Reconfigurable Low-IF Mixer and Tunable Filter for SDR System

Abstract

In the recent, the wireless communication service, such as GSM, IS-95, W-CDMA, GPS, Bluetooth, and WLAN, is developed rapidly and the number of wireless standards is increasing for every year. In order to build such a multi-standard adaptive transceiver, various solutions with single signal path and multi signal path exist. Most existing multi-standard wireless devices use separate signal paths for different standards. However, these methods increase the cost, power consumption and size of the RF module. Clearly, a single path that can operate at two or more frequency bands would be preferable. In this dissertation, a reconfigurable low-IF mixer and a tunable band pass filter for the SDR system is proposed. The operating frequency band of the proposed components is continuously selected by controlling the DC bias voltage of the varactor-tuned diodes. Thus, if the components have a single signal path and a large tuning range with flatness of the characteristics, those can be easily applied to a multi-band system for the SDR system. The proposed reconfigurable mixer is operated between 850 MHz ~ 2 GHz, which includes all commercial mobile communication service. Because the varactor diodes are used to adjust the impedance characteristic of the selected frequency band; to select a specific frequency; and are simultaneously controlled in RF/LO ports, similar performance across the tuning range is maintained. In addition, since the mixer has a single signal path for the multi-band signals and a wide band tuning range, the designed reconfigurable mixer is applicable for the SDR system. A tunable filter with a hairpin line resonator and a loading capacitor is designed. The filter is modified by adding other varactor diodes to the coupling part for loss compensation. Therefore, the filter can be achieved a simple structure and characteristics that include a wide band tuning range of 76.5 % from 458 MHz to 1026 MHz and a low insertion loss of less than 4.42 dB. Since the designed mixer and the tunable filter have a very simple structure as well as good performance, they are suitable in the SDR system.