Abstract
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.
Highlights
Filter has a wide range of applications in the fields of the signal processing, the data transmission and interference suppression [1,2]
This paper presents a design method of analog adaptive filter which use high-performance broadband frequency current converter (F/I) circuit, combined with the log-domain filter with transistors as the core elements to achieve the analog filter whose cutoff frequency can fast adapt the change of processed signal frequency automatically
The input voltage signal Vi gets through the amplifier to output voltage signal Vx . the voltage signal Vx is divided into two paths, the first will get through the limiting circuit and overvoltage comparison circuit which MAX903 is the core component to be shaped to send signal into the broadband F/I circuit, and the bias current signal IB output from
Summary
Filter has a wide range of applications in the fields of the signal processing, the data transmission and interference suppression [1,2]. Adaptive filter plays an important role in the field of the adaptive signal processing and has the distinctive features of filter frequency following the changeof input signal frequency automatically [3,4]. The test signal will inevitably be doped with noise. The filter which has fixed frequency can only realize signal filtering within a small frequency range. The adaptive filter can change the filter frequency according to the change of the signal, it is good to suppress the noise, and it has good filtering performance
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