METHOD AND SYSTEM FOR TRANSITIONING BETWEEN OPERATION STATES IN AN OUTPUT SYSTEM

• US 20090160547A1
• Filed: 12/20/2007
• Published: 06/25/2009
• Est. Priority Date: 12/20/2007
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Krogsgaard, Klaus, Shankar, Asit
• Granted Patent: US 7,554,390 B1
• Time in Patent Office: Days
• US Class Current: 330/10
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/393 with field-effect devices
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602

Abstract

A closed loop amplifier system comprising a modulator that provides a pulse-width modulated (PWM) output signal based on an input signal, the modulator having a variable closed loop transfer function. The system also comprises a ramp generator that provides a ramp signal to the modulator, the variable closed loop transfer function of the modulator varying as a function of the ramp signal. The system further comprises a controller that controls the ramp generator to provide the ramp signal to adjust the variable closed loop transfer function during transitions between operating states of the amplifier system.

Claims

1. A closed loop amplifier system comprising:

a modulator that provides a pulse-width modulated (PWM) output signal based on an input signal, the modulator having a variable closed loop transfer function;

a ramp generator that provides a ramp signal to the modulator, the variable closed loop transfer function of the modulator varying as a function of the ramp signal; and

a controller that controls the ramp generator to provide the ramp signal to adjust the variable closed loop transfer function during transitions between operating states of the closed loop amplifier system.

2. The system of claim 1, wherein the modulator further comprises a first stage and a second stage connected in series, each of the first stage and the second stage having a transfer function that varies based on the ramp signal, at least one of a gain and a phase margin of the first stage being dominant relative to the second stage based on the ramp signal supplied during a first portion of an activation state of the closed loop amplifier system.

3. The system of claim 2, wherein at least one of the gain and phase margin of the second stage is decreased based on the ramp signal that is supplied during a deactivation operating state of the closed loop amplifier system.

4. The system of claim 2, wherein the first stage and second stage each comprises an integrator having a time constant that varies as a function of the ramp signal.

5. The system of claim 1, the modulator further comprising at least one variable time constant integrator, wherein the ramp signal causes gain of the at least one variable time constant integrator to vary as a function of the ramp signal.

6. The system of claim 5, further comprising a clip detector configured to detect the operating state of the modulator, the clip detector providing a reset signal to the at least one variable time constant integrator in response to the clip detector detecting the modulator in a deactivated operating state, the reset signal causing the gain of the at least one variable time constant integrator to be reduced to about zero.

7. The system of claim 5, wherein the at least one variable time constant integrator further comprises a capacitance and a resistance that defines the integration time constant, wherein at least the resistance is controlled based on the ramp signal.

8. The system of claim 1, wherein the operating states comprises an activated state and a deactivated state.

9. The system of claim 1, wherein the modulator further comprises at least two modulators, wherein each of the at least two modulators comprises at least one variable time constant integrator, wherein the ramp signal causes a gain of each of the variable time constant integrators to vary as a function of the ramp signal.

10. The system of claim 9, wherein a time constant of each of the variable time constant integrators further comprises a capacitance and a resistance that defines the integration time constant, wherein at least the resistance is controllable by the ramp signal.

11. The system of claim 10, wherein the at least two operation states comprises an activated state and a deactivated state, the system further comprising a clip detector configured to detect a transition in the operating state of the modulator, the clip detector providing a reset signal to at least one of the variable time constant integrators in response to the clip detector detecting that the modulator has transitioned to the deactivated state.

12. The system of claim 11, wherein the reset signal causes a gain of the at least one of the variable time constant integrators to be reduced to about zero.

13. The system of claim 11, wherein the PWM output signal comprises a differential output signal and the ramp signal comprises a differential ramp signal.

14. A system for transitioning an operation state of a multi-channel system, the system comprising:

means for providing a ramp signal;

means for controlling the means for providing the ramp signal;

means for providing a plurality of pulse-width modulated (PWM) signals that includes a means for filtering according to a transfer function that varies as a function of the ramp signal, wherein each of the plurality of PWM signals is associated with a respective channel that varies based on an input signal and the ramp signal;

means for amplifying the plurality of PWM signals and providing a feedback signal to the means for providing the plurality of PWM signals; and

means for transitioning the means for providing the plurality of PWM signals between at least two operation states based at least in part upon the ramp signal.

15. The system of claim 14, wherein the at least two operation states comprises an activated state and a deactivated state.

16. The system of claim 15, further comprising;

means for detecting the operation state of the means for providing the plurality of PWM signals; and

means for providing a reset signal to the means for transitioning in response to detecting the deactivated state.

17. A method for transitioning an output state of a modulator of an audio system between an activated output state and a deactivated output state, the method comprising:

monitoring a selection signal, the selection signal indicating a change in the output state of the modulator;

a ramp signal generating in response to detecting the selection signal indicating the change in the output state of the modulator; and

varying a closed loop transfer function of the modulator as a function of the ramp signal.

18. The method of claim 17, wherein the modulator further comprises at least one variable time constant integrator, where in a time constant of the at least one variable time constant integrator varies as function of the ramp signal.

19. The method of claim 17, further comprising:

detecting the output state the modulator; and

varying a gain of the modulator to about zero in response to detecting the deactivated output state.

20. The method of claim 17, wherein the modulator defines at least part of a second order, two pole filter system, wherein a first pole of the second order, two pole filter system is dominant relative to a second pole of the second order, two pole filter system during an activated state, and the second pole of the second order, two pole filter system is dominant relative to the first pole of the second order, two pole filter system during a deactivated state.