Commonly available digital logic OR gate IC’s include:.In ECL logic the unused inputs are kept open or floating.In a multiple-input OR gate, the unused inputs can be connected to:.OR gate follows both Commutative and Associative law.Aįrom the above truth table, the circuit diagram represents an OR gate i.e. The input X is connected to output Y when at least one of the switches A and Switch B is closed. Switch Diagram for OR gate is as follows: Next, if both of the inputs A and B are grounded or given logic low/0V, no voltage will appear across the output and out switches to logic low or zero.Īlso, learn more about Ex-NOR Gate, here. Now if both of the inputs are given with logic high/”1″, both diodes will be forward biased. When any one of the inputs is given with logic high, the respective diode becomes forward biased and works as short-circuited hence logic high or ‘1’ will appear at output Y. In the above circuit, if A and B are applied with logic low or 0V, there will be no voltage at the output. Now moving towards the diode circuit of the OR gate. Hence we can conclude that if one or both the inputs are at a logic high value then the output we get is high, otherwise low. The current at this condition takes a short circuit path and flows from both of the transistors which procure high at the output. When both the input is at logic high, say A=1 and B=1, then both transistors are in a saturation state and serve as a short circuit. Now the current passes through the second transistor and we notice the output as high. Similarly, if we provide A=0 and B=1 then the first transistor goes in cutoff while the second transistor is in saturation. Hence all current passes through the first transistor to the output and the output switches to logic one. The first transistor has a voltage greater is in the forward bias acting as a short circuit. In the next case if we consider one input as logic high and the other as a logic low, assume A=1 and B=0. Initially when both the inputs are at logic low both the transistors turn off and go into their cutoff state acting as an open switch which further leads to the output as active low/logic 0. The transistors here are arranged in parallel and their bases are adopted as input. Let us understand the circuit operation of an OR gate using transistors. The output of a three-input OR Logic gate is zero if all the three inputs are at logic zero levels on the other hand the output is one if anyone/two/ three inputs are at logic high.Ĭheck the various types of I nput and Output Devices here. The truth table for three input OR Gate is as shown: The Boolean Expression for a three-input OR gate is Y = A+B+C 3 Input OR Gate SymbolĪs the name implies, if instead of two inputs there are three inputs, this changes the logical symbol and truth table of the OR gate as shown in the symbolic representation. Learn about various types of Computer Storage Devices here. The truth table of a two-input OR gate is as shown. The function of a logical OR gate efficiently finds the maximum between two binary digits, just as the complementary AND function determines the minimum and generates the output accordingly. The Boolean Expression for a two-input OR gate is Y = A+B The symbolic representation of the OR gate is as shown below with A and B as input and Y as the output. Similar to an AND gate an OR gate may have any number of input probes but only one output. If neither input is high, a logic low output (0) results. A logical OR operation has a high output/logic 1 if one or both the inputs to the gate are logic high.

OR Gate SymbolĪn OR gate performs logical OR(addition) operations. This article on OR gate brings to you an introduction to OR GATE by the symbol, truth table for two and three inputs, circuit diagram with images and more.Ĭheck the Components of Computer here.

OR gate is included in the basic three gates.

Circuit coder test 3