MXPA00010017A - Pneumatic tire having a transponder and method of measuring pressure within a pneumatic tire - Google Patents

Abstract

A radio frequency (RF) transponder (200) associated with a pneumatic tire and capable of measuring operating parameters such as temperature and pressure within the pneumatic tire, and transmitting data indicative of the measured parameters to an external reader/interrogator (106, 400). The transponder includes circuitry (226) for controlling windows of time (WT and WP) 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 (Figure 3C) to the reader/interrogator. An excessive temperature condition may also be sensed (MTMS 218) and included in the data steam. 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 external reader/interrogator. Data (NT) indicative of temperature and data (NP) 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 NT/NP, or the"ratioed"response of the temperature count divided by the pressure count, which is determined during calibration of the transponder.

Description

PNEUMATIC RIM THAT HAS AN ANSWERING MACHINE. AND METHOD FOR MEASURING PRESSURE WITHIN A PNEUMATIC RIM Technical Field of the Invention The present invention relates to pneumatic tires that have answering machines or responders, with emphasis on "passive" answering machines which derive their operating power from an external radio frequency (RF) source and, more particularly, to the answering machines. used for the identification of the tires and the transmission of pressure and / or temperature data. BACKGROUND OF THE INVENTION In the manufacture of pneumatic tires, it is convenient to uniquely identify each tire, as soon as possible, during the course of its manufacture. This is usually done by assigning an identification number (ID) to each tire. The ability to uniquely identify the tires through their manufacture, is particularly valuable for quality control, so that the source of manufacturing problems can be easily ascertained. For example, statistical process control and other methods with rim identification can be used to detect process parameters that come from the specification, ¡Y ^ tó * _ to detect the wear, failure or bad adjustments of the machinery. The identification information should be easily discernible throughout the manufacturing process, which includes the post-manufacturing performance stages (for example, inventory control). It is also beneficial to be able to identify only the performance of a tire through its service life (use), for example, for the determination of the warranty, and the retreading of the tire should not adversely affect the ability to identify the tire. It is also important that the identification of the rim is easily discernible when this rim is mounted on a steel or aluminum rim (as is usually the case), which includes when the rim is one of a pair of rims on a set of wheels double (as is common with tractor trailers). Apart from being able to identify only one tire at various stages of its manufacture and service life, it is beneficial to be able to monitor tire pressure when this tire is in use. As is known, the tire's own inflation is important for the best performance of the tire, which includes road handling, wear, and the like. Answering machines or transreceptor type identification systems (transmitters) are well known. receiver) and are generally capable of receiving an incoming interrogation signal and responding to it by generating and transmitting an output response signal. This signal of output response, in turn, is modulated or encoded in another way, in order to identify only or label the particular object to which the answering element is fixed. An example of such an answering type identification system is described in U.S. Patent No. 4,857,893, issued August 15, 1989 to Carroll and incorporated herein in its entirety. This patent describes an answering device, which receives a carrier signal from an interrogation unit. This carrier signal, of frequency F, is rectified by a rectifier circuit, in order to generate operating power. Alternatively, the addition of a hybrid battery allows the device to be converted into a self-energized guidance device. Logic / time circuits derive a clock signal and the second frequency carrier signal F / n from the received carrier signal. A unique identification data word is stored in a Programmable, Read Only Memory (PROM). The data word is coded and mixed with the carrier signal in a balanced modulator circuit, whose output is transmitted to the interrogation unit, where it is decoded and used as an identification signal. All electrical circuits of the answering device are perform on the same chip (icrocircuit) monolithic semiconductor, which can be carried out as a Semiconductor Complementary Metal Oxide (CMOS) device. US Patent: No. 4, 578, 992, issued April 1, 1986 to Galas, et al., And incorporated herein in its entirety, discloses a tire pressure indicating device, which includes a coil and a capacitor (electric capacitor) sensitive to pressure, which forms a passive oscillator circuit, which has a natural resonant frequency, which varies with the pressure of the rim, due to the changes caused to the value of the capacitance of the capacitor. The circuit is energized by the pulses supplied by a coil, placed outside the rim and secured to the vehicle, and the natural frequency of the passive oscillator circuit is detected. This natural frequency of the coil / capacitor circuit is indicative of the pressure in the pressure sensitive capacitor. US Patent No. 758,969, issued July 19, 1988 to Andre, et al., And incorporated herein in its entirety, discloses a device for measuring braking temperature and tire pressure in a set of wheels. The temperature sensors are located in a fixed part of each wheel, and communicate with the central computer by means of wires. A sensor - "-» ^ -..- «.« Pressure is mounted on each wheel, along with electronic elements for the frequency encoding the pressure data. Between each wheel and the fixed part of each wheel, there is a coupling element, preferably a rotary transformer to communicate with the system computer that ures the pressure of the central rim. The electronic elements that code the frequency preferably include a voltage / frequency converter, to convert a voltage constituting the signal delivered by the sensor to a frequency, which is a function of this voltage. The use of radio frequency (RF) answering machines, located or inside the rim or on the rim ring, in conjunction with the electronic circuit system, to transmit an RF signal that carries the inflation data (pressure) of the rim, it is also well known. An example of an RF responder, suitable to be installed in the frame of a pneumatic vehicle tire is disclosed in the International PCR Application Publication, No. WO 96/06 747, issued March 7, 1996 to Andrew, et al., and incorporated here in its entirety. This patent describes a system for inspecting the condition of the rim with a battery power transmission unit ("active") on each wheel of the vehicle, to detect the temperature, pressure and rotation of the vehicle. wheel. A common problem related to such active systems is the life of the battery (power supply), so the transmission unit is arranged so that the power is applied only during the detection and transmission of the data, and the intervals between the Transmissions of the data can be varied, depending on whether the rotation of the wheel has been detected. The transmitter unit (RF responder) includes a pressure (or piezo-resistive or capacitive silicon) detector, a thermistor to detect the temperature and an input to ure the battery voltage. These urements of the sensor are checked periodically, being guided one at a time to an analog to digital converter (A / D) by a multichannel. A microprocessor receives the digitized readings, converts them preferably to units of temperature and pressure, and transmits them periodically. The microprocessor has RAM, ROM and inputs, which include the A / D converter, a clock, a stopwatch, and a centrifugal detector. Controls the general operation of the transmitter unit. An identification number (ID) is stored in a non-volatile ROM and the calibration constants for the data conversion are stored in the RAM maintained by the battery. In normal operation mode, RF transmission, when required, includes ID, temperature reading and pressure reading. The Numerical values in the transmission cord are digitized and encoded for error correction, using Manchester coding. The calibration constants are preferably used to convert the readings of the voltages to suitable units of temperature and pressure, but they can alternatively be stored in the receiving unit of the vehicle and there used, to convert the transmitted voltage readings. In order to minimize the use by minimizing the transmission times, the calibration constants are only transmitted on demand from the receiving unit, preferably in the installation of the rim. The calibration constants include a constant to convert the voltage of the temperature sensor to degrees, and two constants to convert the voltage of the pressure sensor to pressure units, and also to correct for the temperature coefficient of the pressure sensor. An example of an RF answering machine suitable for being installed in the frame of an air vehicle tire is disclosed in US Patent :, No. 5, 51,959, issued September 19, 1995, to Schuermann and incorporated herein by reference. whole. This patent describes an answering system comprising an interrogation unit, for communicating with a plurality of response units. These response units contain a parallel resonant circuit, which has a coil and a capacitor, for the reception of an RF interrogation pulse. Connected to the parallel resonant circuit is a capacitor, which serves as an energy accumulator. A processor may be provided to receive the input signals from a sensor, which responds to the physical parameters in the environment of the response unit 12, for example, at room temperature, ambient pressure or the like. The sensor can, for example, be a sensor sensitive to air pressure. In this case, the response unit can be installed in the frame of a pneumatic vehicle tire and, with the help of an interrogation unit, contained in the vehicle, it is possible to continuously inspect the air pressure in the rim. Another example of an RF answering machine, suitable for being installed in the vehicle's pneumatic tire, is described in U.S. Patent No. 5,581,023, issued December 3, 1996 to Handfield, et al., And incorporated herein by reference. whole. This patent describes an answering machine and a receiving unit, preferably an answering machine APRA each vehicle tire, and this answering machine can be arranged entirely within the vehicle rim. The answering machine includes a pressure sensor and may include several other sensors, such as a temperature sensor. A modality of a Specific Integrated Circuit of . ^ -.- «- J».

