Image Processing Reference
In-Depth Information
V
DD
RST
Pixel
TX
Drive
transistor
Pinned
PD
FD
RS
Load
transistor
φ
1
Column amplifier
with noise cancel
C
1
φ
2
C
2
Second-stage
differential circuit
C
S
C
N
φ
S
φ
R
-
+
Output
FIGURE 5.51
High-gain double-stage noise canceller. (Reprinted with permission from Takahashi, H., Noda, T., Matsuda, T.,
Watanabe, T., Shinohara, M., Endo, T., Takimoto, S. et al.,
Proceedings of the IEEE International Solid-State Circuits
Conference, Digest of Technical Papers
, 28.6, pp. 510-511, San Francisco, CA, 2007.)
Outputs of the column amplifier corresponding to reset and signal level situations are
sampled and held in
C
N
and
C
S
, respectively, and their difference is output by the second-
stage differential circuit. As mentioned in Figure 5.42a, this type of differential circuit is
not formed at each column but arranged as a common circuit at the output part, and it
needs a wide bandwidth.
5.3.3.2 Digital Output Sensors
As described in Sections 1.2 and 1.3, three (space, wavelength, time) of the four factors of
image information are already digitized as built-in coordinate points in imaging systems.
Image sensors only detect light intensity coming into each coordinate point. Currently,
signal voltage proportional to light intensity is obtained by detecting potential change of
FD, to which signal charges are transferred. Thus, light intensity has been treated as an
analog quantity in this topic so far.
