Analysis of a PTAT Sensor and Bandgap Reference with Emphasis on Their Mutual Influence in a CMOS ASIC

In this article, the authors present an in-depth analysis of a PTAT sensor and its role as one of the analogue blocks in a test ASIC. The authors propose some modifications to the PTAT sensor to reduce output signal non-linearities observed following measurements that are more accurate than those in their previous article on a PTAT sensor. The obtained PTAT sensor linearity ranges from R2 = 0.9990 to R2 = 0.9999 in a temperature range from −40 °C to 150 °C for the entire set of measured specimens, and the details of these test sessions are discussed in this manuscript. Moreover, it is demonstrated that at least some of the implemented circuits may have a discernible impact on the operation of the others. This is particularly evident regarding the bandgap reference, whose operation is also presented and analysed. The integrated circuit specimens containing all analysed circuits were manufactured using custom 3 µm CMOS technology on an n-type wafer. Measurements showed that some circuits containing p-diff resistors behave differently compared to those consisting solely of MOS transistors in symmetrical and matched configurations. The spread of resistor values is approximately 20%, thus requiring their skilful operation in this technology. The likely cause of the bandgap reference’s operation modification has been identified, and promising results have been obtained by recreating its malfunction via simulation. The authors found that in this technology, analogue circuits should be designed with a large margin for component dimensions, especially those implanted in p-wells.