Analog and Digital Signals Digital Electronics TM 1.2 Introduction to Analog Analog & Digital Signals This presentation will • Review the definitions of analog and digital signals. • Detail the components of an analog signal. • Define logic levels. Analog & Digital Signals • Detail the components of a digital signal. • Review the function of the virtual oscilloscope. Digital Electronics 2 Analog and Digital Signals Example of Analog Signals • An analog signal can be any time-varying signal. Analog Signals Digital Signals • Minimum and maximum values can be either positive or negative. • Continuous • Discrete • They can be periodic (repeating) or non-periodic. • Infinite range of values • Finite range of values (2) • Sine waves and square waves are two common analog signals. • Note that this square wave is not a digital signal because its • More exact values, but • Not as exact as analog, minimum value is negative. more difficult to work with but easier to work with Example: A digital thermostat in a room displays a temperature of 72. An analog thermometer measures the room 0 volts temperature at 72.482. The analog value is continuous and more accurate, but the digital value is more than adequate for the application and Sine Wave Square Wave Random-Periodic significantly easier to process electronically. 3 (not digital) 4 Project Lead The Way, Inc. Copyright 2009 1 Analog and Digital Signals Digital Electronics TM 1.2 Introduction to Analog Parts of an Analog Signal Logic Levels Before examining digital signals, we must define logic levels. A logic level is a voltage level that represents a defined Period digital state. (T) Logic HIGH: The higher of two voltages, typically 5 volts Frequency: Amplitude Logic LOW: The lower of two voltages, typically 0 volts (peak) 1 F Hz 5.0 v Amplitude T (peak-to-peak) Logic High Logic Level Voltage True/False On/Off 0/1 2.0 v HIGH 5 volts True On 1 Invalid LOW 0 volts False Off 0 Logic 0.8 v Level 5 0.0 v Logic Low 6 Example of Digital Signals Parts of a Digital Signal • Digital signal are commonly referred to as square waves or clock Amplitude: Falling Edge signals. For digital signals, this will ALWAYS be 5 volts. • Their minimum value must be 0 volts, and their maximum value Period: must be 5 volts. The time it takes for a periodic signal to • They can be periodic (repeating) or non-periodic. repeat. (seconds) Time Time High Low Frequency: (t ) (t ) Amplitude H L • The time the signal is high (tH) can vary anywhere from 1% of the A measure of the number of period to 99% of the period. occurrences of the signal per second. (Hertz, Hz) 5 volts Time High (t ): Rising Edge H Period (T) The time the signal is at 5 v. Time Low (tL): 0 volts The time the signal is at 0 v. Frequency: Duty Cycle: 1 t The ratio of t to the total period (T). F Hz DutyCycle H 100% H T T Rising Edge: A 0-to-1 transition of the signal. 7 Falling Edge: 8 A 1-to-0 transition of the signal. Project Lead The Way, Inc. Copyright 2009 2 Analog and Digital Signals Digital Electronics TM 1.2 Introduction to Analog Oscilloscope Virtual Oscilloscope: Multisim Oscilloscope Instrumentation Oscilloscope • The Oscilloscope is a piece of electronic Component test equipment that is used to capture and measure time-varying signals, both analog Markers: and digital. Displayed Signals Movable markers T1 & T2 • Oscilloscopes can be found on the Marker Display: workbench (physical) as well as part of a Displays the voltage & time intersect for the markers simulation tool (virtual). T1 & T2. • We will limit our usage to the virtual Timebase: Channel_X: Channel Selection Adjusts the time scale and Adjusts the horizontal oscilloscope. offset of the signals. This is scale and offset of the 9 common for all channels. selected channel. 10 Example: Digital Signal Example: Digital Signal Example: Solution: Determine the following information for the digital signal shown: Amplitude: 2 V • Amplitude Amplitude 2.5 div div • Period (T) Amplitude 5 v • Frequency (f) 2 ms / div • Time High (tH) 2 v / div • Time Low (tL) Period (T): 2 ms • Duty Cycle (DC) T 4 div div T 8 ms Frequency (f): 1 1 f T 8 ms f 125 Hz 11 12 Project Lead The Way, Inc. Copyright 2009 3 Analog and Digital Signals Digital Electronics TM 1.2 Introduction to Analog Example: Digital Signal Period Measurement with Markers Solution: The markers can be used to measure the Time High (t ): H period tH & tL (next slide). 2 ms tH 2.4 div div tH 4.8 ms 2 ms / div Period (T): Time Low (t ): 2 v / div L T 8 ms 2 ms tL 1.6 div div tL 3.2 ms Duty Cycle (DC): t DC H 100% T 4.8 ms DC 100% 8 ms 13 14 DC 60% tH & tL Measurement with Markers Low High ( tL): tL 3.214 ms Time High ( tH): tH 4.786 ms 15 Project Lead The Way, Inc. Copyright 2009 4 .