KR790001836B1 - Pickup apparatus for video disc information playback - Google Patents

Abstract

A pickup assembly for use in video information playback system, is composed of a pickup means for establishing a reactance subject to a variation of the recorded information, a conductive support housing and a flexibly mounted conductive member (I) supporting the pickup stylus and forming a transmission line with the surrounding support housing. An electrical connection is provided between I and the conductive element of the stylus to tablish a tuned cct. including the reactance of the transmission line and of the variable capacitance formed between the stylus and the record medium.

Description

Pick-up device for playing video disc information

1 is a block diagram of an information reproducing apparatus embodying the principles of the present invention.

2A and 2B are plan and side views of a ton arm assembly used in US Patent Application No. 258,645.

3A and 3B are a plan view and a side view of a tow arm embodying the present invention.

4A and 3A are circuit configuration diagrams showing an equivalent circuit of a tow arm.

4b is an enlarged view of the needle opening shown in FIG. 3a.

4c or 3b an enlarged view of the needle assembly showing coils, capacitors and resistor elements associated with the RF ground feedback of the needle assembly.

TECHNICAL FIELD The present invention relates to an information reproducing apparatus, and more particularly, to a pick-up assembly of a video information reproducing apparatus.

In some information reproducing apparatus, video information is continuously recorded on a disc recorder by modulation which can be detected by capacitive change. Video disc records have a geometric change in the bottom of the spiral groove of the disc surface. The grooved spiral disk surface contains a conductive material thinly painted with a dielectric. The tracking needle has a conductive surface that combines a dielectric coating with a conductive material to form a capacitance that changes due to geometrical changes as the record is rotated during playback. This type of device is shown in US Patent Application No. 126,772, "Information Recording and Playback for It" and US Patent Application No. 258,645.

In the device of the type described above, the needle in the groove of the disc record forms a metallization capacitor on the record and this capacitance changes as the record is rotated. These capacitive changes are components of the tuning circuit, and the resonance frequency of the tuning circuit changes when the capacitance between the needle and the record changes. The tuning circuit is driven through inductive coupling to a fixed frequency oscillator. Since fixed frequency oscillator signals are applied to the tuning circuit, the resonant frequency of the tuning circuit will change due to the change in capacitance between the needle and the record. Therefore, the response of the tuning circuit to the excitation signal voltage changes as a function of record information. It supplies an output signal with varying amplitude as a function of record information. The amplitude change output signals are detected by the double voltage peak detector, amplified, and applied to the reproduction device signal processing circuit.

In the device of the type described above, the percentage modulation of the signals detected by the double voltage peak detector is a function of the rate of change of capacitance between the needle and the record relative to the total equivalent capacitance of the tuning circuit. Since the change in capacitance is very small, the percentage modulation of the detected signal is also very small. This makes it difficult to reproduce the recorded information because of the other noise introduced into the device and the swamping by the circuit. Therefore, it is desirable to increase the modulation percentage of the detected signal since the overall equivalent capacitance of the tuning circuit is minimized. The tuning circuit of the type used in U.S. Patent Application No. 258,645 changes the frequency response of the tuning circuit, thus providing a transmission line for supplying equivalent inductance and capacitance to the tuning circuit having a needle connected to the transmission line for supplying the capacitance change. Have

It can be seen from the above that the reactance of the transmission line and the needle is very critical to the frequency response of the tuning circuit. The exchange of needles and records, and changes in the fabrication and assembly of the device, all affect the capacitance of the tuning circuit. Therefore, it is desirable to limit this change in capacitance as little as possible.

In US patent application 258,645, an electrical connection is arranged between the transmission line and the needle to detect a change in capacitance between the needle and the record. This connection consists of a very fine lead that provides an electrical connection between the needle and the transmission line. Therefore, the wire was connected between the fixed transmission line and the flexible needle. Although the leads are properly connected, they are

1) Easily ruptured due to small diameter,

2) The capacitance and inductance of the equivalent tuning circuit can be changed because the length of the conductor can be changed during the manufacture and assembly of the device.

3) Because the wire is hard, it gives tension to the needle, which has the disadvantage of giving mechanical loss to the tracking needle.

In order to change the needle, the needle must be detachable. Therefore, it is highly desirable to reduce the above mentioned disadvantages as much as possible in the abovementioned operating device.