Application (ASIC) of the answering machine is described. With reference to Figure 9 of the patent. The ASIC OOO) includes an oscillator (322) controlled by an external glass (325), a constant current device (310), which supplies the current flowing through an external pressure sensor (327) of variable resistance, a window comparator circuit (32), having a lower threshold for supplying the pressure information, established by the external resistors (329 and 331) connected in a voltage divider array, and an upper threshold, controlled by a resistor external variable (333). A number of jumpers or bridges (328) of three positions are used to program a serial number of the unique answering unit during its manufacture. The ASIC (300) is energized by an external battery (318), and a transmission circuit (312) is external to the ASIC (300). Another example of an RF responder, suitable for being installed in a pneumatic vehicle tire, is disclosed in U.S. Patent No. 5,661,651, issued August 26, 1997 to Geschke, et al., And incorporated herein by reference. its entirety This patent describes a wireless system for inspecting vehicle parameters, such as tire pressure. RF signals transmitted from different tires can be distributed based on the frequency of the signal transmitted. In order to detect the pressure inside a tire, the tire pressure inspection systems use a pressure sensor located inside the rim. Figure 2 of this patent shows the preferred structure for a parameter sensor and a transmitter circuit, when used to monitor the pressure inside a vehicle tire. The parameter sensor and circuit (20) of the transmitter include a pressure-to-voltage transducer (21), and a battery-powered power supply circuit. The need to monitor tire pressure when this tire is in use, is enhanced in the context of "flat tire operation" (flat tire operation), on tires that are capable of being used in a fully deflated condition. Such tires that operate flat can incorporate reinforced side walls, mechanisms to secure the rim from the rim to the rim, and a non-pneumatic rim (donut or screw) with the pneumatic rim able to drive to maintain control of the vehicle, after a catastrophic pressure loss, and it develops to the point where it becomes less and less noticeable to the driver that the tire has become deflated. The general purpose of using rim that operate flat, is to make it possible for the driver of a vehicle to continue driving with a pneumatic tire deflated by a limited distance (for example, 80 kilometers) before having to repair the tire, rather than stopping on one side of the road to repair the flat tire. Thus, it is generally convenient to provide a low pressure warning system within the vehicle, to alert (for example, by means of a light on the dashboard or a buzzing sound) to the driver of air loss in a pneumatic tire. Such warning systems are known, and do not form part of the present invention per se. Although the use of pressure transducers in pneumatic tires, in association with the electronic circuit system for transmitting pressure data, is generally well known, these tire pressure data systems have been plagued with the difficulties inherent in the rim environment. Such difficulties include, effectively and reliably, the coupling RF signals, the heavy use to which the rim is subjected and the electronic components, as well as the possibility of damaging effects on the rim of the incorporation of the pressure transducer and the electronic parts. in the rim / vehicle system. In the context of "passive" RF responders, which are powered by an external reader / interrogator, another problem is to generate predictable voltage levels and * • - "" "• -i - * a- * lft; '---" "- r stable, within the answering machine, that the circuit system inside the answering machine can perform for its design specification An example of a pneumatic tire, which has an integrated circuit answering machine (IC) and a pressure transducer, is disclosed in the patent USA, No. 5,218,851, commonly owned, issued June 15, 1993 to Brown, et al., And incorporated herein by reference in its entirety. This patent describes an RF answering machine mounted inside a pneumatic tire. In the interrogation (scrutiny) by an external RF signal, provided by a "reader", the answering machine transmits the rim identification and the tire pressure data in coded form Pollack, et al., And incorporated herein in its entirety as a reference. As described in this patent, in a rim that has already been manufactured, the answering machine can be attached to an inner surface of the rim by means of a patch of the rim or other similar material or device. Another example of an RF answering machine in a pneumatic tire is described in U.S. Patent No. 4, 911, 217, commonly owned, issued on March 27, 1990 to Dunn, et al., And incorporated herein by reference in its entirety. This patent discloses an answering machine having two electrodes, the first of which is positioned so that the average spacing of the surface of the first electrode from one of the steel reinforcing components of the rim, such as an annular tension member, in its steel reinforced bead or ridge, it is substantially less than the average spacing of the second electrode surface from the reinforcement component. Figure 1 of this patent also discloses a prior art identification system ("reader") that can be used to interrogate and energize the answering machine within the rim. The identification system includes a hand-held portable module, within which there is an exciter and associated circuit system for indicating to a user the numerical identification of the rim / answering machine, in response to an interrogation signal.

Typically, in an IC answering machine, the IC chip (microcircuit) and other components are mounted and / or connected to a substrate, such as a printed circuit board (PCB). For example, a pressure transducer can be mounted from the PCB and wired, either directly to the IC chip, or indirectly to the IC chip, by means of conductive traces on the PCB. The PCB substrate is suitably an epoxy reinforced laminate, which has a thickness of 508 microns, and has a glass transition temperature exceeding 175 ° (degrees Celsius). A suitable PCB material is available as a "high performance" FR-4 epoxy laminate, sold 65M90, sold by Westinghouse Electric Corporation, Koper Laminates Division, l? 840 Bradley Avenue, Sylmar, CA 91342. A number of RF answering machines, suitable for mounting within a pneumatic tire, have been described so far. The environment within which an answering machine mounted on the tire must operate reliably, which is included during its manufacture and in use, presents numerous challenges to the successful operation of the transducer. For example, the pressure sensor used with the answering machine will preferably have an operating temperature that varies up to 125 ° C, and should be able to withstand a manufacturing temperature of about 177 ° C. For truck tire applications, the pressure sensor must have a operating pressure range of approximately 345 to 827 kP (kiloPascals) and must be able to withstand the pressure during the manufacture of the rim up to 758 kP. Accuracy, which includes the sum of all contributions to its inaccuracy, must be in the order of plus or minus 3% of the full scale. The rtability and stability of the pressure signal must fall within a specified accuracy range. The answering machine must, therefore, be able to operate reliably despite the wide range of pressures and temperatures. Additionally, the answering machine (d) devices formed of a conductive conductive ink variable laminate; and (e) devices formed of an elastomer composition of variable conductance.

