AN ACTIVE RADIO FREQUENCY TAG TRANSPONDER

This invention relates to an active radio frequency tag transponder. More especially, this invention relates to an active radio frequency tag transponder having active temperature compensation of frequency generating means.

Short range wireless systems operate in the unlicenced portion of the radio spectrum. They usually operate at 433MHz, 868MHz, 915MHz or 2.4GHz industrial, scientific medical band. The short range wireless systems can be combined with systems wired to the Internet in order to provide communication over longer distances via an access point.

Short range wireless communications systems find use in automatic identification systems. Radio frequency identification systems are one embodiment of the automatic identification systems. The radio frequency identification systems find use in short range wireless communications apparatus, specified as Low Rate Wireless Personnel Area Network (LR- WPAN) from the IEEE - 802.15.4 standard 203. Typical radio frequency identification apparatus includes a radio frequency identification reader, and a radio frequency identification tag transponder. The reader and the tag transponder are linked together by a radio frequency generated by the reader. The tag transponder is typically attached to an item for identification purposes. The tag transponder can be attached to the item in any suitable

and appropriate way. The item may be a manufactured product or other device.

The tag transponder transmits data for identification by modulating a radio frequency medium. The frequency that is generated is produced by frequency generating means such for example as a frequency generating oscillator. The frequency generating means is typically a crystal vibrating at some fundamental or harmonic of the fundamental. The generated frequency is used by transceiver means to produce a carrier frequency in which the data is modulated by multiplication or use of harmonics of the fundamental. The frequency generating means can have a temperature dependence on the fundamental frequency value. This temperature dependence can have a large affect on the carrier frequency after it has been multiplied within the transceiver means. In a broadband transmission system, this can have a minor affect. In a fixed channel system, this can cause major problems if the transceiver electronic control means selects a channel for operation, but the temperature dependence causes the actual channel of transmission to be different. A difference in environmental temperature between tag transponder devices within active radio frequency identification apparatus may make communication impossible due to channel selection differences.

Active radio frequency identification apparatus includes active tag transponders that contain data for use in individually identifying specific tag transponders. This data is transmitted by a radio frequency medium within the tag transponder to a radio frequency identification reader. The reader is able to access the radio frequency medium and collect the data transmitted

from the tag transponder. For long distance communication or channel based active radio frequency identification apparatus, the carrier frequency is critical to performance. The environmental temperature can affect the frequency generation means to degrade this performance.

There is a need for a means of compensating for temperature and altering the channel of operation to the correct value based on the environmental temperature. It is an aim of the present invention to satisfy this need.

Accordingly, in one non-limiting embodiment of the present invention there is provided an active radio frequency tag transponder having active temperature compensation of frequency generating means, which active radio frequency tag transponder comprises:

(i) the frequency generating means;

(ii) transceiver means for altering a carrier frequency of operation generated by a signal from the frequency generating means;

(iii) electronic control means for controlling operation of the transceiver means; and

(iv) temperature sensing means having a data transfer facility for transferring sensed temperature data from the temperature sensing means to the electronic control means.

The active radio frequency tag transponder of the present invention may operate to use data produced by the temperature sensing means in order to change the channel of carrier frequency to that of correct operation by utilising the electronic control means. The tag transponder may operate to use the environmental calibration data of the frequency generating means (which may be a fundamental frequency generating means). The sensed temperature data can be used for other means at the same time as it is used for the fundamental frequency compensation.

The tag transponder of the present invention may be such that the electronic control means uses data from the temperature sensing means for compensation of environmental temperature over a range of -4O ⁰ C to +85 ⁰ C. The active temperature compensation may enable correct operation of the tag transponder at a given frequency within the industrial, scientific and medical band, independent of variations caused by temperature in the operating range such for example as the range of -40° to +85 ⁰ C.

Preferably, the frequency generating means is a frequency generating oscillator. Other types of frequency generating means may however be employed.

The temperature sensing means may be selected to have exact specifications to meet power consumption and cost criteria, which are critical parameters in the use of active radio frequency tag transponders.

The tag transponder of the present invention may operate such that the electronic control means selects the frequency of the carrier medium by controlling a multiplier within the tag transceiver. The frequency generating

means may provide the fundamental frequency to the transceiver means. The temperature sensing means provides data for the electronic control means. The electronic control means may alter the frequency of the carrier medium to an environmental calibrated value based on calibrated data from the frequency generating means. The calibrated data allows the temperature offset that would normally degrade the performance of the tag transponder. The temperature data may also be used for other means or it may be discarded.

An embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawing which shows radio frequency identification apparatus including an active tag transponder, and reader communication through a radio frequency in a radio frequency medium, with environmental temperature differences.

Referring to the drawing, it will be seen that there is disclosed a radio frequency active tag transponder which contains temperature sensing means 112, frequency generating means 114, transceiver means 116, and electronic control means 110.

The illustrated active radio frequency identification apparatus includes a radio frequency identification reader 101 linked to radio frequency identification tag transponders 112, 124 by means of a radio frequency medium. An "environmental zone" in which the radio frequency identification reader transmission path loss is defined, is illustrated by areas of different shades. The shade 120 represents room temperature or no variation. The shade 122 represents a higher temperature which causes a temperature

variation in the frequency generating means 114. The shade 124 represents a lower temperature causing a temperature variation in the frequency generating means 114.

The radio frequency identification reader shown in the drawing is such that it comprises the electronic control means 110. This electronic control means 110 may be a microcontroller with controlling software, or it may be any other suitable and appropriate electronic means. The radio frequency identification reader also comprises the temperature sensing means 112 which is for the measurement of environmental temperature conditions, and which has a facility for providing the sensed temperature data to the electronic control means 110. The radio frequency identification reader also comprises the frequency generating means 114 which is a fundamental frequency generating means. The radio frequency identification reader further comprises the transceiver means 116 which is for modulation of the data into the radio frequency medium. This modulation of the data may be effected by any suitable and appropriate means. An antenna 118 also forms part of the radio frequency identification reader. The antenna 118 is connected to the transceiver means 116.

The above mentioned construction of the radio frequency identification reader is a preferred construction and other constructions may be employed which provide appropriate temperature compensation facilities.

The operation of the radio frequency identification apparatus shown in the drawing will now be given. In the following explanation of a preferred embodiment of the apparatus, hot is defined as greater than ambient room

temperature, cold is defined as less than ambient room temperature, and room temperature environments are considered.

A single channel of constant frequency for communication is utilised between the active radio frequency identification tag transponders. The active radio frequency tag transponder in the room temperature is considered to be the reader or receiving device. As it is located in a room temperature environment, the frequency generating means is operating without deviation, and the data provided by the active radio frequency identification tag transponder will primarily , be used to report the temperature of the environmental condition or other means as defined by the individual implementation of the active radio frequency identification apparatus.

The active tag transponder in the hot zone 112 uses the temperature data provided by the temperature sensor offset, to control the channel of operation, by looking up the temperature data in a calibration lookup table. The same will happen in the cold zone 124. However, the offset data will be different. Without this offset, the devices would be transmitting on the incorrect frequency channel, or transmission distance would be reduced because losses would occur in the matching network or antenna due to incorrect carrier frequency. With the compensation facility afforded by the present invention, the tag transponders in the hot zone 122 and the cold zone 124 will use the correct carrier frequency and the performance of the apparatus will be improved for non-ambient room temperature operation.

It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawing has been given by way of example only and that modifications may be effected.