Comparators

Comparator – automatic comparison of the input and output voltage

The main purpose of the comparator circuit is to compare two input voltages with each other. At the output of the circuit, it is to give high status (supply voltage) or low status (ground voltage) or negative supply voltage in the case of a symmetrically powered element. In the vast majority of cases, dedicated integrated circuits are used to implement comparators. The gain of the system is very important, which is high so even with the smallest voltage difference the output will be saturated. There are two outcomes to keep in mind. If the voltage at the non-inverting input is greater, the output will be high voltage. On the other hand, if a higher voltage appears at the inverting input, then a low state will be present at the output of the system.

Understanding the above rules, how the comparator works, allows you to know which of the inputs is higher and why. They use comparators, we don't need to know the exact voltage values ​​anymore. What is most important is the result of the voltage comparison made automatically for us by this useful electronic device - the comparator!

Feedback loop and hysteresis in the comparator

The high gain in the comparator circuit usually makes it more susceptible to noise and to hum. Therefore, in a situation where the difference between the input signals is less than the peak-to-peak voltage of the noise present in the input signal, we can experience the bastard of the output signal. This will be due to the rapid changes from high to low and vice versa that occur. This situation is undesirable and problematic. However, there is a solution to this problem.

Currently manufactured comparators have a built-in feedback loop. Thanks to this solution, a phenomenon called hysteresis is obtained. It consists in an uneven behavior of the system in a situation when the voltage difference increases or decreases. The current state of the circuit at a given moment depends on the state of the circuit at the previous moment. Due to the hysteresis phenomenon, the comparator with the feedback loop switches to the high state only when the rising voltage at the input 'gives way' to the reference voltage. Similarly, it works in the opposite situation - the low voltage condition at the output appears only when the voltage drops below the reference voltage.

Why do we use comparators? Few simple examples

Comparators are very practical tools. As we’ve mentioned earlier, they can be easily transformed into simple thermostats. Obviously, this is just an additional function, as these devices are primarily used in various electronic systems.

They are used in control and steering systems to stabilize physical parameters such as temperature, engine speed and lighting intensity. In addition, we can find comparators in various power supply systems and amplifiers. It can be used as an analog-to-digital converter, as well as a generator (after connecting the comparator with the appropriate RC circuit). Due to the use of a feedback loop with a comparator, such a system can operate stably, being extremely resistant to noise and interference in input signals.

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