Another problem associated with the devices described above is the proper choice of (radio frequency) ground feedback. It refers to a technique of bonding clips to a record and electrically coupling the clips to the base of the record support serving as the ground of the device. These clips hold the record on the record turntable while providing an RF ground path between the needle and the ground of the device. The problem with the use of the clip in the device was the introduction of large resistance between the needle and the RF feedback which supplied the added capacitance, inductance, resistive loss of the record, and the like. Since this unnecessary reactance affects the detection capability of the variable capacitance of the record, it is desirable to minimize the reactance between the needle and the RF ground feedback.

In the device of the type described above, the sensitivity of the pick-up device is further reduced when the needle detects a geometric change at the edge of the record than at the center of the record. The drift noise of the pickup is also greater at the edge of the record than when the needle is towards the center of the record. When the record is activated the sensitivity is increased and the pickup's drift noise is reduced. Therefore, it is desirable to correct these fluctuations with a sensitivity such that the sensitivity of the pickup device and the sensitivity to drift noise are kept relatively constant throughout the record.

According to the above-described embodiment of the present invention, the information reproduction contention for reproducing the information recorded in the record medium is composed of the primary device for receiving the information and the conductive support frame. The secondary device containing the signal energy source is connected to the primary device. A flexible component having a primary end and a secondary end and which is flexibly mounted comprises a secondary end connected to the primary device and a primary end movably connected to the support frame. The conductive component mechanically holds the primary device and also forms a transmission line connected to the surrounding holding frame. The tuning circuit consists of a reactance of a transmission line and a reactance of a primary device.

A signal energy source is connected to the tuning circuit to activate the tuning circuit as much as the signal modulated by the record information appears in the tuning circuit.

In accordance with the characteristics of the information reproduction dispute described above, the conductive support frame is adapted such that when placed on the record medium during playback, the low impedance feedback path for the signal appearing in the tuned circuit is advantageously supplied by the capacitance between the record medium and the support frame. It becomes size.

Referring to Figure 1, a needle 10 is shown in the schematic. Needle 10 has a conductive surface that, although not shown, creates a geometric change in the record medium to form a capacitance change between the needle's conductive surface and the record medium. Capacitance changes form a tuning circuit section at the detector and tuning circuit stage 11. The detector and the tuning circuit stage 11 contain a tuning circuit and a double voltage peak detector whose resonance frequency is changed by the geometric change of the record. The oscillator stage 12 provides the detector and the tuning circuit stage 11 with the output signal mutually coupled by inductive coupling. Only the signals coupled to 11 activate the tuning circuit. When the resonant frequency of the tuning circuit changes due to the geometric change of the record medium, the response of the tuning circuit to the excitation voltage from the oscillator changes. These changes are detected by only 11 double-voltage peak detectors and applied to preamplifier stage 15 before being applied to information reproduction contention signal processing circuit 18 by jack 16 and plug 17. The automatic gain control stage 19 detects the level of the signal injected into the tuning circuit of stage 11 by the oscillator 12. The automatic gain control stage 19 adjusts the gain of the oscillator stage 12 such that the output signals of the oscillator stage 12 are injected into the tuning circuit of stage 11 as a signal of a constant amplitude.

The automatic frequency control stage 20 is connected between the detector and the tuning circuit stage 11 and the oscillator stage 12. The automatic frequency control stage 20 adjusts the operating frequency of the oscillator stage to maintain a constant separation between the nominal intermediate frequency of the tuning circuit of stage 11 and the frequency of the oscillator stage output signal. This ensures that the device operates at the desired point on the slope of the tuning circuit response. The regeneration device operating point is at the lowest frequency slope or at the edge of the synchronization circuit frequency response. The automatic gain control stage 19 and the automatic frequency control stage 20 each ensure that the predicted relationship exists between the excitation signal applied to the tuning circuit and the tuning circuit frequency response.

