Wideband modern low noise analog front ends  - Page 1
Forum section: electronics / projects

author: nimish
author_rank: Regular Contributor
timestamp: February 26, 2023, 11:02:43 pm
content: What's a good resource on modern design techniques for wide-ish ~100MHz analog front ends (dc coupled) for data acquisition? Few daq card makers are willing to share their secrets for obvious reasons.Looking for >10 bit ENOB ideally. Especially interested in input voltage protection without compromising leakage current and other noise sources.

author: TimFox
author_rank: Super Contributor
timestamp: February 26, 2023, 11:45:07 pm
content: An overpriced, yet modern, textbook is "Wideband Amplifiers" by Peter Starič and Erik Margan, Springer 2006.https://link.springer.com/book/10.1007/978-0-387-28341-8Please sit down before checking the price: maybe you can find a library copy or used book.

author: jonpaul
author_rank: Super Contributor
timestamp: February 26, 2023, 11:55:48 pm
content: Tektronix Circuits Concept book Oscilloscope vertical amplifiershttp://www.davmar.org/concepts.htmljon

author: mawyatt
author_rank: Super Contributor
timestamp: February 27, 2023, 01:48:23 am
content: Quote from: TimFox on February 26, 2023, 11:45:07 pmGood reference. Used to have this but it "disappeared" from my office bookshelf back before I retired!! Same for my Hard Copy Zvreve Handbook of Filter Synthesis, at least they left the soft copyBest,

author: David Hess
author_rank: Super Contributor
timestamp: February 27, 2023, 03:47:20 am
content: Either or both of the Jim Williams books, "Analog Circuit Design: Art, Science and Personalities" and "The Art and Science of Analog Circuit Design", have chapters discussing oscilloscope vertical amplifier design which apply to your application.And 10 or 12 bit setting time performance at 100+ MHz requires a heroic effort. Just verifying that sort of performance requires a heroic effort. You might want to study the application notes Jim Williams wrote about verifying DAC settling time to get an idea of what is required.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: February 27, 2023, 06:43:20 am
content: I suggest looking at AFE reference designs and evaluation modules at ti.com and analog.com.

author: mawyatt
author_rank: Super Contributor
timestamp: February 27, 2023, 02:21:17 pm
content: Quote from: David Hess on February 27, 2023, 03:47:20 amBoth of those excellent books, along with Bob Pease's book, also "disappeared" from my office bookshelveAnyway, recall Jim (or maybe Bob) book(s) mentioning the brilliant Tektronix Patented Ft Doubler amplifier by Carl Battjes and Trade Secret T-Coil by Bob Ross both of which kept Tek almost a decade ahead of HP in the real time analog scope bandwidth arena!! Also recall that Tek didn't want to patent the Ross's T-Coil and kept it as a Trade Secret so it wouldn't become "public knowledge"!!Best,

author: MasterT
author_rank: Frequent Contributor
timestamp: February 27, 2023, 02:24:49 pm
content: Look at analog.com, there are a few ultralow distortion OPA, like AD8000, AD8007, AD8003

author: dobsonr741
author_rank: Frequent Contributor
timestamp: February 27, 2023, 03:18:03 pm
content: Look at XBUF802:https://www.ti.com/lit/ug/sbau383a/sbau383a.pdfThe EVM shows how to use the X802 buffer for an accurate DC to 1GHz range, has input protection, has low noise so can achieve >10 ENOB.Does not address PGA, filters, differential path, ADC drivers. However TI.com has plenty of additional resources for designing/applying their stuff for those. In the last 10 years TI is the best leading in design support, IMO, since the demise of Linear app notes.

