AU2369999A - Method and apparatus for adjusting RF power in a smart card reader - Google Patents

Description

-1- Method and Apparatus for Adjusting RF Power in a Smart Card Reader Field of the Invention This invention relates generally to a method and apparatus for adjusting RF power in a smart card reader.

Background of the Invention Smart card readers are used for communication with smart cards, which are plastic cards having an electronic chip embedded therein for storing and/or processing data in relation to one or more applications that the owner of the card may require, for example, bank account debiting (electronic purse), automatic ticketing, and various other applications. Smart cards operating in contactless mode offer benefits such as short transaction time and absence of wear on contacts. The reader is also less vulnerable to wear and vandalism. These benefits combined with ease of use have made contactless smart cards a prime candidate for applications, such as transportation.

15 A problem with contactless smart cards is that they cannot be powered directly from the reader's power supply, since there is no contact between them. Consequently, some contactless smart cards are provided with small batteries to provide their power supply. However, this solution is inconvenient, both from the point of view of requiring S-the batteries to be changed, with the consequent cost in time and materials, and from the 20 point of view of the difficulties in mounting such batteries in a card that is designed to be as small and light as possible. Providing the smart cards with electronic components that can obtain the power required for operation from the reader itself, even though there is no contact between them has solved this problem.

There are two types of such contactless smart cards that have no power supply •25 provided therein. Closed-coupled cards operate through inductive or capacitive coupling between the card and the reader and must be positioned less than I mm away from the reader. Remote-coupled cards are subdivided into proximity cards which operate over distances of up to 10 cm, and vicinity cards which have an operating range of 50 cm or ooo•• S"more. Remote-coupled cards communicate by radio frequency signals. International Standards ISO 10536 and ISO 14443 are set for close-coupled and remote-coupled contactless cards respectively. The source of power in smart cards operating in contactless mode is the RF power received from the reader. The level of this power depends on 1. the level of RF power emitted from the reader, 2. the radiation pattern of the reader, 3. the effective cross section of the smart card with respect to the reader, which depends on its distance from the reader and its orientation.

-2- Since a remote-coupled smart card working in a typical contactless environment can be positioned at any distance within a suitable range from the reader, the power induced in the smart card can vary. It is desirable to adjust the level of RF power emitted from the reader to compensate for variations of smart card distance from the reader. One suggestion is for the smart card to send a request signal to the reader to increase or decrease its emitted RF power level. The disadvantage of this approach is that it increases the transaction time. For applications such as transport every effort is made to make the transaction time as short as possible. Another solution to the problem is for the smart card to have a Power Management Unit as part of its operating system to selectively switch on or off different modules within the smart card based on the power level available. This feature makes the operating system inside the smart card more complicated and, again, adds to the transaction time.

In this specification, including the claims, the terms "comprises", "comprising" or similar terms are intended to mean a non-exclusive inclusion, such that a method or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.

Brief Summary of the Invention The present invention therefore seeks to provide a method and apparatus for adjusting RF power in a contactless smart card reader which overcomes, or at least 20 reduces the above-mentioned problems of the prior art.

Accordingly, in a first aspect, the invention provides a method of adjusting RF power in a smart card reader, the method comprising the steps of transmitting an RF signal at a power level from the smart card reader to a smart card, receiving an echo of the transmitted RF signal from the smart card, measuring at least one parameter of the 25 received echo, and adjusting the power level of the RF signal being transmitted based at least in part on the at least one measured parameter.

Although the parameter may be the time between when the RF signal is transmitted and when the echo is received, in a preferred embodiment, the parameter is a S•power level of the received echo, conveniently, an amplitude of the received echo.

In one embodiment, the step of adjusting comprises the steps of comparing the measured amplitude of the received echo with a predetermined level and altering the power level of the RF signal being transmitted depending on the results of the comparing step. Preferably, the step of adjusting comprises the steps of comparing the measured amplitude of the received echo with a minimum predetermined level, and increasing the power level of the RF signal being transmitted if the results of the comparing step indicate that the measured amplitude is less than the minimum predetermined level.

Alternatively, or additionally, the step of adjusting comprises the steps of comparing the measured amplitude of the received echo with a maximum predetermined level, and -3decreasing the power level of the RF signal being transmitted if the results of the comparing step indicate that the measured amplitude is more than the maximum predetermined level.

In a second aspect, the invention provides a smart card RF power adjusting circuit comprising an RF signal transmitter coupled to an RF transmitting antenna for transmitting pulsed RF signals, an RF signal receiver coupled to an RF receiving antenna for receiving an echo of the pulsed RF signals reflected from a smart card, and an RF power control unit coupled to the RF signal receiver and to the RF signal transmitter for adjusting a power level of pulsed RF signals according to a level of the received echo.

