RF transponder and method of measuring parameters associated with a monitored object

• US 6,486,776 B1
• Filed: 08/17/2000
• Issued: 11/26/2002
• Est. Priority Date: 04/14/1998
• Status: Expired due to Fees

• Current Assignee: Goodyear Tire & Rubber Company
• Original Assignee: Goodyear Tire & Rubber Company
• Inventors: Pollack, Richard Stephen, Yones, Dale Lee, Brown, Robert Walter, Black, Donald Lee
• Primary Examiner(s): POPE, DARYL C
• Application Number:
  US09/622,555
• Time in Patent Office: 831 Days
• Field of Search: 340/517, 340/521, 340/539, 340/442, 340/438, 340/445, 340/447, 731/465
• US Class Current: 340/521
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver

Abstract

A radio frequency (RF) transponder (200) capable of measuring parameters associated with an object and transmitting data to an external reader/interrogator (106, 400). In use with a pneumatic tire (104), the transponder measures temperature and pressure within the tire. The transponder includes circuitry (226) for controlling windows of time (W_T and W_P) during which real-time temperature and pressure measurements are made, and for storing (236) calibration data, transponder ID number and the like, and for transmitting this information in a data stream (FIG. 3C) to the reader/interrogator. An excessive temperature condition may also be sensed (MTMS 218) and included in the data stream. The circuitry of the transponder is preferably implemented on a single IC chip (204), using CMOS technology, with few components external to the IC chip. The transponder is preferably passive, deriving its operating power from an RF signal provided by the exernal reader/interrogator. Data (N_T) indicative of temperature and data (N_P) indicative of pressure are both transmitted to the reader/interrogator, along with calibration data. A calibration data stored by the transponder and transmitted in the data stream is a slope of N_T/N_P, or the “ratioed” response of the temperature count divided by the pressure count, which is determined during calibration of the transponder.

Claims

1. A passive RF transponder, including:

an antenna;

a rectifier circuit connected to the antenna to provide electrical power from a RF signal received by the antenna to the other components of the transponder;

a modulator circuit, operatively connected to the antenna to form a RF signal output for the transponder by modulation of the RF signal received by the antenna;

a first parameter sensor for sensing a first parameter;

a second parameter sensor for sensing a second parameter;

a timing generator for generating a first timing window during which the first parameter is measured and a second timing window during which the second parameter is measured;

a first register for capturing first data indicative of the first parameter;

a second register for capturing second data indicative of the second parameter; and

the modulator circuit impressing the first data as a first portion of a data stream on a signal output by the transponder, and impressing the second data as a second portion of the data stream on the signal output by the transponder;

characterized by;

an oscillator outputting a signal having a first frequency which is indicative of the first parameter during the first timing window, and having a second frequency which is indicative of the second parameter during the second timing window; and

a register/counter circuit which counts the oscillations of the oscillator signal during the first timing window to capture the first data in the first register, and which counts the oscillations of the oscillator signal during the second timing window to capture the second data in the second register.

2. A passive RF transponder, according to claim 1, wherein:

the first parameter is temperature, and the first data is a function of temperature; and

the second parameter is pressure, and the second data is a function of both temperature and pressure;

characterized in that;

a ratio of the first data divided by the second data is a function of pressure only.

3. A passive RF transponder according to claim 1, characterized in that:

the oscillator output signal'"'"'s first and second frequencies are both proportional to temperature.

4. A passive RF transponder, according to claim 1, characterized in that:

the antenna is selected from the group consisting of coil, loop and dipole.

5. A passive RF transponder according to claim 1, wherein:

a third sensor provides data indicative of a third parameter; and

the modulator circuit impresses the third parameter data on a third portion of the data stream on the signal output by the transponder;

characterized in that;

the third sensor is an excessive temperature sensor; and

the third parameter is an excessively high temperature condition.

