AUTO BIAS MICROPHONE SYSTEM FOR USE WITH MULTIPLE LOADS AND METHOD OF FORMING SAME

• US 20090046870A1
• Filed: 08/13/2007
• Published: 02/19/2009
• Est. Priority Date: 08/13/2007
• Status: Active Grant

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Turnbull, Robert R.
• Granted Patent: US 8,243,956 B2
• Time in Patent Office: Days
• US Class Current: 381/95
• CPC Class Codes: H04R 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

An autobias vehicular microphone system (300) includes a microphone (301) uses an amplifier (306) for amplifying an output of the microphone. A first feedback path (308) provides an amplifier output signal to the amplifier input for providing amplifier linearity and a second feedback path (305) is used for providing bias to an voltage reference (303). The voltage reference (303) operates to provide an autobias to the amplifier (306) based upon amplifier loading. Thus, a DC feedback loop works as an average voltage sensing circuit operating to center the amplifier (306) to an operating point near one half its supply voltage. By allowing the bias point to vary, a constant clip level can be maintained depending on varying load conditions of electronic devices (307, 309, 311) using the microphone (301).

Claims

1. An autobias vehicular microphone system comprising:

at least one microphone;

an amplifier connected to the at least one microphone for amplifying an output of the at least one microphone;

a first feedback path providing an amplifier output signal to the amplifier input for providing amplifier linearity;

a second feedback path for providing bias to an voltage reference; and

wherein the voltage reference operates to provide an autobias to the amplifier based upon amplifier loading.

2. An autobias vehicular microphone system as in claim 1, wherein the first feedback path is an audio feedback path.

3. An autobias vehicular microphone system as in claim 1, wherein the second feedback path is a direct current (DC) feedback path.

4. An autobias vehicular microphone system as in claim 1, wherein the second feedback path utilizes at least one voltage divider.

5. An autobias vehicular microphone system as in claim 1, wherein the second feedback path utilizes an averaging capacitor.

6. An autobias vehicular microphone system as in claim 1, wherein the at least one microphone is located in a rear view mirror.

7. An autobias microphone system for use in a vehicular mirror comprising:

at least one microphone for producing an audio output;

an amplifier for increasing the amplitude of the audio output;

an audio feedback path for providing feedback from an output of the amplifier to an input of the amplifier for providing amplifier linearity;

a direct current (DC) feedback path for providing a dynamic bias to a voltage reference; and

wherein the voltage reference adjusts the dynamic bias to the amplifier depending on the number of electronic devices using the at least one microphone.

8. An autobias microphone system as in claim 7, wherein the electronic devices include at least a cellular telephone.

9. An autobias microphone system as in claim 7, wherein the electronic devices include at least a navigation system.

10. An autobias microphone system as in claim 7, wherein the DC feedback path utilizes at least one voltage divider.

11. An autobias microphone system as in claim 7, wherein the DC feedback path utilizes at least one averaging capacitor.

12. A method for providing autobias to an automotive microphone system comprising the steps of:

producing an audio output using at least one microphone;

increasing the output of the audio output using an amplifier;

providing an output of the amplifier to an input of the amplifier using an alternating current (AC) feedback from an amplifier output to an amplifier input for providing amplifier stability;

providing a dynamic bias to a voltage reference using a direct current (DC) feedback path; and

adjusting the dynamic bias to the amplifier using the voltage reference depending on at least one electronic device loading the at least one microphone.

13. A method for providing autobias to an automotive microphone system as in claim 12, wherein the at least one electronic device is a cellular telephone.

14. A method for providing autobias to an automotive microphone system as in claim 12, wherein the at least one electronic device is an automotive navigation system.

15. A method for providing autobias to an automotive microphone system as in claim 12, wherein the DC feedback path includes at least one voltage divider.

16. A method for providing autobias to an automotive microphone system as in claim 12, wherein the DC feedback path includes at least one averaging capacitor.

17. A method for providing autobias to an automotive microphone system as in claim 12, wherein the AC feedback path is to a negative input of the amplifier.