Band-Pass Filter Design with Diagnosis Facilities Based on Predictive Techniques

We have studied the feasibility of designing a second-order band-pass filter which can provide itself information about its central frequency when it is led to an specific operation mode (calibration mode). The filter has been built with discrete components around a TL071 Operational Amplifier. When a control digital signal toggles the calibration mode, the filter components are reconfigured into an oscillator thanks to some analog switches. The oscillation frequency allows predicting the filter central frequency with an rms error of 0.33%. Since there are many possibilities to reconfigure the filter into an oscillator and the choice of the best test-mode oscillator in terms of predictability demands a great deal of computational effort, we have found out a simple criterion for choosing the best scheme avoiding that effort. This criterion takes into account the sensitivities of the performance parameters (the central frequency) and the test observables (the oscillation frequency) with respect to the passive and active components of the filter.