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AR# 1897

XC3000/XC3000/XC4000/XC5200 - Logic cells and the FPGA Density Cross Reference Guide

Description

Keywords: logic, cell, clb

Urgency: Standard

General Description:
What are Logic Cells? How do they relate to different device architectures including those of different vendors?

Solution

A "logic cell" (LC) is the primary building block of today's high-density FPGAs and is the best measure of a device's maximum logic capacity. Logic cell utilization will vary by design and product family, thus making the total number of Logic Cells the best "first pass" capacity comparison metric.

A logic cell consists of a 4-input lookup table and a Flip-Flop.

If each 4-input LUT and each register are considered 1/2 of a logic cell, and a 3-input LUT has 3/4 the functionality of a 4 input LUT, then each 3 input LUT can be considered 3/8 of a logic cell. Thus each XC4000 has 2.375 logic cells.

For more information, as well as a comparison of different vendors and architectures, refer to:
http://www.xilinx.com/bvdocs/appnotes/xbrf011.pdf
AR# 1897
Date Created 08/31/2007
Last Updated 08/12/2004
Status Archive
Type ??????