Brief Summary of the Invention It is a general object of the invention to provide an improved pneumatic tire having a radiofrequency (RF) answering machine ("tag"), as defined in one or more of the appended claims and, as such, have the ability to be built to achieve one or more of the subsidiary objects. It is another object of the invention to provide an improved pneumatic tire, having a radio frequency (RF) answering machine ("tag"), capable of transmitting data related to the pneumatic tire and the parameters associated with this pneumatic tire to an external reader / interrogator . It is a further object of the invention to provide an improved radiofrequency (RF) answering machine ("tag") capable of transmitting data relating to a monitored object and the parameters associated with the object to an external reader / interrogator. It is an object of the present invention to provide pressure data from an answering machine associated with a pneumatic tire to a reader / interrogator lüm rfii external, in a manner in which the temperature ddence of the pressure data can be eliminated from the pressure data, which results in a pressure compensated temperature measurement, which is displayed by an external reader / interrogator. According to the invention, a radio frequency (RF) responder is a partner with a pneumatic tire and comprises a circuit system capable of transmitting unique information to the pneumatic tire to an external reader / interrogator. Additionally, one or more sensors (transducers) provide the real time measurement of the rim's operating parameters, inside the pneumatic tire. These measurements are transmitted to the external reader / interrogator, in the form of data, in a data stream in a signal, which is produced by the answering machine, such as by the printing (modulation) of the data stream in a signal of RF transmitted by the answering machine to the external reader / interrogator. According to one aspect of the invention, the answering machine is preferably energized by an RF signal from the external reader / interrogator. However, it is within the scope of this invention that the answering machine is energized by batteries. According to one aspect of the invention, the answering machine is preferably made on a single chip of integrated circuit (IC), with a minimum of external instrumentalities, such as an antenna. According to one aspect of the invention, at least one real-time parameter, which is measured, is the temperature. Preferably, the temperature sensor is embedded ("inside the chip") on the IC chip of the answering machine. According to one aspect of the invention, an additional parameter of real time, which can be measured, is the pressure. The pressure is preferably measured by a separate pressure sensor ("off-chip"), which is preferably of a type that varies in its capacitance value as a function of ambient pressure. Preferably, the temperature sensor is arranged so that it is subjected to substantially the same ambient temperature as the pressure sensor, so a true pressure, compensated for in temperature, can be easily calculated. In accordance with one aspect of the invention, another additional parameter that can be measured is in the form of an indication that an excessively high, albeit transient, temperature condition has previously occurred. It should be understood that this parameter is different in nature than the real-time parameters of temperature and pressure. An example of a suitable sensor to detect and indicate that such a transient over-temperature condition has occurred, it can be found in U.S. Patent No. 5,712,609, issued January 27, 1998, to Mehregany, et al., and incorporated herein by reference in its whole. The Mehregany sensor is said to be exemplary of a Maximum Temperature Measuring Switch (MTMS), for use with the answering machine of the present invention. Reference is also made to U.S. Patent No. 5,706,565, which is incorporated herein by reference in its entirety. The answering machine is preferably located inside the pneumatic tire. However, it is within the scope of the invention that this answering machine is associated with another object that is monitored, such as an animal. In a preferred embodiment, the answering machine comprises: • a circuit system for receiving an RF signal, at a first frequency (Fi), from the external reader / interrogator and processing the received RF signal, to supply the energy pulses and time to another circuit system; "a circuit system for controlling one or more time windows, during which the measurement (s) of real time parameters are made and captured; • a circuit system for storing the calibration constants; and • a circuit system for printing (preferably by the Modulation of Phase Shift Key (PSK)) the measurements of the actual time parameter captured and the indication of the condition of the excessive temperature over a signal, which is transmitted back to the external reader / interrogator again at a second frequency (Fe) that is different from the first frequency (Fi). Other objects, features and advantages of the invention will become apparent in the light of the following description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is now made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The drawings are intended to be illustrative and not limiting. Certain elements in selected drawings can be illustrated, not to scale, for clarity of illustration. Often, similar elements in the drawings can be mentioned by similar reference numbers. For example, the element 199 in a figure (or modality) it may be similar in many respects to element 299 in another figure (or modality). Such a relationship, if any, between similar elements in different figures or modalities, will become evident throughout the specification, which includes, if applicable, the claims and the summary. In some cases, similar elements can be referred to with similar numbers in a single drawing. For example, a plurality of elements 199 may be named 199a, 199b, 199c, etc. The cross-sectional views, presented here, may be in the form of "splices" or "near-view" cross-sectional views, omitting certain background lines that might otherwise be visible in a true cross-sectional view, for clarity of illustration. The structure, operation and advantages of the present preferred embodiment of the invention will become more apparent considering the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a generalized block diagram of an answering system for RF, comprising an external reader / interrogator and an RF responder, within a pneumatic tire, according to the prior art; Figure 2 is a block diagram of the main components of an RF transponder, in accordance with the present invention; Figure 3 is a schematic diagram of major portions of the RF responder of Figure 2, in accordance with the present invention; Figure 3A is a schematic diagram of a portion of the RF answering device of Figure 2, according to the invention; Figure 3B is a schematic diagram of a portion of the RF answering device of Figure 2, according to the invention; Figure 3C is a diagram of a memory space, inside the RF answering machine of Figure 2, illustrating how the data can be arranged and transmitted, according to the invention; and Figure 4 is a schematic block diagram of a reader / interrogator receiving portion according to the invention;Detailed Description of the Invention Figure 1 illustrates a prior art RF answering system 100, comprising an RF (radio frequency) answering machine 102, disposed within (eg, mounted to an inner surface of) a pneumatic tire 104. An antenna, not shown, is mounted inside the rim 10 and connected to the answering machine 102. This answering machine 102 is an electronic device, capable of transmitting an RF signal comprising unique identification information (ID) (eg, its own serial number, or an identification number of the object with which it is associated - in this example, the rim 104) as well as data indicative of a parameter measurement, such as an environmental pressure detected by a sensor (not shown) associated with the answering machine 102 to an external reader / interrogator 106. This external reader / interrogator 106 supplies an RF signal to interrogate the answering machine 102, and includes a rod 108 having an antenna 110, an exhibit panel 112, to display the information transmitted from the answering machine 102, and controls (switches, buttons, knobs, etc.) 114 for a user to manipulate the functions of the reader / interrogator 106. The present invention is directed to Maria to put into practice the RF answering machine. However, certain functionality for a reader / interrogator will be compatible with the answering machine of the present invention discussed below with respect to Figure 4. As shown, the ID and / or measurement information of the parameter can be encoded (printed) in a variety of ways in the signal transmitted by the answering machine 102 to the reader / interrogator 106, and subsequently, "decoded" (retrieved) in the reader / interrogator 106 to display it to the user. The RF responder 102 can be "passive", in that it is energized by an RF signal, generated by the external reader / interrogator 106 and emitted by the antenna 108. Alternatively, the RF responder can be "active", in that It is powered by battery. Answering machine systems, such as the answering system 100 described herein, are well known. Figure 2 is a block diagram of RF responder 200 (compare to 102) of the present invention, illustrating its main functional components. The answering machine 200 is preferably carried out on a single integrated circuit chip (IC), shown inside the dashed line 202, to which a number of external components are connected. Other dashed lines in the Figure indicate major functional "blocks" of the answering machine 200, and include a "core" 204 of the answering machine and a sensor interface 206. Components external to the IC chip 202 include an antenna system 210, comprising an antenna 212 and a capacitor 214 connected through coil 212, to form an LC resonant tank circuit, an external precision resistor ("Rext"). ) 216, an external capacitor ("Cp") 218, which detects the pressure and an optional switch External Maximum Temperature Measurement ("MTMS") 220. The antenna may be in the form of a coil antenna, a loop antenna, a dipole antenna, and the like. Alternatively, the signal produced by the answering machine can be provided on a transmission line. Later, an answering machine having a coil antenna will be described. The answering machine core 204 includes an interface circuitry 222, for processing an RF signal, such as a 125 kHz (kiloHertz) modulated carrier signal, received by the antenna 212. To rectify the received RF signal, and to supply voltages for (Fe) of a signal, which is transmitted by the answering machine to an external reader / interrogator. A time generator / sequencer circuit 226 receives the clock pulses from the clock generator circuit 224 and processes (eg, divides) these clock pulses to generate time windows (Wt and WP, described below) for predetermined periods of time. weather, during which the measurement parameters (for example, temperature and pressure, are made) The time windows (Wt and WP) may be of substantially equal duration or of unequal duration. it also controls the time and sequence of various functions (e.g., pressure and capture measurement, temperature measurement and capture, described below in greater detail) made in the same sensor interface 06, and is preferably performed as a Algorithmic state machine (ASM) The answering machine core 204 further includes a circuit 230 of the recorder / counter, which includes a temperature recorder 232 (for example 12 bits) and a pressure recorder 234 (for example 12) bits) to capture and store the measurements of temperature and pressure (amounts), respectively, and a steerable memory block 236, which includes an array of EPROM. 232 and 234 and the EEPROM array 236 is they show in dashed lines 238, which represent a block of memory that is steerable on the IC chip. Circuit 230 of the register / counter also includes a multichannel and a column decoder 240, as well as a row decoder 242, to control the sequence in which signals (i.e., data) are produced on a line 244 to a modulation circuit 246, which, by means of the circuit system 222 of the interface, communicates the operating characteristics of the rim, measured, selected, in a data stream by means of the interface 210 of the antenna to a reader / external interrogator (106, Figure 1). The answering machine core 204 also includes a baud rate generator 48, which controls the which relates to a predictable characteristic voltage of a temperature-sensitive component (e.g., Vbe of a transistor Ql, described below) which is superimposed on the external resistor (Rext) 216. The output current I (T) in the line 251 is provided to a circuit 252 that governs the current and to a relaxation oscillator 254. In general terms, this relaxation oscillator 254 oscillates at a frequency controlled by a rate of change in voltage (dV / dT) produced in an output line 253 from the circuit 252 that governs the current. The rate of change of voltage on line 253 is a function of the output current I (T) on line 251 and of the internal capacitances (Cp) associated with the relaxation oscillator, as well as the external capacitance (Cp) which was switched in the oscillator circuit. An output signal from the relaxation oscillator 254 is provided on a line 255 which, as will be explained later in detail, is indicative of both the ambient temperature and the ambient pressure. As used herein, the term "ambient" refers to the parameter that is measured in the vicinity of the answering machine, more particularly the respective sensors associated with the answering machine. When this answering machine is mounted inside a pneumatic tire, the "ambient pressure" refers to the pressure inside the tire.

