[sdiy] FPGA multiplier

[James Patchell]

Boy, now you have opened up a can of worms....

16 x 16 multipliers are a trivial issue in todays FPGA's.  Pins really 
don't come into the equation all that much any more.  The minimum size 
package you can get most FPGA's in number in the 100+ pins.  And, if you 
are thinking in terms of just putting a multiplier in the thing, you might 
be thinking a bit narrow.  You really need to be thinking about how big of 
a system can I put in an FPGA....

Right now, I would say that the Xilinx Spartan 3 chips are you best bang 
for the buck.  These chips are very inexpensive.  I would be willing to bet 
that we are talking about $20 US for a fairly modest chip....(Spartan 3 
chips start at 50,000 gates, if I remember correctly).  Also, the spartan 3 
chips have dedicated 18x18 bit multipliers.

The 50K part has 4 of these multipliers, the 200K part has 12 multipliers 
in it.....that is a lot of multipilers.  Plus, with a 200K part, you can 
implement a DSP of proportions that 10 years ago you could only dream about.

Plus, you can download the Webpack for free and write the code in either 
verilog or vhdl or schematic capture, or all three at once...it is a very 
nice software package.

And believe me, 200K gates is an unbelievable number of gates.

There is one drawback...you need to be very familiar with designing high 
speed logic circuits.  Many of the klugey things you can get away with 
using CD4xxx series logic will not work in a xilinx gate array.  The logic 
in the spartan 3 can run up to about 300MHz, and the compilers will let you 
do klugey things.

Still, using an FPGA is the way to go...I have many ideas I would like to 
try myself...time is my only limiation... :-(
At 05:50 PM 12/6/2003 +0100, jbv wrote:
>This one if for FPGA gurus :
>if I need to implement a 16 x 16 bits logic
>multiplier with 32 parallel outputs and latched
>i/o on Xilinx or Altera systems, what kind of
>chip am I supposed to use ?
>The question concerns actually the type of chip
>(package, number of pins, size, PCB room) that
>can be used. I'd like to compare with existing
>multiplier chips...
>
>Thanks,
>JB

         -Jim
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