The search control stage 21 connected to the oscillator stage is operated when the frequency separation between the nominal frequency of the tuning circuit and the frequency of the oscillator stage output signals has exceeded the set limit. However, when a condition that greatly affects the resonant frequency of the tuning circuit occurs at 11, for example, such a deviation occurs when the needle is moved from the record due to a certain instrument. When the search control stage 21 is activated, the operating frequency of the oscillator stage 12 is adjusted to the initial search state. The operating frequency is adjusted such that a known initial relationship is made between the nominal intermediate frequency of the tuning circuit and the frequency of the oscillator stage output signals. In the initial search state, the frequency of the oscillator stage output signal is below its normal operating frequency but within the pull-in range of the automatic frequency control stage 20. The automatic frequency control stage 20 cancels the operating frequency of the oscillator stage 16 until a frequency relating to the frequency between the nominal intermediate frequency of the tuning circuit and the frequency of the reinstalled oscillator stage output signal is predetermined.

Referring to FIG. 2, FIG. 2A is a plan view of a ton arm assembly used in US Patent Application No. 258,645 with the top removed. High frequency signals from the oscillator stage 12 of FIG. 1 are coupled to the input connector 34. The RF input connector is coupled to a terminating resistor 33 connected to the ton armature serving as ground. Conductor 35 is connected to the needle assembly 38 through one end of the tow arm 32 grounded and the other end through a teflon disc insulator 36 and a microconnector 37. Fine connecting wire 37 couples wire 35 to needle assembly 38. Needle assembly 38 contacts record 43 shown in FIG. 2B through opening 44. As the capacitance changes between the needle and the record, the frequency response of the tuning circuit changes. Due to the mutual coupling, the change in signal amplification is detected by a double voltage peak detector, indicated by dashed line 41. This signal is then coupled to video IF output 42 which is coupled to the preamplifier of FIG. Needle assembly 38 is supported by needle support 39. The needle support 39 has a coupling device 40 which allows the movement of the flexible needle support to allow the needle assembly 38 to track the record groove.

FIG. 2B is a side view of the tow arm assembly shown in FIG. 2A with the side removed. As shown, if the lead of the micro lead connection 37 is firm, it will pressurize the needle, and if it is not firm, the lead will break easily due to its thin diameter. Teflon disc insulator 36 also adds capacitance to the transmission line with defects in lead connection 35 and fine lead connection 37. This capacitance is undesirable because it affects the capacitance change detected by the tuning circuit.

Therefore, the needle support 39 must be strong enough to hold the needle assembly 38 and flexible enough for the needle to track. In addition, unnecessary reactance should not be applied that affects the frequency response of the tuning circuit.

3a is a plan view of a tow arm assembly embodying the present invention with the top of the mold removed. The high frequency signal power from the oscillator of FIG. 1 is connected to the terminating resistor 33 via the RF input connector 34. This high frequency signal power is connected to ground through the ton arm 32-1. The conductive member 45 supplies the support of the needle assembly 38 and the reactance required for the tuning circuit.

The conductive part 45 supports the needle assembly 38 and supplies the reactance required for the tuning circuit. In an embodiment of the present invention, conductive component 45 is a hollow metal tube of predetermined length and diameter to provide adequate reactance and flexibility for proper operation of the device. The conductive part 45 acts as a center conductor for the transmission line. The ground conductor of the transmission line is the ton arm 32-1. Line 47 is used to connect conductive part 45 to the shortest distance to ground. In addition to the length of the conductive component 45 and the conductor length from the conductive component 45 to the needle tip of the needle assembly 38, the length of the conductive wire 47 is selected to supply approximately 1/4 wavelength transmission line, which transmits the record to the record variable capacitance and toearm capacitance. The coupling in series places a capacitance load on the needle. As a result, the quarter-wave transmission line becomes resonant at the selected frequency. In an operational embodiment of the present invention, the nominal intermediate frequency is selected as approximately 690 MHz. This frequency is achieved when the conductive part 45 is 3.6 inches long.

