Oscillators – Solid state active element oscillator – Transistors
Reexamination Certificate
1999-05-14
2001-06-19
Kinkead, Arnold (Department: 2817)
Oscillators
Solid state active element oscillator
Transistors
C331S172000, C331S1170FE, C331S167000, C327S165000, C327S166000
Reexamination Certificate
active
06249192
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the recovery of a data clock signal by injecting a data 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) data signal into an LC tank circuit to recover the clock signal for the received data by tuning 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 clock injection system comprises a clocked logic element, and a parasitic capacitance between an input clock signal to the clocked logic element and an output data signal from the clocked logic element. In addition, a capacitor is connected between the input clock signal and the output data signal. The capacitor increases an energy of the clock signal embedded in the output data signal due to the parasitic capacitance.
A method of injecting a clock signal into a data signal in accordance with another aspect of the present invention comprises intentionally increasing a capacitance between a clock signal and an output data signal to increase energy of the clock signal embedded in the output data signal.
REFERENCES:
patent: 4918406 (1990-04-01), Baumbach et al.
patent: 5396195 (1995-03-01), Gabara
Gabara Thaddeus John
Mujtaba Syed Aon
Agere Systems Guardian Corp.
Bollman William H.
Kinkead Arnold
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