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THS6042 Datasheet, PDF (20/33 Pages) Texas Instruments – 350 mA, ±12 V ADSL CPE LINE DRIVERS | |||
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THS6042, THS6043
350 mA, ±12 V ADSL CPE LINE DRIVERS
SLOS264G â MARCH 2000 â 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 ⦠in RF applications.
ȧȱ ȳȧ NF + 10log eni 2
Ȳ È´ ÇeRsÇ2
Because the dominant noise components are generally the source resistance and the internal amplifier noise
voltage, we can approximate noise figure as:
Ç Ç NF
+
ȱ
10logȧȧȧȧ1
ȧȡȢ
)
en
2 ) ÇIN )
4 kTRS
Ȳ
RSÇ2ȧȣȳȧȧȧȧ
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 â Source Resistance â â¦
Figure 39. Noise Figure vs Source Resistance
20
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