Fingerprint Biometrics

Fingerprint biometrics are used in a variety of applications including electronic door locks, smart cards, vehicle ignition control systems, USB sticks with fingerprint controlled access, and many others. Digital signal processing elements in fingerprint scanners perform complex DSP functions such as filters, transforms, feature extraction, matching operations and other algorithms.

Fingerprint sensors can use capacitive, optical, pressure, or thermal technologies to obtain an image of a finger’s features. The most common fingerprint sensor solution first illuminates the print with a laser or LED light and then captures the image using a CCD or less expensive CMOS sensor. Fingerprint sensors are typically self contained modules that include an analog to digital converter to translate the analog information into a digital data stream. Resolution, dynamic range and pixel density are factors that contribute to the image quality and influence the accuracy of the sensor.

Once the image is captured the digital information is transferred to a digital signal processor to generate a match. The first step in the matching process is conditioning the scanned fingerprint. Finger print readers rarely use the full fingerprint for identification. Rather, DSPs use algorithms to extract the unique features and patterns of each print to generate a unique digital code. The second step in the software flow is to take the code generated from the scanned image and compare it to a database of potential matches. The compare step requires the system to have access to print information in a networked database or a non-volatile memory unit.

The need for real-time signal processing in biometric fingerprint scanning makes the C55x DSP a compelling solution for this application. The low power capabilities of the C55x in both active and passive modes make it a match for fingerprint scanning applications because, for a greater percentage of the time, the processor is in a low-power mode. The peripheral integration of the C55x DSP includes on-chip LDOs, on-chip memory and a USB Phy for connectivity. Placing peripherals on-chip lowers the overall system cost by simplifying board layout and reducing the total chip count. When communications peripherals are placed on the same die as the processor it is also important to protect your device from sources of ESD. Any IOs or communication peripherals that could come in contact with human touch or other source of ESD should be protected. Devices like the TPD3E001 provide multichannel ESD protection up 15kV for USB 2.0 interfaces.

The LCD Bridge found on the C55x can be used to display messages or options menus. Integrating a TSC2003 touch screen controller to the application provides a way for the user to select options from a displayed menu. Audio functionality can also be included in this application to provide user feedback in the form of alerts and pre-recorded voice commands. This is accomplished using the I2S capability of the C55x to provide a digital audio stream to an audio DAC. Devices like the DAC3120 Bconvert the digital audio stream into an analog signal and increase system integration by including a built in class AB amplifier capable of driving a 2.5 watt mono speaker.