60 MHz common-mode self-tuned continuous-time filter for mass-storage applications

Mass-storage channels with bit rates in excess of 100 Mb/s require continuous-time filters with cutoff-frequencies above 40 MHz. At those frequencies, even for Q-factors as low as 2, phase errors may justify the use of a separate Q-control if the required linear phase response of the filter is to be guaranteed. Because of the tight power budget, bipolar designs may have an advantage over CMOS and BiCMOS designs, combining high speed, low power, and low noise levels. The filter, built using a 9 GHz bipolar process, is furnished with both frequency- and Q-tuning schemes. It operates up to 60 MHz, and so can be applied in higher-order channel filters working in the 25-40 MHz range. The filter is truly self-tuned, i.e., it can be tuned while processing signals by simultaneously applying to the input a differential-mode (DM) signal and a common-mode (CM) reference.