Photodiode responsivity

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Hi Dhananjay
I would like to mention that Receiver sensitivity is a measure of the ability of a receiver to demodulate and get information from a weak signal. We quantify sensitivity as the lowest signal power level from which we can get useful information. In an Analog FM system the standard figure of merit for usable information is SINAD, a ratio of demodulated audio signal to noise. In digital systems receive signal quality is measured by calculating the ratio of bits received that are wrong to the total number of bits received. This is called Bit Error Rate (BER). Most Land Mobile radio systems use one of these figures of merit to quantify sensitivity. To measure sensitivity, we apply a desired signal and reduce the signal power until the quality threshold is met.
I hope this will help
Thanks

Look at this it may help
The sensitivity of a receiver can be calculated if one knows the following performance parameters: the noise figure (NF), the ENBW, and the carrier to noise ratio (C/N) required to achieve the desired quality signal.
The sensitivity is as follows:
Sensitivity=10×log10(kTB)+NF+C⁄N
This equation defines the signal power in dB·Watts that is present at the demodulator for a desired carrier to noise ratio. Let’s explain each of the terms in this equation.

this is link which may help
http://www.highfrequencyelectronics.com/index.php?option=com_content&view=article&id=553:receiver-sensitivity-and-equivalent-noise-bandwidth&catid=94:2014-06-june-articles&Itemid=189