Application of the hottest ambient light sensor in

2022-08-12
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The application of ambient light sensor in automobile interior

a unique solution we can see more and more in automobile environment is the popularization and application of ambient light sensor throughout the whole automobile interior environment. This paper will discuss the principle of ambient light sensing and the advantages of using this device in automotive environment

considerations for selecting optical sensors

there are usually several methods to detect light, such as using phototransistors, photoresistors or photodiodes, but for the overall light sensing requirements of today's applications, a monolithic photodiode based on IC is one of the best choices. Photodiode is a semiconductor used to detect light and generate current. It is constructed based on monocrystalline silicon, similar to the crystalline silicon used to produce integrated circuits. A typical sensor application frame diagram includes a photodiode, a current amplifier and a passive low-pass filter to detect and process the output voltage signal caused by optical input. Being able to integrate all these devices and adopt small packages is very beneficial for end users, and this is precisely the current market demand

another important aspect of selecting the appropriate optical sensor for the application is to understand which important specification is the most critical and which needs the most attention for the application. Generally speaking, when selecting an optical sensor, the following factors need to be considered:

spectral response/ir suppression: the ambient light sensor should only be sensitive to the range of 400nm to 700nm

lux maximum range: direct sunlight can be up to 130000 lux, but most applications require a maximum range of only 10000 lux

low lux sensitivity: according to the type of lens with the light sensor at the top, the light attenuation can be%. If low photosensitivity is critical (5lux), attention must be paid to the selection of optical sensors that can work in this range

integrated signal conditioning (i.e. amplifier and ADC): some sensors may provide a very small package, but they need an external amplifier. 1. See "equipment proposal" for a detailed introduction to the performance characteristics of the experimental machine; Large or passive components to obtain the required output signal. The optical sensor with higher integration eliminates the need for external components (ADC, amplifier, resistor, capacitor, etc.) that are slightly smaller than Boeing 777

power consumption: for optical sensors that need to withstand high lux level (10000lux), it is best to use a nonlinear light to analog output optical sensor, or a light to digital output optical sensor. This will be explained in detail next

package size: for most applications, the smaller the package, the better. The package available now is 2.0mm 2.1mm optical DFN, while the 1.3mm 1.5mm 4-lead package is the next generation package. The revised access condition is a sieve

once the above important specifications are determined, the next question to consider is what kind of output signal is most conducive to the target application. For most optical sensors, the most common output is linear output current. Although this applies to 12 Electrode tensile testing machine provides a variety of report printing interfaces for some applications, but now there are more options, including linear voltage output, digital output (through I2C interface) or nonlinear current or voltage output. Each has its advantages, as listed below

linear analog output current or voltage output: more common sensor output, fast response time (digital output is limited by integration time), ADC converter is integrated in the controller, and voltage output eliminates the need for external resistance (converting current into voltage) and provides a low impedance output. Current output requires adding passive components to the output to convert current into voltage, set the gain range of the sensor, and add low-pass or high pass filters as needed

nonlinear analog output current or voltage output: allows extremely weak light sensitivity and maximum dynamic range (up to 100, 000lux), sensing light is more similar to the way humans perceive light (nonlinear and linear), the choice of voltage or current nonlinear output, voltage output is low impedance and current output is high impedance

digital output: the output can be directly connected with the controller (without ADC). The digital output itself is more noise immune than the analog output, allowing the sensor to have more digital functions (i.e. more intelligent optical sensors), easier to work on the network of the general I2C bus, and easier to allow multiple optical sensors to be placed on the same I2C bus (address selection pin), Constant power consumption (the loss of analog output circuit is proportional to the incident optical density)

in order to better understand the structure of these sensors, let's observe the architecture of analog and digital output sensors more carefully. The sensor discussed first is Elsil's el7900 linear output current sensor

el7900 integrates PIN photodiode and current mirror gain stage function, which is used for an optical sensor with linearity up to 10000lux. The dynamic range and sensitivity can be easily adjusted by a load impedance (grounding) on the output. Choosing a resistor with a lower resistance value will provide a wider dynamic range, but at the cost of weak light sensitivity. On the other hand, choosing a resistor with a higher resistance value will provide enhanced weak light sensitivity, but at the expense of dynamic range. Therefore, this choice depends entirely on the application of end users and whether they need lower photosensitivity or greater dynamic range

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