# US 2015/0146884 A1 · Circuit for suppressing audio output noise and audio output circuit

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- Number: US 2015/0146884 A1
- Document ID: US20150146884A1
- Status: Published application
- Kind: A1
- Application number: 14/452,685
- Filed: 2014-08-06
- Published: 2015-05-28
- Earliest claimed: 2013-11-26
- Assignees: Spreadtrum Communications (Shanghai) Co., Ltd.
- Applicants: Spreadtrum Communications (Shanghai) Co., Ltd.
- Inventors: Xun ZHANG
- Web page: https://patentgrep.com/patent/US20150146884A1

## CPC

- H04R 3/002: {Damping circuit arrangements for transducers, e.g. motional feedback circuits}
- H03F 1/0277: {Selecting one or more amplifiers from a plurality of amplifiers}
- H03F 1/26: Modifications of amplifiers to reduce influence of noise generated by amplifying elements
- H03F 1/305: {in case of switching on or off of a power supply}
- H03F 3/181: Low-frequency amplifiers, e.g. audio preamplifiers
- H03F 3/20: Power amplifiers, e.g. Class B amplifiers, Class C amplifiers (H03F3/26 - H03F3/30 take precedence)
- H03F 3/211: {using a combination of several amplifiers (H03F3/60 takes precedence)}
- H03F 3/2171: {with field-effect devices (H03F3/2173 - H03F3/2178 take precedence)}
- H03F 3/2178: {using more than one switch or switching amplifier in parallel or in series (H03F3/2173, H03F3/2175 take precedence)}
- H03F 3/45179: {using MOSFET transistors as the active amplifying circuit (H03F3/45278 takes precedence)}
- H03F 3/45183: {Long tailed pairs (H03F3/4521, H03F3/45237 take precedence)}
- H03F 3/72: Gated amplifiers, i.e. amplifiers which are rendered operative or inoperative by means of a control signal
- H04R 3/02: for preventing acoustic reaction {, i.e. acoustic oscillatory feedback (specially adapted for hearing aids H04R25/453)}
- H03F 2203/21142: Output signals of a plurality of power amplifiers are parallel combined to a common output
- H03F 2203/21175: An output signal of a power amplifier being on/off switched
- H03F 2203/45361: the AAC comprising multiple transistors parallel coupled at their drains only, e.g. in a cascode dif amp, only those forming the composite common source transistor
- H03F 2203/45371: the AAC comprising parallel coupled multiple transistors at their source and gate and drain or at their base and emitter and collector, e.g. in a cascode dif amp, only those forming the composite common source transistor or the composite common emitter transistor respectively
- H03F 2203/45396: the AAC comprising one or more switches
- H03F 2203/45646: the LC comprising an extra current source
- H03F 2203/45648: the LC comprising two current sources, which are not cascode current sources
- H03F 2203/45726: the LC comprising more than one switch, which are not cross coupled
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)
- H03F: AMPLIFIERS

## Abstract

A circuit for suppressing audio output noise and an audio output circuit are provided. The circuit for suppressing audio output noise includes: a detecting circuit, configured to detect output voltages of output stages of an audio power amplifier; a control circuit, configured to output at least one control signal, the control signal is related to detection results of the detecting circuit; and a compensating circuit, configured to compensate at least one output stage of the audio power amplifier which includes a differential circuit based on the at least one control signal output by the control circuit, to make parameters of the differential circuit symmetrical or approach symmetrical. Based on detection results of the output stage voltages, the differential circuit in the output stages of the audio power amplifier is compensated. The circuit for suppressing audio output noise has a wider application scope and it is easy to design the circuit.

## Claims

### Claim 1

A circuit for suppressing audio output noise, comprising:
a detecting circuit, configured to detect output voltage values of output stages of an audio power amplifier;
a control circuit, configured to output at least one control signal, the control signal being related to detection results of the detecting circuit; and
a compensating circuit, configured to compensate at least one output stage of the audio power amplifier which comprises a differential circuit based on the at least one control signal output by the control circuit, to make parameters of the differential circuit symmetrical or approach symmetrical.