6. A passive RF transponder, according to claim 1, characterized in that:

the time period of the first timing window and the time period of the second timing window are adjusted to different durations, thereby adjusting the resolution of the counts of one of the first and second data relative to the resolution of the counts of the other one of the first and second data.

7. A passive RF transponder according to claim 1, characterized in that:

a base emitter voltage to current converter circuit utilizes the first parameter sensor and outputs a current to the oscillator, wherein the current is proportional to the first parameter; and

a frequency of the oscillator output signal is proportional to the current output by the first parameter sensor.

8. A passive RF transponder according to claim 1, characterized by:

a current-scaling circuit, connected between the first parameter sensor and the oscillator, for scaling a current output by the first parameter sensor by a factor of 1/N, and providing a scaled current to the oscillator.

9. A passive RF transponder according to claim 8, characterized in that the current-scaling circuit includes:

a current-mirror including two transistors having dissimilar areas, a one of the two transistors being “

N”

times larger in area than an other of the two transistors.

10. A passive RF transponder according to claim 1, characterized in that:

the oscillator includes a relaxation oscillator having a first phase path and a second phase path.

11. A passive RF transponder according to claim 10, further characterized by:

a first fixed-value capacitor disposed in the first phase path; and

a second fixed-value capacitor disposed in the second phase path.

12. A passive RF transponder according to claim 10, further characterized in that:

the second parameter sensor is a variable-value capacitor which is switched into a one of the first and second phase paths, across a respective one of the first and second fixed value capacitors, during the second timing window.

13. A passive RF transponder according to claim 1, characterized in that:

the first parameter sensor, the oscillator, the timing generator, the first parameter register, the second parameter register, and the modulator circuit, are resident on a single integrated circuit (IC) chip.

14. Method of measuring at least two parameters associated with a monitored object and outputting a signal, including the steps of:

deriving electrical power from a received RF signal;

measuring a first of the at least two parameters associated with the monitored object;

measuring a second of the at least two parameters associated with the monitored object;

generating a first timing window during which the first parameter is measured and a second timing window during which the second parameter is measured;

capturing first data indicative of the first parameter during the first timing window;

capturing second data indicative of the second parameter during the second timing window;

modulating the received RF signal to form a RF output signal;

impressing the first data as a first portion of a data stream on the RF output signal;

impressing the second data as a second portion of the data stream on the RF output signal;

characterized by;

generating an oscillating signal having a first frequency which is indicative of the first parameter during the first timing window, and having a second frequency which is indicative of the second parameter during the second timing window; and

counting the oscillations of the oscillating signal during the first timing window to capture the first data, and counting the oscillations of the oscillating signal during the second timing window to capture the second data.

15. Method, according to claim 14, characterized by:

adjusting the time period of the first timing window and the time period of the second timing window to different durations, thereby adjusting the resolution of the counts of one of the first and second data relative to the resolution of the counts of the other one of the first and second data.

16. Method, according to claim 14, characterized by:

generating a current (I(T)) which is a function of one of the at least two parameters; and

causing at least one of the first and second frequencies of the oscillating signal to be proportional to the magnitude of the current.

17. Method, according to claim 16, further characterized by:

scaling the current during a one of the first and second timing windows, thereby adjusting the resolution of the counts of one of the first and second data relative to the resolution of the counts of the other one of the first and second data.

18. Method, according to claim 16, wherein:

the first parameter is temperature, and the first data is a function of temperature; and

the second parameter is pressure, and the second data is a function of both temperature and pressure;

characterized in that;

a ratio of the first data divided by the second data is a function of pressure only.

19. Method, according to claim 18, further characterized by:

a third of the at least two parameters is an excessive temperature condition.

20. Method, according to claim 14, further including the steps of:

measuring a third of the at least two parameters associated with the monitored object;

capturing third data indicative of the third parameter; and

impressing the third data on a third portion of the data stream on the signal;

characterized in that;

the third parameter is an excessively high temperature condition.