During the operation, an RF signal from an external source (ie, the reader / interrogator, not shown, compare at 106, Figure 1) is received by antenna 212. This RF signal is rectified and used to power the answering machine 200 of RF. The modulation information applied to the modulation circuit 236 is used to alter the characteristics of the antenna interface 236 (e.g., impedance, resonant frequency, etc.). These alterations are detected by the external reader / interrogator and thus decoded, providing the communication of the temperature and pressure information again from the answering machine 200 to the external reader / interrogator. The generator / time sequencer circuit 226 controls whether the current I (T) on the line 251 is "governed" on one or the other of the two capacitors (Cp ?? or Cira / described below, with respect to the oscillator 312 of relaxation) associated with the relaxation oscillator 254 and if the capacitance (Cp) 218 that detects the external pressure is or is not included the generation of an output signal (Fose) by the relationship oscillator 254. For example, to measure the temperature, the current I (T) is governed in the capacitors (CFX) of the internal oscillator, but the capacitor (Cp) that detects the pressure is disconnected from (not included in) those capacitances. This means that the frequency of the oscillator output signal, seen on line 255, is a function of temperature alone. When the capacitor (Cp) 218 which senses the pressure is "switched", then the output frequencies of oscillator 254 on line 255, as explained below in greater detail, will be a function of both pressure and temperature. As described in more detail below, an algorithm is used in the reader / interrogator to generate a pressure measurement independent of the temperature. As controlled by circuit 226 generator / time sequencer, any of the 12-bit temperature recorder 232 or the 12-bit pressure recorder 234 (depending on whether the temperature or pressure is measured), how much (captures) the oscillations of the oscillator output signal on line 255. ( The counters, not shown) are associated with these "recorders"). The "window" of time provided by the generator circuit 226 / time sequencer has a controlled, known duration. As a result, the amount that remains in (captured by) the counter (recorder) of the respective temperature or pressure, when the time window "closes" is a function of (proportional to) the oscillation frequency (Fose) of the oscillator 254 of relaxation 254 and, therefore, a function of temperature or pressure, when measured.

The EEPROM 236 array is used to maintain the calibration constants that the reader system uses to convert the temperature and pressure quantities (Nt and NF, respectively, described in more detail below) into the temperature and pressure readings, which can be displayed (for example, by means of the display 112) to a user. The EEPROM array 236 can also store the answering machine ID, calibration data for the answering machine and other particular data to a given answering machine. Figure 3 is a more detailed schematic diagram 300 of several of the components of the answering machine 200 of Figure 2, primarily those components described above with respect to section 206 of the sensor interface of Figure 2. In this schematic diagram 300, conventional circuit symbols are used. For example, the lines that cross each other do not connect to each other, unless there is a "point" in their union (crossing), in this case, the lines are connected to each other. Conventional symbols are used for transistors, diodes, ground connections, resistors, capacitors, switches, comparators, inverters and logic gates (for example "AND" (Y), "NAND" (NO-Y), "OR" (OR ), "ÑOR" (NI) The circuit was described in terms of a CMOS mode, where "P" (for example "Pl") indicates a PMOS transistor (P channel) and "N" (for example "NI") india an NMOS transistor (Channel N). The CMOS transistors are of the FET (field effect transistor) type, each having three "nodes" or "terminals", that is, a "source" (S), a "drain" (D) and a "gate ( G), which controls the flow of current between the source and the drain In the description that follows, it will be evident that the number of PMOS and NMOS transistors are "connected by diode" which means that their drainage or consumption (D) is connects to its gate (G) The general theory of operation of transistors, particularly CMOS transistors, is well known to those of ordinary skill in the art to which the present invention pertains more closely, as will be apparent from the description that follows, a number of CMOS transistors are connected in a mirror-like configuration The concept of mirror-type current is well known and, in its simplest form, comprises two transistors of similar polarity (eg, two PMOS transistors) having their gates connected each other, and one of the pair of transistors is connected by diode. The type of mirror current usually involves causing a current to flow through the diode-connected transistor, which results in a gate voltage in the diode-connected transistor, required to produce that current. In general, the The gate voltage of the diode-connected transistor is forced to become any voltage necessary to produce the mirror current through that transistor. Since the diode-connected transistor, by definition, has no gate current, by applying the gate voltage of the diode-connected transistor to any other identically connected transistor, a mirror-type current will flow through the identically connected transistor. Typically, mirror current type transistors will all have the same physical area, in this case, the mirror current will be essentially the same as the current that is made of the mirror type. It is also known to produce a mirror current, which is either greater than or less than the mirror current, making one of the transistors physically larger or smaller (in area) than the other. When identically connected transistors, which have different areas are connected in a mirror current configuration, their scaled areas (higher or lower) will produce correspondingly scaled (higher or lower) currents. At the essential point the numerous connections between the various components of the circuit are clearly illustrated in the figure, and descriptive emphasis is given to the various functions of the interactions among the various components of the circuit, rather than in exposing extensively each and every individual connection between the various components, all of which is explicitly illustrated in the figure. The antenna system 210 comprises a serpentine antenna 212 and a capacitor 214, connected through the antenna 212, to form a resonant tank circuit LC, with the proviso that an alternating current (AC) output produces a rectifier circuit 302 full wave. This full wave rectifier circuit 302 comprises two PMOS transistors and two diodes, connected in a conventional manner, as shown, and produces a full wave, rectified, direct current (DC) voltage on a line 303. A capacitor 304 is connected between line 303 and ground, to "smooth" (filter) the variations ("curled") in the full-wave rectified DC voltage on line 203. The voltage on line 303 thus becomes a voltage that is can be used for the remaining components of the answering machine - in this case, a positive supply voltage (Vcc) on line 303. A circuit 306, temperature detector, which corresponds approximately to the basic emitter of the current voltage converter 250 of the Figure 2 is connected between line 303 (Vcc) and ground, and includes four CMOS transistors labeled Pl, P2, NI and N2, and a lateral bipolar transistor labeled Q1, and connected to external resistor 216 (Rext). Transistors P2 and NI are connected by diode, as illustrated. The two transistors Pl and P2 are connected in a mirror-type configuration, and the two transistors NI and N2 are also connected in what can be considered as a mirror-type configuration. The source of the transistor NI is connected by means of the transistor Ql to ground, and the source of the transistor N2 is connected by means of an external resistor (Rext) 216 to ground. As will be apparent, the ability of the temperature sensing circuit 306 to produce a signal (i.e., a current) that is proportional to a detected temperature (ambient) (for example, within the rim with which the answering machine associates) is greatly dependent on the characteristic that the base emitter voltage of transistor Ql is a function of highly predictable and repeatable temperature. The resistor (Rext) 216 is an external resistor, of precision, of reference,. whose value is substantially independent of the temperature (in contrast to the temperature dependence of the transistor Ql). A suitable value for the resistor (Rext) 216 is 20.5 kO. The transistor N2 is connected between the transistor P2 and the external resistor 216 (Rext) in a "follower" mode. source. "As the voltage is printed on the gate of transistor N2, its source voltage will" follow "its gate voltage (minus an inherent voltage drop (Vgs) between its gate and its source.) As the current flows through the NI transistor, its gate voltage will be shifted by its gate-source voltage drop (Vgs) above the emitter voltage in transistor Ql, since the NI and N2 transistors are essentially identical, with the same current flowing through of each of the two transistors NI and N2, they will have identical source-gate voltage drops (Vgs). As a result, the voltage of the source of transistor N2 through external resistor 216 (Rext) will be essentially identical to the voltage in the emitter of transistor Ql Thus, by applying the law of Ohm (E = IR or I = E / R), the current through the external resistor 216 (Rext) will be equal to the voltage of the emitter of the transistor Ql divided by the resistance from l External resistor 216 (Rext). In normal operation, all the current flowing through the external resistor (Rext) 216, flows through the source of the transistor N2 and, consequently, through the transistor P2 connected to the diode. By the current type connection in mirror, the current through the transistor P2 is duplicated (mirror shape) in transistor Pl and then duplicated (mirror shape) in transistor P. This ensures that the current flowing through the NI and N2 transistors is the same, at all times, which also helps to ensure that the emitter voltage in transistor Ql and the voltage across the external resistor (Rext) 216 are identical, independent of voltage and process variations. As mentioned before, transistors NI and N2 are connected in what can generally be considered as a mirror-like configuration. However, since they are not strictly connected identically, their function in circuit 306 is mainly to "match" Ql and Rext. In essence, the circuit 306 ensures that the current I (T) flowing through the external resistor (Rext) is predictable, and is a function of the absolute temperature (T) of the transistor (Ql). As described in more detail below, this current, I (T), dependent on temperature, flowing through the external resistor (Rext) 216 is in mirror to a relaxation oscillator (312, described below) to supply a signal indicative of the temperature of the transistor Ql to the external reader (106, Figure 1). As described in more detail below, the frequency output (Fose) of the relaxation oscillator 312 will be a function of the absolute temperature (T) of the transistor Ql. At this point, it is useful to note that it is essentially the transistor Ql which is used as the temperature detecting element of the general answering circuit. This answering circuit advantageously employs an inherent characteristic of such a transistor realized in CMOS technology, that the base emitter voltage of transistor Ql will vary by a predictable amount of -2.2 mv / ° C (millivolts per degrees Celsius). It should be noted that the answering machine of the present invention was described in terms of a "passive" device, relying on the RF energy that is supplied by an external source (106, Figure 1) to energize its circuitry. However, it is within the scope of this invention that the answering machine contains its own power supply, such as in the form of a battery. In any case, when the circuitry is first energized, as described with respect to the temperature sensing circuit 306, it is important to ensure that they rise to their normal operating state from their resting state in a reliable and predictable manner. (controlled). For this purpose, two lines 305 and 307 are illustrated which are connected between the temperature sensing circuit 306 and a "start" circuit 308.