author: David Hess
author_rank: Super Contributor
timestamp: February 27, 2023, 03:30:57 pm
content: Quote from: dobsonr741 on February 27, 2023, 03:18:03 pmNotice that the XBUF802 datasheet only specifies settling time to 1% (0.7ns) and 0.1% (1.3ns). That is outstanding for 8-bit or even 10-bit 200 MHz performance, but what is not shown, and TI has a history of this, is settling time to higher precision, probably because it never settles, at least by itself. Do not expect 12-bit and higher performance out of this part.Admittedly duplicating that performance would be very difficult without hybrid construction, and impossible without building your own instrumentation, so it would be a good part to start from, andthe datasheethas some good example circuits.If I was going to duplicate the performance, I would carefully study the input stage of the Tektronix 7A13 vertical amplifier because of its bootstrapped input stage which should settle to higher accuracy. But duplicating its design would be a good way to make a VHF oscillator and redirect local air traffic. Wideband amplifiers like that love to oscillate. I notice that the X802 does not apparently use bootstrapping.

author: mawyatt
author_rank: Super Contributor
timestamp: February 27, 2023, 04:55:53 pm
content: Maybe not the lowest noise but for extreme bandwidth we've utilized (SiGe BiCMOS) a differential In/Out type amplifier called "Cherry Hooper". Here's good references from Professors Mark Rodwell and Ali Hajimiri.https://web.ece.ucsb.edu/Faculty/rodwell/Classes/mixed_signal/mixed_signal_notes_set_3.pdfhttp://www.infocobuild.com/education/audio-video-courses/electronics/EE114-AnalogCircuitDesign-Caltech/lecture-53.htmlBest

author: nimish
author_rank: Regular Contributor
timestamp: February 27, 2023, 11:12:20 pm
content: Quote from: David Hess on February 27, 2023, 03:30:57 pmThe BUF802 data sheet as well as TIDA-01022 and TIDA-00826 seem to be pretty good, along withhttps://www.ti.com/lit/ug/tidu174/tidu174.pdfCan't find ones from ADI, buthttps://digilent.com/reference/zmod/scope/reference-manualseems comprehensive, though not up to 100MHz.What prompted this whole thing was this digitizer performance sheet:https://www.gage-applied.com/digitizers/digitizer-enob.htmclearly there's some technique that can preserve performance to 100MHz even if it's infeasible for normal people.That said, it doesn't even seem like there are commercial, discrete op-amps with the settling time required for 12 bit ENOB+ beyond the double digit MHz. What do people do to compensate aside from custom ASICs?RED Pitaya's schematics:https://downloads.redpitaya.com/doc/Customer-DOC_STEM250-12_V1r1.pdfthey don't give the AFE details but ADI says they use AD8000, AD9613, AD9746, ADA4817-1, ADA4932-1 (Fromhttps://www.analog.com/en/products/ada4817-1.html)

author: David Hess
author_rank: Super Contributor
timestamp: February 28, 2023, 12:18:42 am
content: Quote from: nimish on February 27, 2023, 11:12:20 pmBut GaGe is only referring to SINAD performance and not settling time. Which matters more depends on your application but in time domain applications I consider settling time more important because it is more difficult to deal with.QuoteWhen settling time matters, they use hybrid or discrete circuits. Integrated circuits have problems with thermal interactions and coupling between circuit elements which limit settling time performance, which is why settling time is specified separately for operational amplifiers. It is not something which can be derived from speed, precision, and distortion specifications.If you are only interested in distortion and noise, then everything is there to evaluate the XBUF802 except spurious free dynamic range which is what I consider the most important since it always seems to be the most limiting factor.

author: nimish
author_rank: Regular Contributor
timestamp: February 28, 2023, 06:04:21 am
content: Quote from: David Hess on February 28, 2023, 12:18:42 amFair enough, but the SINAD figure would include some contribution from settling time induced errors, right? The spectrum will have spurs from that along with other junk.

author: coppercone2
author_rank: Super Contributor
timestamp: February 28, 2023, 06:17:16 am
content: don't forget about SINBAD, just as important as SINAD

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2023, 12:00:04 am
content: Quote from: nimish on February 28, 2023, 06:04:21 amI am not aware of any correlation between SINAD and settling time. Plenty of faster amplifiers with better SINAD have worse settling time.

