AN3203| Application Note
Maxim/Dallas > App Notes > AMPLIFIER AND COMPARATOR CIRCUITS
FILTER CIRCUITS (ANALOG)
Keywords: lowpass filter, step response, time-domain response, signal conditioning, switched-capacitor filter, SC filter
Apr 26, 2004
APPLICATION NOTE 3203
Lowpass Filter Has Improved Step Response
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 timedomain 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.
Figure 1. This lowpass filter maintains a fast step response by dynamically adjusting its cutoff frequency.
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