A Low-Power Cellular/PCS/WCDMA Direct-Conversion Transmitter with Enhanced VCO Remodulation Rejection

This paper presents a fully integrated low-power direct-conversion transmitter for cellular/PCS/WCDMA applications. Low-power consumption is achieved with the architecture of a simplified local-oscillator network, though the harmonics of large output signal could cause interference to the VCO. This inherent problem is effectively alleviated with a wide bandwidth fractional-N frequency synthesizer and an enhanced harmonic rejection technique. The transmitter, which consists of signal-processing blocks and a Sigma-Delta fractional-N frequency synthesizer with an integrated VCO, is fabricated using a 0.35 mum SiGe BiCMOS process. The total current consumption at minimum power is only 23 mA for the cellular and 27 mA for the PCS/WCDMA; the error vector magnitude is 3.91%, 6.98% and 8.56%, respectively.