XRD98L63 Datasheet, PDF (16/41 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

XRD98L63
One Volt Input Option
The CDS amp is designed to normally handle a maxi-
mum signal of 800mV (V_BLACK - V_VIDEO). The One Volt
option allows the CDS amp to handle up to 1.0V with no
distortion. The One Volt option is enabled by writing a
1 to the "OneV" bit in the Control register.
Programmable Gain Amplifier (PGA)
The PGA provides gains from 6 dB to 36 dB in
approximately 0.047 dB steps. The desired gain set-
ting is programmed via the 10 bit gain register in the
Serial Interface.
For gain codes between 0 and 639, the gain can be
calculated by the following equation:
Gain[ dB] =  ^Code × 30  + 6
 ⁶⁴⁰ 
For gain codes ≥ 640, the gain is fixed at 36 dB. The
gain increases by 6dB (a factor of 2x) every 128 codes.
This should help simplify DSP algorithms and control.
An example of setting the gain is as follows: if the CCD
input is limited to 800mVpp (CDSV_IN) and the ADC full
scale differential input (VID) is 1.8Vpp, then a mini-
mum gain is calculated by:
Gain
=
20
log

VID
CDSVin


=
20
log

1.8V
0.8V


=
7.04dB
The gain code would be set to 22 (decimal) for a PGA
gain of 7.03 dB.
36
30
24
18
12
6
0
Gain code, PGA00[9:0]
Figure 7. PGA Gain vs. Gain Code
Rev.1.01
16