参数资料
型号: AD621BRZ-RL
厂商: Analog Devices Inc
文件页数: 4/16页
文件大小: 0K
描述: IC AMP INST LDRIFT LP 18MA 8SOIC
标准包装: 2,500
放大器类型: 仪表
电路数: 1
转换速率: 1.2 V/µs
-3db带宽: 800kHz
电流 - 输入偏压: 500pA
电压 - 输入偏移: 50µV
电流 - 电源: 900µA
电流 - 输出 / 通道: 18mA
电压 - 电源,单路/双路(±): ±2.3 V ~ 18 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SO
包装: 带卷 (TR)
AD621
REV. B
–12–
AD548
TO
REF
C
R
TO
VOUT1
+
+
10
AD621
DAC
0 TO
10V
+
VDIFF
0.5V
INPUT A:
10V CM
VCOM
10V–
+
+
INPUT B:
1V
OFFSET
VDIFF + VOFFSET
(1.25V + 1V)
VOUT1
G = 10
+
10
AD621
VOUT2
TOTAL GAIN = 100
10k
OPTIONAL
USE THIS IN PLACE OF THE DAC FOR ZERO SUPPRESSION FUNCTION.
Figure 6. Suppressing a Large Common-Mode or Offset Voltage in Order to Measure a Small Differential Signal
(VS =
±15 V)
The AD621, as well as many other monolithic instrumentation
amplifiers, is based on the “three op amp” in amp circuit (Fig-
ure 7) amplifier. Since the input amplifiers (A1 and A2) have a
common-mode gain of unity and a differential gain equal to the
set gain of the overall in amp, the voltages V1 and V2 are defined
by the equations
V1 = VCM + G
× V
DIFF/2
V2 = VCM – G
× V
DIFF/2
The common-mode voltage will drive the outputs of amplifiers
A1 and A2 to the differential-signal voltage, multiplied by the
gain, spreads them apart. For a 10 V common-mode 0.1 V
differential input, V1 would be at 10.5 V and V2 at 9.5 V.
A1
A3
+
10k
A2
+
20k
+
V1
V2
INPUT AMPLIFIER
DIFFERENTIAL GAIN = 10
COMMON MODE GAIN = 1
OUTPUT AMPLIFIER
DIFFERENTIAL GAIN = 1
COMMON MODE GAIN = 1/1000
4.44k
Figure 7. Typical Three Op Amp Instrumentation
Amplifier, Differential Gain = 10
The AD621’s input amplifiers can provide output voltage within
2.5 V of the supplies. To avoid saturation of the input amplifier
the input voltage must therefore obey the equations:
VCM + G
× V
DIFF/2
≤ (Upper Supply – 2.5 V)
VCM – G
× V
DIFF/2
≥ (Lower Supply + 2.5 V)
Figure 8 shows the trade-off between common-mode and
differential-mode input for
±15 V supplies and G = 10.
By cascading with use of the optional AD621, the circuit of
Figure 6 will provide
±1 V of zero suppression at gains of 10
and 100 (at VOUT1 and VOUT2 respectively) with maximum TCs
of
±4 ppm/°C and ±8 ppm/°C, respectively. Therefore, depend-
ing on the magnitude of the differential input signal, either
VOUT1 or VOUT2 may be used as the output.
VCM – Volts
1.2
0.2
010
2
V
DIFF
Volts
48
1.0
0.8
0.6
0.4
6
0
12
Figure 8. Trade-Off Between VCM and VDIFF Range (VS =
±15 V, G = 10), for Reference Pin at Ground
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