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- 1. Analog & Digital Signals Digital Electronics
- 2. Analog & Digital SignalsThis presentation will• Review the definitions of analog and digital signals.• Detail the components of an analog signal.• Define logic levels.• Detail the components of a digital signal.• Review the function of the virtual oscilloscope. 2
- 3. Analog and Digital SignalsAnalog Signals Digital Signals• Continuous • Discrete• Infinite range of values • Finite range of values (2)• More exact values, but • Not as exact as analog, more difficult to work with but easier to work withExample: A digital thermostat in a room displays a temperature of 72°. An analog thermometer measures the room temperature at 72.482°. The analog value is continuous and more accurate, but the digital value is more than adequate for the application and 3 significantly easier to process electronically.
- 4. Example of Analog Signals • An analog signal can be any time-varying signal. • Minimum and maximum values can be either positive or negative. • They can be periodic (repeating) or non-periodic. • Sine waves and square waves are two common analog signals. • Note that this square wave is not a digital signal because its minimum value is negative.0 volts Sine Wave Square Wave Random-Periodic (not digital) 4
- 5. Parts of an Analog Signal Period (T) Frequency: Amplitude (peak) 1 F = HzAmplitude(peak-to-peak) T 5
- 6. Logic LevelsBefore examining digital signals, we must define logic levels.A logic level is a voltage level that represents a defineddigital state.Logic HIGH: The higher of two voltages, typically 5 voltsLogic LOW: The lower of two voltages, typically 0 volts5.0 v Logic High Logic Level Voltage True/False On/Off 0/1 HIGH 5 volts True On 12.0 v Invalid LOW 0 volts False Off 0 Logic0.8 v Level0.0 v Logic Low 6
- 7. Example of Digital Signals • Digital signal are commonly referred to as square waves or clock signals. • Their minimum value must be 0 volts, and their maximum value must be 5 volts. • They can be periodic (repeating) or non-periodic. • The time the signal is high (tH) can vary anywhere from 1% of the period to 99% of the period.5 volts0 volts 7
- 8. Parts of a Digital SignalAmplitude: For digital signals, this will ALWAYS be Falling Edge 5 volts.Period: Amplitude The time it takes for a periodic signal to repeat. (seconds) Time Time High LowFrequency: (tH) (tL) A measure of the number of occurrences of the signal per second. (Hertz, Hz) Rising EdgeTime High (tH): Period (T) The time the signal is at 5 v.Time Low (tL): The time the signal is at 0 v. Frequency:Duty Cycle: 1 tH The ratio of tH to the total period (T). F= Hz DutyCycle = × 100% T TRising Edge: A 0-to-1 transition of the signal.Falling Edge: 8 A 1-to-0 transition of the signal.
- 9. Oscilloscope• The Oscilloscope is a piece of electronic test equipment that is used to capture and measure time-varying signals, both analog and digital.• Oscilloscopes can be found on the workbench (physical) as well as part of a simulation tool (virtual).• We will limit our usage to the virtual oscilloscope. 9
- 10. Virtual Oscilloscope: Multisim Oscilloscope Instrumentation Oscilloscope Component Markers: Displayed Signals Movable markers T1 & T2 Marker Display: Displays the voltage & time intersect for the markers T1 & T2.Timebase: Channel_X: Channel Selection Adjusts the time scale and Adjusts the horizontal offset of the signals. This is scale and offset of the common for all channels. selected channel. 10
- 11. Example: Digital SignalExample: Determine the following information for the digital signal shown: •Amplitude •Period (T) •Frequency (f) •Time High (tH) •Time Low (tL) •Duty Cycle (DC) 11
- 12. Example: Digital SignalSolution: Amplitude: 2V Amplitude = 2.5 div × div Amplitude = 5 v 2 ms / div 2 v / div Period (T): 2 ms T = 4 div × div T = 8 ms Frequency (f): 1 1 f= = T 8 ms f = 125 Hz 12
- 13. Example: Digital SignalSolution: Time High (tH): 2 ms t H = 2.4 div × div t H = 4.8 ms 2 ms / div 2 v / div Time Low (tL): 2 ms t L = 1.6 div × div t L = 3.2 ms Duty Cycle (DC): tH DC = × 100% T 4.8 ms DC == × 100% 8 ms 13 DC = 60%
- 14. Period Measurement with MarkersThe markers can be used to measure theperiod tH & tL (next slide). Period (T): T = 8 ms 14
- 15. tH & tL Measurement with Markers Low High ( tL): t L = 3.214 ms Time High ( tH): t H = 4.786 ms 15

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