What is your favorite most versatile op-amp? - Page 1
Forum section: electronics / projects

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 05, 2019, 03:39:27 pm
content: I've been looking for a versatile op-amp that can work close to ideal in a wide range of circuits.Here is my list of requirements:Voltage supply +/- 15VInput voltage offset < 1mVInput bias current <1 nAInput voltage noise < 10nV/sqrt(Hz)GBW >10 MHz but <100 MHz, not prone to oscillationsSlew rate >20 V/usecUnity gain stableOutput current >50 mAIdeally available in PDIP-8 package and as a dual op-amp. So far the best I found is OPA2132. What are other good candidates?

author: OM222O
author_rank: Frequent Contributor
timestamp: May 05, 2019, 04:10:07 pm
content: can I ask why you care about the output current? if you need high current, just use a fet or a bjt as a bufferI know this doesn't meet your requirements but 99% of my projects are low voltage and single supply (0 to 5v), so I always choose rail to rail op amps.my go to is the MCP600x (x can be 1, 2 or 4) which seems to be extremely stable, it has never had stability issues in my experience where other amps have (I remember a particular application where the TLV9002, OPA2333 and a few more had issues with oscillations but the MCP6002 worked like a charm). I know you should design your products to not have stability problems and what I described earlier is "bad practice" but I mean, if it works it's good enough for meFor higher precision applications I usually go with the MAX4238 which dave used in his uCurrent. I bought a few to play around with and test them just for fun, but they performed great and are my other go to for precision applications

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 05, 2019, 04:24:57 pm
content: For single-supply applications the requirements are different, rail-to-rail is more important and easier to use a single transistor buffer. I tend to work on bipolar circuits, so rail-to-rail has not been an issue.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 05, 2019, 07:26:45 pm
content: You didn't mention cost. I think that's expensive. I also like the AD845, but it's even more. For many things the audio opamps like the LME series work well, say LME49720, but I don't know if you can get the LME series anymore (Mouser seems to have 'em). They tend to have good output drive. Don't forget the Japanese parts like NJM4556 and similar. It just depends on what kinds of circuits you build; that's why there are so many choices. I once thought the good old LF411 could do nearly anything, but it's not that fast. Needless to say, I keep more than one part type around!

author: exmadscientist
author_rank: Frequent Contributor
timestamp: May 05, 2019, 08:23:36 pm
content: OPA192/2192/4192 will do for just about any "jellybean" op-amp application. It meets all of your desired specifications and then some, except for not coming in DIP-8. (Something I, personally, could not care less about.) Its downsides are that it's on the pricey side, it's got a bit more input capacitance than you sometimes want (I think due to the special sauce in the offset trim? Might be worth reading the relevant patents here...), and it has the usual RRI offset voltage wobble located at input CM voltages around a couple volts below the positive supply (though it's a small wobble as far as these things go).The cost is no problem for prototype and lab work, but means that the OPA192 is not quite a "production jellybean". However, TI does offer a pretty wide set of cut-down versions that trade off one or more characteristics like offset or speed in exchange for cost, so you can compromise where it doesn't matter.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 05, 2019, 08:44:50 pm
content: OPAx192 looks good indeed. Its $3-4 on Arrow, that's not bad. Its inevitable that one has to stock-up on DIP adapter boards these days, most top-performance chips don't come in DIP packages.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 06, 2019, 12:47:00 am
content: Since you did not specify proximity to rails or cost, I would recommend looking for something LT (now ADI) or OPA (Burr-Brown, now TI), those specs are easily met by parametric search.As for "favorite most versatile amp", that seems like a very misleading subject. It also has the problem of the double superlative -- how could I even have a "favorite" and "most versatile" that's also an amp? Amps don't work that way! What combination of attributes could such a beast even have? Very high GBW at very low supply consumption, say? But even then, high GBW is a liability, so there must be some choice there. And the laws of physics constrain the value of GBW * supply consumption, for a given design, so you can't expect anything special there, either.Nah. None of that. You simply use the part that suits the application!Tim

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 06, 2019, 02:24:27 am
content: If one drops the PDIP requirement, the other two chips that look interesting and even better than OPA2192:OPA2197- cheaper at the expense of higher voltage offsetOPA2189 - zero drift amplifier with good dynamic response and also cheapOPA2156 - high slew rate and low input noise.Quote from: T3sl4co1l on May 06, 2019, 12:47:00 amI like as much as the next guy to scour the parametric search sites for just the right chip in a particular design. But sometimes its nice to pop in a chip without thinking about it and know that it will be more than sufficient .

