Design of a high accuracy BJT-based temperature sensor

A high accuracy BJT-based temperature sensor is proposed and realized on a CMOS technology. It consists of an analog-front-end (AFE) and a zoom ADC. The AFE consists of bias circuits, a temperature sensor and digital control circuits. Chopper is applied in the front-end circuit. Ripples caused by the chopper are removed by low-pass filter. Chopper and the low-pass filter remove low frequency noises and improve accuracy of temperature sensing. To achieve precision digitization to AFE's outputs, the zoom ADC combines including successive approximation register (SAR) coarse conversion and sigma-delta fine conversion is applied. A 5-bit SAR ADC accomplishes coarse conversion to the AFE outputs at first. Then, fine conversion is done by Σ-ΔADC to quantize the residue voltage after coarse conversion. This structure achieves high accuracy and linearity with low power. To verify the proposed design, the temperature sensor is achieved on a 110 nm CMOS, and occupies 0.18mm2. It achieves inaccuracy of ±0.25℃ from -45℃ to +85℃ with conversion time of 4 ms, and the oversampling rate is 128. It draws 12.3μA from a 3V supply.