An Analytic and Graphical Method for LNA Design with Feedback

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  • Author: Alan Victor and Jayesh Nash
An analytic technique and figureof-merit (Fnm) for the trade-off of noise measure and mismatch loss in the design of low noise amplifier is presented. The trade-off between various design parameters as a function of inductive source degeneration is evaluated using the developed design curve. It is shown that the design curves are unique to the selected device. Several devices demonstrated conditions whereby the use of source degeneration leads to instability and must be avoided. The technique is straightforward and permits prescreening of potential devices being considered for low noise amplifier design. The resulting design curves permit accurate selection of the range of acceptable feedback values to achieve desired performance. A new figure-of-merit has been introduced which allows designers to choose the optimum value of source inductance either analytically or graphically. The new methodology is discussed and was applied to low noise pseudomorphic hetero-junction FET (pH-JFET) amplifier designs at 2.10 GHz and 10.24 GHz.