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2019, 03:09:46 am
content: Parts like the Burr-Brown OPA627 and the Analog Devices equivalent meet all of your specifications except output current. There are some other JFET input parts with similar performance although keep in mind JFET input bias current doubles every 10C so the input bias current requirement will be a problem at high temperatures.That high output current requirement conflicts with the precision requirements because of the temperature gradients high power operation creates. The only way to meet all of the specifications is with a composite design with a power booster separated from the input stage.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 06, 2019, 03:26:30 am
content: These are not the requirements for one specific design, more like an amalgam of reasonable requirements one can expect to get across the board- a versatile chip one can pop in many circuits.

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2019, 04:09:12 am
content: Quote from: maxwell3e10 on May 06, 2019, 03:26:30 amThe simultaneous precision and output current requirements conflict to make one or the other unreasonable.The supply voltage and output current requirements also conflict with the DIP-8 packaging requirement; parts with that kind of output current are limited to lower supply voltage, typically about +/- 8 volts. (1) The datasheet for theLT1010 power bufferhas a good discussion about the power limitations of the DIP-8 package. Another place to find discussion of this issue is in the datasheets for +/-15 volt current feedback amplifiers.The LT1010 works well as the output stage of a composite amplifier but even it would not meet your output power requirements without help unless used in the TO-220 package and perhaps not even then. There are some current feedback amplifiers with 50 milliamp output current but they have the same problem.(1) This comes up when driving a double terminated 50 ohm transmission line which presents a 100 ohm load. +/-5 volts into 100 ohms is +/-50 milliamps. Adding another 3 volts for headroom results in the +/-8 volt supply requirement.

author: OM222O
author_rank: Frequent Contributor
timestamp: May 06, 2019, 01:19:33 pm
content: David Hess is right, that was also the first thing that I pointed outjust using a buffer for the power stage seems like the logical option as OP AMPs aren't really meant to drive any loads.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 06, 2019, 02:38:26 pm
content: And yet there are old popular chips, like LM6171 in a PDIP package, and new designs like OPA2156, which have 100mA+ current capability.Of course there will be power dissipation limitations, but often one doesn't need to drive high current continuously. And maybe literally the same chip can't be used to drive high current and have low voltage offset, but its nice to have a circuit that uses the same type of chip both for the input and output stage.The basic question is to find an op-amp that can cover as much parameter space volume as possible without sacrificing too much in any other characteristics.

author: David Hess
author_rank: Super Contributor
timestamp: May 07, 2019, 05:32:44 am
content: Quote from: maxwell3e10 on May 06, 2019, 02:38:26 pmThe LM6171 is a current feedback amplifier in disguise with a buffered inverting input. This is a great topology for high speed but not a precision one.The OPA2156 is typical of misleading TI datasheets. The precision specifications only apply with a high impedance load and low power dissipation. No settling time specifications is given with a high output current because it is 1000s of times worse than the datasheet specification as it would be with any integrated operational amplifier. So you can use it for high output current or high precision but not both at the same time. With that high noise, it is not suitable for low frequency precision applications anyway but that is typical of CMOS processes.The above may seem like nit-picking but consider the lessor known advantage of super-beta input parts like the old 308 and "modern" LT1008/LT1012/LT1097. Their very low input bias current means that a high impedance feedback network can be used minimizing power dissipation in the output stage yielding better precision. Lower noise parts like the OP07/LT1001 or OP27/LT1027 require much lower impedance feedback networks to avoid compromising their lower noise but this requires higher power dissipation in their output stage compromising precision. In this respect, the "universal" part might be the LT6010/LT6011/LT6012 which is a rail-to-rail output version of the LT1012. Note that no such single supply or rail-to-rail part like this can exist because single supply operation conflicts with input bias current cancellation. Of course FET inputs do not require input bias current cancellation but they have their own problems.Also notice that the OPA2156 specifications exclude input capacitance versus common mode voltage and do not mention source impedance in non-inverting applications. That is deliberate. In any real circuit, the non-zero source impedance interacts with the variable input capacitance to produce much higher distortion than they show. There are ways to fix this but I am not sure that they apply to a rail-to-rail input part or standard CMOS process.The OPA2156 is a great part for general purpose use but I would still prefer it to be available in a single version to take advantage of circuits which require access to the power pins. That is a requirement I would add for any part to be most versatile.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 07, 2019, 11:58:28 am
content: Many of these precision parts, like LT1012 and LT6012 have terrible slew rates, so while they maybe good for precision DC applications, they are not good for any dynamic application. A good general chip will not be ideal for any application (not lowest noise or highest slew rate or lowest distortion), but will be pretty good for all of them.What do you think about OPA2189? It seems to have better specs than any other chopper op-amp I have seen?

