I'd like to see a photo of LT1013.
Done that:
There is some silicone potting on the die.
A different part and the die is still in the package.
The die is 2,4mm x 1,9mm.
The design dates back to 1987, manufactured in 2000.
The pink part makes it possible to got down to 0V (with single supply).
Datasheet explains that with other opamps negative voltages on one input of such an input stage can lead to a phase reversal. In my view phase reversal is not really the right naming. With negative voltages the differential amplifier (dark green) can be driven into saturation and so the whole circuit is buggy. The output goes high but that´s not really a phase reversal. In the LT1013 the transistors Q21/Q22/Q27/Q28 supply current to the input stage as soon as the voltage is low enough so there is no saturation problem in the following stage.
There is a small mistake in the datasheet schematic. Q28 is connected to the positive supply.
I´m not perfectly sure what the grey part does. In my view you need these components if you drive the differential stage to hard. The next stage can only source current so too much current has to be drained over Q29/Q8. Q9/Q11/Q12/Q13 compensates the current in the left leg.
The VAS (and it´s drivers Q10/Q18) is cyan.
Steering of lowside-output-transistor Q34 is realized by the yellow part. Quite interesting constellation.
The right blue part generates reference voltages. There are a lot of current mirrors generating the currents for the different stages.
The green part is an overcurrent protection.
Most of the parts can be identified on the die.
Interesting that there is a second V+ bondpad...
The input stage is quite symmetrical and partly cross wired.
The input resistors are placed in parallel too.
That´s interesting. The emitter resistors of the current sources of the input stage can be adjusted (offset adjust).
There are two long resistors. In the red path you can switch in a 2R, a R, a R/2 and a R/4 resistor giving you 16 steps of adjustment. In addition in the green path there is a 4R resistor for inverting the adjustment.
But wait! There are five fuses but only three testpads and one bondpad!
It seems like they found a way to cut only one fuse although there are two in series.
It seems like the metal layer on the green resistors makes it possible to do some bigger adjustment if necessary.
I used my very special simulation tool MS Powerpoint to show the thermal gradients.
Well you can imagine that the placement of the input transistors is optimized so they see very little temperature difference which gives you low offset drift.
Also very interesting are the capacitors. The 21pF- and the 2,5pF-capacitor are obvious and built like we now integrated capacitors.
But there are a lot of other capacitors which need a lot more area. Thankfully these capacitors are reffered to ground. To reduce the necessary silicon area the capacitors are integrated under the active areas. You can see a green frame, that´s the capacitor.
In the lower right corner there is a metal-fuse and a testpad which doesn´t interact with the circuit. I assume that´s a kind of binning...
More pictures here:
https://www.richis-lab.de/Opamp26.htm