Oscillator circuitry

Although QCM has originally been devised as a mass sensor for operation in vacuum or gas, it also appeared to be suitable for measurements of the mass and visco-elastic changes at a solid-liquid interface. That was possible due to elaboration of the dedicated oscillator circuitry [115]. The Sauerbrey Equation (2) was derived for resonator oscillations in vacuum. However, it also holds for solution measurements provided that (1) the deposited film is rigid and (2) it is evenly... 

Fig. 7.18. Low-pressure interfaces to detectors based on flow injection. (A) Interface to a photometric detector across a membrane. (Reproduced with permission of the American Chemical Society.) (B) Interface to a flow-through photometric sensor with prior derivatization by the modified Griess reaction. (Reproduced with permission of the American Chemical Society.) (C) Interface to a piezoelectric detector. P peristaltic pump, C collector, CUC clean-up column, DB debubbler, SA sulfamic acid, NEDD /V-( 1-naphthyl)ethylenediamine dihydrochloride, SV switching valve, W waste, DF displacement flask, IV injection valve, FC-PZ flow-cell-piezoelectric crystal, OC oscillator circuitry, F frequency counter, PC personal computer. (Reproduced with permission of Elsevier.)...

Controlled chaos may also factor into the generation of rhythmic behavior in living systems. A recently proposed modeL describes the central circadian oscillator as a chaotic attractor. Limit cycle mechanisms have been previously offered to explain circadian clocks and related phenomena, but they are limited to a single stable periodic behavior. In contrast, a chaotic attractor can generate rich dynamic behavior. Attractive features of such a model include versatility of period selection as well as use of control elements of the type already well known for metabolic circuitry. 

Roshash I was thinking of this in terms of the transcription versus protein only issue it is a pretty good argument that we might have expected that the kinases would allow it to continue to cycle. In other words, if there is a way to estabhsh an oscillator without the transcriptional circuitry (kinases and post-transcriptional regulation only), one might have expected persistent protein cychng. 

These piezoelectric crystal oscillators are very accurate mass sensors because their resonant frequencies can be measured precisely with relatively simple electronic circuitry. For certain quartz crystals, the resonant frequency is inversely related to the crystal thickness. A crystal resonating at 5 megahertz is typically 300 micrometers thick. If material is coated or adsorbed on the crystal surface, the resonant frequency will change (decrease) in proportion to the amount of material added. The effect of adsorbed mass on the oscillator frequency varies according to the operational mode of the device. In any case, interpretation of mass via changes in frequency or amplitude assumes that the coated films are rigidly elastic and infinitesimally thin (that is, an extension of the crystal). 

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. 

Spencer KM. 2008. Visual gamma oscillations in schizophrenia Implications for understanding neural circuitry abnormalities. Clin EEG Neurosci 39 65-68. 

It is not the goal of the following subsections to provide all the information necessary to build various oscillator and control circuits from scratch, although a q>ropriate references are provided for such an undertaking. Instead, the general principles and the generic components utilized for such circuitry will be described. 

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. ... 

The stability of the drive oscillation and of the exact demodulation substantially determine the achievable tolerances of the sensor. This requires complex and demanding electronic circuitry. 

Finally, noise and systematic errors introduced by the electronic circuitry must be also taken into accoimt, especially when standard instriunents are used. An analysis has been performed in [31]. For driving the crystal in an oscillator circuit a small equivalent resistance of the resonator is beneficial. A large electrode diameter is advised however, separation of harmonic from spurious modes defines a maximum diameter, which decreases with frequency. 

Table 3 summarizes the advantages and drawbacks of the above sensor interface concepts. Oscillators are the best solution for most chemical sensor applications. Low expenses of circuitry and a frequency analog output signal... 

The measuring principle is based on an abrupt decoupling of the sensor driving circuitry from the resonator and monitoring the decay of the quartz sensor oscillation. Fig. 27. The influence of electrical load on the crystal is both minimized and independent of the mechanical load on the crystal. It is possible to measure the resonance frequency for parallel oscillation mode, /p, the resonance frequency for series oscillation mode,/s, the decay constant for parallel oscillation mode. Dp, and the decay constant for series oscillation mode, Ds. 

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