltage level translation, wherein the voltage level translation outputs a second waveform having a similar frequency to the first waveform, wherein the second waveform has an amplitude that varies between the divided reference voltages; and,
an integrator that converts the second waveform into a triangle waveform that can be used with the pulse width modulated digital amplifier.
10. A device useful as a compressor or limiter, comprising:
means for rectifying an audio input signal;
means for DC amplifying the audio input signal;
means for injecting the audio input signal into a circuit for providing improved power supply rejection, the circuit comprising:
a buffering mechanism that buffers divided reference voltages;
an oscillator which outputs a first waveform, wherein the first waveform can be combined with the divided reference voltages;
a subcircuit that performs a voltage level translation, wherein the voltage level translation outputs a second waveform having a similar frequency to the first waveform, wherein the second waveform has an amplitude that varies between the divided reference voltages;
an integrator that converts the second waveform into a triangle waveform;
means for inputting pulse-width-modulated signals to a differential amplifier; and
a lowpass filter to restore audio to the output.