Understanding Oscilloscope specifications - Part 4

One of the most important specification of the Oscilloscope if the band width of the scope. Bandwidth determines the frequency range of the range of the signals that can be captured by the scope. So, when we talk about the bandwidth which frequency are we referring to? Is it analog signal or digital signal? When we look at the actual definition of the scope bandwidth it is actually the sine wave input which is considered for bandwidth definition. Bandwidth is defined as the frequency at which signal amplitude is attenuated to 70.7% of it's original level. This is similar to the 3-dB bandwidth we associate with the filter. The range of frequencies therefore can be measured from DC to 3-dB point. Whether the 3-dB frequency is the maximum frequency up to which the scope can actually be used is another point of discussion. While selecting the bandwidth of the scope, we use a bandwidth of up to 5 times the frequency we want to measure. For example, if we want to measure 50 MHz square wave, we prefer to have scope bandwidth of up to 250 MHz. Remember that we are talking about the exact signal reproduction on the oscilloscope.