Analogue circuits

FIGURE 5.58 Electrical analogue circuit for a mnemonic device for combining different transport mechanisms. 

SPICE [32] simulations indicate that the electrochemical transistor can be used favorably to implement a number of useful digital and analogue circuits. Naturally, the slower speed, compared to traditional electronics (by about a factor 108 ), should be taken into consideration. The area of (silicon-based) electronic circuit theory offers numerous solutions to the implementations of circuits. However, depletion-type transistors are less favorable to use in system designs than their enhancement counterparts. For this reason, it is rare to find circuits that use depletion transistors. One has to go back to the electron tube era to find solutions that can be used as templates for circuits suitable for the electrochemical transistor. 

That Is, the seml-differentlated current measures the differential change in suface concentration of the target species. Hence the semi differentiated voltammogram gives a much narrower pea for each system 100 mV) centred for a reversible system on the E of the substance. The actual operation of semi-differentiation can be achieved by a simple analogue circuit [21]. 

The impedance of small lithium-copper oxide primary cells has been investigated in a frequency range from 5 mHz to 10 kHz. The cells had been stored after assembly for from three weeks up to three years and their state of charge was from 100% down to 20%. After an initial period of electrochemical stabilization, the cells exhibited consistent results and the shape of the impedance locus was found to depend markedly on the state of charge of the cell. An interpretation of the results is given in terms of an analogue circuit which contains components to represent the contribution to the impedance of each electrode and of the electrolyte. 

Fig. 20. Analogue circuit for the cell. The capacitor in parentheses is evident at low frequencies.

Koza, J. R., Bennett III, F. H., Andre, D. and Keane, M. (1999). The design of analogue circuits by means of genetic programming. In Bentley, P. (ed.). Evolutionary Design by Computers, San Francisco, CA Morgan Kaufmann. 

Odum, H. T. Ecological Potential and Analogue Circuits for the Ecosystem. American Scientist 4 (i960) 1-8. 

Integrated Circuits. For analogue integrated circuits (ICs) as frequencies increase, requirements for epitaxy grow at the same rate. For most microwave devices with frequencies over 20 GHz, an epitaxial GaAs layer is required. MBE is preferred for HEMT stmctures with better low noise, while MOCVD is used for HBT devices (see Integrated circuits). 

Tacho generator (TG) - This is an analogue voltage feedback device and can provide a speed input to the inverter control circuit. It provides only a low level of speed regulation, typically x 0.4% of the set speed. 

Photodiodes are the modem analogues to photocells. They increase their electrical resistance under light impact which, as part of an electric circuit, can be measured easily. Many current instruments display diode arrays instead of a single diode. Tens of photodiodes are arranged in a tight area. They are exposed to the sample bound spectrum where they respond to the color that corresponds to their positions in the diode array. A rapid, periodically performed electrical interrogation of all diodes (sequence periodicity in the order of milliseconds) reveals a quasi-stationary stable spectrogram. More sophisticated than photodiodes are phototransistors. They amplify internally the photoelectric effect, but the sensitivity of a photomultiplier cannot be achieved. 

Inductance can be thought of as an electrical analogue to inertia, so cuirent flow is opposed at short times. Strictly speaking, a potential V is induced in the circuit immediately after the circuit is switched on, with V of the opposite polarity to that being applied. The current caused by the application of V tries to stop the net flow of current. 

Analogue noise measurements have been made using high gain amplifier/ filter circuits which permit examination of low frequency fluctuations on a real-time basis. 

From the late 1930s to the mid-1960s, the second generation appeared. These instruments used sensors to convert chemical or physical properties into electrical signals. Electrical circuits were then employed to produce meaningful data (Fig. 8.3). Analysts interacted with these instruments using knobs and switches to obtain data from output devices such as analogue meters and strip chart recorders. 

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