Logic Design for Array-Based Circuits

by Donnamaie E. White

Sizing the Design - Selecting the Array

Cell Capabilities

Cells for each array have different capabilities. The cells for different array series, same technology (bipolar, BiCMOS or CMOS), from the same vendor may also differ widely in the approach used in their design and in their functional complexity.

Example - AMCC Cell Capabilities

An internal cell for the Q5000 Series can support a complex D flip/flop, a 3:1 MUX and D flip/flop, a triple latch, two simple (no RESET, single output) D flip/flops, or triple 2:1 MUXs with common select. The Q20000 Series internal cell alone cannot support a D flip/flop. S- and L-option D flip/flops use two cells while H-option D flip /flops require three.

The Q20000 Series internal cell is roughly comparable to a half-cell for the Q5000 Series if size of function alone is considered as the basis for comparison. The logic cell for the Q20000 Series is defined as the smallest partition possible and each internal cell supports one Turbo macro output. Turbo is a Q20000 feature that provides high drive (18 loads) with less power and less skew.

Cell Types and Resources

The vendor data sheet and design guide or design manual should clearly identify cell types and the number of each on each array in the series. Any restrictions in the use of the cells, either utilization limits or cell count limits should also be readily available.

Included in these descriptions should be a measure of cell functionality, either in a table summarizing the array cell capability or through the macro library documenta tion.

As a part of the cell resources identification, the vendor should be supply a clear description of the fixed power and ground pads and procedures to added additional power and ground pads. These added power and ground macros usually reside on an I/O cell and pad and can affect the number of cells left for circuit signals.

Example - AMCC Cell Types

The basic AMCC logic array is composed of two classes of cells: the internal cells, which is composed of logic (L) and memory (M) cells for bipolar arrays or basic (B) cells for BiCMOS arrays; and the perimeter cells composed of input, output or bidirec tional (I/O) cell. Older AMCC arrays had buffer cells internally and specialized input or output-only interface cells. An array may or may not have specialized I/O cells. AMCC cell types are shown in Table 3-7.

The QM1600S (now the QM1600T) was the first of the AMCC arrays to incorporate memory on a logic array.

Table 3-7 Cell Types

INTERNAL: Logic, Basic, Buffer, Memory

PERIPHERAL: Input, Output, I/O, Special-I/O

Refer to the cell resources table for an approximate idea of the array cell capacity for three series and note the differences. Cell resources for the Q24000 Series are shown in Table 3-8, for the Q5000 Series in Table 3-9 and for the Q20000 Series in Table 3-10. Note that no two series are alike!

Table 3-8 AMCC Q24000 Series Arrays - Cell Resources

Array Name Internal B Cells I/O Cells Pads

Q24280 6880 300 256

Q24140 3360 226 226

Q24091 2268 160 160

Q24060 1440 132 132

Q24021 540 80 80

Q24008 190 66 44

Usage restrictions: Refer to the Q24000 Design Manual for details.

Table 3-9 AMCC Q5000 Series Arrays - Cell Resources

Array Name Internal L Cells I/O Cells Output Limit Memory Cells

Q5000T 352 160 120 -

Q3500T 242 120 - -

Q1300T 84 76 - -

QM1600T 114 106 - 2 (1240 bits)

Table 3-10 AMCC Q20000 Series Arrays - Cell Resources

Array Name Internal Cells I/O Cells (For Signals) I/O Cells (Fixed) (1) Signals - PLL Related Signals - Loop FIlter (2)

Q20120 3414 198 4 - -

Q20080 2044 162 4 - -

Q20045 1227 128 4 - -

Q20P025 595 76 4 13 8

Q20025 733 100 4 - -

Q20P010 177 54 4 13 8

Q20010 267 66 4 - -

* Two pads are used by the AC Speed Monitor and two by the thermal diode.
** Only for the largest arrays, 100_LDCC for the Q20P010 and 132_LDCC for the Q20P025
Add last four columns to find total I/O cells and pads.

Array Name ECL Outputs Limit TTL Outputs Limit PLL Power/Ground Power/Ground (1)

Q20120 172 100 - 78

Q20080 130 80 - 52

Q20045 100 64 - 52

Q20P025 45 (2) 45 (2) 8 26

Q20025 80 48 - 36

Q20P010 23 (3) 23 (3) 8 20

Q20010 50 24 - 32

(1) Add last two columns to find total number of fixed power and grounds.
(2) 51 for external loop
(3) 34 for external loop