A question regarding the history of frequency compensation improvement of opamp IC

[bhl777]

Hi All, I remembered that at the beginning of op-amp IC development in 70', all frequency compensation needed to be designed externally. The application engineer needed to calculate R and C value to complete compensation outside the opamp.
But currently no opamp IC used external frequency compensation any more, could anybody tell me what is the differences between the old product and current products, that makes current OPAMP IC use internal compensation to accommodate different applications?
Thank you!

 

[FvM]

The first OP with internal compensation, uA741 has been released 1968. Although not optimal for all circuits, unity gain compensated OPs are used in the majority of applications.

Previous OP design implemented different compensation schemes, the principle of single capacitor miller compensation can be already found with it's external compensated predecessor LM101. In so far there's no clear difference between both OP types.

 

[bhl777]

Hi FvM, so can we say the only difference between them is that the external cap was not able to be integrated, because of process limitation. And now it can be integrated in the chip, so we no longer need to compensate externally? Thank you!

The first OP with internal compensation, uA741 has been released 1968. Although not optimal for all circuits, unity gain compensated OPs are used in the majority of applications.

Previous OP design implemented different compensation schemes, the principle of single capacitor miller compensation can be already found with it's external compensated predecessor LM101. In so far there's no clear difference between both OP types.

 

[FvM]

o can we say the only difference between them is that the external cap was not able to be integrated, because of process limitation. And now it can be integrated in the chip, so we no longer need to compensate externally?

It's O.K. has an abriged explanation. The other point is this: External compensation allows to taylor OP parameters more exactly to application requirements, but also makes OP usage less convenient. Simple internal compensation was a prerequisite to make OPs a mass product.

 

[dick_freebird]

You can still find op amps specified as "10X gain stable"
etc, which have little or no internal compensation. But
they are relegated to niche uses where you need the
bandwidth@gain, pretty much.

It's a lot easier to get the compensation capacitor you
need in a 5V MOS cap, than a 50V one, if you care about
die size. On the "40V" op amp layouts I've seen, the comp
cap is the single largest feature.

 

[zorro]

At the time the ua741 was intruduced, the integration of the 30 pF capacitor in a monolithic IC was a technological innovation.
The 748 is the same but without internal compensation.