Hello all,

Does anyone know how to construct a multiplier circuit using just logic gates?? Say an 4x4 bit or an 8x8 bit multiplier?

Thanks

 

What kind of speed do you need? I imagine it would be pretty complex to do using discrete logic gates, it might make more sense to use a micro controller

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I agree, using a controller would be alot easier, but that is not an option in my case. The speed is not of great concern, any decent speed would suffice.

Thanks.

 

Well, think about how you would do multiplication on paper. I've been trying for about 20 minutes to explain this with words but I just can't, so perhaps an example will suffice:

So then to implement this in an unclocked design, you'd want to do all of the AND-ing simultaneously and feed it all into a big adder.

If you've got a clock and want to save some parts (or you want to add one just to save some parts) then you can do that sequentially with n AND gates (for an nxn multiplier), an n-bit adder, a 2n-bit shift register to store one of the operands and the result, and an n-bit shift register to store the other operand. The clocked circuit also requires some control logic, which (obviously) varies based on the number of bits involved.

I don't have anything I can draw something with right now, but I'll try to get back to this thread tonight (assuming I can get my computer running) to explain better or draw something.

 

In normal way,You must construct a truth table,An 4*4 bit multiplier need eight-bit outputs,Construct equations for each out bit,Simplify the equations.Then you can build the circuit only with logic gates.
There is an easy way to build the circuit,An 4*4 bit multiplier has two four-bit inputs and eight-bit outputs,You can use a 256*8 bit ROM to do this,high four-bit of address and low four-bit address are inputs,DATA of the ROM is outputs of the multiplier.

 

Sounds like school work to me. If it's not, provide some freegin details.
When someone asks you what kind of speed you need and you respond with 'decent speed' you've provided ZERO information. If you just need a 'decent speed' use a 'decent micro controller' or explain why your design isn't able to incorporate them because no real world application would have that pre-requisite.

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Of course it is school work!!! The majority of the posts on this site are from students requesting information regarding school projects, homework, lectures etc.

And yes, a real world application WOULD have that pre-requisite, its called VLSI design!!

 

Try googling "Wallace Trees"