This paper presents an oscillator-based true random number generator (TRNG) that dynamically unbiases 0/1 probability. The proposed TRNG automatically adjusts the duty cycle of a fast oscillator to 50%, and generates unbiased random numbers tolerating process variation and dynamic temperature fluctuation. A prototype chip of the proposed TRNG was fabricated with a 65 nm CMOS process. Measurement results show that the developed duty cycle monitor obtained the probability of '1' 4,100 times faster than the conventional output bit observation, or estimated the probability with 70 times higher accuracy. The proposed TANG adjusted the probability of '1' to within 50 +/- 0.07% in five chips in the temperature range of 0 C to 75 degrees C. Consequently, the proposed TRNG passed the NIST and DIEHARD tests at 7.5 Mbps with 6,670 mu m(2) area.