Small signal measurements

Furthermore this method can be applied to fast pulse measurements, which are also of great interest in view of memory applications. An example is shown in Figure 17.17. This method can also be applied as small signal measurements on small structures, e.g. C(V) measurements on sub-micron capacitors, and is of great interest to gain further insight in ferroelectric behavior in the nano-scale [12], [13],... 

The field-effect mobility is distinct from the more physically fundamental carrier mobility, which is only one factor in the field-effect mobility. In this chapter, when we refer to the mobility, we are referring to the field-effect mobility, since we will not have occasion to refer to the carrier mobility. We often assume for simplicity that mobility can be treated as constant, but experimentally the mobility is found to depend on V s and V s- Therefore, for extracting mobility from measurements and for accurate simulations, mobility must be treated as a voltage-dependent quantity that is derived from small-signal measurements in the linear region, for very small drain voltages (Vps Vos-Vt),... 

Some authors have used the designation modulus spectroscopy to denote small-signal measurement of M vs. v or co. Clearly, one could also define admittance and dielectric permittivity spectroscopy. The latter is just another way of referring to ordinary dielectric constant and loss measurements. Here we shall take the general term impedance spectroscopy to include aU these other very closely related approaches. Thus IS also stands for immittance spectroscopy. The measurement and use of the complex (< ) function is particularly appropriate for dielectric materials, those with very low or vanishing conductivity, but aU four functions are valuable in IS, particularly because of their different dependence on and weighting with frequency. 

Thus we are challenged by the problem of measuring a small signal against the background of one much stronger. The problem is usually solved by one of two means (a) lock-in-amplifier detection and (b) a boxcar type of detection (to some extent we can include double-input optical multichannel detection in this category). 

Photomultipliers are generally used to convert the spectral radiation to an electrical current and often phase-sensitive lock-in amplifiers are used to amplify the resulting current. AES and AFS require similar read-out systems because both methods are measuring small signals. The difficulty associated with both these methods is the separation of the signal for the atomic transition of interest from the background radiation emitted by excited molecular species produced in the atom reservoir. AFS phase locks the amplifier detection circuit to the modulation frequency of the spectral source. Modulation of the source is also used in AAS. 

In threshold measuring situations small signals are presented and at times when the internal noise is low, the total impact of the noise plus signal may be lower than that of the strongest noise alone. In such a case the subject may say no to a presentation containing the signal (a miss) and yes to a presentation in which only the strong noise was present (a false alarm). 

In order to measure the frequency response of the class AB amplifier, the input voltage source was changed to a small-signal AC stimulus source (AC 1). The breadboard results are shown in Fig. 6.31. The IsSpice, PSpice, and Micro-Cap results are shown in Figs. 6.32, 6.33, and 6.34, respectively. 

Resolution enhancement on the other hand is applied to resolve overcrowded spectral regions or to measure very small signal splitting caused by J-coupling. 

The lower limit of detection given in Equation 5-5 is 3s/m, where s is the standard deviation of a low-concentration sample and m is the slope of the calibration curve. The standard deviation is a measure of the noise (random variation) in a blank or a small signal. When the signal is 3 times as great as the noise, it is readily detectable, but still too small for accurate measurement. A signal that is 10 times as great as the noise is defined as the lower limit of quantitation, or the smallest amount that can be measured with reasonable accuracy. 

The life times of EPR signal with cycles of light-off and -on were measured in vacuum and in 30 Torr of He and N2.n) In vacuum, a small signal (g=2.020,... 

Based on these assumptions the measurement of the large signal ferroelectric hysteresis with additional measurements of the small signal capacitance at different bias voltages are interpreted in terms of reversible and irreversible parts of the polarization. As shown for ferroelectric thin films in Figure 1.24, the separation is done by substracting from the total polarization the reversible part, i. e. the integrated C(V)-curve [18]. 

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