Procedure For Calculating The Logical Effort of A Single Stage
CMOS inverters along the critical path are typically designed with a gamma equal to 2. In other words, the pFET of the inverter is designed with twice the width (and therefore twice the capacitance) as the nFET of the inverter, in order to get roughly the same pFET resistance as nFET resistance, in order to get roughly equal pull-up current and pull-down current.
Choose sizes for all transistors such that the output drive of the gate is equal to the output drive of an inverter built from a size-2 PMOS and a size-1 NMOS.
The output drive of a gate is equal to the minimum – over all possible combinations of inputs – of the output drive of the gate for that input.
The output drive of a gate for a given input is equal to the drive at its output node.
The drive at a node is equal to the sum of the drives of all transistors which are enabled and whose source or drain is in contact with the node in question. A PMOS transistor is enabled when its gate voltage is 0. An NMOS transistor is enabled when its gate voltage is 1.
Once sizes have been chosen, the logical effort of the output of the gate is the sum of the widths of all transistors whose source or drain is in contact with the output node. The logical effort of each input to the gate is the sum of the widths of all transistors whose gate is in contact with that input node.
The logical effort of the entire gate is the ratio of its output logical effort to the sum of its input logical efforts.
Read more about this topic: Logical Effort
Famous quotes containing the words calculating, logical, effort, single and/or stage:
“Sin in this country has been always said to be rather calculating than impulsive.”
—Frank Moore Colby (1865–1925)
“The sensual and spiritual are linked together by a mysterious bond, sensed by our emotions, though hidden from our eyes. To this double nature of the visible and invisible world—to the profound longing for the latter, coupled with the feeling of the sweet necessity for the former, we owe all sound and logical systems of philosophy, truly based on the immutable principles of our nature, just as from the same source arise the most senseless enthusiasms.”
—Karl Wilhelm Von Humboldt (1767–1835)
“Prejudices are so to speak the mechanical instincts of men: through their prejudices they do without any effort many things they would find too difficult to think through to the point of resolving to do them.”
—G.C. (Georg Christoph)
“Home! Yes! she would see Trafalgar Square, again; and Nelson on his plinth; and Chelsea Bridge as it dissolved into the Thames at twilight ... and St. Paul’s, the single Amazon breast of her beloved native city.”
—Angela Carter (1940–1992)
“I know that each stage is not going to last forever. I used to think that when he was little. Whenever he was in a bad stage I thought that he was going to be like that for the rest of his life and that I’d better do something to shape him up. When he was in a good state, I thought he was going to be a perfect child and I would never have to worry; he was always going to stay that way.”
—Anonymous Parent of An Eight-Year-Old. As quoted in Between Generations by Ellen Galinsky, ch. 4 (1981)