Controlling noise transfer function of signal path to reduce charge pump noise

Patent metadata

Field	Value
Publication number	US-2018317007-A1
Application number	US-201815926335-A
Country	US
Kind code	A1
Filing date	Mar 20, 2018
Priority date	Apr 27, 2017
Publication date	Nov 1, 2018
Grant date	—

Abstract

An apparatus for generating an output signal, may comprise a signal path having an analog signal path portion having an analog magnitude droop, a digital signal path portion having a digital magnitude droop, a digital-to-analog converter for converting the digital input signal into the analog signal, a first digital compensation filter that compensates for the analog magnitude droop, and a second digital compensation filter that compensates for the digital magnitude droop, such that the first digital compensation filter and the second digital compensation filter together compensate for magnitude droop of the signal path to ensure a substantially flat passband response of the signal path.
An apparatus may include a delta-sigma modulator for quantization noise shaping of a digital signal, a digital-to-analog converter configured to generate an analog signal from the digital signal, and an amplifier configured to amplify the analog signal and powered from a charge pump, wherein the charge pump is configured to operate at a switching frequency approximately equal to a zero of a modulator noise transfer function of the delta-sigma modulator, such that the impact of charge pump noise on a total harmonic distortion noise of the apparatus is minimized

First claim

1 . An apparatus for generating an output signal, comprising a signal path having:
an analog signal path portion having an audio input for receiving an analog signal, an audio output for providing an output signal, and a selectable analog gain, and configured to generate the output signal based on the analog signal and in conformity with the selectable analog gain, wherein a transfer function of the analog signal path portion has an analog magnitude droop; a digital signal path portion having a selectable digital gain and configured to receive and process a digital input signal in conformity with the selectable digital gain, wherein a transfer function of the digital signal path portion has a digital magnitude droop; a digital-to-analog converter for converting the digital input signal, as processed by the digital signal path portion, into the analog signal; a first digital compensation filter that compensates for the analog magnitude droop; and a second digital compensation filter that compensates for the digital magnitude droop, such that the first digital compensation filter and the second digital compensation filter together compensate for magnitude droop of the signal path to ensure a substantially flat passband response of the signal path.

2 . The apparatus of claim 1 , wherein the first digital compensation filter comprises an oversampling rate magnitude compensation filter.

3 . The apparatus of claim 2 , wherein the oversampling rate magnitude compensation filter improves a stopband attenuation for the signal path.

4 . The apparatus of claim 1 , wherein the second digital compensation filter comprises a baseband magnitude compensation filter.

5 . The apparatus of claim 1 , wherein the first digital filter and the second digital compensation filter improve noise performance of the signal path for higher frequency signals.

6 . The apparatus of claim 1 , wherein:
the first digital compensation filter comprises a baseband magnitude compensation filter; the second digital compensation filter comprises an oversampling rate magnitude compensation filter; and compensation filter coefficients for the first digital compensation filter and the second digital compensation filter are optimized for a plurality of gain configurations of the selectable analog gain and the selectable digital gain and stored in a memory.

7 . The apparatus of claim 1 , wherein the signal is an audio signal.

8 . A method for generating an output signal by a signal path, comprising:
generating the output signal by an analog signal path portion of the signal path having an audio input for receiving an analog signal, an audio output for providing the output signal, and a selectable analog gain, and configured to generate the output signal based on the analog signal and in conformity with the selectable analog gain, wherein a transfer function of the analog signal path portion has an analog magnitude droop; processing a digital input signal in conformity with a selectable digital gain by a digital signal path portion of the signal path having the selectable digital gain and configured to receive and process a digital input signal in conformity with the selectable digital gain, wherein a transfer function of the digital signal path portion has a digital magnitude droop; converting the digital input signal, as processed by the digital signal path portion, by a digital-to-analog converter of the signal path into the analog signal compensating for the analog magnitude droop with a first digital compensation filter; and compensating for the digital magnitude droop with a second digital compensation filter, such that the first digital compensation filter and the second digital compensation filter together compensate for magnitude droop of the signal path to ensure a substantially flat passband response of the signal path.

9 . The method of claim 8 , wherein the first digital compensation filter comprises an oversampling rate magnitude compensation filter.

10 . The method of claim 9 , further comprising improving a stopband attenuation for the signal path by the oversampling rate magnitude compensation filter.

11 . The method of claim 8 , wherein the second digital compensation filter comprises a baseband magnitude compensation filter.

12 . The method of claim 8 , further comprising improving, by the first digital compensation filter and the second digital compensation filter, noise performance of the signal path for higher frequency signals.

13 . The method of claim 8 , wherein:
the first digital compensation filter comprises a baseband magnitude compensation filter; the second digital compensation filter comprises an oversampling rate magnitude compensation filter; and compensation filter coefficients for the first digital compensation filter and the second digital compensation filter are optimized for a plurality of gain configurations of the selectable analog gain and the selectable digital gain and stored in a memory.

14 . The method of claim 8 , wherein the signal is an audio signal.

15 .- 20 . (canceled)

Assignees

• Cirrus Logic Int Semiconductor Ltd

Inventors

• Dhananjay Pradeep
• Duewer Bruce E

Classifications

• H03F2200/331

  Sigma delta modulation being used in an amplifying circuit · CPC title

• H04B14/062

  using delta modulation or one-bit differential modulation [1DPCM] · CPC title

• H03M3/376

  Prevention or reduction of switching transients, e.g. glitches · CPC title

• H03F3/213 Primary

  in integrated circuits · CPC title

• H03M3/50

  Digital/analogue converters using delta-sigma modulation as an intermediate step (digital delta-sigma modulators per se H03M7/3004) · CPC title