1983-05-19
1985-09-17
Rubinson, Gene Z.
29592E, H04R 1901
Patent
active
045422648
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a lead-frame for an electret microphone and associated preamplifier of integrated design.
BACKGROUND ART
As known, an electret microphone consists of a charged and/or polarized polymer film, called an electret film, one surface of which is coated with a thin metal layer which constitutes one of the electrodes in the microphone. The electret film and the metallized electrode are biased having the metallized layer turned upwards along a rear plate which constitutes the second electrode. Between the electret film and the rear plate or the rear electrode a small air gap, called an air film, is formed and an electrostatic field between the two electrodes is created. This field is called a bias field. Upon acoustic influence by sound pressure in front of the microphone, the electret film vibrates and the height of the air gap is changed, whereby the electrostatic field is changed. Due to this variation of the electrostatic field, a varying voltage drop across the two electrodes arises. Thus, if an amplifier having a suitable impedance match is connected between the two electrodes a voltage change depending on the variable sound pressure on the electret film can be obtained.
Since the voltage variation across the two electrodes is weak, it is, as above mentioned, necessary to connect an amplifier with a suitable impedance match to the electrodes. The problem is then to limit the number of parts in the microphone and at the same time to have a good connection between electret and amplifier.
It is previously known for this purpose to build in the electret microphone an integrated circuit containing a preamplifier and to form the same into a single capsule as shown, for example, in the Bell System Technical Journal, September 1979, No. 7, page 1557. Thereby a compact unit is obtained.
SUMMARY OF INVENTION
An object of the present invention is to reduce the number of units in an electret microphone by providing a lead-frame for the electret film and the associated preamplifier, thus provides a compact and simple construction for a microphone-preamplifier unit.
The invention is characterized by the provision of a lead frame for an electret microphone. The lead frame of the invention comprises an H-shaped structure of thin metallic material including spaced parallel legs and a crossbar therebetween. A first plate spaced from the crossbar is located between the aforesaid legs. A lead connects the first plate to the crossbar. A second plate is spaced from the first plate and a lead connects the two said plates. The plates and the leads are monolithic with and coplanar with the H-shaped structure being formed of metallized film. The second plate is provided with holes and an amplifier chip is mounted on the first plate. Leads connect the chip with the aforesaid legs. A first case half supports the aforesaid plates with distant pieces being provided adjacent the second plate and a metalized film being supported on the distant pieces in spaced parallel relation to the second plate. A second case half is superposed on the first case half and is provided with openings corresponding with the aforesaid plate. A cover encircles the two said halves.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully described with reference to the accompanying drawings in which:
FIG. 1 shows a lead-frame according to the invention,
FIG. 2 shows a part of a lead-frame according to FIG. 1 for mounting a monolite circuit,
FIG. 3 is an exploded view of an electret microphone and an amplifier capsule utilizing the lead-frame according to the invention, an
FIG. 4 shows a carrier band with a number of frames according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the lead-frame according to the invention is generally designated 1. It consists of a thin metallic material such as, for example, nickel, brass or copper. In the illustrated embodiment, one part of the frame consists of two leads 2a,2b which have approximately the same width and extend in para
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patent: 4492825 (1985-01-01), Brzezinski et al.
Elektor, "Electret Microphone Preamplifier", vol. 3, No. 12, Dec. 1977, pp. 12-18-12-19.
Aksberg Arvi J.
Johansson Jan H.
Malmkvist Hans G.
Schmidt Henning M.
Byrd Danita R.
Rubinson Gene Z.
Telefonaktiebolaget LM Ericsson
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