Impact of Self-Heating on Frequency Response of Current Mirrors in Bipolar Technology

This paper presents analytical formulations to characterize the frequency domain nonideal effects due to dynamic self-heating in current mirrors designed on silicon-on-insulator bipolar process technology. This analysis shows that the thermally induced "zero-pole doublet" in the transfer function of the output impedance of current mirrors can show peaking in the frequency response, near the thermal cutoff frequency unless design constraints are imposed. Analytical expressions of output impedance, Z_o(s), for the most prevalent current mirrors are derived incorporating thermal effects, and design recommendations are proposed to mitigate such effects. The effects of dynamic self-heating have been demonstrated through simulations in current mirrors using the Vertical Bipolar Inter-Company (VBIC) model in the SPECTRE simulator. The simulation result agrees within 10.0% with the theoretical model.