What are the characteristics of LC resonant filters, quartz crystal filters, and ceramic filters?

LC filters, also known as passive filters, is a traditional harmonic compensation device, the reason why the called passive, as the name implies that the device does not need to provide a power supply, the device consists of a suitable combination of filter capacitors, reactors and resistors, and the harmonic source is connected in parallel, in addition to filtering, but also to take into account the need for reactive compensation, which has the advantages of a simple structure, less investment in equipment, high operational reliability, low operating costs, etc., widely used. It has the advantages of simple structure, low equipment investment, high operational reliability, low operating costs, etc., and is widely used.

Quartz crystal filter is configured in the quartz substrate surface of a number of pairs of metal electrodes constitute a bandpass or bandstop filter. It utilizes the piezoelectric effect of the energy into the theory, the choice of electrode oscillator geometry, return frequency and electrode oscillator spacing, control of ultrasonic acoustic coupling, so as to achieve the purpose of filtering. It is characterized by very steep frequency selectivity, low loss, good stability, high rejection band attenuation, and is now used in a large number of mobile communication equipment, is an indispensable primary mid-frequency filter, and plays an important role in improving the sensitivity of the whole machine and the anti-jamming ability. The practical level of foreign MCF products for the center frequency of a few MHz ~ 150MHz, channel spacing 12.5kHz ~ 25kHz, the smallest package size of 8mm × 8mm × 3.2mm, the weight of only 0.4g. MCF development direction is to develop new piezoelectric materials, expanding the bandwidth, reducing the delay fluctuations in the band, increasing the out-of-band attenuation, expansion and improvement of intermediate frequency points and linearity, Package monolithic size further miniaturization and chip.

Ceramic filter using ceramic materials, low loss, high dielectric constant, frequency temperature coefficient and coefficient of thermal expansion of small, can withstand the characteristics of high power design and production, by a number of 1/4 wavelength-type resonator longitudinal multi-stage series or parallel trapezoidal line composition. Its significant features are small insertion loss, good power resistance, narrow bandwidth, especially suitable for portable phones, car phones, radios, cordless phones, and integrated transceiver duplexers, etc., level to coupling filter. Foreign production of the most is 800MHz ~ 1GHz range of series EMI dielectric filters, its technical indicators for the insertion loss of 2dB ~ 3dB, ripple less than 1dB, the voltage VSWR is about 1.5, out-of-band rejection in the specified frequency band up to 20dB or more. Some special requirements point up to 60dB or so, excellent filtering characteristics. The development direction is to use new dielectric materials and other resonant modes, design and production of new miniaturization, chip, low insertion loss, high attenuation, high-performance EMI dielectric filters.