XRD98L56 Datasheet, PDF (12/35 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 10-Bit A/D

XRD9855/9856
XRD98L55/98L56
CCD
RSTCCD
SHP
SHD
(Internal Signals)
SDRK
SPIX
PGA1
Output
PGA2
Output
ADCLK
Hold Track
Figure 3. Timing Diagram of the CDS Clocks
and Internal Signals, CLK_POL = 1, M2=0
PGA1 provides gains of 0dB, 8dB & 16dB (1x, 2.5x,
and 6.25x). The gain transitions occur at PGA gain
codes 64d and 128d (40h & 80h). PGA2 provides gain
from 6dB to 22dB (2x to 12.5x) with 0.125dB steps.
Figure 4 shows the measured PGA gain vs. Gain
Code. The combined PGA blocks provide a program-
mable gain range of 32dB. The minimum gain (code
00h) is 6dB. The maximum gain (code FFh) is 38dB.
The following equation can be used to compute PGA
gain from the gain code:
Gain[dB]
=
6
+
 ₃₂
×
code
256

where code is between 0 and 255.
Due to device mismatch the gain steps at codes 63-
64 and 127-128 may not be monotonic.
40
FS = 18MHz
35 _{VDD = 3.0V}
VRT = 2.3V
30 _{VTARB==250°.C3V}
25
20
15
10
5
0
0
64
128
192
256
Gain Code
Figure 4. PGA Gain vs. Gain Code
Rev. 1.01
12