[HN Gopher] Choosing an op-amp for your project
___________________________________________________________________
Choosing an op-amp for your project
Author : zdw
Score : 118 points
Date : 2025-01-03 22:51 UTC (4 days ago)
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| elcritch wrote:
| Great write up. And definitely skip the 60 year old models.
|
| Also valuable to look for is ESD protection. Many op amps have
| good 2kV static shock protection. Really sucks to have cascading
| failures due to touching your circuit and blowing an op amp.
|
| For some uses it's also good to checkout input current bias.
| elcritch wrote:
| Another bit I discovered is the quality of resistors. Pretty
| much any op amp circuit will use resistors. Often the resistors
| limit the static offsets.
|
| Don't stick with 1% for analog circuits as 0.1% precision
| resistors are cheap and come with low temp drift as well.
| f1shy wrote:
| To add to this discussion is useful the video or eevlog:
| https://www.youtube.com/watch?v=uq1DMWtjL2U
|
| where Dave discusses the "Jelly bean" op amps
| perriera wrote:
| >f you're designing a new op-amp circuit, here are some decent,
| all-around alternatives made in the 21st century
|
| None of the listed opamps would be an alternative to where an
| LM324 or TL071 are typically used - low cost, 20V-30V supply,
| infinite/guaranteed availability. They are 5V only and cost 10x
| as much.
| bratwurst3000 wrote:
| i build and repair audio electronics and the tl071 is used in
| abundance in audio circuits and is a bad choice imho. But good
| opamps for audio are at least a few dollars
| Archit3ch wrote:
| If you want the mirror the OpAmp distortion from the original
| units for authenticity/character, it makes sense to use the
| TL071, no?
| shermantanktop wrote:
| Based on my experience with vintage music electronics, it
| wouldn't be good enough to use a component that just sounds
| bad like a TL071; it needs to _be_ a TL071 so that the
| marketing copy can claim "vintage-correct parts."
|
| At that point you are engineering with a completely
| different set of tradeoffs than would be expected for a
| modern ground-up design effort.
| bratwurst3000 wrote:
| thats true. I forgot to mention i mean electronics from mid
| 90s onward. Even in higher class electronics. for example
| many of those 2000 euro upwards dj mixer use tl071 and even
| high end dac and soundcards.
|
| I replaced some of them with good opas and burrbrown opamps
| and for me it made , even if not big, audible changes to
| the better. But this could be my imagination.
|
| whatever i prefere some opamps in the range from 2-4 bucks.
| even if its only for the feeling...didnt measure it.
| spamatica wrote:
| Any suggestion for a (reasonably) good and cheap one for new
| designs?
| nicolaslem wrote:
| The book "Small Signal Audio Design" by Douglas Self has an
| entire 50 pages chapter on selecting opamps for audio. The
| chapter roughly ends with this quote:
|
| > One thing is obvious -- the 5532 is still one of the
| great opamp bargains of all time.
| bratwurst3000 wrote:
| i like the opa2134 pa , or in general the bur brown opa, on
| the expensive site and on the cheap one the ne5534.
| ckocagil wrote:
| For any consumer use to play back audio I can't image a
| scenario where TL071 wouldn't be enough. And you'd rarely
| even need an op-amp when integrated solutions are available.
| hn4352 wrote:
| Try the https://www.ti.com/product/TLV9301 $0.5 @ 1s of units
| w/ modern specs and a 40V supply range.
| peteforde wrote:
| I've watched the videos and agree that the OPA2323 does appear to
| sound amazing by subjective comparison to the TL071.
|
| However, it's not enough to say that it costs ~8.7x as much in
| local tokens because that doesn't reflect how much it costs as a
| percentage of the other components around it, many of which have
| a more profound impact on the outcome. This wouldn't stand as a
| good argument except that in many devices, you have a ceiling for
| how much your total BOM can cost before you've priced yourself
| out of competition.
|
| In the end, a 8.7x cost bump is a lot to swallow for a feature
| that most consumers are physically incapable of distinguishing
| between. Every time I've raised the possibility of using the
| fancy new chips, vastly more experienced engineers than me have
| come out of the woodwork to tell me that in almost all scenarios,
| the tradeoff between price and quality isn't worth it.
|
| Of course, if budget is not an issue, use the OPA2323. It really
| does sound great. Or more accurately, the degree to which it
| destroys good sound is as low as we can currently achieve.
