System design considerations for SAW-less front-ends at the example of GSM DCS1800

In this paper, system design implications for SAW-less front-ends are derived from a comparison of a conventional and a SAW-less direct conversion receiver which uses an active interference cancellation technique for front-end filtering. Specifications for the GSM DCS1800 band are cited and a level plan is established with block level specs obtained from circuit level simulations. The level plan is used to judge on trade-offs that have to be made when the SAW band select filter is omitted. It is found that omitting the filter pays a “SAW-less dividend” in the form of improved reference sensitivity as SAW-filter insertion loss does not occurr. Moreover, a trade-off in the proposed SAW-less front-end is identified between selectivity and phase noise due to reciprocal mixing and an optimum sensitivity is determined which maximizes sensitivity for a given blocking condition.