AD7924 Analog Devices, AD7924 Datasheet - Page 19

• Manufacturer Part Number: AD7924
• Description: 4-Channel, 1 MSPS, 12-Bit A/D Converter with Sequencer in 16-Lead TSSOP
• Manufacturer: Analog Devices

Specifications of AD7924

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 1MSPS
• 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 AD7904/AD7914/AD7924 is either
straight binary or twos complement, depending on the status of
the LSB in the control register. The designed code transitions
occur at successive LSB values (that is, 1 LSB, 2 LSBs, and so on).
For the 0 V to REF
the AD7904, REF
the AD7924. For the 0 V to 2 × REF
is 2 × REF
and 2 × REF
teristic for the AD7904/AD7914/AD7924 when straight binary
coding is selected is shown in Figure 16; the ideal transfer
characteristic for the AD7904/AD7914/AD7924 when twos
complement coding is selected is shown in Figure 17.
IN
111…111
111…110
111…000
011…111
000…010
000…001
000…000
/256 for the AD7904, 2 × REF
Figure 16. Straight Binary Transfer Characteristic
IN
/4096 for the AD7924. The ideal transfer charac-
•
•
•
•
•
NOTES
1. V
REF
IN
IN
0V
/1024 for the AD7914, and REF
IS EITHER REF
0V
input range, the LSB size is REF
V
1LSB
ANALOG INPUT
IN
1LSB = V
1LSB = V
1LSB = V
OR 2 × REF
IN
input range, the LSB size
IN
REF
REF
REF
+V
V
/1024 for the AD7914,
IN
REF
/256 AD7904
/1024 AD7914
/4096 AD7924
.
0.1µF
R3
R2
– 1LSB
R1 = R2 = R3 = R4
IN
/4096 for
IN
V
/256 for
REF
R4
R1
Figure 18. Handling Bipolar Signals
Rev. B | Page 19 of 32
REF
V
V
IN
IN
0
3
AD7904/
AD7914/
AD7924
IN
AV
DD
Handling Bipolar Input Signals
Figure 18 shows how the combination of the 0 V to 2 × REF
input range and the twos complement output coding scheme is
particularly useful for handling bipolar input signals. If the
bipolar input signal is biased about REF
output coding is selected, REF
−REF
scale, with a dynamic range of 2 × REF
V
DOUT
DRIVE
IN
is negative full scale, and +REF
COMPLEMENT
011…111
011…110
000…001
000…000
111…111
100…010
100…001
100…000
+REF
–REF
Figure 17. Twos Complement Transfer Characteristic
REF
TWOS
•
•
•
•
IN
IN
IN
–V
(= 2 × REF
(= 0V)
with 0 V to 2 × REF
REF
+ 1LSB
PROCESSOR
MICRO-
AD7904/AD7914/AD7924
DSP/
IN
V
V
)
DD
DD
V
REF
ANALOG INPUT
IN
– 1LSB
1LSB = 2 × V
1LSB = 2 × V
1LSB = 2 × V
becomes the zero code point,
IN
011…111
000…000
100…000
Input Range
+V
REF
IN
IN
IN
.
REF
REF
REF
becomes positive full
– 1LSB
and twos complement
/256 AD7904
/1024 AD7914
/4096 AD7924
IN