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Distributed deflection plates: Difference between revisions
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Distributed deflection plates (view source)
Revision as of 14:24, 11 December 2023
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CRTs have a finite frequency response and distributed deflection structures extend the CRT's bandwidth as well as aid the vertical amplifier by virtually eliminating the capacitive load on the vertical amplifier. | CRTs have a finite frequency response and distributed deflection structures extend the CRT's bandwidth as well as aid the vertical amplifier by virtually eliminating the capacitive load on the vertical amplifier. | ||
The CRT's frequency response is not as simple as an RLC circuit. A voltage step applied to the deflection plates simultaneously affects all the electrons between the plates. Those that are just exiting the plates see nothing as they continue on their way to the phosphor for display. Those that are at the entrance to the plates feel the effects of all voltage changes that take place during their transit through the plates. However, they bear the memory of any deflection plate voltage changes during their journey through the plates. The effects of any deflection plate voltage changes are delayed in proportion to their distance from the exit simply because it takes | The CRT's frequency response is not as simple as an RLC circuit. A voltage step applied to the deflection plates simultaneously affects all the electrons between the plates. Those that are just exiting the plates see nothing as they continue on their way to the phosphor for display. Those that are at the entrance to the plates feel the effects of all voltage changes that take place during their transit through the plates. However, they bear the memory of any deflection plate voltage changes during their journey through the plates. The effects of any deflection plate voltage changes are delayed in proportion to their distance from the exit simply because it takes time for the electrons to travel from the entrance to the exit of the plates. This is what makes the frequency response complex. | ||
For example, if it takes 1 ns for an electron to travel the length of the plates (usually one on each side of the electron beam) and a 1 GHz sine wave is applied between the plates, the full 360 degrees of the sine wave causes the electron to move up and down from entrance to exit. When the drive voltage was going up at the time the beam entered the deflection plate area, by the time it is leaving, the drive voltage will be going down again, pushing the beam back to the center, i.e. the sensitivity is zero at this frequency. | For example, if it takes 1 ns for an electron to travel the length of the plates (usually one on each side of the electron beam) and a 1 GHz sine wave is applied between the plates, the full 360 degrees of the sine wave causes the electron to move up and down from entrance to exit. When the drive voltage was going up at the time the beam entered the deflection plate area, by the time it is leaving, the drive voltage will be going down again, pushing the beam back to the center, i.e. the sensitivity is zero at this frequency. | ||