New trend of the most flaming light sensor

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New trend of optical sensors

there are a variety of optical sensors with small packages, and the price is reasonable. For decades, passive devices have been active in the market. As photoresistors, photodiodes and phototransistors become more and more common and cheap, they are widely used by many consumer products from night lights to digital cameras. The new integrated devices integrate a phototransistor or photodiode with a current amplifier to achieve on-chip calibration, filtering and higher resolution. When the resolution is high, the functions of low light capacity and power supply suppression play a role. Such devices are expanding the application range and effectiveness of ambient light sensors

type of optical sensor

the simplest optical sensor is a photosensitive resistor, which can be identified through the channel between two terminals. The low-end version is made of CDs (cadmium sulfide), while the more expensive version is made of GaAs. GaAs has a small energy band gap, which enables it to absorb low-energy photons in infrared light and make electrons transition to the conduction band. The data of the reference element shows that its illumination range is 1~100lux, but it has various resistance values

various available sensors offer a wide range of price/performance options

photodiodes are more complex. Photons bombard semiconductor junctions, producing an electric current. In order to fully play its role, the photodiode should be back biased. The bias voltage is directly converted into the operation quality, because the large reverse bias voltage can improve the speed and linearity, as well as the dark current and shot noise. Light will generate a forward current and reduce the reverse bias current. An external circuit can be added to the photodiode to linearize the I-V curve to amplify the signal and allow the failure function to be achieved

the general characteristics of the phototransistor are the same as those of the photodiode, and the amplification characteristics are added. It requires a larger bias current, but the noise associated with the current forces the sensitivity of the sensor to a higher lux range, that is, 1K ~ 100klux (rather than 7K ~ 50klux). The response time is similar to that of a photodiode and can be adjusted by using a bias current. The current can also vary with the detected signal level. Phototransistors can roughly determine the ambient light level, such as indoor/outdoor, day/night and bright light/shadow. Such devices also need external circuits to calibrate the output signal and include an enabling function

the shrinking size of components enables people to design integrated devices, such as el7900. The device consists of a photoresistor and a transimpedance amplifier in a package. This combination can shorten the lead length and minimize the parasitic capacitance in the input of the amplifier, which is an ideal condition for realizing minimum noise, high frequency response and convenience. The low noise characteristic can extend the sensitivity of the sensor to 1Lux, while keeping the upper limit at 100lux. The power consumption still depends on the amount of light induced. The current is 0.9ma at 1000lux. In order to save power, a power-down pin is used. In addition to digital cameras, the device is suitable for many occasions

further integration is reflected in devices such as isl29001, which is a package solution for optical sensing and calibration. The temperature compensated optical sensor is a pin diode. Before entering a high pass filter, the output of the sensor is calibrated and fed into an amplifier to eliminate 60Hz noise. After continuously improving the core competitiveness of the enterprise, an analog-to-digital converter (a allows limited financial resources to be invested in other places that need more DC) and I2C interface provide output, which is a signal of an era of fierce competition

using ADC has two advantages: one is that the power consumption can remain unchanged, and the other is that the resolution can reach 15bit. In fact, its current consumption is lower than that of all other active devices in the table. ADC has an internal 327.6khz clock. Set the response time of the device to The frost resistance and color are qualified. It is judged according to the lowest quality level among size deviation, appearance quality and strength level. If one item is unqualified, it is judged that the batch of products is unqualified within 100ms. Even when the delay increases, the serial 15bit output signal makes the sensor suitable for a wide range of applications

application of optical sensor in portable products

isl29001 can reach a resolution of 15bit

optical sensors are widely used in. Some applications use the reflected light of optical detection to sense the position, including bar code reader, laser printer and automatic focusing microscope. Portable electronic products, such as digital cameras and laptops, use light sensors to measure the amount of ambient light. We will further discuss the second type of applications mentioned above

ambient light sensor in notebook computer is used to adjust the backlight of the screen to make it look comfortable. The comfort range of the backlight depends on the light conditions of the room. It is conceivable that the brightness of the screen needs to increase with the brightness of the ambient light. In the case of weak light, the brightness of the screen needs to decrease in order to look comfortable and prolong the battery life

in the design of notebook computer, the ambient light sensor is usually next to the speaker rather than on it. The machine has an opening at the position of the speaker so that light can enter the interior. These audio ports are usually covered with objects to protect the speakers. Due to this protection, the light is blocked, which reduces the amount of light that can be measured. Therefore, a solution with good dark light accuracy is required. In order to obtain the required accuracy under low light conditions, it is best to choose an integrated photodiode with ADC. At the same time, the high pass filter can reduce the power supply noise to the lowest level and prevent it from coupling into the backlight

another common application is ambient light sensing in. In this application, every milliampere saved means an increase in battery life and customer satisfaction. The backlight illumination is adjusted by the light sensor, and the battery life is extended by at least 6 times (assuming that the backlight remains in the full power state when there is no light sensor feedback)

take the el7900 as an example. It senses the ambient light intensity in and outputs a current proportional to the light intensity. The output current is injected into the feedback input of the white LED driver. In a bright environment, the optical sensor sends more current to the feedback node. Therefore, it reduces the output current and output light intensity of the white LED, so as to achieve the purpose of power saving. (end)

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