The electrical conductor between the needle and the conductive part 45 is 47 inches in length. It is noteworthy that the nominal intermediate frequency of the synchronous circuit changes with the position of the circuit components adjacent to the structure of the transmission line. Conductive part 45 is manufactured from a mil thickness and 0.036 inch aluminum tube. In the illustrated device of the type described above, the capacitance change is represented as frequency modulation of the RF carrier, and the frequency-modulated geometrical change over the frequency band from 500 KHz to 7 MHz recorded in the disc record is detected by the needle assembly 38. do. The change in capacitance changes the resonant frequency of the tuned circuit by ± 200 KHz from the nominal frequency from 500 KHz to 7 MHz. Therefore, the tuning circuit is inductively connected to the resistor 33 and its lead wire, and the resonance frequency of the tuning circuit changes the response of the circuit tuned to the excitation signal as the operation of the recorded information. As a result, the change signal energy of the tuning circuit is inductively coupled to the pickup closure 60 of the double voltage peak detector 41 which detects this signal voltage change. The output of the double-voltage peak detector 41 contains a change in signal voltage in response to the change in capacitance between the needle tip and the metal surface of the record as the record rotates and is connected to video IF output 42 and sent to preamplifier 15 in FIG. Lose. Conductive member 45 is connected to flexible connector 46 to allow the needle to move more freely. Needle assembly 38 is placed through the opening of the toe arm 32-1 to engage record 43. As shown in FIG. 3, the needle assembly 38 may be connected to the conductive member 45 by a sleeve assembly 58 having a small lead electrically connecting the transmission line 45 to the needle 38. A more detailed description of the sleeve assembly 58 is described with reference to figure 4c.

3b is a side view of the tow arm 32-1 according to the present invention with the side of the tow arm frame removed. As can be seen in this figure, the microwire connector 37 and the Teflon disc insulator 36 in FIG. 2A do not form part of the tow arm assembly. The present invention also eliminates the need to separate the needle support from the transmission line structure by allowing the transmission line to be used as a needle support. The sleeve assembly 58 electrically connected between the needle assembly and the transmission line is a non-flammable part and can be made larger and the length of the electrical conductors (not shown) of the sleeve assembly 58 can be shorter to predict the reactance of the leads. Therefore, the larger the diameter of the conductor, the less likely it is to break, and the shorter the conductor, the smaller the capacitance and inductance of the conductor.

Another advantage of the tow arm assembly of the present invention described above is the ease of manufacture and reduced number of parts and connections compared to the device used in US patent application 258,645. In addition, by eliminating many components and connections, the drift reactance that affects the frequency response of the tuning circuit is also reduced. By eliminating many elements, tow arm assemblies that have not been easily achieved so far can be more easily achieved with the optimization of physical and electrical properties.

In U. S. Patent Application No. 258, 645, the clips provide RF ground feedback and electrostatic ground feedback. RF signals pass from the needle to the metal surface of the record and along the record metal surface to a ground clip, usually located near the center of the record.

The path of the signal forms a series impedance with variable capacitance between the needle and the record metal surface, while containing an impedance representative of the inductance and resistance of the record between the clip and the needle. As the RF feedback impedance increases, less variation in the variable capacitance will affect the frequency response of the tuning circuit. Therefore, the sensitivity of the device is reduced by the RF ground impedance. In order to prevent such a decrease in sensitivity in accordance with the illustrations of the present invention, RF ground feedback is provided to the toe arm from the metal surface of the record. This eliminates the need for the use of clips as RF feedback. To form such an RF ground feedback, the capacitance formed between the metal surface of the record and the area of the arm frame on the record is used. The parameters for the frame and its position on the record must be precise. A detailed description of this capacitance and how to optimize it will be described with reference to figures 4a, 4b and 4c.

The drift reactance associated with the pickup device affects the frequency response of the tuning circuit. The capacitance change detected from the record (hereinafter referred to as ΔC) is very small, about 4 × 10 ⁻¹⁶ F (0.0004PF).

As described above, ΔC is an element of the tuning circuit, and the change in capacitance changes the frequency response of the tuning circuit from f ₁ to f ₂ . The tuning circuit is supplied with a constant amplitude and a constant high frequency signal of about 700 MHz. This signal is interconnected to the tuning circuit in inductive coupling with resistor 33 and the lead of the resistor. The double-voltage peak detector is interconnected to the tuning circuit through inductive coupling. The change in the frequency response of the tuning circuit due to the change in capacitance between the needle and the recorded information results in a change corresponding to the signal amplitude induced by mutual coupling in the peak detector. It is desirable to have the change in resonant frequency f ₂ / f ₁ as large as possible for a given capacitance change ΔC.

The obtained resonant frequency change is proportional to the change exceeding the minimum overall equivalent capacitance Ceq of the tuning circuit, i.e.,? C / Ceq. Therefore, it is desirable to increase the capacitance change DELTA C and decrease the minimum overall equivalent capacitance Ceq of the tuning circuit. The use of a tow arm assembly incorporating the invention shown in Figures 3a and 3b allows to optimize the physical and electrical properties of the device to reduce the minimum overall equivalent capacitance of the circuit.

