Bonding Wire Inductance VCOs

Abstract

From the phase noise calculations in the previous chapter, clearly the best inductor for a low-noise oscillator is a passive inductor with a series resistance as low as possible. This is an obvious problem for fully integrated VCOs since the only type of passive inductor that is commonly used in ICs is the so-called planar inductor: a spiral metal trace is laid out in one or more of the standard available routing levels of the technology. But these inductors are more known for their parasitics than for their behavior as an inductor. They have a rather high series resistance, a low self-resonant frequency due to capacitive coupling to the substrate, and at high frequencies they suffer from resistive losses in the underlying silicon substrate. Optimization of these spiral or planar inductors for oscillator designs will be discussed in chapter 5.