Opamps - Die pictures - Page 1
Forum section: electronics / projects

author: Noopy
author_rank: Super Contributor
timestamp: June 10, 2020, 07:42:33 pm
content: Hi all,if you are interested in more opamp die pictures I can post them here.Till know I have taken pictures of aRaytheon LM318https://www.richis-lab.de/Opamp05.htmThomson LM318https://www.richis-lab.de/Opamp06.htmSescosem SFC2741https://www.richis-lab.de/Opamp07.htmSignetics NE5534https://www.richis-lab.de/Opamp01.htm

author: magic
author_rank: Super Contributor
timestamp: June 10, 2020, 08:25:26 pm
content: Coincidence: LM318 actually has a somewhat similar three stage topology to NE5534, although it may be hard to see it in this jungle of a schematic.Capacitors are also connected in the same way, only one is not used (or perhaps not included in the datasheet). National's "Linear Brief" LB-17 explains a few things about this design.Did you have some particular interest in this chip or just opened it because somebody from the forum sent you one?Many precision amps like OP-07 or LT1028 (LT1115 is at Zeptobars) also use similar three stage topologies with similar compensation. LM118/318 was the first as far as I know.BTW, those "adjustable" resistors appear to be simply pinch resistors. This has nothing to do with adjustments or precision of any kind, their tolerance is quite poor actually, but everything to do with producing high resistance on minimum die area.

author: Noopy
author_rank: Super Contributor
timestamp: June 10, 2020, 08:34:49 pm
content: Quote from: magic on June 10, 2020, 08:25:26 pmInteresting!Quote from: magic on June 10, 2020, 08:25:26 pmThe opamps just appeared in my inbox.Quote from: magic on June 10, 2020, 08:25:26 pmI agree with you principally.I speculated whether Raytheon changed the length of the overlay to adjust the resistors. Indeed not very accurate...

author: Noopy
author_rank: Super Contributor
timestamp: June 11, 2020, 06:31:59 am
content: Two more words about the suspected adjustable resistors.Since they are pinch resistors they are commonly not very accurate. Anyway one can speculate whether Raytheon had a possibility to tune them (by mask modification perhaps).It seems not plausible that Raytheon puts the least accurate resistors in places where they originally wanted the most accurate.

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2020, 11:55:49 am
content: Quote from: magic on June 10, 2020, 08:25:26 pmUnlike those, the 318 uses emitter degeneration to lower transconductance of the first stage allowing better frequency response but this increases noise and drift making it unsuitable for audio and precision applications. I think it was the first commercial integrated operational amplifier suitable for video applications.

author: magic
author_rank: Super Contributor
timestamp: June 11, 2020, 06:27:14 pm
content: Quote from: Noopy on June 11, 2020, 06:31:59 amYes, I think you're right about the tuning thing. These resistors set things like input/output stage bias currents, etc. Apparently some production variation didn't bother them too much.I thought they simply used this slashed resistor symbol to indicate pinch resistors for whatever reason, but that's clearly not the case. There are pinch resistors drawn normally on the schematic and there is a resistor drawn with a slash which is not a pinch resistor (R2).BTW, this is not Raytheon's schematic. Get the original from National, it has component numbers and typical valuesRaytheon also cheated in the bias circuit and R2 doesn't even exist in their version, but it exists on the Thomson.Quote from: David Hess on June 11, 2020, 11:55:49 amSo does Douglas Self, though not as much.Noise seems about on par with RC4558 which often successfully passes as NE5532 on AliBay10~15nV/rtHz isn't terribly bad for line level signals.On the upside, open loop linearity is improved. There is even an LM318 thread on DIYAudio: somebody swore that it's good for driving an external power stage, but its own DC linearity driving a few kΩ load was reported as "between that of µA709 and µA741".https://www.diyaudio.com/forums/solid-state/349054-lm318-distortion.html

author: Noopy
author_rank: Super Contributor
timestamp: June 12, 2020, 06:27:45 am
content: Quote from: magic on June 11, 2020, 06:27:14 pmYou are right but since Raytheon printed this schematic in their datasheet I wanted to refer to this one.Perhaps they had to change one small thing in their design to make it "legal" and selected R2.

author: magic
author_rank: Super Contributor
timestamp: June 12, 2020, 07:41:44 am
content: The whole bias generator is missing. Look near IN+ - it's a simple 1:3 current mirror fed by that long, snaking resistor. At the beginning of the resistor there might be an emitter follower. In other Raytheon circuits the base would be connected to an n-JFET + zener reference, though I can only identify a JFET here. Not sure what's going on, but it certainly is not the real LM318 bias circuit.Ditto with RC5534. There is a metal layer diagram in the datasheet and it has a black hole where the bias generator ought to be (left of the output transistors). Proper NE5534 bias generator contains a pair of lateral PNPs. Nothing like that is seen anywhere besides the second stage differential pair.

author: Noopy
author_rank: Super Contributor
timestamp: June 12, 2020, 08:37:31 am
content: You are right. The bias circuit is very different, less complex:

