Integrated circuit for remote keyless entry system

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.

TECHNICAL FIELD

This disclosure relates generally to integrated circuits for remote keyless entry (RKE) systems.

BACKGROUND

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.

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.

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

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.

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'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.

DETAILED DESCRIPTION

Conventional Immobilizer and RKE Systems

FIG. 1illustrates an example circuit configuration of a conventional immobilizer system100. In some implementations, system100includes vehicle control bus101, microcomputer102, immobilizer driver103and immobilizer antenna104. Vehicle control bus101can be any known bus system for vehicles, including but not limited to: local interconnect network (LIN), controller area network (CAN) and FlexRay™.

A microcircuit inside a passive key fob is activated by a small electromagnetic field generated by immobilizer antenna104, 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 antenna104, which may be wrapped around the ignition barrel lock. Microcomputer102reads the code and checks for a match with a code stored in microcomputer102. In some implementations, microcomputer102is part of a central board controller. In other implementations, microcomputer102is part of an automobile's Engine Control Unit (ECU). When microcomputer102determines that the code is current and valid, microcomputer102or the ECU activates a fuel-injection sequence so that the vehicle can be started.

FIG. 2illustrates an example circuit configuration of a LF portion of a conventional RKE system. In some implementations, system200includes vehicle control bus101, microcomputer102, LF mode driver200and one or more LF antennas201. LF antennas201may be placed in each door of the vehicle and are driven by LF mode driver200, 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.

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

FIG. 3illustrates an example circuit configuration including integrated drivers sharing a dual mode antenna. In some implementations, circuit300includes voltage source301(e.g., a battery), booster302, regulator303, LF mode driver304, immobilizer driver305and dual mode antenna307. The outputs of LF mode driver304and immobilizer driver305are coupled to common node306(AOP). In some implementations, regulator303includes or is coupled to bypass switch308.

Booster302is an optional component that is used during LF mode operation. Booster302is coupled to voltage source301and generates supply voltage VDS for LF mode driver304and immobilizer driver305(during LF mode operation). LF mode driver304needs voltages higher than voltage source301can provide to fulfill minimum voltage requirements for advanced RKE systems like PE and PEG. Optionally, booster302can also be used for immobilizer mode operation to overcome limitations imposed by minimum battery voltages. Booster302may be, for example, a DC-to-DC converter.

Regulator303is a voltage regulator for supply voltage VDS. Regulator303is coupled to supply voltage VDS and provides a stabilized, regulated supply voltage VTX to immobilizer driver305during immobilizer mode operation. Regulator303provides noise reduction for data transfer between reader hardware (not shown) and a transponder in the key fob. Regulator303also isolates the reader hardware and thus the reader channel from disturbances and spurious interferences coming from the vehicle's power supply grid, voltage source301or, in general, the VDS supply domain. Regulator303also provides noise reduction when booster302is active during immobilizer mode operation. In some implementations, a regulator can be used to regulate voltage VDS as well as VTX.

During LF mode, regulator303is bypassed (e.g., using bypass switch308) to allow the VTX voltage supply pin of immobilizer driver305to be coupled directly to the VDS voltage domain. Bypass switch can be integrated into regulator303or coupled to regulator303. Switch308may implemented using one or more transistors that are biased to operate as a switch.

LF mode driver304is configured to be active during LF mode operation. LF mode driver304is supplied by the boosted battery voltage VDS and outputs a modulated LF signal to dual mode antenna307. When immobilizer mode is active, LF mode driver304is idle and its output is placed in a high ohmic state to prevent current leaking into LF mode driver304and damaging sensitive components in LF mode driver304. To place the output of LF mode driver304in a high ohmic state the unregulated supply voltage VDS of LF mode driver304should be greater than or equal to the regulated voltage VTX input to immobilizer driver305(VDS≧VTX). This condition is fulfilled when bypass switch308of regulator303is opened.

During immobilizer mode operation, immobilizer driver305is configured to be active. The supply voltage for immobilizer304is the regulated VTX voltage output by regulator303. During LF mode operation, the output of immobilizer driver305is placed into a high ohmic state to prevent current leaking into immobilizer driver305and damaging sensitive components in immobilizer driver305. To place the output of immobilizer driver305in a high ohmic state, the supply voltage VTX of immobilizer driver305should be equal to the unregulated supply voltage VDS of LF mode driver304(VDS=VTX). This condition is fulfilled when bypass switch308of regulator303is closed, directly coupling VDS to immobilizer driver305.

Dual mode antenna307is a shared LF antenna that is driven by immobilizer driver305during immobilizer mode operation and driven by LF mode driver304during LF mode operation. Dual mode antenna307may be coupled to LF mode driver304and immobilizer driver305at common node306(AOP).

