Distortion correction in class-D amplifiers

摘要

The present application describes an apparatus and method for reducing distortion in a class-D amplifier. The power output section of the amplifier is driven by an adjusted PWM signal, rather than by a PWM signal created directly from the input analog signal. A reference output, designed to closely track the input analog signal, is compared to the amplifier output. The resulting difference is an error signal which is inverted and summed with a second analog signal corresponding to the directly created PWM signal and changes the timing of the voltage transitions of the second analog signal. The changed voltage transitions are used to create the adjusted PWM signal. The inversion of the error signal causes negative feedback which results in the adjustment of the PWM signal being in a direction which reduces the error signal and thus the distortion of the amplifier.

主权项

1. A class-D amplifier circuit comprising:
a first controller for generating a first PWM signal which alternates between two PWM signal values corresponding to an input signal; a DAC for creating a correction signal which is greater than a first selected value when the PWM signal is at a first one of the two PWM signal values and less than the first selected value when the PWM signal is at the other of the two PWM signal values, and which crosses zero when the PWM signal transitions from one of the two PWM signal values to the other; a second controller for summing the correction signal and an error signal and generating a second PWM signal, the second PWM signal corresponding to the sum of the correction signal and the error signal and changing state when the sum crosses a second selected value; a first switching element and a second switching element connected in series between two voltages for receiving the second PWM signal and producing in response thereto a first output signal of a power sufficient for driving a desired load with a distortion of the input signal; a third switching element and a fourth switching element connected in series between two voltages for receiving the first PWM signal and producing a second output signal with a lower distortion of the input signal than the first output signal; and a third controller for generating the error signal based upon the difference between the first output signal and the second output signal.