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SI1120 Datasheet(PDF) 8 Page - Silicon Laboratories |
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SI1120 Datasheet(HTML) 8 Page - Silicon Laboratories |
8 / 20 page Si1120 8 Rev. 1.0 2.3. Proximity Modes In proximity mode, an LED sends light pulses that are reflected from the target to a photodiode and processed by the Si1120’s analog circuitry. Light reflected from a proximate object is detected by the receiver, and the Si1120 converts the light signal into a pulse at the PRX output of a duration proportional to the amount of reflected light. The LED is turned off at the trailing (rising) edge of the PRX pulse. The detection cycle may be aborted before the end of the PRX pulse by bringing STX low. This allows the system designer to limit the maximum LED “on” time in applications where high reflectivity periods are not of interest, thus saving power and minimizing the LED duty cycle. Aborting the detection cycle at a set time also enables fast threshold comparison by sampling the state of the PRX output at the trailing (falling) edge of the STX input. An active (low) PRX output when STX falls means that an object is within the detection range. Forcing a shorter detection cycle also allows a faster proximity measurement rate thus allowing more samples to be averaged for an overall increase in the signal-to-noise ratio. For long-range detection, PRX400 mode is selected. For short-range detection, PRX50 mode is selected. PRX50H mode is typically used in short-range, single-optical-port applications where the internal optical reflection level is high. The greater reflectance range combined with a lower LED power prevents internal reflections from saturating the receiver circuit. The offset calibration mode works the same way as the other proximity modes but without turning on the LED. This allows precise measurement of the environment and Si1120 internal offsets without any LED light being reflected. The offset calibration mode also allows compensation of drifts due to supply and temperature changes. Figure 3. Proximity Mode Timing Diagram Figure 4. Proximity Mode Timing Diagram (Aborted Cycle) |
Similar Part No. - SI1120_10 |
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Similar Description - SI1120_10 |
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