This paper presents a study on the cut-off frequency of the low noise cascode amplifier with transformer-based input integrated matching. It shows that two poles of the short-circuit current gain are affected by the inductance of the secondary spiral inductor of the integrated transformer, and that it is possible to extend the cut-off frequency by means of a proper sizing. The results of the theoretical analysis are confirmed by circuit simulations in a 180nm CMOS technology commercially available.