A Low-Power, Low-EVM, SAW-Less WCDMA Transmitter Using Direct Quadrature Voltage Modulation

Abstract

This paper describes a low-power, low EVM, SAW-less WCDMA transmitter using direct quadrature voltage modulation. The core of the modulator is a passive voltage mixer driven by 25% duty-cycle LO. In comparison with conventional approaches employing Gilbert mixers, the use of a passive voltage mixer results in significantly improved performance in terms of the output noise, linearity, LO leakage, EVM, and the power consumption in the transmitter. Delivering 4 dBm WCDMA output power at 1950 MHz, the transmitter prototype fabricated in a 45 nm CMOS achieves -48 dBc ACLR at 5 MHz offset, -71 dBc ACLR at 10 MHz offset, -54 dBc LO leakage, and 1.36% EVM, while consuming only 26 mW. The measured noise floor at 4 dBm output is -159 dBc/Hz at the frequency offset above 40 MHz, which is sufficient to safeguard the WCDMA RX band, the DCS band, and the GPS band without needing a TX SAW filter. In addition, optimized for low power consumption, over 80 dB gain control under voltage modulation is demonstrated in this paper.