Research And Design Of Broadband Variable Gain Amplifier

With the development of communication field rapidly,RF front-end,as a key component of wireless communication,puts forward higher performance requirements in the fields of fifth-generation civil communication and electronic countermeasures military radar communication.As an important of the RF transceiver system,variable gain amplifier is a key module for adjusting the gain of the signal and controlling the power of the RF/IF signal to an optimal level.The thesis focuses on wideband variable gain amplifier as the intermediate frequency output module of the receiver in the up and down conversion system.A distributed and link-heterogeneous wideband variable gain amplifier based on0.15?m GaAs p HEMT process is designed,which realizes noise suppression and linearity improvement at low gain.The variable gain amplifier uses single-pole double-throw switch,distributed amplifier and negative feedback adjustable gain stage to achieve an innovative circuit structure.High and low-gain link heterogeneity is realized by controlling the on-off of the SPDT switch,and the low-noise distributed amplifier stage,negative feedback adjustable gain stage and high-linearity output stage are cascaded to achieve high-gain state and low-gain state multiplexing the high linearity output stage which is added to improve the dynamic range of the circuit.A transmission line transformer is used for broadband matching between stages,which realizes the matching between stages and maximum power transmission under different gain modes.The latter stage adopts a distributed cascode structure with sub-threshold state,which realizes a high linearity output stage and reduces DC power consumption.The distributed structure broadens the operating frequency band,optimizes the noise figure of the circuit,and realizes low-gain noise suppression in the low-gain mode of switching.The overall circuit architecture solves the problem of poor output linearity in the low-gain state of the traditional variable gain amplifier.The measured results of the chip show that the operating frequency band is 0.8?4.5GHz,the gain range is 7?27d B,the output 1d B compression point is greater than 13.5d Bm in four gain states,the input and output return losses are greater than 10d B,and the noise figure is less than 6.4d B.The working voltage is 4V,the quiescent current is 70m A,and the chip area is 1.83×4.08 mm~2.Based on the above research on the broadband variable gain amplifier,the performance and function of variable gain amplifier are further improved,the stability of the circuit and the DC filter network are optimized,and the small gain step adjustment is realized by cascading attenuator.The layout simulation results of the improved variable gain amplifier show that in the 0.8?4.5GHz operating frequency band,the input return loss is greater than 11.9d B and the output return loss is greater than 11d B in the 35 gain states of-4?30d B controlled by the switch in steps of 1d B,which has good matching characteristics,and the reverse isolation is greater than 35d B.Under the four main gain states controlled by the switch,the noise figure is 3.2?4.8d B,the output 1d B compression point is greater than 8d Bm,and the d B linear gain error is-1?1.3d B.