Bitstream trimming of a smart temperature sensor

The paper presents a high-resolution trimming technique for use in precision smart temperature sensors. A digital sigma-delta modulator is used to trim the bias current of a bipolar transistor to compensate for process spread. In contrast with conventional trimming techniques, only a small chip area is required. The implementation of this technique in a temperature sensor with a sigma-delta ADC is discussed. On a prototype realized in 0.7 μm CMOS, an 8-bit trimming resolution was measured, corresponding to 0.02°C on a range of 4.5°C.