This design selects FPGA with high integration, low power consumption and short development cycle to complete this design. Taking the ASIC of the system as the research background, it has strong practical significance and broad market space. The Spartan 3E series FPGA of Xilinx company is used as the core control device. This device adopts the advanced technology of 90ns, has a maximum capacity of 500000 gates, can support 32-bit RISC processor, and has 128 Mbit parallel flash, which is enough to meet the design requirements. The project uses the embedded soft core to realize the management of the system, and uses the hardware to realize the recognition algorithm, which ensures the integrity of the system function and the correctness of the recognition.
Fingerprint acquisition module
This design uses Fujitsu’s MBF200 fingerprint sensor, MBF200 hardware block diagram is shown in Figure 6, using SPI mode, so MBF200 and FPGA only pass miso, MoSi, / S / C / s, SCLK four port connection/ S / C / S is the enabling end of MBF200 and SCLK is the system clock of MBF200. When it is necessary to collect fingerprint signal, FPGA sends low level to / S / C / s, and MBF200 starts to work. FPGA sends control commands to MBF200 through MoSi to control the data output mode and transmission mode of MBF200. VDD [3:1] is digital power input, vdda [2:1] is analog power input, VSS [3:1] is digital ground and vssa [2:1] is analog ground, so it is connected as shown in the figure. In order to prevent the interference of digital signal to analog signal, it is separated by 10 ohm resistor. And a capacitor is connected between the digital power input and the corresponding digital ground to generate a DC signal. In order to prevent the interference between digital ground and signal ground, 0 ohm resistance isolation is adopted in this design. 0 ohm resistance is equivalent to a very narrow current path, which can effectively limit the loop current and suppress the noise. Resistance has attenuation effect in all frequency bands (0 ohm resistance also has impedance), which is stronger than magnetic bead.
The mode [1:0] pin is used to set the interface mode of MBF200. In this design, set mode [1:0] to 01 and select SPI transmission mode. In SPI mode, ain, Iset and Fest will not be used, but according to the internal circuit structure of MBF200, it is better to connect the grounding resistor to the ground.