early voltage of mosfet

[vijith133]

could any tell me how to find the early voltage of a mosfet using spctre simulation tool, It would be really grt if you could suggest the steps rather than telling me the equations (plenty of suggestions are there just giving the equations, already posted )

thanks in advance

 

[helpmejerry]

One way would be to use a current mirror see attachment for reference. You do a DC sweep for param vd. To get the Early voltage you will also need to interpolate the line which corresponds to the slope of the channel length modulation in saturation of the transistor and find the crossing with x axis. The crossing with x-axis will be more ore less your Early voltage. I hope this will help you and that it is not to confusing .

BR Jerry

 

[vijith133]

thanks for the reply, i did it in the same way as you have directed. But i did find the slope at saturation and extended the line to meet the x-axis by hand calculations, to get a value of 4.52 V/um as early voltage for the mosfet technology used by me. could you please verify this method is correct, i enclose the graph dat i plotted along with this post.

 

[helpmejerry]

I am guessing that you used minimal length transistors. I would also suggest you play with different widths and lengths of the transistor and find an average value for your Ua.

BR Jerry

 

[vijith133]

thanks for the post. i tried with different length and widths of the transistors but the values varied and i fixed on to the average value.

 

[vijith133]

thanks for the post. i tried with different length and widths of the transistors but the values varied and i fixed on to the average value.

i am sorry.. am mistaken for the above post because i tried its only width i varied and the answer is result of that, but when i was varying the length of the transistor the early voltage changed considerably and am not sure that if i can take the average of those values to use in the final design of the circuit.

I hope it is better to use the individual values for each fixed length during the circuit design or else it would result in the wrong circuit