23 Important Digital Oscilloscope Terms

Digital Oscilloscope

An instrument designed to measure and display signal voltages as a function of time. Voltages are graphed on a screen across the horizontal axis while time is displayed on the vertical axis. Digital oscilloscopes provide improved accuracy and superior storage capabilities as compared to analog oscilloscopes.

Acquisition Rate

Digital oscilloscopes sample waveforms and convert the analog reading to digital information, and as a result, the devices spend some time processing information. In addition, digital oscilloscopes run a number of pre-processing and post-processing operations. The acquisition rate refers to the number of times per second that an oscilloscope can complete the entire process from sample acquisition to display. A higher acquisition rate generally allows for a higher degree of accuracy and superior functionality when monitoring signals for unusual events such as faults.

Auxiliary Input/Output

A feature on some digital oscilloscopes. The auxiliary input can allow users to trigger a scope with an external device, while the output can be used to send the information collected by an oscilloscope to an external device.

Bandwidth

An important variable on digital oscilloscopes, bandwidth refers to the frequencies that the oscilloscope can measure. Frequency attenuated by -3db constitutes the bandwidth of the device. In digital oscilloscopes, bandwidth is affected by sample rate and the converters that change the analog readings to digital information. Analog bandwidth refers to the analog measurement capabilities of the instrument and may not reflect its functional bandwidth.

Cursors

Also known simply as "markers." A visible mark that can be placed on part of the waveform display, which allows an oscilloscope user to conveniently track information. Can also be used to give specific commands to some oscilloscopes, allowing for time base delays and other special functions.

Delay

Refers to the ability of some digital oscilloscopes to delay a sweep until a time during the main sweep, allowing more information to be collected and displayed. This setting is sometimes referred to as delayed time base and can be useful for viewing events that would not be displayed otherwise.

Envelope

The highest and lowest point of a waveform's readings, displayed by an oscilloscope as an outline. Envelopes are usually captured from a large number of readings.

Eye-Diagram Pattern

Information on multiple signals can be superimposed onto the same graph on some oscilloscopes, providing an eye-like graph of the signal as it occurred relative to time. The eye-diagram pattern can be useful when looking for distortion and other common signal issues, as these problems will cause an eye-diagram pattern to appear less symmetrical.

Glitch

An error in a circuit. Glitches can occur extremely quickly, and in order to accurately capture information about glitches, a digital oscilloscope may need to be specially configured to take readings at specific times. The acquisition rate of an oscilloscope is critical when trying to detect glitches.

Interleaved Sample Rate

The rate at which a digital oscilloscope can sample a waveform by interleaving multiple channels. Interleaving is commonly used to increase the effective sample rate of a digital oscilloscope, allowing for improved accuracy.

Interpolation

Oscilloscopes gather information by taking samples of a waveform. Estimated lines are then drawn to connect the various samples in a process called interpolation, allowing the oscilloscope user to view an accurate estimate of the waveform as it's measured. Sample rate affects the quality of interpolation.

Mask Testing

An oscilloscope function that shows when samples of a waveform are detected out of a given range, which is the "mask." Useful in detecting variances from a standard waveform. Most modern digital oscilloscopes support mask testing.

Math Functions

A control on digital oscilloscopes that allows the user to perform a number of automatic calculations on a signal. These calculations can often be displayed as channels on oscilloscope software or as separate graphs.

Memory Depth/Record Length

The buffer memory of a digital oscilloscope. Memory depth is especially important, as when memory depth has been exceeded, a digital oscilloscope will be unable to store more information about a signal. As a result, memory depth is closely related to sample rate, as the high sample rate of an advanced oscilloscope won't be fully functional if the buffer is incapable of storing all of the samples.

Roll Mode

Allows an oscilloscope to display a graph during a sweep and before all data has been acquired. Roll mode can make it easier to note changes in a signal when settings are altered or when inputs are being changed.

Segmented Memory

A feature on some oscilloscopes that allows readings to be stored in the acquisition memory of the device by segmenting this acquisition memory. This allows for less time between readings and is an effective technique for improving the effective acquisition rate of an oscilloscope.

Single-Shot Sample Rate

The rate at which an oscilloscope can measure one-time events as they occur in a signal. A higher sample rate leads to better interpolation and a more accurate graph of the signal.

Slew Rate

The maximum change in any signal, which can be measured and displayed by an oscilloscope.

Time/Division Range

An oscilloscope's ability to change its timebase for more or less accurate readings. The range is typically measured by the fastest possible timebase.

Timebase

The capability of an oscilloscope to time its sweeps. Timebase may be altered to search for unusual events by moving a control marked "seconds/divisions.

Trigger

An oscilloscope circuit that starts a sweep, either when a previous sweep has been completed or when a determined event has been detected. An oscilloscope can usually be set to draw a waveform only when a certain event takes place, for instance when a signal is read at a certain frequency or when a previous sweep reaches a certain point. Modern digital oscilloscopes have trigger mode controls that determine whether or not the scope draws a waveform when no trigger is detected.

Update Rate

The rate at which an oscilloscope updates an interleaved display of a given waveform. Typically measured in the number of signals sent to the display of the scope.

Vertical Resolution

Measured in bits, the vertical resolution shows the accuracy of the analog-to-digital conversion capabilities of a digital oscilloscope. A higher vertical resolution indicates a more accurate scope.