The IEEE 1076.1 Working Group has been created under the auspices of
the IEEE Design
Automation Standards Committee (DASC) with the charter to develop
and to maintain analog and mixed-signal extensions to the VHDL
language. These extensions enhance VHDL such that it can support the
description and simulation of circuits and systems that exhibit
continuous behavior over time and over amplitude.
The IEEE Standard 1076.1-1999 has been approved on March 18,1999 and the 1076.1 Language Reference Manual is available from the IEEE Standards web site. VHDL 1076.1-1999 is a strict extension of VHDL 1076-1993, i.e. it includes the full VHDL 1076-1993 language. Extensions have been carefully designed to maintain the existing philosophy and to smoothly integrate new language definitions.
This is the official site of the 1076.1 Working Group. It provides a lot of information about the working group organization, the development and the maintenance of the 1076.1 language. It also provides links to other related sites, including available VHDL 1076.1 tools.
A final note: VHDL 1076.1 is also informally known as VHDL-AMS where AMS stands for "Analog and Mixed-Signal". The two notations are freely mixed in this site but they refer to the same language.
A list of other EDA Working Groups may be found here.