AD9845AJST Analog Devices Inc, AD9845AJST Datasheet - Page 19

• Manufacturer Part Number: AD9845AJST
• Description: IC CCD SIGNAL PROC 12BIT 48-LQFP
• Manufacturer: Analog Devices Inc
• Type: CCD Signal Processor, 12-Bitr

Specifications of AD9845AJST

• Rohs Status: RoHS non-compliant
• Input Type: Logic
• Output Type: Logic
• Interface: 3-Wire Serial
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Current - Supply: -
• Lead Free Status / RoHS Status: Not Compliant

D10
X
A/D Converter
The AD9845A uses high-performance ADC architecture, opti-
mized for high speed and low power. Differential Nonlinearity
(DNL) performance is typically better than 0.5 LSB, as shown in
TPC 2. Instead of the 1 V full-scale range used by the earlier
AD9801 and AD9803 products from Analog Devices, the
AD9845A’s ADC uses a 2 V input range. Better noise perfor-
mance results from using a larger ADC full-scale range (see
TPC 3).
AUX1 Mode
For applications that do not require CDS, the AD9845A can be
configured to sample ac-coupled waveforms. Figure 30 shows
the circuit configuration for using the AUX1 channel input
(Pin 36). A single 0.1 µF ac-coupling capacitor is needed between
the input signal driver and the AUX1IN pin. An on-chip dc-bias
circuit sets the average value of the input signal to approximately
0.4 V, which is referenced to the midscale code of the ADC.
The VGA Gain register provides a gain range of 0 dB to 36 dB in
this mode of operation (see VGA Gain Curve, Figure 29).
MSB
D9
0
1
1
0.8V
INPUT SIGNAL
SIGNAL
D8
X
0
1
VIDEO
0.4V
0.1 F
D7
X
0
1
0.1 F
??V
AUX2IN
Table VII. VGA Gain Register Used for AUX2-Mode
AUX1IN
D6
X
0
1
BUFFER
0.4V
VIDEO CLAMP
0.4V
CIRCUIT
5k
LPF
D5
X
0
•
•
•
1
VGA GAIN
REGISTER
VGA
9
0dB TO 36dB
D4
X
0
1
REGISTER
VGA GAIN
0dB TO 18dB
VGA
The VGA gains up the signal level with respect to the 0.4 V bias
level. Signal levels above the bias level will be further increased
to a higher ADC code, while signal levels below the bias level
will be further decreased to a lower ADC code.
AUX2 Mode
For sampling video-type waveforms, such as NTSC and PAL
signals, the AUX2 channel provides black level clamping, gain
adjustment, and A/D conversion. Figure 31 shows the circuit
configuration for using the AUX2 channel input (Pin 34). A
external 0.1 µF blocking capacitor is used with the on-chip video
clamp circuit, to level-shift the input signal to a desired refer-
ence level. The clamp circuit automatically senses the most
negative portion of the input signal, and adjusts the voltage
across the input capacitor. This forces the black level of the
input signal to be equal to the value programmed into the Clamp
Level register (see Serial Interface Register Description). The VGA
provides gain adjustment from 0 dB to 18 dB. The same VGA
Gain register is used, but only the 9 MSBs of the gain register
are used (see Table VII.)
10
8
D3
X
0
1
CLAMP LEVEL
REGISTER
ADC
ADC
D2
X
0
1
D1
X
0
1
CLAMP LEVEL
LSB
D0
X
0
1
MIDSCALE
AD9845A
Gain (dB)
0.0
0.0
•
•
•
18.0