This start circuit 308 is connected between the supply voltage (Vcc) on line 303 and ground, and serves two main purposes: (1) to get the current to flow in the temperature sensing circuit. 306, when the answering machine (200) first boots from a low energy state and (ii) gives the type of mirror and converts the current flowing through the transistor P2 from a current with reference to the supply to a current with reference to ground . The start is started by transistor P3. The P3 transistor is manufactured to have a high channel resistance, so as to operate in a "light pull" mode. With its gate connected to ground, it will always be "active" and behave essentially as a resistor, which has a sufficiently high resistance (for example of> 10 k ohms). Since at the start no current flows anywhere in the circuit, transistor P3 operates to pull the gate of transistor N3 towards the supply voltage (Vcc), thereby making transistor N3"active", while effectively connecting source N3 of the transistor to its drain, which, in turn, causes the current to flow through the transistor P2 connected to the diode of the temperature detector 306 in the drain of the transistor N3. This causes the voltage at the source of transistor P2 to decrease, causing the current to flow in transistors Pl and P4. As current flows through transistor P4 inside transistor N5 connected by diode, a mirror current type connection, between transistors N4 and N5 causes a corresponding current to flow through transistor N4, thus pulling the gate of transistor N3 to ground, effectively disconnecting the flow of current through transistor N3. However, with the current flowing now through the mirror current type transistors, Pl, P2 and P4; , the current flowing from the transistor Pl through the transistor NI inside the transistor Ql forces the circuit 306 which detects the temperature to "start" in its stable operating point state (rather than its zero current state). After start-up, transistor N3 essentially "comes out" of the circuit, having performed its intended function. The transistor N5 is connected in the mirror current configuration with the transistor N4 (and, as described below, with the transistor N6). Therefore, essentially, with a current equivalent to the current through the external resistor (Rext) 216 flowing through the transistor N5, the same current flows through the transistor N4, thus establishing a reference voltage (Nbias) on line 309. This reference voltage (Nbvias) on line 309, as well as a supply voltage (Vdd) on line 309 ', are provided to a circuit 310 of current scale. This supply voltage (Vdd) on line 309 ', is provided in any suitable manner, such as a band gap voltage (Vbg) generated in a conventional manner at any location on the chip, and its magnitude (eg example 1.32 volts) must be independent of temperature, as inherent in the silicon process used to obtain the chip. The provision of such stable voltage (for example the band gap) (Vbg) and the supply voltage (for example, Vdd) derived therefrom, is well within the point of view of an ordinary expert in the field to which it belongs the present invention, and is described in more detail below with respect to Figure 3B. The current-scale circuit 310 is constructed in the following exemplary manner. The sources of the transistors, P5 and P6, are connected to the supply voltage Vdd. . The gate of a transistor N6 receives the reference voltage (Nbias) on line 309. The transistor N6 is connected in a configuration of the current type in mirror, with the transistor N5 (as with the transistor N4, mentioned above) and therefore, it will be in mirror with the current flow I (T) through the transistors N4 and N5. Consequently, the flow of the current through the transistor P5, connected will mirror the flow of the current through the transistors N4, N5 and N6. Transistors P5 and P6 are connected in a mirror-like configuration, but are manufactured (using conventional CMOS manufacturing techniques) so that the current flowing through transistor P6 is scaled up or down by the ratio (N ) of the physical area of transistor P5 to the physical area of transistor P6. For example, if transistor P6 is smaller in size than transistor P5 (ie transistor P5 is "N" times larger in area than transistor P6), then the current flowing through transistor P6 will be commensurate (N times ) lower than the current flowing through transistor P5. Thus, the "scaled" current flowing through the transistor P6 is labeled "I (T) / N" in the figure, and is provided on a line 311 to a circuit 312 of the relaxation oscillator, it is well known that the ratio of the currents between transistors P5 and P6, can easily be established by conventional circuit processing techniques, such as by simply doing one of the transistors larger than the other, or making one of the two transistors as the aggregate of two or more transistors of the same size, so that its aggregate area is greater than the area of the other of the two transistors. Circuit 312 of the relaxation oscillator is of a sufficiently conventional design and includes two pairs of transistors at the "front end" of each of its two-phase trajectories - a pair of complementary resistors P7 and N7 at the front end of a trajectory of phase (fl) 31a, and the other pair of complementary transistors P8 and N8, at the front end of the other phase path (f2) 314b. Connected as illustrated, for a given pair of transistors (for example P7 and N7), when their common gate voltage is high (ie, towards the positive supply), their output will be grounded, and when their common gate voltage is low, they will supply the current I (T) / N, which flows on line 311 to one of the respective phase paths (for example 314a) of the relaxation oscillator 31. As is known, in such an arrangement, when the voltage The common gate of one of the pairs of transistors (for example P7 and N7) is high, the common gate voltage of the other pair of transistors (for example, P8 and N8) will be low, and vice versa. In this In this manner, each phase path 314a and 314b has a duty cycle (ie, its "active" time), which may be the same as or may be different from the duty cycle of the other phase path 314b and 314a, respectively . Thus, each pair of transistors (for example, P7 and N7) can be considered as an "input switch" to their respective phase path (e.g. 314a). Each phase path 314a and 314b of the relaxation oscillator 31 has a comparator 316a and 316b, respectively, at its input, and has a CF capacitor? and fixed value CFX2, respectively, connected between the negative (-) input of comparators 316a and 316b and ground. The CFX capacitors? and CFX have exemplary capacitance values of 2-5 pf (picofarads) and 2-5 pf, respectively, and are preferably performed as "on-chip" devices, such as poly-to-poly capacitors, which exhibit a low temperature coefficient ( for example less than 20 ppm). The positive (+) (terminal) inputs of comparators 315a and 316b are joined together and set to a reference threshold voltage Vbg, such as 1.32 volts, which is independent of temperature. An "NI" logic gate, 318a and 318b, is connected to the output of each phase path 314a and 314b, respectively, and the two gates NI, 318a and 318b, are they cross-connect to form a latch circuit having an output on a line 319. The cross-connected NI gates 318a and 318b are thus capable of functioning as a bistable circuit, or an RS latch (re-adjustment / adjustment). When the common gate voltage of one of the input switches (for example P7 and N7) is high, the respective capacitor (for example CFXI) for that phase path (for example, 314a) is connected to ground (shorted, which causes lack of charge). Conversely, when the common gate voltage of one of the input switches (for example, P7 and N7) is high, the I (T) / N scale current is applied to (allowing flow in) the respective capacitor ( for example, CFX1) for that phase path (for example, 314a) and the capacitor and starts charging (acquiring an increasing voltage across the capacitor). When the voltage across the capacitor reaches the comparator reference voltage (for example, 1.32 volts) the comparator output goes low and changes the state of latch output 318a / 318b on line 319. In this way, the oscillator Will relaxation oscillate at a frequency (Fose) determined by the rise time of the Cra and CF2 capacitors and, importantly, by the I (T) / N scale current being supplied to the CF capacitors ?? and CF? 2. With a greater current I (T) / N being supplied, the voltages of the CFX capacitors? and CFX2, will rise faster, crossing the threshold voltage faster, and causing the relaxation oscillator 312 to oscillate faster, thus increasing the frequency of the Trench signal on line 319. The Fose signal on line 319 is reversed by an inverter 320, as shown, for supplying a Fose 'signal on line 321. As described in more detail below, oscillator 312 is controlled to operate in two mutually exclusive modes, a temperature sensing mode (between times tO and ti) and the pressure detector mode (between times ti and t2), as controlled by the time generator / sequencer 226. The frequency of the output signal of the oscillator (and Fose ') will be different in each case. one of these two modes. GENERATION OF TEMPERATURE AND PRESSURE SIGNALS In the exemplary context of the answering machine 200 associated with the pneumatic tire, it is primarily desirable to determine the pressure inside the pneumatic tire. For example, a typical rim of a passenger vehicle can be appropriately inflated to around 221 kP). For example, it is estimated that a decrease of approximately 10% in fuel consumption can be made if the pneumatic tires on the vehicles are They operate at their specified pressure. Although vehicle fleet operators are typically sensitive to this problem and frequently check and adjust the tire pressure, the average operator of a passenger vehicle is often less inclined to check the tire pressure until, for example, the rim has visibly flattened. In such cases, reading the LCD (liquid crystal display) or the like on the dashboard of a car, can supply the information of the dynamic rim to the operator of a vehicle, whose pneumatic tires are equipped with an answering machine, such as that described here. Of no less significance is the emergence of tires that "operate deflated," which were sold by several tire manufacturers. The Goodyear EMT (Extended Mobility Tire) tire series is an example of a flat tire that has a general purpose of allowing a driver to travel up to 80 kilometers with a flat tire at "reasonable" operating speeds. (for example at 96 kilometers per hour), while maintaining normal control over the vehicle. Such tires that operate flat or deflated are generally well known, and do not form a portion of the present invention, per se. When a tire runs flat, it is particularly important that the driver is alerted to the fact that the vehicle is operating in a "Additional borrowed time" as indicated by a signal, either visual or audio (eg, warning sound) that the tire is truly deflated and needs to be repaired or replaced soon for your convenience. By allowing the relaxation oscillator 312 to operate, the frequency of its output signal Fose (and Fose ') will be a function of the absolute temperature of (detected by) the transistor Ql. This is true in both the mode of operation that detects the temperature and in the mode that detects the pressure. In the mode that detects the temperature, and in the case that the values of the capacitance for Cm and CFX2 are equal, which is preferred, the relaxation oscillator 312 will have a symmetrical duty cycle (balanced, 50%). In the mode that senses the pressure, the capacitor (Cp) which senses the pressure, 218, is interrupted by a semiconductor switch 350 through CF? 2, which changes the duty cycle and the output frequency Fose (and Fose '). ) of the relaxation oscillator. In the mode that detects the temperature, only the fixed capacitors, CFX? and CF 2 are alternatively charged (and discharged) resulting in 50% of the duty cycle with a period proportional to the ambient temperature. In the mode that senses the pressure, the capacitor (Cp) that senses the pressure, 218, is switched in the phase path 314b of oscillator 312, Thus, for a given temperature, for the first half of the period of the oscillator, the phase path 314a behaves in the same way as in the mode sensing the temperature, and for the second half of the oscillator period, the phase path 324b behaves in a manner that is proportional to the value of the capacitance of the fixed capacitor CFX2 plus the value of the capacitance of the capacitor (Cp) that detects the pressure. This, in effect, decreases the oscillator and changes its duty cycle. The change in the duty cycle is indicative of the relationship of CP to CFX2. Thus, from the ratio of the two periods (with and without Cp in the circuit, it is directly calculated that the additional capacitance Cp is, here the pressure detected.) As described in more detail below, the temperature dependence of the output of the oscillator in the mode that senses the pressure, can be completely eliminated, in a direct way.This "decrease" of the oscillator, when the capacitor (Cp) that detects the pressure is changed in the oscillator circuit, inevitably results in Relatively smaller oscillator output pulses (reduced output frequency) for counting during a given pressure measurement window (eg, Wp) that during a measurement window and temperature of similar duration (eg, Wt). words, an oscillator "decreased" will reduce the rate at which the indicative quantities of the parameter measurement are collected. In order to increase the resolution (quantity) of the quantities (Np) generated during the window (Wp) of pressure measurement, it is considered that the window (Wp) of pressure measurement can be increased in size (change in duration) in order to allow the capture of an appropriate number of pressure quantities in the pressure recorder 234. This can be easily achieved in a simple way by setting a value (otherwise) greater for time t2, which sets the end of the pressure measurement window (Wp) in the pressure detector mode (between times ti and t2) ), as controlled by the time generator / sequencer 226. For example, the window Wt of temperature measurement (between the times tO and ti) can be of the order of several milliseconds (for example eight) and the window Wp of pressure measurement can be of the order of tens or dozens (for example forty ) of milliseconds. Alternatively, it is considered that the scale current (I (T) / N) flowing out of the current-scale circuit 310 to the relaxation oscillator 312 may be increased during the pressure measurement window (Wp) to increase the fundamental frequency of the relaxation oscillator 312, thus increasing the overall resolution of the amount of pressure. This can be achieved easily, for example, in the case of P6 being smaller in size (area) than transistor P5, simply by changing in a transistor P6 '(not shown, in place of transistor P6, this transistor P61 and having an area larger than transistor P6, so that the ratio of the areas of the transistors P5 and P6 is closer to the unit (i.e., less falling scale) and the current to the relaxation oscillator 31, so its counting rate is increased. of the other transistor P6 'is easily cted with a switch (not shown) comparable to the aforementioned switch 350, which changes in the capacitor (Cp) 218 which detects the pressure A one of ordinary skill in the art to which the present invention pertains, will easily understand the "downward" type displacement of the oscillator, when the capacitor (Cp) 218 of the pressure detector is changed in the oscillator circuit, from the teachings presented here. the answering machine is activated, the temperature and pressure are measured continuously, and these measurements are transmitted back to the external reader / interrogator (106) as data words in the data stream. For example, each temperature and pressure parameter may be transmitted back to the reader / interrogator (106) as 12-bit data words as selected portions. (known) of a larger data stream (for example of 144 bits). A bit in the general data stream can be dedicated to the state (eg, "closed" or "open") of the MTMS switch (220). A complete description of an exemplary data stream being transmitted by the answering machine to the external reader / interrogator and described below with reference to Figure 3C. The temperature is suitably measured by counting the cycle output number of the oscillator 312 for a fixed period of time (time window of tO to ti) with a period T. For example, a descending counter (associated with the temperature recorder (232)) can be synchronized by the oscillator, so that at the end of the window Wt, a quantity Nt of temperature is generated. The relationship between Nt and the temperature is linear. SUPPLY OF OPTIMUM FORM OF PRESSURE SENSITIVITY Obtaining (and displaying) an exact pressure reading is of utmost importance when monitoring the pressure of a pneumatic tire, certain parameters of the responding circuit can be established, to maximize sensitivity of the pressure and, therefore, improve the accuracy of the reading of the pressure displayed by the external reader / interrogator (106). As described above, the answering machine responds to the changing capacitance of the pressure sensor (Cp) 218, changing the value of a 12-bit binary word, which is transmitted to the external reader / interrogator (106). This binary word is the amount of a frequency of the oscillator during a window Wp of time (between ti and t2) established by the time generator / sequencer 226. The pressure response can, therefore, be described as the change in quantities per unit change in capacitance of the capacitor (Cp) which senses the pressure, 218. The sensitivity of the answering machine pressure has been found to be dependent on a number of factors, each of which can be analyzed. For example, it has been determined that: (a) increasing the I (T) / N current to oscillator 312 will proportionally increase the amounts of the pressure, Np for a given capacitor (Cp) value that senses the pressure, 218; and (b) decreasing the values for CFX? and CF? 2 will proportionally increase the pressure amounts Np for a given capacitor value (Cp) that senses the pressure, 218; and (c) increasing the current I (T) / N to the oscillator will proportionally increase the pressure quantities Np (for a given value of Cp) at a rate higher than the decrease in the values for CFX? and CFX2.

