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Crystal Oscillator

IP.com Disclosure Number: IPCOM000094231D
Original Publication Date: 1966-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Evans, PJ: AUTHOR

Abstract

The crystal oscillator is used as a clock circuit in a data processing device. The configuration is basically a Butler oscillator. This comprises two silicon epitaxial NPN transistors T1 and T2 whose emitters are coupled together by the crystal defining the frequency of oscillation.

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Crystal Oscillator

The crystal oscillator is used as a clock circuit in a data processing device. The configuration is basically a Butler oscillator. This comprises two silicon epitaxial NPN transistors T1 and T2 whose emitters are coupled together by the crystal defining the frequency of oscillation.

The collector of T1 is directly connected to the base of T2. Tank circuit LC is connected between the base of T2 and the ground line to which are also connected the base of T1 and the collector of T2. The emitter of T1 is connected to a -3 volt line through resistor R2. The emitter of T2 is connected to the same line through resistor R3. The output is taken from the emitter of T2 by way of resistor R4.

T1 operates as a grounded-base amplifier with a current gain of approximately unity. T2 operates as an emitter-follower with a voltage gain of approximately unity. When the crystal is at resonance, its impedance has a minimum value Rx. The loop gain, which is approximately R1/Rx, is set at approximately 1. 5 so that oscillations build up until symmetrical limiting occurs. Such occurs due to T1 saturating on the negative half-cycles and T2 on the positive half-cycles. Under these conditions the circuit produces an output of approximately 1 volt peak-to-peak.

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