In some implementations, circuit300can be configured to use differential signal chains for processing differential signals by replacing the components in circuit300with differential components.

Description of Modes of Operation

Immobilizer Mode

During immobilizer mode of operation, immobilizer driver305drives dual mode antenna307, 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 antenna307and fed into reader hardware (not shown), where the code is demodulated and decoded if encoded and/or encrypted.

Under normal conditions, booster302is idle during immobilizer mode operation. This results in VDS=(voltage supply301) minus two diode voltages, hereafter referred to as “immobilizer mode1.” One diode is part of booster302and one diode is a reverse polarity protection diode.

In some implementations, the configuration ofFIG. 3allows system architects to activate booster302during immobilizer mode operation to overcome the limitations of minimum battery voltages, hereafter referred to as “immobilizer mode2.”

During either immobilizer mode1or2operation, LF mode driver304is idle and its output is placed in a high ohmic state by providing supply voltage VDS to LF mode driver304, such that during immobilizer mode operation the condition VDS≧VTX is satisfied. The high ohmic output state prevents current from leaking into LFS mode driver304and damaging internal transistors of LF mode driver304.

During immobilizer mode operation, regulator303is active and generates from the VDS voltage at its input a regulated VTX voltage for immobilizer driver305. The regulated VTX voltage is the supply voltage for immobilizer driver305when the system is in immobilizer mode operation. For proper operation of immobilizer driver305, 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.

During immobilizer mode operation, dual mode antenna307is stimulated by a driving signal provided by immobilizer driver305. Immobilizer driver305sends 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 antenna307and fed into reader hardware, where the code is demodulated from the carrier signal and decoded if encoded and/or encrypted.

LF Mode

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, booster302is active. When activated booster302steps voltage source301up 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 driver304. The input signal of LF mode driver304is amplified and fed into dual mode antenna307.

During LF mode operation, regulator303is placed in a bypass mode. For example, switch308is closed, resulting in VTX=VDS. The bypass mode keeps the output of immobilizer driver305in a high ohmic state while maintaining bias conditions that avoid undesired leakage currents to enter immobilizer305due to the presence of a signal at common node306.

During LF mode operation, dual mode antenna307is stimulated by a driving signal provided by LF mode driver304. LF mode driver305causes dual mode antenna307to generate an electromagnetic field that can be detected by the key fob circuitry.

Example Biasing of Integrated Drivers

FIG. 4illustrates an example circuit configuration400for immobilizer mode. When immobilizer mode is selected, LF mode driver304is configured to be idle and immobilizer driver305(transistors403(NM3) and404(NM4)) is configured to drive dual mode antenna307, generating a signal voltage in the range of VTX to ground (GND). The NMOS transistors401(NM1),402(NM2) of LF mode driver304are passive and configured to remain off even when the signal from immobilizer mode operation is present at common node306. The gates of NMOS transistors401-404may be controlled by internal hardware (not shown).

A problem with the circuit configuration ofFIG. 4is that the parasitic diodes DDB, DSBfor NMOS transistors401,402, respectively, may become forward biased during immobilizer mode due to the signal present at common node306, resulting in unintended currents being sent through LF mode driver304. This problem is avoided by keeping the condition VDS≧VTX. This voltage condition causes parasitic diodes DDB, DSBof transistors401,402to be reverse biased, which prevents unintended currents from entering LF mode driver304.

In some implementations, push-pull driver circuit configurations may be used by replacing NMOS transistors401,403with PMOS transistors501(PM1),503(PM3), as shown inFIG. 5. The power management and bias conditions previously described in reference to the circuit shown inFIG. 4are also applicable to the circuit shown inFIG. 5.

FIG. 6illustrates a circuit configuration for LF mode of operation. When LF mode operation is selected, transistors601(NM1) and602(NM2) drive dual mode antenna307. The passive transistors603(NM3) and604(NM4) of immobilizer driver305are configured to remain off even if the signal from LF mode operation is present at common node306.

A problem with the circuit configuration ofFIG. 6is that the parasitic diodes DDB, DSBfor transistors603,604may become forward biased due to the signal present at common node306, resulting in unintended currents through immobilizer driver304. This problem is avoided by keeping the condition VTX=VDS during LF mode operation. This voltage condition keeps the parasitic diodes DDB, DSBfor transistors603,604in reverse bias condition.

In some implementations, push-pull driver circuits may be used by replacing NMOS transistors601,603with PMOS transistors701(PM1),703(PM3), as shown inFIG. 7.

FIG. 8is a flow diagram illustrating an example process800performed by system300while operating in immobilizer mode of operation. In some implementations, process800detects 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.

FIG. 9is a flow diagram illustrating an example process900performed while operating in the LF mode of operation. In some implementations, process900detects 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.