Temperature Compensation in CMOS Ring Oscillator

Sammanfattning

A digital system is often required to operate under a specific frequency. A ring oscillator can be helpful in this circumstance because it can generate a signal with a specific frequency. However, a ring oscillator is also sensitive to the environment temperature. With the increasing requirement of accuracy and stability, many approaches appear worldwide to make a temperature-insensitive ring oscillator. This thesis project presents an approach to compensate the temperature effect on a Current Starved Ring Oscillator(CSRO). More concretely, we researched how to achieve temperature compensation for CSRO in a digitally-controlled configuration. A Phase Frequency Detector (PFD) block is adapted to sense the frequency difference between the reference frequency and CSRO frequency. Two Charge Pumps (CP)are used to quantify the difference in voltage signal. A Dynamic Comparator block compares the signals from CPs. A following Bidirectional Counter block can count up or down to change the current in CSRO by a four-bit signal. In the end, the CSRO can generate an oscillating signal at the appropriate frequency after some adaptation time. This proposed circuit was realized with AMS 0.35 um CMOS technology and simulated using the Cadence tools. Power consumption, temperature compensation analysis and voltage supply compensation analysis under different temperatures are also performed in the project.