|
| (This comment originally stated a 12x factor, but I was terrible
| at math.)
| Majromax wrote:
| Is the cost delta really 12x?
|
| Looking at Mouser Canada, it looks like the cheapest 071 is the
| TL071CDR, at $0.138/each (Canadian) in quantities of 5k. The
| OPA2323IDDFR is $0.49 in the same quantity.
|
| > In the end, a 12x cost bump is a lot to swallow for a feature
| that most consumers are physically incapable of distinguishing
| between.
|
| I think that the performance of an op-amp should very rarely
| have user-visible effects. The more interesting question is
| whether the more expensive chip can make for a simpler design
| elsewhere. For example, can a rail-to-rail amplifier save the
| extra cost of needing charge pumps and split-rail design
| elsewhere?
|
| Also, not all domains should be cost-optimized. Hobbyist or
| prototyping work might best benefit from using a more expensive
| but more capable amplifier as a first choice, saving on the
| number of components that might need to be stocked in the home
| lab.
| peteforde wrote:
| All good points! And I am no expert.
|
| FWIW, here is what I was going off of, price wise:
|
| https://www.digikey.ca/en/products/detail/texas-
| instruments/...
|
| https://www.digikey.ca/en/products/detail/texas-
| instruments/...
|
| In other words, the cheapest TL071 variant and the cheapest
| OPA2323 variant on Digikey Canada, in a quantity of 1 (ie
| wildly expensive). $0.31 vs $2.70 means that I shouldn't
| attempt math before coffee; 8.7x is still a big bump,
| although I acknowledge it's not the 12x I disinformationed
| earlier, with apologies to anyone reading.
| rasz wrote:
| If you are making a one-off $3 is laughable non issue, you
| will spend more for a lunch drink. If you are manufacturing
| something in the thousands the difference goes down to
| 0.252 vs 0.067 so merely $0.2 BOM bump. Also a no brainer
| if performance is on the line.
| stephen_g wrote:
| Yes, and if you are actually buying in that kind of quantity
| you should be able to do even better. TI's budgetary pricing
| estimate is US$0.252 per 1K for the OPA2323IDDFR and US$0.067
| per 1K for the TL071CDR.
| kazinator wrote:
| For good sound, NE5532.
| tobwen wrote:
| But pre-ROHS of course :)
| kragen wrote:
| I think Zalewski's post is aimed at electronics hobbyists
| rather than high-volume producers or competitors. In that
| context, an OPA2323 might cost 98.99C/
| https://www.digikey.com/en/products/detail/texas-instruments...
| vs. 7.958C/ for the TL071
| https://www.digikey.com/en/products/detail/texas-instruments...
| but the Saturday afternoon you spend building and debugging
| your circuit costs hundreds of dollars in foregone income--if
| it's just an afternoon and not every weekend for a month.
|
| So the BOM cost may not be a significant consideration for
| hobbyists, especially when weighed against things like
| familiarity or being able to keep a stock of a smaller number
| of less specialized components, as Majromax points out.
|
| I'm surprised to see you say that a US$1 opamp is as good as we
| can currently achieve. Presumably there are Analog Devices
| chips that are better than the OPA2323 even for audio? Even if
| you can't _hear_ the difference, you ought to be able to
| _measure_ it.
| kragen wrote:
| I found this post extremely interesting and informative, well
| above my expectations even given the eminence of its author. I'm
| not sure that everything in it is covered in _The Art of
| Electronics_ -- it 's the kind of stuff the book covers, but I
| learned things from this post I didn't learn from the book. (But
| possibly it's information that's in the book that I just failed
| to absorb the last few times.)
|
| I was recently looking at opamps as alternatives to the LM324 and
| found some interesting-sounding parts, in particular for a poor
| man's SMU application (precision, low current, and voltage
| requirements, but not much bandwidth). Haven't tried any of them
| yet. Comments would be welcome.
|
| - LM324B: TI's improved LM324, with half the input offset voltage
| and otherwise improved ratings, and just as cheap, but still
| bipolar.
|
| - OPA4197 and family: three dollars but it's a quad RRIO 36V
| 10MHz opamp in a 14-SOIC with +-15nA input bias current, +-100mV
| max input offset voltage, and 120dB min CMRR. The datasheet makes
| it sound amazing for the price. The OPA177 seems like it would be
| better but pricier.
