Dynamic range would likely be limited without very sophisticated implementations of the amplifier, such as log amps. Additionally, it is very difficult, if not impossible, to match the discrete photodiodes closely enough to eliminate infrared interference. It is then possible to subtract the two responses from one another to obtain only the visible light portion, with a minimized infrared section.Īlthough effective, this solution adds to the space required by the discrete circuit described above.
#Ambient light adjustment plus#
One way around this is to use two photodiodes: one with a visible light plus infrared component, and one with only an infrared component. This sensitivity causes false readings under IR-heavy light, such as that from incandescent bulbs or the sun. However, photodiodes rarely replicate this response, since they often have a heavy infrared (IR) sensitivity. This is often described with the CIE photopic curve ( Figure 3). Specifically, it is desirable to ensure that the ambient light is measured in a way that replicates the optical response of the human eye to light. There is a second, more subtle, issue at hand here. Discrete implementation of a photodiode circuit. In applications where space is at a premium, the large number of components required may be problematic.įigure 2. It also includes extra routing to power all of these components and ensure a robust signal chain. As you can see, the circuit requires one or more operational amplifiers: one for I-to-V conversion and, perhaps, a second for additional gain. Block diagram for a system that implements backlight control.įigure 2 shows a discrete implementation of a photodiode circuit. The light sensor must contain a transducer (e.g., a photodiode or CdS photoresistor) to convert light to an electrical signal, some amplification and/or signal conditioning, and an analog-to-digital converter (ADC).įigure 1. The light sensor is a key part of this setup, as it provides information about the environment's light level to the rest of the system. Implementing such a system requires three sections: a light sensor to monitor the amount of ambient light, a device (usually a microcontroller) to process the data, and an actuator to control the current through the backlight.īacklight Control: the Ambient-Light Sensor Figure 1 provides an example block diagram of a system that implements backlight control. It can also improve the user experience, allowing screen brightness to be optimized based on ambient-light conditions. Since backlighting accounts for a significant portion of the system's power budget, dynamic brightness control can translate into substantial power savings. With ALS solutions, system designers can automatically adjust display brightness based on the amount of ambient light. Ambient-light sensor (ALS) ICs are increasingly used in a variety of display and lighting applications to save power and improve the user experience.
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