Acoustic drive circuit

• US 7,171,011 B2
• Filed: 11/26/2002
• Issued: 01/30/2007
• Est. Priority Date: 05/24/2002
• Status: Expired due to Fees

• Current Assignee: LAPIS Semiconductor Co., Ltd. (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Morimoto, Masashi
• Primary Examiner(s): Mei; Xu
• Assistant Examiner(s): CHAU, COREY P
• Application Number:
  US10/303,949
• Publication Number:
  US 20030219135A1
• Time in Patent Office: 1,526 Days
• Field of Search: 330/10, 330/251, 381/120, 381/28, 381/74, 381/111, 381/116, 381/117, 381/400, 381/401
• US Class Current: 381/120
• CPC Class Codes: H04R 5/033 Headphones for stereophonic communication details thereof, e.g. relating to batteries, cables or control elements H04R1/10
• CPC Class Codes: H04S 1/00 Two-channel systems H04S5/00, H04S7/00 take precedence

Abstract

An acoustic drive circuit for driving a headphone for converting variation of magnetic force, occurring to a voice coil, in sound, and outputting the sound, includes a power amplifier for amplifying a signal at a frequency within the speech band, and outputting the signal after amplification, at a voltage with a given bias voltage superposed thereon, to one end of the voice coil of the headphone, and a pulse generation circuit for generating a pulse signal at a frequency higher than those in the speech band, having an average voltage equivalent to the bias voltage, and for outputting the pulse signal to the other end of the voice coil. The pulse generation circuit generates rectangular waves at a frequency higher than those in the speech band, having a duty ratio such that the average voltage is equivalent to the bias voltage.

Claims

1. An acoustic drive circuit comprising:

a first power amplifier having a first input terminal for receiving a first acoustic signal, a second input terminal connected to receive a reference voltage, and a first output terminal,

the first power amplifier including a first differential amplifier having a first negative input, a first positive input connected to the second input terminal, and a first output connected to the first output terminal, and also including a first resistor connected between the first input terminal and the first negative input, and a first feedback resistor connected between the first output and the first negative input of the first differential amplifier;

a second power amplifier having a third input terminal for receiving a second acoustic signal, a fourth input terminal connected to receive the reference voltage, and a second output terminal,

the second power amplifier including a second differential amplifier having a second negative input, a second positive input connected to the fourth input terminal, and a second output connected to the second output terminal, and also including a second resistor connected between the third input terminal and the second negative input, and a second feedback resistor connected between the second output terminal and the second negative input of the second differential amplifier; and

a pulse generator having an output terminal for outputting a pulse signal having a frequency higher than frequencies in a speech band and having an average voltage that is equal to about the reference voltage, wherein the first output terminal of the first power amplifier is connected to one end of a first voice coil of a headphone and the second output terminal of the second power amplifier is connected to one end of a second voice coil of the headphone, and the output terminal of the pulse generator is connected to a common terminal between other ends of the first and second voice coils.

2. An acoustic drive circuit according to claim 1, wherein the reference voltage is equal to about a half of a power supply voltage.

3. An acoustic drive circuit according to claim 1, wherein the frequency of the pulse signal is about 2 MHz.

4. An acoustic drive circuit for driving a voice coil having first and second ends, comprising:

a power amplification circuit having a first input terminal for receiving an acoustic signal having a first voltage level, a second input terminal having a reference voltage applied thereto, and an output terminal connected to the first end of the voice coil and that outputs a drive signal having a second voltage level that is equal to a sum of the first voltage level and a level of the reference voltage; and

a pulse generation circuit connected to the second end of the voice coil, the pulse generation circuit generating a pulse signal having a frequency higher than frequencies of a speech band and having an average voltage level equivalent to the level of the reference voltage,

wherein the power amplification circuit includes a differential amplifier having a negative input connected to the first input terminal, a positive input connected to the second input terminal and an output connected to the output terminal, and

wherein the power amplification circuit further includes an input resistor connected between the first input terminal and the negative input of the differential amplifier.

5. An acoustic drive circuit according to claim 4, wherein the power amplification circuit further includes a feedback resistor connected between the negative input and the output of the differential amplifier.

6. An acoustic drive circuit according to claim 4, wherein the reference voltage is equal to about a half of a power supply voltage.

7. An acoustic drive circuit according to claim 4, wherein the frequency of the pulse signal is about 2 MHz.

8. An acoustic drive circuit according to claim 4, wherein the voice coil is included in a headphone.