A precision current source in SIMOX technology for high temperature applications up to 570 K

This paper describes a precision, pulse-width controlled current source for high temperature applications. The output current is directly proportional to the duty-cycle of a pulse-width modulated input signal. Since the ambient temperature can be as high as 570 K a thin-film SIMOX-CMOS-process has been chosen to fabricate the current source. The power supply voltage of the current source is in the range of 14 V to 30 V. In order to get drain-source-breakdown voltages above 30 V, a drainextention had to be applied. Since even in a SIMOX-process leakage currents dictate the performance limitations of analog, integrated CMOS circuits with respect to temperature, film contacts and a H-shaped gate layout of the transmission gate transistors is necessary. The applied modifications result in drain-source-breakdown voltages above 30V and low leakage currents even at high temperatures.