TI interview question..

[ramraj_gp]

Design an opamp with 0.1-3v common mode input voltage and 0.3-4.5 v output voltage and 5v supply voltage.
Explain what type of active and load transistors(nmos,pmos,bjt or bicmos with reasoning) do u use?

 

[currentmirror2000]

pmos input to achieve 0.1V and push-pull output (nmos+pmos) to achieve 0.3V to 4.5V, is this ok?

 

[ccw27]

Definetely need a pmos input and probably a class AB output

 

[edajason]

N pair + P pair input; output should use Class AB.

 

[electronrancher]

the requirements would be satisfied by a simple miller op amp, no class-ab needed. input pair can't be a single pmos, you'd need cascaded pmos or darlington pnp so you don't crush your differential to single-ended conversion, else use folded and you won't need cascaded pmos.

 

[fantaci]

Why class AB could meet the output common voltage requirement? by using Class AB, I think the input of class AB driver also need 0.3-4.5 v swing. if we could make Class AB driver`s output meet output common voltage requirement, why still need a class AB driver? Class AB is used just for low output impedance and small power consuming?

 

[simov]

Can you provide more questions?

 

[dog1357]

input stage should use PMOS pair, for output,class AB is common

 

[FLEXcertifydll]

Which dept. do you apply? And other more question?

 

[ramraj_gp]

Other questions were easy ..like finding gain of single stage operational amplifier.. what are two capacitances present in a diode and give an example of current mirror and explain its operation with respect to current mirroring..

 

[surianova]

For this kind common mode input requirement, better use rail to rail opmap.


Surianova

 

[avinash]

dear ramraj_gp

what is your exp in ic design.and for what position have you applied at TI.