An integrated phase-locked loop (PLL) with low phase noise is presented, which is robust with respect to variations of device parameters with process, supply voltage, and temperature (PVT). The low-noise CMOS voltage-controlled oscillator (VCO) employs two varactors for fine and coarse tuning. By using a CMOS charge pump with output biasing, the dc fine tuning voltage of the VCO and the loop dynamics of the PLL are well defined and fairly independent of PVT variations. Device noise in the charge pump and linearity of the phase detector are much improved by a two-transistor charge pump architecture for fine tuning. We measured a phase noise below -131 dBc/ Hz at 10 MHz offset and below -94 dBc/Hz at 10 kHz offset over a tuning range of 1.2 GHz. An integrated phase error below 0.6°was measured, corresponding to an rms jitter below 160 fs. The chip was produced in a 0.25 lm low-cost SiGe BiCMOS technology, occupies a chip area of 2.25 mm 2 and draws 60 mA from a 3 V supply.
We present an integrated fractional-N lownoise frequency synthesizer for satellite applications. By using two integrated VCOs and combining digital and analog tuning techniques, a PLL lock range from 8 to 12 GHz is achieved. Due to a small VCO fine tuning gain and optimized charge pump output biasing, the phase noise is low and almost constant over the tuning range. All 16 sub-bands show a tuning range above 900 MHz each, allowing temperature compensation without sub-band switching. This makes the synthesizer robust against variations of the device parameters with process, supply voltage, temperature and aging. The measured phase noise is -87 dBc/Hz and -106 dBc/Hz at 10 kHz and 1 MHz offset, respectively. In integer-N mode, phase noise values down to -98 dBc/Hz at 10 kHz and -111 dBc/Hz at 1 MHz offset, respectively, were measured.
Submarine cables have complicated structures and high production process requirements. In order to make sure the submarine cables to operate safely and reliably, this paper takes into account how the different laying conditions of submarine cables affect the maximum allowable ampacity. A 110kV YJQ-1×500 XLPE submarine cable is taken as the research object, based on the finite element method, the electromagnetic-thermal coupling models of the submarine cable laying in underwater soil, seawater and pipeline is established respectively in Comsol Multiphysics to study their thermal field and ampacities. The results indicate that the laying conditions would affect the cables’ heat dissipation, submarine cable lays in seawater has the highest ampacity and lays in the pipeline in landing section of the cable has the lowest ampacity. Moreover, the variation of temperature of seawater would also influence the ampacity of the submarine cable.
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