E. Sadeghi - IC Design Research Laboratory, Electrical & Robotic Engineering Department, Shahrood University of Technology, Shahrood, Iran
E. Ebrahimi - IC Design Research Laboratory, Electrical & Robotic Engineering Department, Shahrood University of Technology, Shahrood, Iran

Low power consumption, low chip area and fabrication in the standard complementary metal oxide semiconductor (CMOS) process are vital requirements for oscillators used in low-cost bio-implantable and wearable devices. Conventional ring oscillators (ROs) are good candidates for using in biomedical applications. However, their oscillation frequency strongly depends on the temperature. In this study, a temperature compensated ring oscillator with low power consumption is proposed. The transistors of the proposed ring oscillator operate in the subthreshold region to achieve a low power and low voltage performance. Since, in the subthreshold region, the oscillation frequency of a conventional ring oscillator increases with increase in the temperature, two current sources are used to power the proposed subthreshold ring oscillator: a temperature independent current source and a complementary to absolute temperature (CTAT) current source. In the proposed circuit, the CTAT current forms a small part of the total supplied current and its duty is to compensate for the oscillation frequency deviation. Two prototypes of the subthreshold ring oscillator were designed and simulated for a target frequency of ۱MHz using commercially available ۰.۱۸µm RF-CMOS technology. The thermal coefficient (TC) of the uncompensated ring oscillator was ۲۴۰۰ ppm/ºC from -۴۰ºC to ۸۵ºC, though applying the proposed technique reduces the TC of the ring oscillator to ۸۰.۴ ppm/ºC with total power consumption as low as ۱۴.۵µW.

Complementary to Absolute Temperature, Current Reference Ring Oscillator, Subthreshold, Thermal Compensation