31-08-2017, 04:04 PM
A glass filter is an electronic filter that uses quartz crystals for resonators. The quartz crystals are piezoelectric, so their mechanical characteristics can affect electronic circuits. (see mechanical filter). In particular, quartz crystals may exhibit mechanical resonances with a very high Q factor (10,000 to 100,000 and higher - much higher than conventional resonators constructed from inductors and capacitors). Crystal stability and high Q factor allow crystal filters to have precise center frequencies and steep band pass characteristics. The typical attenuation of the glass filter at the band pass is about 2-3dB. Glass filters are commonly used in communication devices such as radio receivers.
A crystal filter is most often found in the intermediate frequency (IF) stages of high quality radio receivers. Cheaper systems can use ceramic filters constructed from ceramic resonators (which also exploit the piezoelectric effect), or tuned LC circuits. The use of a fixed frequency of the FI stage allows using a glass filter because it has a very precise fixed frequency. Very high quality IF filters, called crystal ladder filters, can be constructed using serial crystal matrices.
The most common use of glass filters is at frequencies of 9 MHz or 10.7 MHz to provide selectivity at communications receivers, or at higher frequencies such as a ceiling filter at receivers using upconversion. The quartz crystal cut determines the vibrational frequencies of the crystal, such as the common AT cut used for glass filters designed for radio communications. Quartz cutting also determines certain temperature characteristics of the component, whose quartz has a very high temperature stability.
Ceramic filters tend to be used at 10.7 MHz to provide selectivity in FM broadcast receivers, or at a lower frequency (455 kHz) as the second intermediate frequency filters in a communication receiver. Ceramic filters at 455 kHz can achieve bandwidths similar to crystal filters at 10.7 MHz.
The design concept for the use of quartz crystals as a filtering component was first established by Walter Cady in 1922, but was largely the work of Walter Mason in the late 1920s and early 1930s who devised methods for incorporating crystals into LC lattice filter networks that laid the groundwork for much of the advances in telephone communications. The 1960s glass filter designs allowed the true Chebyshev, Butterworth, and other typical filter characteristics. The design of the crystalline filter continued to improve in the 1970s and 1980s with the development of monolithic polypolar filters, widely used today to provide IF selectivity in communication receivers. Glass filters can today be found in radio communications, telecommunications, signal generation, and GPS devices.
A crystal filter is most often found in the intermediate frequency (IF) stages of high quality radio receivers. Cheaper systems can use ceramic filters constructed from ceramic resonators (which also exploit the piezoelectric effect), or tuned LC circuits. The use of a fixed frequency of the FI stage allows using a glass filter because it has a very precise fixed frequency. Very high quality IF filters, called crystal ladder filters, can be constructed using serial crystal matrices.
The most common use of glass filters is at frequencies of 9 MHz or 10.7 MHz to provide selectivity at communications receivers, or at higher frequencies such as a ceiling filter at receivers using upconversion. The quartz crystal cut determines the vibrational frequencies of the crystal, such as the common AT cut used for glass filters designed for radio communications. Quartz cutting also determines certain temperature characteristics of the component, whose quartz has a very high temperature stability.
Ceramic filters tend to be used at 10.7 MHz to provide selectivity in FM broadcast receivers, or at a lower frequency (455 kHz) as the second intermediate frequency filters in a communication receiver. Ceramic filters at 455 kHz can achieve bandwidths similar to crystal filters at 10.7 MHz.
The design concept for the use of quartz crystals as a filtering component was first established by Walter Cady in 1922, but was largely the work of Walter Mason in the late 1920s and early 1930s who devised methods for incorporating crystals into LC lattice filter networks that laid the groundwork for much of the advances in telephone communications. The 1960s glass filter designs allowed the true Chebyshev, Butterworth, and other typical filter characteristics. The design of the crystalline filter continued to improve in the 1970s and 1980s with the development of monolithic polypolar filters, widely used today to provide IF selectivity in communication receivers. Glass filters can today be found in radio communications, telecommunications, signal generation, and GPS devices.