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Ultra- wideband low phase shift monolithic microwave digital attenuator in the broadband electronic warfare, phased array radar system and broadband microwave synthesized sweep signal generator and other instruments have a wide range of applications . In this paper, six ultra-wideband monolithic microwave digital attenuator insertion phase shift is small, high attenuation accuracy , using this circuit will make the corresponding system eliminates the need to calibrate the amplitude and phase of the additional circuitry , reduce costs, improve reliability, and this circuit can be programmed to control, easy compatibility with computer technology . This paper introduces the 2 ~ 18GHz ultra- wideband low phase shift six MMIC digital attenuator principle, circuit design , simulation, optimization, and layout design . This paper first discusses the microwave monolithic integrated circuit device GaAsPHEMT switch controlling the working mechanism , model and circuit model parameter extraction . Then introduces the basic theory of digital attenuator and analyzes several typical digital attenuator circuit topologies ( such as T- , PI -type , T-type bridge , switch path type, etc. ) works. Design tools using the Advanced Design System 2004 (ADS2004), depending on the amount of attenuation first determine the appropriate digital attenuator circuit topology , the amount of attenuation is calculated based on the topology of the initial resistance , and then join the actual microstrip circuits for attenuation accuracy , low insertion loss , the relative insertion phase shift and input / output VSWR optimization. Each one optimized to meet the design indicators, then each cascaded six digital attenuator , an overall simulation and optimization . After completion of the initial circuit simulation optimization attenuation bits generated for each territory , the final layout of the cascade and design of the compact, occupies a small chip area , and easy to use . Final design of ultra-wideband monolithic six digital attenuator reference state insertion loss, low attenuation , high precision, small insertion phase shift , input / output VSWR is low, small size . 2 ~ 18GHz band at work , the maximum attenuation is 31.5dB, attenuation step of 0.5dB; reference state insertion loss : <3.6dB; Attenuation accuracy typically : ± 0.3dB; total insertion phase shift : -2.018 ° / 2.367 °; input / Output VSWR typical: 1.30 ; chip size : 2.93mm × 1.02mm × 0.1mm. The performance is superior design requirements.
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