US 5,047,734 A · Linear crystal oscillator with amplitude control and crosstalk cancellation

Abstract

A series-feedback crystal oscillator has a crystal element in series with a buffer amplifier. The oscillator maintains a linear oscillation signal by using an amplitude control circuit to hold the oscillation signal to a certain level at which distortion, clipping, or saturation does not occur. A control signal indicative of the amplitude of the oscillation signal linearly multiplies the oscillation signal to control the amplitude of the oscillation signal. Shunt capacitance across the crystal is compensated for by connecting a compensating capacitor to the same input terminal of the buffer amplifier as is connected the crystal. A compensating signal, which is equal in amplitude but opposite in phase to the signal passing through the shunt capacitance of the crystal is fed to the input terminal of the buffer amplifier to cancel the effect of the shunt capacitance. A noninverted tracer signal is injected in the feedback loop and passes through the shunt capacitance. An inverted tracer signal passes through the compensating capacitor to cancel the noninverted tracer signal through the shunt capacitance and thereby compensate for the shunt capacitance of the crystal. Interfering crosstalk signals from one crystal oscillator circuit which are coupled into a second crystal oscillator circuit are reduced by feeding an oppositely phased interfering signal into the second crystal oscillator circuit.

Claims16

Dependent claims

A circuit compensating for the shunt capacitance of a frequency selective crystal element which is in series with a buffer amplifier having input and output terminals in a series-feedback oscillator circuit comprising:

a differential amplifier having an input terminal coupled to the output terminal of said buffer amplifier, said differential amplifier providing a noninverted signal at a noninverting signal output terminal and providing an inverted signal at an inverting signal output terminal;
said crystal element having first and second terminals and having a shunt capacitance between said two terminals, said crystal element having its first terminal coupled to the noninverting output terminal of the differential amplifier and having its second terminal coupled to the input terminal of said buffer amplifier to form said series feedback crystal oscillator circuit;
a compensating capacitor having first and second terminals, said compensating capacitor having its first terminal coupled to the inverting signal output terminal of said differential amplifier and having its second terminal coupled to the input terminals of said buffer amplifier such that the compensating capacitor passes a compensating signal, which is substantially equal in magnitude and opposite in phase to the signal passing through the shunt capacitance of the crystal element, to the input terminal of the buffer amplifier to thereby cancel the effect of the signal passing through the shunt capacitance of the crystal element.

A system for automatic cancelling of a crosstalk interference signal which is generated in a source circuit and which is coupled through a stray coupling impedance to interfere with a crosstalk-sensitive circuit, comprising:

means for injecting a crosstalk tracer signal into said source circuit, said crosstalk tracer signal having a frequency which does not interfere with operation of said crosstalk-sensitive circuit,
crosstalk-cancellation means for coupling an inverted tracer signal from an output terminal of said source circuit to said crosstalk-sensitive circuit, said crosstalk cancellation means including:
an inverter circuit coupled to the output terminal of said source circuit;
amplitude-control means for controlling the amplitude of said inverted tracer signal in response to an inverted-tracer control signal;
means for coupling said inverted tracer signal to an input terminal of said crosstalk-sensitive circuit so that said tracer signal coupled to said crosstalk-sensitive circuit is summed with the oppositely-phased inverted tracer signal to provide a residual tracer signal, which results from imperfect cancellation of said tracer signal and said inverted tracer signal;
means for detecting the amplitude of said residual tracer signal and for generating said inverted-tracer control signal;
wherein said amplitude-control means is controlled by said inverted-tracer control signal to minimize the amplitude of said residual tracer signal so that said crosstalk-cancellation means provides a path for a signal, which is approximately equal in amplitude and opposite in phase to said crosstalk interference signal, to said crosstalk-sensitive circuit to thereby provide for automatic cancellation of said crosstalk interference signal.

4 more elements

Dependencies are inferred from the claim text.

Linear crystal oscillator with amplitude control and crosstalk cancellation

Life of this patent

Linear crystal oscillator with amplitude control and crosstalk cancellation

Life of this patent

Abstract

Claims16