Kazutaka Inoue

A 33W GaN HEMT Doherty amplifier with 55% drain efficiency for 2.6GHz base stations

A 33W average output power Doherty power amplifier (PA) for 2.6GHz band was developed using compact package advanced GaN HEMTs which have Cds reduced 20%. A small-footprint Doherty network was successfully designed with plain small signal analysis, and the method was very practical. The Doherty PA exhibited a saturation output power of 52.5dBm (178W) and a saturated drain efficiency of 65.6%. The Doherty PA also achieved a drain efficiency of 55%, an ACLR of −52.8dBc and a power gain of 13.8dB at the average output power of 45.2dBm (33W) with 4-carrier W-CDMA signal at 2.6GHz using commercially available digital pre-distortion system. These excellent performances show good suitability for 2.6GHz band basestations (BTS), for example, W-CDMA, LTE and WiMAX, and small-sized circuit structure contributes to realize compact remote radio head type of BTS.

A 65 % drain efficiency GaN HEMT with 200 W peak power for 20 V to 65 V envelope tracking base station amplifier

A 200 W GaN high electron mobility transistor (HEMT) device was developed for envelope tracking (ET) base station amplifier. The device, which consists of a single die of 0.6 um-gate GaN HEMT of 43 mm gate periphery, has a saturated current of 680 mA/mm together with sufficiently high break down voltage of 300 V. We have estimated the average power efficiency of ET amplifier by using the GaN HEMT device over 20 V to 65 V drain bias range. As a result, the estimated average power efficiency reaches at 65.2%. Excellent results of RF high temperature operating life (RF-HTOL) test were also obtained. To the best of our knowledge, this is the highest drain voltage operation of the GaN HEMT device, allowing significant improvement of efficiency for ET amplifiers.

A 9.5–10.5GHz 60W AlGaN/GaN HEMT for X-band high power application

In this paper, we report our result of a 60W AlGaN/GaN HEMT with the operating frequency in X-band. The device technology is extension of well-established Eudyna commercial L-/S-band AlGaN/GaN HEMT technology. The device shows output power of over 60W and a high linear gain of 9.6dB in wide frequency range of 9.5-10.5GHz, operating at 40 V drain bias voltage with the pulsed conditions at a duty of 10% with a pulse width of 100 musec. The results show the developed 60W AlGaN/GaN HEMT has high power capability covering practical frequency range for X-band high power applications with proven device technology.

High power and high efficiency GaN-HEMT for microwave communication applications

Microwaves have been widely used for the modern communication systems, which have advantages in high bit rate transmission and the easiness of compact circuit and antenna design. Gallium Nitride (GaN), featured with high breakdown and high saturation velocity, is one of the promising material for high power and high frequency devices, and a kW-class output power has already been achieved [1]. We have developed the high power and high efficiency GaN HEMTs [2–5], targeting the amplifier for the base transceiver station (BTS). This presentation summarizes our recent works, focusing on the developments for the efficiency boosting and the robustness in high power RF operation.

An ultra broad band 300 W GaAs power FET for W-CDMA base stations

An ultra broad band 300 W power FET for W-CDMA base stations systems has been developed. This FET consists of four newly developed 260 mm total gate width (Wgt) chips fabricated with quasi enhancement-mode (E-mode) structure. The broadband performance is obtained by means of multi-stage quarter wave length transformers, which are formed on high dielectric constant thin substrates. The developed FET demonstrated the performance of 300 W (54.8 dBm) saturated power and 11 dB linear gain at 2.15 GHz. In addition 0.2 dB power gain flatness was achieved across 180 MHz bandwidth (at output power 47 dBm). The group delay of this device was 2.14 nanosecond and the phase flatness was less than 0.35 degree between 2.11 and 2.17 GHz. This is the highest output power and widest bandwidth device ever reported.

Linearity Improvement of GaN HEMT for RF Power Amplifiers

The linearity has become more important to expand GaN HEMTs into microwave amplifier markets. This paper describes the outline of the large signal model of our 0.4μm AlGaN/GaN HEMT, considering the pulse biased 24 V operation. The analysis which utilizes the constructed Angelov model proved that the intermodulation distortion (IMD) of more than 10 dB backed off region is determined by the sub-threshold gm profile, namely steep rising gm profile degrades IMD. Thus, we proposed a thin n-GaN layer inserted buffer structure (ini-buffer), which realizes the significant IMD improvement of 8 dB, in the backed-off region.