This paper reports a reliable current compensated reference oscillator without any BJT or external component. To maintain a stable oscillation frequency, the discharging current of the proposed architecture varies with process, supply voltage and temperature (PVT) variations. Fabricated in a 0.18-μm digital CMOS process, this oscillator consumes 0.5 mW from a 1.8-V supply. The post-simulation results show the worst case is 12%. From 500 times Monte Carlo simulation results, the frequency variations are all limited within ±3%. The measurement result of ten samples at room temperature with 10% supply voltage deviation shows variation within ±10%. The maximum variation is -10.19% with process and supply voltage variations from measurement results.