adc12132 National Semiconductor Corporation, adc12132 Datasheet - Page 32

• Manufacturer Part Number: adc12132
• Description: Self-calibrating 12-bit Plus Sign Serial I/o A/d Converters With Mux And Sample/hold
• Manufacturer: National Semiconductor Corporation

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Application Information
For pseudo-differential signed operation, the biasing circuit
shown in Figure 12 shows a signal AC coupled to the ADC.
This gives a digital output range of −4096 to +4095. With a
2.5V reference, 1 LSB is equal to 610 µV. Although, the ADC
is not production tested with a 2.5V reference, when V
V
than 0.1 LSB (see the curves in the Typical Electrical Char-
acteristics Section). With the ADC set to an acquisition time
An alternative method for biasing pseudo-differential opera-
tion is to use the +2.5V from the LM4040 to bias any ampli-
D
+
are +5.0V linearity error typically will not change more
FIGURE 12. Pseudo-Differential Biasing with the Signal Source AC Coupled Directly into the ADC
(Continued)
FIGURE 11. Single-Ended Biasing
A
+
and
32
of 10 clock periods, the input biasing resistor needs to be
600Ω or less. Notice though that the input coupling capacitor
needs to be made fairly large to bring down the high pass
corner. Increasing the acquisition time to 34 clock periods
(with a 5 MHz CCLK frequency) would allow the 600Ω to
increase to 6k, which with a 1 µF coupling capacitor would
set the high pass corner at 26 Hz. Increasing R, to 6k would
allow R
2
to be 2k.
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