AD7764 Analog Devices, AD7764 Datasheet - Page 18

• Manufacturer Part Number: AD7764
• Description: 24-Bit, 312 kSPS, 109 dB Sigma Delta ADC with On-Chip Buffers and Serial Interface
• Manufacturer: Analog Devices

Specifications of AD7764

• Resolution (bits): 24bit
• # Chan: 1
• Sample Rate: 40MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: 6.5 V p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

AD7764
AD7764 INPUT STRUCTURE
The AD7764 requires a 4.096 V input to the reference pin,
V
ADR444. Because the input to the device’s Σ-Δ modulator is
fully differential, the effective differential reference range is
8.192 V.
As is inherent in Σ-Δ modulators, only a certain portion of this
full reference may be used. With the AD7764, 80% of the full
differential reference can be applied to the modulator’s differ-
ential inputs.
REF
+, supplied by a high precision reference, such as the
V
REF
INPUT TO MODULATOR
+ Diff
(
PIN 5 AND PIN 6
)
V
=
IN
2
– AND V
×
. 4
096
IN
+
=
. 8
V
V
V
V
V
V
IN
–0.5dBFS INPUT
–0.5dBFS INPUT
IN
IN
IN
192
IN
IN
+ = 3.6855V
– = 0.4105V
+ = 0.4105V
– = 3.6855V
+ = 2.048V
– = 2.048V
V
INPUT VOLTAGE (V)
Figure 34. AD7764 Scaling: Modulator Input Voltage vs. Digital Output Code
+3.2768V = MODULATOR FULL-SCALE = 80% OF 4.096V
80% OF 4.096V = MODULATOR FULL-SCALE = –3.2768V
OVERRANGE REGION
+4.096V
OVERRANGE REGION
Rev. A | Page 18 of 32
–4.096V
This means that a maximum of ±3.2768 V p-p full-scale can be
applied to each of the AD7764 modulator inputs (Pin 5 and
Pin 6), with the AD7764 being specified with an input −0.5 dB
down from full scale (−0.5 dBFS). The AD7764 modulator
inputs must have a common-mode input of 2.048 V.
Figure 34 shows the relative scaling between the differential
voltages applied to the modulator pins and the respective 24-bit
twos complement digital outputs.
TWOS COMPLEMENT
Modulator
DIGITAL OUTPUT
0111 1111 1111 1111 1111 1111
0111 1000 1101 0110 1111 1101
0000 0000 0000 0000 0000 0001
0000 0000 0000 0000 0000 0000
1111 1111 1111 1111 1111 1111
1000 0111 0010 1001 0000 0010
1000 0000 0000 0000 0000 0000
_
Input
FULLSCALE
=
. 8
192
V
DIGITAL OUTPUT
ON SDO PIN
×
0
8 .
=
. 6
5536
V