What is the principle that enables op amps to achieve rail-to-rail operation?

乱世煮酒论天下

What is the principle that enables op amps to achieve rail-to-rail operation? [Copy link]

The input voltage of a general op amp is usually about 1-2V lower than the power supply voltage. That is to say, if the power supply voltage is plus or minus 15 volts, then the input voltage is about plus or minus 13 volts. However, some op amps with better performance can achieve rail-to-rail input voltage. What is the principle that allows these op amps to achieve this working condition?

There is another type of op amp that can achieve a higher common-mode input voltage, that is, its common-mode input voltage can reach several times or even dozens of times the rated supply voltage, but the op amp parameters require that the common-mode input voltage of the op amp will not exceed the supply voltage. What is the reason for this? What is the principle? Why is this op amp structure used? What are the advantages and disadvantages of this op amp compared to ordinary op amps?

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You can learn about the advantages and disadvantages of general traditional op amps and rail-to-rail op amps.

For example, compared with traditional op amps, rail-to-rail op amps can be used in places where a wide dynamic range is required, such as audio amplification, sensor signals, and low-voltage power supply systems.

maychang

[However, some op amps with better performance can achieve rail-to-rail input voltage. What is the principle by which these op amps can achieve this working condition? ]

This is related to the op amp production process. The performance of op amps composed of bipolar tubes and op amps composed of CMOS tubes is very different. Therefore, to understand how rail-to-rail is achieved, you need to first understand the op amp production process.

maychang

[There is also an op amp that can achieve a higher common-mode input voltage, that is, its common-mode input voltage can reach several times or even dozens of times the rated supply voltage]

Maybe you have misunderstood the term "common-mode input voltage". The common-mode input voltage of an op amp refers to the voltage from the two input terminals of the op amp to the common terminal of the op amp power supply. If a resistor is connected in series to the input terminal of the op amp, the voltage on the resistor cannot be included in the common-mode voltage of the op amp. But we can say that the common-mode input voltage of the amplifier formed by this op amp is...

The common-mode input voltage of this op amp and the common-mode input voltage of the amplifier formed by this op amp must be clearly distinguished.

乱世煮酒论天下

maychang published on 2024-5-7 07:51 [There is also an op amp that can achieve a higher common-mode input voltage, that is, its common-mode input voltage can reach several times or even dozens of times the rated power supply voltage...

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