Props_of_Dig_Cirs

Props_of_Dig_Cirs - Properties of Digital Circuits...

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ECE 3450 M. A. Jupina, VU, 2006 Properties of Digital Circuits Quantized States Voltage Transfer Characteristic (VTC) Voltage Levels Noise Margins Current Levels Fan-In and Fan-out Power Dissipation Propagation Delay Power-Delay Product IC Packaging Technology Trends of MOS Microprocessors and Memories
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ECE 3450 M. A. Jupina, VU, 2006 Some Key Lecture Objectives Before performing the Properties of Digital Circuits practicum, we need to look at the key properties of digital circuits used to compare one technology with another. How voltage levels of a technology not only define the logic states of a technology, but also lead to a definition of noise immunity for a technology. An understanding of how current levels, “loading,” power dissipation, and speed of operation are all inter-related. Reference : Fundamentals of Digital Logic, Chap 1, Sec 3.8, and App E.4.
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ECE 3450 M. A. Jupina, VU, 2006 Transistor-Transistor-Logic (TTL) TTL dominated the IC market from the 1960’s to early 1980’s. This picture changed in the 1980s due to two major factors: Discrete logic gates in static CMOS became competitive in speed at a lower power cost. The advent of programmable logic components such as PLDs and FPGAs made it possible to program complex random logic functions (equivalent to hundreds of TTL gates) on a single component. This results in a large reduction in board real-estate cost, while adding flexibility.
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ECE 3450 M. A. Jupina, VU, 2006 CMOS CMOS stands for Complementary Metal-Oxide Semiconductor. MOS field-effect transistors (n- channel and p-channel) are used to construct logic gates. FETs are voltage controlled and operate nearly as an ideal switch. MOSFETs advantages: Lower power consumption than BJTs so billons of devices can be packed onto a single chip (MOSFETs dimensions are in the sub- micron range).
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ECE 3450 M. A. Jupina, VU, 2006 Quantized States Binary System possible states: 1 or 0, on or off positive logic: 1= high, 0 = low negative logic: 1= low, 0 = high Future Systems – multilevel logic Ex: if three different on-off levels, then 2 3 = 8 logic states
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ECE 3450 M. A. Jupina, VU, 2006 VTC of an Inverter Voltage Levels (V OH , V OL , V IL ,V IH ) are defined at dV o /dV i = -1 V o V i
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ECE 3450 M. A. Jupina, VU, 2006 V out V in V OL 0 V = V OH V DD = V T V IL V IH V DD V T ( 29 V DD V DD 2 Slope 1 = VTC for a CMOS Inverter
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ECE 3450 M. A. Jupina, VU, 2006 Table of Voltage Levels for TTL Families
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ECE 3450 M. A. Jupina, VU, 2006 PSPICE Schematic of LS7404 TTL Inverter
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ECE 3450 M. A. Jupina, VU, 2006 PSPICE VTC Simulation of the LS7404
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ECE 3450 M. A. Jupina, VU, 2006 PSPICE VTC Simulation of the LS7404 V IL = 0.7 V V IH = 1.18 V V OH = 4 V V OL = 0.15 V
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ECE 3450 M. A. Jupina, VU, 2006 Digital Properties Practicum Measured VTC of LS7404
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M. A. Jupina, VU, 2006 Voltage Level Definitions V IH – High Level Input Voltage V input V IH
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Props_of_Dig_Cirs - Properties of Digital Circuits...

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