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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  
REALIZATION OF ACTIVE FILTERS  
BAND-PASS KRC OR SALLEN-KEY FILTER  
CHANNEL SEPARATION  
The low offset voltage and the high CMRR of the OPx177 make  
it an excellent choice for precision filters, such as the band-pass  
KRC filter shown in Figure 67. This filter type offers the capability  
to tune the gain and the cutoff frequency independently.  
Multiple amplifiers on a single die are often required to reject  
any signals originating from the inputs or outputs of adjacent  
channels. OP2177 input and bias circuitry is designed to prevent  
feedthrough of signals from one amplifier channel to the other.  
As a result, the OP2177 has an impressive channel separation of  
greater than −120 dB for frequencies up to 100 kHz and greater  
than −115 dB for signals up to 1 MHz.  
Because the common-mode voltage into the amplifier varies with  
the input signal in the KRC filter circuit, a high CMRR is required  
to minimize distortion. Also, the low offset voltage of the OPx177  
allows a wider dynamic range when the circuit gain is chosen to  
be high.  
C3  
680pF  
R2  
10k  
The circuit of Figure 67 consists of two stages. The first stage is  
a simple high-pass filter where the corner frequency (fC) is  
V+  
2
3
1
8
1/2  
OP2177  
1
6
5
(2)  
V
R3  
33kΩ  
R4  
33kΩ  
OUT  
2π C1C2R1R2  
1/2  
OP2177  
7
C2  
10nF  
C1  
10nF  
C4  
330pF  
and  
4
+
V1  
R1  
20kΩ  
V–  
R1  
(3)  
Q = K  
R2  
Figure 67. Two-Stage, Band-Pass KRC Filter  
where K is the dc gain.  
Choosing equal capacitor values minimizes the sensitivity and  
simplifies Equation 2 to  
10kΩ  
V+  
1
8
100Ω  
6
5
2
3
1/2  
OP2177  
2πC R1R2  
1/2  
OP2177  
7
1
4
The value of Q determines the peaking of the gain vs. frequency  
(ringing in transient response). Commonly chosen values for Q  
are generally near unity.  
+
V1  
50mV  
V–  
Figure 68. Channel Separation Test Circuit  
1
Setting Q =  
yields minimum gain peaking and minimum  
REFERENCES ON NOISE DYNAMICS  
AND FLICKER NOISE  
2
ringing. Determine values for R1 and R2 by using Equation 3.  
S. Franco, Design with Operational Amplifiers and Analog  
Integrated Circuits. McGraw-Hill, 1998.  
1
For  
R1/R2 = 2 in the circuit example. Select R1 = 5 kꢁ  
,
Q =  
2
Analog Devices, Inc., The Best of Analog Dialogue, 1967 to  
1991. Analog Devices, Inc., 1991.  
and R2 = 10 kꢁ for simplicity.  
The second stage is a low-pass filter where the corner frequency  
can be determined in a similar fashion. For R3 = R4 = R  
1
1
2
C3  
C4  
fC  
=
and Q =  
C3  
C4  
2πR  
Rev. G | Page 21 of 24