Abstract:
A radio frequency transponder device in an integrated circuit package requires only one dedicated pin for connection to a parallel resonant tuned circuit for receiving a remote signal. The one dedicated pin has a capacitor which blocks direct current (DC) flow and allows independent DC biasing of a radio frequency amplifier for increased signal amplification gain. Another package pin used for common power or ground connections supplies the second connection to the resonant tuned circuit. Multiple transponder inputs may be implemented in a single integrated circuit package using only one dedicated pin per input plus one common pin which may be used for another purpose, such as a power or a ground connection.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to integrated circuit radio frequency transponders, and more particularly, to an integrated circuit radio frequency transponder requiring only one dedicated input pin for signal connection to an externally connected resonant frequency tuned circuit. 
     DESCRIPTION OF THE RELATED TECHNOLOGY 
     Radio frequency transponders may be used in managing inventory, automatic identification of cars on toll roads, building entry, security systems, keyless electronic access and entry devices, and the like. A transponder generally comprises a radio frequency receiver and a radio frequency transmitter and communicates with another related transponder by either first receiving a coded signal and then responding back with a coded transmitted signal, or transmitting a coded signal first then waiting for the correct response to be returned from the related transponder. Any combination of coded signal “handshakes” may be utilized by two transponders trying to identify a “friend” or “foe.” Once a friendly coded signal is identified and verified a desired action may be taken, i.e., unlocking a car door, opening a garage door, or building access or egress. 
     An example of a transponder system is the KEELOQ® (a registered trademark of Microchip Technology Inc.) Code Hopping Encoder and Transponder, part number HCS412 by Microchip Technology Inc., more fully described in Specification DS41099A (1999), available at http://www.microchip.com, and incorporated by reference herein. 
     Typically, the transponder amplitude modulates a CW RF carrier of an RF generator with a data word bitstream in accordance with the binary values of that data word bitstream. The data word bitstream is a series of on/off pulses which represent, for example, a serial data word synchronization header, a tag number, etc. Parity bits or a checksum value may also be incorporated into the data word bitstream. These series of on/off pulses are received by the related transponder. 
     Heretofore, a parallel resonant tuned circuit required connection to two pins of an integrated circuit transponder system. In an integrated circuit package having, for example, multiple functions and/or a plurality of transponder circuits, input-output pin utilization is critical. Requiring two dedicated pins for each parallel resonant circuit associated with a transponder takes away the possibility of using the limited number of pins on the integrated circuit package for other needed or desired functions. 
     Therefore, what is needed is more effective and better utilization of input-output pins on an integrated circuit package for connecting a parallel resonant circuit to the transponder circuit of the integrated circuit. 
     SUMMARY OF THE INVENTION 
     The invention overcomes the above-identified problems as well as other shortcomings and deficiencies of existing technologies by providing in an integrated circuit package a transponder requiring only a single dedicated input-output pin (of the integrated circuit package) for connection (external to the package) to a resonant frequency tuned circuit. Another package pin which may be used for common power or ground connections may supply the second connection to the resonant frequency tuned circuit. The transponder embodiment of the present invention may be used in security and access devices for unlocking and opening automobile doors, home and office doors, garage doors, security gates and the like. The present invention enables hands-free operation of locks, doors and the like. Since the transponder is able to receive a low power radio frequency signal, verification and activation of the lock or door may occur from a distance and without having to remove the transponder system from ones pocket, purse, or briefcase. 
     It is contemplated herein and within the scope of the present invention that an integrated circuit package comprises a plurality of transponder circuits connected to a plurality of associated resonant frequency tuned circuits, each of the plurality of associated resonant frequency tuned circuits requiring a first connection to only a single dedicated input-output pin, and a second connection to a common pin. 
     It is also contemplated herein and within the scope of the present invention that the dedicated resonant frequency tuned circuit input-output pin(s) may also be used for a secondary function (i.e., dual purpose). 
     In accordance with an embodiment of the present invention, an integrated circuit package having a transponder circuit therein, has an input-output pin connected to an input of a high gain amplifier biased with current sources also connected to the input of the high gain amplifier. A direct current (DC) bias level measurement and control circuit may be connected to and be in control of these current sources. An input to the DC bias level measurement and control circuit may be a signal received at the input-output pin connected to the input of the high gain amplifier. From the amplitude of the measured input signal, the DC bias level measurement and control circuit may change the DC bias level of the high gain amplifier, thus controlling the gain thereof. 
