Achieving reduced EMI using microcontrollers with PLL oscillators

Microcontrollers with integrated PLL (phase-locked loop) oscillators provide significant EMI reductions as compared to microcontrollers with standard oscillators, which typically run at two or four times the frequency of the system clocks. Three microcontrollers have been evaluated: one with a standard oscillator (system clock frequency= 1/4 * oscillator frequency), one with a X1 PLL (system clock=oscillator), and one with a 32 kHz-based PLL which produces a system clock frequency equivalent to that of the other two devices. The EMI contribution of the oscillators has been measured and compared using the SAE J1752/3 method.