JPH06111391A - Electrostatic capacity pickup - Google Patents

Abstract

PURPOSE:To reduce low-frequency noises of an electrostatic capacity detection signal by electrostatically shielding the part of a lead line by a conductive coating which is arranged on the periphery. CONSTITUTION:The electrostatic capacity pickup which has an electrode stylus 15 and the lead line 14 connected to the electrode stylus 15 and detects information recorded on a recording medium as variation in electrostatic capacity has the part of the lead line 14 electrostatically shielded by the conductive coating 35 arranged on the periphery. Thus, the conductive coating 35 is provided and then the capacity between the lead line 14 and conductive coating 35 is interposed between a pickup housing 13 and the surface of the recording medium. This capacity takes a nearly constant value irrelevantly to the attitude of the lead line 14, so low-frequency noises due to variation in the capacity are reducible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance pickup for detecting information recorded on a recording medium in the form of irregularities or polarization directions as a change in capacitance.

[0002]

2. Description of the Related Art Conventionally, information is recorded in the form of unevenness such as pits as an information recording medium used for recording various information such as image signals and audio signals, and as a data memory for computers. Is reproduced by detecting the change in capacitance due to this unevenness (see, for example, Japanese Patent Laid-Open No. 47-37403).

Further, as an information recording medium capable of recording, reproducing and erasing and capable of super-high density recording, Japanese Patent Laid-Open No. 57-2 is known.
As disclosed in Japanese Patent No. 7447, it is known to have a semiconductor layer and a ferroelectric layer formed on the semiconductor layer, and record information by the polarization direction of the ferroelectric. Recording on this information recording medium is performed by moving a conductive head on the ferroelectric layer and applying a voltage to the layer so that only a predetermined portion of the ferroelectric layer is selectively polarized in a predetermined direction. Will be performed. Information reproduction from the information recording medium is performed by detecting a change in capacitance of the recording medium due to a depletion layer formed in the semiconductor layer due to polarization of the ferroelectric substance.

Pickups for reproducing recorded information from these recording media, that is, electrostatic capacitance pickups,
Basically, the circuit board part mainly including the coil part and the detector of the oscillator or the resonator, the electrode needle arranged in the state (contact or non-contact state) facing the recording medium, and connected to this electrode needle It is equipped with a lead wire and the like that form a part of the resonator. The electrode needle and the lead wire connect the recording medium and the capacitance between the electrode needle and the coil portion of the resonator.

[0005]

When the recorded information is reproduced by using the conventional electrostatic capacity pickup having the above-mentioned structure, in addition to the electrostatic capacity change as the signal component, the distance between the electrode needle and the pick-up housing is increased. It has been recognized that the capacitance or fluctuations in the capacitance between the recording medium and the electrode needle may be mixed in the reproduced signal (for example, RCA Review Vol.43).
March 1982 p194-211). That is, the lead wire and the electrode needle function as a coil portion of the resonator, and at the same time, generate stray capacitance between the pickup housing portion and the surface of the recording medium and also function as a capacitor. This stray capacitance easily changes due to changes in mechanical conditions around the pickup, such as the attachment state of the electrode needle to the housing, the extension of the lead wire, and surface wobbling of the recording medium. It occurs. A large amount of these capacitance changes is distributed in the low frequency region (DC to several 100 kHz).

Therefore, conventionally, the influence of this capacitance variation on the signal is eliminated by separating the frequency band of the signal against such capacitance variation.

On the other hand, in reproducing the recorded information from the recording medium as described above, when the electrode needles of the electrostatic capacity pickup are not brought into contact with the recording medium, the distance between these electrode needles and the recording medium is accurately fixed. It is desirable to apply control to keep

As one of such controls, there is considered servo control for detecting the electrostatic capacitance between the electrode needle and the recording medium and moving the electrode needle or the recording medium so that the electrostatic capacitance becomes constant. When such control is applied, the low-frequency component of the detected capacitance is fed back to the drive control circuit of the electrode needle or the recording medium, so this low-frequency component is sufficient for servo control. Na S
Must have / N.

That is, when performing this servo control, not only the low frequency component of the capacitance detection signal is band-separated from the reproduction signal component as described above, but also the noise contained in this low frequency component is removed by the servo control system. Must be kept within the allowable residual error in.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrostatic capacitance pickup capable of sufficiently reducing low-frequency noise of an electrostatic capacitance detection signal. is there.

[0011]

As described above, the electrostatic capacity pickup according to the present invention has the electrode needle facing the recording medium and the lead wire connected thereto, and the information recorded on the recording medium is obtained. In the electrostatic capacitance pickup for detecting as a change in electrostatic capacitance, the lead wire portion is electrostatically shielded by a conductive coating arranged around the lead wire portion.