As a general proposition, the increase of the pressure amounts Np is desirable. However, one skilled in the art to which the invention pertains will readily appreciate that there is a practical upper limit for increasing the amounts of pressure at a frequency which may become unacceptably large for the capacity of certain IC chip circuits. OBTAINING A PRESSURE READING IN THE READER / INTERROGER The fundamental frequency of the oscillator 312 is adjusted by the parameters on the IC chip (eg, 204) and, as described above, is temperature dependent. Therefore, the pressure response is a (hybrid) function of both temperature and pressure, and the ratio of Np to Cp is not linear. Therefore, using a linear equation to calculate the pressure response will inevitably lead to significant errors over a range of pressures that is measured. (for limited ranges of pressures that are measured, for example in the range of 138 kP pressures, using a linear equation may, however, be acceptable.). An important advantage of using the answering machine circuitry described above is that the ratio between Nt / Np to the capacitance of the pressure sensor is linear and does not require any temperature compensation term in the equation (algorithm) used by the reader / interrogator (106) to calculate the pressure, thus greatly simplifying the design of the reader / interrogator. This beneficial "proportional" relation is easily demonstrated by the following equations: (Equation 1) Nt = T "* I (t) / (2 * Vbg * CFX) (Equation 2) NP = Tw = T" * I (t) / (Vbg * (2 * CFX + CP)) Solving for Nt / Np, you get to the following: (Equation 3) Nt / Np = 1 '(Cp / 2 * CFX) Thus, it can be seen that the Nt ratio / NP is just a function of Cp and CFX, and not other variables. Estro means that Nt / Np is only a function of the pressure and is not sensitive to variations in temperature or load currents. Figure 3A illustrates the components involved in the final stage of capturing the temperature and pressure measurements in the answering machine. The signal Fose 'produced by the relaxation oscillator 312 is provided at one input of each two "Y" gates, 360 and 362. One signal ("Capture Temperature) is provided by one generator / sequencer 226 from time to the other input. of the gate "Y" during the window (Wt) that detects the temperature, so the load of the recorder / temperature counter 232 with the quantity (data) Nt is indicative of the measured temperature. data ("Capture Pressure") is provided by the time generator / sequencer 226 to the other input of the "Y" gate 362, during the window (Wp) that senses the pressure, in order to load the recorder / counter 234 of pressure with the quantity (data) Np that indicates the pressure measured. These signals are then shifted out of the recorders 232 and 234 by means of the multichannel MUX 240 to the modulation circuit 246, previously described. GENERATION OF RELIABLE SUPPLY AND REFERENCE VOLTAGES As described above, positive (+) inputs of comparators 316a and 316b are linked together and set to a "band gap" reference voltage Vbg, such as 1.32 volts, which is temperature dependent. As also mentioned above, the supply voltage (Vd) on line 309 'can be provided as a multiple of the band gap reference voltage (Vbg) so as to be a stable operating voltage for the steering circuit of the current and relaxation 312 oscillator. Figure 3B illustrates a circuit 370 suitable for generating supply voltage Vdd. A calculable band gap voltage Vbg, independent of temperature is easily derived, based on the process techniques employed in IC chip fabrication, as inherent to the selected process (e.g., CMOS). This voltage * ^ Band gap Vbg is provided at the "+" input of an operational amplifier 372, connected as shown in a gain having a feedback loop, to supply the supply voltage Vdd as an integral multiple of the voltage Vbg of the voltage gap. band. AN EXEMPLARY CURRENT OF DATA As mentioned before, the information (data) of the answering machine is transmitted to the external reader / interrogator in the form of a data stream, a portion of which is the quantity of the temperature Nt, another portion is the amount of pressure Np, and another portion represents the state (for example "closed" or "open") of the MTMS switch (220). Remaining portions of the data stream may contain information which is customized to a given unit of the answering machine, such as its ID information (e.g., the serial number), calibration constants and the like. Figure 3C illustrates an exemplary architecture for the information that is stored (in memory) within the answering machine, as well as a data stream that is transmitted by the answering machine to the external reader / interrogator. The memory of the answering machine core 204 has, for example, a 144-bit address space, which includes 119 (one hundred and ten-nine) bits of programmable memory and an address location dedicated to the state of the MTMS 220 switch, these 120 (one hundred and twenty) bits of programmable memory constitute the EEPROM memory (136), plus the two registers, 232, and 234, of 12 bits. Each of the 119 bits of programmable memory can be written separately with any combination of data, including synchronization pattern information (Sync), general data, error checking codes, and temperature and pressure calibration data. The EEPROM is a memory 'that can be written in blocks' in the 'write' mode, all 120 bits of the EEPROM are programmed to a logical (binary) value of "1". Individual bits can be 'erased' or set to a logical value of '0', simply by synchronizing the chip to its physical address and placing the chip in the 'erased' mode. The location of the address is preserved. In this example, the first twelve data locations (000..011) in ROW 1 are reserved for Sync. The next seventy data locations (012,082) in ROWS 2 through 7, are for general information and a value for a data validation algorithm, such as the CRC (Cyclic Redundancy Check). The following data location (0.81) contains the logic level (status) of the MTSM switch 220. A logic value of "1" indicates that the MTMS switch is open and a logic value of "0" indicates that the MTMS switch is closed.