author: TimFox
author_rank: Super Contributor
timestamp: March 01, 2023, 04:31:25 am
content: Quote from: David Hess on March 01, 2023, 12:00:04 amIt's not a correlation as such, but certain features such as slew rate would degrade both settling time and SINAD under appropriate conditions.

author: Marco
author_rank: Super Contributor
timestamp: March 01, 2023, 03:23:06 pm
content: Settling time as in ringing is purely linear. A small amplitude oscillation isn't linear, but likely narrow band.Why wouldn't you be able to compensate for these?

author: David Hess
author_rank: Super Contributor
timestamp: March 01, 2023, 04:36:42 pm
content: The problem is that once you get past the bandwidth and slew rate, settling time is controlled by other factors, like mismatch in pole-zero compensation and thermal feedback from output stages to input stages. The former is why fast high gain three stage operational amplifiers have slower settling time, and the later is why integrated operational amplifiers have slower settling time. So settling time depends as much or even more on the construction, design, and process used, than the bandwidth and slew rate. Discrete and hybrid designs have an advantage because they have no thermal feedback and no parasitic elements to a substrate.Of course you can get fast operational amplifiers which have fast settling times ... to lower precision. Because of their lack of open loop gain, they will *never* settle to a higher precision. There are parts optimized for fast settling at high precision, but they are a class of parts all to themselves. Look for operational amplifier intended for 16-bit applications.

author: nimish
author_rank: Regular Contributor
timestamp: March 01, 2023, 05:22:33 pm
content: Quote from: David Hess on March 01, 2023, 04:36:42 pmSettling time must have a component included in SINAD, consider that a very sharp square wave would show settling related ringing errors on the jumps, different from Wilbraham-Gibbs phenomenon (although, I guess, similar in spirit)Also, hybrid circuits have much higher thermal coupling to the ceramic substrate, and therefore to other components, right? Alumina is very thermally conductive compared to fiberglass. It'd help prevent thermal gradients much better. And parasitics would exist regardless, it's a matter of magnitude.All ears for advice related to settling time, it seems to be well hidden in data sheets since it's quite tricky to deal with. 16 bit settling time op-amps have very limited bandwidth for obvious reasons.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 02, 2023, 02:11:00 pm
content: lots of notes and ref designs here.https://www.analog.com/en/design-center/search.html?q=*&Filters=template_fac_s:3f87222389034212a868c5c0cd12cacc|prod_cat_l2_fac_sm:abeceef892a548e1bee9a70103b12378_8ecabf98221e40a4a8e07b076f241d71|prod_cat_l1_fac_sm:abeceef892a548e1bee9a70103b12378

author: gf
author_rank: Super Contributor
timestamp: March 02, 2023, 03:09:34 pm
content: Quote from: nimish on March 01, 2023, 05:22:33 pmOnly if non-linear effects are involved. Any linear filter has a particular impulse/step response and coresponding settling time, too, w/o introducing any additional frequencies / spurs in the spectrum.

author: TimFox
author_rank: Super Contributor
timestamp: March 02, 2023, 03:16:28 pm
content: An anecdote from early in my career, ca. 1982.At that time, Harris made fast normal op-amps for general purposes.I needed a fast-settling amplifier to follow an analog mux.I calculated the settling time based on the required bandwidth, then the required slew rate for that exponential step response, and chose an amplifier from the Harris devices with the required bandwidth that exceeded that slew rate.It settled nicely down to 12 bits or so, but then a longer time kicked in (probably thermal) and it didn't meet the spec down to 16 bits.Experimenting on the breadboard, another Harris op amp, with insufficient slew rate for the previous calculation, worked to the spec.At the beginning, the settling was dominated by the slew rate, but after leaving the slew-rate limit it settled nicely to the spec.As I remember, the second device was much simpler than the first internally.

