• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.5
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• pp.87-93
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• 2010

This paper presents a high resolution, wide input range 2-step time-to-digital converter used in digital PLL. TDC is used to compare the DPLL output frequency with reference frequency and should be implemented with high resolution to improve the phase noise of DPLL. The conventional TDC consists of delay line realized inverters, whose resolution is determined by delay time of inverter and transistor size, resulting in limited resolution. In this paper, 2-step TDC with phase-interpolation and Time Amplifier is proposed to meet the high resolution and wide input range by implement the delay time less than an inverter delay. The gain of Time Amplifier is improved by using the delay time difference between two inverters. It is implemented in $0.13{\mu}m$ CMOS process and the die area is $800{\mu}m{\times}850{\mu}m$ Current consumption is 12 mA at the supply voltage of 1.2 V. The resolution and input range of the proposed TDC are 0.357 ps and 200 ps, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.7
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• pp.8-16
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• 2010

In this paper, we investigated the effects of $O_2$ fraction on the properties of Al-doped ZnO (AZO) thin films prepared by radio frequency (RF) magnetron sputtering. Hall, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) measurements revealed that the p-type conductivity was exhibited for AZO films with an $O_2$ fraction of 0.9 while the n-type conductivity was observed for films with $O_2$ fractions in range of 0 - 0.6. PL and XPS also showed that the acceptor-like defects, such as zinc vacancies and oxygen interstitials, increased in films prepared by an $O_2$ fraction of 0.9, resulting in the p-type conductivity in the films. Hall results indicated that AZO films prepared by $O_2$ fractions in range of 0 - 0.6 can be used for electrode layers in the applications of transparent thin film transistor. We concluded from the X-ray diffraction analysis that worse crystallinity with a smaller grain size as well as higher tensile stress was observed in the films prepared by a higher $O_2$ fraction, which is related to incorporation of more oxygen atoms into the films during deposition. The study of atomic force microscope suggested that the smoother surface morphology was observed in films prepared by using $O_2$ fraction, which causes the higher resistivity in those films, as evidenced by Hall measurements.