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AD7143 데이터시트(PDF) 23 Page - Analog Devices |
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AD7143 데이터시트(HTML) 23 Page - Analog Devices |
23 / 57 page AD7143 Rev. 0 | Page 22 of 56 ENVIRONMENTAL CALIBRATION The AD7143 provides on-chip capacitance sensor calibration to automatically adjust for environmental conditions that have an effect on the capacitance sensor ambient levels. Capacitance sensor output levels are sensitive to temperature, humidity, and in some cases, dirt. The AD7143 achieves optimal and reliable sensor performance by continuously monitoring the CDC ambient levels and correcting for any changes by adjusting the STAGE_HIGH_THRESHOLD and STAGE_LOW_THRESHOLD register values as described in Equation 1 and Equation 2. The CDC ambient level is defined as the capacitance sensor output level during periods when the user is not approaching or in contact with the sensor. The compensation logic runs automatically on every conversion after configuration when the AD7143 is not being touched. This allows the AD7143 to account for rapidly changing environmental conditions. The ambient compensation control registers located at Address 0x002, Address 0x003 and Address 0x004 give the host access to general setup and controls for the compensation algorithm. The RAM stores the compensation data for each conversion stage, as well as setup information specific to each stage. Figure 33 shows an example of an ideal capacitance sensor behavior where the CDC ambient level remains constant regardless of the environmental conditions. The CDC output shown is for a pair of differential button sensors, where one sensor caused an increase, and the other a decrease in measured capacitance when activated. The positive and negative sensor threshold levels are calculated as a percentage of the STAGE_OFFSET_HIGH and STAGE_OFFSET_LOW values based on the threshold sensitivity settings and the ambient value. These values for this example are sufficient to detect a sensor contact, resulting with the AD7143 asserting the INT output when the threshold levels are exceeded. t STAGE_LOW_THRESHOLD STAGE_HIGH_THRESHOLD CDC AMBIENT VALUE CHANGING ENVIRONMENTAL CONDITIONS SENSOR 1 INT ASSERTED SENSOR 2 INT ASSERTED Figure 33. Ideal Sensor Behavior with a Constant Ambient Level CAPACITANCE SENSOR BEHAVIOR WITHOUT CALIBRATION Figure 34 shows the typical behavior of a capacitance sensor with no applied calibration. This figure shows ambient levels drifting over time as environmental conditions change. The ambient level drift has resulted in the detection of a missed user contact on Sensor 2. This is a result of the initial STAGE_LOW_THRESHOLD remaining constant while the ambient levels drifted upward beyond the detection range. The Capacitance Sensor Behavior with Calibration section describes how the AD7143 adaptive calibration algorithm prevents errors such as this from occurring. t CCDC AMBIENT VALUE DRIFTING CHANGING ENVIRONMENTAL CONDITIONS STAGE_HIGH_THRESHOLD STAGE_LOW_THRESHOLD SENSOR 1 INT ASSERTED SENSOR 2 INT NOT ASSERTED Figure 34. Typical Sensor Behavior without Calibration Applied |
유사한 부품 번호 - AD7143_17 |
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유사한 설명 - AD7143_17 |
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