Oscillators – Polyphase output
Reexamination Certificate
1999-09-21
2001-02-13
Grimm, Siegfried H. (Department: 2817)
Oscillators
Polyphase output
C331S048000, C331S052000, C331S055000, C331S17700V
Reexamination Certificate
active
06188292
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improved methods and apparatus for controlling the frequency of oscillator circuits.
BACKGROUND OF THE INVENTION
High-frequency voltage controlled oscillators (“VCOs) are widely used in integrated circuits, ranging from clock recovery in high data-rate optical communications to frequency synthesizer in wireless communications. Frequency tuning for these VCOs can be achieved with varactor diodes. However, the frequency tuning range using this approach is limited by low supply voltages on integrated circuits and maximum variable capacitance available to varactors at high frequencies when inductors are used. Other frequency turning approaches include varying the current in the resonator of the oscillator to alter effective capacitance or varying the relative weighing between two different LC (Inductor-Capacitor) resonators. These techniques are not adequate for tuning frequency.
SUMMARY OF THE INVENTION
The present invention can employ a first and a second fixed-frequency oscillator coupled in a ring topology to generate a variable frequency output. Frequency variation can be achieved by varying the coupling between the two oscillators. The coupling may be varied by using a variable current or voltage source. The first fixed frequency oscillator may generate a first signal which is ninety degrees out of phase with a second signal generated by the second fixed frequency oscillator.
In one embodiment an apparatus is provided comprising a first oscillator producing a first signal, a second oscillator producing a second signal about ninety degrees out of phase with the first signal, a first and second coupling modules coupling the first and second oscillators, and a frequency control circuit. The goal is that the first and second signals should be exactly 90 degrees out of phase i.e. in quadrature with respect to one another. In one embodiment the frequency control circuit varies the coupling of the first and second coupling modules to vary the frequency of the first and second signals. The first and second oscillators may be of the same type, such as fixed frequency, inductive and capacitive oscillators. In one embodiment a method is also provided comprising the steps of producing a first signal, producing a second signal which is about ninety degrees out of phase with the first signal, coupling the first signal with the second signal, and varying the coupling of the first signal with the second signal to vary the frequency of the first signal and the second signal.
REFERENCES:
patent: 5233315 (1993-08-01), Verhoeven
Grimm Siegfried H.
Lucent Technologies - Inc.
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