Feedback amplifier

• US 7,541,869 B2
• Filed: 03/28/2007
• Issued: 06/02/2009
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Adduci, Pietro Mario, Botti, Edoardo
• Primary Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US11/692,597
• Publication Number:
  US 20070229155A1
• Time in Patent Office: 797 Days
• Field of Search: 330/251, 330/10, 330/99
• US Class Current: 330/251
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 1/34 Negative-feedback-circuit arrangements with or without positive feedback H03F1/02 - H03F1/30, H03F1/38 - H03F1/50, H03F3/50 take precedence ; for rejection of common mode signals H03F3/45479
• CPC Class Codes: H03F 1/48 of aperiodic amplifiers
• CPC Class Codes: H03F 2200/153 Feedback used to stabilise the amplifier
• CPC Class Codes: H03F 3/2175 using analogue-digital or digital-analogue conversion H03F3/2173 takes precedence

Abstract

A feedback architecture for a PWM switching audio amplifier is, capable of compensating the effects of the demodulation filter through at least two feedback paths of the voltage applied to a load without degrading the overall loop gain of the device. Each of the feedback paths may include a respective network or filter for compensating a respective frequency pole of the cascade low-pass filter+load and establishing a certain band pass. These networks or filters may be passive networks.

Claims

1. A signal amplifier comprising:

a class D amplifier generating a modulated voltage signal switching as a function of an intermediate signal;

a low-pass filter input with the modulated voltage signal for applying a filtered replica of the modulated voltage signal to a load;

a plurality of feedback paths for generating a plurality of feedback signals of the filtered replica; and

a circuit input with the plurality of feedback signals of the filtered replica and a signal to be amplified and generating the intermediate signal as a combination of the plurality of feedback signals, the signal to be amplified, and an externally generated reference carrier;

said plurality of feedback paths including respective feedback filters, each feedback filter for compensating a respective frequency pole of a transfer function of a cascade of the low-pass filter with the load and for establishing at least one band pass of the signal amplifier.

2. The signal amplifier of claim 1 wherein at least one of the feedback filters establishes a parameter of the transfer function, the parameter being at least one of a phase margin, a cut-off frequency, a total harmonic distortion, a loop gain, and a gain of the signal amplifier.

3. The signal amplifier of claim claim 1 wherein the externally generated reference carrier comprises a square wave signal.

4. The signal amplifier of claim 1 wherein each feedback filter comprises a passive network.

5. A signal amplifier comprising:

an amplifier generating a modulated signal based upon an intermediate signal;

a filter having an input coupled to the modulated signal, and an output coupled to a load;

a plurality of feedback paths coupled to the output of said filter; and

a circuit coupled to said plurality of feedback paths for generating the intermediate signal based upon a combination of an input signal, outputs of said plurality of feedback paths, and a reference signal;

said plurality of feedback paths including respective feedback filters, each feedback filter for compensating a respective frequency pole of a transfer function of said filter coupled to the load.

6. The signal amplifier of claim 5 wherein said amplifier comprises a class D amplifier.

7. The signal amplifier of claim 5 wherein at least one of the feedback filters establishes a parameter of the transfer function, the parameter being at least one of a phase margin, a cut-off frequency, a total harmonic distortion, a loop gain, and a gain of the signal amplifier.

8. The signal amplifier of claim 5 wherein each feedback filter comprises a passive network.

9. A method for making a signal amplifier comprising an amplifier generating a modulated signal based upon an intermediate signal, and a filter having an input coupled to the modulated signal and an output coupled to a load, the method comprising:

coupling a plurality of feedback paths to the output of the filter; and

coupling an input of a circuit with the plurality of feedback paths for generating the intermediate signal based upon a combination of an input signal, outputs of the plurality of feedback paths, and a reference signal;

the plurality of feedback paths including respective feedback filters, each feedback filter for compensating a respective frequency pole of a transfer function of the filter coupled to the load.

10. The method of claim 9 wherein the amplifier comprises a class D amplifier.

11. The method of claim 9 wherein at least one of the feedback filters establishes a parameter of the transfer function, the parameter being at least one of a phase margin, a cut-off frequency, a total harmonic distortion, a loop gain, and a gain of the signal amplifier.

12. The method of claim 9 wherein each feedback filter comprises a passive network.