WO1999051060A1

WO1999051060A1 - Microphone with reduced rf sensitivity

Info

Publication number: WO1999051060A1
Application number: PCT/US1999/007222
Authority: WO
Inventors: Dennis Ray Kirchhoeffer; Frank R. Mitchell
Original assignee: Knowles Electronics, Inc.
Priority date: 1998-03-31
Filing date: 1999-03-31
Publication date: 1999-10-07
Also published as: AU3219899A

Abstract

A microphone (10) for a hearing aid is disclosed having a feedthrough filter capacitor assembly (30), a terminal pin (18, 20, 22) and a conductive adhesive (32). The feedthrough filter capacitor assembly has a pair of capacitor electrodes and is similar to those used to filter undesired interference signals in an implantable medical device. The feedthrough filter capacitor assembly has an opening (24, 26, 28) through which the output terminal pin (18) is placed. The conductive adhesive is placed within the opening of the feedthrough filter capacitor assembly around the output terminal pin to secure the terminal pin within the feedthrough filter capacitor assembly and to make an electrical connection with one of the capacitor electrodes.

Description

MICROPHONE WITH REDUCED RF SENSITIVITY

DESCRIPTION

Technical Field

The present invention relates to microphones with reduced RF sensitivity, and more particularly, to a microphone for a hearing aid incorporating a feedthrough filter capacitor assembly to filter undesired interference signals.

Background of the Invention

Hearing aid microphones are sensitive to electrical interference and noise transmission along the output of the microphone. Typically, a microphone housing is designed to shield the microphone from unwanted radiated interference or noise. However, leads that are connected to the microphone to supply operating power (e.g.,

-Vdd and +Vdd) and to connect the microphone output to additional circuitry within the hearing aid can themselves act as receiving antenna and pickup and feed unwanted interference and noise into the microphone.

Summary of the Invention

The present invention relates to a microphone comprising a feedthrough filter capacitor assembly, a terminal pin and a conductive adhesive. The feedthrough filter capacitor assembly has a pair of capacitor electrodes and is similar to those used to filter undesired interference signals in an implantable medical device. The feedthrough filter capacitor assembly has an opening through which the output terminal pin is placed. The conductive adhesive is placed within the opening of the feedthrough filter capacitor assembly around the output terminal pin to secure the terminal pin within the feedthrough filter capacitor assembly and to make an electrical connection with one of the capacitor electrodes. Brief Description of the Drawings

Figure 1 is a perspective view of a microphone according to the present invention with part of the microphone housing cut away;

Figure 2 is schematic representation of the capacitive filter around each terminal of the microphone of Figure 1; and

Figure 3 illustrates RF immunity in a microphone with and without a feedthrough filter capacitor assembly.

Detailed Description While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated.

A hearing aid microphone, generally designated 10, is illustrated in Figure 1. The microphone 10 comprises a housing 12 having an inlet tube 14 extending outwardly from a wall 16 of the housing 12. The inlet tube 14 receives sound and communicates the received sound into the microphone 10. A diaphragm in the microphone 10 vibrates in response to the sound, resulting in an electrical signal which is transmitted from the output terminal pin 18 of the microphone 10.

Terminal pin 20 connects the positive terminal of a battery (not shown) to the microphone 10, and terminal pin 22 connects the negative terminal of the battery to the microphone 10. Terminal pins 18, 20, 22 are placed into openings 24, 26, 28 in a feedthrough filter capacitor assembly 30. The feedthrough filter capacitor assembly

30 shields or filters undesired external interference signals, such as from digital cell phones, from the pins 18, 20, 22. The feedthrough filter capacitor assembly 30 used in the present invention is provided by Maxwell Laboratories, Inc., Sierra Capacitor Filter Division, Carson City, Nevada, and is disclosed in U.S. Patent No. 5,333,095, the specification of which is incorporated herein by reference. The capacitor 30 includes a plurality of coplanar electrode plates within an electrically insulative or dielectric base structure. Each electrode plate has an aperture for receiving one of the terminal pins.

