Programmable circuits are commonly used class of electronic devices. In practice this term usually refersto microcontrollers with different kind of programmable memories and to programmable logic circuits (PAL, CPLD,FPGA). Most of these devices are digital circuits. Thanks to the huge progress in miniaturization of electronic circuits, the new class of devices – programmable analog circuits – was put on the market. These circuits bring new possibilities to design electronic circuit. One of the most promising fields of application is construction of analog signal conditioning circuits. This paper describes feature and parameters of sample programmable analog circuits. It depicts internal structure and theory of operation of these devices. One of commercially available programmable analog circuits was used in development of signal conditioning block for vibration measurement system.
It works as programmable gain amplifier and low-pass anti-aliasing filter with programmable cut-off frequency. Amplifier transient characteristics for different gain values and frequency response of the filter were measured.
The common trend among the manufacturers ofelectronic devices is to miniaturize their products. Very often this leads to integration of large number of functional blocks of the device in one small, complex integrated circuit. Small dimensions and weight of the device gives the possibility to use it as a portable apparatus. However, this is not the main and sole objective. Using one, specialized integrated circuit instead of many separate ones gives the opportunity to significantly lower the price of the device when the mass production methods are employed. Moreover, a single integrated circuit will require much less electric energy, therefore it can operate much longer using battery power. An important advantage of the “integrated measurement systems” is the ability to improve the parameters of the constructed devices both in the field of precision (e.g. due to minimisation of the influence of the environment noise) and of operation speed. Such systems may integrate advanced analog circuits, signal processor cores and various measurement transducers. It is extremely important for
example for the distributed vibrations measurement system [3, 4], for which it may be possible to mount the measurement modules inside the generator. Manufacturers of the analog integrated circuits have problems manufacturing capacitors, inductors and resistors in the silicon substrate. They take up large amount of space and often turn out to be thermally unstable. Besides, the polysilicon resistors are nonlinear. The solution to these problems are the switched capacitance circuits [6]. They allow to
manufacture complex analog circuits with arbitrary frequency response. The switched capacitance
technique is the basis of the construction of the reprogrammable analog circuits. They are universal circuits for which the user can determine the configuration of the interconnections between internal
elements and set the required values of the passive elements. As a result it is possible to obtain a circuit having virtually any desired functionality and programmatically adjustable parameters (gain, filter frequencies) without any need for external elements.
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