Threshold voltage fluctuations

The wide spreading of the induced signals (see Fig. 5) makes the trimming of the threshold voltages of the comparators very critical. Slight deviations in the thresholds, of the order of 1 % result in differential linearity fluctuations of 10 %. These again manifest themselves as a modulation of the sensitivity over the detector plane of the same magnitude. This is the weakness of this method, which makes it less suitable for accurate measurements. 

The threshold voltages for switehing between the eonducting states varied from metal to metal. A correlation between the work function and the value of the threshold voltage could not be determined because of significant fluctuations from measurement to measurement. 

The notion that a discrete number of conductance units could be measured in nerve membranes originated from an observation in myelinated nerve fibres i.e., the discreteness in the fluctuations of threshold voltage responses [62],... 

The threshold voltage Uth and the f)eriod Wth of the Kapustin-Williams domains are found from the linearized system of equations of nematody-namics in an electric field, as a condition of nontriviality of the fluctuations amplitudes 0 , v , t , where... 

From this equation, Ey (T)/E- -(0) increases monotonically from unity at T=0K to 1,33 at T=Tc. This behaviour differs from one observed in the CDW materials, where Ey exhibits a divergence at T=Tc and a minimum slightly below Tq, which results from an increase in Ey at low temperatures, due to phase fluctuations. Hence, one should expect to observe similar properties of the SDW current-carrying state to ones of the CDW nonlinear current-voltage characteristics, accompanied by broad and narrow band noise, with sharp threshold fields, frequency-dependent conductivity, interference effects between the ac voltage generated in the sample, and an external rf field, hysteresis and memory effects etc. 

The photomultiplier, as shown in Fig. 6, is almost universally used as a photon counter, that is, the internal electron multiplication produces an output electrical pulse whose voltage is large compared with the output electric circuit noise. Each pulse in turn is the result of an individual photoexcited electron. The numbered electrodes, 1-8, called dynodes, are each successively biased about 100 V positive with respect to the preceding electrode, and an accelerated electron typically produces about 5 secondary electrons as it impacts the dynode. The final current pulse collected at the output electrode, the anode, would in this case contain 5 400,000 electrons. The secondary emission multiplication process is random, the value of the dynode multiplication factor is close to Poisson distributed from electron to electron. The output pulse amplitude thus fluctuates. For a secondary emission ratio of = 5, the rms fractional pulse height fluctuation is 1 /V<5 — 1 = 0.5. Since the mean pulse height can be well above the output circuit noise, the threshold for a pulse count may be... 

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