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.
In general, it is the signal level required for a particular quality of received information.
[1] In signal processing, sensitivity also relates to bandwidth and noise floor as is explained in more detail below.
The IEEE dictionary[2][3] states: "Definitions of sensitivity fall into two contrasting categories."
It also provides multiple definitions relevant to sensors among which 1: "(measuring devices) The ratio of the magnitude of its response to the magnitude of the quantity measured.” and 2: "(radio receiver or similar device) Taken as the minimum input signal required to produce a specified output signal having a specified signal-to-noise ratio.”.
The first of these definitions is similar to the definition of responsivity and as a consequence sensitivity is sometimes considered to be improperly used as a synonym for responsivity,[4][5] and it is argued that the second definition, which is closely related to the detection limit, is a better indicator of the performance of a measuring system.
[6] To summarize, two contrasting definitions of sensitivity are used in the field of electronics The sensitivity of a microphone is usually expressed as the sound field strength in decibels (dB) relative to 1 V/Pa (Pa = N/m2) or as the transfer factor in millivolts per pascal (mV/Pa) into an open circuit or into a 1 kiloohm load.
[citation needed] The sensitivity of a hydrophone is usually expressed as dB relative to 1 V/μPa.
[7] The sensitivity of a loudspeaker is usually expressed as dB / 2.83 VRMS at 1 metre.
This is an example where sensitivity is defined as the ratio of the sensor's response to the quantity measured.
Sensitivity in a receiver, such a radio receiver, indicates its capability to extract information from a weak signal, quantified as the lowest signal level that can be useful.
[8] It is mathematically defined as the minimum input signal
Lower input signal power for a given S/N ratio means better sensitivity since the receiver's contribution to the noise is smaller.
When the power is expressed in dBm the larger the absolute value of the negative number, the better the receive sensitivity.
In other words, at a specified data rate, a receiver with a −98 dBm sensitivity can hear (or extract useable audio, video or data from) signals that are half the power of those heard by a receiver with a −95 dBm receiver sensitivity.
can be of many types, like position, force, acceleration, pressure, or magnetic field.
The responsivity of an ideal linear sensor in the absence of noise is defined as
To reach a specified signal to noise ratio at the output
The choice for the SNRo used in the definition of sensitivity depends on the required confidence level for a signal to be reliably detected (confidence (statistics)), and lies typically between 1-10.
The sensitivity depends on parameters like bandwidth BW or integration time τ=1/(2BW) (as explained here: NEP), because noise level can be reduced by signal averaging, usually resulting in a reduction of the noise amplitude as
A measure of sensitivity independent of bandwidth can be provided by using the amplitude or power spectral density of the noise and or signals (
For a white noise signal over the sensor bandwidth, its power spectral density can be determined from the total noise power
Note that in signal processing the words energy and power are also used for quantities that do not have the unit Watt (Energy (signal processing)).
In some instruments, like spectrum analyzers, a SNRo of 1 at a specified bandwidth of 1 Hz is assumed by default when defining their sensitivity.
[2] For instruments that measure power, which also includes photodetectors, this results in the sensitivity becoming equal to the noise-equivalent power and for other instruments it becomes equal to the noise-equivalent-input[9]
[6][10] It has therefore been argued that it is preferable to use detectivity, which is the reciprocal of the noise-equivalent input, as a metric for the performance of detectors[9][11]
As an example, consider a piezoresistive force sensor through which a constant current runs, such that it has a responsivity
For a specified SNRo of 1, this results in a sensitivity and noise-equivalent input of
, such that an input signal of 10 nN generates the same output voltage as the noise does over a bandwidth of 1 Hz.
This article incorporates public domain material from Federal Standard 1037C.