Abstract—In this paper, we present the characterization of the Ring oscillator for submicron technology in terms of the first order design equations of the MOSFETs, and we arrive at the extent upto which the short channel effects influence the oscillating frequency. In addition, a solution is suggested to reduce the duration of metastability upto 50%. The Ring oscillator is designed from 3-stage till 15-stage, and the circuit simulations are performed, with the oscillation frequencies ranging from 1.03 GHz till 5.38 GHz. Additional observations are noted by varying the device widths and lengths. It is found that the frequency of operation is independent of the device width, and is inversely proportional to the square of the device length. As a result, the equation derived using the first order behavior can be utilized for obtaining the frequency of the Ring oscillator circuits in general, by including an empirical constant. Index Terms—Integrated circuit modeling, Ring oscillator, Added delay, SPICE, Parasitic capacitance, MOSFET circuits, Circuit stability. I. INTRODUCTION ING oscillator has been widely used in Voltage Controlled Oscillators in the range of Gigahertz, as the LC oscillators have the limitation of larger chip area due to the spiral inductors, and in addition, have a relatively smaller tuning range [1], [2]. Unlike the LC oscillator, the Ring oscillator’s frequency of operation depends on the delay of each inverter stage, and that particular delay depends on the RC characterization of the MOSFETs. When the frequency requirement is in GHz, it is desirable to have accurate design equations for the Ring oscillator. The circuit diagram of a 3- stage Ring oscillator is shown in Fig. 1. The Ring oscillator requires two transitions at the output to complete one cycle of oscillation. Therefore, the conventional method to calculate the frequency of operation [3] is to Aravinda Koithyar is with the Department of Electronics and Communication, Amrita School of Engineering, Amrita Vishwa Vidyapeetham University, Kasavanahalli, Carmelaram P.O., Bengaluru 560035 India (phone: 080-25183700; e-mail: aravindake@gmail.com). T. K. Ramesh is with the Department of Electronics and Communication, Amrita School of Engineering, Amrita Vishwa Vidyapeetham University, Kasavanahalli,CarmelaraM.Bengaluru,India(tk_ramesh@blr.amrita.edu). express it in terms of the propagation delay (td) and the no. of stages in the oscillator (N), as in (1) , (1) Fig. 1. General diagram of a 3-stage Ring oscillator For operating in the range of Gigahertz, no other RC components are required, and hence the propagation delay is equal to the inverter stage delay. For obtaining the inverter delay, the inverter is modeled in terms of its gate capacitance [4], [5]. With this method, as td is given by (CtotalVdd)/ID, the difficulty arises in accurately computing the value of td, because of the computation of the switching current and the equivalent capacitance. Another alternative is to model the circuit of Ring oscillator in terms of the switching time constants, tPLH and tPHL. Therefore, Baker [6] rewrites (1) as, (2) As this method does not require the value of the switching current, this is more useful for the designer, and it includes the miller capacitance effect [7], which is included by Baker. But this model provides only the total capacitance, Ctot, with reference to the switching point as, 2.5(COXp+COXn), leaving the resistance calculations to the designer [8], [9]. Moreover, this model is meant for the micrometer technology, and hence the submicron parasitic effects are ignored. Hence, an effort is made in this paper, to overcome these limitations. This paper is organized as follows – Section II deals with the switching model of the Ring oscillator, considering the parasitic switching effects. Based on this model, the derivation of the system equation is discussed in Section III. The circuit simulation and the metastability issues are elaborated in Section IV, followed by the verification of the system equation in Section V. Finally, conclusion of the results obtained is discussed in Section VI. Characterization of Submicron Ring Oscillator using the First Order Design Equations Aravinda Koithyar and T. K. Ramesh R 1227 International Conference on Communication and Signal Processing, April 6-8, 2016, India 978-1-5090-0396-9/16/$31.00 ©2016 IEEE