Abstract: A 5～20GHz lumped CMOS attenuator with a low insertion loss and a low phase error is presented. The attenuator is based on bridged-T and π type attenuative networks and implemented with 0.18μm CMOS technology, and it operates with 5 independent attenuative modules by NMOS switches. At the frequency range of 5～20GHz, the attenuator has a 0～31dB attenuation range with 1dB increase. In the attenuator, the series switches are body-source connected by a resistor to minimize the insertion loss without involving too much capacitance, and the shunt switches are ac bodyfloated to improve linearity. The larger attenuative modules are compensated for insertion phase with inductors. As the layout simulation results show, the minimum insertion loss is 6.1dB and the maximum one is 12.6dB. The root mean square (RMS) attenuative amplitude is less than 0.5dB, and the RMS insertion phase is less than 3.4°. The 1dB compression point at the center frequency is 14.13dBm.

Key words: attenuator, step attenuator, CMOS switch, low insertion loss, low phase error