Volterra-Series-Based Distortion Analysis for Optimization of Out-of-Band Terminations in GaN HEMT Devices

摘要

This letter focuses on the critical device-level linearity issues resulting from out-of-band terminations for reliable distortion characterization in future Universal Mobile Telecommunications System–Long Term Evolution (UMTS–LTE). Using Volterra series technique, the key distortion sources arising from the envelope and harmonic components in 0.5-mm GaN HEMT were identified using commercial and in-house bias tees. With the designed in-house bias tee, the baseband performance, in comparison with the commercial bias tee, is tested through drain-bias sensing. In reference to the commercial bias tee, up to 99.3% reduction in drain modulation is achieved using the in-house bias tee. Memory-effect characterization of GaN HEMT exemplified the implications of baseband and second-harmonic load terminations, which was theoretically confirmed through Volterra series technique. Using the in-house bias tee, under two-carrier wideband code-division multiple-access excitation, up to $-$47-dBc 3rd-order intermodulation ratio (IMR3) is achieved at 13.5-dB backoff. This has resulted in a 5-dB IMR suppression together with the minimization of intermodulation-distortion asymmetry, confirming the possibility to achieve the 3rd Generation Partnership Project linearity specification at the device level.