Design procedure for DVB-T receivers large tuning range LP filter

In this paper two different design approaches for a large tuning range LP filter for DVB-T receivers are presented. The LP filter is placed at the beginning of the receiver chain, before to the RF and base band blocks, so that the design is challenging because high out-band frequencies rejection is required while maintaining low input referred noise. Closed-loop topologies have been investigated to comply with the in-band linearity requirements. A system level analysis has been developed using a proper Matlab procedure. This procedure allows optimizing the basic filter parameters - opamp bandwidth, R and C values - in order to satisfy the filter transfer function requirements. Two different design approaches will be considered. The first proposal is based on a 2nd order biquadratic cell. High quality factor is synthesized while guaranteeing the out-of-band frequencies rejection. The second implementation is based on the cascade of two biquadratic cells with more relaxed quality factor requirement. The design is realized using the 90nm CMOS technology. The simulation results for both implementations are presented. The minimum out-of-band rejection is maintained lower than -30dB, the maximum IRN in both cases is 4nV/radicHz and the IM3 is lower than -30dB for two in-band input tones.