Capacitive protection coupling element for stylus electrode discharge

Claim 2

A playback system for use with a video disc record having geometrical variations in a spiral groove on a major surface of the disc record, said surface including a layer of conductive material covering a dielectric substrate, with a dielectric coating overlying said conductive layer; said system comprising: a rotatable turntable of conductive material direct current conductively connected to a point of reference potential; a tracking stylus supported for cooperative engagement with said record groove when said record is in a playback position, with said turntable in supporting engagement with a surface of said record opposed to said major surface; said tracking stylus including an electrode presenting a conductive surface which cooperates with said conductive layer and dielectric coating of said disc record to form a varying capacitance as said record is rotated during playback; means for normally precluding the charging of capacitance exhibited between said conductive layer and the conductive material of said turntable, said charging precluding means comprising conductive means for providing a direct current conductive connection between said conductive layer of said record and said point of reference potential; said charging precluding means being ineffective, however, in precluding the accumulation of charge on any region of said conductive layer undesirably subject to DC isolation from said conductive means; and meaNs for developing electrical signal variations representative of the variations of said varying capacitance, said signal variation developing means including circuit means, separate from said varying capacitance and said conductive means, for establishing an electrical signal path between said stylus electrode and said point of reference potential; and wherein said separate circuit means includes means for limiting the flow of discharging current through said stylus electrode in the event of stylus engagement with a groove surface overlying any region of said conductive layer subject to said DC isolation from said conductive means, said limiting means including a capacitor interposed in said signal path in such manner as to effect DC isolation of said stylus electrode from said point of reference potential.

Claim 3

The invention according to claim 1, wherein said capacitor has a capacitance value substantially greater than said varying capacitance.

Claim 4

The invention according to claim 1, wherein the capacitance value of said capacitor is at least 1 picofarad.

Claim 5

In a video playback system for a video disc record having geometrical variations in a spiral groove on a major surface of said disc record, said record surface including a layer of conductive material covered with a coating of dielectric material, said conductive layer overlying a dielectric substrate, the combination comprising: a rotatable turntable comprising conductive material direct current conductively connected to a point of reference potential; a tracking stylus having a conductive electrode for engaging said spiral groove during rotation of said record in a playback position so that the capacitance exhibited between said conductive electrode and the conductive layer of said disc record varies as said record is rotated, said turntable being in supporting engagement with a surface of said record opposed to said major surface when said record is in said playback position; means for normally precluding the charging of capacitance between said conductive layer and the conductive material of said turntable, said charging precluding means comprising a conductor for providing a direct current conductive connection between the conductive layer of said disc record and said point of reference potential, said charging precluding means being ineffective, however, in precluding the accumulation of charge on any region of said conductive layer undesirably subject to DC isolation from said conductor; an inductive element; a discrete capacitive element; and means for electrically connecting said inductive element and said capacitive element in series between said stylus conductive electrode and said point of reference potential in such manner as to provide a tuned circuit having a resonant frequency which varies as said capacitance between said electrode and said conductive layer varies, with said capacitive element providing direct current isolation of said stylus electrode from said point of reference potential to limit the flow of discharging current through said stylus electrode in the event of stylus engagement with a groove surface overlying any region of said conductive layer subject to said DC isolation from said conductor, said capacitive element having a capacitance value more than an order of magnitude greater than the value of said varying capacitance between said stylus electrode and said conductive layer.

Claim 6

In a video playback system for a video disc record having geometrical variations in a spiral groove on a major surface of said disc record, said record surface including a layer of conductive material covered with a coating of dielectric material, said conductive layer overlying a dielectric substrate, the combination comprising: a rotatable turntable comprising conductive material direct current conductively connected to a point of reference potential; a tracking stylus having a conductive electrode for engaging said spiral groove during rotation of said record in a playback position so that the capacitance exhibited between said conductive electrode and the conductive layer of said disc record varies as said record is rotated, said turntable being in supporting engagement with a surface of said record opposed to said major surface when said record is in said playback position; means for normally precluding the charging of capacitance between said conductive layer and the conductive material of said turntable, said charging precluding means comprising a conductor for providing a direct current conductive connection between the conductive layer of said disc record and said point of reference potential, said charging precluding means being ineffective, however, in precluding the accumulation of charge on any region of said conductive layer undesirably subject to DC isolation from said conductor; an inductive element; a discrete capacitive element; and means for electrically connecting said inductive element and said capacitive element in series between said stylus conductive electrode and said point of reference potential in such manner as to provide a tuned circuit having a resonant frequency which varies as said capacitance between said electrode and said conductive layer varies, with said capacitive element providing direct current isolation of said stylus electrode from said point of reference potential to limit the flow of discharging current through said stylus electrode in the event of stylus engagement with a groove surface overlying any region of said conductive layer subject to said DC isolation from said conductor, said capacitive element having a capacitance value more than an order of magnitude greater than the value of said varying capacitance between said stylus electrode and said conductive layer.