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JAugLessonEight - Key Lecture Concepts for CoE225/EE...

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Key Lecture Concepts for CoE225/EE 271 (Mostly Digital Electronics) LESSON EIGHT: THE CMOS INVERTER: Introduction; Noise Margins; Dynamic Response; Static and Dynamic Power Dissipation; Logic Gates and Complex Network Design; the CMOS Transmission Switch. Lesson Objectives and Overview: Since the early 90s, CMOS transistor circuits have been the enabling technology for the impressive advances in high-speed logic networks and large memory arrays in modern computers. CMOS circuit technology offer three key advantages relative to the NMOS circuits studied so far: a) much lower standby power dissipation for logic arrays; b) a current to charge up the load capacitance equal to the switch current that discharges the load for DMOS circuits; no body effect for the load or switch of an inverter. CMOS technology continues to play a leading role in enabling faster microprocessors, very-large-scale computers, and other systems requiring high-performance low-cost digital and analog electronics. Therefore the reader should look forward to learning about CMOS circuits and some of their applications. You will be given the opportunity to invent the basic CMOS inverter circuit in section A and thus learn something abut the invention process. Section B uses load analysis to show how the transfer curves depends on threshold voltage and K values. Section C describes how the CMOS inverter is made in a silicon chip. Section D describes the superior transfer curves of CMOS versus DMOS. By load analysis, Section E shows why the CMOS switching response is superior to DMOS. Sections F, G and H cover the topics of power dissipation and logic network design. Although the CMOS circuit was invented in the early 60s, DMOS circuits were the dominant logic design technology until CMOS fabrication was perfected in the late 1980s. To make both P and N-type MOSTS on the same chip was a challenge. The previously cited advantages of CMOS, low static power dissipation, no body effect, and higher current to charge up capacitance loading to V DD , was the driving force to solve the fabrication challenge. A) Re-Inventing the CMOS Inverter Let us see if we can learn something about an important function of engineers, inventing. We will lead you to re-invent CMOS circuits from what you learned in lesson seven. Inventions usually occur when a need or problem is clearly recognized. Recall that at the end of lesson seven we asked: “Is there a way to make the load current go to zero (or cut off the load) when the switch is turned on?” If there were, the output voltage could be zero, and not e.g. 0.2 [v]. Then the supply and power dissipation would be zero. At first the idea of an inverter with zero standby power may seem to be a “wild idea” and impossible to implement. However, the most prolific inventors have confidence that there is a solution to every problem. Confidence is critical. You should “capture” your thought, in this case the idea of letting the load transistor know that a high level signal
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by R.H.Cornely, July 09 Edition
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