AD7923 Analog Devices, AD7923 Datasheet - Page 15

• Manufacturer Part Number: AD7923
• Description: 4-Channel 200 kSPS, 12-Bit A/D Converter with Sequencer in 16-Lead TSSOP
• Manufacturer: Analog Devices

Specifications of AD7923

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 200kSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

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
REF
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.
IN
/4096 for the AD7923. The ideal transfer characteristic
111...111
111...110
111...000
011...111
000...010
000...001
000...000
Figure 16. Straight Binary Transfer Characteristic
•
•
•
•
•
NOTES
1. V
REF
0V
0V
IS EITHER REF
V
1LSB
ANALOG INPUT
IN
1LSB = V
OR 2 × REF
REF
V
IN
+V
/4096
REF
0.1μF
R3
R2
– 1LSB
R1 = R2 = R3 = R4
V
R4
R1
REF
Figure 18. Handling Bipolar Signals
Rev. C | Page 15 of 24
REF
V
V
IN
IN
0
3
AD7923
•
•
IN
AV
DD
Handling Bipolar Input Signals
Figure 18 shows how useful the combination of the 2 × REF
input range and the twos complement output coding scheme is
for handling bipolar input signals. If the bipolar input signal is
biased around REF
selected, then REF
negative full scale, and + REF
a dynamic range of 2 × REF
V
DOUT
DRIVE
COMPLEMENT
+REF
–REF
REF
Figure 17. Twos Complement Transfer Characteristic
TWOS
011...111
011...110
000...001
000...000
111...111
100...010
100...001
100...000
IN
IN
IN
•
•
•
•
(= 2 × REF
(= 0V)
IN
–V
IN
with REF
becomes the zero-code point, −REF
REF
and twos complement output coding is
DSP/μP
+ 1LSB
V
V
IN
DD
DD
)
IN
IN
± REF
V
IN
.
REF
ANALOG INPUT
becomes positive full scale with
IN
– 1LSB
011...111
000...000
100...000
1LSB = 2 × V
Input Range
+V
REF
– 1LSB
REF
/4096
AD7923
IN
is
IN