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OPA209 参数 Datasheet PDF下载

OPA209图片预览
型号: OPA209
PDF下载: 下载PDF文件 查看货源
内容描述: 运算放大器连接器 [OPERATIONAL AMPLIFIER]
分类和应用: 连接器运算放大器
文件页数/大小: 25 页 / 763 K
品牌: TI [ TEXAS INSTRUMENTS ]
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OPA209  
OPA2209  
OPA4209  
SBOS426B NOVEMBER 2008REVISED AUGUST 2010  
www.ti.com  
INPUT PROTECTION  
The equation in Figure 33 shows the calculation of  
the total circuit noise, with these parameters:  
The input terminals of the OPA209 are protected from  
excessive differential voltage with back-to-back  
diodes, as shown in Figure 32. In most circuit  
applications, the input protection circuitry has no  
consequence. However, in low-gain or G = 1 circuits,  
fast ramping input signals can forward-bias these  
diodes because the output of the amplifier cannot  
respond rapidly enough to the input ramp. This effect  
is illustrated in Figure 25 and Figure 26 of the Typical  
Characteristics. If the input signal is fast enough to  
create this forward-bias condition, the input signal  
current must be limited to 10mA or less. If the input  
signal current is not inherently limited, an input series  
resistor can be used to limit the signal input current.  
This input series resistor degrades the low-noise  
performance of the OPA209. See the Noise  
Performance section for further information on noise  
performance. Figure 32 shows an example  
en = voltage noise,  
in = current noise,  
RS = source impedance,  
k = Boltzmann's constant = 1.38 × 10–23 J/K,  
and T = temperature in kelvins.  
For more details on calculating noise, see the Basic  
Noise Calculations section.  
VOLTAGE NOISE SPECTRAL DENSITY  
vs SOURCE RESISTANCE  
10k  
EO  
1k  
RS  
OPA209  
100  
configuration that implements  
feedback resistor.  
a
current-limiting  
OPA827  
Resistor Noise  
10  
RF  
EO2 = en2 + (in RS)2 + 4kTRS  
1
100  
1k  
10k  
100k  
1M  
-
Source Resistance, RS (W)  
OPA209  
Output  
Figure 33. Noise Performance of the OPA209 and  
OPA827 in Unity-Gain Buffer Configuration  
RI  
+
Input  
BASIC NOISE CALCULATIONS  
Figure 32. Pulsed Operation  
Low-noise circuit design requires careful analysis of  
all noise sources. External noise sources can  
dominate in many cases; consider the effect of  
source resistance on overall op amp noise  
performance. Total noise of the circuit is the  
NOISE PERFORMANCE  
Figure 33 shows the total circuit noise for varying  
source impedances with the op amp in a unity-gain  
configuration (no feedback resistor network, and  
therefore no additional noise contributions). Two  
different op amps are shown with the total circuit  
noise calculated. The OPA209 has very low voltage  
noise, making it ideal for low source impedances  
(less than 2k). As a comparable precision FET-input  
op amp (very low current noise), the OPA827 has  
somewhat higher voltage noise, but lower current  
noise. It provides excellent noise performance at  
moderate to high source impedance (10kand up).  
For source impedance lower than 300Ω, the OPA211  
may provide lower noise.  
root-sum-square  
components.  
combinations  
of  
all  
noise  
The resistive portion of the source impedance  
produces thermal noise proportional to the square  
root of the resistance. This function is illustrated in  
Figure 33. The source impedance is usually fixed;  
consequently, select the appropriate op amp and the  
feedback resistors to minimize the respective  
contributions to the total noise.  
12  
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Copyright © 2008–2010, Texas Instruments Incorporated  
Product Folder Link(s): OPA209 OPA2209 OPA4209  
 
 
 
 
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