TRIMMABLE CAPACITOR WITH LASER OR MANUALLY OPENABLE SHORT FOR FILTER TRIMMING
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-11
Due to unavoidable component tolerances, prese- lectors and other discrete, L-C falters often need to be tuned. In our factories, this is most easily accomplished by laser trimming, using Dishal's method (Dishal, M. "Alignment and Adjustment of Synchronously Tuned Multiple-Resonant-Circuit Filters:' Electrical Commu- nication, pp. 154-164, June 1952). In this method, each filter pole is tuned individually, with the untuned poles severely detuned or, in practice, shorted. As the tuning proceeds, shorted poles are unshotted one at a time, then tuned. While extremely accurate and repeatable, this trimming method does require that each filter pole be manufactured in a shorted condition, then unshorted during the trimming process. At present, this is accom- plished by separate O-ohm resistors, placed in each falter pole and opened by laser as required. After the tuning procedure is complete, the now-open resistors are left on the circuit board for the lie of the product, serving no function.