Patent ID: 9209762
Filing Date: 2015-12-08
Classification: H03F

Abstract:
1. A circuit for generating an output signal of varying amplitude, the circuit comprising: a first low-dropout linear regulator for generating a positive power supply rail output and having a first reference voltage input; a second low-dropout linear regulator for generating a negative power supply rail output and having a second reference voltage input, wherein a first response of the positive power supply rail output differs from a second response of the negative power supply rail output; a switching circuit having a first power supply rail input coupled to the positive power supply rail output of the first low-dropout linear regulator and a second power supply rail input coupled to the negative power supply rail output of the second low-dropout linear regulator; a switching control circuit having an input for receiving an input signal and generating switching control signals for controlling the switching circuit, wherein the switching control circuit comprises a modulator for generating the switching control signals in conformity with a value of the input signal; and a power supply control circuit having an input for receiving at least one output level control signal and generating at least one power supply control signal supplied to the first reference voltage input of the first low-dropout linear regulator and the second reference voltage input of the second low-dropout linear regulator, wherein the power supply control circuit generates the power supply control signal in conformity with the at least one output level control signal with a controlled rate of change between adjacent steps in the at least one output level control signal, such that asymmetry between the voltages of the positive power supply rail output of the first low-dropout linear regulator and the negative power supply rail output of the second low-dropout linear regulator during changes of the at least one output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of both the first response and the second response such that waveforms of the voltages of the positive power supply output and the negative power supply output are substantially symmetrical when the at least one output level control signal changes.