Current Spread Spectrum Clock Oscillator with Adjustable Output Mode

This paper presents a Spread spectrum clock oscillator for the DC-DC converter. In this design, digital logic control is added based on the RC relaxation oscillator, which makes the charging and discharging current of the oscillator change randomly in the set range. This random change of current can achieve the corresponding spread spectrum to achieve the purpose of reducing EMI. In addition, this oscillator design can achieve four different operational modes through the external control signal: 7 -bit output mode and 8 -bit output mode without spread spectrum, 7-bit output mode and 8-bit output mode with spread spectrum. The simulation results show that the oscillating frequency of the oscillator is 16.7MHz without the spread spectrum under 7-bit output mode, after spreading spectrum, the depth of spread spectrum is $54.4 \%$, which the peak energy is reduced by 24dB compared with that before spreading spectrum. Under 8-bit output mode, the oscillator oscillates at 19.6MHz without spreading spectrum, after spreading spectrum, the depth of spread spectrum is $58 \%$ with the 22dB peak energy reduction.