Tunable Complex Band-Pass Filter on Switchable Capacitors

Abstract

The article is devoted to the development of methods for calculating complex filters on switchable capacitors using analog prototypes. Analog and digital complex filters are described in detail in the technical literature. In recent years also appeared work devoting on the calculation and implementation of complex filters on switchable capacitors. One of the methods of calculating filters on switchable capacitors is the method of converting an active RC filter by replacing resistors with switchable capacitors. The use of identical complex links on inverting integrators allows to simplify the calculation of the block diagram of an analog complex band-pass filter with a high-order LF-prototype. It also becomes possible to restructure the central frequency and bandwidth of a band-pass complex filter by synchronously changing the parameters of identical complex links. In this article describes the complex link's scheme of inverting non-ideal integrators implemented on two operational amplifiers. Offers the method of calculation of complex bandpass filters based on complex links, implemented by using switchable capacitors. In the schemes of complex band-pass filters on switched capacitors, it is possible to independently adjust the central frequency and bandwidth by changing the nominal values of identical capacitors in the links or by changing the corresponding switching frequency. As an example, a schematic diagram of a complex band-pass filter with 2nd order Butterworth LF prototype has been developed. The first model is implemented on the basis of summators and analog complex links. The second model is implemented on the basis of summators and complex links containing operational amplifiers and switchable capacitors. Circuit simulation of complex filters was carried out in the Micro-Cap program. In the frequency domain compared the values of frequency response curve of both filters at different frequencies. These values are almost the same. The simulation results confirm the performance of the proposed method for calculating complex band-pass filters on switchable capacitors and confirm the possibility of independent tuning of the center frequency and bandwidth.