A generic read-out circuit for resistive transducers

This paper presents a flexible read-out circuit applicable to a wide variety of resistive transducers. Compared to recent bridge-transducer read-out circuits, it achieves lower supply sensitivity and requires only one reference resistor. It digitizes an external resistance with respect to this reference with the help of a power-efficient zoom-ADC based on a first-order delta-sigma modulator. A prototype realized in a 0.18 μm CMOS process has an active area of 1.0 mm2 and consumes 130 μA from a 3.3 V supply. It achieves an rms resolution of 13.7 bits in a 100 ms conversion time, and a supply sensitivity of 0.057 %/V. When used to read out a thermistor to sense temperature, 6 samples of the read-out circuit achieve an inaccuracy of less than ±0.015°C from 20°C to 80°C.