X-type attenuator in CMOS with novel control linearization, very low phase variations and automatic matching

In this article a fully differential CMOS attenuator with automatic matching and control linearization is presented. The circuit was measured from 100 MHz to 10 GHz and exhibits a phase variation of only 4° within an attenuation control range of 30 dB. The maximum gain control range is almost 50 dB. The control circuitry draws less than 500 μA from a 1.8 V supply. The circuit was fabricated in 0.18 μm CMOS requiring only 0.044 mm2 of chip area.

I. Introduction

Attenuators are used to precisely control the amplitude of a signal. They are employed in multi antenna systems (both communication and localization), automatic gain control circuits or in measurement equipment. In MIMO systems, amplitude and phase of a signal have to be controlled independently and with high accuracy. Therefore, the phase of the signal should not vary with the attenuation.