84 • Reference Section
MultiClamp 700A Theory and Operation, Copyright 2000, 2001 Axon Instruments, Inc.
Types of Filters
There are many types of filters, distinguished by their effects on both the amplitude
and phase of the signal. The two most common filters used in electrophysiology are
the Bessel filter and the Butterworth filter, both of which are implemented in the
MultiClamp 700A.
Bessel Filter
This is the analog filter used for most signals for which minimum distortion in
the time domain is required. The Bessel filter does not provide as sharp a roll-
off as the Butterworth filter, but it is well behaved at sharp transitions in the
signal, such as might occur at capacitance transients or single-channel current
steps.
Figure 4.10. Filter characteristics, illustrated for a single-pole, low-pass filter. The spectrum has
been normalized so that the signal magnitude in the pass band is 0 dB. The –3 dB frequency has
been normalized to unity.
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