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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

#21

Post by obl »

ttul wrote: post #15
amelius wrote: post #9

Could 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)

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 line (for high speed stuff).

Actually even for digital I'm sure you still have to do manual layout for the most critical pieces of high-performance designs (say a register file on a nvidia gpu).

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

#22

Post by coupdejarnac »

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.

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

#23

Post by hatsunearu »

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.

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

#24

Post by hatsunearu »

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.

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.

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

#25

Post by phaet0n »

kens wrote: post #20
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 don't know about modern chips, but 1970s and 1980s logic chips just used big MOSFETs to drive their outputs. There wasn't any weird timing magic going on. There are also processes like analog BiCMOS that let you mix bipolar analog circuitry and CMOS on the same chip. I also wrote recently about the 76477 sound chip that combined I2L logic with bipolar analog circuits.

Thanks for pointing out your article about the 76477. Fascinating stuff.

As for my second paragraph about "digital-analog", this reference on VCO-based quantizers [1] is not the one I remember but I think is related. Not that I really understand the intricacies, but it's a way of doing analog at low-voltages and finer geometries.

[1] http://ewh.ieee.org/r5/central_texas/cas_ssc/meetings/2012/1...

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

#26

Post by hatsunearu »

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.

Also, there ARE objectively shit op amps that are old and crusty that pretty much nobody uses. I think it was the LM358 that basically had a broken output stage (class-B) that causes horrible output crossover distortion when you transition from sourcing to sinking current or vice versa.

http://www.ti.com/lit/ds/symlink/lm158-n.pdf

Page 13, Figure 16.

Q12 is a common emitter amplifier with an active load, that feeds directly into a class B output stage (pullup is a darlington with Q5 and Q6, and pulldown is Q13, with Q7 being a current limiter). I've never used this personally (for good reason) but I remember my mentors telling me this causes horrible CO distortion.

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

#27

Post by hatsunearu »

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.

Oh man, it's far from state of the art.

"New" op amp features:

- Crazy rail-to-rail input: some chips have onboard charge pumps to bias input stages such that you can input signals with common mode voltages far below and above the normal rails

- Rail-to-rail output: probably the lowest hanging fruit of the "new" features, but still pretty costly

- Stupidly high input impedance: 071 isn't completely blown out of the water but some of the new JFET opamps are nuts. I think there are like femptoamp class input currents these days.

- Stupidly low offset voltage: I'm not even talking about the auto-zero ones, just regular old op amps have amazing performance these days.

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

#28

Post by hatsunearu »

bogomipz wrote: post #13
kens wrote: post #12

Earlier quoted context omitted.

> Is the source permanently connected to power? If so do all transistor in a circuit connect to a shared power rail? Looking at the TL084 schematic, the JFET source is fed from another transistor (a current source in a current mirror). Some of the transistors are connected to V++ and some are connected to V-- but many of them are not connected directly to any power rail. > Must voltage always be present on both the s…

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 impedance, which makes it suitable for driving big loads (like the outside world). Common emitter/common source amplifiers have high output impedance but tons of gain.

The classic op-amp topology is a differential amplifier (long-tailed pair, in the wikipedia template) feeding into a common emitter/source gain stage, then into a common collector/drain follower output stage.

To answer your last question, the output of the gain stage is the drain of the transistor, that feeds the gate of the common drain output stage transistor.

The gate is usually the input terminal, but sometimes the gate is at a fixed voltage and the drain is the input terminal (cascode-y circuits are like this, aka common base or common gate).

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

#29

Post by paulmd »

vvanders wrote: post #17
jstanley wrote: post #16

Earlier quoted context omitted.

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.

There's a series on transistors that covers this. There's basically no mechanical process since everything is done via etching and litho. Leads to the results you see.

Please link it.

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

#30

Post by panic »

paulmd wrote: post #29
vvanders wrote: post #17

Earlier quoted context omitted.

There's a series on transistors that covers this. There's basically no mechanical process since everything is done via etching and litho. Leads to the results you see.

Please link it.

Here's the start of the series: https://technicshistory.wordpress.com/2018/01/20/the-transis...
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