AD8216 데이터 시트보기 (PDF) - Analog Devices
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AD8216 Datasheet PDF : 16 Pages
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AD8216
THEORY OF OPERATION
The AD8216 is a single-supply difference amplifier typically used
to accurately amplify a small differential current shunt voltage in
the presence of a rapidly changing common-mode voltage.
The AD8216 consists of an amplifier (A1), a resistor network,
a small voltage reference, and a bias circuit (not shown),
see Figure 23.
The set of input attenuators preceding A1 consist of RA, RB, and
RC, which feature a combined series resistance of approximately
200 kΩ ± 20%. The purpose of these resistors is to attenuate the
input voltage to match the input voltage range of A1. This
balanced resistor network attenuates the common-mode signal
by a ratio of 1/18. A1 amplifier inputs are held within the power
supply range, even if Pin 1 and Pin 8 exceed the supply or fall
below common (ground). A reference voltage of 250 mV biases
the attenuator above ground, which allows the amplifier to
operate in the presence of negative common-mode voltages.
The input resistor network also attenuates normal (differential)
mode voltages. Therefore, Amplifier A1 features a gain of
54 V/V to provide a total system gain of 3V/V.
Total Gain (V/V) = 1/18 (V/V) × 54 (V/V) = 3 V/V
Data Sheet
The reference inputs, VREF1 and VREF2, are tied through resistors
to the positive input of A1, which allows the output offset to be
adjusted anywhere in the output operating range. The gain is
1 V/V from the reference pins to the output when the reference
pins are used in parallel. When they are used to divide the supply,
the gain is 0.5 V/V.
The ratios of RA, RB, RC, and RF are trimmed to a high level of
precision to allow the CMRR to exceed 80 dB. This performance is
accomplished by laser trimming the resistor ratio matching to
better than 0.01%.
+IN –IN
RA RA
RB RB
A1
RF
RC RC
250mV
AD8216
VOUT
VREF1
RREF
RREF
VREF2
GND
Figure 23. Simplified Schematic
Rev. C | Page 10 of 16
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