The conductive coating is preferably formed so as to extend to the vicinity of the tip of the electrode needle.

[0013]

When the conductive coating as described above is provided, the capacitance between the lead wire and the conductive coating is introduced instead of the stray capacitance of the conventional device described above.
Since this capacitance has a substantially constant value regardless of the posture of the lead wire, the aforementioned low frequency noise due to the change in this capacitance is reduced.

Further, when the conductive coating is formed so as to extend to the vicinity of the tip of the electrode needle, the spread of electric force lines between the electrode needle and the recording medium is suppressed to read out predetermined information on the recording medium. It is possible to prevent the capacitance other than the portion from affecting the reproduction signal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows a main part of a capacitance pickup 10 according to a first embodiment of the present invention, and FIG. 2 shows a schematic structure of an information reproducing apparatus provided with the capacitance pickup 10.

As shown in FIG. 2, a disc-shaped information recording medium 11 in which information is recorded in the form of irregularities such as pits or in the direction of polarization is a turntable rotated at high speed.
Fixed on 12. A lead wire 14 is extended from the housing 13 that houses the pickup circuit, and an electrode needle 15 is attached to the tip of the lead wire 14. This electrode needle 15
Is held by the holding member 16 with its tip facing the surface of the information recording medium 11. Then, a capacitance detection signal Sd is output from the pickup circuit as described later.

Next, the structure of the pickup circuit will be described with reference to FIG. This pickup circuit basically comprises a UHF oscillator 20, a resonance circuit 21, and a detection circuit 22.
Consists of. The resonance circuit 21 includes a coil L1 arranged in the pickup housing 13 and a stray capacitance C1 around the electrode needle 15.
And an LC resonance circuit composed of a capacitance C2 between the recording medium 11 and the electrode needle 15 which changes according to the recorded information of the information recording medium 11 and a variable capacitor Cv, and its resonance frequency. fo is about 1 GHz. On the other hand, the detection circuit 22 is composed of a coil L2 coupled to the coil L1, a diode D, a capacitor C3 and a resistor R.

When a carrier signal having a frequency close to the resonance frequency fo is injected from the UHF oscillator 20 into the resonance circuit 21 via the coil L3, the resonance frequency fo changes according to the electrostatic capacitance C2. The carrier signal undergoes amplitude modulation. Then, the carrier wave signal is detected by the detection circuit 22 to obtain the signal Sd indicating the change in the capacitance C2 (that is, indicating the recording information).

The signal Sd is used not only for reproducing recorded information but also for input to the automatic frequency control circuit 23. The automatic frequency control circuit 23 controls the variable capacitor Cv so as to suppress the fluctuation of the low frequency component of DC to several kHz of the signal Sd (this is due to, for example, the change of the stray capacitance C1).
Change the capacity of. This prevents the variation of the resonance frequency fo in the low frequency region as described above.

Further, particularly in this apparatus, the voltage signal S1 output from the automatic frequency control circuit 23 is input to the addition point 24,
Therefore, the signal S1 is subtracted from the reference signal S2 output by the reference signal generation circuit 25. A deviation signal S3 indicating the deviation between these two signals S1 and S2 is input to the automatic height control circuit 26. The automatic height control circuit 26 inputs a drive control signal S4 corresponding to the deviation signal S3 to the piezo driver 27. This piezo driver 27 is the electrode needle holding member described above.
It drives the piezo element 28 that moves 16 up and down, that is, in the direction in which the distance from the information recording medium 11 is changed. The electrode needle 15 is always maintained in a state of being levitated from the information recording medium 11 by a predetermined distance.

Next, the structure of the capacitance pickup 10 will be described in detail with reference to FIG. The electrode needle 15 of the capacitance pickup 10 is housed in the block 30. The block 30 is formed by stacking an insulating layer 31 and a conductive layer 32 (shown by hatching in the figure) by a known semiconductor manufacturing process, and the conductive layer in the central portion surrounded by the insulating layer 31. Is the electrode needle 15. And block 30
Is attached to the holding member 16 with the surface cleaved in the direction in which the laminated structure is observed facing the information recording medium 11. The rear end of the electrode needle 15 is connected to a contact 33 made of a conductive layer formed on the surface of the block 30.

On the other hand, the lead wire 14 extending from the pickup housing 13 is made of a single wire or twisted wire such as gold or annealed copper, and connects the contact point 33 and the pickup circuit in the housing 13. Around the lead wire 14 is polystyrene,
A high-frequency insulating coating 34 of polyethylene or the like is applied, and a conductive coating 35 of twisted copper wire or the like is provided on the outer side thereof. The conductive coating 35 is connected to the conductive layer 32 of the block 30. The structure including the lead wire 14, the high frequency insulating coating 34, and the conductive coating 35 described above can be formed by a conventionally known coaxial cable manufacturing method. In FIG. 1, the high-frequency insulating coating 34 and the conductive coating 35 are partially cut away.

