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A low power temperature sensor followed by a switched capacitor amplifier, a buffer stage, and a 12-bit successive approximation analogue-to-digital converter (ADC) for autonomous multi-sensor systems is presented. The proposed design is accurate within 0.01°C from -55°C to 125°C . A proportional to absolute temperature source was used as a temperature sensor. The read-out enables a differential reading of a reference and actual temperature. The subsequent ADC digitizes the output signal. The ADC has a figure-of-merit of 66 fJ/conversion-step at a bit-clock of 50 kHz. The system is implemented in an NXP CMOS 0.14-μm technology. The die area is 0.27 mm2, and the whole system consumes less than 16 μW. Design and measurements are presented.