Photodetector resistant to background light noise with extended dynamic range of input signals

Abstract

Measurement of periodic optical information signals in the background light noise with a photodetector with extended dynamic range is an urgent task of modern electronics and thus has become the aim of this study. To increase the dynamic range of the photodetector, a new version of the automatic gain control (AGC) circuit has been developed, which consists of an AGC controller, an output photodetector amplifier and an AGC detector. The authors measured the dynamic range of the photodetector when receiving optical radiation with a wavelength of 1064 nm in the power range from 2.10–8 to 2.10–5 W at a modulation frequency of 20 kHz with the AGC on. Under these conditions, the dynamic range of the photodetector was found to be up to 67 dB. If the AGC was off, the dynamic range did not exceed 30 dB. Thus, the study made it possible to create a photodetector with an extended dynamic range up to 67 dB based on a new version of the AGC circuit. The design of the photodetector allowed choosing a useful signal of a particular modulation frequency in the frequency range from 3 to 45 kHz and effectively suppresses the frequencies caused by optical interference in the low frequency range from the frequency of the input signal of constant amplitude up to 3 kHz inclusive. This compensates the current up to 15 mA, which is equivalent to the power of light interference of about 15 mW. Further research should address the issues of reliability of the proposed photodetector design and optimization of its optical system. The photodetector can be used in geodesy and ambient air quality monitoring.

Algorithm for compensation of background light in a photo-receptive device for FSO

“…To reduce the influence of the background unmodulated signal on the useful signal, a 4 mm thick IKS7 glass cut-off filter according to can be used, which creates a region of spectral sensitivity of the photodiode from 800 to 1100 nm 16 . The wavelength of 980 nm also remains in this range.…”

“…In particular, in our case, the electrical circuit, as well as the optical unit, should provide filtering of the useful signal against the background of optical interference -the unmodulated background photo signal generated by solar radiation. To solve this problem, as before 16 , we used an automatic gain control scheme (AGC) 17 , which can adjust the gain of the photo signal, improving the sensitivity of the PRD and monitor a signal of a certain frequency, which is proportional to the corresponding optical signal 18 . The block diagram of the design of the photo-receiving device is shown in Figure 2.…”