rkrishnan wrote:

I am reading through the excellent book "Solid State Design" by Wes
Hayward et al. I have a specific question on Class C amplifier. On
chapter 2 Fig 15, a Clas C amplifier is shown with a buffer amplifier
link coupled in front.

Why is link coupling needed here, can't the collector be directly
connected to the base? It is for impedance matching or is there any
other motives behind this structure?

73
Ramakrishnan, vu3rdd

Any coupling circuit to a class C bipolar transistor amplifier not only
needs to match impedance, it also needs to supply DC current to the base
of the class C stage. Inductive coupling is nice because the average
voltage at the base is nailed at zero and the inductor will guarantee
that enough DC current flows. If you should capacitively couple then
you need to load the base of the final stage with a back-biased diode or
a resistor to provide the current -- otherwise your coupling capacitor
will just charge up until no current flows into your final's base and
you no longer get amplification.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com