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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

#31

Post by pjc50 »

phaet0n wrote: post #19

Does anyone have a good reference on how analog is done on logic processes, specifically the bits that have to interface off the chip, like gpio, lvds, and serdes. I'd much appreciate it. There's something I once encountered, but can't find the reference to, that suggested a kind of "digital-analog" process whereby voltage levels were replaced by timing measurement (?) due to the limits of feature size in analog desi…

I'd be interested as well; even when I was working with digital logic designers they described this process (eg bandgap references and PLLs) as "black magic", and it's very rare in undergrad or even master's courses.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#32

Post by pjc50 »

jstanley wrote: post #16
ebikelaw wrote: post #2

While 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.

I sometimes wonder whether integrated-circuit manufacturing wasn't sent to us by time-travellers from the future. Our ability to manufacture useful things, on such tiny scales, to such high precision, doesn't seem to match up with our comparatively-poor capabilities in other areas of manufacturing.

> comparatively-poor capabilities in other areas of manufacturing.

[citation needed]

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#33

Post by setquk »

hatsunearu wrote: post #24
coupdejarnac wrote: post #22

Earlier quoted context omitted.

Is there a general purpose op amp that is the modern equivalent of the 741? Something with a much more recent design with widespread use.

What's wrong with the 741? The 071 is also "jellybean" enough; both are still currently used in modern designs because how dirt cheap they are. But they are "high voltage", non rail-to-rail anything, so people tend to use more modern options for new designs.

741 problems: terrible bias current, offset, input range, output range, power consumption, voltage requirements, GBW, noise.

They’re just horrid. Fine for noddy stuff like power supplies and PID loops etc though.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#34

Post by setquk »

hatsunearu wrote: post #23
raverbashing wrote: post #5

Funny, 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,…

If you build ~1MHz circuits with 741s and replace them with 071s, you'll notice how ass the 741s are. Also, I've seen some people use 071s' inputs with no DC path to ground, and see their output slowly drift up/down because of tiny bias currents. Doesn't happen with 741s, usually.

That’s just crappy circuit design if they do that.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#35

Post by setquk »

PhantomGremlin wrote: post #14
ebikelaw wrote: post #2

While 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.

Not only invented decades ago, but built decades ago. The "7949" on the chip means it was manufactured in the 49th week of 1979. Which is nearly 39 years ago. He's lucky to find a part like that. Today nobody is going to build a device in a 14-pin ceramic package and sell it for 15 cents.

The ceramic ones never cost 15 cents.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#36

Post by zokier »

coupdejarnac wrote: post #22
raverbashing wrote: post #5

Funny, 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,…

Is there a general purpose op amp that is the modern equivalent of the 741? Something with a much more recent design with widespread use.

I doubt there is anything recent as iconic. Overall I think we have moved way beyond having individual generic iconic models at all. Digikey has like thousands (hundreds if you are old-fashioned and want through-hole) of different opamps which probably are mostly interchangeable 741 for most purposes, just pick any one of them.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#37

Post by HelloNurse »

jstanley wrote: post #16
ebikelaw wrote: post #2

While 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.

I sometimes wonder whether integrated-circuit manufacturing wasn't sent to us by time-travellers from the future. Our ability to manufacture useful things, on such tiny scales, to such high precision, doesn't seem to match up with our comparatively-poor capabilities in other areas of manufacturing.

Many other things could be manufactured "on such tiny scales, to such high precision", but they wouldn't be useful.

Integrated circuits are one of a few product/technology classes for which miniaturization is unconditionally good (improved power consumption, lower unit cost, possibly higher speed) up to unavoidable physical limits (e.g. randomly arranged doping atoms, noise vulnerability). Integrated circuits are also very easy to interface with the "real world" despite miniaturization because of their electronic nature: a comfortable range of currents and voltages is tolerable for the integrated circuit and acceptable for the larger system.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#38

Post by bogomipz »

hatsunearu wrote: post #28
bogomipz wrote: post #13

Earlier quoted context omitted.

Thank you for the detailed reply. Would these last two points also apply to MOSFETs? In the case of a MOSFET there obviously wouldn't be a "next amplifier stage" but would the output voltage be input to the next transistor's source or the next transistor's gate maybe?

For MOSFETs the story is about the same. For the tree transistor horsemen (BJTs, MOSFETs, JFETs), they can all be fitted into similar transistor amplifier building blocks: https://en.wikipedia.org/wiki/Template:Transistor_amplifiers You can put these things one after the another to get more complex behavior. Roughly speaking, common collector/common drain amplifiers have a gain of approximately 1, but has low output…

Thanks I found the classification in that link quite helpful. Cheers.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#39

Post by coupdejarnac »

hatsunearu wrote: post #24
coupdejarnac wrote: post #22

Earlier quoted context omitted.

Is there a general purpose op amp that is the modern equivalent of the 741? Something with a much more recent design with widespread use.

What's wrong with the 741? The 071 is also "jellybean" enough; both are still currently used in modern designs because how dirt cheap they are. But they are "high voltage", non rail-to-rail anything, so people tend to use more modern options for new designs.

I don't have any particular problem with it. I majored in EE about 15 years ago, and haven't really looked at op amps since studying the 741. Just curious what's popular these days.

Re: Silicon die analysis: inside an op amp with interesting “butterfly” transistors

#40

Post by ttul »

obl wrote: post #21
ttul wrote: post #15

Earlier quoted context omitted.

I modern chip design, simulated annealing is used for placement of parts to minimize the length of routes and optimize parasitic effects.

Not my area but I don't think that's the case for the analog ICs, or the analog part of mixed ICs. The constraints for generic digital logic soup are comparatively "simple" : make wires as short and neat as possible and then check the (simulated) physical timing characteristics. Analog is more artistic since any noise or crosstalk degrades the signal irreversibly (for low noise stuff) and any wire is a transmission l…

You can still run an analog design through simulation, and feed the results of simulation into a layout algorithm.
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