Automotive Design Center

A Passive Keyless Entry solution provides the user with the convenience of unlocking a car door without pressing any buttons. The module inside the door initiates communication by sending out a signal between fixed time intervals to search for the paired Key Fob. Once in the proximity of the car door, the Key Fob sends back an acknowledgment signal. Upon positive authentication by the Receiver block, it signals the car door to be unlocked.

A Low Frequency transmission signal needs to be generated by the module in the car door. This can easily be achieved using the internal PWM module available on several small Microchip microcontrollers such as PIC12, PIC16 and PIC18. To perform the filtering and decryption on the receiver end, Microchip offers standalone and integrated Analog Front End (AFE) devices. These are available on small 8pin or 16pin packages to conserve space on the key fob.
For Ultra High Frequency communication between the KeyFob and the Receiver module in the door, Microchip offers transmitters which allow the user to perform ‘Frequency Shift Keying’ or ‘Amplitude Shift Keying’ modulation to generate the transmissions. Microchip also offers corresponding receivers to perform the filtering and decryption of the wireless data.
The Key Fob is powered through batteries, which provide power for a restricted period of time, making power conservation an important design factor. Microchip has developed the nanoWatt XLP, extreme low power product line, which offers the industry’s lowest currents for quiescent states, extending the application life.
Microchip provides Keeloq, an industry wide recognized and patented encryption algorithm, which allows safe transmission of data over a wireless network. Keeloq is a non-linear encryption algorithm that creates a unique transmission on every use, rendering code capture and resend schemes ineffective. For more information, please visit www.microchip.com/Keeloq