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What is the response time of a photodiode?
The figure below illustrates the transient response of a photodiode to a square pulse of radiation. This is the measure of the photodiode response speed to a stepped light input signal. It is the time required for the photodiode to increase its output from 10% to 90% of final output level.
Which is faster photodiode or phototransistor?
A phototransistor as light sensor is a less expensive device in comparison to any other light sensitive device. Thus is widely used. Photodiodes have the ability to generate an output at a much faster rate when light falls on its surface as compared to the phototransistor.
What are the factors that limit the response time of photodiode?
The response time of a photodetector with its output circuit depends mainly on the following three factors:
- The transit time of the photocarriers in the depletion region.
- Diffusion time of photocarriers outside depletion region.
- RC time constant of the circuit.
How do you identify a photodiode?
It comprises optical filters, built-in lenses, and also surface areas. These diodes have a slow response time when the surface area of the photodiode increases. Photodiodes are alike to regular semiconductor diodes, but that they may be either visible to let light reach the delicate part of the device.
If you search for optical sensors – photodiodes the listed response times range from 30 psec to 2 msec. Turn off when you block the light will be slower than turn on, and won’t really start until the light is completely blocked.
How is the response time of a phototransistor determined?
A phototransistor takes a certain amount of time to respond to sudden changes in light intensity. This response time is usually expressed by the rise time (t R ) and fall time (t F) of the detector where: t R – The time required for the output to rise from 10% to 90% of its on-state value.
Which is slower a photodetector or a phototransistor?
This leads to the general rule that for devices with the same active area, the higher the gain of the photodetector, the slower will be its speed of response. A phototransistor takes a certain amount of time to respond to sudden changes in light intensity.
How is a phototransistor different from a photodiode?
However, the peak response of a phototransistor is at a somewhat shorter wavelength than that of a typical photodiode because the diffused junctions of a phototransistor are formed epitaxially rather than crystal grown silicon wafers.