Smart rings are often praised for their sleek form and passive functionality, but at the heart of these devices lies an incredible piece of technology: the PPG sensor. Short for photoplethysmography, PPG is the silent workhorse that enables vital health insights like heart rate, HRV, blood oxygen levels, and even blood pressure trends.
In this article, we take a deep dive into the sensor technology behind smart rings — particularly how Doni’s proprietary PPG system sets new standards in comfort, accuracy, and continuous tracking.
What Is PPG and How Does It Work?
PPG stands for photoplethysmography, a non-invasive optical method that uses light to measure changes in blood volume in your microvascular tissues. Here’s how it works:
- A light source (usually green, red, or infrared LED) emits light onto your skin.
- As blood pulses through your finger, more or less light is absorbed depending on blood flow.
- A photodetector captures the reflected light and converts it into a digital signal.
- Signal processing algorithms analyze these waveforms to calculate biometrics like heart rate or oxygen saturation (SpO₂).
It’s simple in theory — but incredibly challenging to implement reliably in a miniature wearable that’s always in motion.
Challenges in Ring-Based PPG Sensing
Unlike smartwatches, smart rings have less surface area, limited battery capacity, and a tighter contact zone on the finger. That creates several engineering challenges:
- Motion artifacts from hand movement or loose fits
- Temperature shifts affecting sensor performance
- Power constraints limiting continuous data collection
- Skin tone variability in light absorption
This is why many off-the-shelf solutions fall short when placed into a ring form factor.
Doni’s Proprietary PPG Sensor: Designed for the Finger
At Doni, we built our own PPG module from the ground up — optimized specifically for finger-based sensing.
Here’s what makes our sensor system different:
1. Custom LED Wavelengths
We selected and calibrated multiple LED wavelengths to maximize signal clarity across a wide range of skin tones and physiological states.
2.High-Sensitivity Photodiode Array
Our photodetectors are finely tuned to capture subtle waveform changes even during light motion or low perfusion.
3. AI-Powered Signal Filtering
Raw PPG signals are cleaned using proprietary algorithms trained on clinical and real-world data, reducing motion noise without over-smoothing.
4.Thermal + Fit Compensation
We designed the system to self-calibrate based on finger temperature and ring fit level, ensuring consistent quality day or night.
5.Ultra-Low Power Profile
Despite the sophistication, our sensor runs on optimized firmware that supports long battery life — making 24/7 monitoring possible.
Why It Matters: Accuracy You Can Trust
When it comes to health data, accuracy isn’t optional — it’s foundational. That’s why Doni Ring is clinically validated, and our PPG data pipeline is built to meet medical-grade standards.
This precision enables features like:
- Reliable HRV tracking for stress & recovery
- Early detection of cardiovascular irregularities
- Estimation of blood pressure trends (clinically tested)
- Nighttime oxygen saturation monitoring
The future of health tracking lies in discreet, wearable, intelligent systems — and at the core of it all is the humble PPG sensor. Doni’s custom-designed optical module proves that with the right engineering and medical rigor, smart rings can be more than smart: they can be trustworthy partners in personal health