1 Introduction
In the case of various amplifiers, we often need to calculate the amplifier, but there is no intuitive way to see the impact of the amplifier on the link noise. This article discusses the calculation of the noise figure of an amplifier under various amplifier architectures.
2. Amplifier noise indicator
In electronic component applications, the following five sources of noise are common:
1. Shot noise (white noise, which appears flat in the spectrum)
2. Thermal noise (white noise, which appears flat in the spectrum)
3. Flicker noise (1/f noise)
4. Burst noise (pulse noise)
5. Avalanche noise (noise that occurs when reverse breakdown)
Basically, each amplifier has two indicators of input voltage noise and input current noise. In the frequency domain, its units are usually characterized by nV/rtHz, and pA/rtHz. As shown below:
Figure 1 Input voltage noise and current noise curve legend
Divided by noise type, which contributes roughly to different frequency bands as follows:
Figure 2 Noise type distribution map
If all capacitors and inductors are treated as noise-free devices, the output noise of a common amplifier can be as shown in the following figure:
Figure 3 Amplifier noise component decomposition
Based on this estimate, the voltage noise of the following resistance values ​​can be obtained:
Among the noises output, the components of the above figure contribute as follows:
The noise of the output is the mean square sum of these components:
Figure 4 Amplifier voltage noise equivalent output model
Similarly, for the fourth term in the above equation, the current noise at the negative terminal can also establish such a model:
Figure 5 Amplifier current noise equivalent output model
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