Patent ID: 6175272
Filing Date: 2001-01-16
Classification: H03F

Abstract:
An apparatus comprising:a pulse-width modulator which produces a PWM signal in response to a select signal;a power supply having a PWM signal input terminal which receives the PWM signal from the pulse-width modulator, and a voltage source including a first power-supply output terminal, and a second power-supply output terminal, wherein the voltage source provides a first power-supply voltage on the first power-supply output terminal, and a second power-supply voltage on the second power-supply output terminal, the first and second power supply voltages having levels determined in accordance with the PWM signal; andan amplifier having an input terminal which receives an input signal, a first power-supply input terminal connected to the first power-supply output terminal, a second power-supply input terminal connected to the second power-supply output terminal, and a third power-supply input terminal which provides a third constant voltage, and an output terminal which produces an output signal proportional to the difference between the third constant voltage and at least one of the first and second power-supply voltages.