Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Clockless Logic Review Logic Implementation Styles: Static CMOS logic Dynamic logic, or “domino” logic Transmission gates, or “pass-transistor” logic 1 Static CMOS logic Advantages: output always strongly driven pull-up and pull-down networks are fully-complementary; exactly one of them is “on” always good immunity from noise and leakage both inverting and non-inverting functions implementable each gate is inverting cascade two gates together to get non-inverting logic Disadvantages: slow/big PMOS devices needed (in addition to NMOS) greater chip area higher power consumption slower switching speed 2 Dynamic Logic, or “domino” Key idea: only use NMOS’s to compute function use a single PMOS to reset Advantages: significantly fewer transistors smaller chip area higher speed, lower power less “loading” on wires (drive fewer transistors) for async: no storage elements needed Disadvantages: need extra control input to precharge logic is typically non-inverting only more vulnerable to noise and leakage effects 3 Dynamic Logic, or “domino” (contd.) Gate has 2 phases: precharge (=reset): output reset to ‘0’ evaluate: output computed either stays ‘0’, or switches to ‘1’ control input PC data inputs pull-up network pull-down network controls “precharge” data output controls “evaluation” PC =0 (asserted) precharge PC =1 (de-asserted) evaluate Pull-up and pull-down must never both be simultaneously active: ensure that data inputs are reset while gate is precharging or, add a “footer” device 4 Transmission Gates Key Idea: transistors used in a different configuration when switched on: instead of connecting output to Vdd or Gnd, they connect output to the input Advantage: very efficient for implementing switches and multiplexors Disadvantage: not very useful for logic functions 5