Ultra-wideband Low-phase-shift The Monolithic Six Microwave Digital Attenuator Design And Research

Ultra broadband MMIC microwave digital attenuators with low insertion phase shift are widely used in broadband electronic countermeasures and phased-array radar scanning systems as well as in broadband microwave signal generators, and other synthetic frequency sweep instrumentations. The MMIC 6-bit digital attenuator in this paper with low insertion phase shift, high attenuation accuracy applied in system will allow the system to omit the additional circuits for calibration ,so the costs will reduced and the reliability can be improved. The digital attenuator can be controlled by program, so it's easily compatible with computer technology.This paper mainly introduced the circuit design, layout design and simulation results of this ultra broadband 2-18 GHz MMIC 6-bit digital attenuator with low phase shift. First, the operation principle of PHEMT switch and the small-signal model parameter extraction method for PHEMT modeling are presented in the paper. Then the author described the basic theories of digital attenuators and contrasted the principle of several typical topologies for attenuators (T attenuators, PI attenuators, T-bridge attenuators, switch path attenuators).In this design, Advanced Design System 2004(ADS2004) is used as the EDA tool. After the appropriate topology is selected for each bit and initial values of the ideal resistors are calculated for different attenuation, they are all put in integrated circuits with many micro strip lines. Proper optimized functions are chosen for all optimized goals such as attenuation accuracy, insertion loss, insertion phase shift and input/output VSWR. While each bit has achieved their best states, they can be cascaded for simulation. In layout design, the chip must have compact configuration, small chip size and be easy to use.The final ultra broadband MMIC 6-bit digital attenuator has many excellent characteristics such as low referenced insertion loss, high attenuation accuracy, small insertion phase shift, low input/output VSWR, small chip size. In the operation bandwidth 2-18GHz, the attenuator has 31.5dB dynamic range stepped by 0.5dB; referenced insertion loss: <3.6dB; typical attenuation accuracy:±0.3dB; insertion phase shift: -2.018°/+2.367°; typical input/output VSWR: 1.30; chip size: 2.93mm×1.02mm×0.1mm. All these performances are better than the design requirements.