Introduction
In this tutorial, we will walk through the basics of how to operate a Teledyne LeCroy HDO4000 oscilloscope.
Equipment Requirements
One Teledyne LeCroy HDO4000 series oscilloscope
One passive probe (included with oscilloscope)
Displays shown in the tutorial begin with the following initial setup of an HDO4000 oscilloscope:
- Recall the default setup by pressing the front-panel Default Setup button.
- Press the front-panel Channel 2 button twice to turn off the associated trace. The first press selects Channel 2, making it active, allowing the V/div and offset knobs to control Channel 2. The second press turns the channel off.
- Connect the passive probe to the Channel 1 input of the oscilloscope and connect the probe tip to the Cal output test point to access its 1-kHz, 1-V square wave. Connect the probe’s ground lead to the adjacent ground location.
- Automatically set up the scope by pressing the Auto Setup button on the front panel. Press Confirm in the on-screen pop-up dialog. Optionally, press the Auto Setup button twice to skip the confirmation.
- Press the Normal button in the front-panel Trigger control group.
- The scope display should appear as shown in Figure 1.
This completes the initial setup of the oscilloscope.
Vertical Controls
In the lower left corner of Figure 1 is a trace descriptor box. Its C1 label indicates that data for this trace comes from the Channel 1 input of the oscilloscope. Further, the DC1M notation indicates C1 is set for DC coupling and 1-MΩ input impedance. It also shows that the vertical sensitivity setting is 200 mV/division, and that the DC offset is -505 mV. With C1 the only channel in use, its front-panel C1 button (in the Vertical controls section) lights up in yellow to match the trace’s color. Turn channels on or off by pressing their corresponding buttons (if a channel is active, pressing its button once turns it off. If not, two presses turn it off).
The Vertical controls section has one knob that adjusts volts/vertical division and one for DC offset. These knobs will control the volts/division and DC offset of the currently active channel. Pushing the volts/division knob enables variable control of that parameter; pushing the DC offset knob zeroes out any applied offset.
The active channel is indicated by highlighting of its descriptor box (Figure 2).
Use the DC offset control knob to move the Channel 1 trace up and down on the screen. The offset number in the trace descriptor box will change. Next, change the sensitivity setting. The trace will become larger/smaller and the volts/division number in the descriptor box will reflect the changes.
Horizontal Controls
The Horizontal controls affect all the input channels. The two knobs control the time/division and delay. The acquisition timebase appears in the Timebase descriptor box at the display’s lower right corner. In Figure 1, the timebase is 1.00 ms/div and the delay is 0.00 ms. Note this box also reports the number of samples being acquired (1 MS) and the sampling rate (100 MS/s).
Change the setting of the time/division knob; watch the trace expand or contract and the time/division change in the timebase descriptor box. The HDO4000 automatically assigns enough memory to keep the sampling rate as high as possible for each time/division setting until the maximum memory is in use. At that point, the sample rate begins to drop.
Figure 3 shows the menu that appears when the Timebase descriptor box is touched. Users can assign less than the maximum memory if desired and put the instrument into two-channel mode (in the Active Channels segment), which doubles the memory assigned to the two active channels. In general, it is best to use the maximum memory. If shorter memory is selected, read the short description of the acquisition setup in the Timebase Mode segment of the Timebase dialog to ensure the settings are as desired. In Figure 3, note that the oscilloscope is set to capture 1 MS (1 million sample points) at 100 MS/s (100 megasamples per second), which is equivalent to 1 sample point every 10 ns for the full horizontal span of 10 ns (1 ns/div for 10 divisions).
Next, adjust the Delay knob, which controls the delay time between the trigger and the signals on the screen. A yellow triangle at the bottom of the grid (see Figure 3, again) indicates the triggering point in time. Changing the delay setting moves the trigger time relative to the signal. The trigger time can be all the way on the right-hand edge of the screen, meaning all the data is acquired pre-trigger, or it can be moved off the screen to the left, indicating that the signal on the screen is being acquired post-trigger.
