Very low bias current Op-amp to buffer a Kelvin Varley divider - Page 1
Forum section: electronics / projects

author: splin
author_rank: Frequent Contributor
timestamp: June 11, 2015, 09:27:28 pm
content: I thought this interesting question didn't get much response over on the Test equipment forum so I thought I'd put a link here where it might reach a wider audience:https://www.eevblog.com/forum/testgear/buffer-for-kelvin-varley-divider/The original poster was looking for a very low input bias (preferably < 1pA) op-amp with very low drift, to buffer a KVD with 70k o/p resistance, whilst not compromising the .1ppm linearity spec of the KVD significantly. Jim Williams published an app note covering this exact application, where the errors due to the amps CMRR and finite gain are also pointed out (140dB CMRR equates to .1ppm of linearity error in a voltage follower configuration). That was in 1999 so perhaps there are some better parts available now?Can anyone recommend a better op-amp than the LTC1052 or LTC1152 for a one-off piece of test equipment where selection is possible to a limited extent - for cheaper devices at any rate.I'm also interested if anyone has any suggestions to my question as to why Jim Williams chose to use the LTC1152, which seems to have better specs, rather than the LTC1052 - see reply #11.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 12, 2015, 08:53:18 am
content: The LTC1052 uses external caps and has higher bias currents.More modern AZ Ops would be something like AD8551 or LTC2057. In general the lower noise ones have higher bias currents and often also a higher offset. However Bias currents are relatively stable, and little dependent on temperature (unless very high). For ultimate performance some kind of bootstrapping may be useful, as the bias can depend on common mode voltage, so that input resistance is not as high as one might expect for a CMOS chip.Finding something in the 1 pA range is hard (maybe selected LTC1050 / ICL7650), and will be a rather high noise, but low offset version.

author: splin
author_rank: Frequent Contributor
timestamp: June 12, 2015, 08:44:28 pm
content: Quote from: Kleinstein on June 12, 2015, 08:53:18 amMy datasheets show that the LTC1052 has lower bias current - 1pA typ @25C, 30pA max compared to 10pA typ, 100pA maxQuoteThe LTC2057's could be a good candidate but the bias current is a bit high at 30pA typ @25C, 300pA max. How practical is it to trim it out? It will change as the common mode voltage changes so bootstrapping would help a lot in this respect.When you say bootstrapping do you mean servoing the supply rails to keep the common mode voltage constant to remove the finite gain (Avol) and CMRR error contributions? What are the disadvantages of doing this - presumably the bootstrap amplifier's noise gets added directly?QuoteThe LTC1052C has better specs than the LTC1050 except for Avol, particularly Ib typ of 1pA v 10pA. Any particular reason you suggested the 1050? Of course typical is not guaranteed and both have the same 30pA max spec @ 25C. It may not be possible to find any of those 1pA devices for a reasonable expenditure as they aren't especially cheap parts.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 13, 2015, 12:06:47 pm
content: With bootstrapping the OP I meant adjusting the supply to keep common mode voltage constant.The main disadvantages are the extra effort and the need for extra protection circuit. The protection leads to some extra leakage, but may be needed anyway. There is essentially no extra noise or drift, as the AZ OP is still doing the final amplification and will attenuate noise / drift from the bootstrapping circuit to a large extend (e.g. by common mode rejection or loop gain).One advantage is, that the AZ-OP does not need to be made for the high supply voltage. The choice for AZ OPs at 5 V supply is much larger than at 20-30 V. Also bias may be lower at low supply voltage. The second advantage is, that CM voltage may be chosen for minimal bias.I have not seen directly analog compensating for the bias, but it does not look impossibly. The classical solution with same impedance at both inputs however does not work, as the sign is different. Even with a 100 M resistor 10 pA of bias would only be 1 mV of voltage. So a rather higher resistor may be needed.

