AD9979BCPZ Analog Devices Inc, AD9979BCPZ Datasheet - Page 34

• Manufacturer Part Number: AD9979BCPZ
• Description: IC PROCESSOR CCD 14BIT 48-LFCSP
• Manufacturer: Analog Devices Inc
• Type: CCD Signal Processor, 14-Bitr

Specifications of AD9979BCPZ

• Input Type: Logic
• Output Type: Logic
• Interface: 3-Wire Serial
• Current - Supply: 48mA
• Mounting Type: Surface Mount
• Package / Case: 48-LFCSP
• Supply Voltage Range: 1.6V To 2V, 1.6V To 3.6V, 2.7V To 3.6V
• Operating Temperature Range: -25°C To +85°C
• Digital Ic Case Style: LFCSP
• No. Of Pins: 48
• Svhc: No SVHC (18-Jun-2010)
• Package /: RoHS Compliant
• Ic Function: 14-bit CCD Signal Processor With Precision Timing Core
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9979
Variable Gain Amplifier (VGA)
The VGA stage provides a gain range of approximately 6 dB to
42 dB, programmable with 10-bit resolution through the serial
digital interface. A gain of 6 dB is needed to match a 1 V input
signal with the ADC full-scale range of 2 V. When compared to
1 V full-scale systems, the equivalent gain range is 0 dB to 36 dB.
The VGA gain curve follows a linear-in-dB characteristic. The
exact VGA gain is calculated for any gain register value by
where Code is the range of 0 to 1023.
Analog-to-Digital Converter
The AD9979 uses a high performance ADC architecture,
optimized for high speed and low power. Differential nonlinearity
(DNL) performance is typically better than 0.5 LSB. The ADC
uses a 2 V input range. (See Figure 5 to Figure 7 for the typical
linearity and noise performance plots of the AD9979.)
Gain (dB) = (0.0358 × Code) + 5.75 dB
42
36
30
24
18
12
6
0
127
255
Figure 51. VGA Gain Curve
VGA GAIN REGISTER CODE
383
511
639
767
895
1023
Rev. C | Page 34 of 56
Optical Black Clamp
The optical black clamp loop is used to remove residual offsets
in the signal chain and to track low frequency variations in the
CCD black level. During the optical black (shielded) pixel
interval on each line, the ADC output is compared with a fixed
black level reference, selected by the user in the clamp level
register. The value can be programmed between 0 LSB and
255 LSB, in 256 steps. The resulting error signal is filtered to
reduce noise, and the correction value is applied to the ADC
input through a DAC. Normally, the optical black clamp loop is
turned on once per horizontal line, but this loop can be updated
more slowly to suit a particular application. If external digital
clamping is used during the postprocessing, the AD9979 optical
black clamping can be disabled using CLAMPENABLE, Bit 3 in
Address 0x00. When the loop is disabled, the clamp level register
can still be used to provide fixed offset adjustment.
Note that if the CLPOB loop is disabled, higher VGA gain settings
reduce the dynamic range because the uncorrected offset in the
signal path is gained up.
It is recommended to align the CLPOB pulse with the CCD
optical black pixels. It is recommended that the CLPOB pulse
duration be at least 20 pixels wide. Shorter pulse widths can be
used, but the ability for the loop to track low frequency variations
in the black level is reduced. See the Horizontal Clamping and
Blanking section for more timing information.
Digital Data Outputs
The AD9979 digital output data is latched using the DOUTPHASEx
value, as shown in Figure 42. (Output data timing is shown
in Figure 20.) The switching of the data outputs can couple
noise back into the analog signal path. To minimize any switching
noise while using default register settings, it is recommended
that DOUTPHASEPx be set to a value between 15 and 31. Other
settings can produce good results, but experimentation is
necessary.
The data output coding is normally straight binary, but the coding
can be changed to gray coding by setting Bit 2 of Address 0x01 to 1.