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| THS6212 Datasheet, PDF (27/48 Pages) Texas Instruments – Differential, Line-Driver Amplifier | |||
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THS6212
SBOS758 â MAY 2016
Feature Description (continued)
7.3.4 Differential Noise Performance
The THS6212 is designed to be used as a differential driver in high-performance applications. Therefore,
analyzing the noise in such a configuration is important. Figure 80 shows the op amp noise model for the
differential configuration.
IN
EN
RS
ERS
4 kTRS
TI Device
IN
RF
4 kTRF
RG
EO2
4 kTRG
RF
4 kTRF
IN
TI Device
RS
ERS
EN
IN
4 kTRS
Copyright © 2016, Texas Instruments Incorporated
Figure 80. Differential Op Amp Noise Analysis Model
As a reminder, the differential gain is expressed in Equation 1:
GD = 1 +
2 ´ RF
RG
(1)
The output noise can be expressed as shown in Equation 2:
EO = 2 ´ GD2 ´ eN2 + (iN ´ RS)2 + 4 kTRS + 2(iIRF)2 + 2(4 kTRFGD)
(2)
Dividing this expression by the differential noise gain [GD = (1 + 2RF / RG)] gives the equivalent input-referred
spot noise voltage at the noninverting input, as shown in Equation 3.
EO =
2´
eN2 + (iN ´ RS)2 + 4 kTRS
+2
iIRF
GD
2
+2
4 kTRF
GD
(3)
Evaluating these equations for the THS6212 circuit and component values of Figure 84 gives a total output spot
noise voltage of 38.9 nV/âHz and a total equivalent input spot noise voltage of 7 nV/âHz.
In order to minimize the output noise as a result of the noninverting input bias current noise, keeping the
noninverting source impedance as low as possible is recommended.
Copyright © 2016, Texas Instruments Incorporated
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