### Claim 2 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, further comprising:
a detecting output stage, configured to be connected with an output stage of the audio power amplifier; and
a detecting load, configured to be connected with the detecting output stage,
where the detecting circuit is connected with the detecting output stage and configured to compare an output voltage value of the detecting output stage with a reference voltage value to output a detection result, and the compensating circuit is configured to compensate at least one output stage before the output stage.

### Claim 3 (depends on 2)

The circuit for suppressing audio output noise according to claim 2, wherein the detecting output stage is connected with an output stage next to an end output stage of the audio power amplifier.

### Claim 4 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, the detecting circuit is connected with the end output stage of the audio power amplifier and configured to compare an output voltage value of the end output stage with a reference voltage value to output a detection result.

### Claim 5 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, wherein the detecting circuit comprises a voltage comparing circuit, configured to compare the output voltage values with a reference voltage value to output the detection results.

### Claim 6 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, wherein the compensating circuit comprises at least one compensating component, where the control signal is configured to control the compensating component to connect with a corresponding branch in the differential circuit.

### Claim 7 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, wherein the compensating circuit comprises at least one compensating component which corresponds to one branch of the differential circuit and at least one compensating component which corresponds to another branch of the differential circuit, where connection between the compensating components and the corresponding branches in the differential circuit is controlled by a corresponding control signal.

### Claim 8 (depends on 6)

The circuit for suppressing audio output noise according to claim 6, wherein the compensating component is a transistor, the transistor being controlled to be connected in parallel with a differential transistor in a corresponding branch by a corresponding control signal.

### Claim 9 (depends on 7)

The circuit for suppressing audio output noise according to claim 7, wherein the compensating component is a transistor, the transistor being controlled to be connected in parallel with a differential transistor in a corresponding branch by a corresponding control signal.

### Claim 10 (depends on 6)

The circuit for suppressing audio output noise according to claim 6, wherein the compensating component is a resistor, the resistor being controlled to be connected in parallel with a differential transistor in a corresponding branch by a corresponding control signal.

### Claim 11 (depends on 7)

The circuit for suppressing audio output noise according to claim 7, wherein the compensating component is a resistor, the resistor being controlled to be connected in parallel with a differential transistor in a corresponding branch by a corresponding control signal.

### Claim 12 (depends on 6)

The circuit for suppressing audio output noise according to claim 6, wherein the compensating component is a current source, the current source being controlled to be connected in parallel with another current source in a corresponding branch by a corresponding control signal.

### Claim 13 (depends on 7)

The circuit for suppressing audio output noise according to claim 7, wherein the compensating component is a current source, the current source being controlled to be connected in parallel with another current source in a corresponding branch by a corresponding control signal.

### Claim 14 (depends on 6)

The circuit for suppressing audio output noise according to claim 6, wherein the compensating component is a current source, one end of the current source being controlled to be connected with another current source and a differential transistor in a corresponding branch by a corresponding control signal, and the other end of the current source being grounded.

### Claim 15 (depends on 7)

The circuit for suppressing audio output noise according to claim 7, wherein the compensating component is a current source, one end of the current source being controlled to be connected with another current source and a differential transistor in a corresponding branch by a corresponding control signal, and the other end of the current source being grounded.

### Claim 16 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, wherein the control circuit is configured to determine which branch in the differential circuit of the at least one compensated output stage to be compensated based on the detection results, and to set a logical value for the control signal.

### Claim 17 (depends on 1)

The circuit for suppressing audio output noise according to claim 1, wherein the audio power amplifier is a class G audio power amplifier.

### Claim 18 (depends on 1)

An audio output circuit, comprising an audio power amplifier, a loudspeaker and the circuit for suppressing audio output noise according to claim 1.

### Claim 19 (depends on 18)

The audio output circuit according to claim 18, wherein the loudspeaker is an earphone or a bugle.