Since this reference is associated with (-) pin of the IC, if the voltage Vin at the (+) input goes higher than this reference or becomes more positive than the reference, will force the output Vo to switch to its positive saturation level. Using the voltage divider network formula, we can calculate the refernce voltage value on the (-) input pin of the IC. In the figure we can see an op amp circuit working with a positive reference set at its inverting input pin (-). #741 op amp multisim how to#In the following example we will learn how to effectively use an op amp as a comparator And, in case required the reference can be also connected either to the positive or the negative supply lines, while the input signal is applied at the other input pin. The above explanation and the waveform presented in the image clearly indicates the digital response of the output for a linearly varying input signal.įor normal applications, the reference level doesn't have to be at 0 V, rather can be any positive level as per the requirement. Again, this condition is maintained as long as the Vin input signal stays below the 0 V reference level. Now, as soon as the signal level drops a shade below the 0 V reference, the output is driven to its lower level of saturation. This condition is sustained for so long as Vin signal stays above the 0 V reference. When the input Vin moves even a millivolt over the 0 V reference, the difference is amplified by the internal high gain op amp of the IC, causing the output to go high at the output positive saturation level. This alternately varying sinusoidal signal causes the output to switch between high and low output states, as indicated on the right side of the image. A sinusoidal signal is applied on pin3 which is the noninverting input of the op amp. Here we can see the inverting input pin2 (-) is referenced to ground, or a 0 V level. To study the working of a comparator accurately we can take the example of the IC 741, as shown below: The main component inside any comparator is an op amp circuit, which set at a very high voltage gain. This change of state at the output from -10 V to +10 V indicates that the Vin has become higher than the reference +2 V. If Vin is increased just above +2 V, the output instantly changes state, and turns high to around +10 V. Referring to the above figure above, we can see a standard connection of a comparator circuit having one input (the inverting input in this example) configured with a reference voltage, and the other input pin which is the noninverting input connected to an input signal voltage.ĭuring the time Vin is held at lower voltage than the reference voltage of +2 V, the output stays low at around -10 V. Oppositely, the output into a turns low digital signal, whenever the noninverting input voltage is lower than the inverting input voltage. Here, the output responds with a "high" digital signal, whenever the voltage at the non-inverting (+) input is higher than the inverting (-) input. The output switching response of an op amp is usually slower compared to a comparator IC.Ī classic comparator circuit design can be seen in the following figure:.An op amp can be used to build high gain amplifier circuits, a comparator cannot be used for such applications.An op amp output can work without any pull up or pull down resistors, but a comparator will always require an external pull-up or pull down resistor to enable the output stage to work normally.In contrast, a comparator output can be either open or grounded (negative), or floating. In powered condition, the output of an op amp will be either positive or negative, depending on the input pin voltage levels, but can never be open.However, the output response of these two forms of comparators may have a few major differences.Īlthough an op amp and a comparator both can be configured to compare differential signals at their input pins, the main differences between the two counterparts are: You will find both these units having an identical "triangle" shaped device symbol internally, which we normally recognize and use for drawing comparator circuits. The IC 741 is an ideal example of a single op amp, and the IC LM311 can be considered a good example of a dedicated single comparator. Difference Between a Comparator and Op Amp
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