author: David Hess
author_rank: Super Contributor
timestamp: May 07, 2019, 11:26:54 pm
content: Quote from: maxwell3e10 on May 07, 2019, 11:58:28 amThat is a common theme which applies across all parts. The emitter or source degeneration of the input differential stage has to be minimized to provide high precision. But this results in high transconductance which ultimately limits slew rate. JFET and CMOS transistors inherently have lower transconductance so result in higher slew rates but lower precision.This really shows up with "video" operational amplifiers which add resistive degeneration raising the slew rate but also lowering precision. An early example of this is the 318 which has a 15 MHz gain-bandwidth product and 70 volt/microsecond slew rate. These same parts have higher current output stages to drive 100 or 150 ohm loads but with their lower precision, this is acceptable.The LM6171 uses a different topology which does not suffer from this limitation and is much faster but it requires a complementary process and matching between complementary devices compromises precision. I have designed audio amplifiers with a similar topology.QuoteIts specifications are better than any I have used.Chopper stabilized operational amplifiers can be tricky to apply however. Watch out for its input current noise which looks to be 75 times greater than an old "noisy" LTC1151. That is consistent with larger area input transistors for lower voltage noise. Chopper stabilized amplifiers should be used with low AC impedances limiting their versatility; they are not general purpose parts.Pretty much if you do not have a big feedback capacitor and a big capacitor from the non-inverting input to ground, then you are using the chopper stabilized amplifier wrong.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: June 02, 2019, 06:46:14 pm
content: I tested OPA2189 dynamic characteristics at high frequency. It works pretty well, with a slew rate of 20V/usec and clean response. See below a comparison of 3 op-amps, each driven by a 16Vpp square wave. The frequency of the wave is 500 kHz (330 kHz for OPA2132).I was looking for some weird effects associated with the chopper modulation. What I found is that for a non-inverting gain of 100 if the frequency of the sine is exactly 67.5 kHz, the gain has a periodic modulation. This only happens in about 1 kHz range, must be some interference effect with the chopper frequency.Also OPA2189 is sensitive to high-impedance path on the input due to current injection, as others have also pointed out. This can lead to rather large offsets that depend on the capacitance, so one has to be careful to realize uV stability. When that is not crucial, then OPA2197 looked pretty nice and also inexpensive.

author: Gyro
author_rank: Super Contributor
timestamp: June 02, 2019, 07:09:54 pm
content: This is the second of these 'best op-amp for everything' threads in the past couple of weeks (https://www.eevblog.com/forum/chat/favorite-op-amp/msg2342253/#msg2342253). I don't get it - surely the op-amp you want is the one that's best suited to the specific application. If you try a 'one size fits all' approach then there are going to be massive compromises in all but the most mundane application.You need to look closely enough at the datasheets to spot hidden 'undesirable features' is tricky enough as it is. Maybe a what's your favourite high impedance, DC precision, fast slew rate, high output drive? might have some value, but even then, there are all sorts of requirement combinations that would lead to a non-optimal match.A parametric search is the only way to do it properly. That's what I would advise the OP to do for each of his applications.Trying to tie down to one 'favourite' is just silly..... It would ultimately save the manufacturers the effort of producing many different parts though.

