Author Topic: Why is the 741 op amp still produced?  (Read 19655 times)

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Offline Kleinstein

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Re: Why is the 741 op amp still produced?
« Reply #75 on: September 28, 2020, 09:11:55 am »
There are still a few high voltage OPs available and even new one released, e.g. MCP6V51 is specified to 45 V, though not a direct 741 replacement but AZ and only smaller cases.
At the lower cost end, when the LM358 and related are not an option (e.g. higher supply voltage, speed, cross over) the 741 is still a viable option, but there are alternatives besides the LM301.
 

Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #76 on: September 28, 2020, 12:58:00 pm »
It will be interesting to see what happens to these higher voltage parts as less and less fabs remain functional which can produce them. People do not seem to see enough market size to justify developing new high voltage parts right now, although I guess they will be forced to as the last ancient fabs close. Some people will always need high voltage operation.

What about fabs making HV parts like mosfet drivers, SMPS ICs and that sort of thing? Couldn't they make HV op amps? The market for things like motor drives and power supplies isn't going anywhere.
Of course there is a need for. and will always be, high voltage parts. However, with many of the fabs that make the ancient higher voltage parts reaching their end of life there are going to be some significant changes in the industry. Will the people scrapping ancient fabs replace them? Will new players take up the work? It will be interesting to see.
 

Offline exe

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Re: Why is the 741 op amp still produced?
« Reply #77 on: September 28, 2020, 01:06:00 pm »
Why a new fab cannot produce an old part? (I can see why this is uneconomical == doesn't make sense on current market).
 

Offline T3sl4co1l

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Re: Why is the 741 op amp still produced?
« Reply #78 on: September 28, 2020, 01:26:07 pm »
For one, the part probably has to be redesigned, because all the characteristics are different.

For another, no one's making the high voltage BJTs like the old way.  A 10 or 20V part would be easy enough to do.  But that's nowhere near the original spec.

TLV2372 is probably an example of this, using a high voltage CMOS process (18V max).  Though I don't know offhand if that's metal or poly gate HVCMOS -- there's poly HVCMOS, right?

Which is not to say there aren't any fabs doing that sort of thing.  Discrete BJTs aren't going away any time soon.  I'm not sure why they couldn't simply run a different mask set there (and insert a couple more passes for doping as applicable, and metallization; of course, doping can't be done willy-nilly, that's a whole process refinement step).  Perhaps access to the fabs is poor (who's making BJTs anymore? It's not all China now is it..?).

There are plenty of HV processes, ranging from ~20V amps like the above example, to 50-60V regulators and switchers, to 600V+ gate drivers.  Probably these are optimized for CMOS though, and BJTs are rough on a CMOS process.  (Also, not that the 600V transistors in HVICs are necessarily any good -- they do actually exist, and the HVIC process isn't just a high side isolation thing, transistors are included and that's indeed how they couple signals to the high side -- but not much performance is needed for that, either.)

I suppose LT (now ADI)'s internal fab is one of the most likely candidates; they've been making interesting BJT-based parts for ever.  There aren't many ways you can make a buck regulator operate from 2-30V, but BJTs are a good one.  Datasheets don't usually say much of anything about internal design or process, so it's not obvious from here how much they do that, but obviously it's what they're doing when they show an NPN switch on the block diagram.


Going back to direct substitutes, there are plenty of >30V op-amps out there, some with quite impressive specs.  I don't know how many are bipolar, BiCMOS or what.  The biggest downsides will be: cost, knock-on changes (because the GBW, etc. are different), and approval.

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Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #79 on: September 28, 2020, 01:39:53 pm »
I suppose LT (now ADI)'s internal fab is one of the most likely candidates; they've been making interesting BJT-based parts for ever.
Making them forever is exactly the problem. Ancient analogue fabs are shutting down because they are so old people can't get spares for them any more. It looks like the remaining ones are only being kept alive through the reuse of parts taken from the ones closing down. Nobody is going to invest in new plant for tiny wafers, so a redesign for a process that exists for large wafers is usually needed. The original designers have probably retired, and the original design data has rarely been kept intact, so it will be a redesign from scratch.
There aren't many ways you can make a buck regulator operate from 2-30V, but BJTs are a good one.  Datasheets don't usually say much of anything about internal design or process, so it's not obvious from here how much they do that, but obviously it's what they're doing when they show an NPN switch on the block diagram.
Nobody wants to tell customers about the processes used to make their devices, unless it has marketing value, like "uses TSMC's latest super duper 10pm process, with less than one atom per transistor". It can affect their flexibility in re-engineering parts for lower cost.
 

