Photodiodes are one of the most popular sensor types for applications where light-based measurements are needed. In this article, learn about the considerations that must go into the design of a photodiode sensor circuit.
DC Considerations
It’s important to select an op amp with DC specifications that match your application’s requirements. A related concern is to make sure that the chosen op amp has a low leakage current, as the absence of this could cause measurement errors.
AC Considerations
The two main concerns with a system’s AC performance are the signal bandwidth and the noise bandwidth. It’s important to consider the phase margin and unity-gain bandwidth when selecting an amplifier for this application.
Using Programmable Gains to Extend Dynamic Range
The Johnson noise of the feedback resistor increases with the square root of the resistance, so it makes sense to have as much gain as possible in the photodiode amplifier. It’s possible to maximize this by adding programmable gain.
Using Modulation and Synchronous Detection to Reduce Noise
To increase accuracy, especially in an industrial setting where it may be difficult to shield the photodiode sensor from ambient light, it can be beneficial to introduce modulation to your design. The simplest form of this is to rapidly turn the light on and off so it’s easier to keep distinct from ambient light.
For further information, including circuit diagrams and more in-depth details about the design of photodiode sensor systems, click through to the article.