A Comparison of Higher-Order Active Band-Pass R-Filter Response with Equivalent Band-Pass RC-Filter Response at Varying Q-Factors

Abstract

In this paper a comparison of a sixth-order active band pass R-filter output response with the output response of a sixth-order band pass RC-filter at different quality factors (Q = 2, 5, 7, 8 and 10) was carried out at a fixed frequency of 10 KHz. The architecture used in the design is the multiple feedbacks for both filter networks. The simulated response characteristics show that both filters (R- and RC-filters) have their mid-band gains increasing with Q, while their bandwidths monotonically decreased with Q-values. The bandwidths are in the range of 22.23 dB to 62.97 dB and −55.49 dB to −50.81 dB (Q = 2 to 10) for R- and RC-filters respectively. At higher Q-values, R-filter showed better selectivity with a smaller bandwidth (400 Hz) at the edge of the pass band, when compared to 450 Hz for the RC-filter. The roll-off rate around −58.9 dB/decade for the R-filter appears to be that of a third-order filter response, while the RC-filter has its response in the range −106 to −132 dB/decade which is in the neighbourhood of an ideal sixth-order response (roll-off of 120 db/decade). A shift in the center frequency with Q was observed for the RC-filter only.