Self-Compensated Active Filters

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Active RC Electronic Biquad/Universal Self Compensated Filters


As known to persons skilled in electronics, filters have an essential role.

In fact, starting from a source frequency signal, it’s necessary to process it and obtain another one having phase and amplitude according to a wanted predetermined frequency.

In the telecommunications field particulary, where high amplification is necessary, a system can become critical if the filtering operation is not adeguate, and the useful information can be lost.

Until now analog active filters have had several problems, mainly due the parasitic effects of the amplifiers although many compensation techniques have been studied for.

To obviate the problem, usually several filter stages are cascade connected, but this drammatically increase the cost and can make the system unstable, which is unacceptable.


2° order, 3 base-stages biquad/universal continuous time (CT) analog active filters type resonant and, more particulary, noiseless active full self-compensation techniques to improve the frequency range, the stability and the selectivity of the filters themselves with a very low or as if zero cost, overcoming said problems.

These active filters techniques are revolutionary, because are the only ones in the world that (fully) extend the limited bandwidth of the operational amplifiers employed using, with new direct connections, a single resistor and/or an additional operational amplifier that has a functionally filtering output, and without destabilizing the filter itself.


  • Very easy to manufacture, no special components or procedures are required;
  • They are the most stable (no manual compensation is necessary), and the less noisy* CT single-ended operational amplifiers filters (*noise is the interference signals and the lower is, the higher is the device fidelity);
  • They are inexpensive and require less space, this means:
  • A lower manufacturing cost than a standard compensated filter;
  • Saving power consumption and integrated chip area making more versatile, reliable the circuit(s) and longer its life. Ideal for devices that have to work in space or for long time without any human intervention, in critical enviromental conditions also.


This type of filter may also be adopted in many electronics products which people use every day, improving considerably their performances, such as: TV, radios, walkie talkies, analog/mixed-signal systems, equalizers, SOC (systems on chip), measurement electronic instruments (such as oscilloscopes) and similar devices. Photo of prototype shows their application in a remote infrared reception stage system, wherein high filtering performances are required.


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  • Name:
    Roberto Cavazzoni
  • Type of entry:
  • Patent status: