Active RC filters designed using cascade synthesis method are in practice used very often. Each selective building biquads can be designated using many different circuits. There are divided most often according number of active elements (Operational Amplifiers OAs) to different groups. These circuits with three or four active elements exhibit some advantages. Their outputs enable concurrently to obtain all required kinds of filter types (Low pass LP, high pass HP, band pass BP, band reject BR, all pass AP). The flexibility of above mentioned biquads also allows it to be used in some special applications- as tuning requirements or switchable- filter options. This paper deals with optimized universal biquad blocks with modern active elements, which are usable for many special filter applications. Here are presented some results and achieved parameters of realized tuneable and switchable blocks with modern operational amplifier too. Briefly here are also discussed and presented possible tuning circuits realized using microprocessor technique.
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