X - to Q-Band MMIC Predistortion Linearizers With Tunable Frequency-Dependent Phase Conversion Capacity Using GaAs HEMT Technology

A new design method of microwave monolithic integrated circuit (MMIC) predistortion linearizer compatible with the standard gallium arsenide (GaAs) high-electron-mobility transistor (HEMT) technology is proposed for wideband cancellation of power amplifier (PA)'s frequency-dependent amplitude-modulation (AM)/phase-modulation (PM) distortion. Adopting the dual-branch vector synthetic topology, a modified reflective topology is proposed to improve the extracted nonlinear signal with higher gain expansion dynamic range, and the reversed-biased HEMT-based varactor is deployed to realize variable phase tuning capacity. Phase and time-delay allocation between the linear and nonlinear branches is analyzed to achieve arbitrary monotone frequency-dependent phase predistortion performance. Four linearizer MMICs are designed and fabricated using a commercial 0.15- ${\mu }\text{m}$ GaAs HEMT process based on the proposed method and design procedure, in which the $X$ - and $Q$ -band chips are dedicated for positive phase conversion with the increase in input power, and the $Ku$ - and $K$ -band chips are for negative phase conversion. The $X$ -, $Ku$ -, and $Q$ -band designs are capable of exhibiting monotone increasing phase conversion with frequency, while the $K$ -band design exhibits monotone decreasing phase conversion with frequency. All these results are validated by on-chip measurement. Moreover, measurement conforms that consistent predistortion performance can be maintained by tuning the biasing voltage under different temperatures; static and dynamic measurements are performed with the designed linearizers applying to PA modules, validating the wideband cancellation capacity of frequency-dependent AM/PM distortion and the linearity improvement under wideband modulated signal excitation.