An Automatic I/Q Calibrated RF Down-Converter IC With Full-Band 48–55 dB Image Rejection and 150% Fractional IF Bandwidth for SATCOM Applications

Abstract

This article presents a fully-integrated Ku-band CMOS down-converter for the low earth orbit satellite user downlink applications. To receive satellite signals adequately, a wideband receiver is presented with an automatic in-phase and quadrature (I/Q) mismatch calibration to carry out above 40 dB image rejection ratio (IRR) to the interferences within 2 GHz span concurrently. During the I/Q signal phase adjustment, the proposed wideband I/Q interpolator (IQI) exhibits almost a constant group delay over the wide IF signal bandwidth, which alleviates the iterative calibration between multiple frequency points in a wideband system. Also, the proposed wideband IQI has apparently less influence on signal amplitude than the reported phase interpolator and delay cell while calibrating I/Q phase imbalance. This work utilizes polyphase filters to fulfill on-chip image-rejection integration and exploits logarithmic power detector to realize I/Q mismatch indication in automatic calibration. The receiver delivers a peak measured conversion gain of 37.8 dB, an averaged noise figure of 6 dB, and below ±1.5 dB gain variation within the full signal band. Above all, the down-converter achieves not only high IRR performance but broad bandwidth at the IF frequencies from 0.3 to 2.35 GHz (48-55 dB IRR, 150% fractional IF bandwidth) without any external control, tuning, or assistance. The closest frequency proximity is no more than 0.6 GHz between the received satellite signal and image. To the best of authors' knowledge, this work demonstrates the highest fractional IF bandwidth among the reported wideband CMOS receivers with high image rejection (IRR > 40 dB).INDEX TERMS CMOS, low earth orbit (LEO) satellites, high image rejection, integrated circuit (IC), RF down-converter, auto calibration, wideband, BIST, satellite communication (SATCOM).