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Browse Prior Art Database

REFERENCE OSCILLATOR DESIGN FOR IMPROVED RECEIVER FREQUENCY STABILITY

IP.com Disclosure Number: IPCOM000006059D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2001-Nov-29
Document File: 2 page(s) / 79K

Publishing Venue

Motorola

Related People

Ed Callaway: AUTHOR

Abstract

Frequency drift of narrowband receivers is a major design concern. Frequency drift over temperature, of superheterodyne receivers is largely caused by two factors: local oscillator drift and i.f. filter drift. These drifts must be compensated by widening the i.f. filters, which in turn degrades receiver selectivity. With the introduction of digitally stabilized reference oscillators, local oscillators controlled by the phase locked loop method can be stabilized to 1 ppm or less quite economically, eliminating the local oscillator drift as a concern. This leaves the i.f. filter as the major source of receiver drift. This invention uses the local oscillator to counteract the filter drift, to produce a receiver with significantly greater frequency stability.

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MOTOROLA INC. Technical Developments Volume 12 April 1991

REFERENCE OSCILLATOR DESIGN FOR IMPROVED RECEIVER FREQUENCY STABILITY

by Ed Callaway

   Frequency drift of narrowband receivers is a major design concern. Frequency drift over temperature, of superheterodyne receivers is largely caused by two factors: local oscillator drift and i.f. filter drift. These drifts must be compensated by widening the i.f. filters, which in turn degrades receiver selectivity. With the introduction of digitally stabilized reference oscillators, local oscillators controlled by the phase locked loop method can be stabilized to 1 ppm or less quite economically, eliminating the local oscillator drift as a concern. This leaves the i.f. filter as the major source of receiver drift. This invention uses the local oscillator to counteract the filter drift, to produce a receiver with significantly greater frequency stability.

  Digitally stabilized reference oscillators, such as those now used in the MicroTAC cellular telephone and the MTX portable radio series, employ an EEPROM storing frequency correction values every few degrees centigrade. This corrects the oscillator frequency back to the desired, constant value as the temperature varies. This idea has been used to advantage in transmitter circuits, and in receiver circuits to stabilize the local oscillator frequency. For transmitters this is satisfactory; for receivers the problem is not yet solved due to the i.f. filter drift..

The solution is to warp the local oscillator frequency to correct for the i.f. filter drift as well as its

own temperature drift, in the same way the tran...