Here we present the design and implementation of a 130-MHz on-chip reference oscillator in a 0.18-μm 1-ploy 6-metal digital CMOS process. To compensate for the influences on the oscillation frequency by process, supply voltage and temperature (PVT) variations, the oscillator uses a bias adjustment technique without BJT devices, on-chip inductors or external components. Measurements of 8 samples in the 0 to 100°C temperature range indicate an average deviation of ±4.99% in the oscillation frequency. The process-induced frequency deviation is ±1.13% across chips at room temperature. The deviation of frequency with 10% supply voltage variation is within ±5.4%.