Which of the following describes a 2×4 decoder?

a)-two and gates, four inverters, and one or gate.
b)-two inverters, four and gates, and one or gate.
c)-two or gates, four and gates, and one inverter.
d)-two inverters, four or gates, and one and gate.
e)-two inverters, four and gates, and no or gates.

A decoder is a circuit which has n inputs and 2n outputs, and outputs 1 on the wire corresponding to the binary number represented by the inputs. For example, a 2-4 decoder might be drawn like this:

and its truth table (again, really four truth tables, one for each output) is:

i1  i0  d3  d2  d1  d0

0 0 0 0 0 1

0 1 0 0 1 0

1 0 0 1 0 0

1 1 1 0 0 0

Explanation:

The following circuit generates all four minterms from two inputs, and implements the 2-4 decoder.

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