Tag: VLSI/VHDL Training in Bhopal

What is VLSI?

VLSI (Very-large-scale integration) is a process that means to create integrated circuits by combining thousands of transistor-based circuits into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Nearly all modern chips employ VLSI architectures.

The first semiconductor chips held two transistors each. Subsequent advances added more and more transistors, and, as a consequence, more individual functions or systems were integrated over time. Current technology has moved far past this mark and today’s microprocessors have many millions of gates and billions of individual transistors.

This is the field which involves packing more and more logic devices into smaller and smaller areas.Thanks to the FPGA Board and its VLSI, circuits that would have taken boardfuls of space can now be put into a small space few millimeters across! This has opened up a big opportunity to do things that were not possible before. VLSI circuits are everywhere … your computer, your car, your brand new state-of-the-art digital camera, the cell-phones, and what have you. All this involves a lot of expertise on many fronts within the same field, which we will look at in later sections.

THE VLSI DESIGN PROCESS

A typical digital design flow is as follows:

Specification
Architecture
RTL Coding
RTL Verification
Synthesis
Backend
Tape Out to Foundry to get end product….a wafer with repeated number of identical Ics.

A typical analog design flow is as follows:

In case of analog design, the flow changes somewhat.
Specifications
Architecture
Circuit Design
SPICE Simulation
Layout
Parametric Extraction / Back Annotation
Final Design
Tape Out to foundry.

MOST OF TODAY’S VLSI DESIGNS ARE CLASSIFIED INTO THREE CATEGORIES:

 

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1. Analog: 
Small transistor count precision circuits such as Amplifiers, Data converters, filters, Phase Locked Loops, Sensors etc.

2. ASICS or Application Specific Integrated Circuits: 
Progress in the fabrication of IC’s has enabled us to create fast and powerful circuits in smaller and smaller devices. This also means that we can pack a lot more of functionality into the same area. The biggest application of this ability is found in the design of ASIC’s. These are IC’s that are created for specific purposes – each device is created to do a particular job, and do it well. The most common application area for this is DSP – signal filters, image compression, etc. To go to extremes, consider the fact that the digital wristwatch normally consists of a single IC doing all the time-keeping jobs as well as extra features like games, calendar, etc.

3. SoC or Systems on a chip: 
These are highly complex mixed signal circuits (digital and analog all on the same chip). A network processor chip or a wireless radio chip is an example of an SoC.

What is VHDL (vhsic hdl).

VHDL is a hardware description language used in electronic design automation to describe digital and mixed-signal systems such as field-programmable gate arrays and integrated circuits. VHDL can also be used as a general purpose parallel programming language.

Here V stands for ‘ very high speed integrated circuit & HDL stands for ‘ hardware descriptive language’. Since it is hardware descriptive language we can’t say it as a software.
History
VHDL was originally developed for the U.S Department of Defense in order to document the behavior of the ASICs (Application specific ICs) that supplier companies were including in equipment.
The initial version of VHDL, designed to IEEE standard 1076-1987, included a wide range of data types, including numerical (integer and real), logical (bit and Boolean), character and time, plus arrays of bit called bit_vector and of character called string.
A problem not solved by this edition, however, was “multi-valued logic”, where a signal’s drive strength (none, weak or strong) and unknown values are also considered. This required IEEE standard 1164, which defined the 9-value logic types: scalar std_logic and its vector version std_logic_vector.
The updated IEEE 1076, in 1993, made the syntax more consistent, allowed more flexibility in naming, extended the character type to allow ISO-8859-1 printable characters, added the XNOR operator, etc.[specify]
Minor changes in the standard (2000 and 2002) added the idea of protected types (similar to the concept of class in C++) and removed some restrictions from port mapping rules.
In addition to IEEE standard 1164, several child standards were introduced to extend functionality of the language. IEEE standard 1076.2 added better handling of real and complex data types. IEEE standard 1076.3 introduced signed and unsigned types to facilitate arithmetical operations on vectors. IEEE standard 1076.1 (known as VHDL-AMS) provided analog and mixed-signal circuit design extensions.
In June 2006, the VHDL Technical Committee of Accellera (delegated by IEEE to work on the next update of the standard) approved so called Draft 3.0 of VHDL-2006. While maintaining full compatibility with older versions, this proposed standard provides numerous extensions that make writing and managing VHDL code easier. Key changes include incorporation of child standards (1164, 1076.2, 1076.3) into the main 1076 standard, an extended set of operators, more flexible syntax of case and generate statements, incorporation of VHPI (interface to C/C++ languages) and a subset of PSL (Property Specification Language). These changes should improve quality of synthesizable VHDL code, make test benches more flexible, and allow wider use of VHDL for system-level descriptions.
In February 2008, Accellera approved VHDL 4.0 also informally known as VHDL 2008, which addressed more than 90 issues discovered during the trial period for version 3.0 and includes enhanced generic types. In 2008, Accellera released VHDL 4.0 to the IEEE for balloting for inclusion in IEEE 1076-2008. The VHDL standard IEEE 1076-2008 was published in January 2009.