Analysis of an 1.8 - 2.5 GHz multi-standard high image-reject front-end

In this paper, the analysis of a multi-standard, high image-reject front-end is presented. The front-end is designed to be used for Digital European Cordless Telephone (DECT) systems and wireless communications systems, which operate in the 2.4 GHz Industrial Scientific Medical (ISM) band (like Bluetooth). A double-quadrature low-IF architecture is chosen, because it can provide a high image rejection ratio (IRR) and a flexibility in terms of different systems. In the selected architecture, an RC polyphase filter is applied as an RF I/Q generator. Building block specifications are optimized in order to achieve two goals: a high IRR and a high sensitivity of the receiver. Assuming a mismatch of 1% between the elements of the RC polyphase filter and 2° phase mismatch in the local oscillator path, a simulated IRR of 63 dB is obtained in the frequency range 1.8 - 2.5 GHz. In spite of the fact that the RC polyphase filter deteriorates the front-end noise figure (NF), a NF of 6 dB and a sensitivity of -93 dBm for the DECT receiver has been achieved.