Filtered NIR photodiode for pulse oximetry and proximity
The ADPD2140WBCPZN-R7 is a discrete filtered photodiode from Analog Devices with a 0.363 mm² active area. Its responsivity peaks at 0.4 A/W at 880 nm in the near-infrared band, while the 660 nm red response is only 0.025 A/W — the on-chip filter rejects visible light so the signal chain sees only the NIR LED return. The 0.786 pA switching current is the dark leakage floor; any transimpedance amplifier selected for the front end must have an input bias current well below this to avoid swamping the photocurrent.
Response time and operating temperature envelope
The 258 ms response time is the time constant of the photodiode junction capacitance and the external load resistor — it sets the upper bound on the modulation frequency of the LED drive. For pulse oximetry where the LED is chopped at a few kHz, this is not the limiting factor; the downstream ADC sampling rate will be.