# US 2008/0186090 A1 · Audio system with power-on/off noise suppression and audio amplifier thereof

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- Number: US 2008/0186090 A1
- Document ID: US20080186090A1
- Status: Published application
- Kind: A1
- Application number: 11/671,471
- Filed: 2007-02-06
- Published: 2008-08-07
- Earliest claimed: 2007-02-06
- Assignees: Himax Analogic, Inc.
- Inventors: Kuo-Hung Wu
- Web page: https://patentgrep.com/patent/US20080186090A1

## CPC

- H03F 1/305: {in case of switching on or off of a power supply}
- H03F 2200/03: the amplifier being designed for audio applications
- H03F: AMPLIFIERS

## Abstract

An audio system with power-on/off noise suppression and an audio amplifier thereof are disclosed. The audio system includes a front stage circuit and an audio amplifier. The front stage circuit is powered by a first supply voltage and outputs an audio signal. The audio amplifier amplifies the audio signal to drive a load. When a level of the first supply voltage drops below a threshold, the audio amplifier is disabled.

## Claims

### Claim 1

An audio system comprising:
a front stage circuit powered by a first supply voltage and outputting an audio signal; and
an audio amplifier, amplifying the audio signal to drive a load;
wherein the front stage circuit operates normally only when the first supply voltage is above a threshold and the audio amplifier is disabled when a level of the first supply voltage drops below the threshold.

### Claim 2 (depends on 1)

The audio system as claimed in claim 1, wherein the threshold is 75% of the level of the first supply voltage during a steady state.

### Claim 3 (depends on 1)

The audio system as claimed in claim 1 further comprising:
a first resistor having a first end coupled to receive the first supply voltage; and
a second resistor having one end coupled to a second end of the first resistor and the other end coupled to receive a ground voltage;
wherein the audio amplifier is disabled when a level of the voltage on the second end of the first resistor is lower than a predetermined level corresponding to the threshold.

### Claim 4 (depends on 3)

The audio system as claimed in claim 3 further comprising a capacitor having one end coupled to the second end of the first resistor and the other end coupled to receive the ground voltage.

### Claim 5 (depends on 1)

The audio system as claimed in claim 1, wherein the audio amplifier is powered by a second supply voltage different from the first supply voltage.

### Claim 6 (depends on 5)

The audio system as claimed in claim 5 further comprising:
a first resistor having a first end coupled to receive the first supply voltage; and
a second resistor having one end coupled to a second end of the first resistor and the other end coupled to receive the second supply voltage;
wherein the audio amplifier is disabled when a level of the voltage on the second end of the first resistor is lower than a predetermined level corresponding to the threshold.

### Claim 7 (depends on 6)

The audio system as claimed in claim 6 further comprising a capacitor having one end coupled to the second end of the first resistor and the other end coupled to receive a ground voltage.

### Claim 8 (depends on 1)

The audio system as claimed in claim 1, wherein the first supply voltage is less than the second supply voltage.

### Claim 9 (depends on 1)

The audio system as claimed in claim 1, wherein the load comprises a speaker.

### Claim 10 (depends on 1)

The audio system as claimed in claim 1, wherein the front stage circuit comprises an audio decoder, coder or a micro control unit.

### Claim 11

An audio amplifier powered by a second supply voltage and amplifying an audio signal from a front stage circuit to drive a load, wherein the front stage circuit is powered by a first supply voltage and operates normally only when the first supply voltage is above a threshold, the audio amplifier comprising:
an input pin receiving a detection signal indicating a condition of the first supply voltage; and
a disabling circuit decoupling the second supply voltage from the audio amplifier when the detection signal indicates a level of the first supply voltage lower than the threshold.

### Claim 12 (depends on 11)

The audio amplifier as claimed in claim 11, wherein the threshold is 75% of the level of the first supply voltage during a steady state.