A GaN-HEMT with Floating LF Ground for Reverse Operation in Integrated RF Power Circuits

An integrated GaN-HEMT with floating low-frequency (LF) ground is presented. The floating LF ground enables reverse operation in RF applications making operation at offset DC and LF voltages possible. The RF is capacitive coupled to ground using MIM capacitors. On-chip RF isolation is established through a short-circuited RF $\lambda$/4-line. The transistor shows good agreement between measured and simulated small-signal behavior. Compared to standard two-port devices, the stability of the three-port device is more challenging, particularly in the LF to RF transition region but also in the RF band. The large-signal behavior is verified using load-pull measurements and shows 0.7 dB power degradation compared to the non-floating device but drain efficiency is almost unaffected. At 10 GHz the 1 mm gatewidth device shows a saturated output power of 35.4 dBm (3.5 W) and a maximum drain efficiency of 50 % is achieved. Floating operation at 20 V VDS shows identical small-signal results with the LF ground potential at 8 V as for grounded operation with the LF ground potential at 0 V.