Understanding oscilloscope waveform thickness properties

The oscilloscope waveform reflects the actual electrical signal. When evaluating an oscilloscope’s performance, one of the key factors is its ability to accurately display the shape of the target signal. Assuming the oscilloscope has sufficient technical specifications—such as bandwidth, sample rate, and flat frequency response—the question arises: does a coarse or fine waveform indicate better performance? The answer, like many engineering questions, depends on the situation. To determine whether a waveform appears coarse or fine, it's essential to understand two critical attributes: the oscilloscope’s update rate and noise level. These characteristics help users assess how well the oscilloscope can represent the signal under test. **The Impact of Update Rate on Waveform Thickness** The update rate refers to how many waveforms the oscilloscope can acquire, process, and display per second. A higher update rate means the oscilloscope can capture and display more waveforms in a given time, increasing the likelihood of observing rare events or anomalies. Conversely, a lower update rate results in fewer waveforms being displayed, which may cause the waveform to appear thinner or less detailed over time. For example, consider two oscilloscopes with the same bandwidth but different update rates. One may show a thick waveform while the other shows a thin one. This difference can be attributed to their update rates. In one case, an oscilloscope with a high update rate (e.g., 1 million waveforms per second) will display a thicker waveform, capturing more details. Meanwhile, a slower oscilloscope (e.g., 60 waveforms per second) will show a thinner waveform initially. However, when using infinite persistence, both oscilloscopes will eventually display similar waveform thickness after a few seconds. **The Role of Oscilloscope Noise in Waveform Thickness** Noise plays a significant role in determining waveform thickness. Oscilloscope noise comes from internal components such as amplifiers, ADCs, and probes. It gets added to the signal and affects how the waveform is displayed. If the oscilloscope has high internal noise, the waveform may appear thicker, even if the actual signal is clean. To evaluate this, you can disconnect all inputs and set the oscilloscope to a 50 Ω or 1 MΩ input path. Enable infinite persistence and observe the waveform thickness. A thicker waveform indicates more internal noise. You can also measure the RMS voltage of the noise for a more precise assessment. **Understanding the Target Signal** The target signal itself may have varying levels of noise. Sometimes, it’s hard to tell whether the noise seen on the screen comes from the signal or the oscilloscope. The ADC cannot distinguish between the two, so it captures and displays both. To check, use the method above to evaluate the oscilloscope’s internal noise. Then, compare the waveform in normal mode versus infinite persistence mode to see how the noise affects the display. **Mitigating Noise and Improving Waveform Clarity** Oscilloscopes offer features like averaging and high-resolution mode to reduce noise. Averaging mode works best for repetitive signals, as it averages multiple acquisitions to smooth out random noise. High-resolution mode reduces noise by averaging adjacent samples, resulting in a clearer waveform. However, these modes may reduce the effective sampling rate and bandwidth. In summary, whether a waveform appears coarse or fine depends on several factors, including update rate, noise, and signal characteristics. Understanding these elements allows you to choose the right oscilloscope or adjust settings to achieve the best possible representation of your signal.

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