How is bandwidth defined for an oscilloscope?


Bandwidth determines an oscilloscope’s fundamental ability to measure a signal. As signal frequency increases, the capability of the oscilloscope to accurately display the signal decreases. This specification indicates the frequency range that the oscilloscope can accurately measure. IEEE 1057 defines electrical bandwidth as the point at which the amplitude of a sine wave input is reduced by 3 dB (approximately 30%) relative to its level at a lower reference frequency. In other words, bandwidth is specified at the frequency at which a sinusoidal input signal is attenuated to 70.7% of the signal’s true amplitude.

The optical bandwidth of a device or system is defined as the frequency at which the power out of the same device or system is one half as compared with a frequency near DC. The optical bandwidth, therefore, corresponds to the traditional electrical bandwidth of –6 dB.

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