Phased-lock-loop

Automatic adjustment of mirrors and monochromators by intensity monitors and phase-locked loops is called stabilization. If the feedback breaks down, the beam will slowly move as the temperature of the optical part is changing. 

Besides the two main characteristics of sensitivity as well as specificity of a sensor, the industrial, military, and other standards demand the device to be portable, economical, autonomous, and power efficient. In order to address some of these characteristics, the authors in their respective laboratories have been working on improving the design of the prototype, as shown in Figs. 15.6 and 15.7, respectively. The necessaiy electronics consisting of local oscillators, beat oscillators, smaller cavities, mixers, and phase-locking loops have been assembled in prototypes. As of this date the device needs further evaluation in an operational environment to establish a set of encyclopedic data and for comparison with unknown toxins. 

Circuitry similar to that presented in Figure 8.13b has been used to analyze cells with impedances ranging from 102 to 1011 Q with 1% accuracy and resolution better than 1 part in 104 over a frequency range of 0.005 Hz to 10 kHz [14]. The technique has been especially useful for studies of the reaction kinetics of moderately fast chemical reactions. Kadish et al. [15] used phase-selective techniques to make ac impedance measurements to evaluate reference electrodes for use in nonaqueous solvents. Recent decreases in the cost of integrated function modules such as analog multipliers, oscillators, and phase-locked loops make this type of phase-selective instrumentation more accessible than ever. 

Fig. 4. The first 1992 Garching frequency chain for the measurement of the IS — 2S transition in atomic hydrogen (0 phase-locked loop, SHG second harmonic generation)...

Addition of a phased-lock-loop (PLL) circuit to the PEM driver the PLL circuit made especially for the UCS J-800KCM is able to reduce the phase difference between the load current and the PEM-driving voltage to zero. The PEM is thus efficiently driven at lower voltage, and the lag of resonance frequency related to thermal change is decreased. Consequently, the stability of the PEM driver was raised [27]. 

A phase-locked loop is a bit of a hybrid of the oscillator circuit and the propagation measurement system discussed in the previous two sections. The instrumentation setup, shown in Figure 6.14 (page 374), closely resembles that used for propagation measurements. The phase is locked, or rather maintained at a constant value, in the following manner initially, before any perturbation occurs, the phase difference between the two IDTs of the AW device is recorded when a perturbation affects this phase difference, the frequency of the signal from the source is adjusted to return the phase to its initial value. In this way, the source frequency is constantly retuned to the extent dictated by the perturbation, and the phase difference between the two transducers remains locked. ... 

Figure 6.14 Computer-controlled phase-locked loop configuration for two-porl AW device measurements. The computer adjusts the output frequency of the synthesized frequency source to keep the phase delay between transducers, as measured by the vector...

The main advantage of the computer-controUed phase-locked loop configuration is that it is nearly as rugged as the fixed-frequency perturbation measurement system in terms of continuing to function during large changes in at-... 

This chip die sizes are 5 X 5 and 10 X 10 mm. The first chip (5X5 mm ) of the spectrometer, the front-end chip, has the local oscillator together with the SIS mixer and impedance matching structure for better power delivery and to time out the SIS junction capacitance. The frequency resolution of SISP determined by both the instant linewidth of the LO and its long-time stability along with the noise temperature is one of the major parameters in spectral measurements. The phase-lock loop consisted both on-chip circuitry and room-temperature electronics is employed. ... 

Second-order phase-locked loop) Using a computer, explore the phase portrait of 0 + (l- cos0)0 + sin0 = O for //>0. For some values of fi, you should find that the system has a stable limit cycle. Classify the bifurcations that create and destroy the cycle as jz increases from 0. 

PTCDA 263 ff phase locked loop (PEL) 79 p-photo electron spectroscopy (p-PES)... 

PLL-based oscillators are characterized by a loop with phase detection of two signals in a sensor and reference path. A circuit based on a phase-locked loop (PLL) configuration has been introduced in [46]. The core of this solution is a sensor circuit consisting of a reference and a sensor path. It is essential for the working principle to maintain an identical structure in the sensor and the reference path, in order to minimize systematic differences between them. A phase frequency detector measures the phase difference between the sensor and reference path. An adjustable capacitance in the reference path allows for Co-compensation. The oscillator can therefore work at/s. 

For that purpose, the quartz crystal is simultaneously excited at two frequencies. The response at the lower frequency is processed by a feedback loop dedicated to measure and automatically compensate Cq. The response at the higher frequency is processed by a phase-locked loop that continuously maintains and tracks oscillations at/s. The voltage waveform V hl is the sum of the two sinusoidal signals V h. with frequency/h generated by the voltage controlled oscillator VCO, and Vl, with frequency/, lower than/n, generated by the auxihary oscillator OSC. The frequency/r of the signal Vu is taken as the output frequency/out of the whole circuit. In the frequency domain, the ex-... 

Ml, II and the VCO form a phase-locked loop feedback system. The multiplier makes a synchronous detection of (V2 - Vi) at the frequency/h. The output of II drives the VCO so that the output frequency/h constantly adjusts to the frequency where the admittance of the motional arm Ys of the sensor is real, i.e., to the series resonance frequency/s. Therefore, the oscillator output frequency/out =/h is continuously tracking/. 

Oscillator circuits are a cost-efficient alternative to impedance analysis and ring-down [12,13]. Naturally, most sensors rim on oscillator circuits. Some advanced circuits provide a measure of the dissipation (such as the peak resistance, Ri, see Sect. 6) in addition to the frequency. Most oscillators operate on one harmonic only. Oscillators can be more stable than ring-down and impedance analysis because the latter two techniques periodically turn the crystal on and off in one way or another, whereas oscillators just run quietly on one fixed frequency. If the signal-to-noise ratio is the primary concern, no technique can beat oscillators. There is one pitfall with the use of oscillators worth mentioning the theory below pertains to the series resonance frequency (simply called resonance frequency). The output frequency of an oscillator circuit, on the other hand, usually is not the series resonance frequency (Fig. 2). For instance, phase-locked-loop oscillators keep the phase constant. Many oscillators run at the zero-phase frequency (B = 0, Fig. 2). Importantly, the difference between the zero-phase frequency and the series resonance frequency changes if the bandwidth or the parallel capacitance change (Sect. 6). The... 

However, mixers are relatively broadband devices, such that not just one, but a range of frequencies is observed simultaneously. The local oscillator signal must be extremely stable in frequency (to about 1 part in 10 ), because any drifting with time would cause the sky frequency also to change. This stabilization is accomplished using a phase-lock loop, an electronic circuit that continuously compares the LO signal with a very stable, lower frequency reference, and corrects any change as needed (6). 

Phase shifters range from simple delay lines to mechanically or electronically controlled delay lines to those based on phase locked loops or other active circuits. Quadrature and 180° hybrids as well as DBM s can be used as fixed value broadband phase shifters. This last point is important since most continuously adjustable phase shifters are frequency dependent. Phase shifters in NMR spectrometers are required to set the reference phase in a phase sensitive detector and also to set the relative phases of rf pulses as required for various pulse sequences. 

Gratton, E., US. Patent 4,840,485. Frequency-domain Cross-Correlation Fluorometry with Phase- Locked Loop Frequency Synthesizers. June 20, 1989. 

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