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AT77C102B-CB02YV- Datasheet(PDF) 11 Page - ATMEL Corporation |
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AT77C102B-CB02YV- Datasheet(HTML) 11 Page - ATMEL Corporation |
11 / 19 page 11 5364A–BIOM–09/05 AT77C102B Figure 3-6. Functional Description 3.2 Sensor 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. 3.3 Analog-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. 3.4 Start 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 8 latches Chip temperature sensor Column selection Line sel Odd Even 8 lines of 280 columns of pixels 4-bit ADC ADC 8 1 dummy column 4 4 Amp De0-3 Do0-3 1 2 3 4 4-bit 1 4 3 1 2 1 1124 Clock PCLK Reset RST 4 + 1124 clock pulses to skip the first frame |
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