author: splin
author_rank: Frequent Contributor
timestamp: June 14, 2015, 06:19:40 pm
content: Quote from: EmmanuelFaure on June 13, 2015, 02:18:58 pmYou have to wonder if the author actually built that circuit and tested it or just did a theoretical design. I wonder how stable it is and how low you can reliably cancel the input bias current?I see that Linear's LT1013 datasheet includes a 'Triple Op Amp Instrumentation Amplifier with Bias Current Cancellation' circuit on page 18 with the claim of typical input bias current < 1nA (compared to the typical Ib value of 12nA). Not sure how well such schemes would work with a FET/CMOS amp needed for a KVD buffer though.The alternative to trimming out Ibias is to use a non-autozero op-amp with Ib < 1pA and periodically trim out the offset voltage, which is relatively easy to do by shorting the input, especially if the buffer is already driving a suitable meter/ADC. CMOS amps tend to be a bit noisy, but the OPA140 might be a reasonable choice with .5pA typ, 250nV pk-pk .1 to 10Hz noise and 1uV/C drift?The problem then is which <1pA leakage analog switches/Fets would be suitable if you wanted to automate it? It would seem that most of the devices used in the HP3458A front end are no longer manufactured.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2015, 07:01:50 pm
content: With the bias of a FET or JFET OP, you have to take into account that this is fast increasing with temperature. So the 0.1 pA typical is only at 20 C. Warmed up might be more like 30 C and thus 2 or 3 times more.The suitable switch is a relay. Low leakage FETs might work, but need quite some effort to drive the gate without introducing to much extra leakage. Anyway such low leakage is not only a question if the circuit diagram, but also depends on the layout and actual construction.The tricky circuit from EDN is more about how to create a small negative bias compensating current without a negative supply. There is a chance this solution might produce significant noise - at least that is one point I would look first before using it. The more traditional solution would be a photo-diode (might actually be a normal diode that is somewhat light sensitive) and LED, which usually scales quite well to small currents. This is especially true if the diode is part of input protection anyway and the voltage does not vary much as it is in the bootstrapping circuit.

author: Gyro
author_rank: Super Contributor
timestamp: June 14, 2015, 07:37:47 pm
content: QuoteIn their early dvms (even as far as the 106x), Datron routinely compensated bipolar op-amps (LM312) and matched transistor pairs (typical 3nA bias) to achieve bias currents of <50pA long term stable and drifting at <2pA/C. They used a combination of bias current compensation and bootstrapped supplies.I wonder if, with modern precision bipolar op-amps it might be possible to achieve much more stable results using similar compensation methods than the highly temperature sensitive bias currents of FET devices. Albeit with considerably more effort.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2015, 07:51:14 pm
content: I don't think using BJT and bias compensation is a viable solution: the bias drift before compensation is in the pA/K range even for low bias devices.CMOS and JFETs with bootstrapping can be well below 1 pA up to 30 or even 50 C. So bias drift is more like 0.1 pA/K and less, unless the temperature rises to much. So a low temperature for the input devices is needed. Protection diodes may show similar leakage.If may be possible to use a auto-zero amplifier together with bias compensation, since the bias has low sensitivity to temperature up to something like 50 C. This is especially true if using a bootstrapping setup and thus constant common mode voltage.

author: dom0
author_rank: Super Contributor
timestamp: June 14, 2015, 07:54:40 pm
content: Cooling the whole assy below ambient might be an option since thermoelectric elements have become so cheap...

author: Gyro
author_rank: Super Contributor
timestamp: June 14, 2015, 08:00:34 pm
content: As I say, that was using devices like the LM312 - '70s technology. If you compare the LM312 spec to even something like an OP-77 with similar level of attention to compensation......

author: Kleinstein
author_rank: Super Contributor
timestamp: June 15, 2015, 03:41:16 pm
content: The LTC1052 is one of the few AZ OPs that still use external capacitors. This can help to get a low bias because of the low internal switching frequency. So there may not be a much better solution available.Using an external bootstrapping circuit can help to overcome the limit on the supply voltage. A lower supply may actually help to reduce the bias with some devices (the LTC2057 seem to be an exception). A low voltage also reduces power in the amplifier and thus thermal problems.Cooling seems good at first sight, but can get tricky, because of humidity and thermal EMFs.

author: splin
author_rank: Frequent Contributor
timestamp: June 15, 2015, 11:12:25 pm
content: Quote from: Gyro on June 14, 2015, 07:37:47 pmThat's very interesting. Do you have any links to circuit diagrams?

