Relation between Bandwidth and Rise time

Relation between Bandwidth and Rise time:

The frequency range from f_L to f_H is called bandwidth of the amplifier. Usually f_L<<f_H. So we can approximate the equation for bandwidth as follows,

The relation between rise time with upper frequency as,

So we can relate bandwidth with rise time as follows,

Problem:

If the rise time of BJT is 35ns, what is the bandwidth that can be obtained using this BJT.

Solution:

t_r = 0.35 / f₂ = 0.35 / BW

BW = 0.35 / t_r = 0.35 / (35 * 10^-9) = 10MHz