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low noise resistor

Discussion in 'Electronic Design' started by [email protected], Aug 17, 2007.

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  1. Guest

    What type of resistors are low noise resistors? i am using surface
    mount (SMD) resistors. I learnt that there are thick film and thin
    film resistors. Which types of SMD resistors have lowest noise? kindly
    enlighten on this.
    Thanks
    Kristo
     
  2. Phil Allison

    Phil Allison Guest


    ** Wire wound ones are hard to beat.


    ** Thin films, particularly metal film types have very low "excess " noise.

    Thick film types ( aka cermet or metal glaze) can be very noisy by
    comparison.

    Be aware that resistor self noise is only a issue where there is significant
    DC voltage across the part.

    BTW:

    All resistors have thermal or Johnson noise, which only depends on their
    value and temperature.

    En = sq rt ( 4.K.T.B.R )

    where

    En = rms noise voltage
    K = Boltzman's constant = 1.38 exp-23
    T = temp in degrees Kelvin
    B = measurement bandwidth in Hz
    R = resistance in ohms


    Eg: for 1000 ohms in a 100kHz band at 20C

    En = 1.27 exp-6 volts



    ........ Phil
     
  3. Damon Hill

    Damon Hill Guest

    Generally, thin film, especially metal film. Vishay's bulk foil
    technology is among the lowest, but pricey.

    --Damon
     
  4. Eeyore

    Eeyore Guest

    Most SMD resistors have very poor noise levels.

    If you want good noise performance economically use a leaded metal film part or
    expect to pay a king's ransom for the SMD equivalent which will also be heard to
    obtain.

    Graham
     
  5. Eeyore

    Eeyore Guest

    Yes, dollars per resistor IIRC. Their 'application note' regarding them is the
    biggest load of lies I've ever seen published by a serious component
    manufacturer btw. It panders to the very worst of the audiophool myths.

    For cents you can get a leaded metal film part that will perform essentially
    identically in most circuits.

    Graham
     
  6. BC comps/vishay thin films seem ok
    Fig 3
    in
    http://www.rapidonline.com/netalogue/specs/71-2100e.pdf

    the smaller the body, more hissy stuff gets out, something to do with
    the 1/(magic smoke) ratio


    Martin
     
  7. Guest


    Where did you get that bit of mis-information? Metal film SMD
    resistors
    are usually good enough.

    The trick to low noise design is mostly a matter of decoupling or
    mis-matching the noise sources in a circuit. I've made amplifiers
    with 300pV/rt(Hz) input-referred noise and 50 Ohm input resistance,
    despite opinions that one could never get below about 0.5nV/rt(Hz)
    in a wideband matched system.

    And yes, this was at normal room temperature.

    Jeroen Belleman
     
  8. Hello,

    Has anybody the details about the measurement conditions of current noise.
    Yes I know it's in the IEC60195, but I don't have it. I am only interested
    in the frequency band(start/stop frequency). The datasheets of the
    resitors don't have this information. This makes the numbers there
    not really useful.

    Best regards,
    Helmut
     
  9. Sorry, can't help you with that, probably more of a Win Hill/Tom
    Bruhns question
    but I found another spec sheet, Panasonic stuff, which I have put here
    http://es.geocities.com/mart_in_medina/resnoise.pdf
    rather than attempt to find it in the original URL

    Fig 14, p12 shows thick versus thin film performance


    Martin
     
  10. Eeyore

    Eeyore Guest

  11. Eeyore

    Eeyore Guest

    Good enough for what and where's the data ?

    Graham
     
  12. The data is filed under "climate change"


    Martin
     
  13. Fred Bloggs

    Fred Bloggs Guest

    Looks like Google terminated your account for terms of use violations,
    damned ill-behaved freak.
     
  14. Eeyore

    Eeyore Guest

    Esta página no está disponible.

    Lo sentimos, pero está página no está
    disponible en este momento. Por favor, inténtelo
    nuevamente más tarde, o haga una búsqueda
    en Yahoo! GeoCities de otras páginas que le

    interesen.
     
  15. Eeyore

    Eeyore Guest

    You're an IDIOT.

    I don't post through Google. Never ever have done.

    Graham
     
  16. John Larkin

    John Larkin Guest

    They're all about the same. All resistors have identical Johnson
    noise. If there's voltage across them, some may have "excess noise",
    which should in theory be very small for metal film resistors. I've
    tried to measure the excess noise of various expensive (thin film) and
    dirt-cheap (cermet and carbon film) resistors, without success; they
    all seem the same.

    There is one type of excess noise that's real and measurable:
    temperature fluctuations changing resistance in a voltage divider,
    converting DC to super-low-frequency noise. That would matter in
    instrumantation situations, certainly not audio. We sometimes put
    covers over tender circuits to keep air currents off.

    Most real-life circuits tend to be dominated by inherent signal noise,
    or by the semiconductors, or by bad design.

    John
     
  17. Fred Bloggs

    Fred Bloggs Guest

    Well how many people have that lame "rabbitsfirendsandidiots" email?
     
  18. Fred Bloggs

    Fred Bloggs Guest

    Right, otherwise known as thermoelectric effect. You can make a pretty
    good people detector using that.
     
  19. Phil Allison

    Phil Allison Guest

    "John Larkin About Fuckwit TROLL "



    ** A blind man's opinion of the view.


    ** Yawn ............


    ** So the trolling, autistic fool has no experience to draw from.


    ** A blind man's opinion of the view.

    It all looks dark to him.




    ........ Phil
     
  20. Eeyore

    Eeyore Guest

    You can't be doing serious low noise work in that case.

    You can even HEAR the difference between top quality and cheap metal film
    resistors. It may not be readily measurable though since it tends to be popcorn
    style noise.

    Graham
     
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