author: mawyatt
author_rank: Super Contributor
timestamp: March 02, 2023, 04:39:21 pm
content: When a negative feedback system, op-amp or other type, encounters "slew-rate limiting" the negative feedback loop essentially opens. This causes various nodes/elements/devices within the system to be driven into voltage, current and charge positions that are not normal to the proper closed loop condition.When the system attempts to return to normal and exits the slew-rate limited, thus re-entering the closed loop negative feedback by closing the loop again, some of the nodes/elements/devices are slow to recover because of various reasons including limited available currents, device saturation, and even localized thermal effects. For example, a bipolar bias device may saturate and store significant charge, thus requiring charge removal to return to normal operation and this charge removal is limited by the circuit design.Also devices may change internal temperature (the thermal impedance of a transistor to substrate is quite large, but with a relatively long time constant), so may take some time to re-establish device to device thermal equilibrium when is quite important in precision circuitry (think bias trees, diff amps, and such). For example for a unity step response tail to reach 1 LSB of a 12 bit high open loop gain negative feedback system requires theinput referencedthermal difference between a pair of differential bipolar transistors to reach thermal steady state conditions within ~45uK, at 16 bits this is ~15uK!!! This condition is why many general purpose op-amps have very long thermal tails and why having exceptional thermal equilibrium designs are important, George Erdi's famous cross coupled quad helped solve this, but other designs areas are also important. Recall the early 741 op-amps actually had enough thermal feedback from the output drive transistors to the input single differential pair that the input polarity would reverse (exchange + and - inputs) under heavy output currents with very high loop gains!!Many of the modern IC PDK kits don't have physical thermal device models, the digital CMOS ones that do likely aren't well conceived (digital isn't exactly analog precision!!), and a few fabs (IBM SiGe BiCMOS processes we are familiar with) have pretty good thermal models which might include local proximity effects as well as second order non-linear effects and time constraints. Of course having well developed thermal device models means the fab incurred additional PDK process kit development costs and must pass on to the actual fabrications, good PDK kits ain't cheap!!Anyway, in the old days the IC designers had to try and figure all the thermal effects without much Models/CAD help, and reverted to best guess trial and error approaches. Even today one is wise to allow for multiple design iterations if the settling precision is important, and one is restricted to a process which has limited PDK thermal models.Best,

author: TimFox
author_rank: Super Contributor
timestamp: March 02, 2023, 05:18:16 pm
content: When I encountered that design problem, it was nearly impossible to find an amplifier specified for settling to better than 0.01%, which is less than 14 bits.I agree that my original problem was probably thermal: we always evaluated multiplexer post-amp settling going from high to low (zero), comparing the switching from low/low and high/low.In my case, the swing from high to low was less than the slew rate, but the long tail that prevented hitting 16-bit accuracy was very slow and therefore probably thermal.

author: nimish
author_rank: Regular Contributor
timestamp: March 03, 2023, 01:49:35 am
content: Quote from: gf on March 02, 2023, 03:09:34 pmSure, and settling time is inherently nonlinear since it includes, among other things, slew rate limits. If I stick an ideal square wave in I get a nonlinearly distorted square wave out, no?Also how is the bridged t-coil thing any different from a constant resistance Zobel network? And where would I use it? Anywhere to cancel out unwanted shunt capacitance?OK apparently the technique is usually called bandwidth extension:https://www.researchgate.net/publication/2983288_Bandwidth_Extension_Techniques_for_CMOS_AmplifiersWhat secret sauce was Tek using on top of this? Or did they just realize they could use it?

