A TRANSFORMER TUTORIAL

http://www.nutsvolts.com/magazine/article/a-transformer-tutorial

https://www.google.co.kr/search?q=Transistor+class+a+output+impedance+matching&tbm=isch&tbs=rimg:CUJN-mjBduawIjgSEkJUyiDFqgGitAm_1LYzVjF1FETZnIuQW8v-zLRjDs3VjAOTlE2a2zzMEMVGLEQtAz4tHruODOSoSCRISQlTKIMWqEaBF2sO59OJGKhIJAaK0Cb8tjNUREBpKMwYOxSkqEgmMXUURNmci5BHF2RmSEMdFwSoSCRby_17MtGMOzETW3eIjnUe7ZKhIJdWMA5OUTZrYRts7Q1maE9VoqEgnPMwQxUYsRCxFR2snQeQq4vCoSCUDPi0eu44M5ESDTv8_1wWBjO&tbo=u&sa=X&ved=2ahUKEwjt3vucjeLeAhWLzbwKHWxWAkYQ9C96BAgBEBs&biw=1264&bih=899&dpr=1#imgrc=4CXdvqEUktgPVM:&spf=1542687085443

ZL = Rcoil

ZL = Rcoil + jωL = Rcoil + j2πfL

Section F3: Power Amplifier Circuits - Class A Operation
As mentioned in the previous section, our studies of BJT and FET amplifiers
to date have been of the Class A designation since the output signal is an
amplified version of the entire input. What we’re going to look at now are
some of the useful circuit configurations for Class A power amplifiers, where
the category is determined by the coupling mechanism. Please note that the
configurations we will be discussing are by no means the only configurations
available. Whatever strategy we take; remember that we want to maximize
power delivered to the output. This involves a large current gain and
impedance matching to the load at the output stage.
There is some difficulty in this chapter with the orientation of the
polarized capacitors. I have attempted to make appropriate changes,
both in the notes and the assigned homework, but please be aware
of this problem in case I miss something (but let me know if I do,
ok?)
Inductively Coupled Amplifier

An example of an inductively coupled
amplifier is presented to the right and
is based on Figure 8.6a of your text.
This schematic is our old friend the
common emitter BJT amplifier with an
inductor replacing the collector resistor
RC. Recall that the effective load for a
CE amplifier was RC||RL, and that the
effective load was less than either RC or
RL. Using a properly sized inductor
instead of a resistor in the collector leg
will allow us to increase the output
voltage and, as we’ll see a little later,
increase the efficiency of the amplifier
circuit.
By analyzing the ｅxpression for the impedance of an inductor
ZL = Rcoil + jωL = Rcoil + j2πfL ,
we can see that the impedance consists of the internal resistance of the coil,
Rcoil, and an inductive reactance term that is dependent upon the frequency
of operation, ωL. At dc (ω=0), ZL=Rcoil, while at high frequencies the ωL term
dominates and becomes very large. Harking back to circuit days, remember