Bandpass Discrete Analog Filter

The problem of ensuring the stable functioning of radio engineering systems in conditions of natural and intentional interference, as well as in the conditions of the use of electronic warfare means, is currently one of the urgent tasks. Frequency filtering is one of the main methods of ensuring the required signal-to-noise ratio under these conditions and is one of the most common signal processing operations and can be implemented in both analog and digital form. This article presents an approach to solving the problem of extremely high requirements for the dynamic range of input analog-to-digital converters in digital processing. It is proposed to solve this problem by using pre-frequency filtering in the analog path before converting the input signal to digital. The hardware implementation of such frequency selectors is based on filters with in-ductive-capacitive elements implemented on discrete, strip or waveguide elements, depending on the frequency range. Quartz, piezoceramic, and electromechanical filters are also used, which can provide very high frequency selectivity, but at fixed frequencies. An analysis of existing methods and devices for analog frequency filtering shows that there are options that have high frequency selectivity, but do not provide frequency tuning. Tunable filters have significantly less selectivity and, as a rule, do not retain their parameters in the tuning range. In connection with this, the development and creation of highly selective tunable bandpass analog filters with highly stable characteristics seems promising and relevant. In the proposed version of the bandpass discrete analog filter (BDAF), signal processing is also carried out in the time domain, but is fundamentally different from filters with switched capacitors both in construction and in characteristics. The filter consists of input and output analog switches, N identical low-pass filters (LPF), a clock generator and a switch control circuit. The frequency of the clock generator signal determines the tuning frequency of the BDAF. In this case, the period of connection of the inputs and outputs of each of the N low-pass filters to the input and output of the BDAF must be equal to the period of the BDAF tuning frequency. Based on the proposed approaches and principles of construction and operation of the filter, a filter circuit has been developed and timing diagrams of signals at different points of the filter are presented. The results of the analysis of filter characteristics obtained by computer modeling and prototyping are presented.