接近探测-Ambient Light Sensor & Proximity Detection

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A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.

A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor always requires a metal target.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.

Proximity sensors are commonly used on smartphones to detect (and skip) accidental touchscreen taps when held to the ear during a call.[1] They are also used in machine vibration monitoring to measure the variation in distance between a shaft and its support bearing. This is common in large steam turbines, compressors, and motors that use sleeve-type bearings.

International Electrotechnical Commission (IEC) 60947-5-2 defines the technical details of proximity sensors.

A proximity sensor adjusted to a very short range is often used as a touch switch.

The Ambient Light Sensor & Proximity Detection product family provides both ambient light sensing (ALS) and proximity detection in a single device. The ALS approximates human eye response to light intensity under a variety of lighting conditions and through a variety of attenuation materials. The proximity detection feature allows a large dynamic range of operation for use in short distance detection behind dark glass such as in a cell phone or for longer distance measurements for applications such as presence detection for computer display and monitors.

Proximity Detection
− Calibrated to 100-mm Detection
− Eliminates Factory Calibration of Prox
− Programmable Number of IR Pulses
− Programmable Current Sink for the IR LED — No Limiting Resistor Needed
− Programmable Interrupt Function with Upper and Lower Threshold

Applications
- Cell Phone Backlight Dimming
- Cell Phone Touch Screen Disable
- Notebook/Monitor Security
- Automatic Speakerphone Enable
- Automatic Menu Popup
The proximity detector includes a digital proximity sensor, LED driver, and IR LED, which are trimmed to eliminate the need for end-equipment calibration due to component variations. Excellent background light rejection allows the device to operate in environments from sunlight to dark rooms. The wide dynamic range allows for operation in short distance detection such as a cell phone (behind dark glass). An internal state machine provides the ability to put the device into a low-power mode in between ALS and proximity measurements, providing very low average power consumption.

The light-to-digital device provides on-chip photodiodes, integrating amplifiers, ADCs, accumulators, clocks,
buffers, comparators, a state machine, and an I2C interface. Each device combines one photodiode (CH0),
which is responsive to both visible and infrared light, and a second photodiode (CH1), which is responsive
primarily to infrared light. Two integrating ADCs simultaneously convert the amplified photodiode currents to
a digital value providing up to 16-bits of resolution. Upon completion of the conversion cycle, the conversion
result is transferred to the Ch0 and Ch1 data registers. This digital output can be read by a microprocessor
where the luminance (ambient light level in lux) is derived using an empirical formula to approximate the human
eye response.

A fully integrated proximity detection solution is provided with an 850-nm IR LED, LED driver circuit, and
proximity detection engine. An internal LED driver (LDR) pin, is connected to the LED cathode (LEDK) to provide
a factory calibrated proximity of 100 mm, ± 20 mm. This is accomplished with a proprietary current calibration
technique that accounts for all variances in silicon, optics, package, and most important, IR LED output power.
This eliminates or greatly reduces the need for factory calibration that is required for most discrete proximity
sensor solutions. While the device is factory calibrated at a given pulse count, the number of proximity LED
pulses can be programmed from 1 to 255 pulses, which allows different proximity distances to be achieved.
Each pulse has a 16 μs period with a 7.2 μs on time.

Communication with the device is accomplished through a fast (up to 400 kHz), two-wire I2C serial bus for easy
connection to a microcontroller or embedded controller. The digital output of the device is inherently more
immune to noise when compared to an analog photodiode interface.The device provides a separate pin for level-style interrupts. When interrupts are enabled and a pre-set value
is exceeded, the interrupt pin is asserted and remains asserted until cleared by the controlling firmware. The
interrupt feature simplifies and improves system efficiency by eliminating the need to poll a sensor for a light
intensity or proximity value. An interrupt is generated when the value of an ALS or proximity conversion exceeds
either an upper or lower threshold. In addition, a programmable interrupt persistence feature allows the user
to determine how many consecutive exceeded thresholds are necessary to trigger an interrupt. Interrupt
thresholds and persistence settings are configured independently for both ALS and proximity.


Proximity detection is accomplished by measuring the amount of IR energy, from the internal IR LED, reflected
off an object to determine its distance. The internal proximity IR LED is driven by the integrated proximity LED
current driver as shown in Figure.

厂商：ams
产品：TMD27711等
官方资料：链接

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