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A near-/sub-threshold programmable clock generator is proposed in this paper. The major challenge of the ultra-low voltage (ULV) circuits is that the lock-in range of the delay line is easily affected by the environmental variations. In the proposed clock generator, there is a PVT compensation unit which consists of a set of delay line and a PVT detector. The unit is responsible for adjusting the lock-in range of clock generator to guarantee successful clock lock. In addition, the variation-aware logic design is performed in the clock generator, which improves the reliability on process variation. Also, the adoption of pulse-circulating scheme suppresses process induced output clock jitter. Furthermore, it has the ability to generate the output clock with frequency from 1/8 to 4 times of the reference clock. The clock generator has been designed using UMC 65nm CMOS technology. The frequencies of reference clock are 625 kHz at 0.2V and 5MHz at 0.5V. The power consumptions are 0.18μW and 5.17μW, respectively, at 0.2V and 0.5V. The core area of this clock generator is 0.01mm2.