Abstract: An anti-Electro-Magnetic Interference (EMI) oscillator used in switching power supply converter is designed. Its main innovation is that it is convenient to add frequency jitter and can generate ramp compensation clock signal in switching power supply system. The triangular wave current signal with adjustable slope is generated, and the frequency jitter module is integrated in the oscillator. The oscillator improves the stability of the switching power supply, and introduces the digitally-assisted tuning technology to adjust the charging capacitance in both directions, eliminating the error caused by the process. The oscillator based on 0.18 μm BCD(Bipolar CMOS DMOS‎) process realizes the linear switching of oscillator frequency. The normal operating frequency of the oscillator is 1 MHz, the minimum operating frequency is 100 kHz, and its jitter range is −1.66% - +4.3% of the base frequency. In the range of 2.7 - 5.5 V power supply voltage and −40 - 125 ℃ temperature, the output frequency changes 2.45 kHz, the change rate is 0.245%, the duty cycle shift is 0.653 ns, the compensation current peak shift is 0.125 nA, and the adjustment range is 60.98%.