Design Of 2.4GHz Microwave Low Noise Amplifer

Low noise amplifier is a very important device in modern wireless communication, satellite,radar and other electronic system. As a front device of the receive system, it is used to amplifysignal, inhibit the interference of noise. At the same time, it is also used to improve the sensitivity ofthe system. If a high performance LNA is used in the front of the receive system, and the gain of theLNA is big enough, it will be able to inhibit the noise of the later stage circuit. The noise coefficientof the receive system is decided by the noise coefficient of the LNA.In this paper, I mainly analyze a LNA, which is used in the Bluetooth wireless communication.First, I comprehensively understanded the theoretical principles of microwave amplifier circuit: theanalysis of the microwave two-port network, smith chart, microstrip transmission line theory, RFcharacteristics of the passive components, characteristics of the microwave transistor; Second, Idescribed the main performance indicators of the LNA in detail: the significance and the conditionof the stability, the relationship between the noise coefficient and the noise temperature, dynamicrange, the gain and the flatness of the LNA, noise match and the typical structure, the matchingmethod of the input circuit and the output circuit; Third, I analyzed the typical design structure andmethod of the circuit; Last, I designed a LNA, which work in Bluetooth frequency.This paper use two simulated software, one is ADS 2008 and the other is Microwave 2002. Bythe above two software, we complete all the design and simulation of the circuit. The design processis mainly divided into four steps. The first step is to determine the performance indicators of theamplifier, then to carry out the selection of the transistor, and to design its DC bias circuit. Thesecond step is to judge the stability of the amplifier. After the simulation of the ATF54143 transistor,we find that the transistor is not stable in the target frequency range. So we need a negativefeedback circuit to improve the stability of the amplifier. In this paper, we use the microstrip line inseries with source feedback circuit. The third step is to match the input and the output circuit.Matching the input circuit for the minimize NF and Matching the out put circuit for the maximizepower gain. After the simulating of the single circuit, the fourth step is to match the cascaded circuit.With the optimization and improvement of the circuit, we can get the target of the design. The last isthe PCB design principles and notices of the circuit, we finish the PCB layout design by Protel 99.In the design and simulation of the LNA, the ATF54143 transistor of Avago Technologies isused as a key device in this thesis. In the LNA, working frequency is 2.3 to 2.6 GHz, centerfrequency is 2.45 GHz, that is the LNA working frequency in the Bluetooth wirelesscommunication(2402~2480 MHz). The microstrip line in series with source feedback can ensure thestability of the LNA. Matching the input circuit for the minimize NF in order to make the NF of theLNA less than 1 dB. Matching the out put circuit for the maximize power gain in order to make the gain of the LNA more than 20 dB. The VSWR of the LNA is less than 1.5. The result is basicallyachieved to anticipated effect.In the design of the LNA, its performance indicators are often conflicted, the most prominentis the confliction between the minimize NF and the maximize power gain. Most of the time, the twocan not meet. In fact we usually take a compromise measure to make all the indicators to theanticipated effect.