A Precision Constant Current Source Design with Trimming and Compensation

Abstract

Constant current source that converted from voltage source has worse temperature characteristics, as typical BCD process does not support high precision and low temperature coefficient resistance. On the basis of digital trimming technology, low-temperature coefficient bandgap reference and constant current source are produced by means of switching network to adjust the resistance value and the relationship between MOS transistor and resistance to compensate the temperature characteristic. A new temperature compensation method is proposed through the utilization of a differential temperature detection circuit, which can generate compensating current in the high temperature section and the low temperature section respectively. When added with the current of compensation circuit, temperature coefficient of the trimmed current source can be effectively reduced. Simulation result indicates that temperature coefficients of 2.5V bandgap reference and 32uA constant current source are 7ppm/°C and 8ppm/°C respectively in various technique corners based on HHNEC 0.35μm BCD technology, ranging from -40 to 85°C.