How to Read an Oscilloscope

How to read an oscilloscope
Researchers, engineers, technicians, students, and hobbyists all use today's oscilloscopes because they are such a valuable tool for designing, debugging, deploying, and repairing the electronic designs employed in today's devices.

Oscilloscope Basics

Bandwidth

Bandwidth, the most important performance feature of an oscilloscope, is a good place to start when figuring out what scope you need. Choosing the right Bandwidth makes sure that measurements are accurate and reliable.

The bandwidth of an oscilloscope is typically the -3 dB point which is 70.79% of the voltage. The optimal bandwidth of a device or system is defined as the frequency at which the power out of the same device or system is one half as compared with a frequency near DC. Bandwidth has two major impacts on signal measurements: Amplitude Attenuation and Rise Time.

Bandwidth How to read an oscilloscope

Attenuation is when a signal's strength gets weaker as it moves through a medium. Loss of transmission, reflection, or absorption can all cause attenuation. Attenuation is the drop in voltage that happens as electricity moves through a wire or other transmission line. Attenuated or degraded systems are both ways to talk about the same thing.

Attenuation is measured in decibels (dB), which is the ratio of the power or intensity of the output to the power or intensity of the input. Attenuation values can be anything from 0 decibels, which means a perfect or unobstructed signal, to very large negative numbers. A perfect attenuator with 0 dB of attenuation has a transmission line with an infinite number of taps.

Risetime How to read an oscilloscope

Rise time is the amount of time it takes for an electronic signal to go from 10% of its maximum to 90% of its maximum. The speed at which the signal goes from a high level to a low level is the fall time. Rise and fall times can also slow down how quickly a driver can change the current going to a load. The practical success of a project can depend a lot on how well the output current frequency response is evaluated.

Sample Rate, Memory Depth and Time

A Digital Scope's ability to make long captures is directly tied to the relationship between the instruments sample rate and memory depth. Sample rate is the speed at which the analog-to-digital converter inside the scope records the voltage level of a signal. In an oscilloscope, the length of the waveform in time you capture is closely related to the sample rate and memory depth. The faster the sample rate, the shorter the waveform in time you capture. The more memory you can use, the more time you can store.

By how long the waveform is, you can figure out the sample rate and the amount of memory. Most of the time, we add more memory so that we can keep using the highest sampling rate for as long as possible. For example, with 12 million points of energy, a 1Gsa/second scope can record up to 12 milliseconds of data. To record a 1000-second wave at 2000 samples per second, you need 2 million memory points.

Sample Rate How to read an oscilloscope

Vertical, Horizontal and Trigger Controls

There are three parts to a basic oscilloscope: the vertical system, the horizontal system, and the trigger system. Each system helps the oscilloscope reconstruct a signal as accurately as possible. An oscilloscope's front panel is split into three parts called Vertical, Horizontal, and Trigger. Depending on the model and type of oscilloscope you have, it may also have other parts.

Controls How to read an oscilloscope

Horizontal controls allow for positioning the signal on the time X axis as well as adjust the time-based scaling options. The horizontal menu provides selections for delayed sweep as well as YT, XY and roll mode. Vertical controls allow for the adjustment of amplitude scaling settings, bandwidth limits and probe attenuation as well as positioning the signal on the vertical axis.

The trigger function of an oscilloscope makes sure that the horizontal sweep starts at the right point in the signal. This is very important for figuring out what a signal is. Trigger controls let you keep waveforms from repeating and record single-shot waveforms. By showing the same part of the input signal over and over, the trigger makes waveforms that repeat look static on the oscilloscope display.


Digital and Mixed Signal Oscilloscopes, Spectrum Analyzers and RF Signal Generators, Arbitrary waveform Generators, Sensitive Measurement Products, and Data Acquisition Systems comprise Rigol's product portfolio. Their test solutions combine superior product performance, quality, and innovative product features. Applications of their product include technical education, embedded design, WiFi integration, electromagnetic compatibility, and manufacturing.