This circuit models an Arduino digital output (0 to 5 V) connected to a transistor via a circuit board copper trace. The copper trace has a resistance of 0.3 Ohms and the transistor gate has a capcitance of 128 pF. This results in a time constant tau = RC = 38.4 pF. The 10%-90% rise and fall times are 2.2*tau each, so it takes T_min = ~4.4*tau = 169 ps to get from 10% to 90% and back again in the minimum possible time. The maximum switching frequency is therefore f_max = 1/T_min = 5.92 GHz.
