Path: ...!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: Interesting inductor Date: Thu, 14 Mar 2024 00:03:54 -0000 (UTC) Organization: A noiseless patient Spider Lines: 40 Message-ID: References: <5fb4vidh7pv9io2uuhnghco8cma464pgoe@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 14 Mar 2024 00:03:54 -0000 (UTC) Injection-Info: dont-email.me; posting-host="d5db565760c66749b226998157fdecb0"; logging-data="1295366"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18edNVR4DyJrvM4e5vxCNQp" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:LAsixpq/qgiZPFfCBiHUvZaM1k8= sha1:MVSZ06hWBH7ItbaAdZBHVm2LZzg= Bytes: 2650 Cursitor Doom wrote: > On Tue, 12 Mar 2024 23:17:57 -0400, Phil Hobbs > wrote: > >> So I'm doing a new lab amp product. >> Our existing one is 500 Hz -- 20 MHz, 1.1 nV/sqrt(Hz). >> >> The new one is aiming to be 10 kHz -- 200 MHz, 0.25 nV/sqrt(Hz). The >> spherical cows love it, so we'll see when the test boards arrive later >> this week. >> >> As part of the design, I wanted to make an emitter follower with a >> decent amount of inductance in series with its tail resistor, to avoid >> the transistor turning off on fast negative edges and causing linearity >> problems. >> >> Searching on Digikey, I found this very interesting part: >> . >> >> 4.7 uH 0805 wirewound, with a self-resonant frequency of _210 MHz_, >> which is several times higher than many other parts of that description. >> That corresponds to an effective parallel capacitance of 0.12 pF, >> about that of a resistor of the same size, despite all the copper windings. >> >> Pretty nifty, if true. (Parts on order.) > > As you say, nifty. Do you have some means of verifying that Fo claim, > Phil? Even a NanoVNA would give a pretty good idea if it's really that > high. > Sure, SRF measurements aren’t super subtle. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics