Applications > Bio-Sensor
The RTL8765AC is a PPG AFE, utilizing optically non-invasive measurement, to provide valuable information about cardiovascular system performance. PPG can detect blood volume changes in the microvascular bed of tissue. Its result comprises a pulsatile physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat and is superimposed on a slowly varying baseline with various lower frequency components attributed to respiration or motion artifact.
Realtek's PPG AFE provides wearable devices with accurate heart rate monitoring and smart health metrics. Combined with Realtek's wearable platform, it offers algorithms for heart rate, blood oxygen, dynamic ambient light suppression, and skin-wearing detection.
Extremely low power consumption is ideal for battery device applications; including LEDs, power consumption is only 29μA @ 3.3V.
Even further, making the RTL8765AC suitable for the wearable applications.
System Structures
The RTL8765AC controls the synchronous timing for LEDs (Tx) and PDs (Rx) to obtain PPG signals from testers and transforms them from analog version to digital one. The AFE supports two LED drivers with four configurable LED switches, and two simultaneous Rx channels to enhance dynamic measurement results during exercise.
Flexible measurements can be arranged in the RTL8765AC’s time frame regarding to different LED color sources, or to different PD locations underneath the watch. For each Rx channel, the RTL8765AC dis-patches at most four dedicated processing units for handling the data manipulation to the measurements.
For outdoor exercise, the RTL8765AC’s two simultaneous Rx channels help to enhance the incoming signal quality and reliability. Moreover, the ability for lowering the ambient light affection to the measurement can be as much as about 60 dB directly in the RTL8765AC’s AFE from low AC frequency to up to 1 kHz. The DC components of the PPG and Ambient Light signals can be eliminated by different IDAC settings. The cancellation can be controlled directly by the built-in processing units without host intervention, which can save the system power and lower design complexity of the software algorithm. Moreover, it also can reduce the needed dynamic range for the ADC, and its bit counts as well, to cut the system power.
Practical Application Case
Realtek's proprietary dual-channel Fusion algorithm supports 1/2/4-channel PD input, enabling the measurement of heart rate values with high dynamic range and low error.
The following are actual measurement data compared to a heart rate belt:
Static error <5 BPM = 98%
Static heart rate variability (HRV) = 11 msec
Running average ±1.8 BPM
Static typing average ±1.6 BPM
Application Scenarios
Advantages of Solution
Extremely low power consumption, suitable for battery-powered applications, with a power consumption of only 29μA @ 3.3V including LED.
Excellent ambient light noise cancellation technology, featuring triple cancellation capabilities: LED and ambient light DC IDAC cancellation, and AC noise reduction up to 1 kHz (approximately 60dB reduction).
Two synchronous RX channels contribute to improved input signal quality and reliability.
Recommended Chips
| RTL8765AC | |
|---|---|
| TX Channels | 4 chs |
| LED Driver | 2 sets |
| TX Current/Ch. | 200mA |
| RX Channels | 2 chs |
| PD Port Numbe | 4 |
| Receive SNR @2.5uA | 66.9dB |
| Perfusion Index | 0.5% |
| Measurement Per Frame | 8 max |
| FIFO Size | 256-word |
| Interface | I2C |
| Receive Power @ 25Hz | 20uA |
| Supply (V) | 1. 8V for core and analog 1.8 to 3.3V for IO |
| Package | WLCSP23, 2.50×2.30 |
苏公网安备32059002006558号