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Here is a datasheet for LM324:

https://www.fairchildsemi.com/datasheets/LM/LM2902.pdf

It says: Large DC Voltage Gain: 100dB

Does that mean the "open loop voltage gain is" 100000?

Is "Open loop voltage gain" the same thing with "Large DC Voltage Gain"?

Are they the same thing?

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  • \$\begingroup\$ also have a look at fig.5 \$\endgroup\$ – Vladimir Cravero Mar 4 '16 at 10:25
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    \$\begingroup\$ Possible duplicate of Confusion between Voltage gain & Voltage gain in decibels (dB) \$\endgroup\$ – Dmitry Grigoryev Mar 4 '16 at 10:30
  • \$\begingroup\$ No my question is not about dB. In data sheet there is nothing called "Open loop gain" So I was not sure if Large DC gain is the same thing. I know what dB is \$\endgroup\$ – user16307 Mar 4 '16 at 11:51
  • \$\begingroup\$ Well the closed loop gain is a property of external components and can be unity or even less, so that figure cannot mean the closed loop gain, which leaves only the open loop gain. \$\endgroup\$ – Brian Drummond Mar 4 '16 at 12:38
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Open loop gain and DC gain is actually not the same thing. The open loop gain is the gain without any feedback. The open loop gain falls off with increasing frequency. The open loop gain at DC is often called the "DC voltage gain".

Another important characteristic is the gain-bandwidth product (GBW). Which is the product of the DC voltage gain times the open loop bandwidth of the amplifier. To a first approximation the gain decreases with 20dB (or a factor 1/10) per decade, therefore the GBW is roughly equal to the unity gain frequency of the amplifier.

Usually feedback is used to trade off bandwidth with gain.

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The answer (as alluded to by Vladimir) can be seen from figure 5, which I have annotated).

Open Loop response

At low frequencies (somewhere less than 10Hz), there is a typical gain of 110dB; this is the DC gain, also known as the large signal gain.

The gain starts to roll off quite early, due to the internal compensation of the amplifier.

Even though this is the typical gain, it is not guaranteed; over temperature we can see it can be as low as 83.5dB

enter image description here

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