Abstract: A high-side injection, fixed intermediate frequency (IF), double-quadrature-downconversion and low-IF structure is proposed for wideband receivers. Four image rejection ratios (IRR), and relationship between IRRs and the amplitude errors ΔA or phase errors Δθ of two kinds of double quadrature receiver structures (single-double and double-double quadrature structures) are derived. Comparison of these two structures shows that single-double quadrature conversion is more suitable for wideband receivers. To improve IRRs of the system, two modules, RF filter and polyphase filter before the second downconersion, are added to the single-double quadrature structure. The quantitative IRRs performance of the total RF-end and a design example, DRM receiver RF-end, are given. Simulation results show that this RF-end structure has good IRR performance (when -10°≤Δθ≤10°，-0.1≤ΔA≤0.1, IRRs≥61.16dB). This is an ideal structure for wideband radio receivers, combining the inherent characteristics of a low-IF structure such as suitability for high integrality, ability of supporting multi-standard communication, and immunity to parasitical low frequency noise.

Key words: wideband receiver, RF front-end, dual-conversion, quadrature downconvert, image rejection ratio (IRR)