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.
It is important to note that in the field of electronics different definitions are used for sensitivity. The IEEE dictionary[2] [3] states: "Definitions of sensitivity fall into two contrasting categories." It also provides two definitions relevant to sensors: "(measuring devices) The ratio of the magnitude of its response to the magnitude of the quantity measured.” and "(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] .
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.
The sensitivity of a loudspeaker is usually expressed as dB / 2.83 VRMS at 1 metre. This is not the same as the electrical efficiency; see Efficiency vs sensitivity. The sensitivity of a hydrophone is usually expressed as dB relative to 1 V/μPa.[6]
This is an example where sensitivity is defined as the ratio of the magnitude of the sensor's response to the magnitude of the quantity measured. One should realize that when using this definition to compare sensors, the sensitivity of the sensor might depend on electronic components like voltage amplifiers, that increase the sensor response.
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.[7] It is mathematically defined as the minimum input signal
Si
Si=k(Ta+Trx)B ⋅
| So | |
| No |
where
Si
k
Ta
Trx
B
| So | |
| No |
The same formula can also be expressed in terms of noise factor of the receiver as
Si=Ni ⋅ F ⋅ SNRo=kTaB ⋅ F ⋅ SNRo
where
Ni
SNRo
Because receiver sensitivity indicates how faint an input signal can be to be successfully received by the receiver, the lower power level, the better. Lower power for a given S/N ratio means better sensitivity since the receiver's contribution is smaller. When the power is expressed in dBm the larger the absolute value of the negative number, the better the receive sensitivity. For example, a receiver sensitivity of −98 dBm is better than a receive sensitivity of −95 dBm by 3 dB, or a factor of two. In other words, at a specified data rate, a receiver with a −98 dBm sensitivity can hear signals that are half the power of those heard by a receiver with a −95 dBm receiver sensitivity..
Receiver sensitivity is an example of a case where sensivity is defined as the minimum input signal required to produce a specified output signal having a specified signal-to-noise ratio. This second definition has the advantage that it provides a measure for the Detection limit of a sensor if the minimum detectable SNR is specified.