Bandwidth is defined as the range of frequency for which the gain of the vertical amplifier does not drop more than 3 dB, from its zero frequency value. Bandwidth and rise time are related to each other and this relation plays an important role in the transient analysis of the waveform.

Consider the waveform to be observed on a C.R.O. to be of pulse type. Due to ringing effect, the waveform observed on C.R.O. is as shown in the Figure below:

Figure: Rise Time

Before achieving its peak value, the waveform shows an overshoot and oscillations during transient period. The time required by the waveform to rise from 10% to 90% of its peak value is called Rise time (tr), the bandwidth is inversely proportional to rise time and the relation is given by,

$B.W.=\dfrac{K}{t_r} \approx \dfrac {0.35}{t_r}$

Bandwidth is generally specified in MHz from which rise time of C.R.O. can be obtained. For example, for a C.R.O. having bandwidth of 100 MHz, the rise time is

$t_r = \dfrac{0.35}{100 \times x^6}=3.5 ns$

Rise time is important for time domain measurements while the bandwidth is important for frequency spectrum measurements.