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 .

 

If you send half of the inputs to one of the 2x4 decoders and the other half to the second, which pairs of outputs (one from each decoder) are HI for each possible 4-bit input combination? How could you use an AND gate to produce a single HI signal for each one of those combinations?