Design study on a direct conversion receiver front-end for 280 MHz, 900 MHz, and 2.6 GHz band radio communication systems

The authors describe the required RF stage performance for a direct conversion receiver for 280 MHz, 900 MHz, and 2.6 GHz system applications. The required attenuation level for LO (local-oscillator) leakage for the assumed system terminal is calculated. Furthermore, from test receiver measurements, it was found that LO circuit shielding is necessary for practical system applications. The required out-of-band attenuation level of an RF filter for interference signals was also investigated quantitatively from experimental data obtained from bit-error-rate measurements in an actual radio wave environment and from calculations based on a 1 dB gain compression point of the mixer. Thus, it has been found that an interference rejection filter is necessary for practical direct conversion receiver applications. However, the filter specification is largely relaxed compared with the image rejection filter in a conventional superheterodyne architecture