High level capable audio amplification circuit

Patent metadata

Field	Value
Publication number	US-9083288-B2
Application number	US-79507210-A
Country	US
Kind code	B2
Filing date	Jun 7, 2010
Priority date	Jun 11, 2009
Publication date	Jul 14, 2015
Grant date	Jul 14, 2015

Abstract

The present invention relates to an audio amplification circuit with first and second signal channels which generate first and second digital audio signals with different signal amplifications from a common audio input signal and a method of amplifying a common audio input signal with different signal amplifications to provide first and second digital audio signals with different amplification. The audio amplification circuit is particularly well-adapted for cooperating with an external or integral audio signal controller configured for receipt and processing of the first and second digital audio signals.

First claim

The invention claimed is:

1. An audio amplification circuit comprising:
an input terminal for receipt of an audio input signal,
a first preamplifier having an input operatively coupled to the input terminal and an output operatively coupled to a first analogue-to-digital converter to provide a first digital audio signal with a first signal amplification,
a second preamplifier having an input and an output operatively coupled to a second analogue-to-digital converter to provide a second digital audio signal with a second signal amplification, and
an attenuator, comprising a capacitive voltage divider, operatively coupled in-between the input terminal and the input of the second preamplifier, and responsive to the audio input signal, the attenuator operable to substantially attenuate the audio input signal to the second preamplifier thereby allowing the second analogue-to-digital converter to be capable of handling higher levels of the audio input signal without distortion,
wherein the second signal amplification is smaller than the first signal amplification,
wherein each of the first and second preamplifiers have an audio frequency amplification controlled by an impedance ratio of two impedances,
further wherein the audio amplification circuit is formed on a substrate.

2. The audio amplification circuit according to claim 1 , wherein a capacitive component of an input impedance at the input terminal is smaller than 500 fF measured at 1 kHz.

3. The audio amplification circuit according to claim 1 , wherein an input impedance at the input terminal is larger than 100 MΩ measured at 1 kHz.

4. The audio amplification circuit according to claim 1 , wherein the second signal amplification is at least 10 dB smaller than the first signal amplification throughout a frequency range between 300 Hz and 3 kHz.

5. The audio amplification circuit according to claim 1 , wherein the second signal amplification is at least 20 dB smaller than the first signal amplification measured at 1 kHz.

6. The audio amplification circuit according to claim 1 , wherein the second preamplifier and the first preamplifier have substantially identical small signal transfer functions throughout a frequency range between 100 Hz and 10 kHz.

7. The audio amplification circuit according to claim 1 , wherein a small signal transfer function of the second preamplifier comprises a pole at a lower frequency than a lowest pole frequency than a lowest pole frequency of the small signal transfer function of the first preamplifier.

8. The audio amplification circuit according to claim 1 , wherein a phase difference between respective small signal transfer functions of the first and second preamplifiers is less than either
15 degrees at 1 kHz or
10 degrees at 100 Hz.

9. The audio amplification circuit according to claim 1 , wherein a gain of the second preamplifier is at least 10 dB smaller than a gain of the first preamplifier measured at 1 kHz.

10. The audio amplification circuit according to claim 1 , comprising two or more cascaded non-linear elements operatively coupled between the input terminal and a DC potential comprising at least one of a DC power supply rail and a DC reference voltage to clamp the audio input signal at a first limiting level.

11. The audio amplification circuit according to claim 10 , comprising a one or more cascaded non-linear elements coupled to an input of the first preamplifier to clamp an input signal at the first preamplifier input at a first preamplifier limiting level;
wherein the first limiting level is larger than the first preamplifier limiting level.

12. The audio amplification circuit according to claim 1 , wherein,
the first and second analogue-to-digital converters comprise respective sigma-delta converters adapted to generate the first and second digital audio signals, respectively, at respective oversampled sampling rates.

13. The audio amplification system according to claim 12 , further comprising:
a first decimation filter configured for receipt and down-sampling of the first digital audio signal from a first oversampled sampling rate to a final or Nyquist sampling rate,
a second decimation filter configured for receipt and down-sampling of the second digital audio signal from a second oversampled sampling rate to a final or Nyquist sampling rate.

14. The audio amplification circuit according to claim 13 , comprising a digital audio interface operatively coupled in-between the first and second digital audio signals and the externally accessible output terminal or terminals,
the digital audio interface being configured to convert the first and second digital audio signals at the final or Nyquist sampling rate into a digital audio stream compliant with a standardized data communication or digital audio protocol.

15. The audio amplification circuit according to claim 1 , comprising first and second externally accessible output terminals operatively coupled to the first and second digital audio signals, respectively.

16. The audio amplification circuit according to claim 1 , comprising an externally accessible output terminal adapted to provide a time-multiplexed digital audio stream comprising the first and second digital audio signals.

17. The audio amplification circuit according to claim 1 , comprising a clock input terminal for receipt of an external clock signal,
wherein respective sampling frequencies of the first and second analogue-to-digital converters are set by an internal clock signal of the audio amplification circuit derived from the external clock signal.

18. The audio amplification circuit according to claim 17 , wherein the first and second digital audio signals are transmitted synchronously to the external clock signal via one or more externally accessible output terminals.

19. The audio amplification circuit according to claim 1 , comprising a digital signal scaling function adapted to:
scaling the first or second digital audio signal with a preset or adaptive gain factor to compensate for an amplification difference between the first and second signal amplifications.

20. The audio amplification circuit according to claim 1 , wherein the first preamplifier or the second preamplifier comprises:
a differential amplifier having a non-inverting input operatively coupled to the input terminal for receipt of the audio input signal,
a feedback network coupled between an output an inverting input of the differential amplifier.

21. The audio amplification circuit according to claim 20 , wherein the feedback network is configured to provide a lowpass transfer function from the output of the differential amplifier to the inverting input of the differential amplifier.

22. The audio amplification circuit according to claim 1 , wherein the audio amplification circuit is a part of a miniature capacitive microphone, comprising:
a capacitive transducer element responsive to impinging sound to generate a corresponding transducer signal on a transducer signal terminal,
wherein the semiconductor die or substrate is operatively coupled to the transducer signal terminal via the input terminal for receipt and amplification of the transducer signal.

23. The audio amplification circuit according to claim 1 , wherein the first and second preamplifers each have a first and second differential input.

24. The audio amplification circuit according to claim 1 , wherein impedances of each of the first and second preamplifiers set

Assignees

• Thomsen Henrik
• Henriksen Jens Jorgen Gaarde
• Furst Claus
• Invensense Inc

Inventors

• Thomsen Henrik
• Henriksen Jens Jorgen Gaarde
• Furst Claus

Classifications

• H03F2203/45571

  the IC comprising two diodes, e.g. Gilbert circuit · CPC title

• H03F2203/45552

  the IC comprising clamping means, e.g. diodes · CPC title

• H03F3/187 Primary

  in integrated circuits · CPC title

• H04R19/00

  Electrostatic transducers · CPC title

• H04R2499/11

  Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's · CPC title