GB2149275A

GB2149275A - Identity card recognition system

Info

Publication number: GB2149275A
Application number: GB08328554A
Authority: GB
Inventors: Stanley George Allen
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1983-10-26
Filing date: 1983-10-26
Publication date: 1985-06-05
Also published as: GB2149275B; GB8328554D0

Abstract

Spread spectrum and parallel processing techniques are employed for rapid identification of proximity type identity cards. An electromagnetic field radiated by an antenna (6) is produced in response to a spread spectrum signal obtained by phase modulation of a carrier signal frequency (f0) with a pseudo-random noise signal (PRN). When an identity card is disposed in the field, passive circuitry in the card resonates at a frequency characteristic of that card, absorbing energy from the field in particular frequency bands and resulting in a modified spread spectrum signal for analysis by a spectrum analyser (8). The analyser includes a plurality of parallel arranged sets of band pass filters (9), each with a respective pass band, amplifiers (10) and signal amplitude level detectors (11). A latch (12) produces a parallel n-bit word from the detector outputs which is indicative of the identity of the card disposed in the field. <IMAGE>

Description

SPECIFICATION Identity card recognition system This invention relates to an identity card recognition system and in particular to a recognition system for proximity type identity cards.

In a proximity type identity card recognition system an object or person carrying an identity card is to be recognised when the object or person is positioned within a certain range of, but not necessarily touching, a sensor. The identity card may incorporate a passive reactive circuit adapted to resonate at a particular frequency when excited by an electromagnetic field produced at the sensor. In a known system the electromagnetic field is produced by an electrical signal which is swept through a range of frequencies, which range includes the resonant frequency of the card to be identified, and the sensor senses variations in the response field occuring as the sweep frequency passes through the resonant frequency of the card, thus "identifying" the card presented thereto.In order to accurately identify a card it is necessary for the electrical signal to be swept through the range of frequencies a number of times, possibly up to 20 times, so that background or spurious noises are discounted. Thus requirement of multiple sweeping means that the speed which which a card may be recognised is relatively slow. It is an object of the present invention to provide a system which enables higher speed recognition than is possible with the conventional swept frequency systems.

According to one aspect of the present invention there is provided a recognition system, for use with proximity type identity cards, each incorporating passive circuitry adapted to resonate at a particular frequency when excited by an electromagnetic field, comprising means to produce an electromagnetic field in response to spread spectrum signals, means for detecting spread spectrum signals corresponding to the electromagnetic field as affected in use of the system by disposition of one of said identity cards therein, and analyser means serving to divide both spread spectrum signals into n separate frequency band signals and to process the separate frequency band signals in parallel whereby to produce a parallel n-bit word indicative of said one card.

According to a further aspect of the present invention there is provided a method for use in recognising a proximity type identity card having passive circuitry adapted to resonate at predetermined frequencies when disposed in an electromagnetic field, comprising the steps of producing an electromagnetic field in response to a spread spectrum signal, detecting changes in the electro-magnetic field as affected when the identity card is disposed therein, dividing both spread spectrum signal into n separate frequency band signals and processing the separate frequency band signals in parallel whereby to produce a parallel n-bit word indicative of the identity of the card disposed in the field.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Figure 1 shows a basic circuit diagram of a recognition system; Figure 2 shows a spread spectrum signal produced by the circuit of Fig. 1, together with another possible spread spectrum for use in increasing the number of bits; Figure 3 shows the effect on the spread spectrum of a particular card to be recognised, and Figure 4 shows an example of filter response.

The recognition system circuit diagram illustrated in Fig. 1 comprises an oscillator 1 for producing a carrier frequency fO, a modulator 2, a pseudo random noise signal source 3, an amplifier 4, a coaxial cable connection 5 by means of which the signal processing electronics is connected to an antenna 6 from which an electromagnetic field is to be radiated, an amplifier 7 and a spectrum analyser 8 comprising a plurality (n) of band pass filters (BPF) 9 each with its own amplifier 10 and detector 11, the detector outputs being coupled to a latch 1 2 whose output is a parallel n bit word.

In use of the system the carrier frequency f0 is phase modulated by the pseudo random noise signal output from source 3 and thus the signal applied to the antenna 6 has the spectrum shown in Fig. 2, this being a socalled spread spectrum. The centre portion of the spread spectrum. The centre portion of the spread spectrum may be divided into n bands. If f, = 2R and B = R then for ten bands b = B/10, with fO = 20 MHz (R = 10 Mb/s), B = 10 MHz and b = 1MHz. The centre portion of the spread spectrum is divided up into ten 1 MHz bands in this case.

When an identity card (not shown) having an associated resonant frequency is disposed in the vicinity of the electromagnetic field transmitted from the antenna 6 the electromagnetic field is affected by absorption of energy therefrom by the card causing the amplitude of the corresponding detected spread spectrum signal to dip in particular frequency bands, determined by the cards resonant frequency, as indicated in Fig. 3.

