Question { 3581 }

If the substrate doping concentration increase, or
temperature increases, how will Vt change? it increase or
decrease?

Answer

If the Substrate doping concentration is increased, the number of randomly moving electrons that need to be aligned are increased which means threshold voltage is increased.
And the threshold voltage decreases with increase in temperature.

Question { Wipro, 6342 }

How does a pn junction works?

Answer

When a P-type material and an N-type material are put together, The electrons from N side go to P side and holes from P side go to N side forming a depletion region at the junction. This junction develops a voltage which is dependent on the doping concentration. Now, the free electrons on N-Side require more energy to cross the depletion region. A +Ve voltage applied across the diode(Also called forward bias) can supply this energy.
When a -Ve voltage is applied, it will result in free carriers being pulled away from the depletion region thereby increasing its width. Hence, it will allow the current to pass only in one direction(i.e. when a +ve voltage is applied).

Question { 2626 }

Tell me the parameters as many as possible you know that
used to character an amplifier?

Answer

Input resistance - Must be very high(ideally infinite)
Output resistance - Must be very low(ideally zero)
Open Loop gain - Ideally Infinite
Input offset voltage - Ideally Zero
Output voltage range - Ideally Infinite
Slew Rate - desired to be high - High SR means the output is more sensitive to input
CMRR - Preferred High (Common mode gain should be low)