|
| - OP4177ARUZ: a 16-dollar quad 36V 1.3MHz opamp with +-2nA input
| bias current, 75mV max input offset voltage (at +-15V power
| supply), and min 120dB CMRR
|
| Then I decided I'd screwed up my design sketch by requiring one
| of the opamps to sink significant current very close to the
| negative rail, which is something even "rail-to-rail" opamps
| can't do; I was planning to use millivolts from ground to
| represent measured nanoamps. If you want to look at a simulation
| with idealized opamps, it's at https://tinyurl.com/2aomvpn5, but
| don't take it as exemplary in any sense; it's a novice design
| with novice mistakes (and I would be grateful in the unlikely
| case that someone took the trouble to point some of them out). I
| think I need to redesign the circuit as a bipolarity-supply
| circuit or something, or use a differential output for the
| current measurement, or rethink it entirely.
| dragontamer wrote:
| > Then I decided I'd screwed up my design sketch by requiring
| one of the opamps to sink significant current very close to the
| negative rail, which is something even "rail-to-rail" opamps
| can't do; I was planning to use millivolts from ground to
| represent measured nanoamps.
|
| Get an OpAmp specifically designed for current sense
| applications.
|
| OpAmps for current sense applications have high accuracy near 0
| Volts and Vos measured in single digit microvolts.
|
| Oh, you WILL lose bandwidth with these designs. So make sure
| you are allowed to be much much slower.
| kragen wrote:
| Thanks! This is probably excellent advice, and I wish I could
| follow it.
|
| Being slower is not a big problem, but needing specialized
| parts might be, due to supply-chain issues.
|
| (More detail in
| https://news.ycombinator.com/item?id=42627042.)
| Cervisia wrote:
| Nowadays, it is hard to recommend a general-purpose opamp. Just
| plug the desired parameters into the search function and sort
| what's left by price.
|
| (Distributors like DigiKey and Mouser have somewhat adequate
| search functions; I usually have to go to manufacturers' web
| sites like https://www.ti.com/amplifier-circuit/op-
| amps/general-purpose... to be able to filter by all important
| parameters. I'm mentioning TI because they have a large
| selection and a good search; even when you do not end up
| selecting on of theirs, you see what is possible.)
|
| ___
|
| If you need only a small negative supply and have nothing else,
| the LM7705 charge pump can generate -0.23 V. (This is designed
| to fit into the typically allowed 5.5 V range of a nominal 5 V
| opamp.)
|
| I do not know what a "significant current" is for you, but
| there are opamps with strong outputs. (When comparing opamps,
| you usually have to estimate the drive strength from the short-
| circuit current.)
| dragontamer wrote:
| A general purpose OpAmp is just that, your general purpose
| first choice.
|
| If you know more specific information about your circuit or
| it's application, the. You can specialize. But general
| purpose OpAmps are jack of all trades with specific known
| weaknesses to avoid.
|
| In most cases, you calculate the error bars and none of the
| errors matter, so sticking with a cheap general purpose amp
| is best engineering.
| kragen wrote:
| Thanks! This is very useful advice!
|
| What I meant by "requiring one of the opamps to sink
| significant current very close to the negative rail" is that,
| if you look at the schematic, the differential-to-single-
| ended op-amp that measures the voltage across the current-
| sense shunt resistor is using 10kO resistors in its feedback
| path, and the inverting input to that feedback network might
| be close to the positive voltage rail, say 12V, while the
| single-ended output is ideally millivolts from ground. So you
| have 12 volts across 20kO, which works out to 600mA, which
| has to be sunk into that op-amp's output.
|
| 600mA doesn't sound like a lot, and it certainly isn't going
| to strain the drive strength of any op-amp IC, but in this
| context we're hoping for millivolt precision down near the
| negative rail. The OPA4197 datasheet
| https://www.ti.com/lit/ds/symlink/opa4197.pdf figure 14,
| "Output Voltage Swing from Negative Power Supply vs Output
| Current (Maximum Supply)", shows what you might call a gently
| nonlinear output impedance roughly in the 40-80O range
| depending on temperature (2-4V at 50mA), which means 0.6mA of
| output current works out to tens of millivolts (24-48mV using
| those nominal impedances). Worse, even under no-load
| conditions, it's rated to swing only down to as much as 25mV
| from the negative rail (SS6.7, "Electrical Characteristics:
| VS = +-4 V to +-18 V (VS = 8 V to 36 V) (continued)", p. 8,
| "V[?]: Voltage output swing from rail, Negative rail").
