Fully Differential Direct-Conversion Receiver for W-CDMA Reducing DC-Offset Variation

Hiroshi YOSHIDA  Takehiko TOYODA  Ichiro SETO  Ryuichi FUJIMOTO  Osamu WATANABE  Tadashi ARAI  Tetsuro ITAKURA  Hiroshi TSURUMI  

IEICE TRANSACTIONS on Electronics   Vol.E87-C   No.6   pp.901-908
Publication Date: 2004/06/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit and Device Technologies)
direct conversion,  DC offset canceler,  harmonic mixer,  

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A fully differential direct conversion receiver IC for W-CDMA is presented. The receiver IC consists of an LNA, a quadrature demodulator, low-pass filters (LPFs), and variable gain amplifiers (VGAs). In order to suppress DC offset, which is the most important issue in a direct conversion system, an active harmonic mixer is applied to the quadrature demodulator. Furthermore, a receiving system, including the LNA and an RF filter, adopts a differential architecture to reduce local signal leakage, which generates DC offset. Performance of the entire receiving system was evaluated and DC offset in steady state was measured at only 40 mV. Moreover, DC offset variation at the LNA gain change, which has the largest affect on the receiving performance, was limited to 70 mV, which is less than -10 dB compared to desired signal strength. It was confirmed by computer simulation that the DC offset variation at the LNA gain change did not degrade bit error rate (BER) performance at all.