author: MarkF
author_rank: Super Contributor
timestamp: June 02, 2019, 07:30:38 pm
content: Maybe the title should read "Op-amp Short List"It would be nice to have a list of a dozen op-amps to pick from for general use.There are soo many available that it's overwhelming.

author: Gyro
author_rank: Super Contributor
timestamp: June 02, 2019, 07:56:47 pm
content: Agreed, that would be of more value, particularly if done by category.

author: exe
author_rank: Unknown
timestamp: June 08, 2019, 09:08:51 am
content: Quote from: Gyro on June 02, 2019, 07:09:54 pmI'm yet to see a good parametric search, not to mention across multiple vendors (I don't qualify digikey as good search, but it's a good starting point). Also, many things are not mentioned in datasheets, that's why I'm always interested in more data, measurements and experience about opamps.

author: H713
author_rank: Regular Contributor
timestamp: June 08, 2019, 03:31:13 pm
content: Clearly anything less than an original API 2520 will not do.All kidding aside, from an audio standpoint, the good old 5532 is difficult to beat without paying 5-6 times as much, and it is very low noise.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 08, 2019, 05:29:12 pm
content: Quote from: exe on June 08, 2019, 09:08:51 amThe parametric search at Ti and AD is not that bad, once one gets used to it. For high end OPs there are not that many more sources to search for.Sometimes it is also the bad sides of some OPs, that a worth to remember. So something like well known cross over distortion of the LM358/LM324, phase reversal when leaving the common mode range or the TLC272, that does not like the input near ground and the output near the negative supply at the same time. I just found out that with the TLE2071 the supply current goes up quite a bit if the output is at the negative saturation.

author: Zero999
author_rank: Super Contributor
timestamp: June 08, 2019, 06:31:16 pm
content: Quote from: H713 on June 08, 2019, 03:31:13 pmSome of the parts from New Japan Radio look good, at least on paper, as I haven't tried them. NJM2068, a general purpose but better replacement for the NE5532 and the NJM2122 which is lower noise, but lower voltage.

author: magic
author_rank: Super Contributor
timestamp: June 08, 2019, 10:23:43 pm
content: NJM2068 beats the 5332 on noise, price and power consumption but it's said to be less linear at high frequencies and high gains or with less than a few kΩ load impedance. I think the general consensus is that nothing beats 5534/5532 in every respect at a comparable price. Uncompensated 5534 also has 3x more gain at audio frequencies, 5532 was some 90% of what NJM2068 spec claims. I could swear I've measured NJM2068 too but I can't find the results now.But I have seen those NJM2068 used in some semi-pro soundcards and also stuck them into a Xonar STX in place of the original NJM2114 (JRC's own "improved" 5532) and got barely any difference in RMAA results. I guess that means good enough for undemanding applications.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: June 08, 2019, 10:52:42 pm
content: My preferred OPA in the specified class is the LT1468/1469. It did prove repeatedly to be care free and rock solid when used to the full extent of it's capabilities. It is available in PDIP. But you would have to compromise on some parameters: Input bias current is slightly higher and output current is +/-22mA nominal.I would fully endorse the AD845 too as well as the OPA2727.Some other components to look at: ADA4898, LM6142, OPA602, OPA827, TLE2027, ISL55001 (I have not checked all parameters, but they are >10MHz, around 1 mV or better and they satisfy your +/-15V requirement.)Maybe LM7332, if current is critical.

author: MasterT
author_rank: Frequent Contributor
timestamp: June 08, 2019, 10:54:59 pm
content: Recently I discovered LM4562, it has 100x (!!!) lower distortion level than NE5532. And 5.5 times wider bandwidth and available in DIP8 package.IC is good with 5V power, capable to output about 3 Vp-p no distortion, for comparison NE5532 outputs 2 Vp-p.

