Application of Transient Slope of Zero and Pole in Bode Diagram in Automatic Identification of Filter Parameters

Filters have a wide range of applications in many fields. Engineers generally use signal sources to manually test the characteristics of filters under test. In this research, we propose a system that automatically recognizes the characteristics and parameters of the analog filter throughout the entire process. This paper presents the theoretical conclusion that the instantaneous slope contribution at the n-order poles or zeros point in the Bode plot is ± 10 n dB/dec (where ’+’ represents zeros, and ’−’ represents poles). At the same time, we propose a voltage-controlled adaptive frequency sweep method. The designed automatic test system is based on DDS (Direct Digital Synthesizer), DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array) and ADC (Analog-to-digital converter) to build the hardware platform. According to the sinusoidal excitation method, the original data of the voltage response is obtained by voltage-controlled adaptive frequency sweep and frequency re-sweep of the filter under test with DSP. The information of these special values approximately 10m dB/dec (m is an integer) in the original data is captured by our conclusion of the zero-pole transient slope. The cut-off frequency and bandwidth of filters to be tested are more accurately measured by the local linear method. Combined with the knowledge of fuzzy recognition rule and normalization, an automatic recognition algorithm is designed in DSP according to data classification rules, screening rules and normalization rules. Finally, the system automatically recognizes the types, orders and approximate position of filters’ poles and zeros of and the type of filters to be tested.