Schmitt trigger eqn in Baker's book..correct or incorrect ?

[infinitee00]

Hello designers,
I was trying to derive the equations for threshold values of a Schmitt trigger from the CMOS circuit design and layout book by Jacob Baker.

https://books.google.com/books?id=N...ox-a&cd=8#v=onepage&q=schmitt trigger&f=false

However, on page 525, Equation 18.3, Baker assumes that the transistor M1 is in saturation when the Schmitt switches. But for M1 to be in saturation,

Vx > Vin-Vth1

or

Vx > Vx+Vth2-Vth1 (since Vin = Vx+Vth2 when M2 starts turning on)

or

Vth1 > Vth2

But due to body bias we know that Vth2 > Vth1. So is Baker's assumption incorrect or am I missing something.

Any insight would be great..

Thanks

 

[leon30]

I would want to know too, and also how to size M2 and M4 and why exactly this way. I mean that in the 1st edition it was M2 (M4) should be 5 times larger (or more) than M1 and M3 (M5 and M6), but now it becames M2 should be larger (a little, not 5 times) than M1 OR M3 ?? What is going on and what is the correct one ??

 

[jbaker]

Please see CMOSedu question 30 for a response.