Most efficient logic for 10 bit decoder

[bsun2]

Hello,
What is a good way to implement the logic for a 10 bit (10 to 1024) decoder? A method that is systematic, has low fanout, fanin, propagation delay, and capacitance is desired. It would be helpful if you could find some websites that implement this design.

Thanks,
James

 

[Kenneth Mann]

To be sure, what are you looking for? An A to D converter, for example, or the logic to take a ten-line input and from it, select and enable one of 1024 output lines (that's awfully big)? If it's the latter, you can (simply) take two three-to-eight decoders, and a four-to-sixteen line demux, and feed the proper outputs of these to 1024 three-input NANDs (that's an awful lot of NANDs). For a distributed system, that wouldn't be too bad, but I don't think you'd want to derive that many signals in one place.

As an alternative, if it's distributed (for example, on thirty two cards, each putting out thirty two lines) you could, for example, put two four-to-sixteen line decoders on each, and include the proper select logic for each of the decoders.

Fan-out for the for the ten signal drive lines would be a consideration. Each of the four low-order lines would have to drive sixty four decoder inputs (possibly OK for CMOS, but I wouldn't want to try that directly with TTL; buffering would be needed - - probably at the both - input to each of the daughter boards and the output from the main board). This, by the way, is the type of problem typically encountered when designing memory arrays.

If it all has to be done from a single board or module, you might look to using some form of programmable logic.

KM

 

[Kenneth Mann]

Another driving factor, is what do you intend to do with the output lines? If it is to drive something like a set of commands (on/off, etc.) or to enable sampling inputs (telemetry, etc.), considerations like those above are OK. If, however it is to drive something like a scanned LED display, etc., additional simplification might be possible.

KM