Sensitivity Degradation in a Tri-Band GSM BiCMOS Direct-Conversion Receiver Caused by Transient Substrate Heating

An analysis of transient thermal substrate effects impairing the sensitivity of the DCS path in a tri-band GSM/DCS/PCS BiCMOS radio receiver is presented in this paper. A simple thermal model of the substrate is employed, enabling concurrent electrothermal circuit-substrate simulations within a standard analog circuit simulator. Simulation results obtained with this approach match very closely the measured data, and are used to predict the sensitivity of different circuit layout configurations to thermal gradients in the substrate. Following the guidelines suggested by these analyses, a redesigned version of the receiver displays a sensitivity improvement of 2 dB to 4 dB.