A 25–30 GHz 6-bit digital attenuator with high accuracy and low insertion loss

A 25-30 GHz 6-bit digital attenuator with high accuracy and low insertion loss by 0.15μm GaAs PHEMT process is presented in this work. An improved structure with a parallel capacitor is applied in the attenuator architecture to enhance the attenuation accuracy. To reduce leakage of the RF signal, a cascade structure is proposed to enhance isolation and compensate the insertion loss simultaneously. The On-wafer measurement results show that the 6-bit GaAs digital attenuator has 0.5 dB resolution and 31.5 dB dynamic attenuation rage while the return loss is better than -10 dB for all states; the attenuation accuracy is better than 0.5 dB while the RMS attenuation error is less than 0.21 dB; The insertion loss is less than 5.7 dB while the insertion phase shift is less than -6.0° The total chip size is 2.0mm × 1.0mm.

I. Introduction

As the demand of higher operation frequency and bandwidth range, the key component for gain setting and function controlling digital attenuator with perfect performances is desperately needed in Radar, Communication, Electronic Warfare and other electronic equipments [1]–[2]. Due to the fast speed and high operation frequency, GaAs PHEMT has already been the dominant device. However, because of the low isolation, high substrate loss and the prominent parasitic parameter, the attenuator with high accuracy and low insertion loss is difficult to realize in high operation frequency. Nowadays, high accuracy and low insertion loss are still crucial index for digital attenuator and radio-frequency system.