A 20uA/MHz at 200MHz microcontroller with low power memory access scheme for small sensing nodes

Motion sensing technology has been applied in a wide range of fields of IoT. In the future, sensor device can be highly expected to be applied in the field of sports, but in order to achieve this, we need to reduce the size and weight while maintaining high performance as shown in Figure 1. It is necessary to sample a signal from the 9D sensor (3-axis gyroscope, 3-axis accelerometer and 3-axis compass) by more than 1 K/s of rate to measure the max speed (over 300km/h) for a detailed motion analysis in the sports, and necessary to provide 100-200MHz performance to CPU. Also, in order to put sensor on the body, we must reduce the size of the battery, which is largest and heaviest parts of all. When a button type battery is used for as a power source, the average current in the system will be less than 10mA during operation. In this paper, by using the following two techniques, we have successfully reduced power consumption during system operation while maintaining the high performance. Those two techniques include low-power parallel cache and cache memory with address-mapped mode. They help reduce power consumption of flash memory, memory system, and overall system respectively. By using these techniques, we have succeeded in reducing power consumption during sensing application operation at 20uA/MHz at 200MHz.