When we are comparing two binary or BCD values or variables against each other, we are comparing the “magnitude” of these values, a logic “0” against a logic “1” which is where the term Magnitude Comparator comes from.Īs well as comparing individual bits, we can design larger bit comparators by cascading together n of these and produce a n-bit comparator just as we did for the n-bit adder in the previous tutorial. Secondly, the output condition for A = B resembles that of a commonly available logic gate, the Exclusive-NOR or Ex-NOR function (equivalence) on each of the n-bits giving: Q = A ⊕ Bĭigital comparators actually use Exclusive-NOR gates within their design for comparing their respective pairs of bits. Firstly, the circuit does not distinguish between either two “0” or two “1”‘s as an output A = B is produced when they are both equal, either A = B = “0” or A = B = “1”. You may notice two distinct features about the comparator from the above truth table. For example, a magnitude comparator of two 1-bits, ( A and B) inputs would produce the following three output conditions when compared to each other. Bn, etc) and produce an output condition or flag depending upon the result of the comparison. An, etc) against that of a constant or unknown value such as B (B1, B2, B3, …. The purpose of a Digital Comparator is to compare a set of variables or unknown numbers, for example A (A1, A2, A3, …. Magnitude Comparator – a Magnitude Comparator is a digital comparator which has three output terminals, one each for equality, A = B greater than, A > B and less than A < B Identity Comparator – an Identity Comparator is a digital comparator with only one output terminal for when A = B, either A = B = 1 (HIGH) or A = B = 0 (LOW) There are two main types of Digital Comparator available and these are. The digital comparator accomplishes this using several logic gates that operate on the principles of Boolean Algebra. The binary or digital comparator can be constructed using standard AND, NOR and NOT gates to compare the digital signals present at their input terminals and produce an output depending upon the condition of those inputs.įor example, along with being able to add and subtract binary numbers we need to be able to compare them and determine whether the value of input A is greater than, smaller than or equal to the value at input B etc.
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