XRD98L61 Datasheet, PDF (18/37 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

XRD98L61
Preliminary
Programmable Gain Amplifier (PGA)
The PGA provides gains from 0dB to 36 dB in approximately 0.047 dB steps. The desired gain setting is
programmed via the 10 bit gain register in the Serial Interface.
For gain codes between 0 and 767 the gain can be calculated by the following equation:
Gain[dB]
=


Code
768
×
36

For gain codes ≥ 768 the gain is fixed at 36 dB. The gain doubles every 128 codes to simplify DSP algorithms and
control.
36
30
27
24
18
12
9
6
0
0
Gain Code, PGA[9:0]
Figure 6. PGA Gain vs. Gain Code
An example of setting the gain is as follows: If the CCD input is limited by 800mVpp (CDSV_IN) and the ADC full
scale differential input (VID) is 2Vpp, then a minimum gain is calculated by:
 VID 
2 
Gain ₌ 20 log 
 ₌ 20 log 
 ₌ 8dB
 CDSV_IN 
 0.8 
The gain code would be set to 170d for 8dB of PGA gain.
Rev. P4.00
18