Inductor-less, capacitor-less state-variable electrothermal filters

Electrothermal circuits (ETC) exploit interactions between thermal and electronic properties of devices in an integrated circuit to perform useful electronic functions. An ETC integrator is described which can be used as a building block for state-variable filters. Circuits are given which perform the coefficient-setting function for such filters. Measured data are given for low-pass, high-pass, bandpass, and notch state-variable ETC filters; these filters use only transistors and resistors. For the chip size used, the maximum frequency of the filters is of the order of 200 Hz; an order of magnitude increase is possible with reduced chip size. Methods are described for making filter performance independent of ambient temperature.