Low-Sensitivity Active RC-filter of the Second Order with an Extended Frequency Range
At present, the theory of RC-filters most actively develops in the direction of tunable filters and filters on switched capacitors. In this frame, the new types of active elements, including multi-differential operational amplifiers and various modifications of current conveyors, are also considered. The search for architectures that minimize the effect of the areas of amplification of active components on the main parameters of the active RC-filter continues. However, not all the new active elements, which number exceeds 150 variants today, are available in the form of serial microcircuits. At the same time, the classic operational amplifiers are produced in large numbers, including in the not compact version for "systems in the case". Operational amplifiers are the most common active elements. So, on the international market of microelectronic products, more than 2 000 names of operational amplifiers are presented. In this connection, the search for new architectures of the active RC-filter on operational amplifiers is still of interest. At the same time, it should be noted that in many cases, the architecture of active RC filters based on operational amplifiers can be successfully implemented on the basis of new active elements. The paper proposes a new structure of a universal low-sensitivity active RC-filter of the second order with an extended frequency range. The active RC-filter circuit is implemented on three operational amplifiers and is recommended for use as a universal link in the construction of bandpass filters, as well as low and high-frequency filters. It is shown that due to the introduction of a single new connection in the circuit of the known KHN-filter in the transfer function of the active RC-filter under consideration, additional coefficients appear that depend on the amplification areas of the operational amplifiers. In the final analysis, this reduces the influence of the frequency properties of operational amplifiers on their real characteristics. Computer simulation of the proposed active RC-filter showed that for the case of a bandpass filter the frequency range of operation is approximately 1.5 times greater than in the widely used KHN-filter. And this effect is achieved without the introduction of any additional active and passive elements. In this case, the relative gain on the frequency range will be the higher, the smaller the amplification area of the operational amplifiers used. In the investigated filter scheme, micro-power operational amplifiers can be used, which allows recommending its use in low-temperature analog-to-digital interfaces.