Abstract: A passive entry and immobilizer key for vehicles comprises an integrated front-end circuit (12b) with three battery-supplied receiver channels (14, 16, 18), each connected to an associated external antenna circuit with an inductor-capacitor combination (LR, CR) having a resonant frequency in the very low frequency range. The three antennas are arranged in a three-dimensional configuration. An immobilizer transponder (22) is supplied by energy received from an external transponder antenna circuit and stored in a storage capacitor (CL). The transponder antenna circuit includes an inductor-capacitor combination (LR, CR, CL) having a resonant frequency in the low frequency range. The transponder antenna circuit shares at least one inductive component (LR) with the antenna circuit of one of the three receiver channels.

Abstract: A vehicular tire pressure monitoring system, including a transponder unit (10) for each tire to be monitored, the transponder unit having an incorporated RF transmitter (12) and being physically associated with the tire to be monitored. A pressure sensor for each tire to be monitored is connected to circuitry in a corresponding transponder unit. An interrogator unit (7) is associated with each transponder unit and physically mounted on a vehicle in proximity to a wheel (9) whereon a tire to be monitored is mounted. A central RF receiver (4) for all transponder units is provided. Each transponder unit is inductively coupled with an associated interrogator unit and includes an electric charge accumulation element adapted to be charged by energy inductively supplied from the associated interrogator unit in a first mode of operation, and the charge accumulation element providing a power supply to the RF transmitter of the transponder unit in a second mode of operation.

Abstract: A method for the authentication of a transceiver unit with respect to a second transceiver unit, located at a distance to it. A first signal is transmitted via an aerial connected to the first unit, when second unit is located within the reception area of the first unit. The first signal is received by means of the second unit via an aerial connected to it, whereby, on the basis of the first signal received, a value is measured that characterizes the strength of the electro-magnetic field generated by the first signal at the location of the second unit. A second signal is transmitted via the aerial connected to the second unit that contains information relating to the magnitude characterizing the field strength; and the second signal is received via the aerial connected to the first unit, where, on the basis of the second signal received, a value is measured that characterizes the strength of the electro-magnetic field generated by the second signal at the location of the first unit.

Abstract: A power management circuit for a system that has combined power supplies from an inductively coupled circuit and from a battery comprises voltage sensing circuitry for sensing the voltage of each of the power supplies. A switching arrangement selectively connects one of the power supplies with a user or with plural users. The switching arrangement is controlled by appropriate control circuitry in response to outputs from the voltage sensing circuitry. The power management makes the best use of energy received over the inductive interface to preserve battery lifetime.

Abstract: A security system to enable authenticated access of an individual to a protected area, including a remote control unit (22) with a transponder (28), carried by the individual, which transmits an identification code group on reception of an interrogation signal. A control unit located within the protected area transmits an interrogation signal when activated by the individual, and verifies the identification code group received from the transponder. Access to the protected area will only be permitted on positive verification of the right to access. The transponder (28), contained within the remote control unit (22), is a passive transponder which obtains a supply voltage from the interrogation signal transmitted by the control unit (16) and then feeds this to a supply voltage rail.

Abstract: Transponders present in an interrogation zone can be identified by an interrogator by it sending an RF interrogation signal into the interrogation zone, the RF interrogation signal containing a code string prompting the transponders to generate partial addresses. As soon as one transponder “sees” that the generated partial address agrees with part of its own address, it responds by sending its full address which can then be read by the interrogator. Immediately after having received a full address the interrogator sends a code string characterizing the address of the transponder having responded before so that this transponder is thereby addressable. The signal sent by the interrogator to the transponder with this code string also contains an instruction which prompts the transponder to assume the condition in which it no longer responds to receiving its address or partial address.

Abstract: The invention relates to a procedure for the authentication of a first transceiver unit with respect to a second transceiver unit, located at a distance to it, whereby by means of the first unit a first signal is transmitted via an aerial connected to it; when the second unit is located within the reception area of the first unit, the first signal is received by means of the second unit via an aerial connected to it, whereby, on the basis of the first signal received, a value is measured that characterizes the strength of the electro-magnetic field generated by the first signal at the location of the second unit, and a second signal is transmitted via the aerial connected to the second unit that contains information relating to the magnitude characterizing the field strength; where by means of the first unit the second signal is received via the aerial connected to the first unit, where, on the basis of the second signal received, a value is measured that characterizes the strength of the electro-magnetic fie

Abstract: A security system to enable authenticated access of an individual to a protected area, inlcuding a remote control unit (22) with a transponder (28), carried by the individual, which transmits an identification code group on reception of an interrogation signal. A control unit located within the protected area transmits an interrogation signal when activated by the individual, and verifies the identification code group received from the transponder. Access to the protected area will only be permitted on positive verification of the right to access. The transponder (28), contained within the remote control unit (22), is a passive transponder which obtains a supply voltage from the interrogation signal transmitted by the control unit (16) and then feeds this to a supply voltage rail.

