After 1 year’s hard research, directed by Pro. HEI Yong and Pro. ZHOU Yumei, the team of Dr. HU Xiaoyu completed the assignment of “Low-power sensor ROIC and Pre-process circuit” in CAS knowledge innovation program project entitled “SOC of Multi-sensor and node integration”, and made an important process in multiply-sensor detection SOC.
Recently with the development of “The Internet of Things” in China, sensor has been applied in intelligence traffic, environment protection, public safety and personal health, and becomes the research focus of academe and industry. As the significant part of “The Internet of Things”, sensor node includes analog process circuit and analog-to-digital converter that called sensor readout circuit (ROIC). Nowadays this circuit is usually realized in PCB system, which has single function and occupies large area. So for different sensor application, the research of ROIC becomes the essential of sensor node.
In the process of research, allied with the real-time signal processing, mixed-signal and vehicle electronics group, Pro. HEI Yong led us to complete the ROIC chip design of hydrophone, Giant Magneto resistance (GMR) biosensor and other kinds of sensor.
For voltage detection of hydrophone the ROIC includes Chopper-Stabilized Operational Amplifier of low noise and low residual offset, GM-C low pass filter, voltage gain amplifier and Sigma-Delta ADC. The measurement results show that in 1.8V power supply, the width of input signal can be up to 100KHZ and the input residual offset is 90 µV. The 16bit/100KSPS Sigma-Delta ADC designed by teammate FAN Jun shows SFDR 87dB, SNR 77dB in 12.8MHZ clock frequency that is advanced domestically.

Fig. 1 Sigma-Delta ADC chip Fig. 2 Output spectrum of Sigma-Delta ADC
It is blank in the area of detection application for medical sensor, so Pro. Heiyong and Mix-signal group took this chance, cooperating with corporation MagicIC to start the research of ROIC for GMR biosensor. The basis of GMR biosensor is that the resistor of material changes with different magnetization. So to transform the changing resistor to voltage signal is the fundamental thought of detection. The group made up of Huxiaoyu, Fanjun and Chenchengying made their effort to present a voltage detection solution. The ROIC comprises GMR sensor array, voltage simulation source, signal conversion circuit, ADC, sensor address circuit and output control circuit. The measurement shows in 5MHZ clock frequency, the ENOB is 7.36bit, which can detect as small as 16ohm variation of GMR sensor array. The result is advanced in industry and the product will be presented later of this year.
Fig3. Die micrograph of GMR ROIC Fig4. digital code of output
This process is the result of cooperation of each group, which shows our advantage in Mixed-signal circuit design. In the period of “knowledge innovation 2020”, multiply sensor detection SOC will be the focus of Mixed-signal IC. The accomplishment of this program sets a good foundation for our department in the area of sensor detection. We believe that by the effort of our leaders and research group we will make more process in the future.