author: mawyatt
author_rank: Super Contributor
timestamp: March 03, 2023, 02:50:00 pm
content: Quote from: nimish on March 03, 2023, 01:49:35 amHere's a couple references on Tek secret sauce magic from the 1960s & 70s.https://vintagetek.org/electronic-design-t-coils/And Bob Pease's ref.https://www.electronicdesign.com/technologies/analog/article/21807815/whats-all-this-tcoil-stuff-anyhowThere is a section in Pease's notes that is anabsolute must read if one is interested, actually one should the read the entire article and the book Wideband Amplifiers. This is about a discussion with the brilliant Stanford Prof Tom Lee whom I meet while on a IEEE IMS panel session long ago. Here's a snip from "Talking with Lee at the eFlea";"“They already had T-coil magic that worked for vacuum tubes, but found that transistors were different enough to require new incantations. They had no proper equations for how to design T-coils for bipolar transistors, because the derivation is really, really hard. The input resistance complicates things enormously. Bob says, ‘Ya know, I think I know how to do that.’ He spent the better part of a year trying to figure it out. He says this is the hardest derivation he’s ever done in his entire career. But he figured it out.“Tek felt, rightly, that having the T-coil equations for the lossy, asymmetrical case was equivalent to having nukes when everyone else only had rocks and pointy sticks, so they kept this knowledge as a trade secret. The T-coil was one important bit of magic that allowed Tektronix to maintain such a lead on everybody else, because they could get double or triple the gain-bandwidth product out of an amplifier just by adding a capacitor and a pair of coupled inductors in the right place.”"Interestingly the math behind the Ross solution dates back to K T Wang in 1930, which Bob Ross was exposed to at UC Berkley in 1960s.Best,

author: 2N3055
author_rank: Super Contributor
timestamp: March 03, 2023, 03:14:42 pm
content: Quote from: mawyatt on March 03, 2023, 02:50:00 pm"Wideband Amplifiers" by Peter Starič and Erik Margan is good explanation behind the principles and math of T-coils.Starič worked in Tek:https://vintagetek.org/peter-staric/

author: nimish
author_rank: Regular Contributor
timestamp: March 04, 2023, 12:59:12 am
content: Quote from: 2N3055 on March 03, 2023, 03:14:42 pmI did, and it basically appears to go over inductive peaking and other BW extension techniques inc T-coils but what I was confused by is:a) How is this different from an input impedance transformation using a constant-R Zobel network?b) What was Tektronix's specific advantage beyond applying the well-known constant-R Zobel network -- this had been used in transmission lines and audio for 20 years before Tek existed:https://en.wikipedia.org/wiki/Boucherot_cellinvented in a1919 paper that isn't online(!)And the short answer is "it's not" and Tek's secret sauce was Ross's use of Wang algebra to quickly compute the symbolic solutions to the Kirchhoff equations.For whatever reason computing Cramer's Rule on matrices was hard, so they lucked out in that the bridged-T coil results in a symmetric system of equations so Ross could use the Wang algebra to quickly do the tedious at the time computation:Ross explains it hereDuffin and Bott did more work:http://pi.math.cornell.edu/~hubbard/botttalk.pdfand that's basically the SOTA today for network synthesis. Duffin's got some other papers on applications of Wang algebra:https://homepages.math.uic.edu/~kauffman/DuffinLong.pdfhttps://www.ams.org/journals/tran/1959-093-01/S0002-9947-1959-0109161-6/S0002-9947-1959-0109161-6.pdfhttps://www.jstor.org/stable/1990850And you can hire Ross (via samtec) to consult on SERDES, where using the T-coil techniques and more is ubiquitous to get the ~50GHz BW

