This was the question: Why does decreasing the voltage also decrease the circuit frequency?

It's a good question but was closed because "This question needs details or clarity". So I added details. My edit was rejected because "This edit deviates from the original intent of the post".

This is not true. I just added more details and context to make the question clear and save it. All I did was added the definitions of terms which were already present in the question. Without my edit, the post lacks context. All it states is

Keeping the same clock frequency becomes unsustainable as Vdd is continuously reduced, because the rise and fall times of signals stop meeting the noise margin of the gate.

Other users who are not familiar with this field will have no idea what voltage Vdd refers to here.

So I added

Here, Vdd is the supply voltage of the CMOS gate. Noise margin of the gate is the allowable noise voltage on the inputs of the gate such that the output will not get corrupted. Rise time is the time taken for the output signal of the gate to rise from 10% to 90% of its final voltage value of logic High level. Fall time is the time taken for the output signal to fall from 90% to 10% of its final voltage value for logic Low level.

And slightly modified the last statement to

I don't understand why rise time and fall time increases as voltage Vdd decreases.


1 Answer 1


I'm one of the reviewers who rejected the edit. I thought the edited title and the last statement were improvements but, unless I was and still am missing something, the information in the paragraph you added is not present in the question. Granted, the paragraph consists entirely of things which can be inferred (e.g. VDD is the supply voltage) or are true by definition (e.g. rise/fall time), but it's not something the question author added. The question author may not know these definitions so your edit could give the appearance that the question author has provided more details and is more knowledgeable about the topic than is the case.

Ultimately this is not a good question and should be closed until the author adds details (I'm also one of the close voters). You said yourself in a comment on the question that

Adding the name of the textbook you referred to would be a good idea.

I would want to see a citation of the textbook and a bit more context from the textbook before voting to re-open this question.

  • \$\begingroup\$ Since it is a good question, another option would be for me to ask and answer it again, without quoting from the textbook. Is that right? \$\endgroup\$ Feb 19, 2021 at 14:20
  • \$\begingroup\$ @ShashankVM If the question hasn't already been asked on the site and if you can write up a question that has better context then, yes, you can certainly ask and answer your own question. \$\endgroup\$
    – Null Mod
    Feb 19, 2021 at 14:23
  • 1
    \$\begingroup\$ @ShashankVM If anything it would make sense to close the question you tried to edit as a duplicate of your new question with better context. \$\endgroup\$
    – Null Mod
    Feb 19, 2021 at 14:27

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