What is Sample Rate and What to Be Cautious Of

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The simple lesson with sample rate is that more is better. But did you know that the method of achieving that high sample rate can actually distort your signal and throw off your measurements? We all know sample rate as one of the banner specifications of an oscilloscope. We’ve been taught that the higher the sample rate, the better the measurement will be. Don’t get me wrong, this still holds completely true. However, there is something to be warry of. Do you know exactly how your oscilloscope is achieving that high sample rate? That could make a huge difference in your measurements. Sample rate is the rate at which the sampler collects samples. The sample rate is measured in samples per second. This rate ultimately affects the signal you see on screen. In a well-designed oscilloscope, samples will occur at a consistent rate with no variation. Too low of a sample rate makes your signal look distorted and lacks signal detail. Under sampling could easily cause you to think that your signal is clean, when in fact it has several issues. With a high sample rate we see a nice smooth representation of our signal and can make accurate measurements on it. So, the key point here is the higher the sample rate, the higher the resolution of the trace. This will allow you to make more accurate measurements of your signal and catch any errors that may exist. However, you have to be warry of the method being used to achieve that high sample rate. This method can make or break your measurements, quite literally. The problem I’m referring to is called Interleave Distortion. To achieve high sample rates some scope vendors use 2 or more ADCs. The synchronized ADCs must have the same vertical gain, offset, and frequency response. If these interleaving requirements aren’t satisfied, the phase delay clocks will not be aligned causing inconsistent spacing between samples. The misaligned clocks cause the samples to be collected at varying intervals. Much like the distorted signal with too low of a sample rate that we saw earlier, any measurements you make on a signal like this will be completely inaccurate. So, in this case, the higher sample rate actually produces a less accurate waveform. However, there are many cases where interleaving is implemented correctly, like with the Keysight S ... https://www.youtube.com/watch?v=nLmB1qcXT4Q