AT77C102B

Figure 3-6. Functional Description

1 2 3 44-bit Column selection Line selOddEven 4-bitADC 44 De0-3Do0-3 8latchesChiptemperaturesensor 8 lines of 280 columns of pixels Amp 81 dummy column ADC

3.2Sensor

Each pixel is a sensor in itself. The sensor detects a temperature difference between the begin-ning of an acquisition and the reading of the information: this is the integration time. The integration time begins with a reset of the pixel to a predefined initial state. Note that the integra-tion time reset has nothing to do with the reset of the digital section.Then, at a rate depending on the sensitivity of the pyroelectric layer, on the temperature varia-tion between the reset and the end of the integration time, and for the duration of the integration time, electrical charges are generated at the pixel level.

3.3Analog-to-digital Converter/ Reconstructing an 8-bit Fingerprint Image

An analog to digital converter (ADC) is used to convert the analog signal coming from the pixel into digital data that can be used by a processor.As the data rate for the parallel port and the USB is in the range of 1 MB per second, and at least a rate of 500 frames per second is needed to reconstruct the image with a fair sweeping speed of the finger, two 4-bit ADCs have been used to output two pixels at a time on one byte.

3.4Start Sequence

A reset is not necessary between each frame acquisition. The start sequence must consist in:1.Setting the RST pin to high.2.Setting the RST pin to low. 3.Sending 4 clock pulses (due to pipe-line). 4.Sending clock pulses to skip the first frame.Note that after a reset it is recommended to skip the first 200 slices to stabilize the acquisition. Figure 3-7. Start Sequence

4 + 1124 clock pulses to skip the first frame Clock PCLKReset RST

1 2 3 4 1 1124 1

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5364C–BIOM–3/07