author: splin
author_rank: Frequent Contributor
timestamp: June 16, 2015, 01:59:20 am
content: Quote from: DiligentMinds.com on June 15, 2015, 03:13:52 pmYou're probably right - will start looking...QuoteThe 2057 does have much higher current noise at 170fA/sqrt(Hz) compared to .6, but that only increases the noise to approx 300nV pk-pk with 70k source resistance so still much quieter in this case. CMRR is also 10dB better so it does seem to be a good choice, particularly if the bias current could be reliably compensated. The high voltage ability may not be much of an advantage though as even 150dB of CMRR equates to .032ppm at 10V and 150dB finite gain error another .032ppm, .064ppm total which is close to the KVD's .1ppm so bootstrapping may be required anyway.Do you have any suggestions, or places to look for very low leakage input protection solutions? When I've looked in the past it seems to be not so easy to find suitable devices.QuoteIt may come to that, but I'm interested to see how Datron compensated for Ibias and if similar techniques coiuld be applied to the LTC2057.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 16, 2015, 11:41:07 am
content: Using the LTC2057 and bias compensation might be a good solution.Low leakage diode could be something like the BA199, some JFETs (gate to source+drain), small area photodiodes or just the collector - base junction of small transistors. Here also some degree of bootstrapping can help to limit the voltage over die diodes and thus really bring the leakage down. Photodiodes might also be used to compensate the bias, but even normal diodes in a not perfectly opaque case (e.g. BA199) might be sensitive enough for this purpose.

author: Gyro
author_rank: Super Contributor
timestamp: June 16, 2015, 01:29:53 pm
content: QuoteI do if you're prepared to squint a bit! I've never found a copy online, I meant to scan the whole manual sometime but my trial copy of Scan-n-Stitch expired (they're A3 schematics).Attached are the input board schematic, including i/p protection (Datron used a combination of JFETs, Zeners and an 88k 8W series resistor chain!), Ib compensation and bootstrapped supplies. Q11 (TO92) is thermally coupled (superglue) to the LM312 (TO99) under a plastic cover. The double sided PCB copper is arranged to be as isothermal as possible around them. All resistors are carbon film (apart from the high >10Mohm ones which are carbon composition).As I say, they managed to achieve >10G input resistance, <2pA/'C and 0.2uV/'C using VERY humble parts by today's standards and with no cpu to do auto-zero or correction in these units. My unit holds within 1-2uV from cold to operating temp on the 10mV range (x100 gain) with no appreciable long term drift (well aged by now!)The next generation - 1065/1061 are all evolutions of the same basic starting point, but with a cpu for compensation, autocal, autozero etc.I've also attached the relevant page from the circuit description.Hope it's at least of historic interest anyway.

author: Gyro
author_rank: Super Contributor
timestamp: June 16, 2015, 01:44:12 pm
content: Just for completeness, here is the later input circuit used on the Datron 1041 / 1051.It uses a LM394 dual matched transistor and an LF355 in place of the LM312. Quite a lot of added complexity for very little gain in stability (Instrument specs are identical in fact). The bootstrap supplies are on a different sheet but are identical to the previous one.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: June 16, 2015, 03:51:49 pm
content: The Analog Devices AD8616 might be a good candidate if you apply some bootstrapping. 0.2pA typ, 1pA max. The typ CMRR is only 100dB so you would have to wrap some bootstrapping around it to get the extra 40dB and use it as a buffer stage.

author: poorchava
author_rank: Super Contributor
timestamp: June 16, 2015, 05:47:16 pm
content: As far as I know LMC6001 offers lowest guaranteed bias current at 25fA. It was even featured in 'what is this femtoampere stuff anyway' with Bob Pease. Arcane stuff going on there...Wys?ane z mojego HTC One M8s przy u?yciu Tapatalka

author: dom0
author_rank: Super Contributor
timestamp: June 16, 2015, 05:49:40 pm
content: 10 µV/K offset drift and +-1 mV offset...

author: Marco
author_rank: Super Contributor
timestamp: June 16, 2015, 06:22:07 pm
content: Quote from: Gyro on June 16, 2015, 01:29:53 pmWhich is still 10 times as much as an auto-zero.Just use a AD8638 or a LTC1052 and throw an aggressive low pass filter at it to get rid of the noise and eat the slightly slow response on a setting change (maybe use some nonlinearity to speed it up a bit for large changes).

