Invalidity dossier
US 7787643
System and method for RF immunity of electret condenser microphone
Current assignee: Harman Embedded Audio LLC
Added 9/23/2026, 6:54:06 PM
Active provider: DeepSeek · deepseek-flash
Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
Patent Overview — US 7,787,643 B2
Title: System and method for RF immunity of electret condenser microphone
Assignee/Inventor: Original assignee MWM Acoustics LLC; current assignee listed as Harman Embedded Audio LLC. Inventor: Alan D. Michel.
Key dates: Priority date 2004-11-24; filed 2005-07-21; published as US20060109998A1 on 2006-05-25; granted 2010-08-31; status Active with adjusted expiration 2029-06-30.
Purpose: Electret condenser microphones (used in speakerphones and handsets) can pick up RF energy via their connecting cable, which acts as an antenna. Digital burst/packet modulation schemes (GSM, DECT, TDMA, cellular) cause the JFET amplifier's PN junction to demodulate that energy, producing audible interference. Prior approaches—capacitor placement plus shielding with ferrite beads, conductive tape, etc.—were often ineffective and added significant manufacturing expense. The invention aims to improve RF immunity cost-effectively using common components.
Plain-language scope: The patent places capacitors in a new position and geometry on the back of the electret condenser microphone to minimize RF magnetic fields seen by the internal JFET amplifier. In one embodiment, a capacitor is mounted on a printed wire board (PWB) so its longitudinal axis is perpendicular to the amplifier's longitudinal axis, and offset rather than directly opposite it, so the magnetic field from RF current does not encircle the JFET. In another embodiment, the capacitance is split into two physical capacitors, both perpendicular to the JFET and oriented 180 degrees from each other, so magnetic fields from RF currents tend to cancel near the amplifier. Claims as supplied describe the microphone comprising a PWB, an amplifier, and one or more capacitors arranged with these perpendicular/canceling orientations; methods cover providing and mounting these components. "Longitudinal axis" is defined as the line between a device's output pin and ground pin, not necessarily its longest packaging dimension.
What the excerpt does not establish: It does not provide full claim text, the complete specification, the omitted portion of the description (including FIG. 3C/FIG. 4 details), or independent verification of dates, assignee status, or legal status.
Generated 10/1/2026, 9:42:26 PM
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Assignment history
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Prior art
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