Oscillator circuit

Details Oscillator circuit Oscillator circuit

2000-04-19

2001-08-21

Pascal, Robert (Department: 2817)

Oscillators

With device responsive to external physical condition

C331S096000

Reexamination Certificate

active

06278335

ABSTRACT:

The present invention relates to an oscillator circuit, and more particularly to a tunable microwave oscillator and to motion detectors which utilise such oscillators.
Typically, an electronically tunable microwave oscillator can utilise a reverse biased varactor having a capacitance which varies according to a corresponding variation in an applied reverse modulation voltage. In order to effect a change in varactor capacitance, and hence to utilise the varactor as a practical frequency tuning device, a modulation signal of high magnitude is required. Typically, at a frequency of oscillation of about 10 GHz, a variation of 30 V in the applied reverse modulating voltage brings about a corresponding variation of about 20 MHz in the frequency of oscillation of a tunable microwave oscillator utilising such a varactor. The frequency range over which the frequency of oscillation of a tunable microwave varactor oscillator can be varied is governed, in part, by the degree of capacitance change of the varactor over the range over which the modulating voltage is varied. A varactor oscillator is illustrated and described in “Dielectric Resonators” published by Artech House and in GB2307355A. The relationship between the degree of frequency modulation and applied modulating signal is only linear for varactors over a narrow percentage bandwidth of up to 3%. Further, relatively large reverse biasing voltages are required for varactor oscillators in order to realise sufficient Q to establish and sustain oscillation. A typical biasing voltage is of the order of 20 V to 30 V. At these voltages the tuning range available is very limited. The above renders the use of varactors undesirable for low noise oscillators.
It is an object of the present invention to at least mitigate some of the problems associated with prior art tunable microwave oscillators, preferably, for use in motion detectors.
Accordingly, the present invention provides an oscillator circuit comprising first and second mutually electro-magnetically couplable resonant circuits, the second resonant circuit comprising a dielectric element and excitation means operable to produce a first frequency of oscillation, the first resonant circuit comprising the dielectric element and excitation means, including a forward biased two terminal device, operable responsive to an applied signal, to vary the resonant frequency of the first resonant circuit and thereby vary the frequency of oscillation of the oscillator circuit.
Advantageously, an embodiment of the present invention is provided wherein the forward biased two terminal device comprises a Schottky junction. Suitably, an embodiment is provided wherein the two terminal device is a Schottky device, for example, a Schottky diode.
Operating the Schottky diode in forward bias mode produces a relatively large variation in frequency in response to a relative small variation in modulating voltage. Furthermore, the voltages require to operate a Schottky based oscillator are significantly less than those required to operate a varactor based oscillator.
Preferably, an embodiment of the present invention provides an oscillator circuit wherein the modes of resonance have associated coupling points on the excitation means and the excitation means is arranged such that the coupling points are a substantially equal distance from the dielectric element.
A further embodiment of the invention provides an oscillator circuit wherein the dielectric element comprises an arcuate profile and said excitation means is arranged to follow substantially the arcuate profile of the dielectric element.
Preferably, the excitation means comprises excitation strip lines or microstrip lines.


REFERENCES:
patent: 4481487 (1984-11-01), Brehm et al.
patent: 4737737 (1988-04-01), Khanna
patent: 5079524 (1992-01-01), Sugawara
patent: 5289139 (1994-02-01), Fiedziuszko et al.
patent: 0475262 A1 (1992-03-01), None
Stanley Burns and Paul Bond, Principles of Electronic Circuits, 2nd paragraph in p. 67, 1987.

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