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When Vin = Vout the switching threshold or gate threshold Vm can be pointed out in VTC curve and obtained graphically from the intersection of the VTC with the line given by Vin = Vout as shown in Fig below In this region both PMOS and NMOS are always saturated. As,

Thus the gate threshold voltage is dependent on the βp/βn ratio. If we want to change this Beta ratio we have to change the dimensions of the transistor from the Figure below, it is clear that as the ratio βp/βn is changed the transitions region shifts.