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Circuit Note
CN-0042
Circuit Designs Using Analog Devices Products
Apply these product pairings quickly and with confidence.
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Devices Connected/Referenced
AD7366/
AD7367
Bipolar Input, Dual 12-/14-Bit, 2-Channel,
SAR ADC
AD8021 Low Noise, High Speed Amplifier
Driving the AD7366/AD7367 Bipolar SAR ADC in Low-Distortion DC-Coupled
Applications
Rev.
A
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engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment
at room temperature. However, you are solely responsible for testing the circuit and determining its
suitability and applicability for your use and application. Accordingly, in no event shall Analog
Devices be liable for direct, indirect, special, incidental, consequential or punitive damages due to
any cause whatsoever connected to the use of any “Circuit from the Lab”. (Continued on last page)
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CIRCUIT FUNCTION AND BENEFITS
The circuit described in this document provides single-ended,
low-distortion sampling of an industrial level, dc-coupled
signal. The driver circuit shown in Figure 1 is optimized for
applications requiring best distortion performance. Maximum
AD7366/AD7367 performance is achieved by providing
adequate settling time and low impedance in the circuit.
CIRCUIT DESCRIPTION
The AD7366 and the AD7367 are, respectively, 12-bit and
14-bit, 1 MSPS, 2-channel, simultaneous sampling SAR ADCs.
These devices have a total of four analog multiplexed inputs
(two per channel), which operate in single-ended mode. The
analog input range on the AD7366/AD7367 is programmable
and can support ±10 V, ±5 V, and 0 V to 10 V using the internal
2.5 V reference. An analog input range of ±12 V requires a 3 V
external reference.
The AD7366/AD7367 are fabricated on the Analog Devices,
Inc., industrial CMOS process (iCMOS), which is a technology
platform combining the advantages of low and high voltage
CMOS. The input circuits of the AD7366/AD7367 operate on
V
DD
and V
SS
voltages of ±12 V nominal, while the rest of the
ADC operates on an AV
CC
, a DV
CC
, and a V
DRIVE
o f + 5 V. The
iCMOS process, therefore, allows the AD7366/AD7367 to
accept high voltage bipolar signals in addition to reducing
power consumption and package size.
In applications where the signal source has high impedance,
analog input signals should be buffered before being applied to
the inputs of the AD7366/AD7367 because large source
impedances significantly affect the ac performance of the ADC.
The choice of the op amp used to drive the inputs is a function
of the particular application and depends on the analog input
voltage range selected. The driver amplifier must be able to
settle for a full-scale step to a 14-bit level (0.0061%) for the
AD7367 or a 12-bit level (0.024%) for the AD7366 in less than
the specified acquisition time of 140 ns.
+12V
–12V
V
DD
V
SS
V
A1
V
B1
AGND
AD8021
1kΩ
1kΩ
500Ω
AGND DGND
15pF
C
COMP
= 10pF
–5V/–2.5V
+5V/+2.5V
AD7366/
AD7367*
*ADDITIONAL PINS OMITTED FOR CLARITY.
10µF
+
0.1µF
+
0.1µF
+
+
10µF
+
+5V
08481-001
DV
CC
AV
CC
V
DRIVE
Figure 1. Typical Connection Diagram with the AD8021 for Driving the Analog Inputs of the AD7366/AD7367
(Simplified Schematic, Decoupling and All Connections Not Shown)
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