Silicon die analysis: inside an op amp with interesting “butterfly” transistors
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Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#2While you marvel at this circuit remember that it was invented decades ago, for many purposes it is still state-of-the-art, and it costs fifteen cents.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#3While you marvel at this circuit remember that it was invented decades ago, for many purposes it is still state-of-the-art, and it costs fifteen cents.
TL0x4 latches in certain conditions, not quite state of the art behavior.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#4Ken's reverse engineering articles are always a real pleasure to read, but this one is special in that it looks at an analog chip and how typical analog building blocks (current mirrors, differential pairs) are implemented in silicon.
Also, if you've every looked at an analog IC's schematics and wondered what those weird "double collectors" BJT are (https://electronics.stackexchange.com/questions/105777/what-...) , there's a pretty decent description in there of what a BJT actually looks like when implemented in silicon.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#5Funny, I have actually used this one, the 4 means 4 OPAMPs in a single chip. IIRC there's also the TL082 with 2 OPAMPs.
Much more performant than the 741 (might have to do with 2 things: the 741 came early and was one of the pioneers and it is BJT only)
It's also curious how the the big butterfly transistors are at the input, components with a big die size are usually big for a reason (usually power).
One extra fact, the compensation capacitors are more like a wrench on gears and actually make the circuit "worse" (it lowers the overall bandwidth). But it is needed for stability purposes because good amplifiers will have a tendency to oscillate by themselves.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#6While you marvel at this circuit remember that it was invented decades ago, for many purposes it is still state-of-the-art, and it costs fifteen cents.
TL0x4 latches in certain conditions, not quite state of the art behavior.
I worked on a motor controller that had a problem with PWM IC frying.
Turned out the real problem was when the control signal was over-driven a comparator would latch up. Which would cause both power transistors to turn on. Blowing a 'protection' [1] fuse on the negative supply rail. And then the negative power supply would reverse. And kill the PWM controller IC.
Not a fan of latching OP-Amps and Comparators.
[1] Tip: fuses don't protect circuits from damage they prevent your POS from burning the house down.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#7While you marvel at this circuit remember that it was invented decades ago, for many purposes it is still state-of-the-art, and it costs fifteen cents.
TL0x4 latches in certain conditions, not quite state of the art behavior.
Personally I prefer to have parts that require external protection, rather than parts with robust internal protections that cost more or compromise the performance or that I have to hack around. It's more work, board area, and overall cost to have the external protections to keep an IC within its safe operating area, but I don't mind.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#8Funny, I have actually used this one, the 4 means 4 OPAMPs in a single chip. IIRC there's also the TL082 with 2 OPAMPs. Much more performant than the 741 (might have to do with 2 things: the 741 came early and was one of the pioneers and it is BJT only) It's also curious how the the big butterfly transistors are at the input, components with a big die size are usually big for a reason (usually power). One extra fact,…
> usually power
That may be true but I'm not sure it applies in this context. Another valid reason is because at a larger scale it is easier to get the dimensions to be within a fairly close tolerance of the counterpart and hence to get two parts that function well in tandem.
Matched pairs and current mirrors are exactly the right situations for this and so they tend to be oversized, even if that slows the parts down considerably.
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#9Could a genetic algorithm have come up with this design?
(Electronics seems an interesting application area for automated design, since the search space is relatively small)
Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors
#10I have a few questions about the JFET diagram and JFETs in general if someone wouldn't mind answering:
In the graphic we see S, G and D - Source Gate and Drain. Is the source permanently connected to power? If so do all transistor in a circuit connect to a shared power rail?
Must voltage always be present on both the source and gate in order for current to flow to the drain?
Lastly when the transistor is switched "on" does voltage leaving the drain then become input for a gate of some neighboring transistor in the circuit?