Method and apparatus for efficient mixed signal processing in a digital amplifier

• US 20010005174A1
• Filed: 01/24/2001
• Published: 06/28/2001
• Est. Priority Date: 07/01/1999
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Opris, Ion, Olson, Erlend
• Granted Patent: US 6,933,870 B2
• Time in Patent Office: Days
• US Class Current: 341/143
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/2173 of the bridge type
• CPC Class Codes: H03M 3/43 the quantiser being a single bit one
• CPC Class Codes: H03M 3/496 Details of sampling arrangements or methods
• CPC Class Codes: H03M 7/3006 Compensating for, or preventing of, undesired influence of physical parameters
• CPC Class Codes: H03M 7/3031 characterised by the order of the loop filter, e.g. having a first order loop filter in the feedforward path

Abstract

A system and method of creating a highly efficient digital amplifier which can take either analog or digital inputs, and produce a high power accurate representation of the input to drive speakers or other low impedance load is described. The system employs a transition detector and delay unit which allows the comparator of the signal modulator to ignore its inputs for a pre-determined number of subsequent clock cycles once an output transition has been detected. Through the use of faster clocks and variable clock cycle skips upon the comparator'"'"'s output transition, finer resolution of the feedback'"'"'s clock period for noise-shaping purposes is achieved. Finer resolution of the clock period allows the present invention to employ a more aggressive noise-shaping than previously possible.

In another aspect of the invention, additional delta-sigma modulator noise suppression is obtained by using the common bridge implementation of the power output stage with the improvement of configuring the bridge to create a 3-state condition instead of the conventional 2 states. By controlling the two halves of the bridge independently of one another, an output with 3 states makes for improved noise shaping performance.

Claims

1. A modulation stage for signal shaping comprising:

means for preliminary noise-shaping of an input signal; and

means for discrete-time sampling having a predetermined sampling frequency, the sampling means coupled to the noise-shaping means to produce an output signal with a lower transition rate with respect to said sampling frequency by a predetermined multiple.

2. A modulation stage for signal shaping of

claim 1

wherein the means for discrete-time sampling further comprises means for suppressing sampling of the input signal for a set number of clock cycles.

3. A modulation stage for signal shaping of

claim 2

wherein the means for suppressing comprises means for detecting a transition in the output signal.

4. A H-bridge controller wherein its outputs consist of three states.

5. A H-bridge controller of

claim 4

wherein the gating mechanism for each leg is independently controlled.

6. A digital amplifier comprising:

a modulation stage for signal shaping; and

a H-bridge controller wherein its outputs consist of three states.