AD7266 Analog Devices, AD7266 Datasheet - Page 15

• Manufacturer Part Number: AD7266
• Description: Differential/Single-Ended Input, Dual, Simultaneous Sampling, 2 MSPS, 12-Bit, 3-Channel SAR A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7266

• Resolution (bits): 12bit
• # Chan: 12
• Sample Rate: 2MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref) p-p,(Vref) p-p,2.5V p-p,5V p-p,Uni (Vref),Uni (Vref) x 2,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

Differential Mode
The AD7266 can have a total of six differential analog
input pairs.
Differential signals have some benefits over single-ended
signals, including noise immunity based on the device’s
common-mode rejection and improvements in distortion
performance. Figure 23 defines the fully differential analog
input of the AD7266.
The amplitude of the differential signal is the difference
between the signals applied to the V
differential pair (V
simultaneously driven by two signals each of amplitude V
(or 2 × V
of phase. The amplitude of the differential signal is, therefore
(assuming the 0 to V
to-peak (2 × V
The common mode is the average of the two signals
and is, therefore, the voltage on which the two inputs are
centered.
This results in the span of each input being CM ± V
voltage has to be set up externally and its range varies with the
reference value, V
mode range decreases. When driving the inputs with an amplifier,
the actual common-mode range is determined by the amplifier’s
output voltage swing.
Figure 24 and Figure 25 show how the common-mode range
typically varies with V
V
must be in this range to guarantee the functionality of the AD7266.
When a conversion takes place, the common mode is rejected,
resulting in a virtually noise free signal of amplitude −V
+V
2 × V
from −2 V
REF
REF
(V
range or 2 × V
REF
corresponding to the digital codes of 0 to 4096. If the
IN+
range is used, then the input signal amplitude extends
REF
COMMON
VOLTAGE
+ V
REF
MODE
, depending on the range chosen) that are 180° out
to +2 V
IN−
REF
Figure 23. Differential Input Definition
)/2
), regardless of the common mode (CM).
REF
1
ADDITIONAL PINS OMITTED FOR CLARITY.
IN+
REF
. As the value of V
REF
REF
− V
REF
range, respectively. The common mode
range is selected) −V
after conversion.
V
V
for a 5 V power supply using the 0 to
IN−
REF
REF
). V
p-p
p-p
IN+
and V
V
AD7266
V
IN+
IN+
IN–
REF
and V
increases, the common-
IN−
1
should be
REF
IN−
to +V
pins in each
REF
REF
/2. This
REF
peak-
REF
to
Rev. B | Page 15 of 28
Driving Differential Inputs
Differential operation requires that V
simultaneously driven with two equal signals that are 180° out
of phase. The common mode must be set up externally. The
common-mode range is determined by V
and the particular amplifier used to drive the analog inputs.
Differential modes of operation with either an ac or dc input
provide the best THD performance over a wide frequency
range. Because not all applications have a signal preconditioned
for differential operation, there is often a need to perform
single-ended-to-differential conversion.
Figure 24. Input Common-Mode Range vs. V
Figure 25. Input Common-Mode Range vs. V
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0
0
T
T
A
A
= 25°C
= 25°C
0.5
0.5
1.0
1.5
1.0
2.0
V
V
REF
REF
2.5
(V)
(V)
1.5
3.0
IN+
REF
REF
and V
3.5
(0 to V
(2 × V
REF
, the power supply,
2.0
4.0
REF
REF
IN−
Range, V
Range, V
be
4.5
AD7266
2.5
5.0
DD
DD
= 5 V)
= 5 V)