Browse Prior Art Database

Crystal Oscillator Device With Reliable Start-Up

IP.com Disclosure Number: IPCOM000120626D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Soyuer, M: AUTHOR

Abstract

A new crystal oscillator circuit configuration with reliable start-up is described. A biasing scheme based on a differential pair circuit enables the removal of the conventional shunt bias resistor across the crystal, thus eliminating the start-up problem.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 63% of the total text.

Crystal Oscillator Device With Reliable Start-Up

      A new crystal oscillator circuit configuration with
reliable start-up is described.  A biasing scheme based on a
differential pair circuit enables the removal of the conventional
shunt bias resistor across the crystal, thus eliminating the start-up
problem.

      Crystal oscillators are widely used to generate reference clock
frequencies in various electronic systems. The influence of crystal
and circuit parasitics on oscillator start-up conditions is discussed
in the literature -*-.  It is shown that the presence of resistor and
capacitor parasitics can result in oscillators with unreliable start-
up.  For example, in the commonly used Pierce crystal oscillator
shown in Fig. 1, DC bias is introduced via a very large shunt bias
resistor, RBIAS, which can be considered as a parasitic in AC
operation.  In fact, RBIAS creates a negative feedback path
decreasing the amount of positive feedback provided by the crystal,
XTAL. The inverting gain device T can be implemented in any
technology.  It is shown in [*] that removing RBIAS completely
eliminates the start-up problem.  Therefore, it is desirable to
devise a new biasing scheme which enables the removal of RBIAS as
described in the next section.

      The new circuit configuration is shown in Fig. 2.  T1 and T2
form the differential pair.  T1 acts as a follower and T2 as an
inverting stage.  Note that there is no biasing resistor across the
crystal. ...