THS6022 Datasheet, PDF (26/38 Pages) Texas Instruments – 250-mA DUAL DIFFERENTIAL LINE DRIVER

THS6022
250-mA DUAL DIFFERENTIAL LINE DRIVER
SLOS225C – SEPTEMBER 1998 – REVISED JANUARY 2000
APPLICATION INFORMATION
noise calculations and noise figure (continued)
This brings up another noise measurement usually preferred in RF applications, the noise figure (NF). Noise
figure is a measure of noise degradation caused by the amplifier. The value of the source resistance must be
defined and is typically 50 Ω in RF applications.
+ ^{ȱ ȳ} NF
10log ^{eni 2}
ȧȲ_{ǒ Ǔ ȴȧ eRs 2}
Because the dominant noise components are generally the source resistance and the internal amplifier noise
voltage, we can approximate noise figure as:
ȧȧȧȧȱȲ ^{ȧȡȢǒ Ǔ ǒ Ǔ ȧȣȤȳȴȧȧȧȧ} _{+ ) NF 10log 1}
) ) ²
en
IN
4 kTR_S
RS ²
Figure 52 shows the noise figure graph for the THS6022.
NOISE FIGURE
vs
SOURCE RESISTANCE
20
TA = 25°C
18
16
14
12
10
8
6
4
2
0
10
100
1k
10 k
Rs – Source Resistance – Ω
Figure 52. Noise Figure vs Source Resistance
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