새로운 공통-소스와 공통-드레인 구조를 이용한 캐스코드 FET 믹서의 성능 향상에 관한 연구

Abstract

The wireless communication system has become highly developed of late due to the emergence of various communication technologies, and it is becoming more widely used due to the various information requirements of its users. It has the advantages of mobility and accessibility due to easy information acquisition anytime and anywhere. Thus, the characteristics of low power consumption and high performance are required for the effective power management of the wireless communication system. It depends on a battery for system operation, however, whose efficiency and capacity for highly effective power management is still being investigated. Therefore, as the wireless communication system has limited power, it certainly requires effective RF circuits with low power consumption.

The goal of this study is to develop a wireless communication system circuit with enhanced RF performance: the cascode FET mixer with new common-source and -drain circuit configuration.

For the high performance of a wireless communication system with low power consumption, a well-designed RF circuit is certainly needed due to its large influence on the performance of the whole wireless communication system. If the mixer circuit is well designed, the whole wireless communication system will exhibit high performance.

In this thesis, the enhanced-performance cascode FET mixer using new common-source and -drain circuit configuration is proposed. When the cascode FET mixer using new configuration was compared with the conventional one, it was found that the former has the performance of higher conversion gain at a lower input LO power, a very low noise figure, and very high LO-to-IF isolation. Thus, the proposed cascode FET mixer with enhanced RF performance can improve the performance of the wireless communication system, which can realize effective power consumption because of the use of a local oscillator with lower output power.

The cascode FET mixer using new configuration was designed in this study based on the results of the simulation and measurement for the verification of the enhanced RF performance. The results showed the mixer’s enhanced RF performance compared with the conventional cascode FET mixer. The proposed new common-source and -drain circuit configuration in the cascode FET mixer is reported in this thesis for the first time.

The cascode FET mixer using new configuration showed effective operation by means of the use of a local oscillator with lower output LO power. It also showed higher conversion gain with only the lower input LO power, which does not need a local oscillator with a large output power as it can be operated at lower input LO power compared with the conventional one. This is the important characteristic for the wireless communication system, which requires effective power consumption. The cascode FET mixer using new configuration showed very high LO-to-IF isolation without a LO rejection filter compared with the conventional one. It showed good LO-to-RF isolation. The cascode FET mixer using new configuration also showed a very low noise figure compared with the conventional one. It uses only a FET, which produces the effect to have very low noise figure due to the thermal and shot noise by an active device. The cascode FET mixer using new configuration showed low output IF power and low linearity for the output IF power of the fundamental and third-order intermodulation frequencies, low than those of the conventional one. It also showed the low output IF power spectrum for the intermodulation distortion of the low-side and up-side bands, as opposed to the conventional one. It showed that each reflection coefficients were about -30 dB for the RF frequency of 2.6 GHz, the LO frequency of 2.5 GHz, and the IF frequency of 100 MHz.

Through the aforementioned study results, it is exhibited in this thesis that the proposed cascode FET mixer has enhanced RF performance by means of the new common-source and -drain circuit configuration. It can thus achieve high RF performance without an addition to any other circuit, for the enhancement of the RF performance. Especially, the cascode FET mixer using new configuration showed an indispensable circuit, which it must have to improve the efficiency of the wireless communication system due to the mobility and limited power.