Preferably, the RF power control unit provides a control signal to the RF signal transmitter to increase the power level of the pulsed RF signals if the level of the received echo is below a first predetermined level. Alternatively or additionally, the RF power control unit preferably provides a control signal to the RF signal transmitter to decrease the power level of the pulsed RF signals if the level of the received echo is above a second predetermined level.

~Preferably, the transmission of the RF signal is pulsed.

Brief Description of the Drawings "Two embodiments of the invention will now be more fully described, by way of example, with reference to the drawings, of which: 20 FIG. 1 shows a schematic block diagram of a smart card reader in communication with a contactless smart card; FIG. 2 shows a flowchart of one method of operating the smart card reader of S"FIG. 1 to adjust RF transmitted power; and FIG. 3 shows an RF power control unit that utilizes an alternative method of 25 adjusting RF transmitted power in the smart card reader of FIG. 1.

Detailed Description of the Drawings Thus, as shown in FIG. 1, a smart card reader 1 operating in contactless mode includes an RF power control unit 7, which is coupled to an RF transmitter 8 to control "the transmitter 8 to periodically transmit RF signals 2 from an antenna 3 at a power level determined by the RF power control unit 7. The pulsed RF signals 2 emitted from the reader 1 provide a source of power for a smart card 4 operating in contactless mode by induction. If the level of induced power is too low, the smart card will not be able to operate properly. If, on the other hand, the power is too high, electronic circuits in the smart card may be damaged.

In order to provide the smart card reader 1 with a method of automatically adjusting the level of its emitted power, the smart card reader 1 receives an "echo" 5 of the pulsed RF signals 2 from the card 4 at an antenna 6. This echo 5 is different from a "response" message which the smart card produces at a later time. At this stage the reader is not reading a response to its communication, but is simply receiving an echo of its own pulsed RF signals, in a similar manner to radar equipment. The time of arrival of echo indicates the distance between the smart card and reader. The adjustment of power can be either based on the time difference between sending signal and receiving echo or the magnitude of the received echo. The latter approach is preferable as it compensates for the cases where the smart card is not positioned at correct angle to take the maximum amount of incoming signal. For example, for a card having a thickness of 0.76 mm, the RF reflection from the plastic body and the metallic coil (antenna) inside the card are not distinguishable to the card reader, since they are received by the card reader at about the same time. The RF reflection from the plastic body is also negligible compared with the one reflecting back from the metallic coil, because of very low RF reflection characteristic of plastics compared with metals. This is not a problem since both the plastic reflection and the metallic coil reflection indicate the same thing: the distance of the card from the card reader. Furthermore, both reflections are different from the "response" of the card to the embedded command send by the card reader. That response comes milliseconds later.

In this case, for each transmitted RF pulse, the level of received RF power is "measured and compared with the MAX and MIN values which are the maximum and minimum acceptable RF levels respectively. If the received power level is less than MIN 20 the transmitted power level is increased and if the received power level is more than MAX, then the transmitted power level is decreased.

Thus, the "echo" 5 received by antenna 6 is passed to a receiver 10 under the control of a smart card reader control unit 9. The smart card reader control unit 9 is also used to control the transmitter 8. The receiver 10 is coupled to the RF power control i 25 unit 7 in order to pass the received "echo" 5 to the RF power control unit 7 so that it can adjust the power level of the RF signals generated by transmitter 8 accordingly. It should be emphasized that the blocks in FIG. 1 only serve to clarify the functions that S* "are performed, they do not necessarily represent distinctions in implementation.

°A flowchart illustrating the method of operation of the reader 1 of FIG. 1 will now be further described with reference also to FIG 2. Thus, after sending the pulsed RF signals 2 from antenna 3 (as indicated by step 11 in FIG. the reader goes into receive mode. When an "echo" 5 is received at antenna 6, the strength of the "echo" (amplitude of the received signal) and optionally the time of echo arrival are measured, as indicated at step 12. The difference between transmission time and arrival time indicates the distance of the smart card 4 from the reader 1. The strength of the "echo" is also dependent on this distance, but the strength also conveys information regarding the orientation of the smart card 4 with respect to the reader 1, and in particular, it is dependent on the effective cross section of the smart card, relative to the reader. The RF power control unit 7 then compares the strength of the received "echo" with a minimum value MIN, as indicated at step 13. If the power level is below the minimum level MIN, the RF power control unit 7 sends a command to the transmitter 8 to increase the power level of the signals being transmitted, as shown at step 14, and the process flow is then complete (step 15). On the other hand, if the power level not below the minimum level MIN, then the received power level is compared, as indicated at step 16, with a maximum level MAX. If it is determined that the received power level is above the maximum level MAX, then the RF power control unit 7 sends a command to the transmitter 8 to decrease the power level of the signals being transmitted, as shown at step 17, and the process flow is then complete (step 15). If the power level is not above the maximum level MAX, then no change to the transmitted power level is necessary and the process flow is complete (step An alternative way of carrying out the comparison of the power level of the received "echo" 5 with the predetermined minimum and maximum levels MIN and MAX is shown in FIG. 3. This shows part of a RF power control unit 20 and includes a memory 21 having the predetermined minimum and maximum levels MIN and MAX stored therein and an input 22 for receiving the received "echo" 5 from the receiver The input 22 is coupled to a positive input 23 of a first comparator 24 and to a negative input 25 of a second comparator 26. A negative input 27 of the first comparator 24 is 20 coupled to the memory 21 to receive the predetermined maximum level MAX therefrom and a positive input 28 of the second comparator 26 is coupled to the memory 21 to -receive the predetermined minimum level MIN therefrom.

