參數(shù)資料
型號: THS4081DGN
廠商: Texas Instruments, Inc.
英文描述: 175-MHz LOW-POWER HIGH-SPEED AMPLIFIERS
中文描述: 175 - MHz的低功耗高速放大器
文件頁數(shù): 12/24頁
文件大?。?/td> 384K
代理商: THS4081DGN
THS4081, THS4082
175-MHz LOW-POWER HIGH-SPEED AMPLIFIERS
SLOS274C – DECEMBER 1999 – REVISED MAY 2000
12
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
noise calculations and noise figure (continued)
_
+
RF
RS
RG
eRg
eRf
eRs
en
IN+
Noiseless
IN–
eni
eno
Figure 39. Noise Model
The total equivalent input noise density (e
ni
) is calculated by using the following equation:
eni
en
2
IN
RS
2
IN–
RF
RG
2
4 kTRs
4 kT RF
RG
Where:
k = Boltzmann’s constant = 1.380658
×
10
–23
T = Temperature in degrees Kelvin (273 +
°
C)
R
F
|| R
G
= Parallel resistance of R
F
and R
G
To get the equivalent output noise of the amplifier, just multiply the equivalent input noise density (e
ni
) by the
overall amplifier gain (A
V
).
eno
eniAV
e
ni
1
R
F
R
G
(noninverting case)
As the previous equations show, to keep noise at a minimum, small value resistors should be used. As the
closed-loop gain is increased (by reducing R
G
), the input noise is reduced considerably because of the parallel
resistance term. This leads to the general conclusion that the most dominant noise sources are the source
resistor (R
S
) and the internal amplifier noise voltage (e
n
). Because noise is summed in a root-mean-squares
method, noise sources smaller than 25% of the largest noise source can be effectively ignored. This can greatly
simplify the formula and make noise calculations much easier to calculate.
For more information on noise analysis, please refer to the Noise Analysissection in Operational Amplifier
Circuits Applications Report(literature number SLVA043).
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