A mm-Wave quadrature VCO based on magnetically coupled resonators

Search of a compact quadrature generator at around 60GHz with low phase noise at moderate power is the topic of this work. Discarding a double-frequency VCO followed by dividers-by-two given the high frequency range of operation, the most suitable topology borrowed by RF solutions is represented by cross-coupled LC voltage-controlled oscillators. However, the oscillation frequency dependence on the biasing current makes it susceptible to phase noise, close-in in particular. At mm-Waves, this is exacerbated by core devices of small dimensions to such an extent that 1/f noise remains dominant up to more than ~10MHz, making it unsuitable for stringent applications. On the contrary a ring of two VCOs magnetically coupled to each other has an oscillation frequency dependence on inter-stage passive components only, low 1/f noise together with good quadrature accuracy. The quadrature oscillator has been realized in a 65nm CMOS technology and prototypes show the following performances: 56-to-60.3GHz tunable oscillation frequency, phase noise better than -95dBc/Hz at 1MHz offset in the tuning range, 1.5° maximum phase error while consuming 22mA from a 1V supply.