Weak current College】 【optical sensor of choice should focus on six indicators】.

<br> Application of optical sensors. From portable consumer market (Smartphone, PDA, desktop PC and portable music player, etc.) to consumer TV market (including LCD, plasma, rear projection and CRT TV, etc.), then to the .medical, industrial and automotive markets, optical sensors everywhere. Of these, some applications, such as a barcode reader, laser printer and autofocus microscope optical detection of reflected light on location sensing; other applications such as digital cameras, cell phones and laptops and other .portable electronic products the use of optical sensors to measure the amount of ambient light. <br> <br> Using ambient light sensor system products to provide a more comfortable display quality. This is very important for certain applications. For example, a car dashboard .requirements in all ambient light conditions were able to achieve a clear display effect. During the day, the user needs the maximum brightness to achieve the best visibility, but the brightness at night is too harsh. <br> <br> Light sensor for portable .applications have brought many benefits. With optical sensor system, able to automatically detect the conditions change and adjust the monitor's settings to ensure that the monitor is in the best brightness, and thus reduce overall power consumption. For example, mobile phones, laptops and digital .cameras, through the use of ambient light sensor to automatically display brightness control, thereby extending battery life. <br> <br> Photodiode is the best way to realize <br> <br> Light sensor including photosensitive, photo-transistor or a diode ., etc. The most simple optical sensor is photosensitive resistor. Low-end-from CdS (CDs), and the more expensive of photosensitive materials from GaAs. GaAs band gap is relatively small. It is able to absorb infrared light, low-energy .photon in and make electronic transition to the conduction band. It ranges from 1 Lux ~ 100 Lux. <br> <br> The complexity of the photodiode. Bombardment of photons to produce semiconductor junction. To impose to the photodiode reverse bias. Large reverse .bias can improve the speed of inductive sensors and linearity, but also improves the sensor dark current and shot noise (shotnoise). Photon ionization semiconductor junction, will produce forward current, reducing reverse bias current. In the design, you can increase the external circuit .diode, the linearization of the Iv curve. <br> <br> Photo-transistor's general characteristics and photodiode, but increases the zoom function. It requires greater bias current, but the noise associated with the current force sensor sensitivity towards higher Lux range, .ie 1000 lux ~ 10 000 lux. Photo-transistor test response time and photodiode similar, and can use bias current. Bias current or detected signal level changes. Photo-transistor can roughly determine the ambient light level, such as indoor / outdoor, day ./ night and a bright light / shadow, and other State, therefore, require an external circuit calibration of the output signal. <br> <br> At present, based on the IC-chip photodiode is the light sensor is one of the best .implementations. Manufactured by Silicon photodiode. A typical application components including a sensor photodiodes, a current amplifier and a passive and low-pass filter. For end users, all of these devices can be integrated into a small package is very important. <br> .<br> Light sensor six indicators <br> <br> Select light sensor, the most important point is to understand what specifications are most critical. Generally speaking, the choice of a light sensor, you need to focus on the consideration of factors including .spectral response / IR suppression, Max Lux, photosensitive, integrated signal conditioning, power consumption, and packing size, and other six important specifications. The six specific specifications are described below: <br> <br> 1, spectral response / IR suppression: .ambient light sensor should only on 400nm to 700nm spectral range with induction. <br> <br> 2. the Max Lux: most applications is 1 000 lux. <br> <br> 3, photosensitive degrees: under the light sensor lenses category ., the light through the lens, the optical attenuation can be 25% -50%. Low critical photosensitive degrees (<5 Lux), you must select the range of optical sensors. <br> <br> 4, integrated signal conditioning function .(that is, the amplifier and the ADC): some sensors may provide a very small package, but it requires an external amplifier or passive components to get the desired output signal. More highly integrated light sensor saves external components (ADC, amplifier, resistor ., capacitor, etc) with more advantages. <br> <br> 5. power consumption: for to withstand high Lux (> 1 000 lux) sensor, the best use of nonlinear analog output or digital output. <br> <br .> 6, packing size: for most applications, the package is as small as possible. Now available in a smaller package size approximately 2.0mm × 2.1mm. While the size of the 4-pin package 1.3mm × 1.5mm is a next- .generation package. <br> <br> Once you identify these important specifications, the next question to consider is what type of output signal to the target application. <br> <br> For most light sensor, the most common output linear analog output .. Although this output for some applications is ideal, but now provide more output options, including linear voltage output, digital output (via I2C interface) or nonlinear current or voltage output. Each output has certain advantages. <br>.