1. Waveform 2.1 Basic Digital Waveforms 2 Measurement Paul Godin Updated October 2009

2. Waveform 2.2 Measurement Tools ◊Several instruments are used to analyze Digital Electronic circuits, including: ◊Logic Probes ◊Oscilloscopes ◊Logic Analyzers ◊Tracers ◊Function generators

3. Waveform 2.3 Logic Probes ◊Logic Probes display static logic states at specific points on a digital logic circuit. These states include: ◊High ◊Low ◊Float ◊Logic probes are easy to use.

4. Waveform 2.4 Logic Probes ◊Logic Probes are usually connected to the power supply of the circuit under test. ◊Some logic probes can also detect the presence of an oscillation. ◊Related to probes are: ◊Current tracers, used to detect the location of a short circuit in digital circuits. Works with induction. ◊Pulsers, used to inject an oscillation into the circuit to trace its route.

5. Waveform 2.5 Logic Probes - Limitations ◊Logic probes are designed to measure active circuits only. ◊Logic probes provide the static logic states and cannot measure: ◊Oscillation values (time high / time low) ◊Voltages ◊Transients (short-lived problems)

6. Waveform 2.6 Oscilloscope ◊Oscilloscopes are a common electronics instrument used to measure voltage and frequency. ◊Oscilloscopes can also be used to compare signals. Most oscilloscopes have at least 2 channels.

7. Waveform 2.7 Oscilloscope ◊Oscilloscopes work best with periodic signals. ◊Some more advanced oscilloscopes can: ◊measure aperiodic signals ◊retain measured values in memory ◊have advanced analysis capabilities

8. Waveform 2.8 Oscilloscope - Limitations ◊Oscilloscopes measure active circuits only ◊Expensive ◊Most are not very portable and require an AC power source ◊Requires training and practice to use properly

9. Waveform 2.9 Waveform Measurement 90% 10% 50% Rise Time (t R ) Fall Time (t F ) Pulse Separation Ps Pulse Width Pw Period (T) Rise and fall times are typically measured in nanoseconds (ηs) Amplitude

10. Waveform 2.10 Oscilloscope Measurement ◊Measuring with a scope – Static logic state 1 1 Circuit Ground 1 Set input to DC Probe 5V

11. Waveform 2.11 Oscilloscope Measurement ◊Measuring with a scope - Oscillation 1 1 Set input to DC Circuit Ground Probe 5V

12. Waveform 2.12 Oscilloscope Measurement ◊Several controls need to be adjusted when measuring with the scope: ◊Volts/Division: controls the displayed voltage ◊Time/Division: controls the displayed time ◊Trigger: controls the trigger point for a periodic signal. Must be set within the signal’s amplitude. ◊Coupling: should be set to DC (Direct Coupled) when measuring digital values ◊Horizontal and Vertical position: used to set the position of the ground reference on the display

13. Waveform 2.13 EWB Oscilloscope Normal View with 4 connections Ground must be connected Semi-expanded view Connections correspond to Normal View

14. Waveform 2.14 EWB Oscilloscope – Expanded View Cursors used for measurement. Values between cursors in box below Position of Red Cursor Position of Blue Cursor Adjustable Settings

15. Waveform 2.15 Exercise: EWB Oscilloscope Class activity: ◊Open the EWB file titled scope1 on the site. ◊Use the scope in EWB to measure the output waveforms and complete the worksheet on the next slide.

16. Waveform 2.16 Oscilloscope Worksheet Signal A: ◊Period: ___________ ◊T H (time high):_____ ◊T L (time low):_______ ◊Duty Cycle: ________ Signal B: ◊Period: ___________ ◊T H (time high):_____ ◊T L (time low):_______ ◊Duty Cycle: ________ Signal C: ◊Period: ___________ ◊T H (time high):_____ ◊T L (time low):_______ ◊Duty Cycle: ________ ◊T R (rise time): ______ ◊T F (fall time): ______

17. Waveform 2.17 Logic Analyzer ◊Logic analyzers display multiple dynamic (changing) logic states in a format that resembles a timing diagram. Very useful for analyzing more complex digital circuits. ◊Typical analyzers have 8 or 16 channels.

18. Waveform 2.18 Logic Analyzers - Limitations ◊Logic analyzers display logic states, not voltage values. They may not display poor edges or other similar electrical faults. ◊Expensive ◊Most are not very portable and require an AC power source ◊Requires training to use properly

19. Waveform 2.19 EWB Logic Analyzer Circuit connections Expanded view Internal Clock Set Red Cursor Blue Cursor Cursor Position

20. Waveform 2.20 Exercise: EWB Logic Analyzer ◊Class activity: ◊Open the EWB file titled analyze1 on the site. ◊Use the Logic Analyzer in EWB to measure the P W of the 3 waveforms and record below. Signal A P W : _________ Signal B P W : _________ Signal C P W : _________

21. Waveform 2.21 Function Generators ◊Function Generators generate AC voltages, with control over output: ◊Frequency ◊AC voltage ◊DC offset voltage ◊Wave shape (typically Sine, Triangle, Square) ◊Duty Cycle ◊Some function generators have more features or are more specialized. Example includes generating RF frequency and waveforms.

22. Waveform 2.22 Function Generator Use ◊Function Generators are used to inject signals into circuits to analyze their function. ◊Failure to configure the output of the function generator before connecting it to the circuit will likely result in circuit damage. Check: ◊Output AC voltage ◊Output DC offset voltage (no negative voltage) Most ICs will be damaged if negative voltage is applied.

23. Waveform 2.23 Ohmmeters ◊Most ohmmeters produce a high enough voltage to damage logic circuits and should never be used in a digital electronics environment.

24. Waveform 2.24 END