author: Gyro
author_rank: Super Contributor
timestamp: June 16, 2015, 07:53:08 pm
content: QuoteAgain...only to demonstrate the >25 times improvement that was achieved by supply bootstrapping and Ib / Vos compensation of the basic op-amp. Study / learn / use techniques or not as you wish.

author: splin
author_rank: Frequent Contributor
timestamp: June 17, 2015, 04:55:21 pm
content: Quote from: XFDDesign on June 16, 2015, 03:51:49 pmIts a bit noisy at 2.1uV pk-pk and 1.5uV/C (typ) to 7uVC (max) would be a problem especially if the KVD is used at 1V or less.Oddly figure 9, Ibias v temperature, shows approx 10pA @ 25C. Yet another duff datasheet 'typical' graph. Presumably the .2pA typ/1pA max spec is correct.Its the first time I recall seeing a Voffset v common mode voltage chart in a datasheet (but I probably wasn't looking). Its pretty horrible - see attached. Around 3.5V as far as I can tell, one unit appears to exhibit an input offset change of at least 300uV over a change in common mode voltage of 250mV or so. That equates to a CMRR of only 833 or 58dB! How does that allow them to specify 80dB minimum with Vcm = 0 to 4.5V? Another faulty chart? Wrong units? Is CMRR specified using a box method - ie. 450uV/4.5V = 80dB?The headlined offset voltage is 65uV but the spec, in the Vs=5V table is actually 23uV typ, 60uV max - for Vs at 3.5V and Vcm = 0.5V and 3V. That's cherry-picking! At 5V its 80uV typ and 500uV max.

author: splin
author_rank: Frequent Contributor
timestamp: June 17, 2015, 05:03:08 pm
content: Quote from: poorchava on June 16, 2015, 05:47:16 pmThe LMP7721, LTC6268/9 and LTC6268/9-10 specify 20fA max at 25C, but they are all 'by design' unlike the LMC6001 which is claimed to be 100% tested.

author: splin
author_rank: Frequent Contributor
timestamp: June 17, 2015, 05:29:09 pm
content: Quote from: Marco on June 16, 2015, 06:22:07 pmOn the other thread you pointed out figure 14 in the AD8638 datasheet showing .1pA Ibias at 25C, Vs = +/-8V. Does that seem likely given that it is specc'd as 1.5pA typ at 25C, Vs = 5V (table 2) and 1pA at Vs = 16V? (and shown as 1.5pA for Vs = +/-2.5V in figure 13). One of them is wrong given they are both supposed to be typical (though they don't specify the measurement setup for fig 14).1pA is probably good enough, but there is still the question of how many units you'd have to test before you found a typical one.

author: splin
author_rank: Frequent Contributor
timestamp: June 17, 2015, 05:57:35 pm
content: Quote from: Gyro on June 16, 2015, 01:29:53 pmThank you, very interesting. You have to admire the designer's skills given these date to the 70's (60s?). Even the recently released 34470A 7.5 digit dvm is only specified at < 30pA. I guess its considered good enough and not worth improving, or they'd rather sell you another instrument for your 'specialist application'.I wonder how the 1061 design deals with the LM312's offset variation with input resistance given the latter is in the control of the user?

author: Kleinstein
author_rank: Super Contributor
timestamp: June 17, 2015, 08:29:12 pm
content: The resistance dependent offset is just a different description of bias current. One they compensate for the bias, the offset is not effected by the input impedance.With AZ OPs the offset can also depend on the AC impedance at the internal sampling rate. So one may need to have some capacitance at the input.The 30 pA or so for a modern meter is not only the amplifier but also includes protection circuits, range switching and the layout. With such low bias ratings it's important to look at the temperature and maybe humidity for which this is specified.High end meters often use a very slow auto zero cycle and a discrete JFET amplifier. Like with integrated AZ OPs its finding the right balance between low bias and low noise. The overall performance seems to be not significantly different.Even with a noisy amplifier there may not be much need for filtering, as most meters are not that sensitive to noise. The usually long sampling time is already a very efficient low pass filter.

