Low phase noise MMIC oscillators in InGaP HBT technology

The voltage controlled oscillator (VCO) is a key-element in radio links. Phase instability, i.e, phase noise, in the VCO is one of the main bottle necks preventing more advanced modulation formats required for increased data rate. It is well known from Leeson's classical paper [1] that low phase noise oscillators require high-Q resonators. Very low phase noise can be reached using dielectric resonant oscillators (DROs) [2] known for their high-Q, but it is more economic to use a VCO with integrated tank [3]. In this respect tuned LC oscillators, preferably in HBT technology, associated with low flicker noise, is the best candidate. At this date the lowest phase noise among MMIC VCOs with integrated tank is achieved in InGaP HBT technology [3], [4]. However, there is still room for improvement. By having impact on the varactor geometry it is possible to design special finger varactors [5] with better Q-factor, and hence capability of providing lower phase-noise.