How to Build a 4x16 Decoder Using ONLY two 2x4 decoders ?

[dondon93]

Help please , I am new to circuits and decoders and i need some serious help !!

How to build a 4x16 Decoder Using ONLY two 2x4 decoders ?

Following the steps we took in the lecture , we are supposed to build a 4x16 Decoder . So here taking k to be 4 , k is even , so we will have 2^k so 2^4 = 16 AND gates & 2 decoders each of size 2^(k/2) so 2^2 = 4 .

So we have 16 AND gates & two 2x4 decoders. Each 2x4 decoder has 4 AND gates so we have 8 AND gates that should be connected to the 16 AND gates , how do I do that ????

Your help is highly appreciated .

[WardC]

If we agree that a decoder has 'n' bits or wires of input, and 2^n bits or wires of output,

then a 2x4 has 2 inputs and 4 outputs.

Two of them have 4 inputs and 8 outputs.

If you need 4 inputs and 16 outputs, the question must allow more than just the qty 2, 2x4 decoders, for that isn't even enough PINS to have 16 outputs (which a 4x16 decoder would have).

you mention "the lecture" but not the process. 16 and gates ... doesn't make sense.

A single 2 x 4 decoder cannot be made with and gates. This is because you have to do "not".

assuming the outputs are 0, 1, 2, 3, corresponding to inputs like binary numbers of 00, 01, 10, 11,
then output 3 is (input 1) and (input 2)
but all others require a not or nand:
output 0 = (not input 1) and (not input 2)
output 1 = (input 1) and (not input 2)
output 2 = (not input 1) and (input 2)

If there is some magic trick to doing it (such as if enough time has passed since posting that you got the answer elsewhere) please reply. Thanks!