A 50W Highly Linear 3-Way Integrated Wideband Doherty PA for Small-Cell Application

This article presents the realization and measurement results of a 50W highly linear 3-way integrated Wideband Doherty P A using LDMOS (laterally diffused metal oxide semiconductor) technology. The efficiency / linearity compromise is highly optimized for a power range from 12 dB OBO (output back-off) to 8 dB OBO for the frequency range from 1800 MHz to 2200 MHz. The proposed 3-way integrated combiner uses Cds (drain-to-source capacitance) absorption method to achieve wideband impedance transformation. Linear gain around 16 dB with efficiency >41 %, raw ACPR (Adjacent Channel Power Ratio) of −40dBc was measured at 12 dB back off. At 8 dB back off, efficiency of 45-49% with a raw ACPR< −35 dBc was measured with WCDMA signal. For the optimized Doherty, the measured AMPM(amplitude-to-phase) values at P3dB level has a minimal spread < 5 deg and consistent shape in a fractional bandwidth of 20%. At 39 dBm Pout, 8 dB OBO, the DPA was corrected to <-55 dBc with 60 MHz ISBW in the band B1, B2, B3. The highly linear performance demonstrates that the designed RFIC presents a suitable candidate for multi-band MIMO application for the selected frequency band from 1800 MHz to 2200 MHz.