Here are three gain circuits. To put aside any references to different historic periods and schools of design they are implemented using abstract transconductance devices. I have cheated here: you can't put ideal current sources in series so keep in mind that they are real world devices like transistors or tubes.
A
B
C
They all are actively loaded gain cells. Their active loads works on the same principle: by maintaining constant voltage drop across sense (feedback) resistor(s). Circuit A is a classic CSS loaded gain cell. It works by maintaining the sum of the gain device G2 current and the load current constant. Circuit B is also a CSS loaded cell but in a more pure (?) form where the gain device G2 current is kept constant and G1 accomodates all the the load current swing. This is what is known as SRPP in the tube world. Circuit C shares the load current between G1 and G2 in a push-pull manner depending on the resistors ratio.
The question is how would you call this generalisation and those three special cases?
A
B
C
They all are actively loaded gain cells. Their active loads works on the same principle: by maintaining constant voltage drop across sense (feedback) resistor(s). Circuit A is a classic CSS loaded gain cell. It works by maintaining the sum of the gain device G2 current and the load current constant. Circuit B is also a CSS loaded cell but in a more pure (?) form where the gain device G2 current is kept constant and G1 accomodates all the the load current swing. This is what is known as SRPP in the tube world. Circuit C shares the load current between G1 and G2 in a push-pull manner depending on the resistors ratio.
The question is how would you call this generalisation and those three special cases?
Third circuit has no advantages over the other two and has higher output resistance. Unless you wan to match to a transmision line impedace, is a nonsense.
When using pentodes as lower device and as they have very high ra, #1 & #2 has the same behavior and the output impedande equals upper triode ra.
When using pentodes as lower device and as they have very high ra, #1 & #2 has the same behavior and the output impedande equals upper triode ra.
Yes but those are detail specific to the active device class. Also some may say that they all give different distortion spectral profiles. And there may be many other reasons to prefer one to another. I don't make any statements here.
