Bandgap Reference Optimisation from On-Chip E G , X TI Value Extraction

The temperature dependence of the IC(VBE) relationship can be characterised by two parameters: EG and XTI. They are usually obtained from measured VBE(T) values, using least square algorithm at a constant collector current. This method involves an accurate measurement of VBE and of the operating temperature. A new configurable test structure dedicated to their extraction is presented in this paper. It allows a direct measurement of the die temperature and consequently an accurate measurement of VBE(T). This new technique is implemented on a ST-Microelectronics BiCMOS process. Resulting experimental data are analysed and discussed. An improvement of the bandgap reference design is presented.