Comparator - what is it? The chip and operation

Comparator – is a device used to compare any values (from lat. comparare – "compare"). Is the operational amplifier with a large multiplication factor. Has inputs: direct and inverse. If necessary, the reference signal can be connected to any of them.

How does the comparator?

At one input a constant signal that is called the base. It is used as a sample for comparison. Second comes the test signal. The output is a transistor that changes its state depending on the conditions:

• Voltage direct entry of the above inverse-transistor is opened.
• The voltage of the inverse input direct above – is closed.

Accordingly, the output voltage changes abruptly from minimum to maximum, or Vice versa.

Voltage output stages corresponds to the input levels of most digital circuits. This is necessary for cases where a comparator – a pulse shaper that controls the logical elements.

Comparator

Used in circuits of measurement of electrical signals and analog-to-digital converters. In logical circuits work elements “or” and “not”, which is also the Comparators. Accordingly, the use of this component is not limited to specific examples, because it applies across the Board.

It Should be noted that the device of the comparison can be done with any op amp, but not Vice versa. The gain of the comparator is high enough. Accordingly, his inputs are very sensitive to the difference voltage between them. The difference of a few millivolts significantly changes the output voltage.

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Thus, the comparator allows to observe minimum fluctuation of levels of input voltages. This makes it an indispensable element diagrams comparing and measuring instruments high precision,

• The level of the input signal;
• Metal detectors;
• Micro and millivoltmeters;
• Detectors of electromagnetic radiation;
• Laboratory sensors;
• Mass Comparators;
• The analyzers.

The Principle of operation of the analog comparator

The Analog comparator compares the continuous signals-the input and the measured input sample. How does the device shown in the chart below.

With a slow change of the input signal, multiple switching of the comparator for a small period of time. This phenomenon is called "electron bounce". Its presence significantly reduces the efficiency of the comparison. Because of a frequent change of the output status, enter in a terminal the transistor is in the saturation state.

To reduce the "electron bounce" in a scheme administered POS-positive feedback. It provides a hysteresis-the difference between the voltage level of enable and disable. Some Comparators have built-in PIC, which reduces the number of additional elements of building design. For example, if a minor loss of sensitivity, achieve stable operation of the comparator.

Features of digital comparator

Comparator – a one-bit analog-to-digital Converter. The output voltage is either a logic “0” or “1”. The input can be served both analog and digital signal. The device is used as a pulse driver for coupling schemes of the sensors and display devices. Can be used to analyze the spectrum of a sound or light signal. Comparator – it is also logical elements “or” and “not”, used in computer science.

Theoretically, with negligible small fluctuations of level of the input signal may occur as the uncertainty output. In practice, the equality of the measured and reference voltages does not occur. Because the comparator has a limited gain or positive feedback.

A Typical example is the Schmitt trigger (TS). He's not the same levels of on and off, as determined by POS. This allows us to neglect the discrete obstacle for the comparator.

Comparator chip

The Industry produces a comparator in the form of integrated circuits. Their use allows to create compact devices, with a minimum of external components. Also the advantage of small parts in minor the length of the connecting conductors. In conditions of high electromagnetic radiation they are receiving antennas for all kinds of electrical interference.

The Comparator by operational amplifier

The Comparators there is considerable similarity with operational amplifiers:

• Gain;
• Input impedance;
• The value of the input currents;
• Saturation.

The Sensitivity, different resolution, – this specific parameter. It determines the accuracy of the comparison. Is characterized by a minimum difference signal, which triggers the comparator. It value integrated circuits has hundreds of microvolts. This is slightly worse than the Comparators for operatingamps.

Switching Time Characterizes the performance of Comparators. Determined by the minimum time of the output signal from the comparison point until it resolves. Depends on the difference in the input signals. Time values switching the tens and hundreds of nanoseconds.

How to make a comparator with your own hands?

Who knows how to read schematic diagrams and solder, easily gather the simple Comparators for use in the home. Application field is very extensive. They can build a lot of structures with minimal costs. The simplest comparator – operational amplifier without a positive feedback.

As the basis for the comparator is used OPAMP LM339 series. For control and visibility of the scheme introduced red and green indicators. When you connect the power op-amp should light one led, and which one doesn't matter. This is determined by many factors: network aiming at the scheme, particularly the party and the parameters of op-amp. Even if you take several identical chips, you get different results.

If the input signal is close to “0” – will glow green and if the close to the supply voltage, the red led. Then you can try to change the logic state of the comparator, filing for one input voltage, for example, equal to half the supply voltage uh. The output signal does not depend on the absolute values of the voltages on the direct and inverse input. But only from the difference voltage.

These experiments demonstrate operation of the comparator without POS. Such a comparator can be used where not require special accuracy. Such devices are appliances thermostats, battery chargers for car batteries, the device of desulfuratsii (recovery) of rechargeable car batteries, photocell.

Example of the practical application of the comparator

The concept represented by the ambient light sensor.

The Reference voltage is set by resistors RV1 and R2. Thus, RV1 serves as a sensitivity control design. Indication implemented on the led D1. Sensor LDR1 is the element that changes resistance depending on light conditions. Actually the presented comparator operational amplifier LM324. This simple device demonstrates how the comparator works in practice.

Mass Comparators: concept

The mass Comparator is a device used to clarify the difference between the masses of the weights in the testing of standards of mass and weight, as well as for precision weighing. The most accurate mass Comparators capable of weigh any pattern and compare it with other similar to him. This happens at the atomic level. The need for such devices arises due to the imperfections of the reference samples measures of weight and liquid volume.

Examples and usage of the devices specifying the weight

The Russian standard of mass is a platinum cylinder. It was copied from the French sample 125 years ago. Over the years, the standard has lost in the form of oxides, about 40 mg of the original weight. Accordingly, its use for the needs of industries with high precision mass measurements are difficult.

We developed a new standard of mass. Scientists appointed as such a silicon sphere with an even number of atoms. Now this is the most accurate version of the standard kilogram. Its characteristics accepted by the international community for use.

The Generated sample needs multiple copying. As modern trends in science, especially pharmacology, bioengineering, computer electronics, nanotechnology development require precision accuracy. For such fields of science and technology critical hundredths of a microgram. This should solve the problem of atomic mass comparator-the device is able to determine the difference of a few particles.

Atomic uses a comparator for measuring the reference signal received from a precision crystal oscillator. The measuring voltage is taken from a quantum discriminator, which determines the stability of the line of the smallest particles. Its changes are caused by the difference in the number of atoms of the sample. So now – is the most accurate measurement device.

There are less precise mass Comparators. Their cost is much lower than nuclear, but for all of them is to work in industry, Commerce, standardization.