Transformer-Based Input Integrated Matching in Cascode Amplifiers: Analytical Proofs

The transformer-based input integrated matching allows the realization of the simultaneous optimum noise and maximum power transfer input impedance matching in cascode amplifiers by exploiting the mutual coupling between the two spirals of an integrated transformer. This technique has been adopted to design LNAs operating in the microwave and millimeter-wave frequency ranges; however, the analytical proofs are still missing. This paper addresses for the first time a complete and in-depth study of the circuit topology and design technique in order to provide the analytical proofs. In-depth analyses are also used to get useful circuit insights, derive effective design equations, and carry out a direct comparison with the most widespread cascode low-noise amplifier with inductive degeneration through circuit design under the same conditions.