10 tricks that extend oscilloscope usefulness

-May 09, 2014

Modern mid-range oscilloscopes have more features than most engineers ever use. This article summarizes ten oscilloscope applications that may surprise you. In any event, you may find them useful.

Use the oscilloscope’s fast edge feature and math operations to make frequency response measurements

Frequency response measurements require a source signal that has a flat spectrum. By utilizing the fast edge test signal of the oscilloscope as a step source it is possible to derive the impulse response of the device under test using the scopes derivative function. This can then be applied to the FFT (Fast Fourier Transform) function to obtain the frequency response. Figure 1 shows the steps in the process for both the frequency response of the input signal and that of a 37 MHz low pass filter.

Figure 1. Deriving the frequency response of a filter by applying the fast edge test signal to the filter input (upper left), taking the filter output (upper right trace) differentiating it (right center), and finally taking the average of the FFT (lower right). The spectrum on the lower left trace shows the frequency flatness of the differentiated step input.

The fast edge test signal has a rise time of about 800 ps and a bandwidth of about 400 MHz which is much greater than the 100 MHz span of this measurement.

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