Low-noise directional microphone system

• US 7,409,068 B2
• Filed: 03/06/2003
• Issued: 08/05/2008
• Est. Priority Date: 03/08/2002
• Status: Expired due to Fees

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Sound Design Technologies Limited (ON Semiconductor Corporation)
• Inventors: Ryan, Jim G., Csermak, Brian D.
• Primary Examiner(s): Chin; Vivian
• Assistant Examiner(s): KURR, JASON RICHARD
• Application Number:
  US10/383,141
• Publication Number:
  US 20030169891A1
• Time in Patent Office: 1,979 Days
• Field of Search: 381/92, 381/317, 381/313, 381/97, 381/356, 381111-115, 381/320
• US Class Current: 381/313
• CPC Class Codes: H04R 1/08 Mouthpieces; Microphones; Attachments therefor
• CPC Class Codes: H04R 1/38 in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone
• CPC Class Codes: H04R 2410/01 Noise reduction using microphones having different directional characteristics
• CPC Class Codes: H04R 2430/03 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04R 2430/21 Direction finding using differential microphone array [DMA]
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers

Abstract

A low-noise directional microphone system includes a front microphone, a rear microphone, a low-noise phase-shifting circuit and a summation circuit. The front microphone generates a front microphone signal, and the rear microphone generates a rear microphone signal. The low-noise phase-shifting circuit implements a frequency-dependent phase difference between the front microphone signal and the rear microphone signal to create a controlled loss in directional gain and to maintain a maximum level of noise amplification over a pre-determined frequency band. The summation circuit combines the front and rear microphone signals to generate a directional microphone signal.

Claims

1. A hearing instrument, comprising:

a front microphone that generates a front microphone signal;

a rear microphone that generates a rear microphone signal;

a phase-shifting circuit that implements a frequency-dependent phase shift between the front microphone signal and the rear microphone signal to create a controlled loss in directional gain and maintain a predetermined maximum level of microphone self noise amplification (G_N) over a pre-determined frequency band,

the frequency-dependent phase shift being configured to provide a maximum amount of directional gain given the predetermined maximum level of microphone self noise amplification (G_N);

the frequency-dependent phase shift (θ

_LN) including an inter-microphone phase shift (Δ

θ

) in addition to a time-of-flight delay (θ

_C), such that Δ

θ

=θ

_LN−

θ

_C; and

wherein the frequency-dependent phase shift (θ

_LN) satisfies the following equation;

2. The hearing instrument of claim 1, wherein x satisfies the following set of equations:

3. The hearing instrument of claim 1, wherein the time-of-flight delay (θ

_C) satisfies the following equation;