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| THS4031_16 Datasheet, PDF (21/47 Pages) Texas Instruments – THS403x 100-MHz Low-Noise High-Speed Amplifiers | |||
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Functional Block Diagrams (continued)
VCC
THS4031, THS4032
SLOS224H â JULY 1999 â REVISED JUNE 2016
1INâ 2
1IN+ 3
â8
+
1
1OUT
2INâ 6
5
2IN+
â
+
4
7
2OUT
âVCC
Figure 51. THS4032 â Dual Channel
9.3 Feature Description
9.3.1 Noise Calculations and Noise Figure
Noise can cause errors on very small signals. This is especially true when amplifying small signals. The noise
model for the THS403x, shown in Figure 52, 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 52. Noise Model
The total equivalent input noise density (eni) is calculated by using Equation 1:
eni = (en )2 = (IN + ´ RS )2 = (IN- ´ (RF â RG ))2 + 4kTRs + 4kT(RF â RG )
where
⢠k = Boltzmann's constant = 1.380658 à 10â23
⢠T = Temperature in degrees Kelvin (273+°C)
⢠RF || RG = Parallel resistance of RF and RG
(1)
To get the equivalent output noise of the amplifier, just multiply the equivalent input noise density (eni) by the
overall amplifier gain (AV) in Equation 2.
Copyright © 1999â2016, Texas Instruments Incorporated
Product Folder Links: THS4031 THS4032
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