THS6072

LOW-POWER ADSL DIFFERENTIAL RECEIVER

SLOS290B – FEBRUARY 2000 – REVISED JUNE 2001

14

POST OFFICE BOX 655303

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.

NF

+ 10log

e

2

ni

e

Rs

2

Because the dominant noise components are generally the source resistance and the internal amplifier noise

voltage, we can approximate the noise figure as:

NF

+ 10log 1 )

e

n

2

) IN )

R

S

2

4kTR

S

Figure 41 shows the noise figure graph for the THS6072.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

Source Resistance – RS (Ω)

f = 10 kHz

TA = 25°C

NOISE FIGURE

vs

SOURCE RESISTANCE

10

100

1k

10k

100k

Figure 41. Noise Figure vs Source Resistance