Switched-capacitor filters

D Thyristor switched capacitors Filter circuit to absorb harmonic currents caused by TCR... 

AUstot, D.J. and Black, W.C., Jr. 1983. Technological design considerations for monolitic MOS switched-capacitor filtering systems. Proc. IEEE 71(8) 967-986. 

Switched-capacitor filters An electronic circuit (fabricated from operational amphfiers, transistors, and capacitors) designed to transmit some range of signal frequencies while discriminating others. 

Caves, J.T., Copeland, M.A., Rahim, C.F., and Rosenbaum, S.D. 1977. Sampling analog filtering using switched capacitors as resistor equivalents. IEEE J. Solid-State Circuits SC-12 592. 

El-Masry, E.I. 1983. Strays-insensitive state-space switched-capacitor filters. IEEE Trans, on Circuits and Systems CAS-30 474. 

Hosticka, B.J., Brodersen, R.W, and Gray, PR. 1977. MOS sampled-data recursive filters using switched capacitor integrators. IEEE J. Solid-State Circuits SC-12 600. 

Martin, K. and Sedra, A.S. 1979. Strays-insensitive switched-capacitor filters based on the bilinear z-trans-formation. Elec. Lett. 15 365. 

Maxwell, J.C. 1873. A Treatise of Electricity and Magnetism, p. 347. Clarendon Press, Oxford, England. Moschytz, G.S., ed. 1984. MOS Switched-Capacitor Filters Analysis and Design. IEEE Press, New York. Nakayama, K. and Kuraishi, Y. 1987. Present and future applications of switched-capacitor circuits. IEEE Circuits and Devices Mag. lO(Sept). 

Switched-capacitor filters can also be used. In the switched-capacitor filter, resistors are realized with switched capacitors rather. To understand how switched capacitors can be used to replace resistors, consider the circuit shown in Fig. 10 where a capacitor is connected to two switches and two different voltages. When Si closes with S2 open, and then S2 closes with Si open, the amount of charge transferred from V to V2 is as below ... 

In this part the author provides all relevant aspects of a reactive control and carries out an exhaustive analysis of a system for the most appropriate control. Harmonic effects and inductive interferences as well as use of filter and blocking circuits are covered. Capacitor switching currents and surges and methods of dealing with these are also described. 

These ac current loops should be routed before any other traces in the power supply. The three major components that make up each loop the filter capacitor, the power switch or rectifier, and the inductor or transformer must be located adjacent to one another. The components must also be oriented such that the current path between them is as short as possible. A good example of a layout of the power section of a buck (or step-down) converter can be seen in Figure 3-60. 

This capacitor experiences the same current waveform at the power switch, which is a trapezoid with an initial current of about 1A rising to 2.8 A with very sharp edges. This capacitor has much more rigorous operating conditions than the output filter capacitor. I will estimate the RMS value of the trapezoidal current waveform as a piecewise superposition of two waveforms, a rectangular 1A peak waveform and a triangular waveform with a 1.8 A peak. This yields an estimated RMS value of 1.1 A. The value of the capacitor is then calculated as ... 

One of the problems we faced was a mounting standoff on the primary side that we just couldn t get around satisfactorily. We had EMI filters and other items taking up all remaining space. The only way out was to position the bulk capacitor and the switch on opposite sides of the standoff, as shown in Figure 7-2. Unfortunately, these long traces were... 

Arc furnaces are operated in conjunction with large capacitor banks and harmonic filters to improve the power factor and also to filter the harmonic frequency currents so they do not unduly affect other power users sharing the same power fines. It is not uncommon to see arc furnaces supplied from dedicated utility power fines to minimize their impact on other power users. The presence of large capacitance in an electrical system can result in voltage rise due to the leading reactive power demands of the capacitors, unless they are adequately canceled by the lagging reactive power required by the loads. This is why capacitor banks, whether for power factor correction or harmonic current filtration, are switched on when the furnace is brought on line and switched off when the arc furnace is off line. 

Polystyrene capacitors have exceptionally low tan S values (< 10 q, making them well suited for frequency-selective circuits in telecommunications equipment. Polymer capacitors are widely used for power-factor correction in fluorescent lighting units, and in start/run circuitry for medium-type electric motors used in washing machines, tumble-dryers and copying machines for example. They are also used in filter circuits to suppress radio frequencies transmitted along main leads. Such interference noise may originate from mechanical switches, furnace controllers and switch mode power supplies it not only spoils radio and television reception but can also cause serious faults in data-processing and computer equipment. 

A major use of high-quality pot-core inductors is in combination with capacitors in filter circuits. They were once extensively used in telephone systems but solid state switched systems have replaced them. The soft MnZn and NiZn ferrite systems are dominant for pot-core manufacture, although metal dust cores are used for certain applications. The important design principles can be understood by reference to a simple series LCR circuit to which a sinusoidal voltage U of angular frequency co is applied (Fig. 9.46). The circuit impedance Z = R+](coL - 1/coC) is a minimum when ojZ, = /<<>C. Thus the resonant frequency o0 is given by... 

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