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THS3001 Datasheet, PDF (20/32 Pages) Texas Instruments – 420-MHz HIGH-SPEED CURRENT-FEEDBACK AMPLIFIERS | |||
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THS3001, THS3002
420-MHz HIGH-SPEED CURRENT-FEEDBACK AMPLIFIERS
SLOS217A â JULY 1998 â REVISED JUNE 1999
APPLICATION INFORMATION
noise calculations and noise figure
Noise can cause errors on very small signals. This is especially true for amplifying small signals coming over
a transmission line or an antenna. The noise model for current-feedback amplifiers (CFB) is the same as for
voltage feedback amplifiers (VFB). The only difference between the two is that CFB amplifiers generally specify
different current-noise parameters for each input, while VFB amplifiers usually only specify one noise-current
parameter. The noise model is shown in Figure 49. This model includes all of the noise sources as follows:
⢠en = amplifier internal voltage noise (nV/âHz)
⢠IN+ = noninverting current noise (pA/âHz)
⢠INâ = inverting current noise (pA/âHz)
⢠eRx = thermal voltage noise associated with each resistor (eRx = 4 kTRx )
RS
eRs
en
Noiseless
eni
+
_
eno
IN+
eRf
RF
INâ
eRg
RG
Figure 49. Noise Model
+ Ç¸Ç Ç ) Ç ) Ç ) Ç Ç Ã¸ ÇÇ ) ) Ç Ã¸ Ç The total equivalent input noise density (eni) is calculated by using the following equation:
2
2
2
eni
en
IN
RS
INâ RF RG
4 kTRs 4 kT RF RG
Where:
k = Boltzmannâs constant = 1.380658 Ã 10â23
T = temperature in degrees Kelvin (273 +°C)
RF || RG = parallel resistance of RF and RG
+ + Ç ) Ç To get the equivalent output noise of the amplifier, just multiply the equivalent input noise density (eni) by the
overall amplifier gain (AV).
eno eni AV
eni 1
RF
RG
(Noninverting Case)
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⢠POST OFFICE BOX 655303 DALLAS, TEXAS 75265
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