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ADPD2214ACPZ-RL 数据表(PDF) 10 Page - Analog Devices |
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ADPD2214ACPZ-RL 数据表(HTML) 10 Page - Analog Devices |
10 / 14 page Data Sheet ADPD2214 Rev. 0 | Page 9 of 13 THEORY OF OPERATION OVERVIEW The ADPD2214 is an integrated, low power, optical sensor composed of a deep junction silicon photodiode coupled to a low noise current amplifier in an optically transparent chip scale package. The ADPD2214 is optimized for battery- powered, wearable, medical, and industrial optical sensing applications requiring low power and high SNR. SHOT NOISE LIMITED PERFORMANCE The on-board photodiode of the ADPD2214 is operated in photoconductive mode with a zero bias voltage. This mode of operation allows the diode to operate with no dc dark current caused by leakage across the depletion area of the diode, providing a fundamental limit of shot noise. The noise level is proportional to the square root of the frequency bandwidth. SENSITIVITY AND SNR SNR is a measure of the ability of the sensor to separate the signal of interest from spurious signals that occur from the surrounding environment of the device, such as ambient light, nonlinearity, and noise within the device itself. The ADPD2214 operates its integrated photodiode in a zero biased photoconductive mode to provide near zero dark current and, therefore, no dark shot noise component contribution from the photodiode. The integrated current amplifier requires an internal bias current of 10 nA to improve bandwidth and linearize response at low light levels. This bias generates a shot noise component of 90 fA/√Hz at the output of the current amplifier and establishes the noise floor of the ADPD2214. To optimize the sensitivity of the ADPD2214, it is important to ensure that the optical signal is concentrated on the photoactive area of the integrated photodiode. The on-board precision current amplifier is shielded and is not significantly affected by light hitting its surface, but device sensitivity is based solely on the optical power incident to the photodetector. LINEARITY Linearity is critical to PPG due to the need to accurately extract a small amplitude, pulsatile ac signal modulated onto the large dc component, which is caused by nonpulsatile tissue absorption and ambient light. In pulsed light applications, bandwidth is a critical component of the linearity because fast recovery of the device from dark and/or power-down conditions can have a profound effect on the ability of the sensor to extract the signal of interest. The ADPD2214 is production trimmed to ensure 60 dB linearity at an irradiance of up to EE = 890 µW/cm2, λ = 528 nm, at a supply voltage of 3.3 V. PACKAGE CONSIDERATIONS The ADPD2214 is packaged with a transparent epoxy molding compound. To maintain optimum sensitivity, take care in handling the device to prevent scratches or chemicals that may affect the surface finish above the photodiode. Due to the lack of stabilizing fillers (typically up to 70% silica) used in opaque molding compounds, the maximum storage temperature of the ADPD2214 is 105°C. The temperature profile for soldering is shown in Figure 2. EPAD CONNECTION The EPAD on the ADPD2214 acts as a common electrical, thermal, and mechanical platform for the photodiode and amplifier and must not be connected externally. External cooling is not required due to the extremely low power consumption of the ADPD2214. Analog Devices, Inc., recommends removal of traces beneath the device to eliminate potential coupling of external signals into the sensitive internal nodes of the ADPD2214. |
类似零件编号 - ADPD2214ACPZ-RL |
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类似说明 - ADPD2214ACPZ-RL |
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