     A parallel resonant circuit comprising an inductor connected in parallel with a capacitor forms a pickup sensor or antenna for an externally generated electromagnetic or radio frequency signal. One end of the parallel resonant circuit is connected to a common power or ground pin of the integrated circuit package and the other end of the parallel resonant circuit is connected to one end of a DC blocking capacitor. The other end of the DC blocking capacitor is connected to the input-output pin of the integrated circuit package which is also connected to the input of the high gain amplifier. The reactance of the DC blocking capacitor is preferably substantially less than the input impedance of the high gain amplifier (for example but not limitation: one tenth the impedance) and preferably may also be substantially less than the impedance of the parallel circuit at resonance (for example but not limitation: one tenth the impedance). The DC blocking capacitor thus allows an alternating current (AC) signal coupled to the parallel resonant circuit to pass to the input of the high gain amplifier without the parallel resonant circuit (DC low resistance) affecting the DC bias value from the current sources which are also connected to the input of the amplifier. Alternatively, a DC blocking capacitor may be connected in series with the inductor instead of between the parallel resonant circuit and the input-output pin of the integrated circuit package, and the parallel resonant circuit may then be connected directly to the input-output pin. 
     An internally generated signal for transmission may be applied to the same pin as used as an input to the transponder amplifier or a separate pin may be utilized to transmit the signal from the integrated circuit. Typical receive or input signal frequencies may be from about 100 kHz to about 14 MHz, and a transmitted output frequency may be from about 100 kHz to well into the ultra high frequency (UHF) range. 
     In another embodiment of the present invention, an integrated circuit package has a plurality of transponder circuits and a corresponding plurality of input-output pins, each transponder amplifier having an input connected to a one of the corresponding plurality of input-output pins. A plurality of parallel resonant circuits are adapted for connection to the corresponding plurality of input-output pins through DC blocking capacitors and to a common power or ground pin, or the DC blocking capacitors may be connected in series with the inductors, as disclosed above. The plurality of transponder amplifiers and plurality of parallel resonant circuits may be utilized with one signal frequency in a diversity receiving or voting system, or each one of the plurality of parallel resonant circuits may be tuned to a different frequency and the integrated circuit used as multiple simultaneous transponders. Internally generated transmit signals may be applied to the same pin and tuned circuit or may be applied to other pins of the integrated circuit package. 
     A feature of the present invention is using only one dedicated input-output pin on an integrated circuit package for each transponder function in an integrated circuit. 
     Another feature is a plurality of transponders in an integrated circuit having a minimum number of input-output pins. 
     Still another feature is a space diversity or voting system having a plurality of transponders. 
     An advantage of the present invention is a reduction of the number of input-output pins required for operation of a bi-directional transponder in an integrated circuit. 
     Another advantage is the operation of the transponder over a desired distance without having to remove the transponder system from a pocket, purse, briefcase and the like. 
     Features and advantages of the invention will be apparent from the following description of presently preferred embodiments, given for the purpose of disclosure and taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of an embodiment of the invention; 
     FIG. 2 is a schematic block diagram of another embodiment of the invention; 
     FIG. 3 is a schematic block diagram of a multiple input single channel embodiment of the invention; 
     FIG. 4 is a schematic block diagram of a multiple channel embodiment of the invention; 
     FIG. 5 is schematic diagram of a system utilizing the embodiments of the invention; and 
     FIG. 6 is a schematic block diagram of the embodiment illustrated in FIG. 1, further comprising a radio frequency switch and transmitter-modulator using the same input-output pin as the receiver-amplifier. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is a radio frequency transponder in an integrated circuit package that uses a single dedicated input-output pin and a common power or ground pin (of the integrated circuit package) for connection (external to the package) to a resonant parallel connected inductor-capacitor tuned circuit. The present invention is especially useful in any application requiring not only secure communication of data and commands but also the protection of any valuable asset or property. For example but not limitation: (1) Vehicular applications comprising remote keyless entry, alarm systems, and immobilizers for cars and trucks. (2) Consumer and commercial applications comprising car alarms, garage door openers, burglar alarms, gate locks, door locks, and secure communications for smoke, carbon monoxide and radon detectors. (3) Industrial applications comprising package tracking, parts tracking, package and equipment tags, and identity tokens. The present invention enables hands-free operation of locks, doors, gates and the like. Since the transponder is able to receive a low power radio frequency signal, verification and activation of the lock of a door or gate opening mechanism may occur from a distance and without having to remove the transponder system from ones pocket, purse, or briefcase. 
