| Summary: | This paper presents the structure and realization method of the current-controlled adaptive low-pass
filter which based on the design of LC ladder network. After amplifying, amplitude limiting and shaping, the
input voltage signal was converted into frequency signal. Then by the broadband frequency-current conversion
circuit it was converted into current signal which has a linear relationship with input frequency. The current
signal was as the bias current to adjust the cut-off frequency of the log-domain low-pass filter. So that
frequency of the filter can automatically track the input signal frequency. In this paper, the design principle
was introduced in detail, the design formulas were derived and the circuit of adaptive second order log-domain
low-pass filter was given. The filter can realize the scope of the cut-off frequency up to 30MHz. The tracking
range for the input frequency is from 1MHz to 30MHz. The simulation results show the effectiveness of design
method.
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