Global automotive semiconductors face enormous market opportunities, but design engineers also face technical challenges in terms of cost, power consumption, and security. This article takes the latest intelligent transponders that can receive and send data as an example to introduce to Chinese automotive design engineers the technical methods to solve these challenges in the design of automotive wireless access systems.
In China, the semiconductors used in the safety and confidentiality electronic control module account for approximately 18% of China's automotive semiconductors. From remote keyless gated applications already in use to passive keyless gated (PKE) systems, tires Emerging applications such as air pressure monitoring systems, electronic payment (charge) and Bluetooth hands-free systems, wireless systems are emerging in vehicle applications. These wireless connections are a technical means to improve the performance of security and privacy modules, and are building the driver's hopes. Various features, while other short-range wireless communication solutions for security and privacy applications are limited by the availability of cost-effective technology. In addition to the traditional pressure to reduce time-to-market and increase functionality, design engineers face Cost-effective performance enhancements, power consumption, small size and encryption security.
Table 1: Main technical difficulties and solutions for PKE smart transponders.
For example, let's take a look at a wireless system that represents the many challenges faced by today's system architects—the latest intelligent transponders that can receive and send data. In this two-way communication system, the base station and the transponder can automatically communicate without human intervention. This low-cost, two-way communication transponder can be designed to operate with two frequencies: 125 kHz for receiving data and UHF (315, 433, 868 or 915 MHz) for transmitting data. Due to the non-propagating nature of the 125 kHz signal, the two-way communication distance is typically no more than 3 meters. Since the transponder also has buttons for performing optional operations, a longer one-way transmission distance (from the transponder to the base station) can be supported when the transmit button is pressed.
In these applications, the base station transmits commands at a frequency of 125 kHz while waiting for nearby valid transponders to send back responses at UHF frequencies. The smart transponder is typically in receive mode and waits for any valid 125 kHz base station command. If any valid base station command is received, the transponder sends a response at UHF frequency. This is what we call "passive keyless door control system." Because the PKE system uses a 125 kHz circuit for bidirectional communication, low-cost, small-volume, and low-power PKE transponders can be produced using an integrated system-on-chip (SoC) intelligent microcontroller unit (MCU) with digital and low-frequency front ends.
PKE system challenge
As design engineers gain more system experience, they are increasingly faced with the challenge of reliably designing the PKE transponder functionality to make it a cost-effective alternative to traditional PKE transponders while ensuring that it meets specific systems. aims. Table 1 lists some of the main concerns and solutions faced by system design engineers. Although PKE transponders seem to need to be implemented with complex and expensive circuitry, the challenges faced by design engineers have been met by using some relatively simple, around a smart PIC-type microcontroller (PIC16F639) that includes all the necessary features to meet A low-cost circuit required for secure two-way communication is addressed.
Figure 1 shows an intelligent PKE system. It also has buttons for optional operations, but the main operations can be done without any manual intervention. The two-way communication sequence of the PKE application is as follows: the base station transmits the command with a frequency of 125 KHz; the transponder receives the 125 KHz base station command with three orthogonal LC resonant antennas; if the command is valid, the responder sends a response (encrypted data) through a UHF transmitter; If the data is correct, the base station receives the response and activates the switch.
Figure 1: Intelligent Passive Keyless Gating (PKE) System with Two-Way Communication
One of the challenges faced by design engineers is the cost-effective implementation of system performance enhancements including communication distance, antenna directivity, small package size, encryption security, and low power consumption under door lock "on/off" conditions. A transponder design that reliably accepts base station commands within the 125 kHz signal range and maintains long battery operating time meets critical system enhancement requirements.
Input sensitivity requirements for two-way communication distance
In battery-powered transponder applications, the maximum communication distance with UHF (315/433/915 MHz) is approximately 100 meters, but with low frequencies (LF, 125 kHz) it is only a few meters of communication distance. Therefore, the communication distance of the dual-frequency PKE transponder is mainly limited by the commanded distance of the 125 kHz base station. Due to the non-propagating nature of the low frequency signal, the 125 kHz signal will decay rapidly as the distance increases. For example, assuming that the base station outputs an antenna output voltage of about 300 Vpp, the voltage induced by the coil antenna of the transponder at a distance of about 3 meters is only about 3 mVpp, which is equivalent to the noise level of the application environment. Therefore, how to effectively detect weak signals is a major problem faced by system design engineers.
