What sampling rate is needed to measure various types of signals with an oscilloscope?
We input a signal to the oscilloscope through the probe. After the measured signal passes through the amplification, attenuation and other signal conditioning circuits at the front end of the oscilloscope, the high-speed ADC analog-to-digital converter performs signal sampling and digital quantization. The sampling rate of the oscilloscope is the analog-to-digital conversion of the input signal. The frequency of the sampling clock during conversion is, in layman's terms, the sampling interval. One sampling point is collected at each sampling interval. For example, a sampling rate of 1GSa/s means that the oscilloscope has the ability to collect 1 billion sampling points per second. At this time, its sampling interval is 1 nanosecond.
For real-time oscilloscopes, the real-time sampling method is currently commonly used. The so-called real-time sampling is to perform continuous high-speed sampling at equal intervals on the measured waveform signal, and then reconstruct or restore the waveform based on these continuously sampled sample points. In the real-time sampling process, it is very important to ensure that the sampling rate of the oscilloscope is much faster than the change of the signal being measured.
So how much faster is it? The Nyquist law in digital signal processing says that if the bandwidth of the signal being measured is limited, then when sampling and quantizing the signal, if the sampling rate is more than twice the bandwidth of the signal being measured, it can be completely Reconstruct or recover the information carried in the signal without aliasing.
Next, we will make the time tone smaller, so that the sampling rate will become larger. We will adjust the sampling rate until the sampling rate is 2 times and 10 times the signal frequency to observe the signal changes, that is, 2MSa/s and 10MSa/s. The signal on the left in the figure below is at a sampling rate of 2MSa/s. You can see that the frequency of the signal has changed back to 1MHz, which is the correct frequency value of the signal. But the original sine wave has become a triangle wave, and the waveform has been distorted. When the sampling rate changes to 10MSa/s, which is the signal on the right side of the figure below, you can see that the signal is getting closer and closer to a sine wave, but it is still not very beautiful.
