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Voltage-Controlled Oscillator With Capacitor Formed by Single Diode Biased for High Dynamic Resistance

IP.com Disclosure Number: IPCOM000046469D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Kiciak, PA: AUTHOR

Abstract

A diode is connected to form part of a frequency establishing network of an oscillator and is biased to operate in the region of high dynamic resistance of its voltampere characteristic curve. Because the diode is biased in its forward direction, it can be used in low voltage circuits. A capacitor isolates the oscillator from the biasing current, and the high dynamic resistance of the diode reduces the conductive load on the oscillator.

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Voltage-Controlled Oscillator With Capacitor Formed by Single Diode Biased for High Dynamic Resistance

A diode is connected to form part of a frequency establishing network of an oscillator and is biased to operate in the region of high dynamic resistance of its voltampere characteristic curve. Because the diode is biased in its forward direction, it can be used in low voltage circuits. A capacitor isolates the oscillator from the biasing current, and the high dynamic resistance of the diode reduces the conductive load on the oscillator.

Background

Some oscillators have a crystal 2, an LC circuit 3, and an amplifier 4. The frequency of this circuit is established by the resonant frequencies of the crystal and the LC circuit, and the frequency can be controlled by making small changes in the value of a capacitance that parallels the LC circuit. The parallel capacitor is commonly formed by two diodes that are connected in opposite polarity in a series circuit. Because a diode can store charge in response to a voltage difference across its junction, it forms a capacitor. The width of the junction varies with the voltage, and this effect is used to form a voltage variable capacitor. Conventionally, the voltage at the common connection point of the two diodes is adjusted to change the point on the voltampere characteristic curve where the diode operates. A control circuit 6 receives a measure of the oscillator output and changes the voltage of the diodes in a directio...