Rainbow Electronics ADC12L038 - Manual (Page 29)

Application Hints
(Continued)
TL H 11830 – 48
FIGURE 11 Alternative Pseudo-Differential Biasing
TL H 11830 – 50
FIGURE 12 Fully Differential Biasing
3 0 REFERENCE VOLTAGE
The difference in the voltages applied to the V
REF
a and
V REF b defines the analog input span (the difference be-
tween the voltage applied between two multiplexer inputs or
the voltage applied to one of the multiplexer inputs and ana-
log ground) over which 4095 positive and 4096 negative
codes exist The voltage sources driving V
REF
a or V
REF
b
must have very low output impedance and noise
The ADC12L030 2 4 8 can be used in either ratiometric or
absolute reference applications In ratiometric systems the
analog input voltage is proportional to the voltage used for
the ADC’s reference voltage When this voltage is the sys-
tem power supply the V
REF a pin is connected to V A a and
V
REF
b is connected to ground This technique relaxes the
29