A 2 V 2 GHz Si-bipolar direct-conversion quadrature modulator

Abstract

In recent years, demand for portable equipment such as cellular phones, digital cordless phones, and wireless LANs has grown rapidly. In portable equipment, battery-powered operation is inevitable. Lowering the power-supply voltage is one effective way of simultaneously decreasing power dissipation, weight, and size of equipment. Digital cellular phones and digital cordless phones using the UHF to L bands employ Si-bipolar direct-conversion quadrature-modulator chips that operate at 5 V. One factor preventing supply-voltage reduction is use of double-balanced mixers (DBMs). They need the highest supply voltage of all RF circuit components because they are based on the Gilbert cell. Lowering the supply voltage of a Gilbert cell mixer degrades its linearity and modulation accuracy. This paper describes a 2 GHz Si-bipolar direct-conversion quadrature modulator with a tunable on-chip 90/spl deg/ phase shifter. The above problems are solved by a current-folded double-balanced mixer (CF-DBM) suitable for low-voltage operation. The modulator operates with 2 V supply and consumes 68 mW. Phase-shifter cut-off frequency control allows 0.8 to 2.0 GHz modulator bandwidth.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>