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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  
In the single instrumentation amplifier (see Figure 63), where  
PROPER BOARD LAYOUT  
R4  
R3  
R2  
R1  
The OPx177 is a high precision device. To ensure optimum  
performance at the PCB level, care must be taken in the design  
of the board layout.  
=
R2  
VO =  
(
V2 V1  
)
R1  
To avoid leakage currents, the surface of the board should be  
kept clean and free of moisture. Coating the surface creates a  
barrier to moisture accumulation and helps reduce parasitic  
resistance on the board.  
a mismatch between the ratio R2/R1 and R4/R3 causes the  
common-mode rejection ratio to be reduced.  
To better understand this effect, consider that, by definition,  
Keeping supply traces short and properly bypassing the power  
supplies minimizes power supply disturbances due to output  
current variation, such as when driving an ac signal into a heavy  
load. Bypass capacitors should be connected as closely as possible  
to the device supply pins. Stray capacitances are a concern at the  
outputs and the inputs of the amplifier. It is recommended that  
signal traces be kept at least 5 mm from supply lines to  
minimize coupling.  
ADM  
CMRR =  
ACM  
where ADM is the differential gain and ACM is the common-  
mode gain.  
VO  
VDIFF  
VO  
VCM  
ADM  
=
and ACM =  
1
2
A variation in temperature across the PCB can cause a mismatch in  
the Seebeck voltages at solder joints and other points where dissi-  
milar metals are in contact, resulting in thermal voltage errors. To  
minimize these thermocouple effects, orient resistors so heat  
sources warm both ends equally. Input signal paths should contain  
matching numbers and types of components, where possible to  
match the number and type of thermocouple junctions. For  
example, dummy components such as zero value resistors can  
be used to match real resistors in the opposite input path.  
Matching components should be located in close proximity and  
should be oriented in the same manner. Ensure leads are of equal  
length so that thermal conduction is in equilibrium. Keep heat  
sources on the PCB as far away from amplifier input circuitry as  
is practical.  
VDIFF = V1 V2 andVCM  
=
(
V1 +V2  
)
For this circuit to act as a difference amplifier, its output must  
be proportional to the differential input signal.  
From Figure 63,  
R2  
R1  
R3  
1+  
1+  
R2  
R1  
V = −  
V +  
V2  
1
O
R4  
Arranging terms and combining the previous equations yields  
R4R1+ R3R2 + 2R4R2  
CMRR =  
(1)  
2R4R12R2R3  
The use of a ground plane is highly recommended. A ground  
plane reduces EMI noise and also helps to maintain a constant  
temperature across the circuit board.  
The sensitivity of CMRR with respect to the R1 is obtained by  
taking the derivative of CMRR, in Equation 1, with respect to R1.  
δCMRR  
δR1  
δ
R1R4  
2R2R4 + R2R3  
DIFFERENCE AMPLIFIERS  
=
=
+
δR1 2R1R4 2R2R3 2R1R4 2R2R3  
Difference amplifiers are used in high accuracy circuits to improve  
the common-mode rejection ratio (CMRR).  
δCMRR  
δR1  
1
(
2R2R3)  
R2  
100k  
2 −  
R1R4  
V+  
Assuming that  
7
R1  
2
3
V1  
V2  
6
V
R1 R2 R3 R4 R  
OUT  
OP1177  
4
and  
V–  
R(1 − δ) < R1, R2, R3, R4 < R(1 + δ)  
R3 = R1  
R4 = R1  
R4 R2  
R3 R1  
the worst-case CMRR error arises when  
=
Figure 63. Difference Amplifier  
R1 = R4 = R(1 + δ) and R2 = R3 = R(1 − δ)  
Rev. G | Page 18 of 24