electronics and innovation rf amplifiers
Navigation
 

This page discusses what is meant by a "good match" and provides some helpful advice.

A good match means that the output of one element is matched to the input of another to achieve maximum Power Transfer.

One has to be very careful with analogies in engineering.

However, this is one place that one might help.

Consider the flow of water through a pipe...

  • Water pressure is analogous to voltage
  • Water volume is analogous to current
  • Pipe diameter is analogous to resistance
  • If you take the output of one pipe and put it against the input of one with a smaller diameter you will maintain your pressure but lose volume. If you put it against a pipe with a larger diameter you will not lose volume but you will lose pressure

For maximum power transfer the input and output impedances must be matched.

Now for some Maths (urrrgh)...

Consider the circuit below:


Now Current into the load is IL


Current Power in to load is PL


For maximum power

RL=RS

You don’t believe us?

You are going to have to look at some calculus!

So if PL =  IL2 RL  

And for maximum power


And  PL =  IL2 RL = Vs2 RL (Rs+ RL)-2

Then


So:  (Rs+ RL)-2  = 2RL(Rs+ RL)-3

                       1 = 2RL(Rs+ RL)-1

                   2RL = Rs+ RL

                       Rs= RL