A device for measuring an unknown resistance (R X ), comprising a reference resistance (R REF ) in series with the unknown resistance (R X ). The device is prearranged for measuring a first voltage (V1) and a second voltage (V2), across the reference resistance (R REF ) and of the unknown resistance (R X ), respectively. The device comprises changeover-switch modules (muxA, muxB), which receive at input the first voltage (V1) and the second voltage (V2) and supply values (D1, D2) representing the first voltage (V1) and the second voltage (V2), and a single analog-to-digital converter (ADC), which supplies at output the digital representation (D X ) of the value of the unknown resistance (R X ) as ratio between the values (D1, D2) at input to the converter (ADC). The analog-to-digital converter (ADC) contains two negative feedback loops (D2, D1), which function in an alternative way according to the outputs of the changeover-switch modules (muxA, muxB). The negative feedback loops (D2, D1) are first-order continuous-time sigma-delta converters. In particular, one of the two sigma-delta converters has a constant digital output at the level "1".
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