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2.7: Amplifier Noise

  • Page ID
    46029
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    Section 4.3.6 of [26] presented a discussion of noise in amplifiers. The final result was an expression for the noise figure of an amplifier given the noise parameters of the transistor. This expression was in terms of the magnitudes of complex numbers, which, as has been seen, leads to circles when plotted on the complex plane. Thus the noise figure of an amplifier can be pictured as noise figure circles on a Smith chart. Figure 2.6.6 shows the noise figure circles at \(8\text{ GHz}\), plotted on the input Smith chart for the pHEMT transistor documented in Table 2.3.1. The center of the (almost) concentric circles is \(F_{\text{min}}\) and the noise figure circles show the impact of source mismatch on the noise figure. The loading conditions have little impact on the noise figure of an amplifier as long as the output matching network is lossless and the gain of the amplifier is high. These circles prove useful in making design trade-offs.


    2.7: Amplifier Noise is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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