Basic Edge Triggering
Oscilloscopes require a trigger, which is a point in the acquisition used to synchronize the display of the waveform. The trigger allows stable display of the acquired waveform. The edge trigger is the traditional default trigger type. Other, more complex triggers, called SmartTriggers in Teledyne LeCroy oscilloscopes, are also available. With edge triggering, the oscilloscope is triggered when the source trace crosses the trigger threshold level with the user-specified slope (positive, negative, either, or window).
Bring up the Trigger Setup dialog box by pressing the Trigger Setup button on the front panel or by touching the Trigger descriptor box. The Trigger dialog box should be setup similar to Figure 4.
The Trigger dialog box controls the trigger setup. On the left-hand side are options for the trigger type, with the edge trigger being the default. The other trigger types are specialized SmartTriggers, which are discussed in other tutorials. This tutorial will cover only the edge trigger.
The current oscilloscope settings use Channel 1 (C1) as the trigger source with a threshold level of about 500 mV and a positive slope. These settings are summarized in the Trigger descriptor box on the right side of the screen.
Touch the Source button in the Setup segment of the Trigger dialog box. A popup appears showing the possible trigger sources (Figure 5). The trigger sources include any of the input channels, the Ext (external) input connector on the front panel, the Ext (External) input attenuated by a factor of 10, and the power line (mains).
The instrument is currently triggering on Channel 1 (C1) with a stable displayed waveform. Touch the Line selection. Note that the Channel 1 trace on the display becomes unstable. Re-open the Source popup and select C1 to stabilize the trace.
Figure 6 presents the Coupling segment of the Trigger dialog box. The four options are:
- DC coupling allows both DC and AC components of the trigger source into the trigger circuit.
- AC coupling blocks the DC component so only the AC component is used.
- LF REJ (Low-Frequency Reject) applies a high-pass filter (nominally at a 50-kHz lower cutoff frequency) in the trigger signal path, attenuating lower-frequency components.
- HF REJ (High-Frequency Reject) applies a low-pass filter (nominally at a 50-kHz upper cutoff frequency) to the trigger signal path, attenuating higher-frequency components.
Retain DC coupling as the operative coupling option.
The Slope segment of the Trigger dialog box presents the available slope options (Figure 7).
The trigger occurs on a Positive, Negative, Either, or Window slope.
Change the slope from positive to negative. Note the waveform is now triggering on the falling edge as opposed to the rising edge. This is shown in Figure 8.
On the horizontal display axis, the trigger point is located at the small yellow triangle symbol just below the display grid. Move the trigger location using the horizontal delay control on the front panel or in the Timebase dialog box. As the slope setting is changed from positive to negative, the displayed trace shifts to align the selected slope with the trigger point.
If the Either selection is made, the waveform will ‘jump’ between the positive and negative slopes. Return the slope setting to Positive.
The Window trigger sets a threshold both above and below the nominal trigger level that the signal must exceed to trigger the scope. The slope can be either positive or negative for the window slope.
The Trigger level field in the Trigger dialog box sets the signal level at which the trigger occurs. Control the trigger level from this field or from the front panel Trigger Level control. Additionally, the oscilloscope can automatically find the trigger level by touching the Find Level button in the Trigger dialog box or by pushing the Trigger Level knob on the front panel.
A triangular icon located on the right side of the waveform grid (see Figure 3, again) indicates the trigger level. This icon is visible only when using DC coupling. Vary the trigger level up and down. Note that the waveform becomes unstable or the scope stops triggering if the trigger level is within about 0.3 divisions of the top or bottom of the waveform. This is due to a fixed hysteresis built into the scope’s trigger circuit. Hysteresis helps the scope ignore noise on the signal. When the trigger level is outside the range of the signal, the scope will stop triggering and flash a “Waiting for Trigger” warning message in the lower right corner of the display. This indicates that the scope has stopped triggering.
After investigating the trigger level control, press the trigger level knob to restore the proper trigger level.
