What's the Difference Between Operational Amplifier and Comparator?

What is the difference between op amps and comparators in terms of appearance or drawing symbols, and how can they be differentiated in practical applications? Today, I'll conduct a thorough examination of photographs and words, cement everyone's foundation, and allow engineers to advance to the next level.

First, let's look at their internal difference chart:

Figure. 1

Figure. 2

The output circuit distinguishes an op amp from a comparator, as can be seen in the internal diagram. The comparator employs only one transistor, with the collector linked to the output and the emitter connected to ground, whereas the op amp uses a twin transistor push-pull output.

From the positive power supply wire to the output terminal, the comparator requires an external pull-up resistor that is equal to the transistor's collector resistance.

Linear amplification circuits (negative feedback) and non-linear signal voltage comparisons can both benefit from operational amplifiers (open loop or positive feedback).

Voltage comparators are only suitable for comparing signal voltages, not for linear amplifier circuits (comparators have no frequency compensation).

The comparator is built as a high-speed switch, which has a higher slew rate and shorter latency than an op amp, and can be used for signal voltage comparison.

Ⅰ. Operational amplifier

I won't speak much about this circuit because it's a linear amplifier (the amplifier needs to be discussed separately in the future). This is a regular occurrence in motherboard circuit diagrams. It's commonly found in voltage regulator circuits. When paired with a transistor, a negative feedback circuit is similar to a three-terminal stabilizer. pressure, but more versatile to employ. As seen in the diagram below:

Figure. 3

In many circumstances, knowing which of the two signals is greater or when one signal exceeds a predefined voltage is required (used as a voltage comparison). It's simple to make this with an op amp and a basic circuit. The output is high when the  V+  voltage is greater than the V- voltage. The output is low when the  V+  voltage is smaller than the V- voltage. As shown in Figure. 4.

Figure. 4

Analyze the circuit: 2.5 volts is divided by the resistor to get 1 volts, which is then applied to the V- terminal. The bus voltage is sent into  V+ when it generates 1.2v regularly. The V+ voltage is higher than the V- voltage at this point, and the CPU power management receives a high signal. The chip's EN pin is used to enable the chip. The V+ value is lower than the V- voltage at this moment, and the output is low if the bus voltage is not output or is unusually less than 1v.

Ⅱ. Voltage comparator

The output transistor is turned on and the output is grounded low when the comparator's non-inverting terminal voltage (V+) is lower than the inverting terminal voltage (V-); the pull-up resistor's power output is high. As seen in the diagram below:

Figure. 5

When there is a VCC output, the comparator U8A is connected to the non-inverting terminal (V+) after being divided by the voltage dividing resistor, and its voltage is larger than 5VSB, thus it is connected to the inverting terminal (V-) after the voltage division. The internal transistor is turned off, and the power supply 12v is output via the pull-up resistor (at the same time, the voltage of the non-inverting terminal of the comparator U8B below is greater than the inverting terminal, and the internal transistor is also turned off), the N-channel field transistor Q37 is turned on, and the output VCC5V is turned on. The P-channel field transistor Q293 is also turned off at the same moment. When the inverting terminal voltage exceeds the non-inverting terminal voltage, the internal transistor is activated, the pull-up power supply 12V is reduced, the N-channel field transistor Q37 is switch  ed off, and the P-channel field transistor Q293 is activated, producing 5VSB. This is the 5VDUAL generation circuit.

In practical applications, comparators all require pull-up power supplies, while operational amplifiers generally do not.

Ⅲ. The essential difference between operational amplifier and voltage comparator

(1) The closed-loop characteristics are the key distinction between amplifiers and comparators!

Because most amplifiers operate in a closed-loop mode, they must not be self-excited after closing the loop. And the vast majority of comparators operate in an open-loop mode in order to maximize speed. The amplifier can totally replace the comparator in the case of relatively low frequency (the output level must be addressed), and vice versa. In most circumstances, comparators cannot be utilized as amplifiers.

Because the comparator has been tuned for speed, the closed-loop stable range has been reduced. Because the op amp is tuned for closed-loop stability, the speed is lowered. As a result, comparators and amplifiers of the same price range should ideally be different. Responsibility. It can't be ruled out that a comparator can be utilized as an amplifier, just as an amplifier can be used as a comparator. However, the cost of making it closed-loop stable may outweigh the cost of adding an amplifier.

In other words, the negative feedback depth of the circuit determines whether an op amp is utilized as a comparator or an amplifier. As a result, a shallow closed-loop comparator that is not self-excited can work in the amplifier state. However, many tests must be carried out to verify that the product is stable in all operating modes! You must carefully analyze the cost/risk at this time.

• The operational amplifier and comparator are the same thing. The comparator is essentially an open-loop application of the operational amplifier, but it is built for voltage threshold comparison. The required comparison threshold is accurate, and following the comparison, the output edge rises. Alternatively, the fall time should be short, the output should conform to  TTL /CMOS level/or OC, etc., the intermediate link precision is not necessary, and the driving capability is also different. In general, when employing op amps as comparators, most of them are unable to produce full-scale output, or the edge time after comparison is too long, therefore it is preferable to use less op amps in the design.

Ⅳ. Difference between operational amplifier and comparator

Despite the fact that the comparator and op amp have the same symbols on the circuit diagram, the two devices are extremely distinct and cannot be used interchangeably. The following are the distinctions:

1. The comparator's flipping speed is quick, on the order of ns, whereas the op amp's flipping speed is on the order of us (except for special high-speed op amps).

2. Although the op amp can be connected to a negative feedback circuit, the comparator cannot. Although the comparator contains two input terminals, in-phase and in-phase, the circuit does not work reliably if negative feedback is added since there is no phase compensation circuit inside.The comparator is substantially faster than the op amp since it does not have an internal phase adjustment circuit.

3. The operational amplifier's output stage is typically a push-pull circuit  with bipolar output. Because most comparators have an open-collector output stage, they require a pull-up resistor, have a unipolar output, and are simple to connect to digital circuits.

(3) The comparator output has an open collector (OC) structure, which necessitates the use of a pull-up resistor to enable external current output. The op amp's output stage is a push-pull design with symmetrical sourcing and sinking capabilities. Furthermore, there are few intermediate steps to speed up the comparator's reaction speed, and there is no internal frequency adjustment. For the needs of working in the linear domain, the op amp has a compensating circuit. As a result, comparators aren't appropriate for op amps.