To increase the range of the 125 kHz base station command, two possible solutions are considered: (a) increasing the transmit power of the base station transmitter; and (b) increasing the input sensitivity of the transponder. The maximum transmit power of the base station transmitter is generally limited by the government. Therefore, the second method for improving the sensitivity of the input signal detection is the only effective solution, assuming that the maximum power transmitted by the base station is within the allowable range. In order to achieve a two-way communication distance of 3 meters, the transponder input sensitivity must be around 3 mVpp.
Solution to antenna directivity problem
Any radio signal radiated by the antenna unit will propagate in a certain direction angle, and the signal propagation is more directional (or a narrower radiation angle) when using a better performing antenna. The low frequency (125 kHz) signal radiated by the LC resonant circuit is not as directional as the high frequency signal, but it still has a certain directivity. Under a given transponder design condition, the communication distance (or induced voltage) of the low frequency signal depends on the degree of coupling of the base station antenna to the transponder antenna. When the two antennas face each other, their coupling is optimal.
For hands-free PKE applications, the direction in which the transponder is placed in your pocket can be arbitrary. Therefore, the chance of the transponder antenna facing the direction of the fixed base station antenna is only about 30% (x, y, z direction). But if the transponder has 3 orthogonal antennas, the chance can be increased to nearly 100%. The antennas are placed in the x, y, and z directions, respectively. By utilizing three orthogonally placed antennas, the transponder can obtain base station signals in any given direction.
Figure 2: Various applications with wireless secure access.
Wake-up filter saves battery energy
The wake-up filter effectively controls the operation of the microcontroller PIC16F639 to conserve battery power. In addition, the microcontroller must also operate with minimal circuitry during the inactive mode. The PIC16F639 chip in the transponder contains a low-frequency front-end and digital circuitry. The low-frequency front end is always searching for input signals, while the digital part is in sleep mode to conserve battery drain and is only woken up (or activated) when a valid base station command is received. ). This can be done by using a special wake-up filter in the low-frequency front end portion. In addition, the low frequency detection circuit is also programmable to have an output only if the input signal has a predetermined data packet header.
The wake-up filter is used to prevent the digital portion from being woken up by noise or undesired input signals. Therefore, the operating current and battery energy can be effectively saved.
Power management
In addition to utilizing special filters to conserve battery power, the PIC16F639 also features patented nanoWatt technology that gives system designers greater control over on-chip peripherals, including several software-selectable speed options. Reduce the frequency to an 8 MHz internal oscillator of 32 KHz. Very low sleep current consumption and a fast-start internal oscillator support low power system designs. The periodic wake-up mechanism includes low-power real-time clock operation, ultra-low power wake-up characteristics, and an extended low-power watchdog timer. With these broad power management features, design engineers can implement power-saving concepts in their applications and gain tighter control over overall system power at lower system cost.
Encryption support
The patented KEELOQ encryption technology, a global standard, provides a cost-effective solution for authentication, keyless gating and other remote access control systems, as shown in Figure 2. KEELOQ encryption technology uses an industry-proven code hopping encoding method that automatically changes and securely transmits coded devices when they are activated. In an implementation based on the encoder/decoder pair, the encoder is located at the far end and sends a rolling code ID# and counter value; the decoder is located in the receiver and decodes the message sent by the remote encoder. It stores the remote device identification number and counter value it hears, and the decoder only allows access when it listens to the remote device. KEELOQ encryption is a highly secure algorithm implemented by complex formulas and 32-bit random number generators.
Conclusion of this paper
Design engineers of wireless security access systems in the future may encounter various challenges. Microcontrollers like the PIC series provide a mature, reliable building block for wireless systems in vehicles. A low-cost two-way communication transponder implementation with an integrated system-on-a-chip solution is a good example of a wireless system that provides drivers with enhanced security and privacy. Without any manual intervention, the PKE transponder can receive low frequency base station commands and respond with encrypted data via the UHF transmitter. A small PKE transponder that fits into the driver's pocket and automatically opens and closes the door without any intervention. For the parking lot entrance application, the driver can directly enter the parking lot without stopping the parking, because the system will automatically recognize the PKE transponder within the effective use distance of about 3 meters.
The wireless security access system meets the increasing security and confidentiality requirements of some drivers. In addition to consumers, government authorities and automakers themselves are launching (or planning to launch) plans to improve safety and confidentiality in their vehicles. The next step in the security and privacy program will be the integration of individual subsystems to increase the competitive advantage of automakers by enhancing wireless security access systems.
Corn Sheller,Hand Corn Sheller,Corn Sheller Machine,Hand Crank Corn Sheller
Hunan Furui Mechanical and Electrical Equipment Manufacturing Co., Ltd. , http://www.thresher.nl