author: exe
author_rank: Unknown
timestamp: June 09, 2019, 07:40:33 am
content: There are several NE5532 on the market, at least two from on semi and TI. Rumors say they are quite different. They are also different from different years of manufacture. I think I found on the Internet that TI did at least once shrinkage of the die. This badly affected noise (according to the.As for distortion, I wouldn't care that much. According to Rod Elliot distortion of any good sound amplifier (not just opamp, but the whole circuit) is inaudible. So, 100x reduction of inaudible distortion is still inaudible.PS did someone mention this document?http://www.nanovolt.ch/resources/ic_opamps/pdf/opamp_distortion.pdf. An interesting reading with tons of plots showing how opamps compare to each other in terms of distortion under different operating conditions. I refrain myself from drawing any conclusions as final performance is depends a lot on the circuit.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2019, 09:11:26 am
content: Quote from: MasterT on June 08, 2019, 10:54:59 pmAccording to the data sheet, it's got over double the input current noise of the NE5532 at 1kHz, so it's not necessarily an improvement.

author: MasterT
author_rank: Frequent Contributor
timestamp: June 09, 2019, 01:47:47 pm
content: From NE5532 DS TI : Equivalent Input Noise Voltage: 5 nV/√Hz Typ at 1 kHzOnSemi: Input Noise Voltage: 5.0 nVń Ǹ Hz (Typical)LM4562 TI : Input Noise Density: 2.7nV/√Hz (typ)Regarding distortion, audio is not the only area for OPA application, measurements is another. To have anything above 4.5 digits, OPA must be very low distortion. THD level at 0.002% put a limit same as 15-bits ADC

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2019, 03:51:02 pm
content: Quote from: MasterT on June 09, 2019, 01:47:47 pmYou've misread my post. I know the voltage noise is lower. I was taking about thecurrent noise, which is higher, than the NE5532 at 1kHz. The LM4562 has 1.6pA/√Hz vs only 0.7pA/√Hz for the NE5532. If the impedance seen by the input is greater than about 2k925, the LM4562 will be more noisy, than the NE5532.The current and voltage noise densities add at the op-amp inputs. The current noise forms a voltage noise source, when if flows through the resistance, connected to the input.VN_TOT= √(VN2+(IN×ZIN)2)So if you have an inverting amplifier.Rin= 10kIIN= 0.7pA√HzVN= 5nV/√HzVN_TOT= √(10k×0.7p)2+5n2= 8.6nV/√HzIf Rf= 100k then the gain will be 100 so the output voltage noise will be 860nV/√Hz.

author: nemail2
author_rank: Regular Contributor
timestamp: June 09, 2019, 04:07:28 pm
content: OPA2197 it is, for me...

author: MasterT
author_rank: Frequent Contributor
timestamp: June 09, 2019, 04:19:01 pm
content: Quote from: Zero999 on June 09, 2019, 03:51:02 pmI see, the point of this thread is to define a priority list of the OPA's parameters. Since there is no perfection in this world, no OPA that would satisfy all requirements. Current noise is the last line of all spec I'd care about.Voltage offset is close to the middle of the list. Its' easy to fix in hardware or software. The THD is the most important, difficult to straight up and it's directly limit accuracy of the circuits. DC accuracy is no exception, basically THD is equivalent to INL / DNL in the ADC-DAC specification. Long time THD is associated with audio, or AC in general, but IMHO it's a big mistake to use LM358 at the front end of the anything with >12-bits resolution. And input offset is not an issue.

author: exe
author_rank: Unknown
timestamp: June 09, 2019, 04:27:14 pm
content: Quote from: MasterT on June 09, 2019, 04:19:01 pmIsn't THD frequency-dependant? If so, can lm358 still be good for low-frequency signals?As for offset, why do you say it's not an issue? If DC accuracy is required, it is an issue.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 09, 2019, 04:35:02 pm
content: One thing to note about the NE5532 is that (at least in the TI datasheet for the NE5532 that I have) there is no figure to be seen regarding distortion. Did I stupidly miss it? Does anyone have a datasheet stating distortion? And if we're going to use NE5532's made by TI, how are we going to know what to expect in terms of distortion?I've used the LME49720 with very good results for current-to-voltage output stages for audio DACs.

