A voltage-controlled amplifier based on Gm cells for multistandard OFDM integrated receivers

This paper presents a variable-gain amplifier (VGA) based on transconductors (Gm cells); it consists of two instantiations of the same Gm core and three scaled output stages. The core is optimized for high linearity that is not affected by the gain setting as the gain variation is achieved through a differential current steering scheme. The proposed VGA is well suited for multistandard radio receivers: its bandwidth and linearity are largely independent of the gain setting and both the gain range and the bandwidth can be programmed through digital controls. The structure is fully differential, with the output common-mode voltage controlled by a novel scheme, that does not require the placement of additional circuitry in the differential signal path. The VGA was designed in a standard 0.18um CMOS technology; simulation results show that it can cover the gain range of -6dB to +24dB while handling signals with amplitudes up to 1Vpkpkdiff without significant distortions. The bandwidth remains above 40MHz while driving up to 1pF and can be controlled through the programmable capacitance placed at the VGA output. The VGA power consumption is 7mW for gains up to 18dB and 12mW above than, from a 1.8V supply.