CHAPTER 5 - Amplifier Design
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5.3.3.2 Simultaneous Conjugate Match
Our unilateral matching video tutorial (video 5.5), shows the limitations of the
unilateral matching technique and highlights the fact that, due to the inaccuracies introduced
by an S12 parameter which is not negligible, we may end up having to go through several
iterations before we can achieve the desired specifications.
If our aim is to extract the maximum small signal gain from out transistor however, there is
an exact technique which we may use, which takes into account S12 and the connection between
input and output, called simultaneous conjugate match.
This technique is pretty simple. One simply employs analytical expressions to work out what
impedances should be presented both at the input (GM1) and output (GM2) of the transistor in
order to achieve maximum small-signal gain. Then two matching networks are employed to
transform the source impedance into GM1 and the load impedance into GM2. Unlike the case of
unilateral matching, in this case you cannot chose to just have one matching network at either input
or output ports, you must have both ports matched in such as way as to make the transistor see
GM1 across its input terminals and GM2 across its output terminals. Also, no selective mismatch
may be applied to "tune" the gain to specific values.
I find the formulae for the input and output terminations not at all intuitive or informative in
the way they are formulated and hence they will not be repeated here.
However Microwave Office allows you to calculate GM1 and GM2 very easily through two dedicated
measurements, called GM1 and GM2.
Video tutorials 5.6 and 5.7 give us a much greater insight into this technique.
Conquer Radio Frequency
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