Noise countermeasures for ameliorating sensor malfunction

Need for sensor noise suppression


Sensors are key devices of the Internet of Things (IoT) and self-driving cars, and they are expected to be used even more in many types of equipment in the future.

However, there are also cases where serious accidents may result if sensors do not correctly transmit the sensed data.
This makes noise suppression both important and essential for various types of sensors.

This chapter investigates the malfunction mechanisms and noise suppression methods, using one-chip type sensors*1 (digital output type) as an example.

 
*1 With the development of MEMS technology, one-chip type sensors are becoming the mainstream.


Recommended noise suppression circuit for one-chip sensors


Target interface

I2C or SPI
 

Target interface :  I2C
Signal frequency :  100kbps(50kHz)、400kbps(200kHz)、3.4Mbps(1.7MHz)etc → Maximum approx. 2MHz
Cut-off frequency
(Signal frequency x 5): 
10MHz
Recommended circuit

Signal line insertion loss Power line insertion loss



 

Target interface :  SPI
Signal frequency :  1~2Mbps(1MHz)、20Mbps(10MHz)etc → Maximum approx. 10MHz
Cut-off frequency (Signal frequency x 5): 
50MHz
Recommended circuit

Signal line insertion loss Power line insertion loss



In view of the above, we recommend :

Recommended noise suppression filters for one-chip sensors
The typical interfaces used by digital one-chip sensors are I2C and SPI.
The signal frequencies are not constant, but the cut-off frequencies required of filters are around 10 MHz for I2C and around 50 MHz for SPI, so the above-noted filters are suitable.


For further "problems" that can be anticipated,

We will explain the mechanisms of sensor malfunction due to noise, and the key points of countermeasures >