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OP27GS 参数 Datasheet PDF下载

OP27GS图片预览
型号: OP27GS
PDF下载: 下载PDF文件 查看货源
内容描述: 低噪声,高精度运算放大器 [Low-Noise, Precision Operational Amplifier]
分类和应用: 运算放大器光电二极管
文件页数/大小: 16 页 / 366 K
品牌: ADI [ ADI ]
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OP27  
3. Sudden motion in the vicinity of the device can also  
“feedthrough” to increase the observed noise.  
2
1/2  
Voltage Noise  
+
(
)
2
Total Noise = Current Noise × R  
+
(
)
S
4. The test time to measure 0.1 Hz to 10 Hz noise should not  
exceed 10 seconds. As shown in the noise-tester frequency  
response curve, the 0.1 Hz corner is defined by only one  
zero. The test time of 10 seconds acts as an additional zero  
to eliminate noise contributions from the frequency band  
below 0.1 Hz.  
2
Resistor Noise  
(
)
Figure 4 shows noise versus source-resistance at 1000 Hz. The  
same plot applies to wideband noise. To use this plot, multiply  
the vertical scale by the square root of the bandwidth.  
5. A noise-voltage-density test is recommended when measuring  
noise on a large number of units. A 10 Hz noise-voltage-  
density measurement will correlate well with a 0.1 Hz to 10 Hz  
peak-to-peak noise reading, since both results are determined  
by the white noise and the location of the 1/f corner frequency.  
100  
50  
1
OP08/108  
UNITY-GAIN BUFFER APPLICATIONS  
2
OP07  
10  
When Rf 100 and the input is driven with a fast, large signal  
pulse (>1 V), the output waveform will look as shown in the  
pulsed operation diagram (Figure 3).  
1 R UNMATCHED  
S
5
5534  
e.g.R = R = 10k, R = 0  
S
S1 S2  
2 R MATCHED  
S
During the fast feedthrough-like portion of the output, the input  
protection diodes effectively short the output to the input and a  
current, limited only by the output short-circuit protection, will  
be drawn by the signal generator. With Rf 500 , the output is  
capable of handling the current requirements (IL 20 mA at 10 V);  
the amplifier will stay in its active mode and a smooth transition  
will occur.  
e.g.R = 10k, R = R = 5kꢅ  
S1 S2  
S
OP27/37  
R
S1  
R
S2  
REGISTER  
NOISE ONLY  
1
50  
100  
500  
1k  
5k  
10k  
50k  
R
SOURCE RESISTANCE ꢅ  
S
Figure 4. Noise vs. Source Resistance (Including Resistor  
Noise) at 1000 Hz  
When Rf > 2 k, a pole will be created with Rf and the amplifier’s  
input capacitance (8 pF) that creates additional phase shift and  
reduces phase margin. A small capacitor (20 pF to 50 pF) in  
parallel with Rf will eliminate this problem.  
At RS <1 k, the OP27s low voltage noise is maintained. With  
RS <1 k, total noise increases, but is dominated by the resis-  
tor noise rather than current or voltage noise. lt is only beyond  
RS of 20 kthat current noise starts to dominate. The argument  
can be made that current noise is not important for applica-  
tions with low to moderate source resistances. The crossover  
between the OP27, OP07, and OP08 noise occurs in the 15 kto  
40 kregion.  
R
f
2.8V/s  
OP27  
Figure 5 shows the 0.1 Hz to 10 Hz peak-to-peak noise. Here  
the picture is less favorable; resistor noise is negligible and current  
noise becomes important because it is inversely proportional to  
the square root of frequency. The crossover with the OP07  
occurs in the 3 kto 5 krange depending on whether bal-  
anced or unbalanced source resistors are used (at 3 kthe IB  
and IOS error also can be three times the VOS spec.).  
+
Figure 3. Pulsed Operation  
COMMENTS ON NOISE  
The OP27 is a very low-noise monolithic op amp. The outstanding  
input voltage noise characteristics of the OP27 are achieved mainly  
by operating the input stage at a high quiescent current. The input  
bias and offset currents, which would normally increase, are held  
to reasonable values by the input bias-current cancellation circuit.  
The OP27A/E has IB and IOS of only 40 nA and 35 nA at 25°C  
respectively. This is particularly important when the input has a  
high source resistance. In addition, many audio amplifier design-  
ers prefer to use direct coupling. The high IB, VOS, and TCVOS  
of previous designs have made direct coupling difficult, if not  
impossible, to use.  
1k  
OP08/108  
500  
5534  
OP07  
1
2
100  
OP27/37  
1 RS UNMATCHED  
50  
e.g.RS = RS1 = 10k, RS2 = 0  
2 RS MATCHED  
Voltage noise is inversely proportional to the square root of bias  
current, but current noise is proportional to the square root of  
bias current. The OP27’s noise advantage disappears when high  
source-resistors are used. Figures 4, 5, and 6 compare OP27’s  
observed total noise with the noise performance of other devices  
in different circuit applications.  
e.g.RS = 10k, RS1 = RS2 = 5kꢅ  
RS1  
RS2  
REGISTER  
NOISE ONLY  
10  
50  
100  
500  
1k  
5k  
10k  
50k  
R
SOURCE RESISTANCE ꢅ  
S
Figure 5. Peak-to-Peak Noise (0.1 Hz to 10 Hz) as Source  
Resistance (Includes Resistor Noise)  
–12–  
REV. A