A 7-Bit 0.22 dB Step Variable Attenuator with Flat States and Low Phase Variation at 1.5–13.5 GHz using iNMOS Switches

This paper presents a step variable attenuator with 0.22 dB flat attenuation states and low phase variation between 1.5–13.5 GHz. This work consists of 7 switched ΠT-type attenuation blocks. The parasitic effects of conventional NMOS transistors degrade the performance of attenuators in terms of insertion loss and attenuation flatness. Therefore, isolated NMOS (iNMOS) devices were preferred instead of conventional NMOS devices to utilize switching to improve RF performance. Also, attenuation states degrade at higher frequencies. Thus, a parallel capacitor was inserted in each Π-type attenuation bits to achieve flat attenuation states. This chip was designed and fabricated with IHP Microelectronics 0.13 μm SiGe BiCMOS technology. The measured attenuator can cover 28 dB with 0.22 dB incremental states. The root mean square (RMS) amplitude error of this chip is less than 0.22 dB between 2 to 9.5 GHz. The RMS amplitude error at 13.5 GHz is 0.27 dB. RMS phase error was measured less than 2.5° between 1.5–13.5 GHz. The measured input referred 1-dB compression point (IP1dB) of the attenuator is 12 dBm at 7.5 GHz. The insertion loss (IL) of the fabricated attenuator was measured less than 15.8 dB. The dimensions of the fabricated chip are 1.592∗0.793 mm².