On chip measurement of IC(VBE) characteristics for high accuracy bandgap applications

The E_G and X_TI coefficients are sufficient to completely characterise the temperature dependence of I_C(V_BE) relationship of bipolar transistors (BJT). They are usually obtained from measured V_BE(T) values, using least square algorithm at a constant collector current. This method involves an accurate measurement of V_BE and of the operating temperature. We propose in this paper, a configurable test structure dedicated to the extraction of the temperature dependence of I_C(V_BE) characteristic for the BJT designed with bipolar or BiCMOS processes. This allows a direct measurement of the die temperature and consequently an accurate measurement of V_BE(T). First, the classical extraction method is explained. Then, the implementation technique of the new method is discussed and finally, an improvement of a bandgap design is presented.