Lecture_4

Lecture_4 - ECE 331 Digital System Design Circuit Design...

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ECE 331 – Digital System Design Circuit Design Considerations and Programmable Logic Devices

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ECE 331 - Digital System Design 2 Representing Logic Values with Voltage Ranges
ECE 331 - Digital System Design 3 Logic value 1 Undefined Logic value 0 Voltage V DD V 1,min V 0,max V SS (Gnd) Voltage Levels in Logic Circuits

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ECE 331 - Digital System Design 4 Voltage V DD V IH V IL V SS (Gnd) Voltage Levels in Logic Circuits V OH V OL NM = V - V NM = V - V Undefined
ECE 331 - Digital System Design 5 Fan-out

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ECE 331 - Digital System Design 6 Fan-out Fan-out is the number of gate inputs that can be properly driven by a single gate output - Current must flow between gates - Current is limited by gate technology - Current limits fan-out DC Fan-out is the fan-out when the output is at steady-state. - Both high (1) and low (0) output states must be considered when implementing logic circuit design - Select worst-case as limit
ECE 331 - Digital System Design 7 x f (a) Inverter that drives n other inverters To inputs of n other inverters N 1 Fan-out

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ECE 331 - Digital System Design 8 Interfacing between Logic Devices
9 Interfacing between Logic Devices Devices in the same logic family have the same electrical characteristics. Devices in different logic families often have different electrical characteristics. In order to interface between logic devices - Must consider the voltages levels of the driving and load devices. -

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This note was uploaded on 01/24/2011 for the course ECE 331 taught by Professor Staff during the Spring '08 term at George Mason.

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Lecture_4 - ECE 331 Digital System Design Circuit Design...

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