Solved: Please identify this 0603 component (it's Kyocera AVX RF MLO) - Page 1
Forum section: electronics / projects

author: hanakp
author_rank: Regular Contributor
timestamp: September 30, 2024, 09:19:29 am
content: Edit:It seems to be Kyocera AVX RF MLO (Multilayer Organic Capacitors) series:https://www.kyocera-avx.com/products/rfmicrowave/capacitors/mlo-series-size-0603/It has 0603 package size, I made photos from all 4 sides. I found it in input stage of a photodetector amplifier (PIN diode transimpedance amplifier). I tried measuring its characteristic with Keithley 6487, but there was negligible current up to 200 V (I didn't want to go higher). It has capacitance of 1.4 pF up to about 30 MHz, then it slowly increases. I think it's polymer ESD protector, or maybe single-layer capacitor. However, I'd like to know exact type, if possible.Thanks for any tips!

author: thm_w
author_rank: Super Contributor
timestamp: October 01, 2024, 09:56:53 pm
content: Input stage where? Surrounding circuitry would be helpful.The highest 0603 TVS I see is 150V and doesn't look like this, though some other parts do look vaguely similar.This almost looks like a SRF or something, but, probably not if its open circuit.

author: hanakp
author_rank: Regular Contributor
timestamp: October 02, 2024, 01:46:34 pm
content: I'm attaching schematic. The unknown component is connected in parallel with the feedback resistor, I triple-checked it. It's an odd place for ESD or other protection component. But there is no reason to use an exotic capacitor either, because the device works only up to 1 MHz or so. Visually, the closest components I could find are these polymer ESD suppressors, but they have solderable terminals only on the bottom, whereas my part also has them on top:https://cz.rs-online.com/web/p/diody-tvs/1713897Notice that in my photos, the terminals are rectangular on one side, but have arc cutout on the other side.

author: hanakp
author_rank: Regular Contributor
timestamp: November 28, 2024, 05:03:53 pm
content: I found the same component today, on a different board from the same producer. And again, it was connected in TIA opamp feedback, only this time there was 2 ohm resistor in series with it. I tried it again on Keithley 6487, but I turned its source up to full +-500 V. Up to 400 V, the current was negligible, then it started to go higher. But even at 500 V, it was only 150 pA, regardless of polarity. However, when I kept the component at 500 V, the current started to slowly creep up. It took about 5 minutes to reach 1 nA, then I turned it off. When I reversed the polarity, the current was roughly the same, i.e. the component "remembered" it was subjected to the voltage. It "remembered" the current even when I turned voltage source off, waited a few minutes and then turned it on again. It seems the high voltage started to degrade something within the component.

author: mikerj
author_rank: Super Contributor
timestamp: November 28, 2024, 05:42:55 pm
content: 500v is a lot for any 0603 component so I'm not surprised. This position in the feedback of a TIA circuit would suggest it's a capacitor to compensate for the PIN diode capacitance (minimising peaking or instability)

author: TimFox
author_rank: Super Contributor
timestamp: November 28, 2024, 06:13:07 pm
content: Surface-mount ceramic MLCC capacitors are rarely marked on their surfaces.In photodiode TIA amplifiers, a capacitor across the feedback resistor is mandatory, since there is a lot of phase shift in a feedback network comprising only a feedback resistor with the amplifier input capacitance and photodiode shunt capacitance.Generally, it is only a few pF for a few megohms of feedback resistance.As a quantitative example, 1 pF in parallel with 100 k\$\Omega\$ would give a response down by 3 dB at 1.6 MHz.What is the feedback resistance in your circuit?

author: hanakp
author_rank: Regular Contributor
timestamp: November 29, 2024, 09:23:09 am
content: I'm attaching a simplified schematic of this second TIA. As I wrote in OP, the unknown component has capacitance of about 1.4 pF. The feedback resistor is 3k9, which would give about 30 MHz bandwidth. But it looks unlike any MLCC or even single-layer cap I've ever seen. And why would they use such an exotic part, anyway? Any ordinary NP0 MLCC would do fine here, and presumably be cheaper, too. Plus, I suspect PCB parasitics alone will be higher than 1.4 pF.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 29, 2024, 09:57:39 am
content: It looks odd, but could be a single-layer ceramic cap.I for one don't really see what else it could be.Yes, unless the amplifier was for very high frequencies, not sure why they used any exotic part here. Maybe they used this part in other designs. That's often what explains apparently odd choices in BOMs.

author: mtwieg
author_rank: Frequent Contributor
timestamp: November 29, 2024, 03:22:29 pm
content: Probably a SLCC, they often look weird and it would make sense in that sort of circuit (need very low capacitance with extremely high SRF)edit: beaten!

author: hanakp
author_rank: Regular Contributor
timestamp: December 02, 2024, 12:05:49 pm
content: I think I found it. It's indeed a multilayer capacitor, but a polymer one. Yep, I was surprised too, it's apolymer MLCC. It seems to be Kyocera AVX RF MLO (Multilayer Organic Capacitors) series, but generic green image on theofficial siteis misleading. Real-life photos are scarce, but structure on the side seems to be matching my photos (click Enlarge on the right or see attachment):https://mouser.com/new/kyocera-avx/avxorganiccaps/They are rated up to 250 V and the polymer composition would explain why they started to permanently degrade at 500 V. Their main advantage seems to be tight production tolerances:The ability to fabricate these components on large area substrates and state of the art laser direct imaging allow for improved cost benefits and tolerance control. The end result is a state of the art low ESR and high SRF low profile RF capacitor that can support frequencies well above one GHz. Available in capacitance values from .1pF to 5.1pF at a working voltage from 50-250VDC. Tolerances available as tight at ± 0.02pF.That's hardly relevant in this application however, so indeed it seems the producer simply re-uses these caps from other products, like @SiliconWizard suggested.

author: tszaboo
author_rank: Super Contributor
timestamp: December 02, 2024, 12:28:47 pm
content: Quote from: hanakp on November 29, 2024, 09:23:09 amThey probably selected the capacitor for the tolerance, and not the RF properties.