Capacitor switching circuits for adjusting crystal oscillator frequency

Claim 1

A piezo-electric oscillator comprising: a quartz crystal having input and output terminals; an inverting amplifier connected across the input and output terminals of said quartz crystal; a first capacitor normally connected to the input terminal of said quartz crystal; a second capacitor; and electronic switching means connected between said input terminal of said quartz crystal and said second capacitor for controlling connection of said second capacitor relative to the input terminal of said quartz crystal for thereby adjusting an operating frequency of said quartz crystal to a prescribed value, said electronic switching means comprising a transmission gate having first and second control gate terminals, a first resistor, said first control gate terminal of said transmission gate being connected to the positive side of a power supply through said first resistor, a second resistor, said second control gate terminal of said transmission gate being connected to the negative side of said power supply through said second resistor, a first lead connecting said first control gate terminal directly to the negative side of said power supply, a second lead connecting said second control gate terminal directly to the positive side of said power supply, whereby said transmission gate is nonconductive to interrupt connection between the input terminal of said quartz crystal and said second capacitor, and said first and second leads being cut by a laser trimming to allow said transmission gate to turn on for thereby connecting said second capacitor to the input terminal of said quartz crystal to adjust the operating frequency thereof.