The Optimal Design Of The RC Active Filter

RC active filter (which consists of resistors, capacitors and operational amplifiers) is a device that allows some frequencies pass, and suppress other frequency components. It is widely applied in communication, signal processing, instrumentation, automatic control and other areas. As an important element of the integrated circuit, the circuit optimization method has important reference and practical values. After several decades of development, the structure of RC active filter circuit is quite mature; however, the key of the circuit design is how to optimize the circuit R, C parameters. The traditional method that the resistor is firstly determined and the capacitor is then re-matched is relatively simple; unfortunately, the choice of the capacitor parameter is challenging. Although the circuit realization is simple, the system stability cannot be guaranteed. With the emergence of a variety of advanced optimization algorithm, the R, C parameters can be optimized by computers. The obtained resistance and capacitance parameters are hardly in the range of standard resistance and capacitance values, which gives a great challenge for hardware debugging.This article systematically summarizes the current research advance of RC active filters. Based on the detailed study of design methods of RC active filter, the optimal capacitor parameters methods of RC active filter are presented and the optimization of the circuit design was verified by simulation software Mutisiml2. Results indicate that capacitance parameter optimization method makes the filter design with the merits of good amplitude-frequency characteristics, stable and reliable system. Most importantly, parameters optimization of the actual circuit capacitance leads to great convenience of the debug circuitry. This paper contains the following three parts:1. Based on the typical transfer function analysis of second-order filter circuit, the damping coefficient and circuit gain have been optimized. Optimization process and circuit design principles are given, in which two capacitance parameters are easily selected in second-order filter. Simulation analysis was analyzed for the optimized circuit. Results show that the optimization system of the second-order filter design is stable and reliable, and has good amplitude-frequency characteristics.2. Frequency conversion from low-pass to high-pass filter was investigated. Fourth-order low-pass filter circuit was optimized technologically. The optimization design of fourth-order high-pass filter, in which the choice of capacitance parameter is simple, was proposed. Theory and simulation proved that this method is feasible.3. To overcome the shortcomings that network parameters of the high-order RC filter is difficult to select, this paper discussed in detail the design method of high-order RC active filter. Based on the optimized design method of second-order filter, the method is extended to higher order. Data processing was carried out by Matlab software, and the optimization design of high-order filters was performed by capacitance parameter optimization method. At the same time, this paper presents two high-order Butterworth filter design examples (low-pass and high-pass). Good simulation results were obtained (Good amplitude-frequency characteristics and stable and reliable system), which was consistent with theoretical analysis. Optimization design of high-order filters addressed the difficulty of RC filter parameters selection.