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2019, 04:36:01 pm
content: Quote from: MasterT on June 09, 2019, 04:19:01 pmIf depends on what you're doing.Noise can't be accounted for in software, so it's pretty important in my opinion. Current noise dominates voltage noise, at higher input impedances and voltage noise is dominant at low impedances. This is very often overlooked. Someone might choose the NE5532 over the TL072, on the bases it has a much lower voltage noise of 5nV/√Hz vs the seemingly massive 18nV/√Hz of the TL072, but the TL072 has a current noise of just 0.01pA/√Hz vs the 0.7pA/√Hz for the NE5532. Then they wonder why it's so noisy, as the input impedance of the amplifier is 100k: the correct choice would have been the TL072 of course.Quote from: exe on June 09, 2019, 04:27:14 pmVoltage offset is often unimportant nowadays, as the op-amp is more often than not, before an ADC. The circuit can be zeroed in software by shorting the inputs, taking a reading, storing it in memory and subtracting it from subsequent readings.The one thing to watch out for is drift, which can't be corrected for, unless it's convenient to frequently zero the circuit.

author: magic
author_rank: Super Contributor
timestamp: June 09, 2019, 07:11:11 pm
content: Quote from: exe on June 09, 2019, 04:27:14 pmCMRR spec is 85dB, presumably only valid with light load, meaning that 20V of input swing produces 1mV change in offset voltage. And it's not even guaranteed to be linear, its slope may be flat close to ground and get steeper towards VCC or vice-versa or any other bizarre thing.If you look at the schematic, the output is class A up to 50µA. If you want to sink more, the voltage gain stage needs to swing 3 diode drops down to turn off the upper darlington and turn on the lower sink transistor. Given 100dB open loop gain at DC, that's a 15µV step in offset voltage just to respond to changing polarity of load current.But you are right that crossover distortion at 1Hz or so will not be as bad as at audio frequencies, where open loop gain is lower.That's also a problem for most of those rail-to-rail input amps, like OPAx192. If you read the datasheet, they very carefully avoid specifying any CMRR number within that problematic region from 3V to 1.5V below VCC and instead tell you to have a look at figure 13-14 in "typical characteristics", which doesn't look pretty to say the least.Quote from: SiliconWizard on June 09, 2019, 04:35:02 pmNope. I have datasheets from TI, Philips, Signetics, JRC, Fairchild, ON Semi - no one specifies it.Quote from: SiliconWizard on June 09, 2019, 04:35:02 pmOne Samuel Groner published quite comprehensive distortion measurements of a few dozen opamps. I think I saw a link earlier in this thread or just search for it. Beware it's 35MB.Or, as Douglas Self puts it:Quote

author: exe
author_rank: Unknown
timestamp: June 09, 2019, 07:16:29 pm
content: Quote from: magic on June 09, 2019, 07:11:11 pmJust don't make it sink. I mean, if we are talking about ADC, crossover distortion is irrelevant, isn't it?

author: Zero999
author_rank: Super Contributor
timestamp: June 09, 2019, 10:01:38 pm
content: Quote from: exe on June 09, 2019, 07:16:29 pmI don't see why not. Crossover distortion is only irrelevant for DC or when the output is continuously sourcing/sinking.

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: June 09, 2019, 11:23:56 pm
content: Quote from: Zero999 on June 09, 2019, 10:01:38 pmCrossover distortion doesn't make it into the discrete samples.

author: MasterT
author_rank: Frequent Contributor
timestamp: June 09, 2019, 11:39:53 pm
content: Quote from: exe on June 09, 2019, 04:27:14 pmIt is affected by frequency, but it does not go to 0% (THD) at DC level. So, no, LM358 and NE5532 are not good above 12-bits.Quote from: Zero999 on June 09, 2019, 04:36:01 pmNoise easy to null out by averaging in software. Though ADC sampling rate needs to be higher.Quote from: SiliconWizard on June 09, 2019, 04:35:02 pmI love LME49721, pity charts depicted THD just to 6-7 kHz.NJM5532 has THD at page 3, THD vs. Output VoltageTI has data for NE5534, I'd think 32/34 as a twins.Quote from: exe on June 09, 2019, 07:16:29 pmAnd this is most interesting parts. Interfacing to high resolution ADC is tricky, +-15V power is not applicable since next question would be safety of the ADC. Tweaking with high end adc (16 /18 bitters from TI and AD, ad7988, ad7984, ads8866) I came to conclusion that all worlds leaders failed to make R2R ultra low THD (0.0001%) OPA.AD on their AD7988 evaluation board, follow old fashion design - demanding -2.5 +7.5V power for OPA just to keep THD under control. So, crossover still in there, and it's not the only one of source THD to keep an eye on.

