subthreshold op amp design?

[branred]

Dear all,

i am trying to design an op amp with subthreshold operation. May i know which MOS are allowed operates in subthreshold region? the input pair? the active load? what about folded cascode configuration? As far as i know, the current mirror must be in saturation to ensure accurate copying.

is there any good books or paper regarding how to design a subthreshold op amp?

thank you so much

regards,
branred

 

[saiaditya]

You can bias the input pair in subthreshold, active load in saturation, that way it would be more beneficial

 

[leo_o2]

Input pair working in sub-threshold region is genrenal case.

 

[erikl]

i am trying to design an op amp with subthreshold operation. May i know which MOS are allowed operates in subthreshold region? the input pair? the active load? what about folded cascode configuration? As far as i know, the current mirror must be in saturation to ensure accurate copying.

MOS operation in subthreshold has nothing to do with operation in the saturation region!

See e.g.
Allen/Holberg "CMOS Analog Circuit Design"
David M. Binkley "Tradeoffs and Optimization in Analog CMOS Design"
Behzad Razavi "Design of Analog CMOS Integrated Circuits"

 

[threekingtiger]

Pay attention to the two concepts. For stong inversion, you have tri. and sat. regions. For weak inversion(subthreshold), you also have tri. and sat. regions.

 

[dgnani]

Pay attention to the two concepts. For stong inversion, you have tri. and sat. regions. For weak inversion(subthreshold), you also have tri. and sat. regions.

Very good point! EKV model makes this somewhat simpler to picture (e.g. see Jesper's book on gm/Id method)