Study Of CMOS Low Noise Amplifier

With the development of the society, wireless communication has deep into many aspect ofindustry, and human daily life. one of the most important part of the wireless communicationsystem is Low noise amplifier, which can reduce the noise of the circuit after itself, and take acrucial role of the receiver’s sensitivity.Compare with compound semiconductor and other technology, CMOS technology is mostmature, the lowest cost, the highest level of integration. So it is significant to research CMOS lownoise amplifier. The commonly used devices of RF circuit, as MOSFET, capacitance, inductanceand resistance, is introduced and their structure, working principle and performance characteristicsis studied, in this paper. Besides, the noise performance of MOSFET is analyzed, the conditions ofconjugate matching, minimum the noise and the expression of the noise is given, with two portnetwork method.Narrowband low noise amplifier main design scheme is introduced: according to the MOStransistor two-port network noise theory, this paper introduces the principle and the design methodof traditional inductively degenerated common-source amplifier.It is further introduced someimproving structure of narrow-band LNA based on inductively degenerated common-sourceamplifier.On that basis, A 2.4GHz single-ended input and differential output low noise amplifier forwireless LAN is designed based on SMIC 0.18μm CMOS technology in this paper. The dualbranches current-reused technique is adopted to achieve low power, low noise and high gaincharacteristics. The symmetry of the circuit is achieved by increasing a stage of amplifier with thecommon gate in the output of circuit. And the phase deviation problem of differential output signalis solved by adding a series inductor in the common source branch. Simulation results show that theproposed low noise amplifier has the noise figure of 1.83dB, a gain of 20dB, the 1.8V power supplyand consumes only 8.5mW.Then it introduces wide-band low noise amplifier’s realization, gives the circuit structure, andanalyzes the principle of the circuit , impedance matching and noise performance. Based on IBM 90nm RF-CMOS technology, a 0.4-4GHz wide-band LNA is designed. Feedback structure of sourcefollower is used to reduce the circuit noise; the complementary structure by NMOS and PMOS, toachieve low power consumption, high power gain, low noise performance; The whole circuit avoidto the use inductance, diminishing the chip area, which is only 0.4*0.28μm2. Post simulation shows that the proposed LNA has the S21 14.7～15.4dB, a gain of 2～2.3dB. And the test result show thatthe hightest gain is 12.5dB, offsetting the losses of Buffer is 20.3dB, the noise is 3.7～4.3dB.Generally the gain of wide-band LNA is not so well than narrowband amplifier. A new structureof wide-band LNA is designed based on IBM 90nm RF-CMOS technology. Input a signal to thecommon-gate MOSFET, making the phase opposite from signal of the source. That can restrain theeffect of channel modulation effect of short channel device to the circuit gain. And the circuit gainwill be further improved. The simulation results show that the compare with circuit being improvedbefore, in the operation band of 0.4~4GHz, the gain increases 3dB, to 17.6~18.4dB. And otherperformance parameters virtually unchanged.In conclusion, this paper gives the main structure of narrow-band LNA and wide-band LNA.On the basis of SMIC 0.18um RF-CMOS technology, accomplish the design of 2.4GHz LNA usedin WLAN. And based on IBM 90 nm RF-CMOS technology a 0.4-4GHz wide-band LNA isdesigned. And on this basis, through the structure innovation improve circuit gain.