     Referring now to the drawings, the details of preferred embodiments of the invention are schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix. 
     Referring now to FIG. 1, a schematic block diagram of an embodiment of the invention, is illustrated. A transponder is generally indicated by the numeral  100 . According to an embodiment of the present invention, the transponder  100  comprises a high gain signal amplifier  120 , current sources  114  and  116 , and a DC bias level measurement and control circuit  118  in an integrated circuit package  102 ; and a parallel tuned circuit  106  comprising a capacitor  110  and an inductor  108 , and a DC blocking capacitor  112  connected between an input-output pin  124  of the integrated circuit package  102  and the parallel tuned circuit  106 . The signal return of the parallel tuned circuit  106  is through a common power or ground pin  122  (ground pin illustrated). However, the use of a common power pin for a signal return is also contemplated and within the scope of the present invention). 
     The DC blocking capacitor  112  allows an independent DC bias level to be set at the input of the amplifier  120 . The DC bias level measurement and control circuit  118  controls the current sources  114  and  116  so that a preferred DC bias value is applied to the amplifier  120  to optimize the available signal amplification thereof. The DC bias level measurement and control circuit  118  can also control the gain of the amplifier  120  by changing its DC bias value. The amplification of the amplifier  120  may be optimized to receive signals of 1 millivolt or greater. 
     The parallel tuned circuit  106  is adapted to receive electromagnetic or radio frequency (RF) energy from a signal source. The received energy is in the form of an alternating current (AC) signal which is coupled through the blocking capacitor  112  and amplified by the amplifier  120 . The amplified signal from the output of the amplifier  120  is then detected (demodulated) as information for processing in logic circuits (not illustrated). The blocking capacitor  112  has an AC impedance substantially lower than the input impedance of the amplifier  120 . Thus, the blocking capacitor  112  introduces very little attenuation of the received AC signal at the parallel tuned circuit  106 . 
     Referring now to FIG. 2, a schematic block diagram of another embodiment of the invention is illustrated. A transponder is generally indicated by the numeral  200 . According to the embodiment of the present invention, the transponder  200  comprises a high gain signal amplifier  120 , current sources  114  and  116 , and a DC bias level measurement and control circuit  118  in an integrated circuit package  102 ; and a parallel tuned circuit  206  comprising a capacitor  110   a , an inductor  108  and a DC blocking capacitor  112   a  connected in series with the inductor  108 . The parallel tuned circuit  206  is connected to the input-output pin  124  of the integrated circuit package  102 , and the signal return of the parallel tuned circuit  206  is through a common power or ground pin  122  (ground pin illustrated). However, the use of a common power pin for a signal return is also contemplated and within the scope of the present invention). 
     The DC blocking capacitor  112   a  allows an independent DC bias level to be set at the input of the amplifier  120 , and the DC bias level measurement and control circuit  118  controls the current sources  114  and  116  as disclosed hereinabove. The parallel tuned circuit  206  is adapted to receive electromagnetic or radio frequency (RF) energy from a signal source. The received energy is in the form of an alternating current (AC) signal which is coupled through the blocking capacitor  112  and amplified by the amplifier  120 . The amplified signal from the output of the amplifier  120  is then detected (demodulated) as information for processing in logic circuits (not illustrated). The blocking capacitor  112   a  has an AC impedance substantially lower than the input impedance of the amplifier  120  and the AC impedance of the capacitor  110   a . Thus, the blocking capacitor  112  introduces very little attenuation of the received AC signal at the parallel tuned circuit  206  and does not materially affect the resonant frequency of the parallel tuned circuit  206 . The blocking capacitor may also be connected between a parallel connected tuned circuit  206   a  and common or ground, as indicated in FIG.  2 . 
