OSCILLATOR REACTIVE TUNING

Publishing Venue

Motorola

Related People

Abstract

Present solutions for frequency adjusting a crystal oscillator include, adjustable coils, trimmer capacitors, adjustable resistors in conjunction with a varactor or a combination of all. This adjustment is necessary to account for the build tolerances of the circuit parts and the crystal.

Volume 3 March 1983

OSCILLATOR REACTIVE TUNING By Ft. Jacobson and D. Marvin

STATEMENT OF PROBLEM

*

   Present solutions for frequency adjusting a crystal oscillator include, adjustable coils, trimmer capacitors, adjustable resistors in conjunction with a varactor or a combination of all. This adjustment is necessary to account for the build tolerances of the circuit parts and the crystal.

   Because of the physical size, cost and complexity of the existing warp schemes, a new means of adjusting frequency was deemed necessary. Since the nature of the designs is leaning toward small and compact size, circuit complexity has to be kept at a minimum.

The last criteria is to be able to automate the frequency adjust if necessary with the least amount of mechanization.

SOLUTION

    All the above disadvantages can be overcome by using the circuit in the attached figure, which is simply a parallel R-C network 100 placed directly into the loop of an oscillator. In operation, the total reactance of the network is a direct function of the values chosen for R and C. If C is held constant and the R is made variable then this network will have a variable reactance.

For an oscillator loop, the reactance seen by the crystal determines the frequency of oscillation. By varying the amount of reactance in the loop, the frequency can be corrected to account for the part
.tolerances and the crystal make tolerance.

B+

RENZ NR WORK 100 RL

1 OUTPUT

0 Motorola, Inc. 1963 21