Coded data generation or conversion – Analog to or from digital conversion – Nonlinear
Reexamination Certificate
1998-09-25
2001-09-25
Wamsley, Patrick (Department: 2819)
Coded data generation or conversion
Analog to or from digital conversion
Nonlinear
C341S154000
Reexamination Certificate
active
06295013
ABSTRACT:
BACKGROUND
The present application relates to an active pixel sensor with an embedded A to D converter. More specifically, the present application describes using a flash A to D converter that has a nonlinear aspect.
FIG. 1
shows standard input/output curves of a video monitor. Curve
100
is an ideal I/O characteristic which would be completely linear between input and output. However, it is well known that most monitors have a more realistic characteristic shown as curve
102
. The lower end of the brightness scale has less gain. The upper end of the scale blooms and cuts off.
These characteristics lead to a known complementary correction being applied to the output of image devices. This correction usually has two components: a gamma (&ggr;) correction at the lower end and knee correction at the upper end. Curve
104
shows these conventional corrections. The gamma correction increases the contrast at the lower end of the signal range to compensate for reduced gain at the lower end of the monitor responsivity characteristic. The knee correction extends the dynamic range of the monitor at the upper end.
These corrections can be done in many different ways. One correction uses nonlinear CMOS diodes which operate as nonlinear resistors. However, these processes are difficult to fabricate reliably in a CMOS process. Another way is by using a digital signal processor.
The correction must be applied at video rates, thus necessitating fast signal processing for digital output sensors.
SUMMARY OF THE INVENTION
The present system defines using an A to D converter which has an embedded correction as part of its circuitry.
REFERENCES:
patent: 5059980 (1991-10-01), Katzenstein
patent: 6-276538 (1994-09-01), None
Carbone et al, “Stochastic-Flash Analog-to-Digital Conversion,” IEEE, 1998.*
Kawahito et al, “A Compressed Digital Output CMOS Image Sensor . . . ,” IEEE, 1997.*
Tanner et al, “An 8-bit Low-Power ADC Array for CMOS Image Sensors,”IEEE, 1998.
Barna Sandor
Blerkam Daniel Van
Fossum Eric R.
Fish & Richardson P.C.
Photobit Corporation
Wamsley Patrick
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