Calculation of noise figure for cascaded amplifier

Q.  For a three stage cascade amplifier, calculate the overall noise figure when each stage has a gain of 12 DB and noise figure of 8dB.
- Published on 15 Oct 15

a. 12
b. 24
c. 13.55
d. 8

ANSWER: 13.55
 
As the signal passes through various stages of an amplifier, the output has the original signal and some noise that gets amplified at different stages of amplifiers. So the final noise figure of the cascaded amplifier is obtained by

FN = F1 + (F2 - 1)/ G1 + (F3 - 1)/ G1G2+......+(FN- 1)/ G1G2G3 GN
F1, F2, F3 .. FN, G1,G2, G3.... GN are the noise figures and the gains respectively of the amplifiers at different stages.
F1 = 12, F2 = 12, F3 = 12
G1 = 8, G2 = 8, G3 = 8
FN = 12 + (12- 1)/ 8+ (12- 1)/ 8 * 8
= 12 + 11/8 + 11/64
= 13.55

Related Content

➨ Post your comment / Share knowledge


Enter the code shown above:

(Note: If you cannot read the numbers in the above image, reload the page to generate a new one.)
▲