Impedance relation between 2 Bjts

[samy555]

If there are two BJT small signal amplifiers (common Emitter) cascade connected using a suitable decoupling cap
The first preamp has an o/p imeadance Zo, and the second has an i/p impedance Zin
Now we have Zo and Zin and a cap betwwen them
My question is: Is the connection series or parallel? That, is the o/p voltage divided or the o/p current?

 

[BobK]

Zout and Zin form a voltage divider. The actual input voltage seen by the second amplifer is is calcluated from that, i.e. V = Vin * Zin / (Zin + Zout)

Bob

 

[samy555]

Yes, thats a good answer
but, why in many electronic books, when there is a load resistance RL connected to the collector of a transistor has a collector resistance RC,,, why take RL and RC in parallel?
note: there is a coupling cap between RC & RL.
thanks alot

 

[BobK]

The coupling capacitor is chosen to pass the AC signal of interest, so effectively it has no resistance for the signal.

Bob