For a detector connected to a simple resistor, the dark noise is given by ![]() Thermal energy provided by ambient heating generates the additional carriers that contribute to the noise current. In order to improve the SNR in a spectrometer, the design choices must increase the power in the measurement signal while at the same time minimize the noise sources as much as possible.ĭark noise, also commonly referred to as thermal noise () arises from statistical changes in the number of electrons available to conduct current, even without light incident on the detector. The measurement can now provide useful and reliable information about the sample. In Figure SNR.1 (b), the signal current greatly exceeds the noise current in magnitude, making the signal current easier to distinguish and separate from the noise. One can see that in this condition, the spectrometer cannot separate the signal containing information about the sample from the noise signal, and thus the measurement provides no useful data. In Figure SNR.1 (a), the signal current (numerator of SNR) and the noise current (denominator of SNR) are about equal – i.e., the SNR ≈ 1. To better understand the SNR equation, consider the two conditions in Figure SNR.1 below. Where is the average optical power in the desired signal, and refers to the variance of the i th source of noise current, in A 2, which describes the average power in a random signal based on Fourier Transform theory. The noise signal arises from a number of sources, both electrical and optical. In a spectrometer, the desired signal consists of the optical power at a given wavelength directed by the diffraction grating (and by the DMD, in a DLP-based system) to the detector. The SNR compares the average power available in the signal to the average power contained in the noise, which includes any signal from sources other than the target signal source. ![]() The signal-to-noise ratio (SNR) provides a measure of the signal quality. Ultimately, the ability of the spectrometer to make accurate measurements depends on the quality of the signal obtained from the detector and the subsequent electrical circuits.
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