The first comparator 24 thus compares the signals at its two inputs 23 and 27 and provides a logical at its output 30 if the received "echo" signal 5 is greater than the 25 predetermined maximum level MAX. This output 30 therefore provides a command to the transmitter 8 to increase the power level of the transmitted signal. The second comparator 26 similarly compares the signals at its two inputs 25 and 28 and provides a i "logical" 1" at its output 31 if the received "echo" signal 5 is smaller than the predetermined minimum level MIN. This output 31 therefore provides a command to the transmitter 8 to decrease the power level of the transmitted signal.

It will therefore be apparent that the RF power control unit can work independently and in parallel with the smart card reader control unit 9. This is advantageous because it can keep updating power levels after each transmission of RF modulated messages from the reader to the smart card.

It will be appreciated that although only one particular embodiment of the invention has been described in detail, various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention.

Claims (13)

1. A method of adjusting RF power in a smart card reader, the method comprising the steps of: transmitting an RF signal at a power level from the smart card reader to a smart card; receiving an echo of the transmitted RF signal from the smart card; measuring at least one parameter of the received echo; and adjusting the power level of the RF signal being transmitted based at least in part on the at least one measured parameter.

2. A method of adjusting RF power in a smart card reader according to claim 1, wherein the parameter is time between when the RF signal is transmitted and when the echo is received.

3. A method of adjusting RF power in a smart card reader according to claim 1, wherein the parameter is a power level of the received echo.

4. A method of adjusting RF power in a smart card reader according to claim 3, 20 wherein the parameter is amplitude of the received echo.

5. A method of adjusting RF power in a smart card reader according to claim 4, wherein the step of adjusting comprises the steps of: comparing the measured amplitude of the received echo with a predetermined 25 level; and altering the power level of the RF signal being transmitted depending on the results of the comparing step.

6. A method of adjusting RF power in a smart card reader according to claim wherein the step of adjusting comprises the steps of: comparing the measured amplitude of the received echo with a minimum predetermined level; and increasing the power level of the RF signal being transmitted when the results of the comparing step indicate that the measured amplitude is less than the minimum predetermined level.

7. A method of adjusting RF power in a smart card reader according to either claim or claim 6, wherein the step of adjusting comprises the steps of: comparing the measured amplitude of the received echo with a maximum predetermined level; and decreasing the power level of the RF signal being transmitted when the results of the comparing step indicate that the measured amplitude is more than the maximum predetermined level.

8. A method of adjusting RF power in a smart card reader according to any preceding claim, wherein the transmission of the RF signal is pulsed.

9. A smart card RF power adjusting circuit comprising: an RF signal transmitter coupled to an RF transmitting antenna for transmitting pulsed RF signals; an RF signal receiver coupled to an RF receiving antenna for receiving an echo of the pulsed RF signals reflected from a smart card; an RF power control unit coupled to the RF signal receiver and to the RF signal transmitter for adjusting a power level of pulsed RF signals according to a level of the S"received echo.

10. A smart card RF power adjusting circuit according to claim 9 wherein the RF 20 power control unit provides a control signal to the RF signal transmitter to increase the power level of the pulsed RF signals when the level of the received echo is below a first predetermined level.

11. A smart card RF power adjusting circuit according to either claim 9 or claim :i 25 wherein the RF power control unit provides a control signal to the RF signal transmitter to decrease the power level of the pulsed RF signals when the level of the received echo is above a second predetermined level.

12. A method of adjusting RF power in a contactless smart card reader substantially as hereinbefore described with reference to the drawings.

13. A smart card RF power adjusting circuit substantially as hereinbefore described with reference to the drawings.