A 10–67-GHz CMOS Dual-Function Switching Attenuator With Improved Flatness and Large Attenuation Range

A 4-bit CMOS dual-function switching attenuator is designed using new architecture and method to obtain not only fine attenuation flatness and large attenuation range over an extremely wide frequency range, but also switching ability. Specifically, the inherent frequency responses of conventional Pi-, T- and distributed attenuators are utilized along with the transistor´s body-floating technique to improve the attenuation flatness and range, as well as lower the insertion loss. The switch constituent of the attenuator is also designed to contribute to extra isolation at low frequencies as well as to produce reflective switching. Analysis for the new attenuator is derived and its performance is verified through simulations and measurements. Over 10-67 GHz, the measured results show the attenuation flatness of 2.4-6.8 dB, attenuation range of 32-42 dB, and isolation of 42-67 dB. The same attenuator could achieve 2- and 3-dB attenuation flatness if the operation frequency is limited to 12.5-37 GHz and 10-43 GHz, respectively. The minimum attenuation is 8.4-15.2 dB across 10-67 GHz. The 1-dB compression power is more than 14 dBm. The attenuator is fabricated using 0.18-μm BiCMOS technology and its size is 1450 μm ×530 μm.