Abstract: For reading the data stored in a transponder by means of an interrogation device, the interrogation device at first receives the background noise for the purpose of detecting interference frequencies present in this background noise. On the basis of the interference frequencies acquired, coefficients for an adaptive filter are computed by means of which this filter may be tuned in such a way as to suppress the interference frequencies. The response signal from the transponder with the superimposed background noise is received by the interrogation device and routed through the adaptive filter which acts to suppress the interference frequencies. The signal available at the output of the filter can then be demodulated for the purpose of reading the data stored.

Abstract: A corrected digital response signal is generated from a corrupted transponder response signal by receiving the response signal an odd number of times, greater than one, and sampling each received response signal a predetermined number of times. Then, the sample values from each transponder response signal are compared to one another and a majority sample value is obtained. The majority sample value is the value ordained by the majority and therefore represents the corrected response signal value. Alternatively, if time does not permit reception of more than one transponder response signal, additional response signals may be generated from the originally received response signal by shifting the received response by a predetermined number of samples to the right and by shifting the received response by a predetermined number of samples to the left to generate second and third response signals.

Abstract: A transponder unit (10) includes an N cycle counter (30) and an M cycle counter (28). The N cycle counter (30) has a different cycle value than the M cycle counter (28). During the transmission of information from the transponder unit (10), the duration for data bits having a binary zero value is controlled by the N cycle counter (30). The duration of data bits having a binary one value is controlled by the M cycle counter (28). The use of different cycle values within the N cycle counter (30) and the M cycle counter (28) allows for the transmission of binary one and binary zero data bits having the same bit length despite different frequencies representing the binary one and binary zero bits respectively.

Abstract: Transponder signal collision avoidance system incudes a reader and wireless HDX or FDX type transponders (A, B) are disclosed, interrogated by the reader (R) by alternately powering and then reading through cycles corresponding to a number of possible transponders in the interrogation field. The cycles, which include reader power pulses, signify addresses of respective possible transponders, whether in or out of the field. The transponders for this purpose count reader power pulses by end-of-burst detection, increasing a stored count value with each reader power pulse. The transponder responds to the reader by transmission if and only if a stored count value in a read cycle matches a respective transponder address, preventing the transponders from transmitting telegrams interfering with each other.

Abstract: A method of determining the exact location of a transponder with respect to a reader antenna, with no additional components to the existing system required, is disclosed. An existing pin of the reader IC, the RSTP pin, provides an analog fieldstrength signal from which the distance to the reader antenna is deduced via known in the art signal processing methods. A grid or even an exact position location along a route is also achievable with initial set-up of at least two transponders a predetermined distance apart and a reader antenna.

Abstract: Apparatus and method of identifying a plurality of transponders (10-16) entering into an inquiry field (18) of an interrogation unit (20) are provided. The transponders (10-16) are each assigned a unique identification code. Upon receipt of an interrogation pulse from the interrogation unit (20), each transponder (10-16) responds with its respective identification code. Depending on the spatial distance of each transponder (10-16) with respect to the interrogation unit (20), the interrogation unit (20) detects and receives the strongest response. The received identification code is stored. The interrogation unit (20) repeatedly sends interrogation pulses containing any stored identification code until all of the transponders (10-16) are identified and read.

Abstract: Apparatus and method for identifying a plurality of transponders (10-16) located within an inquiry field (18) of an interrogation unit (20) are provided. Each transponder (10-16) is assigned an unique identification code, and the interrogation unit (20) dynamically constructs and modifies a bit string used to solicit responses from selected transponder(s) until each transponder (10-16) in the inquiry field (18) is identified. The bit string is transmitted to the transponders, which compares it with the least significant bits of their respective identification codes. A mismatch between the identification code and the bit string results in suppressing the response from the transponder.