|
| In retrospect, it seems obvious that the op-amp's output
| isn't going to be able to reach beyond the input rails
| (unless it integrates a charge pump like the LM7705
| internally) and is going to have trouble getting too close to
| them when it's sinking any current (for the negative rail, or
| sourcing for the positive). Because where is that current
| being sunk _to_? You need _some_ voltage drop to get the
| electrons and holes to move in the desired direction through
| the silicon. A small negative supply might be the right
| solution. Or a differential output, which would be easy.
| shadowpho wrote:
| >Nowadays, it is hard to recommend a general-purpose opamp.
| Just plug the desired parameters into the search function and
| sort what's left by price.
|
| This 100%. If you need a comparator get a comparator not an
| op amp. Current measuring? There are specialized chips for
| that as well, etc.
| kragen wrote:
| In this strong form, this is excellent advice for someone
| who is not me and is not doing what I am doing.
|
| I live in a third-world country where importing chips from
| abroad is expensive, unreliable, slow, and sometimes
| dangerous. There are circuits I cannot build because I
| cannot get the very specialized parts they need. Obviously
| a linear power supply that can measure how much current
| it's supplying is not such a circuit, unless you have very
| stringent precision requirements.
|
| It would be to my benefit to figure out a relatively small
| set of parts I can buy, ahead of time, in bulk, to cover a
| wide range of possible circuits. Better still if they're so
| popular that local distributors have them in stock. An
| analog comparator probably needs to be in that set. A chip
| specialized for current measuring probably does not.
|
| If you're designing a product for mass production that
| needs to be competitive in the market, you can't do it that
| way. Super-specialized parts will always have better
| performance, and usually better price/performance than
| overpowered general-purpose parts. (Also, you need to live
| in Shenzhen.) But hobbyists have other priorities.
| cushychicken wrote:
| Oh boy you need to take another look at ToEv3 if you think this
| has better coverage on opamp topics. It has so much about
| opamps in it that it's hard to tell you where to find it all -
| it's so ubiquitous and spread out in the text.
|
| Recommend Ch5 for Precision Design and Ch8 (or 9? Can't
| remember) on noise.
| kragen wrote:
| I didn't mean that this post was "better" overall, but rather
| that it contained some information I didn't see in AoE (or
| didn't retain). Clearly AoE's presentation of opamps is far
| more comprehensive.
| dragontamer wrote:
| Vos doesn't matter until it does. I find it surprising to see Vos
| mentioned as likely unimportant right next to CMRR, as CMRR and
| Vos are innately related in some circuits.
|
| In particular, any low voltage current sense circuit is going to
| require very precise Vos. Let's say you have a 0.01 Ohm current-
| sense resistor on a 5-Amp or so circuit.
|
| Your current-sense is now in the range of +/- 0.05Volts (!!!!).
| So a Vos of 0.005 would represent a 10% error. Likely too much
| for most applications.
|
| In effect, CMRR has become hyper-sensitive to Vos in this
| particular use case, to the point that Vos is suddenly the most
| important statistic.
|
| Fortunately, there are specially designed low-offset chopper or
| auto-zeroing OpAmps like MCP6V26 or whatever out there.
|
| MCP6V26 has Vos of 2uV, or in relatable terms... 0.000002 Volts
| (!!!!). Meaning it is more than sufficient at reliably making
| this current-sense application. Indeed, you can drop down to
| 0.0001Ohm resistance and still have high accuracy (and power
| savings compared to the earlier assumption).
|
| ------
|
| Alas, nothing is ever free in life. Chopper Amps have noise
| issues and other designs have very very low bandwidth (which is
| truly an important statistic for most circuits).
|
| Choosing a chopper amp specifically is making a Vos tradeoff with
| Bandwidth. So only choose if you know what you are doing (aka,
| dealing with very low voltages and needing the precise zero).
| nine_k wrote:
| For current measurement, I'd rather use a Hall sensor. But to
| measure the signal from that sensor a sensitive opamp is
| needed, and your comment applies :)
| blackguardx wrote:
| Using Hall-effect sensors to measure current isn't that
| common when currents are in the uA to mA range. I've also
| never seen them used even for Amp range measurements when the
| application is purely on-board power supply meaurement.
