THS6062 Datasheet, PDF (21/31 Pages) Texas Instruments – LOW-NOISE ADSL DUAL DIFFERENTIAL RECEIVER

THS6062
LOW-NOISE ADSL DUAL DIFFERENTIAL RECEIVER
SLOS228B – JANUARY 1999 – REVISED JUNE 1999
APPLICATION INFORMATION
noise calculations and noise figure (continued)
For more information on noise analysis, please refer to the Noise Analysis section in Operational Amplifier
Circuits Applications Report (literature number SLVA043).
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 _{e 2}
+ _{ȧ ȧ} NF 10log ⁿⁱ
2
Ȳ^{ǒ Ǔ} ȴ ^eRs
Because the dominant noise components are generally the source resistance and the internal amplifier noise
voltage, we can approximate the noise figure as:
ȧȧȧȧȱȲ ^{ȧȡȢǒ Ǔ ǒ Ǔ ȧȣȤȳȴȧȧȧȧ} _{+ ) NF 10log 1}
) ) ²
en
IN
4 kTRS
2
RS
Figure 40 shows the noise figure graph for the THS6062.
NOISE FIGURE
vs
SOURCE RESISTANCE
16
f = 10 kHz
14 ^{TA = 25°C}
12
10
8
6
4
2
0
10
100
1k
10 k
Source Resistance – Ω
Figure 41. Noise Figure vs Source Resistance
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