Hi I am designing a two stage MOSFET amplifier.
The first stage is a Common-Source, the second is a Common-Drain (Source follower): https://www.circuitlab.com/editor/#xb82e5
The circuit has to be output and input independent as much as possible. So as low magnitude error as possible at a source with non-trivial output R and for small loads.
I would like ideas on additional stages or changing something on the design to reach the most load independent result!
I'm running a simulation of your schematic. Things are going well, it appears.
My observations:
1.
Your incoming signal has a certain amount of impedance. It would be appropriate to include an inline resistor as a way of indicating this impedance. Its value can be the maximum you expect under normal circumstances.
2.
If you attach a low resistance load, it will draw greater current at the output. In that case you will need to increase the capacitor value at the output, or else you will get reduced low frequency response.
You might want to bias M3's source output to be in the middle of the supply voltage. Thus the voltage divider output of R11 and R13 should be adjusted to a higher voltage, to include the Vgs threshold voltage of M3.
You might want to bias M3's source output to be in the middle of the supply voltage. Thus the voltage divider output of R11 and R13 should be adjusted to a higher voltage, to include the Vgs threshold voltage of M3.