Philips Semiconductors TDA8752B
Triple high-speed Analog-to-Digital Converter 110 Msps
Product specification Rev. 03 — 21 July 2000 18 of 38
9397 750 07338 © Philips Electronics N.V. 2000. All rights reserved.
The default programmed value is:
•Programmed code = 127
•Clamp code = 0
•ADC output = 0.
9.1.2 Coarse and fine registers
These two registers enable the gain control, the AGC gain with the coarse register
and the reference voltage with the fine register. The coarse register programming
equation is as follows:
(5)
Where: Vref = 2.5 V.
The gain correspondence is given in Tabl e 6. The gain is linear with reference to the
programming code (NFINE = 0).
The default programmed value is as follows:
•NCOARSE =32
•Gain = 0.825
•Vi to be full-scale = 1.212 V.
Tomodulate this gain, the fine register is programmed using the above equation. With
a full-scale ADC input, the fine register resolution is a 1⁄2LSB peak-to-peak
(see Tabl e 7 for NCOARSE = 32).
Table 5: Coding
Programmed code Clamp code ADC output
0−63.5 underflow
1−63
2−62.5
... ...
127 0 0
... ... ...
254 63.5 63 or 64
255 64 64
256 120 120
... ... ...
287 136 136
Table 6: Gain correspondence (COARSE)
NCOARSE Gain Vi to be full-scale (V)
32 0.825 1.212
99 2.5 0.4
GAIN NCOARSE 1+
Vref 1NFINE
32 16×
------------------
–


⋅
------------------------------------------------1
16
------
×NCOARSE 1+
Vref 512 NFINE
–()⋅
-------------------------------------------------- 32×==