A

Typical Oscilloscope Block Diagram

Oscilloscope Basics Displayed waveform in the time domain format (YT mode): a graph of voltage as a function of time. Two input channels that can be displayed simultaneously (Chop Mode). The vertical axis is in volts/division. The horizontal axis is in seconds/division. A trigger circuit is used to obtain a stable display.

Trigger Control To obtain a stable (stationary) display. Trigger means to begin the trace at reference time zero. The source of the trigger signal may be channel 1, channel 2, or an external source. In the NORMAL trigger Mode: no trace is displayed until a trigger occurs. In the AUTO trigger mode: a trace will be displayed even if there is no signal or trigger event. The trigger LEVEL and trigger SLOPE control set the magnitude and slope of the input signal that will cause a trigger (begin a trace on a specified event).

Triggering

Trigger Controls (cont.) Trace @ reference time 0 Trig Menu Trigger level

Trigger on the Falling Edge @ 2V Level Trace @ reference time 0

Vertical Controls The vertical axis has 8 major vertical divisions. Vertical Sensitivity Control (Volt/DIV knob): adjustable from 10mV/DIV to 50V/DIV. The Vertical Position control move traces on each channel vertically. Input coupling to DC, AC, or GND. AC coupling :only AC signals displayed. DC coupling: both DC & AC signals displayed. GND: connects input to ground.

DC / AC Coupling DC Coupling of 4Vpeak to peak AC Coupling of the same signal square wave with 2V DC offset

DC / AC Coupling (cont.) DC Coupling of 6Vpeak to peak AC Coupling of the same signal Sine wave with 3V DC offset

Horizontal Controls The Time Base (Sec/DIV knob) sets the calibration of the horizontal axis. 10 major divisions: 5ns to 50 sec/divisions.

Time Measurement Using Cursors Trigger position: time 0

Voltage Measurement Using Cursors

Peak-to-Peak Voltage Measurement

Period Measurement

Mean (Average) Voltage Measurement

Probe Attenuation Setting Probe has attenuation factor of 1X and 10X which affects the vertical scale of the signal. Be sure that the Attenuation switch on the probe matches the Probe option in the scope.

Display Type Vectors: Vector fills space between adjacent sample points (2500 points in Sample Acquisition mode) Dots: display only sample points. Chop Mode: On analog oscilloscope, Chop Mode causes the oscilloscope to draw small parts of each signal by switching back and forth between them. On digitized oscilloscope, it means displaying two channels.

Display Type (cont.)

Scan Mode Display Waveform updates from left to right, erases the old points as it displays the new points. Scope changes to Scan acquisition mode when SEC/DIV = 100ms/div or slower Auto Trigger To disable Scan mode, push TRIG MENU button and set the Mode option to Normal.

1. An oscilloscope can be used to graph versus time. a. Voltage b. Resistance c. Current d. All of the above Floyd, Digital Fundamentals, 10th ed

2. The horizontal axis of an oscilloscope is in. a. volts/division b. seconds/division c. amps/division d. None of the above Floyd, Digital Fundamentals, 10th ed

3. A circuit is used to obtain a stable display. a. sweep b. amplifier c. trigger d. None of the above Floyd, Digital Fundamentals, 10th ed

4. Which of the following are valid input coupling settings on an oscilloscope? a. DC b. AC c. GND d. All of the above Floyd, Digital Fundamentals, 10th ed

5. Which oscilloscope button can be used to select various voltage, time, or duty-cycle measurements? a. Utility b. Measure c. Display d. None of the above Floyd, Digital Fundamentals, 10th ed

Answers: 1. a 2. b 3. c 4. d 5. b Floyd, Digital Fundamentals, 10th ed