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2019, 03:57:04 am
content: Quote from: MasterT on June 09, 2019, 11:39:53 pmIf flicker noise could be averaged away, then there would be no need for chopping.

author: H713
author_rank: Regular Contributor
timestamp: June 10, 2019, 04:54:30 am
content: LM4562 has come down in price considerably over the last few years, so that has a considerable impact. I didn't realize just how much its price came down over the last few years. IMO, (again from an audio point of view), applications where a 5532 or 5534 is suitable, the LM4562 is probably a better choice, because if the relatively high current noise of a 5532 isn't a problem, the LM4562's even higher current noise may not be an issue either.Again, this really does come down to application. A microphone preamplifier has different requirements from an EQ circuit, and the digital world (which I don't deal with very much) will likely have different (in some cases more stringent) requirements.The discrete op amp is a great example. It seems foolish, after all it is a costly and large, and the DC precision is poor compared to even a 741. The noise performance and linearity, however, can be excellent, and they can be designed to handle very high supply rail voltages. For some applications it is a poor choice, but for others it makes perfect sense.Still, I think if one is going to make a list of good, versatile op-amps to stock, the LM4562 (not a whole lot more costly than a 5532 these days) and perhaps something like an OPA2134 would be on my list.With that said, there are a ton of comparably decent FET input op amps, some of which may or may not be relevant now. I still have a large stock of OPA604s and AD713s, but their cost makes them hard to recommend at this point over something like an OPA2134. Even the TL072 is perfectly adequate for many applications, and they're cheap as chips.

author: magic
author_rank: Super Contributor
timestamp: June 10, 2019, 07:15:14 am
content: Quote from: exe on June 09, 2019, 07:16:29 pmCMRR is still crap, though.Quote from: MasterT on June 09, 2019, 11:39:53 pmDamn, I missed itQuote from: MasterT on June 09, 2019, 11:39:53 pmThey aren't, 5532 has its open loop gain reduced to stay stable in voltage followers and it shows as more distortion at audio frequencies. Also lower unity gain frequency and slew rate.Quote from: MasterT on June 09, 2019, 11:39:53 pmOPA365 comes close by using internal charge pump to generate beyond-the-rails voltage supply for its input stage. Other similar opamps may exist, but most R2R input designs combine two input stages and have bad "input crossover" distortion.

author: RES
author_rank: Regular Contributor
timestamp: June 10, 2019, 07:38:26 am
content: LT6015 (SOT-23-5)https://www.analog.com/media/en/technical-documentation/data-sheets/601567ff.pdf

author: Zero999
author_rank: Super Contributor
timestamp: June 10, 2019, 08:04:21 am
content: Quote from: MasterT on June 09, 2019, 11:39:53 pmNot true. If you're talking about averaging, then all you're doing is reducing the bandwidth, which is only acceptable in a DC application. Then there's 1/f noise, which increases at lower frequencies and equates to offset drift, which needs to be frequently nulled.Quote from: Neomys Sapiens on June 09, 2019, 11:23:56 pmIt does if some of the samples are taken at the point when the output current is changing direction.

author: exe
author_rank: Unknown
timestamp: June 10, 2019, 09:20:17 am
content: Quote from: MasterT on June 09, 2019, 11:39:53 pmDC offset can be nulled. I did a couple of experiments on lm358 and ne5532 from TI measuring offset voltage vs input vs supply voltage on a breadboard at room temperature (unity-gain configuration, no load). In addition, I also heated the opamp with hotair gun to ~110C. I include the best and the worst opamp. I used soic opamps, mounted on a dip adapter, the circuit assembled on a breadboard using crappy wires, flux wasn't cleaned. Please find the data attached. In total, I tested two samples of ne5532 from TI, two samples from OnSemi, and four samples of lm258/lm358 from various vendors. All bought from reputable distributers (Farnell and TME). For NE5532 I include my best sample, as well average sample. For lm358 I just include "typical" performance.I did measurements in 2017, so don't remember all the details. The goal was exactly to understand if they are suitable for 12bit ADC. My NE5532 samples showed that Vos is stable within 0.05mV if enough voltage headroom is given (as measured by UT61C). Temperature coefficient is about 1.5-3uV/C (but I measured only two datapoints: at 25C and ~100C on a breadboard, thermocouple issues etc were not taken into account, I let the temperature stabilize for ~1min to avoid die stress due to non-uniform temperature).It's up to the reader to decide how good they are. But I disagree that 12bit is their limit.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 10, 2019, 01:04:47 pm
content: Averaging for noise reduction only works as long as the noise is reasonably random, or at least uncorrelated to the signal (probably a workable assumption here) AND the signal of interest is identical from one capture to the next. Otherwise you're just basically low-pass filtering and will lose bandwidth.Averaging is often used for repetitive signals triggered by some event, not as a noise-reduction technique for non-repetitive or unsynchronized signals.

