A 48 GHz fully integrated differential VCO in InP DHBT technology

We describe the development of a 48 GHz fully integrated differential VCO, using InP/InGaAs double heterojunction bipolar transistors (DHBTs), for 40 Gbit/s optical communication systems. This VCO is based on a balanced Colpitts-type topology where a coplanar transmission line is used as the inductive resonator element. The oscillation frequency is tuneable by varying the base-collector junction capacitance of DHBTs without using any external varactors. The VCO exhibits 46.4-49.5 GHz (6.5%) tuning range over a tuning voltage range of 1 V. The circuit provides a non-corrected single-ended output power between -10.5 and 13.5 dBm while the phase noise varies between -75 and -80 dBc/Hz at 1 MHz offset.