Single Phase-locked Loop Research Articles

Broadband suppression of phase-noise with cascaded phase-locked-loops for the generation of frequency ramps

Abstract. The generation of analogue frequency ramps with non-fractional phase-locked-loops (PLL) is a cost effective way of linearising varactor controlled oscillators (VCO). In case that the VCO shows a high phase-noise level, a single non-fractional PLL is not able to suppress the phase-noise of the VCO sufficiently. The reason for this is the limited loopbandwidth of the PLL. In the field of precise measurements a high phase-noise level is mostly not tolerable. Examples of VCO-types with an extremely high phase noise level are integrated millimetre wave oscillators based on GaAs-HEMT technology. Both, a low quality factor of the resonator and a high flicker-noise corner frequency of the transistors are the main reason for the poor phase-noise behaviour. On the other hand this oscillator type allows a cost effective implementation of a millimetre-wave VCO. Therefore, a cascaded two-loop structure is presented that is able to linearise a VCO and additionally to reduce its phase-noise significantly.

A dual phase-locked loop for vortex flow metering

A vortex-shedding flow meter produces an approximately sinusoidal signal whose average frequency is proportional to volumetric flow rate. The frequency of vortex shedding varies over a large range (up to 1:100), depending on the size of the flow meter. The conventional frequency estimator uses a zero-crossing algorithm (ZC), but this approach fails at low flows, where the signal-to-noise ratio is poor. An alternative is to use a phase-locked loop (PLL), but typical single PLL designs cannot cope with a wide frequency range at high noise levels. This paper describes a dual PLL structure that can be used to track the vortex shedding frequency over the flow meter’s full range of operation. This dual PLL provides improved accuracy and tracking ability compared with the conventional zero-crossing algorithm.

The dynamics of phase-locked loops

The locking and the tracking of single phase-locked loops are treated employing an apparently new approximation. The results obtained are in agreement with the numerical solutions and experimental tests which were made.