A hybrid fine/coarse auto-tuning scheme for digitally programmable VHF Gm-C filters

This work focuses on the improvement in the CT programmable G_m-C filter design, which is required in wireless sensor networks. More precisely, this paper describes the automatic frequency tuning of digitally programmable G_m-C filters with a wide operation range based on a hybrid analog/fine-digital/coarse master-slave scheme. The main block of the tuning method is a digital phase comparator included in the PLL, leading to a high-precision tunability. An error of plusmn4% for the digital frequency tuning is obtained and the maximum settling time when changing between two consecutive digital words is 0.3 mus. Once the DW is fixed, the fine tuning finely adjusts the value of the characteristic frequency to the reference with a maximum error of plusmn5% and a settling time of 0.2 mus.