Systems and methods for dynamic range enhancement using an open-loop modulator in parallel with a closed-loop modulator

Patent metadata

Field	Value
Publication number	US-2016118948-A1
Application number	US-201414524867-A
Country	US
Kind code	A1
Filing date	Oct 27, 2014
Priority date	Oct 27, 2014
Publication date	Apr 28, 2016
Grant date	—

Abstract

An integrated circuit may have two signal paths: an open-loop modulator (which may comprise a digital-input Class-D amplifier) and a closed-loop modulator (which may comprise an analog-input Class-D amplifier). A control subsystem may be capable of selecting either of the open-loop modulator or the closed-loop modulator as a selected path based on one or more characteristics (e.g., signal magnitude) of an input audio signal. For example, for higher-magnitude signals, the closed-loop modulator may be selected while the open-loop modulator may be selected for lower-magnitude signals. In some instances, when the open-loop modulator is selected as the selected path, the closed-loop modulator may power off, which may reduce power consumption. In addition, one or more techniques may be applied to reduce or eliminate user-perceptible audio artifacts caused by switching between the open-loop modulator and the closed-loop modulator, and vice versa.

First claim

1 . A system comprising:
an open-loop modulator configured to receive an input signal and generate an output signal based on the input signal when the open-loop modulator is selected as a selected path; a closed-loop modulator configured to receive the input signal and generate a closed-loop output signal based on the input signal when the closed-loop modulator is selected as the selected path; and a control subsystem configured to select one of the open-loop modulator and the closed-loop modulator as the selected path based on one or more characteristics of the input signal.

2 . The system of claim 1 , wherein the open-loop modulator comprises a digital-input Class-D amplifier.

3 . The system of claim 1 , wherein the closed-loop modulator comprises an analog-input Class-D amplifier.

4 . The system of claim 1 , wherein the open-loop modulator and the closed-loop modulator each comprise and share:
a switched output stage configured to drive an output load with the output signal; and a predriver stage configured to drive one or more predriver signals to the output stage based on the input signal, wherein the output signal is a function of the one or more predriver signals.

5 . The system of claim 4 , wherein the predriver generates the one or more predriver signals based on a control signal which is a function of the input signal.

6 . The system of claim 5 , wherein the control signal is a pulse-width modulated signal.

7 . The system of claim 1 , wherein the input signal is a pulse-width modulated signal.

8 . The system of claim 1 , wherein the control subsystem is configured to power on the closed-loop modulator for a period of time prior to switching selection of the selected path from the open-loop modulator to the closed-loop modulator.

9 . The system of claim 1 , wherein the control subsystem is configured to select the selected path based on a magnitude of the input signal.

10 . The system of claim 1 , wherein the control subsystem is configured to select the selected path based on whether a magnitude of the input signal crosses a threshold value within a period of time after a zero-crossing event of the input signal.

11 . The system of claim 10 , wherein the control subsystem is configured to:
select the closed-loop modulator as the selected path when the magnitude of the input signal crosses above the threshold value within a period of time after a zero-crossing event of the input signal; and select the open-loop modulator as the selected path when the magnitude of the input signal remains below the threshold value within a period of time after a zero-crossing event of the input signal.

12 . The system of claim 1 , wherein the control subsystem is configured to select the selected path based on a slew rate of the input signal at a zero-crossing event of the input signal.

13 . The system of claim 12 , wherein the control subsystem is configured to:
select the closed-loop modulator as the selected path when a magnitude of the slew rate of the input signal is greater than a threshold slew rate at the zero-crossing; and select the open-loop modulator as the selected path when the magnitude of the slew rate of the input signal is lesser than a threshold slew rate at the zero-crossing.

14 . The system of claim 1 , wherein the open-loop modulator includes a digital equalization filter configured to match a transfer function of the open-loop modulator to a transfer function of the closed-loop modulator.

15 . The system of claim 14 , wherein the digital equalization filter may be calibrated in accordance with a calibration operation to match the transfer function of the open-loop modulator to the transfer function of the closed-loop modulator.

16 . The system of claim 1 , wherein the closed-loop modulator comprises a low-pass filter configured to convert an error signal equal to the difference between the analog version of the input signal and a feedback signal generated by the closed-loop modulator into a filtered error signal.

17 . The system of claim 16 , wherein the closed-loop modulator further comprises a feedforward path that bypasses the low-pass filter and combines the input signal with the filtered error signal.

18 . The system of claim 1 , wherein the controller is further configured to power off the closed-loop modulator when the open-loop modulator is the selected path.

19 . A method comprising:
selecting one of an open-loop modulator and a closed-loop modulator based on one or more characteristics of an input signal; generating an output signal based on the input signal by the open-loop modulator when the open-loop modulator is selected as a selected path; and generating an output signal based on the input signal by the closed-loop modulator when the closed-loop modulator is selected as a selected path.

20 . The method of claim 19 , wherein the open-loop modulator comprises a digital-input Class-D amplifier.

21 . The method of claim 19 , wherein the closed-loop modulator comprises an analog-input Class-D amplifier.

22 . The method of claim 19 , further comprising:
driving an output load with the output signal by a switched output stage shared by the open-loop modulator and the closed-loop modulator; and drive one or more predriver signals to the output stage based on the input signal by a predriver shared the open-loop modulator and the closed-loop modulator , wherein the output signal is a function of the one or more predriver signals.

23 . The method of claim 22 , further comprising generating the one or more predriver signals based on a control signal which is a function of the input signal.

24 . The method of claim 23 , wherein the control signal is a pulse-width modulated signal.

25 . The method of claim 19 , wherein the input signal is a pulse-width modulated signal.

26 . The method of claim 19 , further comprising powering on the closed-loop Class-D modulator for a period of time prior to switching selection of the selected path from the open-loop modulator to the closed-loop modulator.

27 . The method of claim 19 , further comprising selecting the selected path based on a magnitude of the input signal.

28 . The method of claim 19 , further comprising selecting the selected path based on whether a magnitude of the input signal crosses a threshold value within a period of time after a zero-crossing event of the input signal.

29 . The method of claim 28 , further comprising:
selecting the closed-loop modulator as the selected path when the magnitude of the input signal crosses above the threshold value within a period of time after a zero-crossing event of the input signal; and selecting the open-loop modulator as the selected path when the magnitude of the input signal remains below the threshold value within a period of time after a zero-crossing event of the input signal.

30 . The method of claim 19 , further comprising selecting the selected path based on a slew rate of the input signal at a zero-crossing event of the input signal.

31 . The method of claim 30 , further comprising :
selecting the closed-loop modulator as the selected path when a magnitude of the slew rate of the input signal is greater than a threshold slew rate at the zero-crossing; and selecting the open-loop modulator as the selected path when

Assignees

• Cirrus Logic Inc

Inventors

• Zanbaghi Ramin

Classifications

• H03F2200/129

  there being a feedback over the complete amplifier · CPC title

• H03F2200/03

  the amplifier being designed for audio applications · CPC title

• H03K7/08

  Duration or width modulation {; Duty cycle modulation} · CPC title

• H03F1/0277 Primary

  Selecting one or more amplifiers from a plurality of amplifiers · CPC title

• H03F3/2171

  with field-effect devices (H03F3/2173 - H03F3/2178 take precedence) · CPC title