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ADPD2214ACPZ-RL Arkusz danych(PDF) 9 Page - Analog Devices |
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ADPD2214ACPZ-RL Arkusz danych(HTML) 9 Page - Analog Devices |
9 / 14 page ADPD2214 Data Sheet Rev. 0 | Page 8 of 13 TERMINOLOGY Optical Power Optical power is defined as the photon energy per unit of time measured as radiant flux (Φ) or radiant power, which is radiant energy (Q) per unit of time. Responsivity Photodiode responsivity, ρ, is a constant that correlates incident optical power (POPT) with photodiode current (IPD) and is typically expressed in units of amperes per watt (A/W). Responsivity is essentially the quantum efficiency of the ability of the sensor to convert light into electron/hole pairs and is highly dependent upon the wavelength of the incident light as well as sensor material and temperature. Photodiode Area Photodiode area is a measure of the photosensitive area of the diode. In PIN diodes, this is the photosensitive area of intrinsic silicon between the positive and negative doped diffusion areas. In general, larger photodiodes demonstrate greater sensitivity as the output signal increases linearly with photosensitive area while noise increases at the sum of the square of the photosensitive area. A larger photodiode area has a higher capacitance and longer carrier diffusion paths adversely affecting bandwidth. Photoconductive Mode Photoconductive operation of a photodiode occurs when photons entering the silicon generate electron/hole pairs that are swept by the electric field to the opposite terminal. These carriers are presented at the terminals of the photodiode as a current proportional to the luminous flux incident on the junction of the photodiode. Shot Noise Shot noise is a statistical fluctuation in any quantized signal such as photons of light and electrons in current. The magnitude of the shot noise is expressed as a root mean square (rms) noise current. Shot noise is a fundamental limitation in photodetectors and takes the form of Shot noise = √(2qIPD) where: q is the charge of an electron (1.602 × 10−19 Coulomb). IPD is the photodiode current. Photoplethysmography (PPG) Photoplethysmography uses light to measure biological functions by sensing changes in the absorption spectra of soft tissue due to changes in hemoglobin volume and composition. Linearity Linearity is a measure of the deviation from an ideal change in output current relative to a change in optical power falling on the sensor. Linearity is specified as the deviation from a best straight line fit of the current output of the sensor over a speci- fied range of optical power. Linearity is a critical specification in PPG measurements due to the requirement of sensing small ac signals impressed upon large dc offsets. Static Bias The ADPD2214 has an internal 10 nA bias that linearizes the input current mirror at low input levels and prevents transient reverse bias of the amplifier input stage. This bias is fixed and appears on the output as a 240 nA typical offset. Noise Equivalent Power (NEP) Noise equivalent power is the amount of incident light power on a photodetector, which generates a photocurrent equal to the total noise current of the sensor. The noise level is proportional to the square root of the frequency bandwidth; therefore, NEP is specified with a 1 Hz bandwidth. NEP is the fundamental baseline of the detectivity of the sensor. |
Podobny numer części - ADPD2214ACPZ-RL |
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Podobny opis - ADPD2214ACPZ-RL |
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