Responsivity
Encyclopedia
Responsivity measures the input–output gain
of a detector system. For a system that responds linear
ly to its input, there is a unique responsivity. For nonlinear systems, the responsivity is the local slope (derivative).
In the specific case of a photodetector
, responsivity measures the electrical output
per optical input. Many common photodetectors respond linearly as a function of the incident power.
Responsivity of a photodetector is usually expressed in ampere
s per watt
, or volt
s per watt, of incident radiant power
. Responsivity is a function of the wavelength
of the incident radiation
and of the sensor properties, such as the bandgap of the material of which the photodetector is made. One simple expression for Responsivity (Rλ) commonly used with photodetectors is listed below, where
is the quantum efficiency
(conversion efficiency of photons to electrons) of the detector for a given wavelength.
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.
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
of a detector system. For a system that responds linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
ly to its input, there is a unique responsivity. For nonlinear systems, the responsivity is the local slope (derivative).
In the specific case of a photodetector
Photodetector
Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...
, responsivity measures the electrical output
Output
Output is the term denoting either an exit or changes which exit a system and which activate/modify a process. It is an abstract concept, used in the modeling, system design and system exploitation.-In control theory:...
per optical input. Many common photodetectors respond linearly as a function of the incident power.
Responsivity of a photodetector is usually expressed in ampere
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
s per watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
, or volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s per watt, of incident radiant power
Radiant flux
In radiometry, radiant flux or radiant power is the measure of the total power of electromagnetic radiation...
. Responsivity is a function of the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of the incident radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
and of the sensor properties, such as the bandgap of the material of which the photodetector is made. One simple expression for Responsivity (Rλ) commonly used with photodetectors is listed below, where
is the quantum efficiencyQuantum efficiency
Quantum efficiency is a quantity defined for a photosensitive device such as photographic film or a charge-coupled device as the percentage of photons hitting the photoreactive surface that will produce an electron–hole pair. It is an accurate measurement of the device's electrical sensitivity to...
(conversion efficiency of photons to electrons) of the detector for a given wavelength.
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
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
.
Deprecated synonym sensitivity
Sensitivity (electronics)
The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...
. 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
- ResponsivenessResponsivenessResponsiveness as a concept of computer science refers to the specific ability of a functional unit to complete assigned tasks within a given time, but also may incorporate the ability of an artificial intelligence system to understand and carry out its tasks in a timely fashion. It is one of the...
, a related concept from interaction designInteraction designIn design, human–computer interaction, and software development, interaction design, often abbreviated IxD, is "the practice of designing interactive digital products, environments, systems, and services." Like many other design fields interaction design also has an interest in form but its main...
/ HCI.