Introduction to oscilloscope related terms (Part 2)

Oscilloscope Performance-Related Terminology

The following terms may be used when you discuss oscilloscope performance with your friends. Understanding these terms can help you evaluate and compare the performance of different models of oscilloscopes.

bandwidth:

Bandwidth is the primary indicator of an oscilloscope. This indicator tells us the frequency range of the signal that the oscilloscope can accurately measure. When the signal frequency reaches a certain level, as the signal frequency increases, the oscilloscope's ability to accurately measure the signal will weaken.

The bandwidth of an oscilloscope refers to the frequency point at which the amplitude of a sine wave is attenuated to -3dB (70.7%) when a sine wave is added to the input of the oscilloscope. If we use an oscilloscope with a bandwidth of 100MHz to measure a sine wave with an amplitude of 1V and a frequency of 100MHz, the actual amplitude obtained will be no less than 0.707V.

The higher the bandwidth of the oscilloscope, the more accurate the actual measurement will be. Of course, the price and cost will also be higher. So what bandwidth do we need for an oscilloscope? Generally, 5 times the maximum frequency of the measured signal is the most suitable bandwidth.

Rise Time:

Rise time is another parameter that describes the frequency range that an oscilloscope can measure. When you want to measure pulses and edges, rise time may be a more appropriate performance parameter to consider. When the rise time of a pulse is faster than the nominal rise time of the oscilloscope, the signal cannot be measured accurately.

Vertical scale:

The vertical scale refers to the voltage value of each grid on the ordinate of the oscilloscope, and also indicates the degree to which the vertical amplifier can amplify weak signals. It is usually indicated by mV/div or V/div. The minimum vertical scale of a general oscilloscope is 1mV per grid.

Time base:

The time base refers to the time of each grid on the horizontal axis of the oscilloscope.

Gain Accuracy and Vertical Resolution:

Gain accuracy refers to the accuracy of the vertical system attenuation or amplification of the signal. The gain accuracy of the commonly used oscilloscope is <±2%

Vertical resolution refers to the accuracy with which the oscilloscope's analog-to-digital converter converts the input voltage into a digital value. Vertical resolution is expressed in bits, for example, the vertical resolution of the Microsonic STO series oscilloscope is 8 bits. Computational techniques can improve effective resolution.

Sampling Rate:

The waveform displayed by the oscilloscope is actually composed of points one by one. The sampling rate represents the ability of the oscilloscope to capture how many sampling points per second. The more sampling points the oscilloscope can capture, the closer the waveform is to the signal itself and the less likely it is to be distorted. Most oscilloscopes are rated at their maximum sampling rate. If you want to observe a waveform for a long time, the minimum sampling rate of the oscilloscope is very important because the sampling rate is based on the oscilloscope's memory depth (record length) and changes with the length of the waveform record.

Memory Depth (Record Length):

The memory depth parameter indicates how many waveform points the oscilloscope can display on one screen. Some oscilloscopes support adjusting the memory depth. Since the oscilloscope can store a limited number of sampling points, we must make a trade-off between waveform details and waveform duration when testing. Choose a short waveform, but you can see more waveform details. Or choose to record a long waveform, but it may cause waveform distortion.

Waveform capture rate:

An oscilloscope can capture signals and then display them on the screen through calculation. However, the two actions of capturing signals and calculating and displaying signals cannot be performed at the same time. In other words, when the oscilloscope is calculating and displaying signals, it will not capture signals, and this part of the signal will be lost, which is also called dead time. The number of times an oscilloscope can capture a waveform per second is the waveform capture rate of the oscilloscope, expressed in waveforms per second (wfms/s). The sampling rate indicates the oscilloscope's ability to capture the number of data points per second, and the waveform capture rate indicates how fast the oscilloscope can collect waveforms per second.

An oscilloscope with a high waveform capture rate can better observe signal characteristics and greatly increase the probability of the oscilloscope quickly capturing transient abnormal signals, such as jitter, runt pulses, glitches, and transition errors.

trigger:

The trigger function of the oscilloscope synchronizes the scan at the correct signal point, which can stabilize the repetitive waveform or capture a single waveform. By repeatedly displaying the same part of the input signal, the repetitive waveform can be stably displayed on the oscilloscope screen. If each scan starts from a different position on the signal, the waveform on the screen will be very messy and difficult to observe and calculate.

No triggered screen