第一季第三十六集:电阻特性参数详细解析10_电阻的重要参数四：噪声-->热噪声和电流噪声，主要是热噪声_电子发烧友学院

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目的：对高精度的电路，对于信噪比的要求比较高

1.在电阻中主要存在两种噪声：热噪声和电流噪声，热噪声占主导地位，电流噪声只有在电阻很大的情况下才会产生很大影响，电流噪声也叫1/f噪声；其实噪声要么以交变的电压形式要么以交变的电流形式表现出来

2.热噪声：Thermal noise: Thermal noise is the noise that we most often refer to when we talk about resistor noise. Another name is Johnson noise. Thermal noise results from the random motion of electrons through the resistor, and is given by sqrt(4kBTR), as stated in the article. Most critically, the rms thermal noise is proportional to the square root of the temperature (Kelvin scale) and to the square root of the bandwidth of whatever is measuring the noise.

3.电流噪声，接触噪声：Contact noise: It's not exactly clear what the article is discussing here, but he distinguishes this noise by its 1/f characteristic. Noise with 1/f dependence could arise from the current passing through the barriers between the carbon grains in a carbon resistor (which would be why the article recommends other types) or by current passing through the boundary between the metal leads of the resistor and the carbon resistive material. This is the only type of noise that the original article claims will be reduced by using a higher-wattage resistor. This could be explained by the higher-wattage resistor having more parallel paths through different grain or interface boundaries, resulting in noise contributions averaging out.

4.两种噪声的进一步解释：Thermal and current noise
There are two types of noise: the thermal noise and the current noise. To understand their principle, they will be discussed in more detail. In all materials, the electrons permanently move. As temperature increases, the movements increase. The vibrations of the electrons cause an electric signal (AC) across the terminals of the component. Because the vibrations are completely random, the electrical signal is noise. This is called thermal noise or Johnson noise. It is the main contributor to noise for resistors. Thermal noise is constant over a wide frequency range. Current noise however, declines when frequency is increased. The thermal noise increases with a larger resistance value, while the current noise decreases.

5.噪声标准：Noise standards
The way to measure resistor current noise is defined in norm IEC 60195. This makes the comparison of different manufacturers possible. The current noise of a resistor is described by the current noise index with a code number.

6.低噪声电阻：Low Noise Resistor
Thin film, metal foil and wire wound resistors have better noise characteristics than other types. Therefore they are often specified in low-noise amplifying applications. The carbon composition resistor and thick film are of the worst types. They cope with high noise due to the construction and material.

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