ADC12030CIWM National Semiconductor, ADC12030CIWM Datasheet - Page 32

• Manufacturer Part Number: ADC12030CIWM
• Description: Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold
• Manufacturer: National Semiconductor

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Application Hints
An alternative method for biasing pseudo-differential opera-
tion is to use the +2.5V from the LM4040 to bias any ampli-
fier circuits driving the ADC as shown in Figure 13 . The value
of the resistor pull-up biasing the LM4040-2.5 will depend
upon the current required by the op amp biasing circuitry.
In the circuit of Figure 13 some voltage range is lost since
the amplifier will not be able to swing to +5V and GND with
a single +5V supply. Using an adjustable version of the
FIGURE 12. Pseudo-Differential Biasing with the Signal Source AC Coupled Directly into the ADC
(Continued)
FIGURE 13. Alternative Pseudo-Differential Biasing
32
LM4041 to set the full scale voltage at exactly 2.048V and a
lower grade LM4040D-2.5 to bias up everything to 2.5V as
shown in Figure 14 will allow the use of all the ADC’s digital
output range of −4096 to +4095 while leaving plenty of head
room for the amplifier.
Fully differential operation is shown in Figure 15 . One LSB
for this case is equal to (4.1V/4096) = 1 mV.
DS011354-47
DS011354-48