Abstract:
An integrated circuit for use in remote keyless entry (RKE) applications is disclosed that integrates two drivers with a shared dual mode antenna. The drivers may be integrated on a single integrated circuit chip using high voltage (HV) complementary metal-oxide-semiconductor (CMOS) processes. In immobilizer mode of operation, an immobilizer driver coupled to the dual mode antenna is configured to drive the dual mode antenna, while an LF mode driver coupled to the dual mode antenna is configured to be idle. In LF mode of operation, the LF mode driver is configured to drive the dual mode antenna, while the immobilizer driver is configured to be idle. In some implementations, the drivers are coupled to a common node coupled to the dual mode antenna and are selectively biased with different supply voltages based on the current mode of operation to prevent current leakage and component damage.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to integrated circuits for remote keyless entry (RKE) systems. 
       BACKGROUND 
       [0002]    RKE systems have replaced the traditional mechanical ignition key as the standard for vehicle access applications. Conventional RKE systems use an ultra-high frequency (UHF) link from a key fob to the vehicle that triggers a lock/unlock mechanism in the vehicle in response to a user pushing a button on the key fob. In recent years, more advanced RKE systems, such as passive entry (PE) and passive entry go (PEG) have been introduced into vehicles. These advanced, second-generation RKE systems provide vehicle owners with easier access than first generation RKE systems. Contemporary PE and PEG systems may use radio-frequency identification (RFID) technology, which requires Low Frequency (LF) antennas to be distributed throughout the vehicle for use in unlocking doors, trunks, etc. 
         [0003]    For many years, antitheft systems called “immobilizers” have been installed in vehicles. Many conventional immobilizer systems also use RFID technology. These conventional immobilizer systems include a reader antenna and other reader hardware in the vehicle that reads an RFID tag in the key fob. A successful read of an RFID tag releases an electronic immobilizer mechanism that prevents the engine of the vehicle from being started. 
         [0004]    While immobilizer systems and contemporary RKE systems may use similar RFID techniques and frequencies, the two systems are often installed in vehicles as separate systems and do not share components. 
       SUMMARY 
       [0005]    An integrated circuit for use in RKE applications is disclosed that integrates two drivers coupled to a shared dual mode antenna. The drivers may be integrated on a single integrated circuit chip using high voltage (HV) complementary metal-oxide-semiconductor (CMOS) processes. In immobilizer mode of operation, an immobilizer driver coupled to the dual mode antenna is configured to drive the dual mode antenna, while an LF mode driver coupled to the dual mode antenna is configured to be idle. In LF mode of operation, the LF mode driver is configured to drive the dual mode antenna, while the immobilizer driver is configured to be idle. In some implementations, the drivers are coupled to a common node coupled to the dual mode antenna and are selectively biased with different supply voltages based on the current mode of operation to prevent current leakage and component damage. 
         [0006]    Particular implementations of the integrated driver for vehicle immobilizer/access applications provide one or more of the following advantages: 1) better cost efficiency by using a single LF antenna for both immobilizer and vehicle access systems instead of two separate antennas; 2) higher level of system integration achieved by using a single integrated circuit chip instead of two chips for the immobilizer and access systems; 3) relaxed limit for minimum car battery voltage by using a voltage booster stage during immobilizer operation; 4) lower number of components and thus lower overall bill of materials (BOM) for easier integration into a customer&#39;s system solution; 5) lower effort for logistics and stock keeping due to fewer components; and 6) reduced number of components for the overall system resulting in enhanced reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates an example circuit configuration of a conventional vehicle immobilizer system. 
           [0008]      FIG. 2  illustrates an example circuit configuration of a LF portion of a conventional RKE system. 
           [0009]      FIG. 3  illustrates an example circuit configuration including integrated drivers sharing a dual mode antenna. 
           [0010]      FIG. 4  illustrates an example circuit configuration for immobilizer mode. 
           [0011]      FIG. 5  illustrates an example circuit configuration for immobilizer mode using push-pull stages. 
           [0012]      FIG. 6  illustrates an example circuit configuration for LF mode. 
           [0013]      FIG. 7  illustrates an example circuit configuration for LF mode using push-pull components. 
           [0014]      FIG. 8  is a flow diagram illustrating an example process performed during immobilizer mode. 
           [0015]      FIG. 9  is a flow diagram illustrating an example process performed during LF mode. 
