Design and Measurements of an Electrothermal Filter Using CMOS Technology

Electronic circuits and systems often require continuous monitoring of their temperature. For most sensors, voltage is the temperature-sensitive parameter; however, electrothermal filters are one of a few exceptions, for which signal frequency or phase is the measure of temperature. Such filters are an essential part of temperature sensors, based on the measurement of material thermal diffusivity, in which the input signal of the filter is a square wave. However, the phase shift introduced by the filter depends on the signal frequency. Thus, the authors decided to explore this dependence in more detail by measuring filter response to sinusoidal input signals. The investigations presented in this paper were carried out for an electrothermal filter designed and manufactured in an ASIC using 3 µm CMOS technology. The obtained measurement results confirmed the hypothesis that both the gain and the phase shift in the filter strongly depend on the input signal frequency. Accurate data on the thermal impedance of filters is crucial for the optimization of their performance.