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LNA Using Active Inductor

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Published in: Networking
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Low Noise Amplifier Using Active Inductor

Najeemullah B / Hyderabad

8 years of teaching experience

Qualification: M.Tech (Moguls Institute of learning - 2007)

Teaches: Algebra, Computer Science, Mathematics, Physics, B.Tech Tuition, Electronics, M.Tech Tuition, Railways Exams, RRB, Sub-Inspector Exam, UGC Exams, Chemical, Electrical, Embedded Systems, Hardware Training, Informatica, MCA Subjects

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  1. LOW VOLTAGE LOW NOISE AMPLIFIER USING DIFFERENTIAL ACTIVE INDUCTOR
  2. Low noise amplifiers Low noise amplifiers are one of the basic building blocks of any communication system. The purpose of the LNA is to amplify the very week received signal captured by an to acceptable antenna levels with minimum self-generated additional noise. An LNA is a key component which is placed at the front-end of a radio receiver circuit. Per Friis' formula, the overall noise fiqure (NF) of the receiver's front-end is dominated by the first few stages (or even the first stage only). Gain, NF, non-linearity and impedance matching are four most important parameters in LNA design.
  3. Receiver Antenna BPFI LNA BPF2 Mixer BPF3 IF Amp: RF front end Demodulator
  4. DIFFERENT AMPLIFYING TOPOLOGIES FOR INPUT IMPEDANCE MATCHING Initially a study of the basic tradeoffs between different amplifying topologies with respect to the gain, NF and impedance matching was made. After this comparison it is concluded that inductor degenerated common source topology gives the best performance to meet the gain, NF, and impedance matching goals with minimum power consumption in case of narrow band designs. It is preferred in current RF designs that the input of LNA be matched to 50Q. 1 -The easiest way is to shunt the gate with a resistor of 500 . Disadvantaqes: - Poor Noise Figure since Rsh adds extra noise. - Input signal attenuated by the voltage divider - At high frequency, shunt L is needed to tune out Cgs - Reduced gain. von Vout Rs Vs Zin
  5. 2.shunt feedback amplifier NFI 1 & RF tusually 50 Q Features: - Better performance than CS amplifier - RF induces noise - At higher f a shunt inductor needed to tune out Cgs von Vout - Broadband Amp @ Lower frequency - To make NFL RF > Rs and gmRs I Vs Zin
  6. 3.Common gate amplifier also offers 50Q input impedance match and solves the input matching problem. vs Zin Vout
  7. 4.1nductor source degenerated LNA Vout Zin
  8. Writinq K VL at the input + iojoLs jar io = gmiin X joc- Substituting (2) in (1) (1) (2) For matching Lg + 1.4 are canceled out by So at frequency ofinterest COO oocs, = 50Q-
  9. - Very good NF value - Narrow band matching - with 1 200R,C:, - The Q value is dependent upon Lg + Ls, LS usually small so Q depends mainly upon Lg Gain m where Gm Noise Figure gmRsQ2m
  10. Draw backs: 1 .RL generates noise RL generates noise so replace RL with LD so that's 1 coo VDD vs
  11. 2.Reverse isolation depends upon capacitance between output and input. To make it less the cascode architecture can be use cc
  12. passive inductors such as spiral and bonding wire have been widely used by designers. But at high frequencies, series resistance due to skin effect causes series losses and magnetic current of the inductor induces eddy currents in the substrate which results in substrate losses. This leads to reduction of Q-factor. In planar spiral inductors the inductance is directly proportional to the number of turns of the coil. This limits the inductance value. While the inductance of stacked inductors increases linearly with the increase in the number of spiral layers, the self resonant frequency of inductor decreases in a non-linear fashion. There is also an existence of parasitic capacitance between spiral layers [4]. So in order to overcome the limitations of passive inductors such as low Q-factor, low self resonant frequency, small and non tunable inductance and large area, active inductors are preferred.

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