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EVAL-AD7923CBZ View Datasheet(PDF) - Analog Devices

Part Name
Description
MFG CO.
'EVAL-AD7923CBZ' PDF : 24 Pages View PDF
ADC TRANSFER FUNCTION
The output coding of the AD7923 is either straight binary or
twos complement, depending on the status of the LSB in the
control register. The designed code transitions occur at succes-
sive LSB values (for example, 1 LSB, 2 LSBs). The LSB size is
REFIN /4096 for the AD7923. The ideal transfer characteristic
for the AD7923 when straight binary coding is selected is
shown in Figure 16 and the ideal transfer characteristic for the
AD7923 when twos complement coding is selected is shown in
Figure 17.
111...111
111...110
111...000
011...111
000...010
000...001
000...000
0V 1LSB
1LSB = VREF/4096
+VREF – 1LSB
ANALOG INPUT
NOTES
1. VREF IS EITHER REFIN OR 2 × REFIN
Figure 16. Straight Binary Transfer Characteristic
AD7923
011...111
011...110
000...001
000...000
111...111
100...010
100...001
100...000
1LSB = 2 × VREF/4096
–VREF + 1LSB
+VREF – 1LSB
VREF – 1LSB
ANALOG INPUT
Figure 17. Twos Complement Transfer Characteristic
with REFIN ± REFIN Input Range
Handling Bipolar Input Signals
Figure 18 shows how useful the combination of the 2 × REFIN
input range and the twos complement output coding scheme is
for handling bipolar input signals. If the bipolar input signal is
biased around REFIN and twos complement output coding is
selected, then REFIN becomes the zero-code point, −REFIN is
negative full scale, and + REFIN becomes positive full scale with
a dynamic range of 2 × REFIN.
VREF
VDD
0.1μF
REFIN AVDD
VDRIVE
VDD
V
R4
AD7923
DSP/μP
R3
TWOS
COMPLEMENT
R2
VIN0
DOUT
0V
V
VIN3
+REFIN (= 2 × REFIN)
011...111
R1
R1 = R2 = R3 = R4
REFIN
000...000
(= 0V)
–REFIN
100...000
Figure 18. Handling Bipolar Signals
Rev. C | Page 15 of 24
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