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The Ultra Low Power On-Chip Oscillator

IP.com Disclosure Number: IPCOM000118564D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Kimura, S: AUTHOR [+2]

Abstract

Disclosed is a circuit to drastically reduce power consumption of the on-chip oscillator. In addition to the conventional Pierce oscillator, the supplementary devices are utilized to obtain higher driveability at the start-up of oscillation. After it is stabilized, its additional devices are cut down to minimize power consumption of the total on-chip oscillator.

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The Ultra Low Power On-Chip Oscillator

      Disclosed is a circuit to drastically reduce power consumption
of the on-chip oscillator.  In addition to the conventional Pierce
oscillator, the supplementary devices are utilized to obtain higher
driveability at the start-up of oscillation.  After it is stabilized,
its additional devices are cut down to minimize power consumption of
the total on-chip oscillator.

      Fig. 1 shows the conventional and basic Complementary Metal
Oxide Semiconductor (CMOS)-type on-chip oscillator.  It relatively
needs the big NFET and PFET devices for the normal oscillation for
starting it up, which means superfluous power is consumed even at the
stabilized condition.  Fig. 2 shows the oscillator based on a new
idea to reduce power consumption.  In this circuit, PFET_1,PFET_2 and
NFET_1,NFET_2 are newly added to the basic Pierce circuit shown in
Fig. 1.  CNTLP is fixed to 'LOW' and CNTLN to 'HIGH' to activate the
PFET_2 and the NFET_1 only when high driveability is required for the
stable oscillation for starting it up.  Then, after oscillation has
been stabilized in 10 or 20 milliseconds, CNTLP is switched to 'HIGH'
and CNTLN to 'LOW' to disable the PFET_2 and the NFET_1.  It
consequently leads to smaller drain current.

      Thus, the on-chip oscillator with the 32KHz crystal, shown in
Fig. 2, can attain the ultra low current of less than 1 microamp at
the voltage range of 2.0 to 3.6.