High temperature operational amplifier with low offset voltage

In this paper circuit design techniques for high temperature electronics are presented. It will be shown that standard Bulk-CMOS technology may be suitable for circuits operating well at temperatures up to 250°C, if special design techniques are considered. While using standard circuits at elevated temperatures, main difficulties arise from the drain leakage current of MOSFETs which is amplified by a parasitic bipolar transistor (known from latch-up) and therefore becomes much higher than the original diffusion leakage current caused by the pn-junction of the drain-bulk diode. A low leakage current for MOSFETs can be achieved by a special circuit design technique. Further problems result from the drift of the threshold voltage depending on temperature and time. As an example a Commutating Automatic Zero Operational Amplifier (CAZ-OPA) is presented in order to demonstrate the capabilities of standard Bulk-CMOS. This CAZ-OPA works with a digital circuit for offset compensation