Offline exe

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Re: Why is the 741 op amp still produced?
« Reply #80 on: September 28, 2020, 01:58:09 pm »
it will be a redesign from scratch.

I recall reading that TI shrank their opamps two or four times, but I can't find any die shots to confirm this.
 

Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #81 on: September 28, 2020, 02:58:14 pm »
it will be a redesign from scratch.

I recall reading that TI shrank their opamps two or four times, but I can't find any die shots to confirm this.
In the early days the geometries were enormous. Devices could be shrunk quite a long way before people had to worry about how to maintain a high voltage tolerance. And they were shrunk. Quite often. While trying to avoid letting customers know how much things had changed, as it might worry them. Until characteristics changed, designs in production broke, and they had to quietly admit to specific customers what was going on. I went through this a couple of times in the 1970s.
 

Offline magic

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Re: Why is the 741 op amp still produced?
« Reply #82 on: September 28, 2020, 03:04:18 pm »
They also do apparently migrate them to new processes on larger wafers from time to time. They discontinued a big chunk of National's audio line a few years ago quoting this very reason. Several TI dice on zeptobars show timestamps from the '90s or 2000s, no idea what was that which they replaced.

As for opamps, I kinda assume it's bipolar unless stated otherwise. I have been hearing that bipolar tends to give more practical gain in analog applications. Also remember reading propaganda from National which claimed that complementary bipolar is advantageous over CMOS at high speeds because base width is controlled by diffusion depth rather than lithography resolution, which is cheaper to produce. That was a paper from the 2000s, though.

OTOH, low power, low input bias, outputs reaching within a few mV of the rails - that smells CMOS.
 

Offline David Hess

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Re: Why is the 741 op amp still produced?
« Reply #83 on: September 28, 2020, 11:13:00 pm »
It will be interesting to see what happens to these higher voltage parts as less and less fabs remain functional which can produce them.

There will be industry consolidation until all analog ICs are made by Texas Instruments.

Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Making them forever is exactly the problem. Ancient analogue fabs are shutting down because they are so old people can't get spares for them any more. It looks like the remaining ones are only being kept alive through the reuse of parts taken from the ones closing down. Nobody is going to invest in new plant for tiny wafers, so a redesign for a process that exists for large wafers is usually needed. The original designers have probably retired, and the original design data has rarely been kept intact, so it will be a redesign from scratch.

Getting supplies like wafers for old processes is a problem also.  You may have to buy the manufacturer of your wafers if you want to keep them available, and then what if they were also supplying your competitor?
 

Offline exe

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Re: Why is the 741 op amp still produced?
« Reply #84 on: September 29, 2020, 11:17:55 am »
Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Doesn't this compromise reliability? How to know if they can sustain this for prolonged period?
 

Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #85 on: September 29, 2020, 12:09:01 pm »
Getting supplies like wafers for old processes is a problem also.
I suspect that sourcing small wafers for old fabs only becomes a problem when the last small wafer fab closes. The problem is the cost per square mm will be higher, as it becomes more of a specialist product.
 

Offline David Hess

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Re: Why is the 741 op amp still produced?
« Reply #86 on: September 29, 2020, 09:04:26 pm »
Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Doesn't this compromise reliability? How to know if they can sustain this for prolonged period?

No, why would it compromise reliability?  That is how the parts are tested in the first place.

For a 44 volt 741, I would test the voltage follower configuration over the common mode input range while measuring the supply and input bias current at low and high temperature, for hours to days.

Getting supplies like wafers for old processes is a problem also.

I suspect that sourcing small wafers for old fabs only becomes a problem when the last small wafer fab closes. The problem is the cost per square mm will be higher, as it becomes more of a specialist product.

No, what I described has already happened even decades ago; old but popular parts may be redesigned for manufacturing on a new process simply because wafers for the old process are no longer available.
« Last Edit: September 29, 2020, 09:07:56 pm by David Hess »
 

Offline floobydust

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Re: Why is the 741 op amp still produced?
« Reply #87 on: September 29, 2020, 10:44:51 pm »
Are we saying there's been no improvements in analog IC technology? We should settle for 5V parts or just eat the 10x price hit to beat the 741's "features"?  :rant:

I saw National Semiconductor's standardized processes, high voltage (even to 170V) bipolar with better feature size, speed.
I think you can do more with less silicon when you take these old parts and move them to modern, standard processes.  We could compare 741 die shots to see how much it has shrunk.

