Invalidity dossier
US 4885799
Load pull isolation switch for a fast locking synthesizer
Current assignee: Motorola Solutions Inc
Added 9/21/2026, 9:27:02 AM
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Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
Patent Overview — US 4,885,799
Title: Load pull isolation switch for a fast locking synthesizer
Patent number: US4885799A | Application: US07/069,796 | Inventor: Mark I. Van Horn | Original assignee: Motorola, Inc. (Schaumburg, Illinois, a corp. of DE) | Current assignee listed: Motorola Solutions Inc (Google notes assignees may be inaccurate and that no legal analysis is represented) | Priority/filing date: 1987-07-01 | Grant/publication date: 1989-12-05 | Status: Expired – Lifetime; anticipated expiration 2007-07-01.
Purpose: The invention relates generally to signal source isolation stages, and more particularly to solid state radio frequency isolation switches for mobile radio transceivers. The problem addressed is "load pull": the variable input impedance presented by an RF power amplifier (PA) as it is keyed up can disturb a voltage controlled oscillator (VCO) in a frequency synthesizer. Prior approaches used high performance buffer stages, which add current drain and limit how fast the radio can transmit — a drawback for high speed data or time-division-multiplex systems.
Plain-language scope: A signal source is selectively coupled through an isolation switch to either a first load having a fixed terminating impedance of the desired value, or a second load whose impedance varies about that desired value. A controller/sensor detects that both the source frequency and the variable load have settled to values very nearly equal to their proper values, then causes the switch to change conductive state and divert the signal to the variable load. The switch may be a PIN diode network (with quarter-wavelength transmission lines, coupling capacitor, current-limiting resistors, and decoupling chokes) or a coaxial relay; a logic implementation uses a time delay and an AND gate. A mobile radio embodiment employs a programmable fast-locking synthesizer, an RF PA, and a microprocessor-controller; a flowchart and timing diagram show the sequence.
Source: https://patents.google.com/patent/US4885799/en
What the excerpt does not establish: The excerpt omits the issued claims' full text, the abstract, and most of the detailed description and drawings; it does not establish claim scope as allowed, the precise t1–t4 timing values, or any litigation, ownership-transfer, validity, or prior-art conclusions.
Generated 10/1/2026, 10:02:22 PM
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Litigation summary
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PTAB challenges
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Assignment history
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Prior art
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Obviousness
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Derivative works
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