In this article, we present the modelling, design and characterization of a 3-Vppd linear-output-swing 90-GBd PAM-4 modulator driver, realised in III-V Lab's in-house 0.5-μm InP DHBT technology (380/520-GHz ${f_{T}/f_{{\max}}}$, 4.2-V ${BV_{\text{CE0}}}$). The driver exhibits 13-dB equalisation capabilities at 95 GHz with a bandwidth well beyond 110 GHz. It features a 0.67-W power consumption, resulting in a 1.5-GBd FoM with good output signal quality. To the best of our knowledge this linear driver shows the highest >64 GBd PAM-4 performance in current state-of-the-art, without DSP nor pre-emphasis. We also report on a newly developed 0.5-μm InP DHBT technology and its modelling using small-value external parasitic EM-simulation extraction, showing improved high-frequency prediction accuracy at circuit level.