Datasheet
AD9979
Rev. C | Page 32 of 56
Input Configurations
The CDS circuit samples each CCD pixel twice to extract the
video information and to reject the low frequency noise (see
Figure 43). There are three possible configurations for the CDS:
inverting CDS mode, noninverting CDS mode, and SHA mode.
CDSMODE (Address 0x00[9:8]) selects which configuration is
used (see Table 24).
SHA1
SHA2
SHD
SHP
DIFF
AMP
CDS OUTPUT
CCDINP
CCDINM
0
5957-045
Figure 43. CDS Block Diagram (Conceptual)
Inverting CDS Mode
For this configuration, the signal from the CCD is applied
to the positive input of the CDS system (CCDINP) and the
negative side (CCDINM) is grounded (see Figure 44). The
CDSMODE setting for this configuration is 0x00. Traditional
CCD applications use this configuration with the reset level
established below the AVDD supply level, by the AD9979 dc
restore circuit, at approximately 1.5 V. The maximum saturation
level is 1.0 V below the reset level, as shown in Figure 45 and
Table 18. A maximum saturation voltage of 1.4 V is also
possible when using the minimum CDS gain setting.
IMAGE
SENSOR
SHA/
CDS
CCDINM
CCDINP
AD9979
NOTES
1. COUPLING CAPACITOR IS NOT REQUIRED FOR CERTAIN
BLACK-LEVEL REFERENCE VOLTAGES.
05957-046
Figure 44. Single-Input CDS Configuration
(N) SIGNAL SAMPL
E
(N) RESET SAMPLE (N + 1) RESET SAMPLE
V
DD
RESET LEVEL
(V
RST
)
SIGNAL LEVEL
(V
FS
)
05957-047
Figure 45. Traditional Inverting CDS Signal
Table 18. Inverting Voltage Levels
Signal Level Symbol Min Typ Max Unit
Saturation V
FS
1000 1400 mV
Reset V
RST
V
DD
− 500 V
DD
− 300 V
DD
mV
Supply Voltage V
DD
1600 1800 2000 mV
Noninverting CDS Mode
If the noninverting input is desired, the reset level signal (or black
level signal) is established at a voltage above ground potential.
Saturation level (or white level) is approximately 1 V. Samples are
taken at each signal level (see Figure 46 and Table 19).
(N) SIGNAL SAMPLE
(N) RESET SAMPLE
(N + 1) RESET SAMPLE
GND
RESET LEVEL
(V
RST
)
SIGNAL LEVEL
(V
FS
)
05957-048
Figure 46. Noninverting CDS Signal
Table 19. Noninverting Voltage Levels
Signal Level Symbol Min Typ Max Unit
Saturation V
FS
1000 1400 mV
Reset V
RST
0 250 500 mV