author: MasterT
author_rank: Frequent Contributor
timestamp: June 10, 2019, 01:32:23 pm
content: Quote from: David Hess on June 10, 2019, 03:57:04 am"Hardware averaging" - putting a few devices in parallel ?What I'm getting at, there are solutions to minimize noise & offset, but distortion /non linearity are different species. This is why I'd move to #1 in my priority list.Probably, DC accuracy may get better by increasing open loop gain using 2+ OPA as combine or composite whatever it's called. Anyway it's not so easy like paralleling for noise reduction.

author: Zero999
author_rank: Super Contributor
timestamp: June 11, 2019, 04:46:39 pm
content: Some types of non-linearities can be corrected in software, as long as they are known and repeatable. For example, a single supply op-amp might be non-linear near the negative rail, even at DC, but if we can compile a table of the input and output voltages, compared to the expected (ideal) output voltages, then we can apply a correction factor later.

author: David Hess
author_rank: Super Contributor
timestamp: June 11, 2019, 06:50:34 pm
content: Quote from: MasterT on June 10, 2019, 01:32:23 pmAveraging by paralleling devices (parallel averaging?) or using larger ones is a prime way to lower flicker noise when chopping cannot be used.What does not work effectively is averaging over time to remove flicker noise.QuoteIt is just application dependent. Broadband noise, drift (essentially low frequency noise), non-linearity, and distortion (non-linearity in the AC domain) can all be improved in either the analog or digital domain. "Predistortion" is a common digital technique for combating distortion in RF power amplifiers now.QuoteNoise can usually be reduced to a very small subset of a properly designed circuit. Lots of different things besides excess gain contribute to DC accuracy.

author: MasterT
author_rank: Frequent Contributor
timestamp: June 11, 2019, 09:54:01 pm
content: Quote from: David Hess on June 11, 2019, 06:50:34 pmI know how they do predistortion, was thinking to build ultra low thd generator ( <-120 dBc). Can't find an adc that could prove my algorithm is good. ADS127L01 comes in "hate to solder" package. And evaluation board costs a fortune.Though, it would be quite expensive method to correct cheap OPA non-linearity by introducing extra linear adc on chip, converting input to digital, pre-distort, than convert back to analog again by extra linear dac, don't you think?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: June 12, 2019, 02:53:51 am
content: I think the question is not how to overcome op-amp limitations or to get to state-of-art performance in one particular spec. The question is how to get to 90% (in log space) of the state-of-art in many specs at once.That is why I prefer FET-input op-amps. They have a little more voltage noise, but allow one to use larger input resistances and not worry about it. +/- 15V supplies also make it more versatile. Power dissipation is a different aspect, but usually I don't care about it.

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2019, 08:20:41 pm
content: Quote from: MasterT on June 11, 2019, 09:54:01 pmIt would be expensive and also futile because there are simple techniques to reduce distortion in differential input feedback amplifiers. Once these are used to remove first (second?) order distortions, improvements through digital distortion correction would be futile because distortion can be below the noise floor.These techniques are not often used simply because distortion is already usually better than needed and even less understood because they are easy to overlook in other designs. They include:1. The most obvious one is to use inverting instead of non-inverting stages to remove common mode effects.2. Match the impedance and not just the resistance at differential inputs.3. Bootstrap the supplies to increase common mode rejection.4. Unload the outputs of integrated devices to remove thermal feedback.