A filter is a device used to eliminate unwanted noise, which filters the input or output to obtain pure alternating current. You can derive the most common types of filters: low-pass, band-pass, high pass, notch, and elliptical filters through the fundamental filter building blocks - second-order universal filter transfer functions.
The parameters of the transfer function - f0, d, hHP, hBP, and hLP - can be used to construct filters of all types. The frequency f0 is the frequency at which the s term initially occupies the allocation function. Planners consider frequencies below this value as low frequencies, frequencies above this value as high frequencies, and frequencies near this value as in band frequencies. Damping d is used to measure how a filter changes from low frequency to high frequency, and it is a guideline for the filter to tend towards oscillation. Change the practical damping value from 0 to 2 (Table 1). The high pass coefficient hHP is the coefficient that allocates molecules to frequencies higher than the transition frequency. The bandpass coefficient hBP is a coefficient for molecules that allocate frequencies near the transition frequency. The low-pass coefficient hLP is a coefficient that distributes molecules with frequencies lower than the transition frequency. Planners only need these 5 parameters to define a filter.
The Past, Present, and Future of Filters
Any device capable of signal processing can be called a filter. Filters are widely used in modern telecommunications equipment and various control systems; Among all electronic components, filters are the most commonly used and have the most messy skills. The quality of filters directly determines the quality of products, so the research and production of filters have always been valued by countries around the world.
The unfolding process of the filter
In 1917, American and German scientists respectively developed LC filters, which led to the presentation of the first multiplexing system in the United States the following year. Passive filters became increasingly sophisticated in the 1950s. Since the 1960s, due to the development of computer skills, integrated processes, and materials industry, filters have reached a new level and are striving towards low power consumption, high precision, small size, multifunctionality, stability and reliability, and low cost. Among them, small size, multifunctionality, high precision, and stability and reliability have become the main focus since the 1970s, leading to the rapid development of various filters such as RC active filters, digital filters, switched capacitor filters, and charge transfer devices. By the late 1970s, the single-chip integration of the above-mentioned filters was developed and applied. In the 1980s, efforts were made to improve the functionality of various new filters and gradually expand their application plans. Since the 1990s, we have been primarily committed to applying various filters to the development and research of various products. Of course, research on filters themselves is still ongoing.
The widespread use of filters in our country dates back to the 1950s, when they were primarily used for voice and broadcast filtering. After half a century of development, China has made certain progress in the research, production, and application of filters. However, due to the shortage of specialized research institutions, the integration process and material industry cannot keep up, resulting in a gap between the development and application of many new filters and the international level.
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