Sony SS-HQ1 Application Notes page 169

CCD blemish threshold levels
The blemish detection threshold level (DETREFL/M) is determined by the following equation:
• DETREFL/M (10bit)
= 1023×DETACCT×BLMDETAGC×(blemish level threshold value mV during accumulation of 1 field) / 1000mV
• DETACCT
• BLMDETAGC
As shown in Fig 11.2-3, the accumulation time is determined by applying the electronic shutter control
DETACCT (CAT11_Byte12_bit0-7) to the light-shielded CCD. This is because the blemish level and
accumulation time are proportionate to each other.
• Accumulation time = 2field × DETACCT / 2
Next, in order to transfer the CCD output to the CXD3172AR, the CXA2096N performs sample hold and
performs AGC processing.
The output from the CXA2096N is A/D-converted inside the CXD3172AR. In order to perform blemish
detection by Z1 block, DETREFL/M (10bit) is compared with the value which pulled the black level (equivalent
to the offset voltage) to the 10bit AD (1Vpp input) conversion value. (A blemish is recognized if Det_signal is
greater than DETREF).
Dark
CCD
Shutter Pulse
Period = 2 field * DETACCT / 2
: Number of fields accumulated in CCD during blemish detection operation
: AGC gain during blemish detection operation
(2-field increments)
CXA2096N
AGC /
Black
offset
AGC Voltage
Fig 11.2-3 Blemish detection block diagram
10
Black
AD
Clump
(1Vpp)
Det_signal
EVR0
10
10
TG
DETREF(m/l)
CXD3172AR
163
- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
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