author: Gyro
author_rank: Super Contributor
timestamp: June 17, 2015, 09:27:52 pm
content: QuoteAbsolutely. Early 70s certainly. The days when men were men and sheep were nervousIt's all too easy today. Lots of lessons still to be learned from the challenges overcome in vintage stuff.As for the input current, yes I guess leakages start to dominate - lots of PTFE standoffs in the Datron, don't know about the Agilent, but both would have active guarding.As for the modern AZ amps, Ib and Vos compensation probably have much less importance but supply bootstrapping would probably still give a significant improvement in CMRR and probably other parameters, as well as allowing a greater i/p swing (outside the supply limits of the AZ amp).

author: TimFox
author_rank: Super Contributor
timestamp: June 18, 2015, 02:17:01 pm
content: To avoid current from common-mode voltage, the guarding referred to above is essential. Even a PTFE standoff can have leakage resistance from humidity (although PTFE is naturally "hydrophobic"), so having a guard ring with appropriate drive at its base is a good idea.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 18, 2015, 04:49:55 pm
content: Having a bootstrapped supply, bootstrapped protection circuit and driven guards can be often combined to to together in one circuit.With guards and a few cuts, one may get around extra standoffs.Whether you need bias compensation depends on the AZ amplifier. The very low noise versions have a bias that is to high to be tolerated - in the 100 pA range. With supply bootstrapping the bias compensation may be as little as a very high value resistor and a trimmer.

author: Echo88
author_rank: Frequent Contributor
timestamp: September 10, 2017, 08:31:38 pm
content: Maybe someone can help me out with the understanding of the KVD-buffer mentioned here and in the AN86 Page 9:http://cds.linear.com/docs/en/application-note/an86f.pdfI only ever thought about CMRR in difference amplifiers which measure tiny signals. In this case its mentioned together with a voltage follower; how does the CMRR manifest as an error in this circuit?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2017, 08:50:41 pm
content: A buffer made from an OP makes the op see the input voltage as common mode voltage at the input. So if there is a common mode error, this would would cause the amplification to be of from 1 by that small amount. A 120 dB CMRR would thus translate to a 1 ppm gain error. So like open loop gain, the CMRR is an important parameter for a precision buffer.The usually very good CMRR of AZ OPs helps a lot.Bootstrapping the supply can be a nice trick to improve a buffer, as the critical OP will not see the full common mode voltage, but a much smaller one (the error of the 1st approximation).

author: David Hess
author_rank: Super Contributor
timestamp: September 11, 2017, 01:55:59 am
content: Quote from: Echo88 on September 10, 2017, 08:31:38 pmFor an operational amplifier, the common mode rejection ratio represents the change in offset voltage for a change in voltage at the non-inverting input. So a 120dB CMRR means that for every 1 volt change at the non-inverting input, the offset changes by 1 microvolt.So CMRR is a critical parameter when dealing with non-inverting amplifiers and can limit performance in precision applications. With inverting amplifiers, the non-inverting input is fixed so CMRR ratio is irrelevant; audio circuits often use common mode suppression to remove distortion caused by limited CMRR. With difference amplifiers, the non-inverting input changes by some fraction of the common mode input voltage.

author: Echo88
author_rank: Frequent Contributor
timestamp: September 11, 2017, 04:15:53 pm
content: Thanks! Since all other topologies apart from the voltage follower necessitates resistors, seems we no choice but to use the voltage follower. I also took a look again at the AoE-book and there was also the note that inverting amplifiers dont suffer from CMRR-problems. But i couldnt find a description how supply bootstrapping (like done in the Fluke 5700A Page 542 with the LTC1052https://xdevs.com/doc/Fluke/5700a/5700A_old_sm.pdf) affects CMRR, only that bootstrapping allows the use of low supply OPs (with its sometimes better specs) while allowing bigger voltage input/output-swings.Is it because CM-voltage is related to the middle of the supply voltages and always follows the input signal, so that the CM-voltage is constant?Ive read that diodes, which are illuminated to generate a minimal current, could be used to cancel the remaining bias current. Are there any existing designs which use this concept?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2017, 05:34:03 pm
content: The common mode voltage is relative to the supply (middle or one side - if the supply changes there would be an additional effect of the finite PSRR). So bootstrapping to a good approximation avoids a changing common mode voltage seen by the OP.It is possible to use photocurrent (e.g. from a diode) to compensate. The downside is that photocurrent is inherently paired with shot noise. Current through a high value resistor can (with the right type of resistor) be without extra shot noise. The resistor noise can be smaller. A low leakage diode might be needed for protection anyway - however low leakage diodes are usually in a light tight case.

