Image Processing Reference
In-Depth Information
transistor. When the signal
Tx
is activated, the pass transistor is enabled and the sensor
provides a capacitance to the bus, one that is proportional to the incident light. An
active
pixel
includes an amplifier circuit that can compensate for limited fill factor of the photodiode.
The select signal again controls presentation of the sensor's information to the bus. A
further reset signal allows the charge site to be cleared when the image is rescanned.
V
DD
Tx
Reset
Incident
light
Incident
light
Column bus
Select
Column bus
(a) Passive
(b) Active
Figure 1.9
Pixel sensors
The basis of a CCD sensor is illustrated in Figure
1.10
. The number of charge sites gives
the resolution of the CCD sensor; the contents of the charge sites (or buckets) need to be
converted to an output (voltage) signal. In simple terms, the contents of the buckets are
emptied into vertical transport registers which are shift registers moving information towards
Horizontal transport register
Signal
condi-
tioning
Video
output
Control
inputs
Control
Pixel sensors
Figure 1.10
CCD sensing element
