Abstract
In this paper, 6bit SAR ADC tolerant to ionizing radiation is presented. Radiation tolerance is achieved by using the Dummy Gate Assisted (DGA) MOSFET which was proposed to suppress the leakage current induced by ionizing radiation and its comparing sample is designed with the conventional MOSFET. The designed ADC consists of binary capacitor DAC, dynamic latch comparator, and digital logic and was fabricated using a standard 0.35um CMOS process. Irradiation was performed by Co-60 gamma ray. After the irradiation, ADC designed with the conventional MOSFET did not operate properly. On the contrary, ADC designed with the DGA MOSFET showed a little parametric degradation of which DNL was increased from 0.7LSB to 2.0LSB and INL was increased from 1.8LSB to 3.2LSB. In spite of its parametric degradation, analog to digital conversion in the ADC with DGA MOSFET was found to be possible.
본 논문에서는 본 연구실에서 제안된 Dummy Gate Assisted MOSFET을 이용하여 6bit SAR (Successive Approximation Register) ADC를 설계하였으며 이에 대한 대조군으로 Conventional MOSFET으로 동일한 회로를 설계하여 두 회로의 Co-60 Gamma Ray에 의한 누적방사선 영향을 비교 분석해 보았다. 설계된 SAR ADC는 Binary Capacitor DAC과 Dynamic Latch 형태의 Comparator 그리고 Logic으로 구성이 되었으며, 0.35um standard CMOS공정으로 제작되었다. 방사선 조사 후 Conventional MOSFET을 이용한 ADC는 정상동작하지 못하였지만, Dummy Gate Assisted MOSFET을 사용한 ADC는 방사선 조사 후 DNL은 0.7LSB에서 2.0LSB, INL은 1.8LSB에서 3.2LSB로 다소 증가하였으나 정상적인 A/D 변환이 가능하다는 것을 확인하였다.
