I don't think that terminology is the issue here. I may be confused as all get-out, but I understand what impedance is.[email protected] wrote:I think we're running into some confusion about the term 'impedance'.
Just to benchmark that, impedance is the generalized form of resistance. It includes resistance per se (converting electrical energy to heat) and reactance (temporarily storing electrical energy in an electrical or magnetic field). All forms of impedance give voltage something to push against as it tries to make charge carriers move.
A resistor has no reactive properties, so its impedance is the same as its ordinary resistance.
The sketch above says any current that reaches the output has to travel through Rc, so the impedance looking back into the amplifier will be Rc.
Based on your diagram alone, yes... I agree that the impedance is Rc.
Let me try asking my question in a different manner....
The formula for gain for my transistor-based amplifier is approximately G = - Rc / Re. Re in my test circuit is a fixed 100 ohms. The operating frequency of my test circuit is "fixed" at about 1MHz.
If I increase the value of Rc, my gain should increase until I hit rail voltage. I would therefore expect see something very close to a square wave -- but as you reminded me a few posts ago, the RLC portion of my test circuit filters out the harmonics, so I get a sine wave.
Question: The "sweet spot" in my circuit occurs at about Rc=3k. If I continue to increase the value of Rc, I observe that the amplitude of this sine wave starts to decrease. Why doesn't the amplitude of the sine wave max out and just stay there? It is not something that I would have predicted given the formula for gain.