Combinational Circuit to detect the largest of three inputs

Question

Using combinational circuits, such as AND and OR, including MUX's and Decoders, how do you design a circuit that has 3 8bit inputs with the output as the largest of the 3 inputs?

||...||       ||...||       ||...||  <- Inputs
----------------------------------
|                                |
|                                |
----------------------------------
              ||...||                <- Output

What would the circuit need to look like in order to achieve such an outcome?

Answer 1

We could reduce the problem to find a combinational circuit that has 2 8bit inputs with the output as the largest of the 2 inputs. If we solve this problem, we can basically duplicate this circuit we found and use the inputs as being the output from the first comparison and the third 8bit input. So, let's do it.

First, we could make our circuity like this:

A               B
|               |
|               |
-----------------
| Comparator    |->-----------------
-----------------                  |
                                 -----
                                 |Mux|
                             A->-| 0 |
                                 |Out|->- Bigger
                             B->-| 1 |
                                 -----

The comparator is a module that will output 1 if B > A, 0 otherwise. This module can be built based on any simple circuit available online.

This solve the problem with only two inputs. So you can use this module and build new ones with as many inputs as you desire.