A Robust Oscillator for Embedded System without External Crystal

The robust voltage-controlled oscillator is presented by using the constant current reference and the ring oscillator for the embedded system application. The constant current reference generates the constant current for the succeeding ring oscillator to produce a stable 4MHz oscillation frequency. The proposed VCO circuit was fabricated in a 0.35 μm CMOS technology and worked with a supply voltage of 3.3 V. The chip area of the VCO was 150 μm × 130 μm. According to measured results, the oscillation frequency drift of the proposed VCO was 986 ppm/C over a temperature range of -25C to 100C. The phase noise of -62.29 dBc/Hz was obtained at 1 MHz offset from the carrier. Moreover, total current consumption of the entire VCO was 234.72 μA. Therefore, the proposed VCO is suitable for integration into the embedded system.