WIRELESS HEALTH monitoring is quickly expanding, thanks to the convenience that it offers to patients, doctors, and healthcare centers. Among the recent innovations in this area is an integrated sensor-node solution. This system-on-a-chip (SoC), which was designed and implemented in 0.18-m CMOS, was the work of Singapore Polytechnic's Tee Hui Teo; the Data Storage Institute's Xinbo Qian; Pradeep Kumar Gopalakrishnan from the RV-VLSI Design Center; Yee Shan Hwan from Broadcom Singapore; Kuruveettil Haridas from Huawei Technologies; and Chin Yann Pang, Hyouk-Kyu Cha, and Minkyu Je from Singapore's Institute of Microelectronics.
The team set out to design and implement a low-cost, small-form-factor device that provides high-quality electrocardiogram (ECG) signal acquisition and long battery life. The SoC houses a sensor interface circuit, analog-to-digital converter (ADC), digital signal processor (DSP), and RF transmitter. The sensor node was developed in conjunction with the prototype personal server. The researchers found that the acquired ECG signal could be transmitted to and monitored by that personal server beyond 5 m.
With continuous real-time monitoring applications, more than 90 percent of the total power can be dissipated in the wireless unit. Yet this SoC consumes just 700 W at a 0.7-V supply voltage when it acquires the ECG signal from the patient and transmits it at -16 dBm through the 433.92-MHz channel. Using a typical button- cell battery, the sensor-node solution vows to enable continuous and real-time health monitoring for more than 200 h before the battery has to be replaced.
The researchers found that current Bluetooth and ZigBee chips generally consumed 10 mA of current, which is too high for continuous health-monitoring applications. They also discovered that much higher power consumption was needed for transmission at 2.4 GHz versus 433.92 MHz. See "A 700-W Wireless Sensor Node SoC for Continuous Real-Time Health Monitoring," IEEE Journal Of Solid-State Circuits, Nov. 2010, p. 2292.