Signal amplitude-selected signal predistortion in an amplifier

Patent metadata

Field	Value
Publication number	US-11539331-B2
Application number	US-202117348982-A
Country	US
Kind code	B2
Filing date	Jun 16, 2021
Priority date	Apr 12, 2021
Publication date	Dec 27, 2022
Grant date	Dec 27, 2022

Abstract

An amplification system with an output driver stage for providing an output signal to acoustic output transducers such as speakers or haptic output devices removes signal distortion caused by output stage non-linearities by pre-distorting an input signal. The system includes the output driver stage, an input stage for receiving the input signal, and a processing block that receives the input signal and provides an output signal to the output driver stage. The processing block includes a pre-distortion circuit that applies a pre-distortion function to the input signal to generate the output signal if a signal level of the input signal is greater than a threshold amplitude, and if the signal level is less than or equal to the threshold amplitude, generates the output signal from the input signal by bypassing the pre-distortion circuit.

First claim

What is claimed is:

1. A method of reducing distortion in an amplifier for providing a drive signal to an acoustic output transducer, the amplifier comprising:
determining whether a signal level of an input signal being amplified by the amplifier is greater than a threshold amplitude;
responsive to determining that the signal level is greater than the threshold amplitude, applying a pre-distortion function to the input signal that cancels distortion introduced by the amplifier prior to amplification by the amplifier, whereby the amplifier amplifies a modified signal; and
responsive to determining that the signal level is less than or equal to the threshold amplitude, amplifying the input signal without applying the pre-distortion function to the signal.

2. The method of claim 1 , further comprising responsive to determining that the signal level is less than the threshold amplitude, disabling a pre-distortion circuit that applies the pre-distortion function to the signal to conserve energy consumed by the amplifier.

3. The method of claim 1 , wherein the applying a pre-distortion function to the input signal comprises computing the modified signal by applying a polynomial or telescoped polynomial to values of the input signal.

4. The method of claim 1 , further comprising:
subsequent to determining that the signal level is greater than or equal to the threshold amplitude and applying the pre-distortion function to modify the input signal, determining whether or not that the signal level is greater than another threshold amplitude less than the threshold amplitude by an amplitude hysteresis value;
responsive to determining that the signal level is greater than the another threshold amplitude, continuing to apply the pre-distortion function to the input signal to generate the modified signal; and
responsive to determining that the signal level is less than or equal to the another threshold amplitude, ceasing application of the pre-distortion function to the signal, whereby the amplifier amplifies the input signal without pre-distortion.

5. The method of claim 1 , wherein the amplifier includes multiple amplification paths that are selectively enabled, and wherein the method further comprises:
receiving an indication to change selection between the multiple amplification paths; and
responsive to receiving the indication, changing a currently-selected one of the multiple amplification paths to another newly-selected one of the multiple amplification paths for amplifying the signal; and
further responsive to receiving the indication, changing one or both of the amplitude threshold or the pre-distortion function in conformity with the another newly-selected one of the multiple amplification paths.

6. The method of claim 1 , further comprising:
subsequent to determining that the signal level is greater than or equal to the threshold amplitude and applying the pre-distortion function to modify the input signal, determining whether or not that the signal level is greater than another threshold amplitude greater than the threshold amplitude;
responsive to determining that the signal level is greater than the another threshold amplitude, applying another pre-distortion function to the input signal to generate the modified signal, whereby the pre-distortion function used to generate the modified signal is varied with the amplitude of the input signal.

7. The method of claim 6 , further comprising:
responsive to determining that the signal level is less than the threshold amplitude, disabling a pre-distortion circuit that applies the pre-distortion function to the signal to conserve energy consumed by the amplifier;
responsive to determining that the signal level is greater than or equal to the threshold amplitude, enabling a portion of the pre-distortion circuit that applies the pre-distortion function to the signal to conserve energy consumed by the amplifier; and
responsive to determining that the signal level is greater than the another threshold amplitude, enabling another portion of the pre-distortion circuit that applies the another pre-distortion function used to generate the modified signal, wherein energy consumption of the pre-distortion circuit is dependent on whether the pre-distortion function or the another pre-distortion function is being applied to the input signal.

8. The method of claim 1 , further comprising responsive to determining that the signal level is greater than the threshold amplitude, applying a time-variant scaling function to the pre-distortion function to ramp up the effect of the pre-distortion function on the modified signal to prevent transients due to enabling pre-distortion.

9. The method of claim 8 , further comprising subsequent to and during application of the pre-distortion function to the input signal and responsive to determining that the signal level is less than or equal to the threshold amplitude, applying a time-variant scaling function to the pre-distortion function to ramp down the effect of the pre-distortion function on the modified signal to prevent transients due to disabling pre-distortion.

10. The method of claim 1 , further comprising detecting a change in a power supply voltage received by the amplifier or a device temperature of the amplifier, adjusting one or both of the amplitude threshold or the pre-distortion function in conformity with the change in the power supply voltage or the device temperature.

11. The method of claim 1 , further comprising:
detecting zero-crossings of the input signal; and
delaying a change between applying the pre-distortion function to the input signal or amplifying the unmodified input signal to synchronize the change to a zero-crossing of the input signal.

12. The method of claim 1 , further comprising:
measuring an output of the amplifier to determine a measure of distortion of the output signal of the amplifier;
removing fundamental components due to the input signal from a result of the measuring; and
adjusting the pre-distortion function according to a result of the removing.

13. The method of claim 12 , wherein the measuring is performed responsive to detecting a change in a power supply voltage received by the amplifier or a device temperature of the amplifier.

14. The method of claim 12 , wherein the measuring is performed periodically according to a timer.

15. An amplification system for providing an output drive signal to an acoustic output transducer, comprising:
an input stage for receiving an input signal to be amplified;
an output driver stage for providing the drive signal to the acoustic output transducer; and
a processing block for receiving the input signal and providing an output signal to the output driver stage, wherein the processing block comprises a pre-distortion circuit that applies a pre-distortion function to the input signal that cancels distortion introduced by the output driver stage to generate the output signal if a signal level of the input signal is greater than a threshold amplitude, and if the signal level is less than or equal to the threshold amplitude, generates the output signal from the input signal by bypassing the pre-distortion circuit.

16. The amplification system of claim 15 , wherein the processing block further disables the pre-distortion circuit if the signal level is less than the threshold amplitude to reduce energy consumed by the amplification system.

17. The amplification system of claim 15 , wherein the pre-distortion circuit computes the output signal by applying a polynomial or telescoped polynomial to values of the inpu

Assignees

• Cirrus Logic Int Semiconductor Ltd
• Cirrus Logic Inc

Inventors

• Vellanki Amar
• Zhao Xin
• Bai Jing
• Melanson John L
• He Ku
• Shum Wai-Shun
• Fei Xiaofan
• Morton Alan M

Classifications

• H03F1/3241 Primary

  using predistortion circuits (H03F1/3211, H03F1/3217 take precedence) · CPC title

• H04R3/00 Primary

  Circuits for transducers (arrangements for producing a reverberation or echo sound G10K15/08; amplifiers H03F) · CPC title

• H03F1/32 Primary

  Modifications of amplifiers to reduce non-linear distortion (by negative feedback H03F1/34) · CPC title

• H03F1/02

  Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation · CPC title

• H04R29/001

  for loudspeakers (H04R29/007 takes precedence) · CPC title