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Distributed deflection plates (view source)

Revision as of 16:37, 11 December 2023

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Meshes that shield the deflection plates from the strength of post electron acceleration field and electron lenses both trade off sensitivity against spot size to varying degrees.  They do, however, contribute net performance improvements.
Meshes that shield the deflection plates from the strength of post electron acceleration field and electron lenses both trade off sensitivity against spot size to varying degrees.  They do, however, contribute net performance improvements.


CRTs have a finite frequency response and distributed deflection plates extend the CRT's bandwidth as well as aid the vertical amplifier by virtually eliminating the capacitive load on the vertical amplifier.  
All CRTs have a finite frequency response but distributed deflection plates 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.  Therefore 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 to exit of the plates.  This is what makes the frequency response so complicated.
Even the CRT with a single pair of deflection plates has frequency response is not as simple as an RLC circuit.  A voltage step applied to a single pair of 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.  Therefore 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 to exit of the plates.  This is what makes the frequency response so complicated.


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 during transit.  If the drive voltage is going up at the time an electron enters the deflection plate area, 1 ns later the drive voltage will be going down again, pushing the beam back to the center, i.e. there is no net deflection and 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 during transit.  If the drive voltage is going up at the time an electron enters the deflection plate area, 1 ns later the drive voltage will be going down again, pushing the beam back to the center, i.e. there is no net deflection and the sensitivity is zero at this frequency.
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