Noise-Equivalent-Power

A figure of merit which has been largely superseded by D for infrared detectors, but still finds application in optical detectors, is the noise equivalent power, or NEP, frequently symbolized as P - The NEP is the rms incident radiant power 

As is true for responsivity and detectivity, the NEP can be either monochromatic (spectral) or black body, depending upon the reference source. The units of NEP are watts. 

Detectivity is defined as the signal-to-noise ratio per unit radiant power. Thus it is the reciprocal of the noise equivalent power, having units of (watts) . Confusion has arisen over the term detectivity, which has also been applied to D. The above definition will be employed herein. 

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Bock et al [4] have an electrical NEP (noise-equivalent power) of 4 x 10 W Hz when cooled to 300 mK. For those who desire less exotic cryogenic options, conmiercially available Si-composite bolometers offer an... 

Noise Equivalent Power. The total system electronic noise V j may be combiaed with the responsivity, to give the noise equivalent power equation ... 

There are important figures of merit (5) that describe the performance of a photodetector. These are responsivity, noise, noise equivalent power, detectivity, and response time (2,6). However, there are several related parameters of measurement, eg, temperature of operation, bias power, spectral response, background photon flux, noise spectra, impedance, and linearity. Operational concerns include detector-element size, uniformity of response, array density, reflabiUty, cooling time, radiation tolerance, vibration and shock resistance, shelf life, availabiUty of arrays, and cost. 

Detectivity. Detector sensitivity (1,2) is expressed in terms of the minimum detectable signal power or noise equivalent power (NEP) given in units of watts or W. The reciprocal function when normalized for detector area, M, and noise bandwidth, is defined as detectivity, D, in units of /W. Thus,... 

A noise power equivalent to one photon generates an interference signal which has an amplitude equals to twice the rms photon noise of the source. But as only the in-phase components of the source generates an interference with the local oscillator, the result is that the spectral Noise Equivalent Power of the heterodyne receiver is hv. 

The SNR of the detected signal is defined as the ratio of the signal change (produced as a result of the intensity modulation in the measurement cell) to the noise equivalent power (NEP) of the detection system for a given average received light intensity. In order to derive a figure for the NEP, various assumptions about the optical receiver must first be made. 

The main parameter which characterizes a calorimeter is the resolution, whereas in astronomical bolometers the qualifying parameter is the NEP (noise equivalent power, see later). Also the size is very different bolometers are usually very smaller. Their more sophisticated technology allows the realization of large arrays of detectors. In operation, bolometers usually handle a chopped signal (tens of Hertz) of much smaller energy than calorimeters. 

Noise correlation function, 22 113 Noise equivalent power (NEP), 19 133 Noise spectral density, 19 134-135 Nomarski, Georges, 16 480 Nomarski-modified Wollaston prism, 16 481... 

The fundamental performance parameter of any detector is its noise equivalent power (NEP). This is simply the input irradiance power necessary to achieve a detector output just equal to the noise. This NEP is dependent on a number of detector and signal variables such as modulation frequency and wavelength (the input signal is defined as sine wave modulated monochromatic light), and detector area, bandwidth and temperature. 

Assuming that the noise is white noise, that is, S f) = S0, Eq. (18) is simplified and the signal-to-noise ratio is determined from Eqs. (17) and (18). Equation (18) is simplified by the definition of the noise-equivalent power (in watts per Hz1/2)... 

NEP = Detector noise equivalent power, 1 Hz Band (watts), Act = Spectral resolution (cm-1),... 

There are a variety of FPA detectors available that are sensitive in the NIR spectral region. The optimal choice of detectors depends on several factors desired wavelength range, whether the application will be laboratory based or part of a process environment, the sensitivity needed to adequately differentiate sample spectra and price. The figure of merit most often used to describe detector performance is specific detectivity or D, which is the inverse of noise equivalent power (NEP), normalized for detector area and unit bandwidth. NEP is defined as the radiant power that produces a signal-to-dark-current noise ratio of unity. 

It is evidently insufficient to consider only the response of a detector when analysing its usefulness for a particular application. It is generally necessary to analyse both intrinsic and extrinsic noise signals and compare them with the response. The result of this comparison can be expressed in many different ways. One of the most useful is the noise-equivalent power nep which is the power of an rms signal input (in watts) required to give a response equal to the total rms noise voltage AVN. Then ... 

The noise level can be expressed in terms of the power incident on the detector necessary to give a signal equivalent to the noise. If the noise voltage is A EN then the noise equivalent power (NEP) is defined by... 

NEA NEP NFP NMR NP negative electron affinity noise equivalent power near field pattern nuclear magnetic resonance no-phonon... 

Typical detectivity values as a function of wavelength for PbS photoconductive and various photovoltaic detectors. is a figure of merit defined as A /NEP, where A is the detector area and NEP is the noise-equivalent power, the rms radiant power in watts of a sinusoidally modulated input incident on the detector that gives rise to an rms signal equal to the rms dark noise in a 1-Hz bandwidth. Data from Hughes Aircraft Company. 

The responsivity (E) or specific detectivity (D ) and the noise equivalent power NEP (Wn), are often used to measure the sensitivity of a detector. The responsivity depends on the wavelength of the radiation and the temperature of the detector. The NEP, also called minimum detectable power, is the quotient of detector noise (N) divided by voltage responsivity (E). The D is the reciprocal of NEP, thus W = NIE and D = 1/Wn- A more sensitive detector has a smaller NEP and larger D, which results in less noise and a faster response time. 

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