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
** 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
" snipped-for-privacy@hotmail.com" wrote in news: snipped-for-privacy@j4g2000prf.googlegroups.com:
Generally, thin film, especially metal film. Vishay's bulk foil technology is among the lowest, but pricey.
--Damon
Looks like Google terminated your account for terms of use violations, damned ill-behaved freak.
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
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