If two input signals are applied to the two input terminals the operation is referred to as “double-ended”.The output obtained is thus driven by both the collectors. In single-ended operation a single input applied, drives both the transistors due to the common-emitter connection.If an input signal is applied to either of the input terminals to the other input terminal connected to ground, the operation is called “single-ended”.It can be noted that a positive input at pin #3 gives a positive output, hence the name non-inverting input terminal. The reduction in V BE2 causes the emitter current I E2 to decrease and consequently I C2 also reduced.
The base of Q2 is grounded, so the positive voltage at its emitter causes a reduction in its base-emitter voltage V BE2. Since Q1 and Q2 emitters are connected together, the emitter of Q2 also gets pulled up by the positive input at the non-inverting terminal.
When a positive voltage is applied to the non-inverting input terminal, the base of Q1 is pulled up by the input voltage and its emitter terminal follows the input signal. Therefore, I E1 + I E2 = (V EE – V BE) / R E If both Q1 and Q2 bases connected to ground, The emitter current is given by the relation, If both transistors base terminals are connected to ground, the emitter currents I E1 and I E2 are equal and both I E1 and I E2 flow through the common resistor RE. Where, V RC is the voltage across the resistor R C and V BE3 is the base-emitter voltage of transistor Q3.Īssume that the transistors Q1 and Q2 are matched transistors i.e., they have equal V BE levels and equal current gains. The output of the basic op-amp circuit V OUT is given as, Transistor Q3 operates as an emitter follower and provides low output impedance. Transistors Q1 and Q2 forms a differential amplifier, where the difference input voltage is applied to the base terminals of Q1 and Q2. Practical op-amp circuits are much more complicated than the above shown basic op-amp circuit. An op-amp has a differential amplifier input stage and emitter follower output stage. The basic circuit of an operational amplifier is as shown in the figure above. Op-amps exhibit little dependence on temperature-changes or manufacturing variations, which makes them ideal building blocks in electronic circuits. Op-amps are used for a variety of applications such as AC and DC signal amplification, filters, oscillators, voltage regulators, comparators and in most of the consumer and industrial devices. Today, op-amps are very popular building blocks in electronic circuits. The operational amplifier is called so because it has its origins in analog computers, and was mainly used to perform mathematical operations.ĭepending on its feedback circuit and biasing, an op-amp can be made to add, subtract, multiply, divide, negate, and interestingly even perform calculus operations like differentiation and integration.