In the above structure, the conductive coating 35 arranged around the lead wire 14 provides electrostatic shielding.
That is, instead of the stray capacitance between the lead wire 14 and the pickup housing 13 or between the lead wire 14 and the information recording medium 11, the capacitance between the lead wire 14 and the conductive coating 35 is introduced. Since this capacitance has a substantially constant value regardless of the posture of the lead wire 14, it is possible to prevent low frequency noise from occurring in the capacitance detection signal Sd due to the change in the capacitance.

Further, in the present embodiment, the electrode needle 15 is also electrostatically shielded by the conductive layer 32 around the insulating layer 31,
Therefore, generation of low-frequency noise due to a change in stray capacitance between the electrode needle 15 and the pickup housing 13 or between the electrode needle 15 and the information recording medium 11 is also prevented.

In the above-mentioned configuration without electrostatic shielding, the low-frequency noise of the electrostatic capacitance detection signal Sd corresponds to 0.1 μm in the distance between the electrode needle 15 and the information recording medium 11. On the other hand, in the structure in which the electrostatic shield is provided, the low frequency noise of the electrostatic capacitance detection signal Sd is reduced to the magnitude corresponding to 0.01 μm in the distance between the electrode needle 15 and the information recording medium 11. Therefore, for example, even when servo control is performed to set the flying height of the electrode needle 15 from the information recording medium 11 to 0.05 μm, the capacitance detection signal Sd can be used for this servo control.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. In the second embodiment, as shown in the plan view of FIG. 4, microstrip lines 41, 42 and 43 forming inductors are formed on a printed circuit board 40 arranged in the pickup housing. The microstrip lines 41 and 42 are connected to an oscillator and a detection circuit, respectively, and the lead wire 14 is connected to a microstrip line 43 which serves as an inductor of a resonance circuit. As shown in the side cross-sectional view of FIG. 5, the lead wire 14 has a sharpened tip by electrolytic polishing or the like and has an information recording medium.
It extends to a position facing 11 and also serves as an electrode needle.

Also in this structure, since the lead wire 14 is electrostatically shielded by the conductive coating 35, the same effect as in the first embodiment can be obtained. Conductive coating 35
Is extended to the vicinity of the tip of the lead wire 14 serving as an electrode needle, the spread of the electric force line E between the lead wire 14 and the recording medium 11 is suppressed, and a predetermined information reading portion on the recording medium 11 is suppressed. It is possible to prevent the capacitance other than that from affecting the reproduction signal. By the way, when the electrostatic shield is not applied, the spread of the lines of electric force E becomes large as shown in FIG.
The electrostatic capacitance other than the predetermined information reading portion on 11 easily affects the reproduction signal.

As the coupling structure of the lead wire 14 and the pickup, the conductive coating 35 is directly connected to the end portion of the waveguide structure pickup (for example, the pickup housing portion: see FIG. 3), and the lead wire 14 and A structure for connecting the inductor of the resonance circuit, or as shown in FIG. 7, a coupling portion 50 between the oscillator and the inductor of the resonance circuit and a coupling portion 51 between the detection circuit and the inductor of the resonance circuit are connected to the conductive coating 35. It is possible to adopt a structure that is taken in.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing a capacitance pickup according to a first embodiment of the present invention.

FIG. 2 is a schematic side view showing a reproducing device using the electrostatic capacity pickup.

FIG. 3 is an electric circuit diagram of the capacitance pickup.

FIG. 4 is a partial plan view of a capacitance pickup according to a second embodiment of the present invention.

FIG. 5 is a partial side sectional view of the capacitance pickup of the second embodiment.

FIG. 6 is a partial side sectional view of a conventional capacitance pickup.

FIG. 7 is a partial side sectional view showing a part of still another embodiment of the present invention.

[Explanation of symbols]

 10 Capacitance pickup 11 Information recording medium 13 Pickup housing 14 Lead wire 15 Electrode needle 31 Insulating layer 32 Conductive layer 33 Contact point 34 High frequency insulation coating 35 Conductive coating

Claims (1)

[Claims] 1. A capacitance pickup having an electrode needle facing a recording medium and a lead wire connected to the electrode needle, and detecting information recorded on the recording medium as a change in electrostatic capacitance. A capacitance pickup in which a line portion is electrostatically shielded by a conductive coating provided around the line portion.