2 stage OP AMP Flashcards
Draw a simple 2 stage op amp and show were the 2 points of high impedance are and why they are a problem
The points are at the output of the longtail and and the output of the 2 stage. The reason high impendence is a problem is due to the parasitic capasitor causing phase change that causes postive feedback
where would you add the capacitor to fix the pole problem , why does this reduce bandwidth?
Across the second gain stage OP AMP, at high frequencies the capacitor becomes shorted
what is miller’s problem? draw the Opamp and derive the the problem
Large Capacitance due to feed back gain `
what is the problem of gm6 being gm2?
Noise within the circuit will be amplified
What the best way removing the zero caused by the capacitor shorting , what the value needed ?
Use a resistor to bootstrap the capacitor, 1/gm6 or to remove a pole by making it = to the zero
Where can cascode the in the 2 stage op amp , what does it do and why is it a problem ?
in-between the current mirror , increasing input resistance gain goes up but however moves the pole value down reducing frequency and stability.
Draw and explain the level shifter ?
reduces the vbe of the last transistor
why is a single-stage Cascode op-amp Useful and draw it
Only one high impedance point
what is folded cascode and draw it
has low impedances due to linking npn and pnp types back to back
