In the case of automotive and medical semiconductors requiring high reliability, there are limits to the EMI level. A typical method used to reduce EMI is to apply a Spread Spectrum Clock Generator (SSCG). However, this system operation involves reading a signal from a sensor and digital signal processing, and because the operation should conform to a fixed sampling frequency, it is not easy to apply SSCG, and furthermore due to current consumption cycles in the sampling frequency, EMI of the corresponding frequency occurs.
The conventional art modulates the sampling frequency in a predefined pattern (Spread Spectrum Sampling), and changes a sampled signal to a signal of the modulated sampling frequency through a complex algorithm.
To modify a signal, a complex operation (e.g., division) is needed. Additionally, additional hardware (SSCG) that modulates the clock in a preset pattern is necessary. Further, since the clock modulation method is hardware implementation, flexibility is low when it is necessary to vary the amount of modulation based on the sampling period.
FIG. 1 is a block diagram of a general sensor system according to the related art. An analog signal from a sensor is converted to a digital signal through the ADC, and a digital signal processing algorithm runs on the MCU. The signal-processed digital signal is transmitted to an actuator or other chip depending on the field of application.
In this instance, because periodicity of read & write is very important, phase-locked loop (PLL) clock output of a fixed frequency generates periodic interrupts in the timer circuit. The MCU performs read, DSP, and write in a sequential order with respect to the interrupts.
In this instance, because the entire system periodically consumes an electric current due to interrupt generation, there is a problem of EMI noise occurring in the corresponding cycle.