     Referring now to FIG. 3, a schematic block diagram of a multiple input single channel embodiment of the invention is illustrated. A transponder having a plurality of signal inputs is generally indicated by the numeral  300 . According to this embodiment of the present invention, the transponder  300  comprises high gain signal amplifiers  120   a - 120   d , DC bias level measurement and control circuits  118   a - 118   d , (current sources  114   a - 114   d  and  116   a - 116   d  are not illustrated for clarity), a best signal selection circuit  326  and a signal detector  328  in an integrated circuit package  302 ; and parallel tuned circuits  106   a - 106   d , and DC blocking capacitors  112   a - 112   d  connected between input-output pins  124   a - 124   d  of the integrated circuit package  302  and the parallel tuned circuits  106   a    106   d.    
     The parallel tuned circuits  106   a - 106   d  comprise capacitors  110   a - 110   d  and inductors  108   a - 108   d . The signal returns of the parallel tuned circuits  106   a - 106   d  are through a common power or ground pin  122  (ground pin illustrated). However, the use of a common power pin for a signal return is also contemplated and within the scope of the present invention). 
     The DC blocking capacitors  112   a - 112   d  allow independent DC bias levels to be set at the inputs of each of the amplifiers  120   a - 120   d . The DC bias level measurement and control circuits  118   a - 118   d  control the current sources  114   a - 114   d  and  116   a - 116   d  (not illustrated), respectively, so that preferred DC bias values are applied to the amplifiers  120   a - 120   d  to optimize the available signal amplification thereof The DC bias level measurement and control circuits  118   a - 118   d  can also control the gain of the amplifiers  120   a - 120   d , respectively, by changing the respective DC bias values thereof. The amplification of the amplifiers  120   a - 120   d  may be optimized to receive signals of 1 millivolt or greater. 
     The parallel tuned circuits  106   a - 106   d  are adapted to receive electromagnetic or radio frequency (RF) energy from a signal source(s). The received energy is in the form of an alternating current (AC) signal which is coupled through the blocking capacitors  112   a - 112   d  and amplified by the amplifiers  120   a - 120   d . The amplified signals from the outputs of the amplifiers  120   a - 120   d  are compared in the best signal selection circuit  326 , wherein the best (i.e., strongest) signal is selected and then detected (demodulated) in the signal detector  328 . The detected information is processed in logic circuits (not illustrated). The blocking capacitors  112   a - 112   d  each have an AC impedance substantially lower than the input impedance of the amplifiers  120   a - 120   d . Thus, the blocking capacitors  112   a - 112   d  introduce very little attenuation of the received AC signals at the parallel tuned circuits  106   a - 106   d . Four tuned circuits and amplifiers are illustrated for clarity, however, it is contemplated and within the scope of the present to invention that any number of tuned circuits and amplifiers may be utilized by the embodiment of the present invention. 
     Referring to FIG. 4, a schematic block diagram of a multiple channel embodiment of the invention is illustrated. A transponder having a plurality of signal inputs for a plurality of different channels is generally indicated by the numeral  400 . According to this embodiment of the present invention, the transponder  400  comprises high gain signal amplifiers  120   a - 120   d , DC bias level measurement and control circuits  118   a - 118   d , (current sources  114   a - 114   d  and  116   a - 116   d  are not illustrated for clarity) and signal detectors  428   a - 428   d  in an integrated circuit package  402 ; parallel tuned circuits  106   a - 106   d , and DC blocking capacitors  112   a - 112   d  connected between input-output pins  124   a - 124   d  of the integrated circuit package  402  and the parallel tuned circuits  106   a - 106   d . The parallel tuned circuits  106   a - 106   d  comprise capacitors  110   a - 110   d  and inductors  108   a - 108   d . The signal returns of the parallel tuned circuits  106   a - 106   d  are through a common power or ground pin  122  (ground pin illustrated). However, the use of a common power pin for a signal return is also contemplated and within the scope of the present invention). 
     The DC blocking capacitors  112   a - 112   d  allow independent DC bias levels to be set at the inputs of each of the amplifiers  120   a - 120   d . The DC bias level measurement and control circuits  118   a - 118   d  control the current sources  114   a - 114   d  and  116   a - 116   d  (not illustrated), respectively, so that preferred DC bias values are applied to the amplifiers  120   a - 120   d  to optimize the available signal amplification thereof. The DC bias level measurement and control circuits  118   a - 118   d  can also control the gain of the amplifiers  120   a - 120   d , respectively, by changing the respective DC bias values thereof. The amplification of the amplifiers  120   a - 120   d  may be optimized to receive signals of 1 millivolt or greater. 
