Study and Implementation of a Pvt Insensitive Cmos Oscillator

Today virtually every consumer electronics device contains one or more integrated circuits (ICs) that require clock signal generation. This signal must present a certain level of frequency stability even in non-nominal conditions. Ideally, the clock generator block should exhibit a reasonably low frequency deviation when subject to process, voltage, and temperature (PVT) variations, such as changes in temperature caused by device heating, low power supply ripple rejection ratio (PSRR), or process parameter fluctuations during the fabrication process. Typically, clock references are based on crystal oscillators which rely on piezoelectric materials to generate precise frequencies. However, with ever decreasing semiconductor process nodes and a growing trend in system integration, the use of external components like crystal references increases size and cost. The use of simple oscillator topologies so that they can be fully integrated on-chip is possible, but does not provide any compensation in regards to PVT changes. As such, to realize a more reliable oscillator, a compensation scheme must be integrated so that the oscillation frequency can be stabilized. The main objective of this work is the CMOS circuit implementation of a PVT insensitive oscillator suitable for full on-chip integration. A study on the key design considerations for realization of PVT insensitive oscillators is also presented. The covered topics include an overview on the performance of several oscillator topologies implemented in different process nodes, as well as an analysis of selected compensation circuits. An alternative methodology for the tuning of the compensation circuits is proposed, comprising an automatic optimization algorithm. A novel process compensation circuit is also presented, focusing on the concept of orthogonal PVT compensation. Finally, a complete implementation of a fully integrated PVT compensated oscillator in a deep-submicron process node is presented. It uses a novel open-loop temperature and process compensation circuit and comprises a current starved ring oscillator, as well as an on-chip voltage reference.