Research On Ultra-Wideband Variable Gain Amplifier Chip Based On PHEMT Process

Along with the rapid development of communication systems,wireless communication technology has been attracting attention and favor from academia and industry,and is being widely applied in many fields including satellite navigation,radar remote sensing and phased array systems.As a critical component of wireless communication system,variable gain amplifier（VGA）can achieve controlled amplitude adjustment of RF signal,which is particularly significant in the automatic gain control of transceiver link and the amplitude control chain of phased array system.In order to cater to the development trend of integrated ultra-wideband communication system and realize the wideband,high integration and high consistency characteristics of wireless communication RF front-end,it is necessary to conduct in-depth research on the high performance ultra-wideband VGA chip,and the development of this chip is of great theoretical and practical significance to realize the comprehensive independent and controllable integrated wideband RF front-end of China.In this thesis,based on GaAs p HEMT process,an in-depth research is carried out for ultra-wideband VGA chip,and the specific work is as follows:1.Based on 0.25um GaAs p HEMT process,a 0.05-6GHz VGA chip is designed and implemented.The chip adopts a fixed gain amplification cascade attenuation network architecture to combine the advantages of high precision amplitude control and low noise and high gain amplification capability.The amplifier adopts the Darlington-cascode structure to increase the gain,and the RL frequency-select network is used to improve the stability of the circuit,while quantitative analysis is performed for low-frequency noise,and utilizes the RC negative feedback network at the active bias structure to achieve low frequency noise optimization without affecting the circuit gain.2.Passive attenuator with positive voltage drive capability is applied to the investigation of attenuation network in chip architecture,addressing the shortcoming of the conventional p HEMT attenuator requiring negative voltage control.The frequency-select attenuation parallel（FSAP）network is utilized to effectively suppress high-frequency attenuation fluctuation and achieve flat attenuation characteristic over the wide frequency band.Simultaneously,the analysis is carried out for the dc-block network,and the Lossy DC-Block（LDB）network is proposed for the purpose of eliminating the low-frequency resonance phenomenon in the high attenuation state.The actual measurement results of the final packaged VGA chip show that:in the operating band to achieve 31.5d B±0.5d B gain control range,input and output return loss are better than 10d B,the output1d B compression point(OP_{1d B})is greater than 15d Bm,the noise figure is less than 5.4d B and the gain variation bit error and step error are within the±0.5d B.3.Design and implementation of a 2-18GHz VGA chip based on 0.15um GaAs p HEMT process.This chip adopts a similar architecture as the previous chip.The attenuator adopts T-type,π-type and SPDT-type attenuation topologies,combined with the FSAP network to achieve phase compensation.The amplifier adopts a 5-stage cascode-distributed structure to obtain wideband gain,and the RC series structure is used to absorb the reverse propagation signal at both the gate and drain transmission line terminals to improve the gain flatness.The final chip layout simulation achieves the gain control in 0.5d B step,the typical controllable gain range is-21.2～10.3d B,the input and output return loss are better than 10d B,the OP_{1d B} is greater than 8.8d Bm,the noise figure is less than 4.05d B,and the 64-state gain and phase root mean square（RMS）error are less than 0.3d B and 4.7°respectively.