VLSI designs

Very Large Scale Integration is one wicked field to be studying in school. I find it very exotic to work with cmos and mask design for the layering process on the silicone waffle. Free downloads included of designs, microwind mask files and icarus verilog code.

The understanding of NMOS/PMOS functionality is critical. Who does the gate command the drain-source current? When is it blocked, when is it saturated or in linear behavior? After this  you could get a look on popular designs of basic logic functions – and, or, xor and the transmission gate. Here’s the xor gate:

If A is 1, the output of the right inverter outputs 0 (ground). This turns the circuit linked to B in an CMOS inverter, with pmos source to Vdd and Nmos source to ground, thus outwire is non-b. The two transistors in the center act as a T-Gate with output in high impedance (Z). When A is 1, XOR outputs non-b. 1^0 = 1, 1^1 = 0

If A is 0, the right inverter outputs 1. Now the CMOS where B is linked is blocked (hanging), while the two transistors in the center act as a transmission gate, outputing B. Hence, when A is 0, the output of XOR gate is B. 0^0 = 0, 0^1 = 1.

Here you have a screenshot of the masks design in Microwind:

The archive also includes Icarus Verilog code for the and, xor, or, tgate and 4bit right rotate  gates, altogether with mask files and screenshots of designs and simulations.

The Right Rotate gate features a 5 input pins – the four data bits and an enable wire. When enabled, it outputs the 4 bits rotated (1 bit shift with the carry placed in the MSB). When enable=0, the four bits are output without changes (identity gate). Some noise in microwind/orcad simulation when enable is null. The gate is basically a collection of transmission gates commanded by enable wire (the “optimized” verilog source in archive). I have also included a version using mux-s, but that one makes use of far too many transistors.

Free Download: zip VLSI designs
(1.52 MB, zip) - Complete designs of AND, OR, XOR, TGATE, 4bit Right Rotate gates: CMOS designs, microwind mask files, icarus verilog sources. 1696 downloads

  • http://pulse.yahoo.com/_6OORJDJFGU2FJXHY2HJ6RV6WJI Anms Anms

    Very helpful, thank you.

  • chriss

    that’s a great kick-start!