Basic Measurements
The power of digital oscilloscopes lies in their ability to numerically quantify signal/device performance. Parameters are the most commonly used method for characterizing the shape of a signal. Touch the Measure button on the display to open the drop-down menu and then touch Measure Setup.
Parameters are pre-programmed measurements that eliminate the need to set up cursors for standardized measurements like rise time, fall time, peak-peak amplitude, and so on. They automatically calculate many attributes of a signal. The HDO4000 can make common measurements on one or more waveforms, and display up to eight parameter measurements at one time. It can also display statistics – maximum, minimum, average, standard deviation, and the number of measurements taken. Note that when measuring rise time or other parameters that can occur many times across the screen in a single acquisition, the HDO4000 will measure all instances of the parameter.
Measurements are set up by selecting Measure then Measure Setup from the pull down menu at the top of the screen (Figure 9).
Touch any of the icons for P1 – P8 and assign a measurement to the selected parameter. Once a parameter is selected the user defines which channel is the source of the measurement (in this tutorial the only signal of interest is C1) and any other factors necessary to define the measurement.
Select a few parameters and put them on the display by checking the box labeled Show Table. Turn on statistics by checking that box. Display the distribution of the set of measurement results accumulated for each parameter by checking the Histicons box. Figure 10 shows an example of four parameter measurements with statistics and histicons.
Basic Math
Set up math operations on waveforms by pressing the Math button on the front panel or by selecting Math and then Math Setup from the menu bar at the top of the screen. Another method is to touch the C1 descriptor box and then touch Math in the section labeled Actions for Trace C1.
In the pop-up dialog called Math on C1, all operators will appear by default (Figure 11). The Category column of buttons narrows these down into Basic Math, Frequency Analysis, and Functions. Examples of Operators include Add, Subtract, Multiply, Divide, and FFT. Math operators can be applied to input channels, zoom traces, or memories (reference waveforms). Some operators require two sources, and some only one source.
Math traces are always displayed in a separate half-height grid at the bottom of the display, separate from other traces. This makes it easier to interpret Math information if the math scale is different from the channel scales. If the scope also has active Zoom traces, then three grids are shown on the display, each at one-third the height. Figure 11 shows an FFT in the lower trace.
Try setting up the math function for average, reciprocal, square or FFT using C1 as the source. Check the box labeled Trace On to display the Math trace. Note the Math trace has a descriptor box similar to that of the input channel. In a Math trace descriptor:
- The top line shows how the Math trace is defined (for example, an FFT of C1).
- The 2nd line contains vertical scaling information.
- The 3rd line contains horizontal scaling information.
Touching the descriptor of a Math trace makes it the active trace. Thus, the front-panel horizontal and vertical controls can be used to change the position and scale of the Math trace.
Zooming In For Details
HDO4000 oscilloscopes contain many more points of data in their memory than the number of pixels on the screen. There are times when it is desirable to view more detail concerning the shape of a signal or a math trace. There are three ways to activate a zoom trace:
- Drawing a box around the zoom area with a finger, stylus, or mouse.
- Using the front-panel Zoom button.
- Opening the C1 dialog box and touching Zoom in the segment called Actions for trace C1.
The zoom trace will be displayed on a separate grid. The display timebase is different than the acquisition timebase because the zoom trace contains only a portion of the whole signal. In Figure 12, the acquisition timebase is 1 ms/division whereas the zoom detail is displayed at 100 µs/division. The zoom shows much more detail, but it is only 1/10 of the total signal. It is possible to zoom down to a display timebase that shows the individual data samples in great detail. For example, the oscilloscope can show short glitches or the shape of fast overshoot on an edge.
The oscilloscope can perform parameter measurements or math operations on a zoom trace in the same fashion as an acquisition channel. Accomplish these tasks by defining the zoom trace as the source (for example, Z1 in Figure 13). If there is interesting noise on a portion of a signal, zoom into that portion and perform an FFT of the zoom to look at frequency components. Try setting up some parameters and math on a zoom of C1.
This completes the tutorial.
