Greetings!
I've been working on building a discrete voltage regulator centered on a differential amplifier/differential pair. I am however stuck on some theoretical aspects.
Having asked around and researched it a bit, it seems that the differential amplifier can be thought of as a single stage transconductance amplifier, having a large input resistance, as well as a big output resistance. Comparing the bare long tail pair with a simplified version of an op amp I notice that there are several stages missing, lack of a miller integrator etc.
The basic design of a series pass voltage regulator includes a voltage reference, an error amplifier, the feedback network and a pass transistor. The pass transistor together with the feedback resistors form a buffer with low output resistance.
The error amplifier can be either a transconductance amplifier, or an op amp. Both will be buffered by the pass transistor.
I select the transconductance amplifier and an NPN as pass transistor, like shown below.
When asked what the open loop amplification of the error amplifier is, what will I answer?
a) the voltage gain of the differential amplifier i.e. gm * Rout
b) something else (perhaps taking the pass transistor to be part of the error amplifier??)
My main sources of information are:
Circuit analysis:
https://ee.kpi.ua/~yv/edu/ep/book/Gray_Forth_Edition.pdf (pages 288 - 293)
Simple op amp circuit:
https://slideplayer.com/slide/17577620/Simple OTA:
https://people.engr.tamu.edu/spalermo/ecen474/lecture10_ee474_simple_ota.pdfThanks!