author: David Hess
author_rank: Super Contributor
timestamp: September 11, 2017, 05:45:36 pm
content: Quote from: Echo88 on September 11, 2017, 04:15:53 pmEffectively it is although I do not know if it is specifically defined that way. If the supply voltages follow the signal at the non-inverting input, then it is just as if the operational amplifier has no common mode input voltage change.If the common mode input voltage is fixed and the positive supply voltage is changed, then the positive power supply rejection ratio (+PSRR) applies. If only the negative supply voltage is changed, then the negative power supply rejection ratio (-PSRR) applies. If both supplies are fixed in value but shift together, then the CMRR applies.Bootstrapping the supply voltages is easy enough and adds the common mode rejection ratio of the amplifier and the bootstrap circuit together. (1) This could be done to achieve the 140dB or higher CMRR needed in this application while using a non-chopper CMOS or JFET input operational amplifier for even lower input current and lower broadband noise at the expense of increased 1/f noise which is probably what matters in this application. Chopper stabilized operational amplifiers have flat 1/f noise making them especially suited for low noise DC applications. Broadband noise is easy to filter out so there is no reason to minimize it. Electrometer applications do not have a choice and have to put up with the greater drift and 1/f noise of a JFET or CMOS device.QuotePhotodiodes are not required for that and I think they would be a bad choice. There are a couple of ways to implement fixed or adjustable bias current cancellation externally using diodes or transistors or even a second operational amplifier of the same type. I have never seen this done though for a chopper stabilized operational amplifier.(1) It adds the separate common mode rejection ratios in dB. As a fraction or ratio, they multiply.

author: Echo88
author_rank: Frequent Contributor
timestamp: September 15, 2017, 12:04:34 pm
content: Just like Santa i made a list, to check which OP behaves naughty or nice. Maybe someone else finds it useful. If i made an error please point it out, the prices mentioned may not be all accurate or for the particular op-amp-grade.Anyway, at the moment im lacking the knowledge to make a better voltage follower than the one made by Jim Williams. So i continue looking at Datron DMM-service manuals (1051 and 1061 for example) for info on supply bootstrapping and the infos from AoE3 and Bob Peases articles about femtoampere- and teflon-stuff.

author: Cicada
author_rank: Regular Contributor
timestamp: September 15, 2017, 12:23:11 pm
content: Might be worth your while using TI's paramateric search.Just select Vos, Offset driftand Input Bias current tick boxes. Sort by Vos and scroll down to where you see the input bias is below 1 pA.https://www.ti.com/amplifier-circuit/op-amps/products.htmlMaybe?https://www.ti.com/product/opa2320https://www.ti.com/product/lmp2232You can Analog devices as wellhttp://www.analog.com/en/parametricsearch/11070

author: danadak
author_rank: Super Contributor
timestamp: September 15, 2017, 12:39:50 pm
content: A related topic -http://www.electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhowRegards, Dana.

author: chuckb
author_rank: Frequent Contributor
timestamp: September 16, 2017, 02:09:58 pm
content: There are some examples of Bootstrapping the power supplies for improved op amp performance in this old Burr Brown App note.

author: MisterDiodes
author_rank: Frequent Contributor
timestamp: September 19, 2017, 05:48:06 pm
content: Just be very careful picking an op-amp from a parametric list looking at input bias current alone - usually low Ib means higher voltage noise in an IC amp. By the same token be aware that the typical AZ amp input current noise datasheet spec is generally hundreds of times lower than the -actual- gate current injection noise spikes that occurat the switching freq. That's not a deal breaker but you have to be ready for it - keep that switching noise current on AZ amp inputs and power rails contained in a safe way inside small area current loops.Be aware that the ancient '1010 that shows up in old LT app notes: Even though it gives you some current drive, that comes at the expense of some relatively strong noise density.It all depends on what your acceptable noise level is on the final output, and how many of those KVD dials are you -really- planning on using?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: March 20, 2019, 01:20:18 pm
content: ADA4530-1 ??