User`s manual

Exp-A/D1262 s I/O Configurations
The Exp-A/D12s eight inputs (ANx+ and ANx) are routed to the U4 A/D
converter chip by two analog multiplexers (MUX) and several differential
amplifiers, as shown in Figure 7-3. Gains of unity, 2, 6, 22, 42, 102, and
202X can be software selected.
Figure 7-3. Exp-A/D12 Analog Inputs
The Multiplexers
The Exp-A/D12s multiplexer circuit consists of two DG509A chips, U11
and U12. Only one can be enabled at a time. The output lines IN+ and
IN route the selected input signal directly to the A/D converter chips
input pins CH0 and CH1, providing unity gain. They also pass the signal
to a multistage differential input amplifier.
The Op-Amps
Outputs from the various amplifier stages (lines G1G6) are directed to the
A/D converter chips input pins CH2CH7. The gain on each line is
shown in Figure 3-10.
202X
EEPROM
AN[0-3]+
AN[0-3]
–
+
–
AN[4-7]+
AN[4-7]
–
+
–
MUX
MUX
IN+
IN
–
22X
42X
102X
6X
2X
CH0
CH1
G1
G2
G3
G4
G5
G6
REF+
+V Reg
–V Reg
VREF
+2.5 V
Ratiometric Reference
+V
U11
U12
U4
CH2
CH3
CH4
CH5
CH6
CH7
+5 V
-5 V
A/D
Converter
J4