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Chapter 6 - digital 1

# Chapter 6 - digital 1 - Chapter 6 Digital Electronics...

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Chapter 6 Digital Electronics EE4313 Electronic Circuits II

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Chap 6 - 2 Chapter Goals Introduce binary digital logic concepts Explore the voltage transfer characteristics of ideal and nonideal inverters Define logic levels and logic states of logic gates Introduce the concept of noise margin Present measures of dynamic performance of logic devices Review of Boolean algebra Investigate simple transistor implementations of the inverter and other logic circuits Explore basic design techniques of logic circuits
Chap 6 - 3 Brief History of Digital Electronics Digital electronics can be found in many applications in the form of microprocessors, microcontrollers, PCs, DSPs, and an uncountable number of other systems. The design of digital circuits has progressed from resistor- transistor logic (RTL) and diode-transistor logic (DTL) to transistor-transistor logic (TTL) and emitter-coupled logic (ECL) to NMOS and now complementary MOS (CMOS) The density and number of transistors in microprocessors has increased from 2300 in the 1971 4-bit 4004 microprocessor to 25 million in the more recent IA-64 chip and it is projected to reach over one billion transistors by 2010

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Chap 6 - 4 Ideal Logic Gates Binary logic gates are the most common style of digital logic The output will consist of either a 0 (low) or a 1 (high) (Positive Logic Convention) The most basic digital building block is the inverter
Chap 6 - 5 The Ideal Inverter The ideal inverter has the following voltage transfer characteristic (VTC) and is described by the following symbol V + and V - are the supply rails, and V H and V L describe the high and low logic levels at the output

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Chap 6 - 6 Logic Level Definitions An inverter operating with power supplies at V + and 0 V can be implemented using a switch with a resistive load
Chap 6 - 7 Logic Voltage Level Definitions V L – The nominal voltage corresponding to a low-logic state at the output of a logic gate for v i = V H V H – The nominal voltage corresponding to a high-logic state at the output of a logic gate for v i = V L V IL – The maximum input voltage that will be recognized as a low input logic level V IH – The maximum input voltage that will be recognized as a high input logic level V OH – The output voltage corresponding to an input voltage of V IL V OL – The output voltage corresponding to an input voltage of V IH

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Chap 6 - 8 Logic Voltage Level Definitions (cont.) Note that for the voltage transfer characteristic (VTC) of the nonideal inverter, there is now an undefined logic state.
Chap 6 - 9 Noise Margins Noise margins represent “safety margins” that prevent the circuit from producing erroneous outputs in the presence of noisy inputs Noise margins are defined for low and high input levels using the following equations: NM L = V IL – V OL NM H = V OH – V IH

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Chap 6 - 10 Noise Margins (cont.) Graphical representation of where noise margins are defined Noise margins are needed to absorb voltage differences that may arise between the outputs ad inputs of various logic gates due to a variety of sources.
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