Research On Ultra-wideband Microwave Low Noise Amplifier

Modern communication system with the increase in the amount of information explosion,for the bandwidth,information capacity requirements are increasing,ultrawideband(UWB)can perfectly solve those problems.Acting as the per-stage circuit of the receiver?Low noise amplifier's performance is important to the overall parameter index of the circuit such as noise figure,sensitivity,linearity.Therefore,it is one of the key technologies to realize the design of low noise amplifier with flat gain in multi octave,which has important research value and broad prospects for development.At the same time,microwave monolithic integrated circuit(MMIC)technology has developed rapidly for its small size,light weight,good consistency,high reliability.And it has been used in the design of low noise amplifier.Four different broadband topologyies are analyzed here,and the traveling wave distributed structure is selected according to the design bandwidth requirement.The combination of the input,output capacitors of the transistor and the interstage inductance constitutes the gate and drain equivalent artificial transmission lines.When the equivalent characteristic impedance is equal to the port impedance,UWB multi-octave matching can be realized.Using a narrow microstrip line(ribbon inductor)to achieve the the inductors required for the artificial transmisson lines,the spiral inductor is not suitable because the parasitic capacitance is too large.The width of the stripline is as narrow as possible to expand the working bandwidth under the premise of meetting the DC current handling requirment and fabricationg limits.Due to the gate-and drain-line losses,the optimum number of sections can be acquired according to the equivalent circuit model of the transistor,the design parameters of the MMIC and the principle of the distributed amplifier.The circuit adopts the distributed amplifier structure,and uses the cascode structure as the gain unit,which has lower gate-drain feedback capacitance and higher output parallel resistance than the common source structure,so that the circuit has a wide frequency band,Higher gain and higher linearity.And this only adds a small amount of layout area.For the gate-source capacitance is much larger than the characteristics of the drain-source capacitor,a m-derived section is connected in series on the drain line to effectively equalize the phase velocity of the gate line and the drain line to ensure that the signal is superimposed on the drain.Chip area is1.8mm×1.2mm.Based on the French OMMIC 0.15 ?m GaAs pHEMT process,a distributed amplifier monolithic circuit was fabricated.Test results show that the chip at 0.5-18 GHz the gain is larger than 10 dB,unevenness is less than ± 1dB.The input return loss is less than-10 dB,the output return loss is less than-12 dB,and the in-band noise figure is averaged 3.5dB.The chip area is1.8mm×1.2mm.