Amplifier compensation designs

This completes the design of the feedback loop compensation elements, and the error amplifier curves and the overall plots are also included in Figure 3-66. This also completes the design of the major portions of the switching power supply. The schematic is shown in Figure 3-67. 

Before starting the design for the compensation of the error amplifier, it is desirable to know what constitutes a stable closed-loop system. The rule is elementary ... 

Fig. 6. Schematic design of a pressure sensor. A flexible stainless steel membrane interfaces the pressure-sensitive elements (bridged piezo-resistors) from the measuring liquid. Some products contain the amplifier electronics in the housing and are (somehow) temperature compensated. The shown 2-strand cabling mode resulting in a current signal is very convenient...

Double-beam insirunicnts offei iho advamage that they compensate for all bui ihe most sliori-ierm fluc-luations in the radiant output of the source as well as for drift in the transducer and amplifier. They also compensate for wide variations in source intensity with wavelength (sec Figures 13-11 and 1.3-12). Furthermore, the double-beam design lends itself well to the continuous recording of transmittance or absorbance spectra. 

A comprehensive overview of frequency-domain DOT techniques is given in [88]. Particular instraments are described in [166, 347, 410]. It is commonly believed that modulation techniques are less expensive and achieve shorter acquisition times, whereas TCSPC delivers a better absolute accuracy of optical tissue properties. It must be doubted that this general statement is correct for any particular instrument. Certainly, relatively inexpensive frequency-domain instruments can be built by using sine-wave-modulated LEDs, standard avalanche photodiodes, and radio or cellphone receiver chips. Instruments of this type usually have a considerable amplitude-phase crosstalk". Amplitude-phase crosstalk is a dependence of the measured phase on the amplitude of the signal. It results from nonlinearity in the detectors, amplifiers, and mixers, and from synchronous signal pickup [6]. This makes it difficult to obtain absolute optical tissue properties. A carefully designed system [382] reached a systematic phase error of 0.5° at 100 MHz. A system that compensates the amplitude-phase crosstalk via a reference channel reached an RMS phase error of 0.2° at 100 MHz [370]. These phase errors correspond to a time shift of 14 ps and 5.5 ps RMS, respectively. 

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