On June 22, the “4th Smart Watch Technology Trends Summit” jointly organized by Rising Sun Big Data, Chaodian Think Tank and Smart Wearable Industry Alliance was warmly opened in Shenzhen. Chipsea Technology (stock code: 688595) debuted with a new high-end PPG AFE product CS1262.
 
As a key performance indicator, Chipsea’s CS1262 catches up with the industry’s first-class level. It is the first PPG product compatible with OpenHarmony, which is compatible with mainstream AFE designs and can provide users with high configuration, high-precision measurement, super anti-interference, low power consumption, Seven core values ​​of full skin color support, high reliability and ease of use.
 
The following will reveal the mystery of CS1262 carefully for you!
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Chipsea Technology booth site
Chipsea 1262 Application: Blood Pressure Watch
 
Peng Hongwei (second from left), senior product manager of Chipsea Technology, attended the roundtable discussion
 
At present, with socio-economic development, population aging, and the continued ravages of COVID-19, people’s health awareness continues to increase. At the same time, with the continuous advancement of microelectronics technology, vital sign measurement technology has also developed rapidly. More and more wearable devices on the market support the monitoring of vital signs, such as smart bracelets, earphones, health watches, etc.
 
As one of the three major wearable vital signs measurement technologies (PPG, ECG, BIA), PPG can continuously measure health indicators such as heart rate, blood oxygen SPO2, heart rate variability HRV, and blood pressure in a non-invasive and non-sensing way. Through the terminal products of health watches and smart bracelets, health measurement algorithms and AIoT connections can be used to create private health guards.
 
one,Principle of PPG measurement technology

Figure 1 PPG signal detection system

Figure 2 PPG signal
 
PPG is the abbreviation of Photoplethysmograph photoplethysmography, which is a technology that uses photoelectric signals to detect blood volume changes caused by arterial pulsation. PPG waveform is a pulse wave that changes with blood volume.
 
As shown in Figure 1, the PPG measurement system is composed of LED, PD (photoelectric sensor) and AFE (driving LED and detecting PD signal). The LED light illuminates the surface of human skin, tissues and blood vessels to generate optical signals of arterial pulsation modulation information. Then it is detected by PD photoelectric sensor to obtain data information.
 
As shown in FIG. 2 , the signal includes two parts: one is the light signal AC signal IAC modulated with the arterial change information, and the other is the light without modulating the arterial change information, that is, the stable DC signal IDC. The heart rate HR value can be obtained by analyzing the AC signal, and the blood oxygen SPO2 value can be obtained by analyzing the AC and DC proportional relationship of red light and infrared light according to the Lambert-Beer law.
Figure 3 Simulation of photon motion trajectory
Since Takuo Aoyagi invented the PPG measurement method in 1974, the traditional nail oximeter has been very mature. In recent years, the emergence of health measurement watches has brought new challenges. The measurement part changes from the finger to the wrist, and the measurement scene changes from the rest to the full-scene motion type, which puts forward more stringent requirements for the AFE chip.
 
As shown in Figure 3, the trajectories of 10 photons are depicted in the tissue optical simulation of the wrist, and only 1 photon marked in red captures a valid AC signal. In fact, the effective signal of the finger is dozens of times that of the wrist. In addition to the artifacts caused by the processing motion, new requirements are put forward for the performance indicators of the AFE. Chipsea’s CS1262 is an AFE with high SNR, low power consumption and considering all-scenario applications.
 
two,Summary of Product Advantages of CS1262
 
Figure 4 CS1262 system block diagram
CS1262 is a high performance PPG AFE. High accuracy: up to 110dB dynamic range, supports 48 channels of effective data acquisition with 4PD*12 phases, and the built-in LED Driver with a driving capacity of up to 250mA can support 8 channels of LED output. Super anti-interference: PSRR is greater than 90dB, and the ambient light suppression ability is strong. The analog ambient light reduction is up to ±200uA. Low power consumption: [email protected]@[email protected] ambient light reduction, [email protected]@[email protected] ambient light reduction.
 
three,Weak signal capture capability of CS1262
 
Figure 5 CS1262 SNR VS Gain Resistor
 
Fig.6 PPG signal at the wrist with PI≈0.1%
 
Up to 110dB dynamic range, 97.5dB [email protected]Ω (dBFS) and ±63.875uA LED current cut, provide CS1262 with powerful weak signal capture capability. Compared with the 109dB dynamic range of the competitor, the 96dB [email protected]Ω (dBFS) is better.
 
As shown in Figure 6, CS1262 collects red light and infrared PPG signals on the wrist, the PI perfusion level is one-thousandth, and the pulse waveform is clearly visible, which provides strong support for subsequent algorithm processing.
 
4. CS1262 satisfies all-scenario applications
 
 
 
Figure 7 PPG signal spectrum in resting, walking, running and other scenarios
 
CS1262 has a dynamic range of up to 110dB, with automatic analog ambient light reduction, ±200uA reduction range and excellent low residual characteristics of phase signals, making it capable of capturing PPG signals in complex motion scenes. Powerful LED driving capability and photoelectric sensor matrix layout up to 8LED*4PD ensure high-accuracy detection in complex skin color and complex test environment.
 
As shown in Figure 7, in the multi-sport scenario, the heart rate spectrum collected by CS1262 is clear and continuous and stable.
 
5. Low power consumption characteristics of CS1262
Table 1 Power consumption in different usage scenarios
The working current of PRF is as low as 13.3uA at 5Hz. In wearable devices and sleep health monitoring application scenarios, CS1262 is never absent, and it is a lasting and reliable personal health guard. The power consumption of CS1262 is as low as [email protected], which is better than the [email protected] of friends. This low power consumption feature provides wearable devices with a higher energy efficiency ratio and longer battery life.
 
CS1262 is not just a single product plan, but an important component of Chipsea’s smart health measurement product series. In the future, it will form a series of chip combinations with the company’s BIA, ECG and other SOC/analog front-end chip products. With health measurement algorithm, wireless connection and supporting standard solutions, it realizes the integration of health and intelligence, and empowers more high-end health equipment and high-end consumer electronic products.
 

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