US 4,365,213 AGranted

Low frequency astable oscillator having switchable current sources

AssigneeMotorola, Inc.

InventorsKenneth A. Hansen, Ronald H. Chapman

Life of this patent

Estimating the term…

Loading patent…

Abstract

A low frequency oscillator of the astable type having good frequency stability, fast starting, good immunity to DC loading, and suitable for fabrication in integrated circuit form. First and second switching transistors of the astable multivibrator are cross-coupled by a coupling capacitor and a frequency determining crystal. Base drive to the respective switching transistors and charging current to the capacitor and crystal are provided by a pair of differential amplifiers which are referenced to a forward biased diode. The differential amplifiers are also connected to respective collector terminals of the switching transistors. The capacitor is of small value suitable for containment within an integrated circuit with the oscillator circuit. The differential amplifiers substantially increase the impedance levels in the oscillator and shift base drive to the switching transistors to minimize the effects of DC loading at the output terminals of the oscillator.

Claims4

Dependent claims

A low frequency oscillator of the astable type comprising:

first switching transistor means having emitter, base and collector electrodes;
second switching transistor means having emitter, base and collector electrodes;
said emitter electrodes of said first and second switching transistor means coupled to a predetermined DC reference level;
the base electrode of the first transistor means adapted to be connected to the collector electrode of the second transistor means through a frequency determining element;
capacitive means cross-coupling the base electrode of the second transistor means to the collector electrode of the first transistor means;
first switchable current source means coupled to the base electrode of said first switching transistor means to supply base drive to the first switching transistor means and to provide charging current to the frequency determining element;
second switchable current source means coupled to the base electrode of the second switching transistor means to supply base drive to the second switching transistor means and to provide charging current to the cross-coupling capacitive means;
and
said first and second switchable current source means respectively including first and second differential amplifier means, a first input of each of the respective differential amplifier means referenced to a reference voltage, a second input of the first differential amplifier means coupled to the collector electrode of the first switching transistor means, and a second input of the second differential amplifier means coupled to the collector electrode of the second switching transistor means.

6 more elements

Dependencies are inferred from the claim text.