Cascade
Understanding Cascade
Cascade analysis uses Friis' formula to calculate the overall noise figure of a chain of amplifiers and lossy elements. The first stage dominates the system noise figure, which is why low-noise amplifiers are placed at the front end of receiver chains.
For gain, cascade gain is the product of individual stage gains (sum in dB). For linearity, the cascade IP3 is dominated by the stage with the lowest referred input IP3, typically the last high-gain stage.
Frequently Asked Questions
Why is the first stage so important in a cascade?
Per Friis' formula, the noise contribution of subsequent stages is divided by the gain of preceding stages, so a high-gain, low-noise first stage minimizes overall system noise figure.
How is cascade IP3 calculated?
The cascade IP3 is calculated by referring each stage's IP3 to the input and combining them reciprocally, with the weakest stage dominating.