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understanding the slew rate step of implementing gm/id method question


Advanced Member level 3
Sep 12, 2019
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Hello,i am trying to follow method descibed in the article bellow. we need GBW=100MHz SLEW_Rate=50 V/us Load=1pF In step "A" they try to find Width of NMOS we have the plots Gm/Id Vs Id/W, ft vs Gm/Id, gm /gds vs gm/Id for L = 180 nm

Gm/Id=GBW/SR=12.6 So when we go to Id/W vs Gm/Id plot we get that Id/W=17.3 Slew rate units is Volts/seconds why they put 50u instead of Id in equation 5? W=Id/(Id/W)=50u/17.3
gm/Id is for linear interests IMO, and slew rate is just the output current
you can get with a hard-steered front end (with some influence of the
gate drive "stiffness" against Miller capacitance once it begins to move).
I think you should step back and assess appropriateness of the method
to the task.

But I've never used gm/Id in any of the op amps, error amps, reference
buffers etc. that I've designed, so maybe there's some use for it in this.
If so I'm sure your assessment will turn it up.

In my observation a lot of people are really keen to discuss gm/Id and
it seems to be viewed as The One True Religion by some (professors,
for sure). But professors get to pick the problems they have to solve.
And they loves them some closed form algebra just when you were
wanting to get on with transistor-slappin'. Doesn't mean they are good
(or competent, even) IC designers. In fact the smart money would
follow the money and bet against it. So listen and learn, but reserve
your faith.
Hello , I know that from slewrate we can get the current that needs to flow on the load capacitor using I=C*dV/dt
but its not the current that flows into the NMOSFET. as shown in the photo bellow.
How they get the desired current of the Nmosfter from the load?

SO we have the load current ,then we need to know the current that flows on PMOS to know what current flows on the NMOS. I_PMOS=I_NMOS+I_Load How do get the PMOS current then?
is the capacitor current is DC current or AC current?

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