I want to design an Op-Amp using CMOS technology. For that I have been designing a differential amplifier as an input stage. I am stuck at transistor sizing. Recently I came across gm/id methodology for transistor sizing. I would like to know how this method can be used to decide the aspect ratio of transistor. Please share some material, if possible.
Dear Mr. Saumil Vora,
first take a reference that describe gm/IDS as a function of IDS/(W/L) of the Silveira and Prof. Denis Flandre and try to design an amplifier.
Besides, MunEDA is a software that is capable to help you to design analog ICs.
If you need some more, let me know.
Prof. Salvador Pinillos Gimenez.
For example, once you have the relationship between gm/IDS and IDS/(W/L) (extracted from simulations or using a transistor model valid in all inversion regions, for example ACM), you can select the desire inversion level of your transistor (gm/IDS) and the desire transconductance which defines your necessary current. Then using the above mention relationship you can obtain the aspect ratio of your transistor. You can see, from that relationship, that a high gm/ID implies a better efficiency in the generation of gm at expenses of bigger transistors. Here is an example of the design of an ultra low power low offset symmetric OTA using the gm/ID methodology.
Francisco Veirano
Conference Paper Design method for an ultra low power, low offset, symmetric OTA
It depends, if you high frequency response (some transistors have to operate in strong inversion regime, that depends on of the circuit architecture ) you are right, but if you need more voltage gain (some transistors have to operate in weak inversion regime), and besides, if you have a good compromise between voltage gain and high unit voltage gain frequency, some transistors have to operate in moderate inversion regime).
I hope that I could help you.
Thank you.
Prof. Salvador Pinillos Gimenez.
id= un cox w/l (vgs-vt)^2
gm =2id/(vgs-vt) (0r) gm =root(2id un cox w/l)
gain=gm*rd
rd=ve L\id
0r=rd=1/lmbda *id
these enough use technology parametre fix the gain what you want ?
these may help you
Try this one; http://www.designers-guide.org/Forum/Attachments/Gm_BY_ID_Methodology.pdf
Check this paper for step-by-step procedure
https://www.sciencedirect.com/science/article/pii/S0026269217307905
Hesham Omran How to get "gm" expression in ADS ?
Or in better words how to plot gm/Id vs Vgs in ADS ?
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