author: mawyatt
author_rank: Super Contributor
timestamp: March 04, 2023, 02:18:01 am
content: @ nimish,You bring up an interesting topic, suggest you create a IEEE Circuits & Systems, or IEEE Proceedings paper on the subject of the Tektronix T-Coil and Ross's contributions or lack thereof.I'm sure Professors Tom Lee, Hajimiri, Rodwell and others would welcome, critique and maybe even contribute, and we all would gather a much better understanding of what transpired back then and as you seem to infer maybe it's not that big a deal, altho HP couldn't solve this and you can bet they certainly tried!!Even in hindsight Lee seemed to have some difficulty, per his comment here from Pease's article:"A Tektronix engineer, whose name Lee can’t recall, wrote him and asked who at Tek told Lee about the T-coil derivation. Lee told him, “I did this independently, since you guys never published this stuff.” The Tek engineer said T-coils were a Tek trade secret, to which Lee responded, “I’ve got blood-soaked pages to prove that I did this on my own, because I did it wrong many more times than I did it right.” The Tek engineer then engaged in some good-natured ribbing that Lee only solved the symmetrical case, where both coils have the same value.That engineer referred Lee to John Addis, of the Tektronix Museum near Portland. The engineer said that Addis was “Mr. T-coil.” Addis was Tek's most prolific and able designer of T-coil-based amplifiers, but he pointed Lee to Bob Ross as the engineer who had derived the equations. Addis then introduced Lee to Ross. Professor Lee recounts the story:“That started a friendship with Bob, who told this amazing story that starts in China in the 1930s. There was this gifted engineer, K.T. Wang, who was way too smart to work on just his power plant management job. He made up electrical engineering brain teasers for himself and then solved them. Over years of doing this to keep his mind from turning into oatmeal, he noticed there was a pattern to some of these problems. They would be easy to set up, then horribly horrible to solve, and in the end the beast would collapse to something much simpler and very elegant. He wondered, ‘Is there a way to get to the end without going through the middle.’ So, he came up with these weird ad-hoc rules that enabled him to shortcut a lot of the ugly math.“Not knowing anything about Wang, I had come up with my own method and published what is, as far as I know, the first T-coil derivation in the open literature [Planar Microwave Engineering, Ch. 12 Appendix, Cambridge Press, 2004]. It was not a general method. It was only good for the lossless symmetrical case; it cannot be gracefully extended to anything else. Tektronix had the Full Monty, the lossy asymmetrical case, and I wanted to figure out, who the heck did that, and how? I wanted to meet that guy. Well now I’ve met that guy, the brilliant Bob Ross."Best,

author: mawyatt
author_rank: Super Contributor
timestamp: March 04, 2023, 02:58:35 am
content: If we revisit the past back in the 1960s the high frequency transistors available were 2N918, 2N2857, and a few others we can't remember. New high frequency transistors weren't introduced often and the designers had to squeeze as much bandwidth as they could with what was available and not bank on a much faster device coming along anytime soon.This is why the Tektronix Ft Doubler Circuit and the T-Coil were so important IMO, they could get much more bandwidth for a given set of transistors than HP or anyone else.Best,

author: Terry Bites
author_rank: Super Contributor
timestamp: March 04, 2023, 04:52:27 pm
content: This is interesting:

author: nimish
author_rank: Regular Contributor
timestamp: March 05, 2023, 03:38:38 am
content: Quote from: mawyatt on March 04, 2023, 02:18:01 amMy distillation is that Ross didn'tinventthe bridged T-coil as it's a special case of a constant-R bridged-T Zobel network, but hewasable to get the design equations for it as well as asymmetric extensions, which is non-trivial. Zobel had invented them before 1928:https://ieeexplore.ieee.org/abstract/document/6769393, and Boucherot had used a special case even earlier in 1919 and perhaps as early as 1895:https://patents.google.com/patent/US548511A/enfor what we'd now call passive power factor correction.So I think it's fair to say Ross was critical to the development of the T-coil as a practical tool to construct constant-R input filters that allowed Tektronix to maintain an edge against the competition for decades, which is a ridiculous achievement if you think about it. From the Staric and Margan book you can see it getting >2x BW improvement with some tradeoffs.Now, of course, they are everywhere. The BUF802 data sheet even uses a shunt inductive peaking filter to compensate for the 2.4pF input capacitance so as to maintain the 50 ohm input impedance over a longer bandwidth, though their choice of 6.8nH vs, say, 3.3 nH, is a little odd.Anyway,https://epubs.siam.org/doi/book/10.1137/1.9781611975826has a good review andhttps://link.springer.com/chapter/10.1007/978-3-319-67068-3_21is good too, co-authored by the guy who invented the inerter / J-damper passive mechanical circuit element as used in F1.

