Digital Phase-locked Loop Circuit Research Articles

Digitally controlled chirped pulse laser for sub-terahertz-range fiber structure interrogation.

This Letter reports a sweep velocity-locked laser pulse generator controlled using a digital phase-locked loop (DPLL) circuit. This design is used for the interrogation of sub-terahertz-range fiber structures for sensing applications that require real-time data collection with millimeter-level spatial resolution. A distributed feedback laser was employed to generate chirped laser pulses via injection current modulation. A DPLL circuit was developed to lock the optical frequency sweep velocity. A high-quality linearly chirped laser pulse with a frequency excursion of 117.69GHz at an optical communication band was demonstrated. The system was further adopted to interrogate a continuously distributed sub-terahertz-range fiber structure (sub-THz-fs) for sensing applications. A strain test was conducted in which the sub-THz-fs showed a linear response to longitudinal strain change with predicted sensitivity. Additionally, temperature testing was conducted in which a heat source was used to generate a temperature distribution along the fiber structure to demonstrate its distributed sensing capability. A Gaussian temperature profile was measured using the described system and tracked in real time, as the heat source was moved.

A novel flash fast-locking digital phase-locked loop: design and simulations

A flash digital phase-locked loop (DPLL) is designed using 0.18 μm CMOS process and a 3.3 V power supply. It operates in the frequency range 200 MHz-2 GHz. The DPLL operation includes two stages: (i) a novel coarse-tuning stage based on a flash algorithm similar to the algorithm employed in flash A/D converters, and (ii) a fine-tuning stage similar to conventional DPLLs. The flash portion of the DPLL is made up of frequency comparators, an encoder and a decoder which drives a multiple charge pump (CP)/lowpass filter (LPF) combination. Design considerations of the flash DPLL circuit components as well as implementation using Cadence design tools are presented. Spectre simulations were also performed and demonstrated a significant improvement in the lock time of the flash DPLL as compared to the conventional DPLL. By increasing the number of frequency comparators, the lock time is expected to be always less than 100 ns in the above-mentioned frequency range.

Scanning Hall Probe Microscopy (SHPM) Using Quartz Crystal AFM Feedback

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.

A real-time multiradian phase detector for interferometry based on a digital phase locked loop circuit

A real-time phase detector based on a digital phase locked loop circuit for interferometry in fusion plasma experiments has been constructed. The device can measure phase shifts from -1*2 pi up to 15*2 pi with a resolution of about 1/100*2 pi . The measuring range can easily be expanded to larger values. The new phase counter is very insensitive to electrical noise. The ability of the phase counter to follow fast density changes depends only on the beat frequency of the heterodyne interferometer. It has been successfully tested for the density and positional feedback system of the TEXTOR tokamak.

ディジタルPLLを用いたしま画像からの実時間形状復元処理 (第2報)

A real-time method is developed for measuring 3-dimensional profiles from fringe patterns generated by moire-topography or a deformed grating method. This paper presents theoretically relationship between object shapes and phases of fringes. It also describes the construction of an experimental system which uses a Digital Phase-Locked Loop (DPLL) circuit. Furthermore, experimental results that confirm the DPLL circuit's performance are reported. In the system, a video-camera scans the fringe patterns across the array of fringe stripes. The video signal has a sine-wave form. The low frequency component of the wave is eliminated by a high-pass filter and its output is digitized by an A/D converter. The phase restoration of the digital signal is performed by the DPLL circuit. The obtained phase signal is proportional to relative distance between the camera and the object. Then the phase signal is converted into analog signal by a D/A converter and the results are displayed as gray-level images on a CRT monitor and also as perspective diagrams on an oscilloscope. An exact profile of the object can be obtained at the video-rate with this method.