Load detection

Patent metadata

Field	Value
Publication number	US-11653150-B2
Application number	US-202117516830-A
Country	US
Kind code	B2
Filing date	Nov 2, 2021
Priority date	Dec 11, 2018
Publication date	May 16, 2023
Grant date	May 16, 2023

Abstract

This application relates to audio driving circuitry ( 100 ), and in particular to audio driving circuitry for outputting first and second audio driving signals for driving a stereo audio load ( 106 ), which may be a stereo audio load of an accessory apparatus ( 102 ) removably coupled to the audio driving circuitry in use. A load monitor ( 111 ) is provided for monitoring to monitor, from a monitoring node ( 112 ), an indication of a common mode return current passing through a common return path, together with an indication of a common mode component of the first and second audio driving signals and to determine an impedance characteristic of the stereo audio load. The load monitor ( 111 ) can provide dynamic monitoring of any significant change in load impedance. In some embodiments the load monitor ( 111 ) comprises an adaptive filter ( 301 ) which adapts a parameter of the filter which is related to the load impedance so as to determine the indication of load impedance.

First claim

The invention claimed is:

1. Audio driving circuitry comprising:
first and second audio channels for outputting first and second audio driving signals for a stereo audio load comprising first and second audio loads;
a common return path for the first and second audio loads to a defined reference voltage; and
a load monitor configured to monitor an indication of a common mode return current passing through the common return path and an indication of a common mode component of the first and second audio driving signals and determine an impedance characteristic of the stereo audio load when the first and second audio channels are outputting said first and second audio driving signals comprising audio content.

2. Audio driving circuitry as claimed in claim 1 wherein the load monitor comprises an adaptive filter for adapting a parameter related to the impedance of the stereo audio load.

3. Audio driving circuitry as claimed in claim 2 wherein the adaptive filter is configured to minimise an error between a first value and a second value, wherein the first value is based on the indication of a common mode return current and the parameter related to impedance.

4. Audio driving circuitry as claimed in claim 3 wherein the second value is based on the indication of common mode component of the first and second audio driving signals.

5. Audio driving circuitry as claimed in claim 3 wherein the adaptive filter comprises a controller configured to iteratively adapt a present value of the parameter related to impedance by an adaption value proportional to the error between the first and second values.

6. Audio driving circuitry as claimed in claim 5 wherein the controller is configured such that the adaption value is also proportional to the first value based on the indication of the common mode return current.

7. Audio driving circuitry as claimed in claim 6 wherein the controller is configured to determine the first value as a function of the indication of the common mode return current such that a ratio between the first value and the indication of the common mode return current is greater for at least some values of the indication of the common mode return current in a lower range than for at least some values of the indication of the common mode return current in a higher range.

8. Audio driving circuitry as claimed in claim 5 wherein the controller is configured such that the adaption value is also proportional to a convergence factor wherein the controller is configured to vary a value of the convergence factor based on an indication of expected signal level such that the convergence factor is greater for at least some lower expected signal levels than for at least higher expected signal levels.

9. Audio driving circuitry as claimed in claim 2 wherein the adaptive filter implements a least mean squares algorithm.

10. Audio driving circuitry as claimed in claim 2 wherein the adaptive filter comprises a single tap adaptive filter.

11. Audio driving circuitry as claimed in claim 1 wherein the common return path comprises a resistance between a monitoring node and the defined reference voltage and the indication of the common mode return current comprises a voltage of the monitoring node.

12. Audio driving circuitry as claimed in claim 1 wherein the load monitor comprises a common-mode module configured to receive an indication of the first and second audio driving signals and determine said indication of the common-mode component.

13. Audio driving circuitry as claimed in claim 12 wherein the common-mode module is further configured to determine a differential component of the first and second audio driving signals and wherein the load monitor is configured to determine if there is insufficient common-mode component of the driving signals compared to the differential component, and, in the event that an insufficient common-mode component is detected, to pause determination of the impedance characteristic.

14. Audio driving circuitry as claimed in claim 13 wherein the load monitor is configured to determine if there is an insufficient common-mode component compared to the differential component, if the common-mode component is below a defined common-mode threshold whilst the differential component is above a differential threshold.

15. Audio driving circuitry as claimed in claim 1 wherein the load monitor comprises a level detector configured to determine whether the indication of common mode return current is at least one of:
above a defined upper magnitude threshold corresponding to an upper limit of an impedance range classified as low impedance; and
below a defined lower magnitude threshold corresponding to a lower limit of an impedance range classified as high impedance.

16. Audio driving circuitry as claimed in claim 15 wherein the level detector configured to determine whether the indication of common mode return current is below a noise threshold and wherein the load monitor is configured to pause determination of the impedance characteristic if the indication of common mode return current is below the noise threshold.

17. Audio driving circuitry as claimed in claim 1 wherein each of said first and second audio channels comprises a respective audio output driver powered by a power supply and wherein, based on the indication of impedance determined by the load monitor, the audio driving circuitry is configured to control at least one of:
a maximum output voltage magnitude of an audio output driver; and
a maximum output voltage magnitude from the power supply to the audio output driver.

18. An electronic device comprising audio driving circuitry as claimed in claim 1 and a connector for making a removable mating connection with an accessory apparatus in use, wherein said first and second audio channels are configured to output said first and second audio driving signals to first and second electrical contacts of said connector and the common return path connects to a third electrical contact of said connector.

19. Audio driving circuitry comprising:
first and second audio channels for outputting first and second audio driving signals for a stereo audio load comprising first and second audio loads;
a common return path for the first and second audio loads to a defined reference voltage; and
a load monitor configured to monitor an impedance characteristic of the stereo audio load so as to detect any changes in impedance characteristic in use when the stereo load is being driven with the first and second audio driving signals;
wherein the load monitor is configured to receive an indication of a common mode return current passing though the common return path and an indication of a common mode component of the first and second audio driving signals and determine said impedance characteristic.

20. Audio driving circuitry comprising:
first and second audio channels for outputting first and second audio driving signals for a stereo audio load comprising first and second audio loads;
a common return path for the first and second audio loads to a defined reference voltage;
a load monitor configured to determine an impedance characteristic of the stereo audio load;
wherein the load monitor is configured to determine a common mode component of the first and second audio driving signals being output to the stereo load and monitor an indication of a common mode return current passing though the common return path to determine said impedance characteristic.

Assignees

• Cirrus Logic Int Semiconductor Ltd
• Cirrus Logic Inc

Inventors

• Lesso John Paul
• Mccloy-Stevens Mark James
• Bowlerwell John Bruce
• Suryono Yanto
• Zhao Xin
• Prior Morgan Timothy

Classifications

• H04R2201/107

  Monophonic and stereophonic headphones with microphone for two-way hands free communication · CPC title

• H04R29/001

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

• H03F2200/03

  the amplifier being designed for audio applications · CPC title

• H04R5/02

  Spatial or constructional arrangements of loudspeakers · CPC title

• H03G3/3005

  in amplifiers suitable for low-frequencies, e.g. audio amplifiers (H03G3/32, H03G3/34 take precedence) · CPC title