     The parallel tuned circuits  106   a - 106   d  are adapted to receive electromagnetic or radio frequency (RF) energy from a plurality of signal sources which may be at different operating frequencies and contain independent information from each of the plurality of signal sources. The received energies are in the form of alternating current (AC) signals which are coupled through the blocking capacitors  112   a - 112   d  and amplified by the amplifiers  120   a - 120   d . The amplified signals from the outputs of the amplifiers  120   a - 120   d  are detected (demodulated) in the signal detectors  428   a - 428   d . The demodulated information signals from the signal detectors  428   a - 428   d  are processed in logic circuits (not illustrated). Four information channels are illustrated for clarity, however, it is contemplated and within the scope of the present invention that any number of information channels may be received and processed by an embodiment of the present invention. 
     The blocking capacitors  112   a - 112   d  each have an AC impedance substantially lower than the input impedance of the amplifiers  120   a - 120   d . Thus, the blocking capacitors  112   a - 112   d  introduce very little attenuation of the received AC signals at the parallel tuned circuits  106   a - 106   d.    
     Referring now to FIG. 5, a schematic diagram of a system utilizing the embodiments of the invention is illustrated. A generally secured environment having an embodiment of the present invention is represented by the numeral  500 . The environment  500  may be an automobile, office building, garage with a remotely controlled access gate, warehouse, boat, plane or train, i.e., anything which is secured by a locked entrance and allows access by authorized personnel. Signal pickup sensors  552   a - 552   d  represent herein the tuned parallel circuits  106   a - 106   d , respectively, of the embodiments disclosed hereinabove. For example, a space diversity receiving system may be implemented using the embodiment illustrated in FIG.  3  and disclosed hereinabove, by placing the signal pickup sensors  552   a - 552   d  (tuned parallel circuits  106   a - 106   d ) at various locations on the environment  500 . This space diversity system allows better reception of, for example but not limitation, a keyless entry system to the environment  500  no matter where the keyless transmitter is in relation to the environment  500 . The signal pickup sensors  552   a - 552   d (tuned parallel circuits  106   a - 106   d  ) may also be utilized with the embodiment of the invention illustrated in FIG.  4  and disclosed hereinabove. 
     An example of a transponder security system which may benefit from the embodiments of the present invention is described more fully in the KEELOQ® (a registered trademark of Microchip Technology Inc.) products, and more specifically, in the device entitled “Code Hopping Encoder and Transponder,” part number HCS412 by Microchip Technology Inc., more fully described in Specification DS41099A (1999) available at http://www.microchip.com, and incorporated by reference herein. The HCS412 requires two dedicated package pins for connection to a parallel tuned circuit, as illustrated in FIG. 2—2 of the HCS412 data sheet. The present invention maintains the functionality of the HCS412 but reduces the number of pins required for external connections to the integrated circuit package. 
     Referring now to FIG. 6, a schematic block diagram of the embodiment illustrated in FIG. 1, further comprising a radio frequency switch and transmitter-modulator using the same input-output pin as the receiver-amplifier, is illustrated. The transponder embodiment of FIG. 6 is generally indicated by the numeral  600 . The transponder  600  further comprises a switch  654 , for example but not limitation, metal oxide field effect transistors (MOSFET) and a transmitter-modulator circuit  656  in the integrated circuit package  602 . The switch  654  transfers connection of the input-output pin  124  to either the input of the amplifier  120  for receiving a signal picked up on the turned circuit  106 , or to the transmitter-modulator  656  for transmitting a digitally encoded signal from the tuned circuit  106 . Thus, the transponder function of interrogation and acknowledgement is performed by the transponder using the same pin  124  and tuned circuit  106  for an antenna. 
     It is also contemplated and within the scope of the present invention that a separate transmitting antenna and pin on the integrated circuit package may be used, i.e., the receiver and transmitter frequencies are different. The present invention allows better utilization of the fixed number of pins on an integrated circuit package, thus, enabling more features to be offered for a given integrated circuit package size. 
     The invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While the invention has been depicted, described, and is defined by reference to particular preferred embodiments of the invention, such references do not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alternation, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts. The depicted and described preferred embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving fill cognizance to equivalents in all respects.