author: mawyatt
author_rank: Super Contributor
timestamp: March 06, 2023, 02:49:24 pm
content: Would be interesting to see where researchers are today with ultra-wideband techniques, devices and amps. I know DC to 100GHz was passed a couple decades ago, and DC to THz a decade ago, suspect today some folks are approaching literally "DC to Daylight"Best,

author: Martinn
author_rank: Frequent Contributor
timestamp: March 06, 2023, 08:42:19 pm
content: Quote from: nimish on March 05, 2023, 03:38:38 amWhen I read that passage in the datasheet, I wondered whether one could apply this technique to an oscilloscope input through terminator? I just purchased a R&S RTB2k which lacks the input termination (so needs a 50 Ohms BNC through terminator for 50 Ohm sources). My guess would be that for 300 MHz BW it's not really necessary - and had I needed 1 GHz, I would have bought a different scope (which would then have had the proper switchable input termination).

author: mawyatt
author_rank: Super Contributor
timestamp: March 06, 2023, 09:16:52 pm
content: Quote from: Martinn on March 06, 2023, 08:42:19 pmEvidently Tek utilized these T-Coils in Scope probes and Current probes back in the day, and took advantage everywhere of this unique bandwidth extension knowledge. You can imagine what HP was going thru trying to figure out this T-Coil stuff that Tek was utilizing, and exactly why Tek didn't want to file any patents and kept the Ross solutions a trade secret!!I mean HP had some really smart folks, and you can bet they certainly were trying!!http://www.davmar.org/TE/TekConcepts/TE/TekConcepts/TekProbeCircuits.pdfOf course everything seems simple in hindsight!!Best,

author: David Hess
author_rank: Super Contributor
timestamp: March 07, 2023, 12:38:02 am
content: Quote from: TimFox on March 02, 2023, 05:18:16 pmThis is the kind of modern "16-bit" operational amplifier was thinking of:https://www.analog.com/en/technical-articles/lt1468-an-operational-amplifier-for-fast-16-bit-systems.html

author: nimish
author_rank: Regular Contributor
timestamp: March 07, 2023, 01:13:22 am
content: Quote from: mawyatt on March 06, 2023, 09:16:52 pmA certain W. R. Hewlettinventedthe distributed amplifier concept (look at the Negative Mutual-Inductance Circuit in that paper), so I doubt HP was unaware.Was he still around by then? Would have been incredible if the knowledge was forgotten.

author: mawyatt
author_rank: Super Contributor
timestamp: March 07, 2023, 02:35:50 am
content: Quote from: nimish on March 07, 2023, 01:13:22 amAs we suggested earlier, since you have so much conflicting information regarding Tektronix, Ross and the T-Coil, strongly suggest you create a paper and submit to the IEEE for a peer review. I'm sure this will catch the attention of many knowledgable folks, maybe some still around from that era that participated in the Tek/HP analog scope wars!!Back then the HP rep tried his best to get us to use HP analog scopes, even almost giving us them. We always ended up using Tektronix, they were just the masters of these Time Domain Instruments. HP also lacked in the triggering circuitry, Tek's clever use of ECL gates and circuitry just worked better in real world lab use, same as the rest of the Tek scope features.Of course this is just my opinion, and we had no dislike for HP, in fact almost everything else in our labs was HP!!BTW Bill Hewlett was certainly around back then as he passed away at 87 in Jan 2001, and was President until 1977, so obviously not suffering from any mental lapses during this time.Best,

author: David Hess
author_rank: Super Contributor
timestamp: March 08, 2023, 02:24:25 am
content: Quote from: mawyatt on March 07, 2023, 02:35:50 amThe story my father tells is that when he was working at a national lab in the 60s and 70s, the quality of the HP oscilloscopes was lacking compared to the Tektronix oscilloscopes, and that was the determining factor.