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BIASING ARRANGEMENT FOR DIODE SWITCHED CRYSTAL OSCILLATORS

IP.com Disclosure Number: IPCOM000005442D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 72K

Publishing Venue

Motorola

Related People

Roger Jellicoe: AUTHOR

Abstract

A configuration for biasing a multi-channel pin diode switched crystal oscillator minimizes current drain, component count and circuit strays.

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@ MOIYlROLA Technical Developments Volume 2 January 1982

BIASING ARRANGEMENT FOR DIODE SWITCHED CRYSTAL OSCILLATORS By Roger Jellicoe

ABSTRACT

A configuration for biasing a multi-channel pin diode switched crystal oscillator minimizes current drain, component count and circuit strays.

INTRODUCTION

   The most popular means for selectively switching one of several crystals to a single oscillator is via pin diodes between the oscillator transistor and each of the crystals with its associated warp com- ponents. Figure 1 shows a typical circuit. The pin diode for the selected channel is biased on, and the diodes for all the non-selected channels are biased off, thus isolating them from the circuit.

The disadvantage of this arrangement is the additional current required to bias the pin diodes. In ad- dition the circuit strays introduced by the extra biasing resistors are in practice not negligible.

CIRCUIT DESCRIPTION

   Figure 2 shows the new configuration. The circuit has been demonstrated to work successfully with up to 10 crystals. The resistors Rl. R2 and R3 are adjusted to give the correct forward bias current for the on pin diode and the optimum operating point for the transistor. The blocking capacitor Cl and resistors R4 and R5 of the previous circuit are then no longer necessary and can be removed.

   An additional advantage of the new circuit, if the switch used is a break before make type, is that a Step voltage is applied to the base of the transistor during switc...