DESIGN OF CMOS QUADRATURE VCO USING ON-CHIP TRANS-DIRECTIONAL COUPLERS

This work presents a quadrature voltage-controlled oscillator (QVCO) realized by on-chip trans-directional (TRD) couplers. The TRD coupler is implemented by sections of parallel-coupled lines connected by shunt capacitors periodically. The TRD couplers allow decoupling the DC path between input and output. Thus, it can make connections with active circuits easier, eliminating some off-chip biasing circuits. Since the quadrature signals are generated by 90°hybrid couplers, the oscillator core can be optimized for circuit performance without considering the generation of quadrature signals. A Ka band QVCO fabricated in CMOS 0.18 μm technology was designed to verify the effectiveness of the proposed QVCO structure. The measurement results reveal that the quadrature output signals of QVCO have about -1.52 dBm output powers with less than 1 dB amplitude imbalance and less than 6°phase difference in the frequency range of 31.9 to 32.7 GHz. The best measured phase noise of the QVCO is -110.6 dBc/Hz at 1 MHz offset from the center frequency. The figure-of-merit of the circuit is 187.5 dBc/Hz.