weak or strong inversion??

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

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..

Actually I am working with Mentorgraphic using Eldo simulator

learning_curve said:

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..

Click to expand...

senan said:

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

Click to expand...

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

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

erikl said:

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

Click to expand...

senan said:

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??

Click to expand...

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

senan said:

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??

Click to expand...

Depends on your power consumption vs. bandwidth requirement.