Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By phase
Reexamination Certificate
1999-12-21
2001-09-11
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By phase
C327S048000, C327S160000
Reexamination Certificate
active
06288574
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to phase detectors and, more particularly, to a digital phase detector which receives two signals and generates a numerical value based on the time difference between the arrival times of the two signals.
Referring to
FIG. 1
, there is shown a tangential (fast-scan) view of a prior art raster output scanner
10
of a printing system. The raster scanning system
10
utilizes a laser light source
12
, a collimator
14
, pre-polygon optics
16
, a multi-faceted rotating polygon mirror
18
as the scanning element, post polygon optics
20
and a photosensitive medium
22
.
The laser light source
12
sends a light beam
24
to the rotating polygon mirror
18
through the collimator
14
and the pre-polygon optics
16
. The collimator
14
collimates the light beam
24
and the pre-polygon optics
16
focuses the light beam
24
in the sagittal or cross-scan plane onto the rotating polygon mirror
18
. The facets
26
of the rotating polygon mirror
18
reflect the light beam
24
and cause the reflected light beam
24
to revolve about an axis near the reflection point of the facet
26
. The reflected light beam
24
is utilized through the post polygon optics
20
to scan a document at the input of an imaging system or can be used to impinge upon a photographic film or a photosensitive medium
22
, such as a xerographic drum at the output of an imaging system. Hereinafter, for the purpose of simplicity the “rotating polygon mirror” will be referred to as “polygon”.
In this process, depending on the manufacturing tolerances, each facet might have different characteristics such as a minute width variation which can cause the line scanned by this facet to be scanned faster or slower than average scan time. This type of error is called facet to facet error. In order to correct this problem, it is best to check the error of each facet compared to the average speed of the polygon (average scan time) which is the average speed of all the facets of the polygon.
To find the facet to facet or the reference frequency errors, the time difference between the arrival times of the end of scan and end of count signals of each facet has to be measured. Typically, an analog phase detector is used to measure this time difference. However, analog circuits and analog outputs are not practical in the digital world.
It is an object of this invention to design a digital phase detector which is capable of generating a digital numerical value for the time difference between arrival times of two signals.
SUMMARY OF THE INVENTION
According to the present invention, a digital delay determining apparatus utilizes a comparing means, a delaying means, and a delay determining means. The comparing means receives a first and a second signal and generates an output signal with a duration based on the time difference between the arrival times of the first and second signals. The delaying means has a plurality of delay stages and is electrically connected to the comparing means for receiving the output signal from the comparing means and passing it through its plurality of delay stages. The delay determining means is electrically connected to the delaying means for determining the number of delay stages that cover the duration of the output signal from the comparing means.
REFERENCES:
patent: 5392347 (1995-02-01), Ito et al.
patent: 5440592 (1995-08-01), Ellis et al.
patent: 5818265 (1998-10-01), Meller et al.
Cox Cassandra
Tran Toan
Virga Phil
Xerox Corporation
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