Direct-Conversion 수신기에서 국부 발진기 누설신호 제거에 관한 연구

Abstract

A low cost, low power consumption, and small size are targets in implementing the radio frequency transceiver. The research of IC technologies is most interested in portable wireless communication devices. The trend of research is developing the system-on-chip which reduced the RF/IF chip set.

Double hop down-converter is used for conventional heterodyne receiver. Therefore, it occurs power loss during converting and needs expensive SAW filter. Also, this is difficult to integrate circuit. To overcome that, architecture of direct conversion and double conversion have been studying.

Direct conversion has several advantages of comparison with heterodyne receiver. The first, the problem of image frequency is not considered because the IF is zero in direct conversion. The second, the IF SAW filter and the subsequent stages are replaced with low pass filters and baseband amplifiers, respectively. These component are amenable to monolithic integration.

In this thesis, the DC offset removing method of direct conversion are investigated. LO signal leakage due to the reflected signal from the antenna, LNA and, the external scatters is self-downconverted and converted to DC component at the mixer. In oder to cancel these leakage signals, the leakage signal cancellation method is applied to the receiver. The leakage signals generated by the reflected signals are easily controlled and removed at attenuator and phase shifter.

The performance of leakage signal cancellation method at LO is evaluated by HP's ADS simulation tool. When E_b /N_0 is 14dB, the error performance of 10^-7 is obtained.