A compact integrated impedance-matching output transformer with multiple primary windings connected in parallel

Multiple centre-tapped primary windings 407,408 of the output transformer for a CMOS RF power amplifier 402,403 are connected in parallel. The terminals 420,421 of the primary windings are driven by differential outputs of the amplifier. The transformer may have a planar, stacked or multi-layer structure (figures 9-12). Series or parallel resonant circuits (figure 8) may be coupled to centre taps of the primary windings to suppress or enhance harmonics. The amplifier may comprise several amplifiers each with outputs feeding the primary windings (figure 3).