Abstract
In recent years, common-mode resonance at twice the oscillation frequency has been proven to be an effective method to improve the FoM and phase noise performance of LC VCOs [1]–[4]. In [2], the implicit common-mode is proposed to merge the common-mode resonance tank into the VCO's main tank to save the chip area as shown in the left of Fig. 1. The VCO in [3] boosts both the common-mode impedance at 2ND harmonic and differential-mode impedance at 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RD</sup> harmonic frequency to improve the FoM as shown in the middle of Fig. 1. However, manual harmonic tuning to align those harmonic resonance frequencies is needed in both VCOs in [2] and [3] to uphold an optimal performance over the tuning range. To avoid the manual harmonic tuning, an extra resonator is added to the main tank in [4], improving phase noise over a wide bandwidth. However, the extra head resonator inevitably increases the VCO's chip area.
Published Version
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