Abstract:
The Sallen-Key low-pass biquad shows a decrease
in attenuation at high frequencies because the real operational
amplifier has a finite transit frequency. As a result, the course
of the actual frequency response deviates from the ideal.
Generally, this phenomenon occurs only in even-order filters in
both Voltage Mode (VM) and Current Mode (CM) but is no
longer observed for odd-order filters. When determining the
order of the filter, it is always necessary to round the calculated
value upwards, so it is discussed whether it is appropriate to
round it up to the nearest odd number. Finally, this method of
attenuation decrease correction is compared with the correction
using another active element.