In a three-stage amplifier.
A) the noise ratio of the last stage is usually insignificant.
B) Friss's formula can be used to determine the overall noise effect of all three stages.
C) the noise ratio of all three stages is mainly due to the noise figure of the first stage.
D) all of the above

Question

Quizplus · Accepted Answer

In a multi-stage amplifier, the noise figure of the first stage is the most critical because it sets the noise floor for the entire system. Friss's formula can indeed be used to calculate the overall noise figure of a series of stages, taking into account the noise figure and gain of each stage. The noise contribution of the last stage is usually less significant because the signal has been amplified by the preceding stages, making the signal-to-noise ratio higher at the input of the last stage.

In a Three-Stage Amplifier