Cadence Design Systems was founded in 1988 by the merger of SDA Systems and ECAD, Inc. For years it had been the largest company in the EDA industry. Today, most of the universities offering VLSI design related courses, expose their students to EDA tools by Cadence.
Cadence happens to be the most preferred design tool for Analog VLSI. The Virtuoso Schematic and Layout editors along with Spectre Simulator is the considered the industry standard. This website deals with in depth tutorials for Virtuoso and its associated tools.