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무선 통신용 수신기에 대한 요소 기술 연구

무선 통신용 수신기에 대한 요소 기술 연구
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As the wireless communication technology has been rapidly developed, many kinds of mobile communication devices have been introduced in our daily life. Among receivers for the systems, a direct conversion receiver(DCR) has implemented for a valuable solution for low cost and low power implementation. However, it is still difficult to design the DCR with the CMOS due to comparatively inferior properties, such as poor noise performance, low breakdown voltage, and small gain
the critical problem is the poor noise performance. In the DCR, a double balanced Gilbert Mixer is the most popular one due to low RF and LO feed-through. However, high noise figure of the mixer degrades the whole receiver performance. Noise figure of an RF CMOS mixer is strongly affected by flicker noise. The noise figure can be improved using PMOS switch circuits, which insert current at the on/off crossing instants of LO switch stage, because the circuits reduce the flicker noise injection. When it is applied to a conventional Gilbert mixer, the injection efficiency and linearity are degraded by the non-linear parasitic capacitances of the PMOS switch circuits and the leakage through the parasitic path. We propose the PMOS switch circuits with an inductor, which tunes out the parasitic components at 2fo and closes out the leakage path. The mixer fabricated in 0.13 um CMOS at 2.4 GHz center frequency has provided improved characteristics for linearity and noise figure. Nowadays many kinds of TV standards, such as cable, analog, and digital, have been introduced in our daily life. The can tuners are heavily used for the TV systems but they are being replaced by integrated IC chips, due to lower cost and smaller size. The TV standards require service across the wide-band of 40~1000 MHz. A wideband LNA should be the first amplifying stage in the system. The LNA should have not only a high gain and a low noise figure (NF) but also a high linearity and good input impedance matching over the 40~1000 MHz. We propose the wideband CMOS LNA using a dual feedback for the tuner application, which can suppress the second and the third order distortions with a low noise and a suitable gain. In the dual feedback, the weak negative feedback improves the linearity of the transconductance partially, thereby maintaining the high gain and low noise. The residual distortion and the distortion of the buffer are cancelled by the positive feedback. Consequently, the roposed wideband LNA with the dual feedback improves the noise figure and linearity with a high gain. The LNA fabricated in 0.18 um RF CMOS demonstrates the expected performances. Recently, the receiver system is highly desirable to integrate the various functions on a single chip due to low cost and low power consumption. For the multiband operation, the conventional systems have employed several parallel narrowband receivers, but it is a high cost solution with high pin count and large chip area. Therefore, research for the multiband receiver has been focused on the tunable receiver. It requires a tunable LNA or wideband LNA, as the first amplifying stage in the system. A differential common gate low noise amplifier (LNA) has been widely used for a wideband LNA. However, it has poor linearity due to the nonlinear transconductance in a MOSFET and poor noise performances from the common gate configuration. We propose a differential common gate LNA with a negative gm cell for the improvement of the linearity and noise figure. The cell comprises cross coupled transistors instead of a current source. The negative gm cell creates the opposite phased harmonic, canceling the distortion. The noise figure is improved by canceling the noise from the common gate transistors through the negative gm cell. The LNA is fabricated in 0.13 um RF CMOS. The LNA has a bandwidth of 0.7~3.5 GHz and provides the expected characteristics for linearity and noise figure.
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