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Help in deriving Zin small-signal expression

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Wimberleytech:

--- Quote from: The Electrician on May 25, 2018, 01:44:33 am ---

I can't help you here.  Perhaps danmc can help.

--- End quote ---

I am jumping in on page 2 of this thread...have already done a promach torture test.

Take a look at CMOS Analog Circuit Design by Allen/Holberg  first edition, chapter 4, second edition Appendix B, third edition Appendix C.
Zero-field mobility is the same for all models...as is Cox.

You can download it here: https://archive.org/details/Allen2011CmosAnalogCircuitDesign3e

promach:
I am now reading https://archive.org/stream/Allen2011CmosAnalogCircuitDesign3e/allen%202011%20-%20cmos%20analog%20circuit%20design%203e#page/n673/mode/2up/search/appendix

Could you elaborate on "Zero-field mobility is the same for all models...as is Cox." ?  I am not very familiar with CMOS device details and I am bit confused with your sentence.

Wimberleytech:

--- Quote from: promach on May 26, 2018, 04:40:36 pm ---I am now reading https://archive.org/stream/Allen2011CmosAnalogCircuitDesign3e/allen%202011%20-%20cmos%20analog%20circuit%20design%203e#page/n673/mode/2up/search/appendix

Could you elaborate on "Zero-field mobility is the same for all models...as is Cox." ?  I am not very familiar with CMOS device details and I am bit confused with your sentence.

--- End quote ---

There are many models that have been developed for MOS transistors over the years.  Some parameters used in models have significance or meaning only within that model.  U0 and Cox are physical parameters that do not depend on the model.  So, any model that needs a value for U0 and/or Cox will use the same values as any other model.

promach:

--- Quote ---U0 and Cox are physical parameters that do not depend on the model.
--- End quote ---

Why would this be the case ?

Besides, in this case, how do I obtain the value of U0 and Cox ?

Wimberleytech:

--- Quote from: promach on May 28, 2018, 03:09:34 am ---
--- Quote ---U0 and Cox are physical parameters that do not depend on the model.
--- End quote ---

Why would this be the case ?

--- End quote ---
U0 is carrier mobility.  Yes, it depends on crystal orientation and perhaps other things, but most circuit-simulation models start with a value for mobility at zero field and adjust that value as a function of temperature, electric field, and other stuff. 

Same for Cox.  It is essentially e/tox where e is permitivity.  So e, is e, tox is the oxide thickness grown over the gate channel.


--- Quote ---Besides, in this case, how do I obtain the value of U0 and Cox ?

--- End quote ---
Cox can be measured directly using several devices with appropriate geometries.  U0 can be measured indirectly as well.

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