
AD9826
–14–
REV. A
adjust pin. A voltage applied to this pin will be subtracted from
the voltages applied to the Red, Green, and Blue inputs in the first
amplifier stage of the AD9826. T he input clamp is disabled in this
mode. For more information, see the Circuit Operation section.
T iming for this mode is shown in Figure 4. CDSCLK 1 should
be grounded in this mode. T he rising edge of CDSCLK 2 should
not occur before the previous falling edge of ADCCLK , as shown
by t
ADC2
. T he output data latency is three ADCCLK cycles. T he
offset and gain values for the Red, Green, and Blue channels are
programmed using the serial interface. T he order in which the
channels are switched through the multiplexer is selected by
programming the MUX Configuration Register.
1-Channel CDS Mode
T his mode operates the same way as the 3-Channel CDS mode.
T he difference is that the multiplexer remains fixed in this mode,
so only the channel specified in the MUX Configuration Regis-
ter is processed.
T iming for this mode is shown in Figure 2.
1-Channel SHA Mode
T his mode operates the same way as 3-Channel SHA mode,
except that the multiplexer remains stationary. Only the channel
specified in the MUX Configuration Register is processed.
T iming for this mode is shown in Figure 6. CDSCLK 1 should
be grounded in this mode of operation.
Configuration Register
T he Configuration Register controls the AD9826’s operating
mode and bias levels. Bits D8 and D1 should always be set low.
T able II. Configuration Register Settings
D
8
D7
D6
D5
D4
D3
D2
D1
D0
Set
to
0
Input Range Internal VREF
3CH Mode
CDS Operation
Input Clamp Bias
Power-Down
Set
to
0
Output Mode
1 = 4 V
*
0 = 2 V
1 = Enabled
*
0 = Disabled
1 = On
*
0 = Off
1 = CDS Mode
*
0 = SHA Mode
1 = 4 V
*
0 = 3 V
1 = On
0 = Off (Normal)
*
0 = 2 Byte
*
1 = 1 Byte
*
Power-on default value.
Bit D7 controls the input range of the AD9826. Setting D7 high
sets the input range to 4 V while setting Bit D7 low sets the
input range to 2 V. Bit D6 controls the internal voltage refer-
ence. If the AD9826’s internal voltage reference is used, then
this bit is set high. Setting Bit D6 low will disable the internal
voltage reference, allowing an external voltage reference to be
used. Setting Bit D5 high will configure the AD9826 for 3-
channel operation. If D5 is set low, the part will be in either
2CH or 1CH mode based on the settings in the MUX Configu-
ration Register (See T able III and the MUX Configuration
Register description). Setting Bit D4 high will enable the CDS
mode of operation, and setting this bit low will enable the SHA
mode of operation. Bit D3 sets the dc bias level of the AD9826’s
input clamp.
T his bit should always be set high for the 4 V clamp bias, unless
a CCD with a reset feedthrough transient exceeding 2 V is used.
If the 3 V clamp bias level is used, then the peak-to-peak input
signal range to the AD9826 is reduced to 3 V maximum. Bit D2
controls the power-down mode. Setting Bit D2 high will place
the AD9826 into a very low-power “sleep” mode. All register
contents are retained while the AD9826 is in the powered-down
state. Bit D0 controls the output mode of the AD9826. Setting
Bit D0 high will enable a single byte output mode where only
the 8 MSBs of the 16 b ADC will be output on each rising edge
of ADCCLK (see Figure 8). If Bit D0 is set low, then the 16b
ADC output is multiplexed into two bytes. T he MSByte is
output on ADCCLK rising edge and the LSByte is output on
ADCCLK falling edge.
T able I. Internal Register Map
Register
Name
Address
A2
A1
Data Bits
D5
A0
D8
D7
D6
D4
D3
D2
D1
D0
Configuration
0
0
0
0
Input Rng
VREF
3CH Mode
CDS On
Clamp
Pwr Dn
0
1 Byte Out
MUX Config
0
0
1
0
RGB/BGR
Red
Green
Blue
0
0
0
0
Red PGA
0
1
0
0
0
0
MSB
LSB
Green PGA
0
1
1
0
0
0
MSB
LSB
Blue PGA
1
0
0
0
0
0
MSB
LSB
Red Offset
1
0
1
MSB
LSB
Green Offset
1
1
0
MSB
LSB
Blue Offset
1
1
1
MSB
LSB