While designing low noise amplifier (LNA), we are using both passive feedback and active feedback. what are its importance and limitations of active and passive feedback, while designing LNA
Passive feedback means we are using R,L, C as the feedback elements in LNA
Active Feedback means we are using Transistor as the feedback element in LNA
In the design of LNA, the importance is given to achieve the desired noise figure. Accordingly, input and output matching network is designed. In this process, the LNA will have unstable operation and as a result it oscillates at some frequencies.
In order to improve the stability (no oscillations), feedback is introduced in the amplifier. If feedback is through LC circuits, no additional noise figure is added. If R is used, noise figure degrades.
Basically, feedback network should not introduce the noise in the amplifier. Active feedback may introduce the noise and thus noise figure of LNA may degrade.
Dear Sir,
Feedback advantage is only improve the stability of the amplifier.
As Prof. AR Reddy mentioned feedback generally used to improve the bandwidth and stabilize the circuit but it affects the gain since gain bandwidth product is constant value. you can review Analog integrated circuits for Razavi chapter 8
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