weak or strong inversion??

[Junus2012]

Dear all

after long time of dealing with op-amp design still I am stuck with many basic things, I found my chance in this forum to ask you about it...

how could i know if my op-amp is working in the strong inversion or in the weak inversion??, i read from many resources that i have to check the overdrive voltage if it is below 50 mV then it is working in the weak inversion. is it right?? or if you have any suggestions then i am looking forward for it

Thank you

 

[learning_curve]

If you are working in cadence...you can check the region of operation of the devices...
its coded as follows
region 2 means saturation(strong inversion), Vgs > Vth and Vds > Vgs-Vth
region 3 means subthreshold(weak inversion), Vgs < Vth but Vds > Vdsat

hope somebody else can clarify too about the weak inversion condition..

 

[Junus2012]

Actually I am working with Mentorgraphic using Eldo simulator

If you are working in cadence...you can check the region of operation of the devices...
its coded as follows
region 2 means saturation(strong inversion), Vgs > Vth and Vds > Vgs-Vth
region 3 means subthreshold(weak inversion), Vgs < Vth but Vds > Vdsat

hope somebody else can clarify too about the weak inversion condition..

 

[erikl]

how could i know if my op-amp is working in the strong inversion or in the weak inversion??, i read from many resources that i have to check the overdrive voltage if it is below 50 mV then it is working in the weak inversion. is it right?? or if you have any suggestions then i am looking forward for it

See this image from D. Binkley's book: IMHO the best book on this theme.

 

[Junus2012]

it mean that if Veff is less than 225mV the transistor will work in the moderate inversion, this will be problem in my design because the transistor model I am using is BISM3v3 where there is no accurate representation for this region so all the results i am getting are not accurate, isnt it??

Also i would ask you, do we apply the concept of weak and strong inversion to all the op-amp transistors or just for the input differential transistors??

Thank you very

See this image from D. Binkley's book: IMHO the best book on this theme.

 

[erikl]

it mean that if Veff is less than 225mV the transistor will work in the moderate inversion, this will be problem in my design because the transistor model I am using is BISM3v3 where there is no accurate representation for this region so all the results i am getting are not accurate, isnt it??

No. BISM3v3 models should reproduce operating in moderate and weak inversion quite well.

Also i would ask you, do we apply the concept of weak and strong inversion to all the op-amp transistors or just for the input differential transistors??

Depends on your power consumption vs. bandwidth requirement.