THS6042_16 Datasheet, PDF (20/46 Pages) Texas Instruments – 350mA,12V ADSL CPE LINE DRIVERS

THS6042, THS6043
350 mA, ±12 V ADSL CPE LINE DRIVERS
SLOS264G − MARCH 2000 − REVISED DECEMBER 2001
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.
ȧȱ ^{ȳȧ NF + 10log eni 2}
Ȳ ȴ ^ǒe_Rs^Ǔ2
Because the dominant noise components are generally the source resistance and the internal amplifier noise
voltage, we can approximate noise figure as:
ǒ Ǔ _NF
+
ȱ
10log^{ȧȧȧȧ}1
ȧȡȢ
)
en
2 _{) ǒIN )}
4 kTR_S
Ȳ
RS^Ǔ2_{ȧȣȤȳȧȧȧȧ}
È´
Figure 39 shows the noise figure graph for the THS6042/3.
16
f = 10 kHz
14
TA = 25°C
12
10
8
6
4
2
0
10
100
1k
10 k
RS − Source Resistance − Ω
Figure 39. Noise Figure vs Source Resistance
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