Design of a system-in-package based low phase noise VCO using 3-D integrated passives on a multilayer liquid crystalline polymer substrate

This paper presents the design of a transformer based LC oscillator in a novel multilayer laminate-type process technology that uses multiple layers of liquid crystalline polymer (LCP) dielectric material. The VCO core employs a lumped-element transformer as the resonator to achieve low phase noise at low power consumption. The VCO is designed at 1.9 GHz and measures a phase noise of -116 dBc/Hz @ 100 KHz offset from the carrier at 12 mW of DC power consumption, inclusive of the output buffer. The paper uses a comparative experimental approach to determine the key passive elements of the resonator that significantly contribute to the VCO phase noise. To verify the approach, two identical Si bipolar VCOs with resonators of different group delay were fabricated on a novel six metal layer LCP process with each VCO occupying an area of 5.3 × 5.8 mm₂ (including RF output and supply pads). This paper experimentally verifies that the parasitic EM coupling between the resonator components at frequencies well beyond the third harmonic causes the VCO frequency to shift to the frequency of coupling. A full-wave EM solver and a macro-modeling tool were used to develop a broad-bandwidth circuit model (∼ 10 GHz) of the resonator. This model was used in circuit simulations to analyze and eliminate the spurious oscillatory behavior of the VCO due to the EM coupling between the resonator elements.