Resistive-sensor interface

Patent metadata

Field	Value
Publication number	US-2017227586-A1
Application number	US-201615261126-A
Country	US
Kind code	A1
Filing date	Sep 9, 2016
Priority date	Feb 8, 2016
Publication date	Aug 10, 2017
Grant date	—

Abstract

A device to read a variable resistor has an analog to digital converter (ADC), a first switch and a second switch. The ADC has a first ADC input, a second ADC input and an ADC output. The first switch selectively couples a first voltage indicative of a voltage across a first resistance to the first ADC input. The second switch selectively couples a second voltage indicative of a voltage across a second resistance to the second ADC input. The ADC outputs a signal indicative of a value of the second resistance.

First claim

1 . A device, comprising:
an analog to digital converter (ADC) having first ADC input, a second ADC input and an ADC output; a first switch having a first switch input and a first switch output and which, in operation, receives at the first switch input a first voltage indicative of a voltage across a first resistance and selectively couples the first switch input to the first ADC input; a second switch having a second switch input and a second switch output and which, in operation, receives at the second switch input a second voltage indicative of a voltage across a second resistance and selectively couples the second switch input to the second ADC input, wherein the ADC, in operation, outputs at the ADC output a signal indicative of a value of the second resistance.

2 . The device of claim 1 wherein the signal indicative of the value of the second resistance is a ratio of a value of the first voltage and a value of the second voltage.

3 . The device according to claim 1 wherein said ADC comprises two negative feedback loops, which, in operation, function according to a value of the first switch output and a value of the second switch output.

4 . The device according to claim 3 wherein said two negative feedback loops comprise first-order continuous-time sigma-delta converters.

5 . The device according to claim 4 wherein, in operation, alternatively one or the other of the two sigma-delta converters has a constant digital output at a level of 1.

6 . The device according to claim 4 wherein the ADC comprises an integrator, and each sigma-delta converter comprises a comparator and a sequential electronic circuit coupled to the integrator.

7 . The device according to claim 6 wherein said sequential electronic circuits are D flip-flops.

8 . The device according to claim 6 wherein said first switch and said second switch are multiplexers having respective selection inputs coupled to respective outputs of said sequential electronic circuits of the sigma-delta converters, and, in operation, the outputs of the sequential electronic circuits provide negative feedback of the negative feedback loops.

9 . The device according to claim 6 , comprising:
low-pass filters coupled to respective outputs of said sequential electronic circuits; and a digital divider having respective inputs coupled to respective outputs of the low-pass filters, wherein the digital divider, in operation, outputs a digital representation of the value of the second resistance as a ratio between values representing said first voltage and said second voltage.

10 . The device according to claim 1 , comprising:
a comparator, wherein,
said first switch comprises a third switch input, and, in operation the third switch input receives the second voltage and the first switch selectively couples the third switch input to the first ADC input;
said second switch comprises a fourth switch input, and, in operation the fourth switch input receives the first voltage and the second switch selectively couples the fourth switch input to the second ADC input; and
the comparator, in operation, compares the first voltage and the second voltage and generates a signal to control the first and second switches based on the comparison.

11 . The device according to claim 10 wherein said first and second switches comprise first multiplexers having selection inputs coupled to an output of the comparator.

12 . The device according to claim 11 wherein the ADC, in operation, generates a signal based on a ratio of a voltage at the first input of the ADC and a voltage at the second input of the ADC.

13 . The device according to claim 11 , comprising:
two second multiplexers each having:
an input coupled to the ADC output;
an input which, in operation, is fixed at a value of 1; and
a selection input coupled to the output of the comparator.

14 . The device according to claim 13 , comprising:
a digital-divider having inputs coupled to respective outputs of the second multiplexers, wherein in operation, the digital divider generates a digital representation of a value of the second resistance.

15 . The device according to claim 11 , comprising:
a digital divider having an input coupled to the output of the ADC; and an output multiplexer having a first input coupled to the output of the ADC, a second input coupled to an output of the digital divider, and a selection input coupled to an output of the comparator.

16 . A system, comprising:
a sensor including a variable resistor; and circuitry coupled to the sensor, which, in operation, generates a signal indicative of a resistance of the variable resistor, the circuitry comprising:
an analog to digital converter (ADC) having first ADC input, a second ADC input and an ADC output;
a first switch having a first switch input and a first switch output and which, in operation, receives at the first switch input a reference voltage and selectively couples the first switch input to the first ADC input;
a second switch having a second switch input and a second switch output and which, in operation, receives at the second switch input a second voltage indicative of a voltage across the variable resistor and selectively couples the second switch input to the second ADC input.

17 . The system of claim 16 wherein the signal indicative of the resistance of the variable resistor is a ratio of a value of the reference voltage and a value of the second voltage.

18 . The system according to claim 16 wherein said ADC comprises:
an integrator; and
two negative feedback loops, said two negative feedback loops being first-order continuous-time sigma-delta converters having a comparator and a sequential electronic circuit coupled to the integrator.

19 . The system according to claim 18 wherein said first switch and said second switch are multiplexers having selection inputs coupled to respective outputs of said sequential electronic circuits of the sigma-delta converters, and, in operation, the outputs of the sequential electronic circuits provide negative feedback of the negative feedback loops.

20 . The system according to claim 19 wherein the circuitry comprises:
low-pass filters coupled to respective outputs of said sequential electronic circuits; and
a digital divider having inputs coupled to respective outputs of the low-pass filters, wherein the digital divider, in operation, outputs a digital signal indicative of the resistance of the variable resistor.

21 . The system according to claim 16 wherein the circuitry comprises:
a comparator, wherein,
said first switch comprises a third switch input, and, in operation the third switch input receives the second voltage and the first switch selectively couples the third switch input to the first ADC input;
said second switch comprises a fourth switch input, and, in operation the fourth switch input receives the reference voltage and the second switch selectively couples the fourth switch input to the second ADC input; and
the comparator, in operation, compares the reference voltage and the second voltage and generates a signal to control the first and second switches based on the comparison.

22 . The system according to claim 21 wherein the circuitry comprises:
two output multiplexers each having:
an input coupled to the ADC output;
an input which, in operation, is fixed at a value of 1; and
a selection input coupled to the output of the comparator; and

a digital-divider having input

Assignees

• St Microelectronics Srl

Inventors

• Poletto Vanni
• Rogledi Nicola

Classifications

• G01R27/02

  Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) · CPC title

• G01R27/14 Primary

  Measuring resistance by measuring current or voltage obtained from a reference source (G01R27/16, G01R27/20, G01R27/22 take precedence) · CPC title

• H03M1/12 Primary

  Analogue/digital converters ({H03M1/001 – } H03M1/10 take precedence) · CPC title

• H03M3/458

  Analogue/digital converters using delta-sigma modulation as an intermediate step · CPC title