Distributed deflection plates: Difference between revisions

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[[File:Distributed deflection plates.jpg|300px|thumb|right|Distributed vertical deflection plates and delay lines in a [[T581]] CRT (beam direction left to right)]]

[[File:Distributed deflection schematic.jpg|thumb|300px|right|Simplified schematic of distributed deflection structure]]

In [[CRT]]s, a trade/off exists between writing rate, deflection sensitivity and spot size. Within a given technology (e.g. mono acceleration, post deflection acceleration or microchannel plate (MCP)), these three characteristics can be traded off against each other. Improve one and one or both of the others suffer. Improve the technology and all three can be improved simultaneously. Writing rate is important for observing single short-lived events, but is not important for repetitive signals. Spot size is important in showing detail in the waveform. Sensitivity is important mostly to permit greater bandwidth in vertical amplifiers.

In [[CRT]]s, a trade/off exists between writing rate, deflection sensitivity and spot size. For example, a slower beam improves the sensitivity but hurts writing rate and spot size due to mutual repulsion between electrons. Within a given technology (e.g. mono acceleration, post deflection acceleration or microchannel plate (MCP)), these three characteristics can be traded off against each other. Improve one and one or both of the others suffer. Improve the technology and all three can be improved simultaneously. Writing rate is important for observing single short-lived events, but is not important for repetitive signals. Spot size is important in showing detail in the waveform. Sensitivity is important mostly to permit greater bandwidth in vertical amplifiers.

~~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~~.

Shaped meshes provide magnification and shield the deflection plates from the strength of post electron acceleration field but scatter the electrons and thus hurt spot size. Electron lenses do not scatter electrons but never-the-less magnify spot size along with beam deflection. Both do, however, contribute net performance by isolating the deflection structure from the acceleration potential.

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.

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 capacative load on the vertical amplifier.

Even a CRT with a single pair of deflection plates has frequency response 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.

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 [[File:Distributed deflection plates.jpg|300px|thumb|right|Distributed vertical deflection plates and delay lines in a [[T581]] CRT (beam direction left to right)]]
 [[File:Distributed deflection schematic.jpg|thumb|300px|right|Simplified schematic of distributed deflection structure]]
-In [[CRT]]s, a trade/off exists between writing rate, deflection sensitivity and spot size.  Within a given technology (e.g. mono acceleration, post deflection acceleration or microchannel plate (MCP)), these three characteristics can be traded off against each other.  Improve one and one or both of the others suffer.  Improve the technology and all three can be improved simultaneously.  Writing rate is important for observing single short-lived events, but is not important for repetitive signals.  Spot size is important in showing detail in the waveform.  Sensitivity is important mostly to permit greater bandwidth in vertical amplifiers.
+In [[CRT]]s, a trade/off exists between writing rate, deflection sensitivity and spot size.  For example, a slower beam improves the sensitivity but hurts writing rate and spot size due to mutual repulsion between electrons.  Within a given technology (e.g. mono acceleration, post deflection acceleration or microchannel plate (MCP)), these three characteristics can be traded off against each other.  Improve one and one or both of the others suffer.  Improve the technology and all three can be improved simultaneously.  Writing rate is important for observing single short-lived events, but is not important for repetitive signals.  Spot size is important in showing detail in the waveform.  Sensitivity is important mostly to permit greater bandwidth in vertical amplifiers.
-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.
+Shaped meshes provide magnification and shield the deflection plates from the strength of post electron acceleration field but scatter the electrons and thus hurt spot size.  Electron lenses do not scatter electrons but never-the-less magnify spot size along with beam deflection.  Both do, however, contribute net performance by isolating the deflection structure from the acceleration potential.
-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.
+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 capacative load on the vertical amplifier.
 Even a CRT with a single pair of deflection plates has frequency response 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.

Distributed deflection plates: Difference between revisions

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