After the discussion of bonding wire inductors in the previous chapter, we will now investigate the more “normal” type of integrated inductor, i.e. the spiral or planar inductor. This is indeed the dream of every RF VCO designer : be able to use a simple spiral metal track laid out in the standard metal routing levels of the IC as an inductor. If the required specifications can be achieved with this technique, the cost will certainly be lower than a design using bonding wire inductors. The die area can be reduced by an order of magnitude, and the variations in inductance value due to nonuniform bonding are of course no longer present. Once the processing masks are made, the inductor geometry will always be the same, since the processing accuracy (< 0.1 µm) is certainly negligible with respect to the size of the coil (≈ 100µm). So the inductance value variations do no longer have to be compensated for by the VCO tuning range.
KeywordsPhase Noise Series Resistance Eddy Current Parasitic Capacitance Magnetic Field Effect
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