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Strategies for minimizing resistor-generated noise

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re: Strategies for minimizing resistor-generated noise
salva004   7/10/2009 7:51:13 PM
I appreciate E.G.P.'s comments. I will be using the WW and the Bulk Metal Foil resistors on a headphone amplifier design and would appreciate any hints on how to best test these two type of resistors and offer independent analysis. My power requirement is 2W, and resistance is 25 ohms. Both parts will be Vishay, one is the the WSC and the other is: http://www.vishay.com/resistors-discrete/list/product-63001/

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re: Strategies for minimizing resistor-generated noise
E.G.P.   3/7/2009 2:40:47 AM
Interesting article but some details is lacking. What kind of test fixturing did you use, what are the details of the amplifiers used. How were the tests performed. There appears to be differences in the signal levels in Fig. 2 & 3 which are not accounted for. Resistor noise is in nV/sq rt Hz and therefore must be carefully amplified and the amplifier's noise subtracted out. What are the details of the components used for these two figures. I frankly do not believe them as they stand. Fig.2's noise appears to be full of popcorn or shot noise which is only found in carbon comp to any great degree or op-amp noise. It is curiously absent in Fig. 3, where is the amplifier's noise in this? Even if the resistor has no 1/f noise amplifiers do. Are you using bandwidth filtering? If so, what is the bandwidth? Your foil resistors must have thermal noise, there are no exceptions, therefore they cannot be noise free by any definition. If you used the same gain for both figures, there would be white noise in fig.3 which I do not see. To answer Tamas' question, metal oxide resistors are made with tin oxide instead of the alloys used in foil or wire wounds. They have higher noise levels than metal film, foil or WW but are good in many applications that do not need the lowest noise. TCR is the measurement of a resistor's ohmic variation with temperature and is usually stated in PPM/'C and is often both positive and negative depending on the type of resistor. Example: +/-350 PPM/'C Wire wounds and foil resistors have the lowest TCR of all resistor types. There really isn't enough space here to discuss all the considerations you should look at for choosing a resistor, to put it short...it all depends on what you need to do.

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