The detected signal is analysed in analyser 8, there being a separate band pass filter 9 associated with each of the 1 MHz bands of the spread spectrum. The output of the latch 1 2 is a parallel ten bit word which can be employed as required for a particular type of recognition system. For example, in a clocking-in system in the time of recognition of a particular card will be recorded, or in a secu rity door locking system a door will only be opened if the ten bit word recognised corresponds to one of a list of acceptable ten bit words and an alarm may be sounded if it does not so correspond.In order to reduce the affect of background or spurious noise the spread spectrum signal level may be required to change by more than a predetermined threshold amount (indicated by the dotted line in Fig. 3) when a card is presented for recognition, this may be achieved by suitable choice of the amplifiers 10 and detectors 11 associated with the band pass filters 9. The spectrum analyser 8 comprising the band pass filters, amplifiers and detectors may together with the latch 1 2 be constituted by a single integrated circuit. The filters 9 may have the response indicated in Fig. 4.This is based on a four element Butterworth filter, that is a constant-k filter designed to give a response of maximum flatness through the pass band, which gives - 3dB at f, + 1/2 MHz, dB at f0 + 1 MHz and Q=fo/b= 20.

The choice of ten parallel channels gives 1024 possible combinations, this may be increased if necessary by for example also employing a second lower carrier frequency f0 with the resultant additional spread spectrum indicated in dotted lines on Fig. 2, and, if a twenty bit word is employed, doubling the number of band pass filters 9 and resulting in > 106 possible combinations.

In addition to performing the recognition function the basic circuit can be used for additional functions. In particular secure remote monitoring of data is possible. If data is injected at a low bit rate before the modulator 2, as indicated in Fig. 1, the data will be transmitted from the antenna 6 but can only be received at a point remote from the antenna in an intelligible form if demodulated at a spread spectrum receiver having a demodulator to which is applied precisely the same pseudo-random noise signal as was applied at the modulator 2 of the transmitter. Alternatively, remote entry of data to a central processor (not shown), as for example by security guard patrolling a security compound to which the basic system is fitted, may be achieved by injecting tones at the antenna.

In addition to the advantage of higher speed of recognition, provided by the parallel processing, the transmitted spectral density at the antenna is less than that of the conventional swept frequency system thus reducing the possibility of unwanted radio interference.

Claims

1. A recognition system, for use with proximity type identity cards, each incorporating passive circuitry adapted to resonate at a particular frequency when excited by an electromagnetic field, comprising means to produce an electromagnetic field in response to spread spectrum signals, means for detecting spread spectrum signals corresponding to the electromagnetic field as affected in use of the system by disposition of one of said identity cards therein, and analyser means serving to divide both spread spectrum signals into n separate frequency band signals and to process the separate frequency band signals in parallel whereby to produce a parallel n-bit word indicative of said one card.

2. A recognition system as claimed in claim 1, wherein the analyser means comprises a parallel arrangement of n sets of components. each set including a bandpass filter with a respective pass-band and a detector serving to indicate when the bandpass filter output amplitude is below a certain level, and a latch, the outputs of the detectors being applied to the latch whose output comprises the parallel n-bit word.

3. A recognition system as claimed in claim 2 wherein the analyser means is comprised of an integrated circuit.

4. A recognition system as claimed in any one of the preceding claims, wherein said spread spectrum signals are produced by phase modulating the frequency of a carrier signal with a pseudo random noise signal.

5. A recognition system as claimed in claim 4 in combination with a spread spectrum receiver whereby to form a secure remote monitoring system, including means in the recognition system whereby data to be transmitted to the receiver is injected onto the carrier signal prior to modulation thereof, whereby to produce a corresponding electromagnetic field, and wherein the spread spectrum receiver serves to demodulate the received signal by means of a pseudo random noise signal equivalent to that employed for modulation.

6. A recognition system as claimed in any one of claims 1 to 4 in combination with means whereby data can be remotely entered into, which means serve to provide tones corresponding to said data for affecting the electromagnetic field to produce a signal which is applied to the analyser means and converted to a corresponding parallel n-bit data word.

7. A method for use in recognising a proximity type identity card having passive circuitry adapted to resonate at predetermined frequencies when disposed in an electromagnetic field, comprising the steps of producing an electromagnetic field in response to a spread spectrum signal, detecting changes in the electro-magnetic field as affected when the identity card is disposed therein, dividing both spread spectrum signals into n separate frequency band signals and processing the separate frequency band signals in parallel whereby to produce a parallel n-bit word indicative of the identity of the card disposed in the field.

8. A method as claimed in claim 7, wherein the spread spectrum signal is obtained by phase modulating the frequency of a carrier signal with a pseudo random noise signal.

9. A method as claimed in claim 7 or claim 8, wherein the spread spectrum signals are divided by means of n band pass filters with a respective pass band, wherein the band pass filter outputs are applied to respective detectors which serve to indicate when the band pass filter output is below a particular level, and wherein the detector outputs are applied to a latch whose output comprises the parallel n-bit word.

10. A system for recognising proximity type identity cards substantially as herein described with reference to and as illustrated in the accompanying drawings.

11. A method for use in recognising a proximity type identity card substantially as herein described with reference to and as illustrated in the accompanying drawings.