The answering unit is properly calibrated before it is installed on a tire. This basically involves determining the slope (inclination) and intercepting the temperature and pressure values generated by the answering machine at various temperatures and pressures in the test chamber, and programming these characteristic calibration values associated with the answering machine in the memory space. The next twelve data locations (084..0.95) in ROW 8 maintain the temperature calibration data (eg, intercept) ("Temp. Comp."). The next twelve data locations (095..107) in ROW 8, maintain the pressure calibration data (for example, intercept) ("PRESS COM"). The next twelve data locations (108..113 and 114..118) in ROW 10, maintain the information of the calibration slope for temperature and pressure, respectively. In accordance with one aspect of the invention, it has been determined that characteristic values for the slope of Nt / Np, or the "proportioned" response of the temperature amount divided by the amount of pressure, is linear with respect to the value of the capacitor Cp which detects the pressure. Additionally, it has been determined that the proportionate value of Nt / Np is less sensitive to variations in the coupling between the reader / interrogator and the respondent than any of these measurements taken alone. Thus, determining (during calibration) and storing the calibration data for the provided NT / NE value in the answering machine, the ability to determine a true pressure reading, which is relatively not sensitive to variations in the coupling between the reader / interrogator, and the answering machine, is both simplified and made more reliable. This value of the calibration provided for Nt / Np is stored in the answering machine memory and is included in the data stream transmitted to the reader / interrogator Relevant government permits that allow (conversely, that restrict) data transmissions of the type indicated here in selected portions of the general RF radio frequency spectrum. An example of suitable operating frequencies for the operation of the answering machine in the United States of America is 60 KHz to 490 KHz. The answering machine can be scrutinized (and energized) by the reader / interrogator on a first "interrogation" frequency (Fi) and the data stream can be transmitted back to the reader / interrogator on a second frequency of the "data carrier" "(Fe) which is, conveniently, a multiple integer or a fraction of the interrogation frequency. For example, Fe = Fi / 2. O, Fe = Fi / 4. The frequency (Fe) at which the data stream is transmitted back to the reader / interrogator is independent of the data rate, which is established by the clock generator 224 and the generator 28 of the baud rate. However, one of ordinary skill in the art to which the invention pertains will recognize that the range of available baud rates will typically be significantly less than the interrogation frequency (Fi). The baud rate is preferably derived from the frequency (Fi) of interrogation of the reader / interrogator, such as a fraction of a number total. For example, the baud rate can be set in Fi / 32 (or, in the case of Fc = Fi / 2, the baud rate can be adjusted in Fc / 15). For example, the interrogation frequency (Fi) can be 125 KHz, and the data carrier (Fe) can be set to 62.5 KHz, or half the interrogation frequency. In another example, the interrogation frequency (Fi) of 13.56 MHz has been found to be adequate. The data stream, cut as an exemplary stream of data, described with respect to Figure 3C, is printed by the modulator circuit 246 on the antenna 212, and transmitted to the reader / interrogator. It is within the scope of this invention that any suitable modulation scheme can be employed, which includes modulation of amplitude (AM), frequency modulation (FM), frequency shift key (FSK) and phase shift key. However, the phase shift key (PSK) is preferred. AM modulation is not particularly well suited to digital transmission. Frequency modulation schemes, such as FM or FSK can be somewhat problematic with respect to the propagation of the output signal of the modulated dataphone, through the medium of a pneumatic tire.

