Method of interfacing a LC sensor and related system

Patent metadata

Field	Value
Publication number	US-10162038-B2
Application number	US-201514739195-A
Country	US
Kind code	B2
Filing date	Jun 15, 2015
Priority date	Jul 9, 2014
Publication date	Dec 25, 2018
Grant date	Dec 25, 2018

Abstract

A method of interfacing a LC sensor with a control unit is provided. The control unit may include first and second contacts, where the LC sensor is connected between the first and the second contact. A capacitor is connected between the first contact and a ground. To start the oscillation of the LC sensor, the method may include during a first phase, connecting the first contact to a supply voltage and placing the second contact in a high impedance state such that the capacitor is charged through the supply voltage. During a second phase, the first contact may be placed in a high impedance state, and the second contact connected to the ground such that the capacitor transfers charge towards the LC sensor. During a third phase, the first contact and the second contact may be placed in a high impedance state so the LC sensor is able to oscillate.

First claim

That which is claimed is:

1. A method of interfacing an LC sensor, comprising an inductor and a first capacitor, with a controller, the controller comprising first and second contacts with the LC sensor being coupled between the first and second contacts of the controller and a second capacitor, different from the first capacitor, being coupled between the first contact and a reference voltage, wherein the reference voltage comprises a first reference voltage and at least one second reference voltage, the method comprising:
during a first phase, connecting the first contact to a supply voltage and placing the second contact in a high impedance state so that the second capacitor is charged through the supply voltage;
during a second phase, placing the first contact in the high impedance state and connecting the second contact to the reference voltage so that the second capacitor transfers charge to the LC sensor;
during a third phase, placing the first contact and the second contact in the high impedance state so that the LC sensor oscillates;
monitoring a voltage at the second contact during the third phase to vary a duration of the second phase to regulate a voltage at the second capacitor at a beginning of the third phase to define a middle point voltage of an oscillation occurring at the second contact, wherein monitoring the voltage at the second contact comprises comparing the voltage at the second contact with the at least one second reference voltage to generate a comparison signal comprising a first comparison signal and a second comparison signal;
monitoring a voltage at the first contact with a Schmitt Trigger so that the second comparison signal is set to high when the voltage at the first contact is above a given upper threshold, and to low when the voltage at the first contact is below a given lower threshold; and
performing a calibration, wherein performing the calibration comprises:
during a first calibration phase, connecting the first contact to the supply voltage and placing the second contact in the high impedance state that the second capacitor is charged through the supply voltage;
during a second calibration phase, placing the first contact in a high impedance state and connecting the second contact to the first reference voltage so that the second capacitor transfers charge to the LC sensor;
during a third calibration phase, once the second comparison signal indicates that the voltage at the first contact is below the given lower threshold, connecting the first contact to a supply voltage so that the second capacitor is charged through the supply voltage; and
during a fourth calibration phase, once the second comparison signal indicates that the voltage at the first contact is above the given upper threshold, determining the duration of the third calibration phase.

2. The method of claim 1 , wherein monitoring the voltage at said second contact comprises counting a number of pulses in the comparison signal.

3. The method of claim 2 wherein varying the duration of the second phase to regulate the voltage at the second capacitor at a beginning of the third phase comprises varying the duration of the second phase to ensure a minimum number of pulses in the comparison signal.

4. The method of claim 1 , wherein between the second calibration phase and the third calibration phase, once the second comparison signal indicates that the voltage at the first contact is below the given lower threshold, further comprising connecting the first contact to the supply voltage so that the second capacitor is recharged through the supply voltage, wherein a recharge duration is determined as a function of the duration of the second calibration phase to define the middle point voltage of an oscillation occurring at the second contact.

5. A system comprising:
an LC sensor comprising an inductor and a first capacitor;
a controller comprising first and second contacts with the LC sensor being coupled between the first and second contacts of the controller; and
a second capacitor, different from the first capacitor, coupled between the first contact and a reference voltage, wherein the reference voltage comprises a first reference voltage and at least one second reference voltage;
said controller being configured to
during a first phase, connect the first contact to a supply voltage and place the second contact in a high impedance state so that the second capacitor is charged through the supply voltage,
during a second phase, place the first contact in the high impedance state and connect the second contact to the reference voltage so that the second capacitor transfers charge to the LC sensor,
during a third phase, place the first contact and the second contact in the high impedance state so that the LC sensor oscillates;
monitor a voltage at the second contact during the third phase to vary a duration of the second phase to regulate a voltage at the second capacitor at a beginning of the third phase to define a middle point voltage of an oscillation occurring at the second contact, wherein the controller monitors the voltage at the second contact by comparing the voltage at the second contact with the at least one second reference voltage to generate a comparison signal comprising a first comparison signal and a second comparison signal;
monitor a voltage at the first contact so that the second comparison signal is set to high when the voltage at the first contact is above a given upper threshold, and to low when the voltage at the first contact is below a given lower threshold; and
perform a calibration, wherein the controller is configured to perform the calibration by:
during a first calibration phase, connecting the first contact to the supply voltage and placing the second contact in the high impedance state that the second capacitor is charged through the supply voltage;
during a second calibration phase, placing the first contact in a high impedance state and connecting the second contact to the first reference voltage so that the second capacitor transfers charge to the LC sensor;
during a third calibration phase, once the second comparison signal indicates that the voltage at the first contact is below the given lower threshold, connecting the first contact to a supply voltage so that the second capacitor is charged through the supply voltage; and
during a fourth calibration phase, once the second comparison signal indicates that the voltage at the first contact is above the given upper threshold, determining the duration of the third calibration phase.

6. The system of claim 5 , wherein said controller monitors the voltage at the second contact by counting a number of pulses in the second comparison signal.

7. The system of claim 6 wherein said controller varies the duration of the second phase to regulate the voltage at the second capacitor at the beginning of the third phase by varying the duration of the second phase to ensure a minimum number of pulses in the second comparison signal.

8. The system of claim 5 wherein said controller comprises:
a first switch configured to selectively connect the first contact to the supply voltage or place the first contact in the high impedance state;
a second switch configured to selectively connect the second contact to the reference voltage or place the first contact in the high impedance state; and
a comparator configured to monitor the voltage at the second contact.

9. The system of claim 8 , wherein the first switch comprises three-state output driving circuitry associated with the first contact; wherein said second switch comprises three-state output driving circuitry associated with the second contact; and wherein said comparator comprises input sensing

Assignees

• St Microelectronics Srl

Inventors

• Condorelli Riccardo
• Mangano Daniele

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

• G01D3/028

  mitigating undesired influences, e.g. temperature, pressure · CPC title

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• G01R35/00

  Testing or calibrating of apparatus covered by the other groups of this subclass · CPC title

• H02J7/345

  using capacitors as storage or buffering devices · CPC title