A new on-line bandwidth tuning approach for biquad OTA-C filters

A new and general bandwidth (BW) tuning strategy for biquad OTA-C filters is presented. We have taken benefit of the advantages of the classical Phase-Locked Loop (PLL) scheme to on-line tune the central frequency fo and we have applied it to tune also the bandwidth BW of biquad filters. The proposed design procedure uses only two different sizes of OTAs. This methodology has been applied to five biquad band-pass OTA-C filters, allowing fo-tuning and BW-tuning in an independent way. Furthermore, the influence of OTA non-idealities is discussed by including compact and general expressions for fo and BW for all these filters. Simulation results validate our proposal with excellent BW-tuning accuracies: an rms error of 0.73% with respect to the bandwidth desired.