Features of CMOS Circuits-Introduction to Microelectronic Circuits-Lecture 27 Slides-Electrical Engineering, Slides of Microelectronic Circuits

Download Features of CMOS Circuits-Introduction to Microelectronic Circuits-Lecture 27 Slides-Electrical Engineering and more Slides Microelectronic Circuits in PDF only on Docsity! 1 Lecture 27, Slide 1EECS40, Fall 2003 Prof. King Lecture #27 ANNOUNCEMENTS • Extra Office Hours this week: – Prof. King: Thu. 10/30 1:15-2 PM – Steve: Fri. 10/31 12-2 PM – Farhana: Sat. 11/1 4-5 PM; Sun. 11/2 3-5 PM (regular office hours cancelled next week) OUTLINE – The CMOS inverter (cont’d) – CMOS logic gates – The body effect Reading (Rabaey et al.) Chapter 5.5.1 (p.174); 6.2.1 (pp.199-202); Chapter 3.3.2 (pp.58-60) Lecture 27, Slide 2EECS40, Fall 2003 Prof. King Features of CMOS Circuits • The output is always connected to VDD or GND in steady state → Full logic swing; large noise margins → Logic levels are not dependent upon the relative sizes of the devices (“ratioless”) • There is no direct path between VDD and GND in steady state → no static power dissipation 2 Lecture 27, Slide 3EECS40, Fall 2003 Prof. King The CMOS Inverter: Current Flow during Switching VIN VOUT VDD VDD0 0 N: off P: lin N: lin P: off N: lin P: sat N: sat P: lin N: sat P: sat A B D E C i i S D G G S D VDD VOUTVIN Lecture 27, Slide 4EECS40, Fall 2003 Prof. King Power Dissipation due to Direct-Path Current VDD-VT VT time vIN: i: Ipeak VDD 0 0 i S D G G S D VDD vOUTvIN peakDDscdp IVtE =Energy consumed per switching period: tsc 5 Lecture 27, Slide 9EECS40, Fall 2003 Prof. King CMOS NOR Gate A F B A B VDD 011 001 010 100 FBA Lecture 27, Slide 10EECS40, Fall 2003 Prof. King CMOS Pass Gate A X Y A Y = X if A 6 Lecture 27, Slide 11EECS40, Fall 2003 Prof. King VT is a function of VSB: The “Body Effect” ( )       = −++= i B F FSBFTT n N q kT VVV ln where 220 φ φφγ γ is the body effect coefficient When the body-source pn junction is reverse-biased, |VT| increases. Usually, we want to minimize γ so that IDsat will be the same for all transistors in a circuit. Lecture 27, Slide 12EECS40, Fall 2003 Prof. King Example (0.25µm CMOS technology) -2.5 -2 -1.5 -1 -0.5 0 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 V BS (V) V T (V )