       
    
    
     DETAILED DESCRIPTION 
     Conventional Immobilizer and RKE Systems 
       [0016]      FIG. 1  illustrates an example circuit configuration of a conventional immobilizer system  100 . In some implementations, system  100  includes vehicle control bus  101 , microcomputer  102 , immobilizer driver  103  and immobilizer antenna  104 . Vehicle control bus  101  can be any known bus system for vehicles, including but not limited to: local interconnect network (LIN), controller area network (CAN) and FlexRay™. 
         [0017]    A microcircuit inside a passive key fob is activated by a small electromagnetic field generated by immobilizer antenna  104 , which induces a current flow inside the key fob body, which in turn causes the microcircuit to broadcast a wireless signal carrying a unique binary code. The binary code is received by immobilizer antenna  104 , which may be wrapped around the ignition barrel lock. Microcomputer  102  reads the code and checks for a match with a code stored in microcomputer  102 . In some implementations, microcomputer  102  is part of a central board controller. In other implementations, microcomputer  102  is part of an automobile&#39;s Engine Control Unit (ECU). When microcomputer  102  determines that the code is current and valid, microcomputer  102  or the ECU activates a fuel-injection sequence so that the vehicle can be started. 
         [0018]      FIG. 2  illustrates an example circuit configuration of a LF portion of a conventional RKE system. In some implementations, system  200  includes vehicle control bus  101 , microcomputer  102 , LF mode driver  200  and one or more LF antennas  201 . LF antennas  201  may be placed in each door of the vehicle and are driven by LF mode driver  200 , which is also located in the vehicle. When a user pulls a vehicle door handle a switch activates a request to a central board controller or ECU to establish LF communication over a LF downlink between the vehicle and the LF tag in the key fob. The LF tag in the key fob triggers the UHF transmitter in the key fob to transmit current and a valid code to the UHF receiver of the vehicle. 
         [0019]    Typical vehicle installations include separate integrated circuits for driving separate antennas for engine immobilizer and RKE applications, resulting in a larger number of parts and the associated costs of those parts. As described below, a single integrated circuit includes two drivers coupled at a common node that is coupled to a shared “dual mode” antenna. The dual mode antenna is capable of being operated in one of two modes: immobilizer mode and LF mode. By sharing the same silicon and the same antenna, the number of parts of the overall system and associated cost for those parts are reduced. 
       Example Functional Blocks and Modes of Operation 
       [0020]      FIG. 3  illustrates an example circuit configuration including integrated drivers sharing a dual mode antenna. In some implementations, circuit  300  includes voltage source  301  (e.g., a battery), booster  302 , regulator  303 , LF mode driver  304 , immobilizer driver  305  and dual mode antenna  307 . The outputs of LF mode driver  304  and immobilizer driver  305  are coupled to common node  306  (AOP). In some implementations, regulator  303  includes or is coupled to bypass switch  308 . 
         [0021]    Booster  302  is an optional component that is used during LF mode operation. Booster  302  is coupled to voltage source  301  and generates supply voltage VDS for LF mode driver  304  and immobilizer driver  305  (during LF mode operation). LF mode driver  304  needs voltages higher than voltage source  301  can provide to fulfill minimum voltage requirements for advanced RKE systems like PE and PEG. Optionally, booster  302  can also be used for immobilizer mode operation to overcome limitations imposed by minimum battery voltages. Booster  302  may be, for example, a DC-to-DC converter. 
         [0022]    Regulator  303  is a voltage regulator for supply voltage VDS. Regulator  303  is coupled to supply voltage VDS and provides a stabilized, regulated supply voltage VTX to immobilizer driver  305  during immobilizer mode operation. Regulator  303  provides noise reduction for data transfer between reader hardware (not shown) and a transponder in the key fob. Regulator  303  also isolates the reader hardware and thus the reader channel from disturbances and spurious interferences coming from the vehicle&#39;s power supply grid, voltage source  301  or, in general, the VDS supply domain. Regulator  303  also provides noise reduction when booster  302  is active during immobilizer mode operation. In some implementations, a regulator can be used to regulate voltage VDS as well as VTX. 
         [0023]    During LF mode, regulator  303  is bypassed (e.g., using bypass switch  308 ) to allow the VTX voltage supply pin of immobilizer driver  305  to be coupled directly to the VDS voltage domain. Bypass switch can be integrated into regulator  303  or coupled to regulator  303 . Switch  308  may implemented using one or more transistors that are biased to operate as a switch. 
