AD621ACHIPS(RevA) 查看數據表（PDF） - Analog Devices
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AD621ACHIPS Datasheet PDF : 16 Pages
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+5V
3kΩ
3kΩ
3kΩ
3kΩ
1.7mA
AD621
3
7
20kΩ
8
AD621B
6
1
5
10kΩ
2
4
20kΩ
1.3mA
MAX
0.10mA
AD705
0.6mA
MAX
REF
IN
ADC
AGND
DIGITAL
DATA
OUTPUT
Figure 31. A Pressure Monitor Circuit which Operates on a +5 V Power Supply
Pressure Measurement
Although useful in many bridge applications such as weigh-
scales, the AD621 is especially suited for higher resistance pres-
sure sensors powered at lower voltages where small size and low
power become more even significant.
Figure 31 shows a 3 kΩ pressure transducer bridge powered
from +5 V. In such a circuit, the bridge consumes only 1.7 mA.
Adding the AD621 and a buffered voltage divider allows the sig-
nal to be conditioned for only 3.8 mA of total supply current.
Small size and low cost make the AD621 especially attractive for
voltage output pressure transducers. Since it delivers low noise
and drift, it will also serve applications such as diagnostic
noninvasion blood pressure measurement.
Wide Dynamic Range Gain Block Suppresses Large Common-
Mode and Offset Signals
The AD621 is especially useful in wide dynamic range applica-
tions such as those requiring the amplification of signals in the
presence of large, unwanted common-mode signals or offsets.
Many monolithic in amps achieve low total input drift and noise
errors only at relatively high gains (~100). In contrast the
AD621’s low output errors allow such performance at a gain of
10, thus allowing larger input signals and therefore greater
dynamic range. The circuit of Figure 32 (± 15 V supply, G = 10)
has only 2.5 µV/°C max. VOS drift and 0.55 µ/V p-p typical
0.1 Hz to 10 Hz noise, yet will amplify a ± 0.5 V differential sig-
nal while suppressing a ± 10 V common-mode signal, or it will
amplify a ± 1.25 V differential signal while suppressing a 1 V
offset by use of the DAC driving the reference pin of the
AD621. An added benefit, the offsetting DAC connected to the
reference pin allows removal of a dc signal without the associ-
ated time-constant of ac coupling. Note the representations of a
differential and common-mode signal shown in Figure 32 such
that a single-ended (or normal mode) signal of +1 V would be
composed of a +0.5 V common-mode component and a +1 V
differential component.
Table I. Make vs. Buy Error Budget
Error Source
AD621 Circuit
Calculation
Discrete Circuit
Calculation
ABSOLUTE ACCURACY at TA = +25°C
Input Offset Voltage, µV
Output Offset Voltage, µV
Input Offset Current, nA
CMR, dB
125 µV/20 mV
N/A
2 nA × 350 Ω/20 mV
110 dB→3.16 ppm, × 5 V/20 mV
(150 µV × 2/20 mV
((150 µV × 2)/100)/20 mV
(6 nA × 350 Ω)/20 mV
(0.02% Match × 5 V)/20 mV
DRIFT TO +85°C
Gain Drift, ppm/°C
Input Offset Voltage Drift, µV/°C
Output Offset Voltage Drift, µV/°C
5 ppm × 60°C
1 µV/°C × 60°C/20 mV
N/A
Total Absolute Error
100 ppm/°C Track × 60°C
(2.5 µV/°C × 2 × 60°C)/20 mV
(2.5 µV/°C × 2 × 60°C)/100/20 mV
RESOLUTION
Gain Nonlinearity, ppm of Full Scale
40 ppm
Typ 0.1 Hz–10 Hz Voltage Noise, µV p-p 0.28 µV p-p/20 mV
Total Drift Error
40 ppm
(0.38 µV p-p × √2)120 mV
Total Resolution Error
G = 100, VS = ± 15 V.
(All errors are min/max and referred to input.)
Grand Total Error
Error, ppm of Full Scale
AD621
Discrete
16,250
N/A
12,118
12,791
17,558
13,300
13,000
N/A
13,690
12,140
121,14
121,54
11,472
15,000
12,150
121,53
14,988
20,191
12,600
15,000
12,150
15,750
12,140
12,127
121,67
36,008
REV. A
–11–
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