THS6007 Datasheet, PDF (26/36 Pages) Texas Instruments – DUAL DIFFERENTIAL LINE DRIVERS AND LOW-POWER RECEIVERS

THS6007
DUAL DIFFERENTIAL LINE DRIVERS AND LOW-POWER RECEIVERS
SLOS334– DECEMBER 2000
APPLICATION INFORMATION
noise calculations and noise figure
Noise can cause errors on very small signals. This is especially true for the receiver amplifiers which are
generally used for amplifying small signals coming over a transmission line. The noise model for
current-feedback amplifiers (CFB) is the same as voltage-feedback amplifiers (VFB). The only difference
between the two is that the 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 82.
This model includes all of the noise sources as follows:
• e_n = Amplifier internal voltage noise (nV/√Hz)
• IN+ = Noninverting current noise (pA/√Hz)
• IN– = Inverting current noise (pA/√Hz)
• e_Rx = Thermal voltage noise associated with each resistor (e_Rx = 4 kTR_x )
RS
eRs
en
Noiseless
eni
+
_
eno
IN+
eRf
Rf
IN–
eRg
Rg
Figure 82. Noise Model
+ ^{Ǹǒ Ǔ} ) ^ǒ ) ^Ǔ ) ^{ǒ ǒ} ø ^ǓǓ ) ) ^ǒ ø ^{Ǔ The total equivalent input noise density (eni) is calculated by using the following equation:}
2
2
2
eni
en
IN
RS
IN– RF RG
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
+ + ǒ ) Ǔ ^{To get the equivalent output noise of the amplifier, just multiply the equivalent input noise density (eni) by the}
overall amplifier gain (A_V).
eno eni AV
e_ni 1
R_F
R_G
(Noninverting Case)
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