New Concept for Power Compression Improvement of GaN Cascodes in Broadband Power Amplifiers

This paper presents a new concept to reduce high-frequency power compression in broadband power amplifiers using cascodes (CCs). Although CCs are well suited for broadband power amplifier designs, at higher frequencies, the gm-compression of the common-gate stage reduces the compression point. To reveal the improvement of the new CC concept compared with that of the concept of the conventional CC topology, two monolithic microwave integrated circuit feedback amplifiers were designed using an AlGaN/GaN technology on SiC. Both designs offer a 13-dB gain with a bandwidth of 17 GHz and a small-signal matching of better than -10 dB. The new CC design significantly improves the gain compression of the feedback power amplifier at higher frequencies without changing the small-signal performance. The 0.5 dB compression point is improved by ≈2 dB at the upper band edge using the proposed concept. Also, the P1dB is improved by 1 dB over the conventional CC design. All PA designs exhibit a saturated output power of 1 W. At low frequencies, the linearity can be enhanced as well, by increasing the harmonic distance second order and harmonic distance third order up to 5 dB. Despite the additional active circuit, a minimum noise figure of 3.5 dB is achieved for both designs.