OBTAINING A READING OF COMPENSATED TEMPERATURE PRESSURE Figure 4 illustrates a pertinent portion of a reader portion of a reader / interrogator 400. It should be clearly understood that the answering machine of the present invention is suitable for use with virtually any reader / interrogator properly configured. The description that follows is limited to the broad functions in the architecture that can be performed in the reader / interrogator. An ordinary expert in the field to which the present invention pertains will be able, from the description set forth herein, to carry out these functions in an otherwise "generic" reader / reader. The answer signal output modulated in data is received by antenna 410 (compare to 210) of reader / interrogator 400 (compare to 200). The signal, received is demodulated and decoded in a demodulator / decoder circuit 420 (DE-MOD / DEODE), so that different portions of the data stream can be appropriately segregated from each other. The data relating to the temperature and pressure calibration (Compress temp., PRESS comp., Temp. / PRESS SLOPES), the quantity of temperature (Nt) and quantity of pressure (NP) are provided to an arithmetic logic unit 422, able to generate a signal pressure compensated in temperature ("PRESSURE") on a line 423 to exhibitor 412 (compare to 112) as well as a calibrated temperature signal ("TEMPERATURE") on line 422. This information may be displayed to the user or selectively or simultaneously with other pertinent information, such as the status of the MTMS switch 220, as well as data (DATA) relative to the identification of the rim and similar. While the invention has been described in combination with its preferred embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art of the foregoing description. Accordingly, the invention seeks to encompass these alternatives, modifications and variants as they fall within the broad scope of the appended claims.

Claims (19)

1. CLAIMS 1. In combination with a pneumatic tire, a passive answering machine, arranged inside the pneumatic tire, this answering machine is characterized by: an antenna; a rectifier circuit, connected to the antenna, to supply electric power from a radio frequency signal received by the antenna to the other components of the answering machine; a modulator circuit, operatively connected to the antenna, to form a radiofrequency signal, produced by the answering machine by modulating the radiofrequency signal received by the antenna; a temperature sensor, to detect the temperature inside the rim; a pressure sensor, to detect the pressure inside the rim; a clock signal generator, for generating a first synchronization window, during which the temperature is measured, and a second synchronization window, during which the pressure is measured; a temperature recorder, to capture the first data indicative of the temperature inside the rim; a pressure recorder, to capture second data indicative of the pressure inside the rim; and a modulator circuit, which prints the first data as a first portion of a data stream in a signal produced by the answering machine, and prints the second data as a second portion of the data stream in the signal produced by the answering machine; characterized by: an oscillator, which produces a signal, having a first frequency, which is indicative of the temperature inside the rim, during the first synchronization window, and having a second frequency, which is indicative of the pressure inside the rim, during the second synchronization window; and a recorder / counter circuit, which quantizes the oscillations of the oscillator signal, during the first synchronization window, to capture the first data in the first recorder, and what quantity the oscillations of the oscillator signal, during the second window of synchronization, to capture these second data in the second recorder.
2. 2. In combination with a pneumatic tire, a passive answering machine, according to claim 1, wherein: the first data is a function of temperature; and the second data is a function of both temperature and pressure; characterized by: a relation of the first data divided by the second data, which is a function only of the pressure.
3. 3. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: the first and second frequencies of the output signal of the oscillator are both proportional to the temperature.
4. 4. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: the signal produced by the answering machine is a radiofrequency signal and is transmitted by the antenna.
5. 5. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: the antenna is selected from the group consisting of antennas in the form of a coil, picture antennas and dipole antennas.
6. 6. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: an excessive temperature sensor supplies third data indicative of an excessively high temperature condition; wherein: the modulator circuit prints the third data in a third portion of the data stream in the signal produced by the answering machine.
7. 7. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: the time period of the first synchronization window and the time period of the second synchronization window are adjusted to different durations, whereby the resolution of the quantities of one of the first and second data is adjusted, in relation to the resolution of the quantities of the other of the first and second data.
8. 8. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: the base-emitter voltage to the current converter circuit includes the temperature sensor and it produces a current to the oscillator, where this current is proportional to the temperature; and a frequency of the output signal of the oscillator is proportional to the current output by the temperature sensor.
9. 9. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: a current scaling circuit, arranged 10 between the temperature sensor and the oscillator, for the scale of the current produced by the temperature sensor by a factor of 1 / N, and supply a scale current to the oscillator.
10. 10. In combination with a pneumatic tire, a passive answering device according to claim 9, wherein the current scaling circuit is characterized by: a mirror current, which includes two transistors, having dissimilar areas, one of the two transistors is "N" times greater in area than the other of the 20 two transistors.
11. 11. In combination with a pneumatic tire, a passive answering machine, according to claim 1, wherein the oscillator is characterized by: ^^^^^^^ 5 ^^ £ «¡g ^^ _ a relaxation oscillator, which has a first phase path and a second phase path.
12. 12. In combination with a pneumatic tire, a passive answering machine, according to claim 11, further characterized by: a first fixed value capacitor, disposed in the first phase path; and a second fixed value capacitor, arranged in the second phase path
13. 13. In combination with a pneumatic tire, a passive answering machine, according to claim 12, further characterized in that: the relaxation oscillator has a duty cycle of fifty%.
14. 14. In combination with a pneumatic tire, a passive answering machine, according to claim 11, further characterized in that: the pressure sensor is a capacitor of variable value, which is switched in one of the first and second phase paths, according to one of the first and second fixed-value capacitors, respectively, during the second time window.
15. 15. In combination with a pneumatic tire, a passive answering machine, according to claim 1, characterized in that: The temperature sensor, the oscillator, the clock generator, the temperature recorder, the pressure recorder and the modulator circuit are resident in the chip (microcircuit) of the integrated circuit.
16. 16. In combination with a pneumatic tire, a passive answering machine, according to claim 15, characterized in that: the pressure sensor is external to the integrated circuit chip.
17. 17. Method for measuring the pressure inside a pneumatic tire, which includes the steps of: supplying a passive radio frequency responder inside a pneumatic tire, which includes the steps of: supplying a passive radio frequency responder inside the rim, this answering machine Passive radio frequency includes a temperature sensor and a pressure sensor; transmit a quantity of temperature, which is a function of temperature; transmit a quantity of pressure, which is a function of temperature and pressure, this method is characterized by: determine a pressure reading only, dividing the amount of the temperature by the amount of the pressure. Method, according to claim 17, further characterized by: on the answering machine, storing the calibration data related to the response in proportion to a temperature quantity divided by a quantity of pressure, as determined during the calibration of the answering machine. 19. Method, according to claim 17, further characterized by: transmitting the calibration data related to the response in proportion to a quantity of the temperature divided by a quantity of pressure, as determined during the calibration of the answering machine, and which is stored in this answering machine. Summary of the Invention A radio frequency (RF) answering machine (200), associated with a pneumatic tire and capable of measuring operating parameters, such as temperature and pressure, within a pneumatic tire, and transmitting data indicative of the measured parameters to an external reader / Interrogator (106, 400). This answering machine includes a circuit system (226), to control the time windows (Wt and WF) during which the measurements are made. 10 temperature and pressure of the real time, and to store (236) calibration data, identification number (ID) of the answering machine and the like, and to transmit this information in a data stream (Figure 3C) to the reader / interrogator. A condition of excessive temperature 15 can also be detected (MTMS 218) and included in the data stream. The answering machine's circuitry is preferably carried out on a single chip (microcircuit) of the integrated circuit (IC) (204), using CMOS technology, with few external components to this 20 IC chip. The answering machine is preferably passive, which derives its operating power from a radiofrequency signal provided by the external reader / interrogator. Data (Nt) indicative of the temperature and data (NP) indicative of the pressure are both transmitted to the 25 reader / interrogator, together with the calibration data. A Calibration data stored by the answering machine and transmitted in the data stream is a slope of NT / NF, or the "proportional" response of the amount of temperature divided by the amount of pressure, which is determined during responder calibration.