- Responsivity
Responsivity measures the input–output
gain of a detector system. For a system that respondslinear ly to its input, there is a unique responsivity. Fornonlinear system s, the responsivity is the local slope (derivative). [cite book | title = Multielement Detection Systems for Spectrochemical Analysis | author = Kenneth W. Busch, Marianna A. Busch | publisher = Wiley-Interscience | year = 1990 | isbn = 0471819743
url = http://books.google.com/books?id=9H0W1J-Rku4C&pg=PA371&dq=responsivity&as_brr=0&ei=T4AdR8y4MaL6pwKkvZER&sig=Y-eF_UkViCv9V7XkMViMRZOSlz4 ]In the specific case of a
photodetector , responsivity measures the electricaloutput per opticalinput . Many common photodetectors respond linearly as a function of the incident power.Responsivity of a photodetector is usually expressed in
ampere s perwatt , orvolt s per watt, of incident radiant power. Responsivity is a function of thewavelength of the incident radiation and of the sensor properties, such as thebandgap of the material of which the photodetector is made.The term responsivity is also used to summarize input–output relationship in non-electrical systems. For example, a neuroscientist may measure how neurons in the visual pathway respond to light. In this case, responsivity summarizes the change in the neural response per unit signal strength.
The responsivity in these applications can have a variety of units. The signal strength typically is controlled by varying either intensity (intensity-response function) or contrast (contrast-response function). The neural response measure depends on the part of the nervous system under study. For example, at the level of the retinal cones, the response might be in photocurrent. In the central nervous system the response is usually spikes per second. In functional neuroimaging, the response measure is usually BOLD contrast. The responsivity units reflect the relevant stimulus and physiological units.
When describing a specific part in which the mechanisms are well understood, such as an amplifier, the more common term is
gain ."Deprecated synonym" sensitivity. A system's sensitivity is the inverse of the stimulus level required to produce a threshold response, with the threshold typically chosen just above the noise level.
See also
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Responsiveness , a related concept frominteraction design / HCI.References
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