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2020, 09:38:38 pm
content: Quote from: magic on June 11, 2020, 06:27:14 pmI should have said low noise audio like microphone amplifiers. After the first gain stage, the added noise is irrelevant unless it limits dynamic range.QuoteThe datasheets I have show twice the broadband noise and 6 times the low frequency noise of the RC4558.QuoteThe 318 has about twice the output current capability as common lower power parts and its high speed allows it to operate inside of a feedback loop. In the past I have used it as a driver for these reasons.

author: Noopy
author_rank: Super Contributor
timestamp: June 27, 2020, 08:14:52 pm
content: Hi all!Today I can show you an opamp configured to act as voltage follower:https://richis-lab.de/Opamp08.htmLM310 built by Silicon GeneralSchematic is taken from National Semiconductor datasheet.It´s a differential amplifier (red) with an output stage (purple). No VAS since a voltage follower needs no voltage amplification. And with lower amplification you need less negative feedback. With less negative feedback a bigger bandwith is still stable.The die is not extremly interesting...

author: magic
author_rank: Super Contributor
timestamp: June 27, 2020, 09:12:56 pm
content: Well, one interesting thing is that the circuit uses a bunch of superbeta NPNs and it looks like there is no obvious way to tell them apart visually.And class A output stage. Probably that's the true reason why it's so fast: no dirty PNPs in the signal path

author: Noopy
author_rank: Super Contributor
timestamp: June 28, 2020, 05:36:17 am
content: You are right. There should be superbeta NPNs but as far as i know you can´t really distinguish them from "normal" NPNs. The base is just thinner…There is a application note advertising the speed of the LM310 and explaining it with the use u NPNs.

author: magic
author_rank: Super Contributor
timestamp: June 28, 2020, 06:28:24 am
content: It's a common thing in "high speed" amplifiers built on 1970's noncomplementary processes. The 318/5534 also bypass their PNP differential stage with capacitors to yield an amplifier which is 100% NPN at high frequencies.There is one textbook author who will want you to believe that all of these capacitors are for nested Miller feedback, ignore him and read LB-17

author: Noopy
author_rank: Super Contributor
timestamp: June 28, 2020, 10:08:08 am
content: Yes, the right mixture of negative feedback and feedforward. That's the trick.What's LB-17?

author: magic
author_rank: Super Contributor
timestamp: June 28, 2020, 10:49:57 am
content: The NatSemi paper about LM118/318 which I mentioned before.

author: Noopy
author_rank: Super Contributor
timestamp: June 28, 2020, 12:05:15 pm
content: Of course! Sorry, I was confused somehow.

author: SeanB
author_rank: Super Contributor
timestamp: June 28, 2020, 12:55:45 pm
content: Now I know how those hundreds of SFC2741 op amps I changed over the years look like inside, thank you. most were changed because of offset drift going outside the limits that could be compensated, which was not bed after 20 years of being alternately baked and chilled.

author: Noopy
author_rank: Super Contributor
timestamp: June 28, 2020, 01:11:05 pm
content: More coming soon!

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2020, 04:23:22 pm
content: Check outLinear Technology application note 16where Widlar himself describes some details of PNPs on an NPN only process in these types of integrated circuits.

author: Noopy
author_rank: Super Contributor
timestamp: July 07, 2020, 08:49:17 pm
content: Today I have a comparator, a LM306, for you:https://www.richis-lab.de/Opamp09.htmIt´s a comparator, not a normal opamp. Note the difference.

author: Hydron
author_rank: Super Contributor
timestamp: July 08, 2020, 09:53:33 pm
content: Love the pictures!Have you looked at any of the more exotic modern analogue parts? Or are they normally covered with lots of metal etc, obscuring the interesting bits? I'm thinking of stuff a bit out of the ordinary like a AD8129/8130 (I assume there will be trimmed parts etc involved in one of those).

author: Noopy
author_rank: Super Contributor
timestamp: July 09, 2020, 03:22:27 am
content: That´s nice to hear!Right at the moment I just decap the parts people have donated. Often these parts are from the older generation but basically I decap everything.Especially in the opamp category I mostly have older parts. But I put the AD8129 on my to-do-list. Sounds interesting!

author: magic
author_rank: Super Contributor
timestamp: July 09, 2020, 06:55:44 am
content: Quote from: Hydron on July 08, 2020, 09:53:33 pmPerhaps not covered by lots of metal, but newer parts may use more than one metal layer which gives a bit of extra headache. You can see what it looks like on Noopy's AD587 voltage reference photos; thankfully that one had only two layers.The amplifiers you listed certainly use a true complementary process which means NPN and PNP will be much more similar to each other.Zeptobars probably has photographs of some more advanced analog parts.

author: macboy
author_rank: Super Contributor
timestamp: July 09, 2020, 01:11:33 pm
content: Quote from: magic on June 11, 2020, 06:27:14 pmI have an old instrument, "Precision Filters 602 Dual Anti-Alias Filter", which uses LM318H and LM301 in TO-99 cans for the analog circuitry. Measured with 80 kHz bandwidth, I measure around 3 ppm (0.0003%) THD+N. The THD only (20 harmonics) measures at 0.8 ppm (0.00008%) which is equivalent to the measurement floor of my VP-7722, so it is perhaps much less, but not higher than that. The instrument dates back to ca. 1970's.