Browse Prior Art Database

HIGH PULLABILITY VOLTAGE CONTROLLED CRYSTAL OSCILLATOR

IP.com Disclosure Number: IPCOM000005478D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2001-Oct-08
Document File: 1 page(s) / 56K

Publishing Venue

Motorola

Related People

Paul Gailus: AUTHOR [+2]

Abstract

A voltage controlled crystal oscillator was developed which has extended tuning range while main- taining good Cl and temperature stability. With the circuit values indicated in the attached figure, * f .045% tuning was achieved over a 2.12V steering line change.

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Volume 3 March 1983

HIGH PULLABILITY VOLTAGE CONTROLLED CRYSTAL OSCILLATOR

By Paul Gailus and Jan Vanderspool

A voltage controlled crystal oscillator was developed which has extended tuning range while main- taining good Cl and temperature stability. With the circuit values indicated in the attached figure,

* f .045% tuning was achieved over a 2.12V steering line change.

It is well known that adding a series inductor to a crystal can extend the inductive region between the series and parallel resonant frequencies, allowing increased tuning range. However, this degrades

L oscillator Q. The new oscillator circuit incorporates a number of features which minimize the extra in- ductance (Et), (10) required for a given tuning range, leading to improved performance. The use of a source follower (14) and series resistor (16) minimize the loading on the crystal (12) and its associated network. The large real part of this load impedance improves the Q. The large imaginary part insures that the capacitance ratio capabilities of the varactors (16), (20) are fully utilized, which increases the tuning range. The back-to-back diodes (24) (26) across the tuned tank of transistor (22) limit the peak drive to the Pierce type crystal network to approximately 0.7V. Since the varactors appear as shunt elements in the crystal network, they can be biased down toOV without conduction no matter how high the network Q. Hence, the tuning range is extended.

   An inverting bipolar stage (22) p...