Topic: Communications
In a three stage cascade amplifier, each stage has a gain of 10 dB and noise figure of 10 dB. The overall noise figure is
- A. 10.99
- B. 10
- C. 1.09
- D. 10.9
Answer: A. 10.99
Explanation: Using Friis formula for noise figure in linear scale: $F_{total} = F_1 + \frac{F_2 - 1}{G_1} + \frac{F_3 - 1}{G_1 G_2}$.
Given Gain $G = 10$ dB, which is $10$ in linear scale. Noise Figure $F = 10$ dB, which is $10$ in linear scale.
$F_{total} = 10 + \frac{10 - 1}{10} + \frac{10 - 1}{10 \times 10} = 10 + \frac{9}{10} + \frac{9}{100} = 10 + 0.9 + 0.09 = 10.99$.