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High-frequency oscillators developed in CMOS technologies for space applications are vulnerable to single-event transient (SET) effects caused by ionizing radiation strikes. We have designed a phase-locked loop (PLL) with a quadrature phase current-controlled oscillator (QCCO) to overcome this limitation. The feedback mechanism in the QCCO helps in improving the SET tolerance, while parallel coupling achieves wide tuning range. The oscillator is irradiated with laser pulses at a certain pulse repetition frequency, which results in spurious tones in the oscillator output spectrum. The strengths of these spurs are used for evaluating the SET tolerance of the oscillator. Under identical conditions, experiments show that the QCCO has an average of 15-dB lower spur level compared to a conventional single-phase $LC$ voltage-controlled oscillator (SVCO) and an SVCO-based PLL loses lock at a certain laser pulse energy, while the QCCO-based PLL remains in the locked state. These results confirm that the QCCO significantly improves the reliability of high-frequency PLLs in radiation environments. [ABSTRACT FROM AUTHOR] more...

In this brief, we present a wide operating range quadrature phase LC oscillator with seamless tunability. A combination ofseries-couplingandparallel-couplingbetween two resonant LC tanks has been employed. Series-coupling ensures that the desired phase sequence is achieved. At the same time, variable strength parallel coupling network helps in getting a wide tuning range. Seamless tunability across the operating range is achieved by changing the polarity of the parallel coupling network without hard switching. This approach helps in getting a wide operating range without usage of varactors which are lossy at high frequencies. A VCO with the proposed architecture has been designed and fabricated in a 65-nm (low-leakage) CMOS technology. Silicon measurement results show a tuning range, with seamless tunability, of 44.7% around the center frequency of 14.3 GHz. To the best of our knowledge, this is the widest operating range LC oscillator with seamless tunability reported till date. The VCO exhibits an FOMTof 185 dB, which is comparable to the state-of-the-art reported in the literature for oscillators operating above 10 GHz. [ABSTRACT FROM AUTHOR] more...