| nine_k wrote:
| The example uses 5A.
|
| For mA range, of course not.
| auxym wrote:
| Correct.
|
| A 10% error can be calibrated out if it is constant (in
| practice it probably varies a bit with temperature).
|
| But for measuring thermocouples or strain gauges, for example,
| 50 mV (your example) can be 100-500% of the signal, which
| becomes impractical to calibrate-out (due to maximum output
| levels, etc).
|
| For these applications, Vos is one of the first things to look
| at. Another one is the temperature coefficient on the gain.
| High frequency noise metrics such as CMRR and PSRR are
| sometimes important if you're looking at high frequency
| signals, but most of the time mechanical phenomena don't have
| much interesting content above a few 100s of Hz, and high
| frequency PS or CM noise can be removed by a simple high pass
| filter.
| kazinator wrote:
| Power supply and common mode noise can be 60 Hz.
| kragen wrote:
| And its harmonics, if you're standing near a fluorescent
| lamp.
| dragontamer wrote:
| > A 10% error can be calibrated out if it is constant (in
| practice it probably varies a bit with temperature).
|
| Unfortunately, Vos on cheaper general purpose OpAmps is the
| kind of thing that varies by... voltage. Ick.
|
| > For these applications, Vos is one of the first things to
| look at. Another one is the temperature coefficient on the
| gain. High frequency noise metrics such as CMRR and PSRR are
| sometimes important if you're looking at high frequency
| signals, but most of the time mechanical phenomena don't have
| much interesting content above a few 100s of Hz, and high
| frequency PS or CM noise can be removed by a simple high pass
| filter.
|
| No. CMRR is about DC in the applications I'm talking about.
| It's weird because CMRR is listed in decibels but it's
| absolutely a DC spec.
|
| If you have a high side current sense circuit with common-
| mode voltages of 24V +/- 0.05V (ex: 24V power supply that
| dips to 23.95V at 5Amps), CMRR tells you how accurate you are
| here.
|
| Your typical 60db (btw I need to kill the engineer who
| decided db measures DC noise/errors....) means that the 24V
| of common mode voltage (which is the 24V DC power supply in
| this case) leaks into your measurements.
|
| Or in other words: 60db * 24V == 3 decades or 24mV of 'Noise'
| aka your +/-50mV signal/measurement got completely wiped out
| by your DC errors. Like 50% error bars on your signal now,
| good luck with that.
|
| That's the real issue with OpAmps. There's surely an OpAmp
| out there that solves your problems. But it requires knowing
| the general tradeoffs and picking-and-choosing different
| parts for different purposes.
|
| Secondly, the specs are not intuitive. 60db CMRR sounds like
| a high frequency issue but becomes DC in this case.
|
| You could of course go full isolation (optoisolators) that
| allows you to shift voltages down to near zero (removing CMRR
| issues) but that's money and additional parts.
|
| You could go low-side voltage sense but this doesn't work for
| all circuits (most circuits are fine with Vcc error, not
| Ground errors). So high side current sense is the most
| flexible and generic well engineered solution. So long as you
| choose the correct OpAmps.
|
| -------
|
| As far as when this could be useful: consider Maximum
| PowerPoint Tracking for solar. 0-24 V and 0-1 Amps. And a
| need to accurately measure Amps and Volts from this entire
| range. (A variable load + voltage converter like a switch-
| mode power supply + battery can search for the optimal
| Voltage/Current combination to maximize the Solar Panels
| power).
|
| Yes the microcontroller will do the bulk of the math. But the
| initial multiplies and subtract is best handled by an OpAmp.
| hn4352 wrote:
| > It's weird because CMRR is listed in decibels but it's
| absolutely a DC spec.
|
| If you get the Franco book equation 5.27 (my edition is the
| 3rd) explains why they do that. Long story short: It's a
| convenient form when CMRR = dVcm/dVos due to the orders of
| magnitude involved.
| Tade0 wrote:
| Back in college I was told to not think too hard about Vos, as
| it's typically temperature dependent so you need to assume it's
| non-zero or will be in some circumstances and compensate with
| feedback anyway.
| kragen wrote:
| How do you compensate for Vos with feedback?
| hn4352 wrote:
| You probably don't, but your opamp might.
| https://www.analog.com/en/resources/technical-articles/to-
| ch...
