Image Processing Reference
In-Depth Information
Noise
CCD
MOS
CMOS
Amplifier noise
PD reset noise
kTC noise
(vertical
signal line)
Pixel reset noise
Pixel amplification
transistor noise
1/f noise
•ermal noise
RTN
Output amplifer noise
Reset noise
1/f noise
ermal noise
Temporal
noise
VCCD dark current
Preamplification
transistor noise
PD dark current shot noise
Optical shot noise (at high illumination)
PD dark current
(buried PD is effective)
Scene noise (nonuniform sensitivity between pixels)
Fixed-pattern
noise
VCCD dark current
nonuniformity
Column select
switching noise
reshold voltage variability
of pixel amplification
transistor
(effective cancel circuit)
Note:
PD, photodiode.
FIGURE 3.3
Noise classification of each type of sensor.
CCD, MOS, and complementary MOS (CMOS) image sensors will be discussed in
Chapter 5. The major types of noise are classified in Figure 3.3.
The main temporal noise of a CCD sensor is amplifier noise. An example is reset
noise at floating diffusion (FD), which belongs to circuitry noise. Other types of noise
are 1/f and thermal noise, both of which are generated at MOS field-effect transis-
tors (MOSFETs). The main types of temporal noise of an MOS sensor are kTC noise of
signal lines and preamplifier noise caused at an off-chip transistor. The main types of
temporal noise of CMOS sensors are pixel reset noise, 1/f noise of the pixel amplifica-
tion transistor, and thermal noise and RTN, both of which are transistor noise. Dark
current shot noise in a photodiode and optical shot noise are common for the three
types.
As for FPN, its source is dark current nonuniformity in CCD. CMOS sensors equip an
amplifier in each pixel, and the threshold voltage variation of the amplification transistor
causes serious FPN. Although this problem had prevented commercial viability, the bar-
rier was removed by on-chip noise cancelation circuitry, as will be discussed in Section 5.3.
3.2 Circuitry Noise (kTC Noise)
kTC noise is a phenomenon caused at the time of setting a capacitor to a certain voltage by
switching it on and off to connect to a voltage source through devices having finite electri-
cal resistance.
