Current diversion technique for the design of broadband variable gain amplifiers

This paper presents a new technique for the design of broadband variable gain amplifiers (VGA). The proposed technique uses current diversion concept to provide gain variation function for the broadband amplifier. Since gain variation is achieved without compromising voltage headroom, it facilitates low power design of the VGA. Since DC levels of output signals of each stage stay constant, it also enables DC coupling between cascaded stages of the VGA. Both voltage controlled and digital controlled VGAs can be realized using the proposed technique. To demonstrate the feasibility of the technique, a digital controlled VGA was implemented in 90 nm CMOS which has bandwidth from 10 MHz to 2.8 GHz, gain ranging from 22 to 42.9 dB with 3 dB gain steps, and power consumption of 1.94 mW.