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:
“[The] elderly and timid single gentleman in Paris ... never drove down the Champs Elysees without expecting an accident, and commonly witnessing one; or found himself in the neighborhood of an official without calculating the chances of a bomb. So long as the rates of progress held good, these bombs would double in force and number every ten years.”
—Henry Brooks Adams (1838–1918)
“It is merely a linguistic peculiarity, not a logical fact, that we say “that is red” instead of “that reddens,” either in the sense of growing, becoming, red, or in the sense of making something else red.”
—John Dewey (1859–1952)
“Never mind if you fall far short of the thing you want to do,—encourage your effort. If no one else will say it to you, say it to yourself. “Not so bad.” It will make the next effort easier and better.”
—Josephine Demott Robinson (1865–1948)
“We know only a single science, the science of history. One can look at history from two sides and divide it into the history of nature and the history of men. However, the two sides are not to be divided off; as long as men exist the history of nature and the history of men are mutually conditioned.”
—Karl Marx (1818–1883)
“If any proof were needed of the progress of the cause for which I have worked, it is here tonight. The presence on the stage of these college women, and in the audience of all those college girls who will some day be the nation’s greatest strength, will tell their own story to the world.”
—Susan B. Anthony (1820–1906)