题目/Title：A 0.35–0.5-V 18–152 MHz Digitally Controlled Relaxation Oscillator With Adaptive Threshold Calibration in 65-nm CMOS

作者/Author：
                        Yudong Zhang,Woogeun Rhee,Taeik Kim,Hojin Park,Zhihua Wang

期刊/Journal：IEEE Transactions on Circuits and Systems II: Express Briefs

年份/Issue Date：2015Aug.

卷（期）及页码/Volume（No.）&pages：Vol.62, No.8, pp. 736 - 740

摘要/Abstract：
This paper describes a pseudo-digital oscillator design for low voltage applications. To overcome the startup problem of the digitally-controlled ring oscillator (DCRO) with an ultra-low supply voltage, a digitally-controlled relaxation oscillator (DCRXO) which utilizes an inverter-based comparator is proposed. The pseudo comparator (PC) which is a variable threshold inverter (VTI) followed by an inverter is introduced, and a digital calibration circuit is used to automatically set the threshold of the PC for process-insensitive operation in the initial state. The DCRXO implemented in 65 nm CMOS consumes 17.8 mW from a 0.35 V supply at 26 MHz output and achieves a tuning range of 18.2-29.2 MHz with a sufficient overlap between tuning curves. The phase noise of –104 dBc/Hz at 1 MHz offset is measured at 26 MHz output frequency. When the supply voltage of 0.5 V is used, the DCRXO consumes 59 mW at 100 MHz output with the tuning range of 43.5-152 MHz. The core area of the DCRXO is 0.0362 mm2.