Design Of A 0-4GHz MMIC Digital Step Attenuator Integrated With Serial-to-parallel Converter

Digital step attenuator is the key component in active phased-array radar transmit/Receive(T/R)module.This paper presents the design and development of a MMIC attenuator integrated with serial-to-parallel converter.The motivation behind this development is to reduce the size and lightweight,increase reliability for an active phased-array radar T/R module by integrating the attenuator and serial-to-parallel converter on one MMIC chip.We studied the design principle for GaAs digital circuits and low insertion loss MMIC attenuator chip from various logic families and several classic attenuation typologies.A 0.5um GaAs pHEMT process was chosen to fabricate this MMIC attenuator chip.Direct-coupled FET logic was used to design the serial-to-parallel converter,and an advanced T-structure and a switch type attenuation bit was built in attenuator design to get low insertion loss and additive phase shift.The entire circuit has been co-simulated to make the performance reach the requirements.An automatic test and measure system was designed and built to measure performance parameter after the attenuator chip was fabricated.The system is based on probe station and vector network analyzer for small signal analysis.Automatic testing program was supplied to test the total 64 states of the attenuator.The test result shows that in the working band,the attenuator has 0.5dB resolution and 31.5dB attenuation range.The measurements shows-2.3dB reference insertion loss at 4GHz.Attenuation rms error<0.3dB.Phase shift varies from 0 to 2 0.Return Loss of all states are less than-14 dB.the size of the chip is 2.0mm x 1.7mm.The excellent characteristics of the fabricated MMIC attenuator chip meets the requirements.