Oscillators – Electromechanical resonator – Crystal
Reexamination Certificate
2000-08-11
2001-09-04
Mis, David (Department: 2817)
Oscillators
Electromechanical resonator
Crystal
C331S1160FE, C331S179000
Reexamination Certificate
active
06285264
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to frequency generators generally and, more particularly, to a timing crystal oscillator that may be tuned after production.
BACKGROUND OF THE INVENTION
Conventional approaches to implementing crystal or other resonant oscillators generally involve manufacturing a fixed capacitive load that is attached to the resonator. The fixed load is generally fabricated during the manufacturing process. As a result, the accuracy of the manufacturing process in a conventional oscillator plays an important role in determining the accuracy of the output clock, as does the manufacturing accuracy of the resonator.
Referring to
FIG. 1
, a circuit
10
illustrates one such conventional approach. The circuit
10
generally comprises a resistor
12
, an inverter
14
, a resistor
16
, an inverter
18
, a capacitor C
1
, a capacitor C
2
and a crystal
20
. One side of the crystal
20
is coupled between the capacitor C
1
and the input of the inverter
14
. A second side of the oscillator
20
is coupled to the capacitor C
2
and the resistor
16
. The resistor
16
is also coupled between the output of the inverter
14
and the input of the inverter
18
. The output of the inverter
18
presents a signal FOUT. The signal FOUT oscillates at a particular frequency that is generally a function of the size of the capacitors C
1
and C
2
. As a result, to change the frequency of oscillation of the signal FOUT, the size of the capacitors C
1
and C
2
must be adjusted during fabrication of the circuit
10
.
Manufacturing processes generally have a certain amount of inherent inaccuracy. Since the circuit
10
relies on the accuracy of the manufacturing process to produce the signal FOUT, the overall accuracy of the circuit
10
may not be acceptable in certain design applications having specifications that demand extremely accurate tolerances for the frequency of oscillation of the signal FOUT. A computer motherboard is one example of such an application.
Oscillators used in watches may have configuration bits configured to trim the accuracy of the oscillator after production. The oscillator may typically be tuned to the range of parts per million. However, the oscillators used in watches are typically low speed oscillators and are generally not appropriate for high speed computer applications. Furthermore, the tuning is generally achieved with a mechanical trimming capacitor which is less desirable than electronic trimming.
SUMMARY OF THE INVENTION
The present invention concerns a timing crystal oscillator circuit that may be tuned after production. The circuit generally comprises a microprocessor configured to present one or more control signals, one or more load devices that may be activated in response to the control signals and a crystal oscillator for presenting an output signal having a frequency which is generally dependent on the number of load devices activated.
The objects, features and advantages of the present invention include providing a timing crystal oscillator that presents an output signal having a frequency that may be tuned after production.
REFERENCES:
patent: 3868597 (1975-02-01), Gollinger
patent: 5036294 (1991-07-01), McCaslin
patent: 5084685 (1992-01-01), Moller et al.
patent: 5117206 (1992-05-01), Imamura
patent: 5182528 (1993-01-01), Zuta
patent: 5457433 (1995-10-01), Westwick
patent: 5486795 (1996-01-01), Spence et al.
patent: 5568093 (1996-10-01), Holzer
patent: 5703540 (1997-12-01), Gazda et al.
patent: 5764112 (1998-06-01), Bal et al.
Cypress Semiconductor Corp.
Maiorana P.C. Christopher P.
Mis David
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