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OPA846ID 参数 Datasheet PDF下载

OPA846ID图片预览
型号: OPA846ID
PDF下载: 下载PDF文件 查看货源
内容描述: 宽带,低噪声,电压反馈运算放大器 [Wideband, Low-Noise, Voltage-Feedback OPERATIONAL AMPLIFIER]
分类和应用: 运算放大器放大器电路光电二极管
文件页数/大小: 23 页 / 388 K
品牌: TI [ TEXAS INSTRUMENTS ]
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guideline ensures that the noise added at the output due to  
the Johnson noise of the resistors does not significantly  
increase the total noise over that due to the 1.2nV/Hz input  
voltage noise for the op amp. Higher resistor values can  
certainly be used where the application requires it, but can  
start to add significantly to the output noise power as de-  
scribed in the Setting Resistor Values to Minimize Noise  
section.  
APPLICATIONS INFORMATION  
WIDEBAND, NONINVERTING OPERATION  
The OPA846 provides a unique combination of features. Low  
input voltage noise, along with a very low distortion output  
stage, gives one of the highest dynamic range op amps  
available. The very high Gain Bandwidth Product (GBP) can  
be used either to deliver high signal bandwidths at high gain,  
or to deliver very low distortion signals at moderate frequen-  
cies and lower gains. To achieve the full performance of the  
OPA846, careful attention to PC board layout and compo-  
nent selection is required, as discussed in the following  
sections of this data sheet.  
WIDEBAND INVERTING GAIN OPERATION  
Operating the OPA846 as an inverting amplifier has several  
benefits and is particularly appropriate when a matched input  
impedance is required. Figure 2 shows the inverting gain  
circuit used as the basis of the inverting mode of the Typical  
Characteristic curves.  
Figure 1 shows the noninverting gain of a 10V/V circuit used  
as the basis of the Electrical Characteristics and most of the  
Typical Characteristic curves. Most of the curves are charac-  
terized using signal sources with a 50driving impedance,  
and with a 50load impedance presented by the measure-  
ment equipment. In Figure 1, the 50resistor at the VIN  
terminal matches the source impedance of the test genera-  
tor, while the 50series resistor at the VO terminal provides  
a matching resistor for the measurement equipment load.  
Generally, the data sheet voltage swing specifications are at  
the output pin (VO in Figure 1), while the output power (dBm)  
specifications are at the matched 50load. The total 100Ω  
load at the output, combined with the 503total feedback  
network load, presents the OPA846 with an effective output  
load of 83for the circuit of Figure 1.  
+5V  
VCC  
+
0.1µF  
6.8µF  
RS  
50Load  
VO  
50Ω  
0.1µF  
91Ω  
OPA846  
RG  
50Ω  
RF  
1kΩ  
50Source  
VI  
+
0.1µF  
6.8µF  
+5V  
+VCC  
VEE  
5V  
+
0.1µF  
6.8µF  
FIGURE 2. DC-Coupled, G = 20V/V, Bipolar Supply, Speci-  
50Source  
fication and Test Circuit.  
50Load  
RS  
50Ω  
VI  
VO  
50Ω  
OPA846  
Driving this circuit from a 50source, and constraining the  
gain resistor (RG) to equal 50, gives both a signal band-  
width and noise advantage. RG acts as both the input  
termination resistor and the gain setting resistor for the  
circuit. Although the signal gain (VO/VI) for the circuit of  
Figure 2 is double that for Figure 1, the noise gains are in fact  
equal when the 50source resistor is included. This has the  
interesting effect of doubling the equivalent GBP of the  
amplifier. This can be seen by observing the 200MHz band-  
width for the inverting gain of 20. This implies a GBP of  
4GHz, when in fact this extended bandwidth is given by the  
reduced noise gain when the matched source resistor is  
included. If the signal source is actually the low impedance  
output of another amplifier, RG is increased to the minimum  
load resistance value allowed for that amplifier and RF is then  
adjusted to achieve the desired gain. For stable operation of  
the OPA846, it is critical that this driving amplifier show very  
low output impedance at frequencies beyond the expected  
closed-loop bandwidth for the OPA846.  
RF  
453Ω  
RG  
50Ω  
0.1µF  
6.8µF  
+
VEE  
5V  
FIGURE 1. DC-Coupled, G = +10V/V, Bipolar Supply, Speci-  
fication and Test Circuit.  
Voltage-feedback op amps (unlike current-feedback designs)  
can use a wide range of resistor values to set the gain,  
although these resistors usually have low values to maintain  
a low total output noise. The circuit of Figure 1, and the  
specifications at other gains, use the constraint that RG be  
set to 50and RF adjusted to get the desired gain. Using this  
OPA846  
10  
SBOS250C  
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