Electronics > Beginners

opamp simulation

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Wimberleytech:
L and C in that schematic have no impact during transient...they are there for the ac simulation, but for transient unity gain, I kinda make them invisible.  Easier than deleting components and then adding them in later.

I did not investigate phase margin.

What phase margin are you wanting to achieve?

promach:
Is it possible to achieve phase margin of 70 degrees with opamp3.asc ?

Could you also explain analytically on cascn, cascp and biascn ?

Wimberleytech:

--- Quote from: promach on April 15, 2019, 01:32:41 pm ---Is it possible to achieve phase margin of 70 degrees with opamp3.asc ?

Could you also explain analytically on cascn, cascp and biascn ?

--- End quote ---

You can increase the two compensation capacitors, or you can reduce the gain (load it with a 10k resistor).

I created the bias string before making any other tweaks...thinking I might need several bias references.  In the end I only needed but two of them (the two cascodes) but left the string intact.

promach:
For improving phase margin of opamp3.asc , I use an extra series resistor to put a zero near the unity gain frequency.
but then, good accurate resistor is hard to fabricate.

So, let me ask: anyone have any idea on how to replace both the ideal current source and the extra resistor with a mosfet in ohmic region without using any extra bias voltage source ?

In other words, is it possible to use constant gm bias circuit in your opamp3.asc or my opamp.asc circuit ?

Wimberleytech:

--- Quote from: promach on April 15, 2019, 02:26:57 pm ---
In other words, is it possible to use constant gm bias circuit in your opamp3.asc or my opamp.asc circuit ?



--- End quote ---

Yes.  Both of your references are sound.

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