This work proposes an optimum design and implementation of fractional-order Butterworth filter of order (1 + α), with the help of analog reconfigurable field-programmable analog array (FPAA). The designed filter coefficients are obtained after dual constraint optimization to balance the tradeoffs between magnitude error and stability margin together. The resulting filter ensures better robustness with less sensitivity to parameter variation and minimum least square error (LSE) in magnitude responses, passband and stopband errors as well as a better –3 dB normalized frequency approximation at 1  rad/s and a stability margin. Finally, experimental results have shown both lowpass and highpass fractional step values. The FPAA-configured outputs represent the possibility to implement the real-time fractional filter behavior with close approximation to the theoretical design.

Noise spectroscopy and I-V characteristic non-linearity measurement were applied as diagnostic tools in order to characterize the volume and contact quality of positive temperature coefficient (PTC) chip sensors and to predict possible contact failure. Correctly made and stable contacts are crucial for proper sensing. I-V characteristics and time dependences of resistance were measured for studied sensors and, besides the samples with stable resistance value, spike type resistance fluctuation was observed for some samples. These spikes often disappear after about 24 hours of voltage application. Linear I-V characteristics were measured for the samples with stable resistance. The resistance fluctuation of burst noise type was observed for some samples showing the I-V characteristic dependent on the electric field orientation. We have found that the thermistors with high quality contacts had a linear I-V characteristic, the noise spectral density is of 1/f type and the third harmonic index is lower than 60 dB. The samples with poor quality contacts show non-linear I-V characteristics and excess noise is given by superposition of g-r and 1/fn type noises, and the third harmonic index is higher than 60 dB.