|
| Technically you probably could do it externally in most
| cases but it would require a bunch of extra stuff, and be a
| pain, so usually it's best to use the stuff built into the
| amplifier itself.
| kragen wrote:
| Oh, sure. You could totally build a chopper op-amp out of
| two discrete op-amps. I'd never thought about actually
| doing that...
| dragontamer wrote:
| I've seen designs that use a Chopper Op-Amp to actually
| auto-zero a power-OpAmp, effectively transferring the low
| Vos characteristics to a different OpAmp with completely
| different characteristics.
| kragen wrote:
| If the op-amp has a stable Vos I feel like maybe you
| could zero it by hand with a trimpot? You just need a
| button to short the inputs together while you're trimming
| it.
| kragen wrote:
| I was puzzled about that too, so I appreciate you confirming
| what I thought.
|
| I'd think the main benefit of using lower-value current-sense
| resistors in this application would be that the resistor would
| heat up less, so its resistance would be more stable?
| dragontamer wrote:
| Accuracy is likely secondary. I expect that most applications
| are good with 1.5 digits (aka 95% accurate or so). You don't
| want to blow the entirety of this 5% allowable error on one
| micro-spec of one component, but I don't expect that most
| people especially need lots of accuracy here.
|
| The issue is that any circuit with 1 to 5 amps of current is
| a serious amount of power, meaning power efficiency is likely
| one of the top priorities.
|
| A 5-Amp circuit with a 0.01 Ohm sense resistor wastes 250mW
| on the resistor alone, likely more than the entirety of your
| microcontroller!! You can actually run an entire Linux
| capable microprocessor + Low-power DRAM off of that kind of
| power!!
|
| Dropping down to 0.0001 Ohms uses 1/100th the power or 2.5mW.
| which is likely a more reasonable cost.
| kragen wrote:
| That depends on what "most applications" means. I remember
| a paint program I saw in high school that some kids had
| written to draw sprites and backgrounds for their video
| games. The documentation explained that it could only edit
| 320x200x256 images, but that that should be adequate for
| "most projects". Depends on the context!
|
| In the contexts _I 'm_ thinking of, I would think that, if
| your load is drawing 5 amps of current at 3.3 volts, which
| is 16.5 watts, an extra 0.25 watts in the 10mO current
| shunt is not likely to be a big problem. And if it's 5 amps
| at 48 volts or 240 volts, it's even less of a problem,
| relatively speaking. I guess you're thinking of different
| contexts, contexts where the power-measurement system is
| paid for from a different budget than the load, but I can't
| figure out what they are.
| dragontamer wrote:
| You're sniffing out the fact that I didn't have an exact
| application in mind when I wrote my earlier posts, lol.
| But yes, you are correct on this front.
|
| The more I post on this subject, the more I'm
| "backwardsly-targetting" a solar-powered MPPT circuit.
|
| Maximum Power Point Tracking circuits improve your solar-
| panel's efficiency by changing the current (through the
| use of a buck-boost converter, changing the voltage-and-
| current downstream). Or maybe you have excess current
| sunk ionto a battery of some kind. Either way, you have
| some kind of configurable-load and can therefore maximize
| the solar panel's Voltage/Current curve characteristics
| to seemingly magic energy out of nothingness.
|
| If it costs you 250mW to just *sense* the current and run
| the calculations, it becomes much harder to justify the
| small gains of any MPPT circuitry.
|
| ------
|
| But yes, I'm changing the target application to suit my
| argument style. Apologies on that but I think you can
| forgive me on this!! The point of MPPT is to magic more
| energy out of nearly nothingness so efficiency is of
| great concern here!
| kragen wrote:
| Oh, I see! And you might very plausibly be getting 5 amps
| at 0.7 volts or something there, if you're controlling a
| single solar cell? (I might be misunderstanding how they
| work.) If you're controlling a whole 200-watt panel it's
| less of an issue because usually they have several cells
| in series to get a more convenient output voltage.
|
| I feel like a car's transmission or a bike derailleur may
| be a good analogy to explain it to people, though an MPPT
| tracker is a ratcheting CVT.
| pjc50 wrote:
| > I remember a paint program I saw in high school that
| some kids had written to draw sprites and backgrounds for
| their video games. The documentation explained that it
| could only edit 320x200x256 images
|
| Sudden memories of
| https://en.wikipedia.org/wiki/Autodesk_Animator , which
| was commercial software with exactly those limits (due to
| inheriting them from VGA). Despite the limited resolution
| it had a spectacular array of features.
