+ Post New Thread
Results 1 to 4 of 4

16th January 2020, 16:28 #1
 Join Date
 Oct 2019
 Posts
 15
 Helped
 0 / 0
 Points
 154
 Level
 2
Finding W and L of transistors from DC operating point.
Hi guys,
I have a schematic of OTA amplifier:
I want to know the W and L that were used to design this OTA. I don't have more information other than the ones provided in this picture.
since all transistors are in saturation, I thought about using the saturation current equation to find (W/L) ratio.
by assuming that I know un*Cox and up*Cox. but the problem that I don't know them. but I have the same technology and same cadence version on which this OTA was designed. which means by running an extra circuit, I can deduce what un*Cox and up*Cox are since I know all the parameters for the other circuit.(also by using saturation current equation because I don't known how to find un*Cox and up*Cox from the cadence tool ) and by substituting them in saturation current equation for the first circuit, I can find W/L ratio.
the question is if un*Cox and up*Cox are the same for all simulations used in the same technology?
or there is some other way to find W and L or the ration between them depending on the information in the picture only?
Note: I'm using 28n technology.
thanks
Firas

Advertisement

17th January 2020, 09:32 #2
 Join Date
 Nov 2001
 Location
 US
 Posts
 892
 Helped
 308 / 308
 Points
 10,272
 Level
 24
Re: Finding W and L of transistors from DC operating point.
Wouldn't it be easier to just design the circuit yourself such that at least it produces the same gm and Vdssat, gain for the bias currents that you see on the picture?

Advertisement

18th January 2020, 03:02 #3
 Join Date
 Jan 2008
 Location
 Toronto area of Canada
 Posts
 8,813
 Helped
 2068 / 2068
 Points
 54,087
 Level
 56
Re: Finding W and L of transistors from DC operating point.
The negative image could not be seen with daylight so I changed it to be a positive image:

Advertisement

24th January 2020, 02:23 #4
 Join Date
 Dec 2019
 Posts
 31
 Helped
 0 / 0
 Points
 174
 Level
 2
Re: Finding W and L of transistors from DC operating point.
the question is if un*Cox and up*Cox are the same for all simulations used in the same technology?
As suggested above, you might be better to start off from scratch to match the same performance. That being said, if you insist on reverse engineering the circuit, you basically have 2 unknowns, the u*Cox (let's call it K) and W/L, you also have 2 equations you can form based on the fact that Ids (sat) and gm is known, you can form these 2 equations and solve for the 2 variables. And then you can try them on different transistors of the same type (NMOS to NMOS) and check if you can get the right Ids & gm.
Note that you technically have also the channel length modulation effect which introduce another variable (lambdha) into the equations if you want to include them.
+ Post New Thread
Please login