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In this study, we proposed a pre-distorted driver of a power amplifier in which the driver stage can serve as a pre-distorter of the power stage. In order to secure the linearity of the power amplifier, AM-PM distortions according to the input power of the common-source (CS) and two stacked-FET structures were analyzed and compared with the simulated results. Based on the analyzed AM-PM distortions of the two structure, it was verified that the driver stage with CS structure can act as a pre-distorter of the power stage with the two stacked-FET structure by optimizing the bias voltages of the two structures. The Ka-band power amplifier was designed with a 65-nm CMOS process to verify the feasibility of the proposed pre-distorted driver stage. At 28 GHz, the measured P1dB, saturated output power (P $_{\mathrm {SAT}}$ ), and peak power-added efficiency (PAE) were 18.6 dBm, 19.7 dBm, and 32.9%, respectively. The measured small signal gain was 24.1 dB. When 5G-NR modulation signals (64-QAM, 100-Msym/s, 9.7-dB PAPR) were used, under conditions where the EVM was less than –25 dB, the measured output power and ACLR were 13.3 dBm and –29.4 dBc, respectively.

In this study, a 3-bit digital step attenuator (DSA) based on the GaN HEMT process was designed. A distributed structure was adopted to secure stable RF characteristics within a given operating frequency band. To suppress the phase variation according to the attenuation level in the distributed structure, a technique that utilizes a tail capacitor connected in series with a switch transistor has been proposed. The theoretical functionality of the proposed technique has been verified with a numerical analysis. For experimental feasibility verification of the proposed structure, a 3-bit DSA was designed using a 150-nm GaN HEMT process providing two metal layers. The chip size of the designed attenuator was 0.95 mm2. The measured total attenuation range was 7 dB with 1 dB step. It was confirmed that the measured insertion loss was suppressed to less than 1.7 dB in the range of 26.5 to 40.0 GHz. The RMS amplitude and phase errors were measured to be less than 0.16 dB and 4.87°, respectively.