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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 3203
Maxim > Design Support > Technical Documents > Application Notes > Filter Circuits (Analog) > APP 3203
Keywords: lowpass filter, step response, time-domain response, signal conditioning, switched-capacitor
filter, SC filter
APPLICATION NOTE 3203
Lowpass Filter Has Improved Step Response
Jun 22, 2004
Abstract: Adding optimization circuitry to a lowpass filter allows the filter to adjust its cutoff frequency
dynamically, preserving the step-response time for relatively low cutoff frequencies.
A common problem when designing lowpass filters for signal conditioning is their effect on the system's
time-domain response. Because pushing the cutoff frequency lower slows the step response, the system
may fail to recognize significant changes in time.
The Figure 1 circuit allows lower cutoff frequencies without sacrificing the step-response time. A window
comparator monitors the delta (difference) between the filter's input and output. When the delta exceeds
±50mV, the filter increases its slew rate by increasing its cutoff frequency an order of magnitude.
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