A new "series-type" Doherty amplifier for miniaturization

A new topology of Doherty amplifier is proposed to reduce the circuit size by eliminating the bulky 3 dB 90° hybrid coupler. Unlike the classical Doherty amplifier, the carrier and peak amplifiers are connected in series together with an impedance-inverting network connecting the outputs of both amplifiers. A simple matching circuit between the peak and carrier amplifier replaces the input hybrid coupler. In this way, the need for an input hybrid coupler is eliminated, facilitating integration and miniaturization. The fabricated 2.45 GHz amplifier module using the proposed topology demonstrates enhanced efficiencies in the low- to mid-power ranges and shows good gain flatness. This approach is promising for highly-integrated Doherty-type amplifiers for handset applications.