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VCA2611Y/2K 参数 Datasheet PDF下载

VCA2611Y/2K图片预览
型号: VCA2611Y/2K
PDF下载: 下载PDF文件 查看货源
内容描述: 双通道,可变增益放大器,具有低噪声前置放大器 [Dual, Variable-Gain Amplifier with Low-Noise Preamp]
分类和应用: 放大器
文件页数/大小: 23 页 / 1040 K
品牌: TAOS [ TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS ]
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RF  
VCA NOISE = 3.8nVHz, LNP GAIN = 20dB  
LNP Noise  
14  
12  
10  
8
nV/Hz  
6.0E-10  
8.0E-10  
1.0E-09  
1.2E-09  
1.4E-09  
1.6E-09  
1.8E-09  
2.0E-09  
RS  
LNPIN  
A
RIN  
RIN  
6
Active Feedback  
RF  
4
=
= RS  
1 + A  
2
RS  
0
0
100 200 300 400 500 600 700 800 900 1000  
A
Source Impedance ()  
RS  
FIGURE 7. Noise Figure for Conventional Termination.  
noise figure for active and conventional termination methods.  
The left-most set of data points in each graph give the results  
for typical 50cable termination, showing the worst noise  
figure but also the greatest advantage of the active feedback  
method.  
Conventional Cable Termination  
FIGURE 5. Configurations for Active Feedback and Conven-  
tional Cable Termination.  
A switch, controlled by the FBSWCNTL signal on pin 45,  
enables the user to reduce the feedback resistance by  
adding an additional parallel component, connected between  
the LNPINP and SWFB terminals. The two different values of  
feedback resistance will result in two different values of  
active-feedback input resistance. Thus, the active-feedback  
impedance can be optimized at two different LNP gain  
settings. The switch is connected at the buffered output of  
the LNP and has an ON resistance of approximately 1.  
the user-selected gain of the LNP, and RIN is the resulting  
amplifier input impedance with active feedback. In this case,  
unlike the conventional termination above, both the signal  
voltage and the RS noise are attenuated by the same factor  
of 2 (6dB) before being re-amplified by the A gain setting.  
This avoids the extra 3dB degradation due to the square-root  
effect described earlier, the key advantage of the active  
termination technique.  
This previous explanation ignored the input noise contribu-  
tion of the LNP itself. Also, the noise contribution of the  
feedback resistor must be included for a completely correct  
analysis. The curves given in Figures 6 and 7 allow the  
VCA2616 and VCA2611 user to compare the achievable  
When employing active feedback, the user should be careful  
to avoid low-frequency instability or overload problems. Fig-  
ure 8 illustrates the various low-frequency time constants.  
RF  
VCA NOISE = 3.8nVHz, LNP GAIN = 20dB  
9
VCM  
LNP Noise  
nV/Hz  
8
CF  
0.001µF  
200kΩ  
7
6
5
4
3
2
1
0
6.0E-10  
8.0E-10  
1.0E-09  
1.2E-09  
1.4E-09  
1.6E-09  
1.8E-09  
2.0E-09  
44pF  
44pF  
CC  
Buffer  
Buffer  
LNPOUT  
N
RS  
LNPOUTP  
Gain  
200kΩ  
Stage  
VCM  
0
100 200 300 400 500 600 700 800 900 1000  
(VCA) LNP  
Source Impedance ()  
FIGURE 6. Noise Figure for Active Termination.  
FIGURE 8. Low-Frequency LNP Time Constants.  
VCA2616, VCA2611  
12  
SBOS234E  
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