Multi-Layer Realization of Symmetrical Differential Inductors for RF Silicon IC´s

The performance of multi-layer differential inductors is compared with that achievable by single-layer ones, referring in particular to silicon technology. It is demonstrated that through a proper sequence of strips on metal layers, a saving of chip area and a notable increase in self-resonance frequency can be obtained, with only a limited reduction of the quality factor in comparison with a single layer structure of equal inductance. The solution is mainly interesting for applications like choke inductors in VCO´s, which require compact inductors of high values of inductance and tolerate moderate quality factors.