| hn4352 wrote:
| I was kinda shocked by the Vos comment as well.
|
| On CMRR, in some mathematical treatments it's modeled as a
| change in offset voltage with respect to common mode, which
| indirectly effects output voltage of course so at the end of
| the day it's the same result. (See:
| https://www.google.com/books/edition/Design_With_Operational...
| highly recommended )
|
| It's also odd that the 741 was dismissed, as it should be, but
| the TLV9301 was not recommended. This part is specifically
| called out on TI's 741 page as what to use instead in 2025. Not
| only does it perform better in basically every possible spec,
| it's also a drop in replacement for most, if not all,
| applications.
|
| https://www.ti.com/product/LM741
| https://www.ti.com/product/TLV9301
|
| TLV9301 ($0.5) is also cheaper than a MCP6272 ($0.88)
| squarefoot wrote:
| Any comments on the LM4562? As per data sheet it appears to be
| really good for audio wrt noise and distortion, yet I see it
| rarely mentioned. https://www.ti.com/lit/ds/symlink/lm4562.pdf
| formerly_proven wrote:
| It and the LME49720 (same part) were discontinued a couple
| years ago along with the entire LME Overture series.
| ckocagil wrote:
| Potential replacements for ultra low THD would be: OPA1612,
| OPA1656 and OPA1642 with bipolar, cmos and jfet inputs
| respectively.
| magic_smoke_ee wrote:
| There's a massive (old) list of them in Horowitz & Hill
| TAOE 3e Table 8.3a p. 522. I'm sure you can just go to
| Digikey or Octopart and do a parameter search for high-
| voltage, low-noise, BJT-input op-amps too. If one wanted to
| "use a Ferrari to go the grocery store", they could always
| use a $20 AD797 or LT1115 for audio applications. :o)
| ckocagil wrote:
| I picked those particular chips is due to their extremely
| good performance at a reasonable cost. Check their THD
| against AD797 and LT1115! :)
| omgJustTest wrote:
| "Frequency response: The most important AC parameter of an op-amp
| is known as bandwidth gain product (fGBP or fGBWP). Standard,
| fully-compensated devices are designed to have an internal gain
| that rolls off proportionally to signal frequency. At fGBP, this
| gain is reduced to one:"
|
| "Stuff not to worry about:
|
| Despite what content-farmed articles imply, most of the other
| parameters in the spec can be usually glanced over. For example,
| the exact value of open-loop gain (AOL) is almost never of real
| consequence; the same goes for input offset voltage (VOS) -- even
| in high-precision instruments, the absolute value is less
| important than drift over time. In any case, the parameters are
| usually only eyeballed in most specs, so if you're building
| sensitive instrumentation, you will still need to calibrate the
| readings using a known reference."
|
| I rarely think about fGBP and AOL as separate ideas, the author
| could make the point more directly by saying they are related and
| that one is easier to select from a single decimal value. AOL or
| fGBP is a primary design consideration.
| buescher wrote:
| Be aware in a microcontroller design, an lm324-type op amp might
| outperform the on-chip ADC you're using anyway. Even the cheapest
| op amps from major players are better characterized and specified
| on their data sheets than most microcontroller ADCs. There's no
| virtue in spending other people's money and supply chain risk to
| use a "better" part just because it wins a bench race or it's
| newer or whatever.
| pythonguython wrote:
| What does it mean for an op amp to outperform an ADC?
| buescher wrote:
| It can have wider bandwidth, lower noise+distortion, smaller
| Vos, maybe other things I'm not recalling off the top of my
| head. In practical terms, you might not be able to run any
| test with the ADC that can find the limits of the op amp.
| bsder wrote:
| I'm really disappointed that the article didn't mention what is
| probably the single most important characteristic in an opamp
| when being chosen by an amateur:
|
| Unity gain stable
|
| Sure, the other characteristics are important, but a whole bunch
| of circuits that beginners are likely to use rely on opamps being
| unity gain stable. If they're not unity gain stable, the circuit
| will do very weird things, and a beginner won't know why.
|
| Of course, debugging issues like that are how you eventually
| become an expert.
| HelloUsername wrote:
| Previous "discussion"
|
| https://news.ycombinator.com/item?id=39944839
|
| April 2023
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