The feedthrough filter capacitor assembly 30 is mounted onto the microphone housing using, for example, a conductive cement 32, and terminal pins 18, 20, 22 are mounted onto feedthrough filter capacitor assembly 30 using a conductive cement or solder 34.

Figure 2 is a schematic representation of the capacitor plates of the feedthrough filter capacitor assembly 30 around the terminal pins 18, 20. Although each capacitor depicted in Figure 2 is shown to have a pair of electrode plates, it is to be understood that each schematically depicted capacitor plate can include a plurality of conductive plates stacked in coplanar relationship with each other and electrically coupled together. In the schematic representation, one plate 36, 38 of each capacitor is grounded, via terminal pin 22, while the other plate 42, 44 is connected to the respective terminal pin 18, 20. Terminal pin 22 is grounded.

Figure 3 illustrates RF immunity in a microphone 10 with and without the feedthrough filter capacitor assembly 30. Accordingly, the feedthrough filter capacitor assembly provides a low impedance path to ground for suppressing unwanted signals that can cause interference or noise in the microphone output. For example, these unwanted signals can be generated by digital cellular phones and the like. While the specific embodiment has been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection is only limited by the scope of the accompanying Claims.

Claims

CLAIMSI CLAIM:

1. A microphone comprising: a feedthrough filter capacitor assembly having an opening and a capacitor with at least one pair of electrically conductive plates; an output terminal pin placed within the opening of the feedthrough filter capacitor assembly; and a conductive adhesive placed within the opening of the feedthrough filter capacitor assembly around the output terminal pin to electrically couple the terminal pin to one of the conductive plates of the capacitor.

2. The microphone of claim 1 further including a ground terminal pin operably coupled to one of the conductive plates of the capacitor.

3. The microphone of claim 1 wherein the feedthrough filter capacitor assembly includes a second opening for receiving a voltage supply terminal pin and a capacitor operably connected to the supply pin.

4. The microphone of claim 3 further including a ground terminal pin operably connected to both of the capacitors of the filter capacitor assembly.

5. The microphone of claim 1 wherein the filter capacitor assembly is attached to a hearing aid microphone housing.

6. A microphone comprising: a hearing aid housing; a feedthrough filter capacitor assembly attached to the housing and having an opening and a capacitor with at least one pair of electrically conductive plates; an output terminal pin placed within the opening of the feedthrough filter capacitor assembly; a conductive adhesive placed within the opening of the feedthrough filter capacitor assembly around the output terminal pin to electrically couple the terminal pin to one of the conductive plates of the capacitor; and wherein a low impedance path is provided to ground for substantially preventing unwanted signals from interfering with the output terminal.

7. The microphone of claim 6 wherein the low impedance path includes a ground terminal pin operably coupled to one of the conductive plates of the capacitor.

8. The microphone of claim 6 wherein the feedthrough filter capacitor assembly includes a second opening for receiving a voltage supply terminal pin and a capacitor operably connected to the supply pin.

9. The microphone of claim 8 wherein the low impedance path includes a ground terminal pin operably connected to both of the capacitors of the filter capacitor assembly.

10. A microphone comprising: a hearing aid housing; a feedthrough filter capacitor assembly attached to the housing and having first and second openings and first and second capacitors with at least one pair of electrically conductive plates; an output terminal pin received within the first opening of the feedthrough filter capacitor assembly and operably coupled to one of the conductive plates of the first capacitor; and a voltage supply terminal pin received within the second opening of the feedthrough filter capacitor assembly and operably coupled to one of the conductive plates of the second capacitor.

11. The microphone of claim 10 further including a ground terminal pin operably connected to both of the first and second capacitors of the filter capacitor assembly.

12. The microphone of claim 11 wherein the output pin provides a transmission path for an electrical signal responsive to an audible sound.