National Semiconductor Develops New Complementary Bipolar Process
A Complementary Bipolar Technology Family With a Vertically Integrated PNP for High-Frequency Analog Applications
 

Offline T3sl4co1l

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Re: Why is the 741 op amp still produced?
« Reply #88 on: September 30, 2020, 12:43:16 am »
What do you mean no improvements?  We can do a heck of a lot more in 3.3V and less, than was ever possible in +/-15V or more, back in the day.  Mainly because we aren't limited in complexity by keeping everything analog.  The only place the voltage and current matter are where it touches the outside world; inputs can be divided down with precision resistors, leaving power output the last remaining at-scale, fully-analog challenge.  The higher cost of which is easily justified by the much greater overall functionality, no?

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Offline rstofer

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Re: Why is the 741 op amp still produced?
« Reply #89 on: September 30, 2020, 12:07:23 pm »
My Comdyna GP-6 analog computers are full of 741s,  The model in the metal can which costs about $13 at DigiKey.

https://www.oldcomputermuseum.com/comdyna_gp6.html
https://www.digikey.com/product-detail/en/texas-instruments/LM741H-NOPB/LM741H-NOPB-ND/148206

I suppose I could substitute more modern op amps but I won't.  I have two of the GP-6s to maintain.
 

Offline exe

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Re: Why is the 741 op amp still produced?
« Reply #90 on: September 30, 2020, 12:30:11 pm »
Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Doesn't this compromise reliability? How to know if they can sustain this for prolonged period?

Shouldn't parts be designed to withstand a certain voltage? I can try, say, supply a 5V opamp with 10V and it might even work for a while, but I bet it won't last long due to overstress (of course, 100% increase in voltage is on the extreme side.).
 

Offline floobydust

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Re: Why is the 741 op amp still produced?
« Reply #91 on: September 30, 2020, 06:16:18 pm »
I can't see how we're getting more - rail voltages are lower, costs are much higher even with the cheaper packages.
Semi manufacturers could easily modernize the IC (i.e. 741) as a new part - but it makes sense to not upset the op-amp portfolio by offering a medium performance part that is low cost, and scuttle profits.

I noticed TI added new LM358B with 36V rail, 3mV VOS, up from 0.7 to 1.2MHz bandwidth. 44 years of progress as the near cheapest op-amp they offer at $0.05/1ku.
Wow still the same 1971 Ford Pinto 0.5V/usec slew rate, can you feel the speed.
 

Offline james_s

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Re: Why is the 741 op amp still produced?
« Reply #92 on: September 30, 2020, 06:45:11 pm »
There are lots of cases where more speed is not needed, or could even be a detriment. Faster parts are more likely to oscillate or pick up and amplify noise. If you're doing something where a slow part is fast enough and the cost is lower, there's nothing wrong with using the slow part.
 

Offline tszaboo

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Re: Why is the 741 op amp still produced?
« Reply #93 on: October 01, 2020, 07:46:54 am »
Are we saying there's been no improvements in analog IC technology?
Yes, or almost yes. Look at all the improvements that were made in the realm of reference voltages.
The LTZ1000, 30 years ago could do sub ppm tempco. The LM399 ditto. In the meantime, there was the REF102 with 2.5ppm, released in 2000.
Meanwhile in the last 20 years, the biggest improvement is probably the LTC6655. 2ppm. But whoopty do, they placed it in a hermetically sealed package, and charged 8 dollars for it. You know, the same package, that every 10 cent crystal oscillator comes in.
You want to measure something accurately? Use the 30 year old part, because nobody managed to make any new parts that come close to it. And all these things are a handful of PN junctions and precision resistors.

So yes, we have 24 bit ADCs in 2020, and nothing to drive them properly.
« Last Edit: October 01, 2020, 07:50:09 am by NANDBlog »
 

Online rsjsouza

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Re: Why is the 741 op amp still produced?
« Reply #94 on: October 01, 2020, 05:19:25 pm »
Don't forget that evolution usually is also tied to potential revenue. The fact nobody ever refined a process to reach LTZ or LM levels may be due simply to a lack of interest or too narrow of a market to be tapped into. The number of different voltage references available when compared to 30 years ago is impressive, but they are all competing in a segment with more relaxed demands.
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Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #95 on: October 01, 2020, 05:42:35 pm »
Don't forget that evolution usually is also tied to potential revenue. The fact nobody ever refined a process to reach LTZ or LM levels may be due simply to a lack of interest or too narrow of a market to be tapped into. The number of different voltage references available when compared to 30 years ago is impressive, but they are all competing in a segment with more relaxed demands.
I've been in new product discussions a few times where someone proposes something, people look at the numbers, and conclude that any more players in such a small market will mean everyone ends up making a loss. These projects do NOT move forwards. People are concerned about tit for tat move - we screw up their nice little niche, and they'll screw up one of ours. While you don't see new very high stability references appearing, you see plenty of improvement in the medium (5PPM to 20PPM) integrated references reaching into ever cheaper complex ICs. That's where the volume is.
 

