Complete RF-System Analysis of Direct Conversion Receiver (DCR) for 802.11a WLAN OFDM System

This paper presents a detailed analysis of RF system parameters, including phase noise, noise figure, the in-band third-order intercept point (IIP3), the in-band second-order intercept point (IIP2), and the in-phase/quadrature (I/Q) imbalance, of the direct conversion receiver (DCR) for an 802.11a wireless local-area-network (WLAN) orthogonal frequency-division-multiplexing system. A design example of DCR RF parameters planning for a 5-GHz 802.11a WLAN is presented and discussed. It is found that the critical specifications to realize a 5-GHz 802.11a WLAN DCR are the local-oscillator phase noise and I/Q imbalance. However, since there is a 312.5-kHz empty region around zero frequency for the 802.11a standard, dc offset and flicker noise are less sensitive. Hence, the DCR architecture is still an attractive choice for the 802.11a WLAN system. The study can be very useful for RF circuit design in wireless-communication systems.