Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1998-08-14
2001-01-16
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S045000, C331S172000, C331S167000, C331S132000, C331S11300A, C455S260000
Reexamination Certificate
active
06175285
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the injection of an AC signal into an LC tank circuit to control an oscillating frequency thereof. More particularly, it relates to the injection of a single-ended or balanced (differential) oscillating signal into an LC tank circuit to tune the oscillating frequency of the LC tank circuit.
BACKGROUND OF THE INVENTION
Oscillators are common devices used in a wide variety of devices, including radio equipment and modems. Oftentimes, the oscillator must be extremely stable and accurate, but as frequencies of devices increase and as the integration of components in integrated circuits increases, oscillator design and operation become extremely challenging.
For many systems, an oscillator exhibiting an oscillation frequency within a small range of a particular value is required. Pre-screening of oscillator devices and/or of the components in the oscillator device permits selection of an oscillator having as accurate a frequency as is required for the particular application. However, pre-screening is expensive and results in low yields.
Crystal oscillators, while having a high quality factor (Q factor), are not conventionally formed on an integrated circuit. On the other hand, inductor/capacitor (LC) tank circuits, another form of oscillator, have been used to provide an oscillator on an integrated circuit, albeit with a lower Q factor.
One way to improve the precision of the oscillation is to use closed-loop techniques for synchronizing an oscillator frequency and/or phase, either to an input signal such as a data stream or to a predetermined reference oscillator. Perhaps the most prevalent closed-loop technique for synchronizing an oscillator to another signal is with the use of a phase-locked loop (PLL), e.g., as shown in FIG.
1
.
In particular,
FIG. 1
shows the use of a PLL
400
to sense a frequency and phase of a carrier in an incoming modulated signal. The PLL
400
provides a phase and frequency corrected recovered carrier signal to the phase/frequency detector
102
for comparison with the actually received modulated signal (which due to real world conditions contains noise in the form of phase and frequency variations).
In
FIG. 1
, a phase/frequency detector
102
receives both the incoming modulated signal on line
420
and the output of the PLL
400
at point
422
. The phase/frequency detector
102
compares the phase and frequency of the received modulated signal on line
420
with the phase and frequency generated by the PLL
400
to detect the actual phase and frequency of the carrier frequency as it is received in the receiver. This accurately determined carrier frequency is subtracted from the received modulated signal to result in an output of the recovered information signal.
In more detail, the received modulated signal is input to the PLL
400
at line
420
. A band pass filter
408
band pass filters the input modulated signal such that sideband information beyond that desired is eliminated. A phase detector
406
, charge pump
404
and loop filter
402
provide a comparative phase for the received modulated signal and the locally sensed carrier frequency, and generate a DC signal for control of a voltage controlled oscillator (VCO)
430
. The VCO
430
outputs a particular frequency based on the voltage level of its control input.
While having certain advantages, the requirement of a PLL adds cost and complexity to a circuit, which is of particular concern in lower end applications such as low end cordless telephones or other wireless applications. Moreover, the closed-loop nature of the PLL slows the acquisition time necessary to acquire phase lock with changes in the input signal, and thus may limit the maximum frequency, modulation and overall performance of the receiver in certain applications.
There is thus a need to provide an open-loop oscillator circuit which is capable of being formed in an integrated circuit and which is capable of highly precise and accurate operation.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a tunable oscillator comprises an LC tank circuit comprising an inductor and a capacitor. An impedance is in communication with the LC tank circuit, the impedance being adapted and arranged to allow injection of an AC signal corresponding to a desired oscillation frequency of the LC tank circuit.
In accordance with another aspect of the present invention, a tunable oscillator comprises an LC tank circuit comprising an inductor and a capacitor. A plurality of impedances are in communication with the LC tank circuit, each of the plurality of impedances being adapted and arranged to allow injection of a respective phase of an AC signal corresponding to a desired oscillation frequency of the LC tank circuit.
In accordance with yet another aspect of the present invention, a tunable quadrature oscillator comprises a quadrature LC tank circuit comprising an inductance and a capacitance. The quadrature LC tank circuit has at least four nodes. The tunable quadrature oscillator further includes at least four impedances corresponding to the at least four nodes of the quadrature LC tank circuit, each of the plurality of impedances being adapted and arranged to allow injection of a respective phase of an AC signal corresponding to a desired oscillation frequency of the LC tank circuit.
A method of tuning an oscillator in accordance with the principles of the present invention comprises injecting an AC signal corresponding to a desired oscillation frequency into an oscillator circuit, whereby the oscillator circuit is tuned to the desired oscillation frequency.
REFERENCES:
patent: 4918406 (1990-04-01), Baumbach et al.
patent: 5396195 (1995-03-01), Gabara
patent: 5920235 (1999-07-01), Beards et al.
Bollman William H.
Kinkead Arnold
Lucent Technologies - Inc.
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