This section provides overview, applications, and principles of comparator. Also, please take a look at the list of 15 comparator manufacturers and their company rankings.
A comparator is an element that compares two input signals and produces different outputs depending on the results. Generally, two inputs are provided: an input of the signal to be measured and a reference signal.
This makes it possible to perform conditional branching in the circuit, such as to perform a specific operation when a signal (current or voltage) that exceeds the reference value is input.
The comparator input is analog, but the output signal is digital. The input of the comparator is analog, but the output signal is digital. Therefore, the comparator is sometimes used as an interface between analog and digital circuits.
Comparators can be used to build logic circuits that perform comparisons between input signals (current and voltage) and reference signals. For example, they can monitor excessive rises or drops in voltage and alert you if they are out of range, or they can control the operation of equipment.
Another conditional branching can also be performed, such as automatically adjusting the temperature of a refrigerator or air conditioner or limiting the performance of a cell phone or PC when the battery is low.
Comparators have five pins, each consisting of a positive and negative power supply pin, two inputs, and an output pin. It has almost the same configuration as an operational amplifier, with the only difference being whether or not inverting amplification is performed. Originally, operational amplifiers had the property of outputting the power supply voltage when there is a difference in input voltage, and comparators make use of this property.
Conversely, if a circuit is built to apply feedback from the output terminal of comparators to the negative input terminal, it can be used as an operational amplifier. Since comparators do not have a mechanism for inverting amplification, they do not provide phase compensation to prevent oscillation as operational amplifiers do.
Therefore, the most crucial feature of comparators is that comparators have superior responses compared to operational amplifiers. Moreover, if multiple comparators are used, and the reference value is set in steps, they can be used as AD converters. AD converters with this structure can perform high-speed conversions.
If the comparators have a single threshold for comparison, unexpected external noise superimposed on the analog signal will cause the comparators to repeat High/Low in response to the noise. This causes malfunction instead of switching with the original input value, so comparators called hysteresis comparators were invented.
Hysteresis comparators are characterized by having two threshold values depending on the output state. When the output switches, it switches to another threshold value different from the previous threshold value, thus preventing unexpected noise-induced malfunctions.
The circuit configuration of the hysteresis comparators applies positive feedback from the output terminal of conventional comparators to the input terminal via a resistor or the like. Incidentally, this circuit is called a Schmitt trigger after the inventor's name (Otto Schmitt).
Schmitt triggers are generally combined with active elements such as Zener diodes to prevent supply voltage fluctuations, making the circuit more versatile. There are two types of hysteresis comparators thresholds: those that can be set symmetrically plus or minus with respect to 0 V and those that can be set asymmetrically. This is because a large hysteresis width improves immunity to external noise but deteriorates the sensitivity to the input value that you originally want to judge.
Therefore, care should be taken not to increase the hysteresis width beyond the actual noise value. For a more balanced design, the ratio of the threshold voltage to the comparator's supply voltage should also be considered.
*Including some distributors, etc.
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