Offline David Hess

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Re: Why is the 741 op amp still produced?
« Reply #96 on: October 01, 2020, 05:50:06 pm »
Are we saying there's been no improvements in analog IC technology? We should settle for 5V parts or just eat the 10x price hit to beat the 741's "features"?  :rant:

I saw National Semiconductor's standardized processes, high voltage (even to 170V) bipolar with better feature size, speed.
I think you can do more with less silicon when you take these old parts and move them to modern, standard processes.  We could compare 741 die shots to see how much it has shrunk.

The 741 and 324 style operational amplifiers rely on the very high base-emitter breakdown voltage of their PNP transistors to support a high differential input voltage range.  New "optimized" processes do not allow that.  I am not even sure how they make high differential input range parts on a modern high voltage process; I did a search a couple months ago and they were all limited to 7 volts at most.  Low voltage parts of course have no issue with this because they should never see a high differential input voltage.

JFET input parts could do it, and this is one of their advantages, but how many of those are made on a modern process?  None?
« Last Edit: October 01, 2020, 05:52:12 pm by David Hess »
 

Offline David Hess

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Re: Why is the 741 op amp still produced?
« Reply #97 on: October 01, 2020, 05:57:51 pm »
Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Doesn't this compromise reliability? How to know if they can sustain this for prolonged period?

Shouldn't parts be designed to withstand a certain voltage? I can try, say, supply a 5V opamp with 10V and it might even work for a while, but I bet it won't last long due to overstress (of course, 100% increase in voltage is on the extreme side.).

For 741s and similar ICs which were originally built on the old NPN only process, it is more of a yield problem.  The criteria for failure at a higher voltage was excessive leakage which depended on process variation.  As far as I know, there was no separate process for 44 volt parts as this would have been completely uneconomical.

The same is true of bipolar transistors; the maximum Vceo varies considerably from part to part and the same part will be graded into multiple part numbers reflecting its tested Vceo.

A part designed for 5 volts maximum, like TTL, usually takes advantage of the maximum Vbe of roughly 5 volts which varies much less than the Vceo.  5 volt parts do not have to be designed to consider base-emitter breakdown.  These same parts however can usually support much higher output voltages on their open collector outputs.
« Last Edit: October 01, 2020, 06:02:14 pm by David Hess »
 

Offline coppice

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Re: Why is the 741 op amp still produced?
« Reply #98 on: October 01, 2020, 06:47:41 pm »
For 741s and similar ICs which were originally built on the old NPN only process, it is more of a yield problem.
When the 741 was designed a 5% yield was considered a good day. Now its close to 100% for simple devices like that. Times have definitely changed.
 

Offline SilverSolder

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Re: Why is the 741 op amp still produced?
« Reply #99 on: October 01, 2020, 06:59:09 pm »
Not all '741s are rated to 44V. The LM741C is only rated to 36V maxium.

Nothing stops you from testing and grading your own LM741Cs for a 40 or 44 volt operation.  Tektronix used to do exactly this for some reason.

Doesn't this compromise reliability? How to know if they can sustain this for prolonged period?

Shouldn't parts be designed to withstand a certain voltage? I can try, say, supply a 5V opamp with 10V and it might even work for a while, but I bet it won't last long due to overstress (of course, 100% increase in voltage is on the extreme side.).

For 741s and similar ICs which were originally built on the old NPN only process, it is more of a yield problem.  The criteria for failure at a higher voltage was excessive leakage which depended on process variation.  As far as I know, there was no separate process for 44 volt parts as this would have been completely uneconomical.

The same is true of bipolar transistors; the maximum Vceo varies considerably from part to part and the same part will be graded into multiple part numbers reflecting its tested Vceo.

A part designed for 5 volts maximum, like TTL, usually takes advantage of the maximum Vbe of roughly 5 volts which varies much less than the Vceo.  5 volt parts do not have to be designed to consider base-emitter breakdown.  These same parts however can usually support much higher output voltages on their open collector outputs.

I have a batch of transistors whose actual breakdown voltage is astronomical compared to the specification.   Does/did it ever happen in production, that the process improved to the point where even the lowest specced parts easily achieved the performance of the (older) highest rated parts - so the lower rated parts effectively became price/performance "bargains" (but not advertised, so nobody would ever know)?

 


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