Recently, the performance of the commercial PCS (Personal Communication Service) system has been improved to the uppermost limit and ultimately the next generation mobile communication is to be realized by IMT-2000 (International Mobile Communication-2000) to provide multimedia services.
Therefore, the new type receiving system is researched actively and one of the most important part in a receiver is direct conversion method. The direct conversion method is suitable for low power consumption, small size, MMIC, and low price, which is to be adopted to the next generation mobile communication systems. In this case, however, several problems occur due to DC-offset. The DC-offset suppresses amplification of the required signal becasue of the leakage signal of frequency synthesizer in the system.
In this thesis, the removing method of DC-offset was considered. There are four removing techniques of DC-offset, which are AC-coupling, large capacitor, dc-feedback loop, and dc-free coding. Among these, the AC-coupling method is the most simplest method and the dc-feedback loop method has the best performance. Then, the performance of the AC-coupling method and dc-feedback loop method are evaluated by HP's ADS simulation tool.
As a result, the AC-coupling method cannot be used to the digital communication systems due to data loss. On the other hand, it was confirmed that the dc-feedback loop method is suitable for the direct conversion receiver.