Help me clarify questions about MOS circuit

[srikanth1986]

Hi,

Please clarify the following questions for the circuit given. I had simulated the circuit in spice and got the confirmed results. (voltage source connected between Y and ground)

1. Why is the V/I across the resistance not equal to the R of the resistor?
2. What determines the resistance of the MOS pair?
3. What determines the current through the MOS pair
4. Please explain why the node voltages are like this?

 

[subharpe]

Re: Mos circuit problem

Are you sure there is nothing connected at P or Q other than what you have depicted?

It should not happen that the V/I across the resistor R is not equal to R........

 

[srikanth1986]

Re: Mos circuit problem

No, nothing is connected... I have verified the operation once again... Same results...

 

[lsimeon]

Mos circuit problem

the R looking thru Y which is equal to 37.5 is actually the total resistance between Y and ground, that's why it is not equal to 20 ohms which is obviously smaller than the total because it is just a part of the summation of the total resistance which is (from Y) 20ohms + Res of the channel of transistor 1 + Resistance of the channel of the transistor 2

Added after 2 minutes:

for number 2:

the resistance of the MOS pair is determined by the length of the channel, width, UxCox, etc..

 

[subharpe]

Re: Mos circuit problem

The problem with the firest part of the problemm is:

If you look at Vy, Vq, and I the relation [Vy-Vq]/I = R is not being valid. This is what, to my understanding, is being asken in the first part of the problem.

 

[srikanth1986]

Re: Mos circuit problem

@subharpe: Precisely... I don't understand why the difference in vg would cause a "violation" in ohms law...

 

[lsimeon]

Mos circuit problem

ok gotcha...
can you give the source code that you used in the simulation in Spice?

 

[srikanth1986]

Re: Mos circuit problem

hmm... Can't give that out.. Company proprietary you see... I, will, however tell you the statement that you require...

 

[lsimeon]

Mos circuit problem

i need to know the parameters that you used in your NMOS, the exact node locations, if you used LASI as your schematic editor and Spice as your output generator, maybe you have an error on the NTXT or PTXT that you entered or maybe the header code that you used is incorrect...

 

[srikanth1986]

Mos circuit problem

Virtuoso by Cadence is the editor used and HSPICE as the simulator... Used standard decks for options and includes...

 

[strabush]

Re: Mos circuit problem

You certainly and without doubt have an error somewhere.
It can be in reading the voltages, current or the operating point simulation didn't converged.
Ohm law should be OK on the resistor without any doubt!!!