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OP4177ARZ1 参数 Datasheet PDF下载

OP4177ARZ1图片预览
型号: OP4177ARZ1
PDF下载: 下载PDF文件 查看货源
内容描述: 精密,低噪声,低输入偏置电流运算放大器 [Precision Low Noise, Low Input Bias Current Operational Amplifiers]
分类和应用: 运算放大器
文件页数/大小: 24 页 / 479 K
品牌: ADI [ ADI ]
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OP1177/OP2177/OP4177  
V
CC  
Plugging these values into Equation 1 yields  
1
R9  
200k  
C1  
2.2µF  
CMRRMIN  
ADR293  
2δ  
V+  
R3  
47kΩ  
R7  
80.6kΩ  
0.1µF  
where δ is the tolerance of the resistors.  
10µF  
D1  
R6  
50Ω  
Lower tolerance value resistors result in higher common-mode  
rejection (up to the CMRR of the operational amplifier).  
D1  
TR  
R2  
10µF  
R8  
1kΩ  
4.02kΩ  
7
Cu  
2
3
(–)  
6
V
Using 5% tolerance resistors, the highest CMRR that can be  
guaranteed is 20 dB. Alternatively, using 0.1% tolerance resistors  
results in a common-mode rejection ratio of at least 54 dB  
(assuming that the operational amplifier CMRR × 54 dB).  
OUT  
OP1177  
T
V
TC  
J
R5  
100Ω  
TR  
Cu  
(+)  
10µF  
4
10µF  
R1  
50Ω  
R4  
50Ω  
ISOTHERMAL  
BLOCK  
0.1µF  
With the CMRR of OPx177 at 120 dB minimum, the resistor  
match is the limiting factor in most circuits. A trimming resistor  
can be used to further improve resistor matching and CMRR of  
the difference amplifier circuit.  
V–  
Figure 64. Type K Thermocouple Amplifier Circuit  
LOW POWER LINEARIZED RTD  
A common application for a single element varying bridge is an  
RTD thermometer amplifier, as shown in Figure 65. The excita-  
tion is delivered to the bridge by a 2.5 V reference applied at the  
top of the bridge.  
A HIGH ACCURACY THERMOCOUPLE AMPLIFIER  
A thermocouple consists of two dissimilar metal wires placed in  
contact. The dissimilar metals produce a voltage  
VTC = α(TJ TR)  
RTDs may have thermal resistance as high as 0.5°C to 0.8°C  
per mW. To minimize errors due to resistor drift, the current  
through each leg of the bridge must be kept low. In this circuit,  
the amplifier supply current flows through the bridge. However,  
at the OPx177 maximum supply current of 600 ꢀA, the RTD  
dissipates less than 0.1 mW of power, even at the highest resis-  
tance. Errors due to power dissipation in the bridge are kept  
under 0.1°C.  
where:  
TJ is the temperature at the measurement of the hot junction.  
TR is the temperature at the cold junction.  
α is the Seebeck coefficient specific to the dissimilar metals used  
in the thermocouple.  
V
TC is the thermocouple voltage and becomes larger with  
increasing temperature.  
Maximum measurement accuracy requires cold junction compen-  
sation of the thermocouple. To perform the cold junction compen-  
sation, apply a copper wire short across the terminating junctions  
(inside the isothermal block) simulating a 0°C point. Adjust the  
output voltage to zero using the R5 trimming resistor, and remove  
the copper wire.  
Calibration of the bridge is made at the minimum value of  
temperature to be measured by adjusting RP until the output is zero.  
To calibrate the output span, set the full-scale and linearity  
potentiometers to midpoint and apply a 500°C temperature to  
the sensor or substitute the equivalent 500°C RTD resistance.  
Adjust the full-scale potentiometer for a 5 V output. Finally,  
apply 250°C or the equivalent RTD resistance and adjust the  
linearity potentiometer for 2.5 V output. The circuit achieves  
better than 0.5°C accuracy after adjustment.  
The OPx177 is an ideal amplifier for thermocouple circuits  
because it has a very low offset voltage, excellent PSRR and  
CMRR, and low noise at low frequencies.  
It can be used to create a thermocouple circuit with great  
linearity. Resistor R1, Resistor R2, and Diode D1, shown in  
Figure 64, are mounted in an isothermal block.  
Rev. G | Page 19 of 24