I was overwhelmed by the very common question being asked to me after my previous post, and these were from all levels of people (even people from verification and embedded background). "Why do we need to learn SPICE?" And, that was exactly what I was expecting. "For the things we have to learn before we can do them, we learn by doing them". Though, this will be discussed in detail in my upcoming course of SPICE, let me try to give a glimpse of it here itself

1. The Big Question

2. "The best scientists and explorers have the attributes of kids!
They ask question and have a sense of wonder. They have
curiosity. 'Who, what, where, why, when and how'! They never
stop asking questions, and I never stop asking questions, just
like a five year old" - Sylvia Earle

3. I was overwhelmed by the very common question being
asked to me after my previous post, and these were from
all levels of people (even people from verification and
embedded background). "Why do we need to learn
SPICE?"
And, that was exactly what I was expecting. "For the
things we have to learn before we can do them, we
learn by doing them". Though, this will be discussed in
detail in my upcoming course of SPICE, let me try to give a
glimpse of it here itself
Below is a snippet from my existing course on Clock Tree
Synthesis

5. It has 2 kinds of clock buffers, say '1' and '2'. Now, to
calculate the delay of these buffers, the only input, we have
are delay models. These could be "non-linear delay
models" or "constant-current source models". Let's take a
simple example of below "non-linear delay model." This is
how it looks. It has a "input slew" one side and output
capacitance on other side. A more complex model (to be
discussed separately), and time units on one side and
normalized voltage on other side.

7. Both buffers can be of different type (or different sizes and
drive strength), so each buffer '1' and '2' has their own
table.
Now, say, output capacitance of buffer '1' is 60fF and input
slew is 'say' 40ps, below is the section of the table that we
need to look into to compute its delay. This technique is
called 'interpolation'. We need to interpolate the delay
value between 50fF and 70fF, for an output cap of 60fF

9. Similarly, for an input slew of 'say' 60ps and output load of
'50fF', the delay value of buffer '2' will be about 'y15', as per
below table

11. I haven't yet answered your question. Why do we need to
learn SPICE? I will answer it now. Where, do you think,
the delay values in the table come from?
Let's say we have this below inverter (simple buffer is 2
inverters connected back to back), with the below IO
characteristics.

13. Now, observe very carefully to all above waveforms
(specially the last one present in bottom right). Do they
remind you of look-alike waveforms, for which we just
calculated the delay? Does the waveform at the top-
middle, remind you of the waveforms we derived in last
post using a SPICE simulator? Do they look like Id-Vds
curves for NMOS? Do you relate how delay of cells are
actually derived from NMOS-PMOS-CMOS transfer
characteristics?

14. I think I gave enough hints over here. I will see you in class
of "VLSI Academy - Circuit design and SPICE
simulations" on Udemy
"You can swim all day in the Sea of Knowledge and still
come out completely dry. Most people do." Norman
Juster
If so, you are on the right path.
Stay with me @ vlsisystemdesign.com and I will notify you
more about this course

15. For more, please refer to below courses
Circuit design & SPICE simulations
https://www.udemy.com/vlsi-academy-circuit-design/?couponCode=forSlideshare
Physical design flow
https://www.udemy.com/vlsi-academy-physical-design-flow/?couponCode=forSlideshare
Clock tree synthesis
https://www.udemy.com/vlsi-academy-clock-tree-synthesis/?couponCode=forSlideshare
Signal integrity
https://www.udemy.com/vlsi-academy-crosstalk/?couponCode=forSlideshare
VLSI – Essential concepts and detailed interview guide
https://www.udemy.com/vlsi-academy/?couponCode=forSlideshare

16. THANK YOU