         [0024]    LF mode driver  304  is configured to be active during LF mode operation. LF mode driver  304  is supplied by the boosted battery voltage VDS and outputs a modulated LF signal to dual mode antenna  307 . When immobilizer mode is active, LF mode driver  304  is idle and its output is placed in a high ohmic state to prevent current leaking into LF mode driver  304  and damaging sensitive components in LF mode driver  304 . To place the output of LF mode driver  304  in a high ohmic state the unregulated supply voltage VDS of LF mode driver  304  should be greater than or equal to the regulated voltage VTX input to immobilizer driver  305  (VDS≧VTX). This condition is fulfilled when bypass switch  308  of regulator  303  is opened. 
         [0025]    During immobilizer mode operation, immobilizer driver  305  is configured to be active. The supply voltage for immobilizer  304  is the regulated VTX voltage output by regulator  303 . During LF mode operation, the output of immobilizer driver  305  is placed into a high ohmic state to prevent current leaking into immobilizer driver  305  and damaging sensitive components in immobilizer driver  305 . To place the output of immobilizer driver  305  in a high ohmic state, the supply voltage VTX of immobilizer driver  305  should be equal to the unregulated supply voltage VDS of LF mode driver  304  (VDS=VTX). This condition is fulfilled when bypass switch  308  of regulator  303  is closed, directly coupling VDS to immobilizer driver  305 . 
         [0026]    Dual mode antenna  307  is a shared LF antenna that is driven by immobilizer driver  305  during immobilizer mode operation and driven by LF mode driver  304  during LF mode operation. Dual mode antenna  307  may be coupled to LF mode driver  304  and immobilizer driver  305  at common node  306  (AOP). 
         [0027]    In some implementations, circuit  300  can be configured to use differential signal chains for processing differential signals by replacing the components in circuit  300  with differential components. 
       Description of Modes of Operation 
     Immobilizer Mode 
       [0028]    During immobilizer mode of operation, immobilizer driver  305  drives dual mode antenna  307 , which generates a wireless signal that provides power to a transponder in a key fob and additionally carries a triggering signal that is expected by the transponder. When the transponder is activated by the power, the transponder responds to the triggering signal by generating a response carrier signal modulated with a code. The response carrier signal is received through dual mode antenna  307  and fed into reader hardware (not shown), where the code is demodulated and decoded if encoded and/or encrypted. 
         [0029]    Under normal conditions, booster  302  is idle during immobilizer mode operation. This results in VDS=(voltage supply  301 ) minus two diode voltages, hereafter referred to as “immobilizer mode 1.” One diode is part of booster  302  and one diode is a reverse polarity protection diode. 
         [0030]    In some implementations, the configuration of  FIG. 3  allows system architects to activate booster  302  during immobilizer mode operation to overcome the limitations of minimum battery voltages, hereafter referred to as “immobilizer mode 2.” 
         [0031]    During either immobilizer mode 1 or 2 operation, LF mode driver  304  is idle and its output is placed in a high ohmic state by providing supply voltage VDS to LF mode driver  304 , such that during immobilizer mode operation the condition VDS≧VTX is satisfied. The high ohmic output state prevents current from leaking into LFS mode driver  304  and damaging internal transistors of LF mode driver  304 . 
         [0032]    During immobilizer mode operation, regulator  303  is active and generates from the VDS voltage at its input a regulated VTX voltage for immobilizer driver  305 . The regulated VTX voltage is the supply voltage for immobilizer driver  305  when the system is in immobilizer mode operation. For proper operation of immobilizer driver  305 , the regulated VTX voltage has to fulfill challenging requirements, which may be defined by sensitivity requirements of other hardware used in the immobilizer application, such as a wireless signal receiver in the reader hardware. 
         [0033]    During immobilizer mode operation, dual mode antenna  307  is stimulated by a driving signal provided by immobilizer driver  305 . Immobilizer driver  305  sends out a signal to a transponder in the key fob, which responds with a carrier signal modulated with a code (e.g., unique binary code). The response signal is received by dual mode antenna  307  and fed into reader hardware, where the code is demodulated from the carrier signal and decoded if encoded and/or encrypted. 
       LF Mode 
       [0034]    The LF mode is the mode of operation for advanced RKE applications like PE and PEG. The LF mode of operation is used for the transmission of an LF signal expected by the key fob to trigger a system wake up procedure. During LF mode operation, booster  302  is active. When activated booster  302  steps voltage source  301  up to a voltage level VDS that is sufficient for proper operation of the RKE application and provides the VDS voltage as a voltage supply to LF mode driver  304 . The input signal of LF mode driver  304  is amplified and fed into dual mode antenna  307 . 
