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5962-8964601PA 参数 Datasheet PDF下载

5962-8964601PA图片预览
型号: 5962-8964601PA
PDF下载: 下载PDF文件 查看货源
内容描述: 450 V / us的精密电流反馈运算放大器 [450 V/us, Precision, Current-Feedback Op Amp]
分类和应用: 运算放大器放大器电路
文件页数/大小: 12 页 / 513 K
品牌: ADI [ ADI ]
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AD846  
A simple equation can, therefore, be used to determine the band-  
width of an amplifier employing the AD846 in the inverting  
configuration.  
23  
3 dB Bandwidth =  
R + 0.05 1+ G  
(
)
F
where: The 3 dB bandwidth is in MHz  
G is the closed-loop inverting gain of the AD846  
RF is the feedback resistance in k.  
Figure 39. AD846 Three-Terminal Model  
NOTE: This equation applies only for values of RF between  
10 kand 100 k, and for RLOAD greater than 500 . For RF =  
1 kthe bandwidth should be estimated from Figure 41.  
Figure 41 illustrates the closed-loop voltage gain vs. frequency  
of the AD846 for various values of feedback resistor. For com-  
parison purposes, the characteristic of a conventional amplifier  
having an 80 MHz unity gain bandwidth is also shown.  
Figure 40. Op Amp Three-Terminal Model  
A more detailed examination of the closed-loop transfer func-  
tion of the AD846 results in the following equation:  
RF  
RS  
RF   
Closed-Loop Gain G(s) =  
1+ CCOMP RF + 1+  
RIN  
s
R
S   
Compare this to the equation for a conventional op amp:  
RF  
RS  
Figure 41. Closed-Loop Voltage Gain vs. Bandwidth for  
Various Values of RF  
CCOMP  
gM  
RF   
Closed-Loop Gain G(s) =  
1+  
1+  
s
For the case where RF = 1 kand RS = 100 (closed-loop gain  
of 10), the closed-loop bandwidth is approximately 28 MHz. It  
should also be noted that the use of a capacitor to shunt RF, a  
normal practice for stabilizing conventional op amps, will cause  
this amplifier to become unstable because the closed-loop band-  
width will increase beyond the stable operating frequency.  
R
S   
where: CCOMP is the internal compensation capacitor of the am-  
plifier; gM is the input stage transconductance of the amplifier.  
In the case of the voltage amplifier, the closed-loop bandwidth  
decreases directly with increasing values of (1 + RF/RS), the  
closed-loop gain. However, for the transimpedance amplifier,  
the situation is different. At low gains, where (1 + RF/RS) RIN is  
small compared to RF, the closed-loop bandwidth is controlled  
by the internal compensation capacitance of 7 pF and the value  
of RF, and not by the closed-loop gain. At higher gains, where (1  
+ RF/RS) RIN is much larger than RF, the behavior is that of a con-  
ventional operational amplifier in which the input stage transcon-  
ductance is equal to the inverting terminal input impedance of  
the transimpedance amplifier (RIN = 50 ).  
A similar approach can be taken to calculate the noise perfor-  
mance of the amplifier. A simplified noise model is shown in  
Figure 42.  
The equivalent mean-square output noise voltage spectral den-  
sity will equal:  
RF  
R
2  
S   
V
2 = R I  
2 + 1+  
[VN2 + R I  
2 + 4 kT RP ]  
(
)
(
)
ON  
F
NN  
P
NP  
RF  
+ 4 kT RF  
+1  
R
S
–9–  
REV. C