The invention provides a direct-current bias oversampling digital-to-analog converter. A voltage-controlled oscillator circuit comprises a multi-stage ring oscillator, wherein the multi-stage ring oscillator comprises a plurality of series connection anti-phase stages, and each series connection anti-phase stage is composed of n channels and p channel transistors. The oscillation frequency of the ring oscillator is controlled through response control current signals. A voltage/current converter converts a tuning voltage input signal into a corresponding output current signal without being influenced by the channel strength of the n channels and the p channel transistors.