EMC Question of the Week: July 28, 2025
A signal measured on a digital oscilloscope is sampled in the time-domain and displayed in the frequency domain. The resolution bandwidth in the frequency domain is primarily determined by the
- acquisition time
- sampling rate
- windowing function
- scope bandwidth
Answer
The best answer is “a.” The Δf between samples in the frequency domain is the inverse of the acquisition time. To achieve greater resolution in the frequency domain, it is necessary to sample the signal for a longer period of time. For example, if the signal is sampled for 1 millisecond, the samples in the frequency domain will be spaced 1 kHz apart. If the signal is sampled for 100 microseconds, the Δf between samples in the frequency domain will be 10 kHz.
The sampling rate has no effect on the resolution in the frequency domain. However, higher sampling rates extend the high-end of the frequency-domain representation of the signal. To avoid aliasing, the signal cannot have significant power at frequencies greater than half the sampling rate.
The windowing function helps to suppress artifacts caused by any sudden change in the signal amplitude as the acquisition period starts and stops.
The scope bandwidth dictates the maximum bandwidth of signals that can be accurately measured and displayed on the oscilloscope but does not affect the resolution bandwidth.
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