Microphone bias circuit

Patent metadata

Field	Value
Publication number	US-9710000-B2
Application number	US-201514696998-A
Country	US
Kind code	B2
Filing date	Apr 27, 2015
Priority date	Apr 25, 2014
Publication date	Jul 18, 2017
Grant date	Jul 18, 2017

Abstract

A bias circuit supplies a bias voltage V BIAS to a microphone. A variable gain amplifier amplifies a reference voltage V REF . A low-pass filter removes a high-frequency component from the output of the variable gain amplifier. A voltage follower amplifier receives the output voltage of the low-pass filter, and supplies the output voltage to the microphone.

First claim

What is claimed is:

1. A bias circuit structured to supply a bias voltage to a microphone, the bias circuit comprising:
a variable gain amplifier structured to amplify a reference voltage;
a low-pass filter structured to remove a high-frequency component of an output of the variable gain amplifier; and
a voltage follower amplifier structured to receive an output voltage of the low-pass filter, and structured to supply the output voltage to the microphone,
wherein the bias circuit further comprises:
a first line;
a second line having a potential lower than that of the first line; and
a voltage source that is coupled between the first line and the second line and structured to generate the reference voltage, and wherein the variable gain amplifier comprises;
a first operational amplifier coupled between the first line and the second line, and having its non-inverting input terminal receiving the reference voltage, its inverting input terminal and its output terminal; and
a first resistor and a second resistor provided in series between the output terminal of the first operational amplifier and the second line, wherein a node where the first resistor and the second resistor meets is coupled to the inverting input terminal of the first operational amplifier,

and wherein the voltage follower amplifier comprises:
a second operational amplifier coupled between the first line and the second line, and having its non-inverting input terminal receiving the output voltage of the low-pass filter and its inverting terminal directly coupled to its output terminal.

2. The bias circuit according to claim 1 , wherein the low-pass filter has a cutoff frequency that is lower than 50 Hz.

3. The bias circuit according to claim 1 , wherein the low-pass filter is configured as an RC filter.

4. The bias circuit according to claim 1 , wherein the variable gain amplifier is configured as a non-inverting amplifier.

5. The bias circuit according to claim 1 , wherein the variable gain amplifier comprises:
an operational amplifier structured to receive the reference voltage via a non-inverting input terminal thereof; and
a variable voltage-dividing circuit structured to divide an output voltage of the operational amplifier with a variable dividing ratio, and structured to input the voltage thus divided to an inverting input terminal of the operational amplifier.

6. An audio interface circuit comprising:
the bias circuit according to claim 1 ;
a microphone amplifier structured to amplify an output signal of the microphone;
an A/D converter structured to convert an output of the microphone amplifier into a digital signal; and
a digital signal processing unit structured to perform signal processing on the digital signal.

7. The audio interface circuit according to claim 6 , monolithically integrated on a single semiconductor substrate.

8. An electronic device comprising:
a microphone; and
the audio interface circuit according to claim 6 .

Assignees

• Rohm Co Ltd

Inventors

• Yamada Kenta
• Ego Hirotsugu

Classifications

• H03F3/187

  in integrated circuits · CPC title

• G05F1/10 Primary

  Regulating voltage or current  (G05F1/02 takes precedence) · CPC title

• H04R1/04

  Structural association of microphone with electric circuitry therefor (in electric hearing aids H04R25/00) · CPC title