         [0035]    During LF mode operation, regulator  303  is placed in a bypass mode. For example, switch  308  is closed, resulting in VTX=VDS. The bypass mode keeps the output of immobilizer driver  305  in a high ohmic state while maintaining bias conditions that avoid undesired leakage currents to enter immobilizer  305  due to the presence of a signal at common node  306 . 
         [0036]    During LF mode operation, dual mode antenna  307  is stimulated by a driving signal provided by LF mode driver  304 . LF mode driver  305  causes dual mode antenna  307  to generate an electromagnetic field that can be detected by the key fob circuitry. 
       Example Biasing of Integrated Drivers 
       [0037]      FIG. 4  illustrates an example circuit configuration  400  for immobilizer mode. When immobilizer mode is selected, LF mode driver  304  is configured to be idle and immobilizer driver  305  (transistors  403  (NM3) and  404  (NM4)) is configured to drive dual mode antenna  307 , generating a signal voltage in the range of VTX to ground (GND). The NMOS transistors  401  (NM1),  402  (NM2) of LF mode driver  304  are passive and configured to remain off even when the signal from immobilizer mode operation is present at common node  306 . The gates of NMOS transistors  401 - 404  may be controlled by internal hardware (not shown). 
         [0038]    A problem with the circuit configuration of  FIG. 4  is that the parasitic diodes D DB , D SB  for NMOS transistors  401 ,  402 , respectively, may become forward biased during immobilizer mode due to the signal present at common node  306 , resulting in unintended currents being sent through LF mode driver  304 . This problem is avoided by keeping the condition VDS≧VTX. This voltage condition causes parasitic diodes D DB , D SB  of transistors  401 ,  402  to be reverse biased, which prevents unintended currents from entering LF mode driver  304 . 
         [0039]    In some implementations, push-pull driver circuit configurations may be used by replacing NMOS transistors  401 ,  403  with PMOS transistors  501  (PM1),  503  (PM3), as shown in  FIG. 5 . The power management and bias conditions previously described in reference to the circuit shown in  FIG. 4  are also applicable to the circuit shown in  FIG. 5 . 
         [0040]      FIG. 6  illustrates a circuit configuration for LF mode of operation. When LF mode operation is selected, transistors  601  (NM1) and  602  (NM2) drive dual mode antenna  307 . The passive transistors  603  (NM3) and  604  (NM4) of immobilizer driver  305  are configured to remain off even if the signal from LF mode operation is present at common node  306 . 
         [0041]    A problem with the circuit configuration of  FIG. 6  is that the parasitic diodes D DB , D SB  for transistors  603 ,  604  may become forward biased due to the signal present at common node  306 , resulting in unintended currents through immobilizer driver  304 . This problem is avoided by keeping the condition VTX=VDS during LF mode operation. This voltage condition keeps the parasitic diodes D DB , D SB  for transistors  603 ,  604  in reverse bias condition. 
         [0042]    In some implementations, push-pull driver circuits may be used by replacing NMOS transistors  601 ,  603  with PMOS transistors  701  (PM1),  703  (PM3), as shown in  FIG. 7 . 
         [0043]      FIG. 8  is a flow diagram illustrating an example process  800  performed by system  300  while operating in immobilizer mode of operation. In some implementations, process  800  detects an immobilizer mode operation ( 802 ), activates an immobilizer driver, deactivates an LF mode driver ( 804 ) and drives a dual mode antenna with the immobilizer driver ( 806 ). The immobilizer driver and LF mode driver have outputs coupled to a common node, which is coupled to the dual mode antenna. During immobilizing mode of operation, parasitic diodes of the transistors in the LF mode driver are reverse biased to prevent currents from entering the LF mode driver due to a signal present at the common node due to operation of the immobilizer driver. 
         [0044]      FIG. 9  is a flow diagram illustrating an example process  900  performed while operating in the LF mode of operation. In some implementations, process  900  detects an LF mode operation ( 902 ), activates an LF mode driver, and deactivates an immobilizer driver ( 904 ) and drives a dual mode antenna with the LF mode driver ( 806 ). The immobilizer driver and LF mode driver have outputs coupled to a common node, which is coupled to the dual mode antenna. During LF mode operation, parasitic diodes of the transistors in the immobilizer driver are reverse biased to prevent currents from entering the immobilizer driver due to a signal present at the common node due to operation of the LF mode driver. 
         [0045]    While this document contains many specific implementation details, these should not be construed as limitations on the scope what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination.