According to one embodiment, a power-efficient, low noise photoplethysmographic (PPG) sensor module is provided herein comprising at least one light emitting diode (LED) and at least one photodetector. The LED is generally configured for emitting light, and is positioned on the PPG sensor module for transmitting the emitted light into biological tissue. The photodetector is generally configured for detecting a portion of the light that is transmitted by the LED into the biological tissue and reflected back to the photodetector. The photodetector is an elongated photodetector having a longer dimension that is at least 1.5 times larger than a shorter dimension of the elongated photodetector. By positioning the elongated photodetector on the PPG sensor module, such that the longer dimension is facing towards the first LED, the elongated photodetector is configured to collect substantially more of the reflected light, thereby increasing the signal-to-noise ratio of the detected signal.