4a is an equivalent circuit of reactance components of a tuning circuit in the apparatus shown in FIGS. 3a and 3b.

Inductor 51 and capacitor 52 contain the equivalent reactance of the transmission line formed by conductive part 45 and conductive frame 32-1 in FIG. As in the above embodiment, capacitor 52 is about 0.45 PF and inductor 51 is about 0.005 microhan. In FIG. 4, the reactance device in dotted line 57 represents a drift reactance component that must be adjusted to maintain a moderate change in the resonant frequency of the tuning circuit with the change in capacitance of the record.

Variable capacitor 53 represents the capacitance change ΔC that occurs as the record rotates between the needle and the metal surface on the record medium. Capacitor 54 connected in parallel with capacitor 53 represents the minimum capacitance between the needle and the record metal surface. In the embodiment described above, this capacitance is on the order of 0.1 to 0.15 PF.

Capacitor 56 connected in parallel with capacitor 52 in FIG. 4A shows the capacitance between the conductive element of needle assembly 38 and the ton arm 32-1. This capacitance is inversely proportional to the distance between the toe arm and the needle. By increasing the distance between the needle assembly 38 and the toe arm 32-1 (e.g. by increasing the opening 44 in the toe arm 32-1), the capacitor 56 can be reduced, but as the distance between the needle and the toe arm frame increases, The impedance 55 of the equivalent circuit becomes large. Impedance 55 represents the equivalent resistance 55-1 to the record and the equivalent impedance 55-2 between the needle and the return to the RF ground, and this also moves the RF signal over the record until the RF signal reaches the return to the RF ground. Proportional to distance. The larger the equivalent impedance 55, the less the change in capacitor 53 will affect the frequency response of the tuning circuit.

In order to explain the influence of the size of the opening 44 of the mold on each of the parameters 55 and 56 of the light circuit of FIG. 4A, the opening area of the needle assembly 38 and the enlarged mold 32-1 through the openings of FIGS. This is an enlarged view of the top and side views respectively.

In the enlarged view of FIGS. 4B and 4C, the needle assembly 38 includes needle 38-2, needle support 38-3 and lead connector 38-1. The needle feeder 38-3 mechanically holds the needle 38-2 so that the needle tip reaches the desired position in the record groove. Lead connector 38-1 makes an electrical connection to the conductive electrode of needle 38-2. For a description of the structure in which the needle 38-2 is used, reference may be made to "information reproduction device needle" of US Patent Application No. 286,657. Sleeve assembly 58 contains flammable connector 58-1 and lead 58-2. Sleeve assembly 58 connects mechanically and electrically conductive component 45 to needle assembly 38. Flammable connector 58-1 mechanically secures conductive part 45 to needle support 38-3 and leads 58-2 bonded to conductive part 45 for electrical coupling between conductive part 45 and conductive electrode of needle 38-2. And wire connector 38-1.

The distribution capacitance (capacitor 56 of FIG. 4A equivalent circuit) between the tow arm 32-1 and the needle assembly in FIG. 4B is shown as capacitor 56-1. In FIG. 4C, the resistance of the ground feedback path and the inductance elements (impedance 55 of the equivalent circuit in FIG. 4A) are shown as impedance 55-3 in FIG. The size of opening 44 in frame 32-1 is chosen to allow for acceptable equilibrium between conflicting demands to reduce the value of distributed capacitance and reduce the value of impedance 55. The allowable equilibrium size is about 3.17 mm in the circular part of the opening with an adjacent grooved part about 4.57 mm wide and 10.16 mm long. As a result, the capacitor 56 of the equivalent circuit of FIG. 4A has a capacitance value of about 0.03PF.

4A, the capacitor 48 of the equivalent circuit is connected in series with the impedance 55 between the parallel coupling of the capacitors 53 and 54 and the ground end of the inductor 51. Capacitor 48 is shown in Figure 4c as capacitance elements 48-1 corresponding to the distribution capacitance between the ton arm 32-1 and the metal surface on record 43. By positioning the opening of the frame sufficiently far from the inner edge of frame 32-1 (through needle assembly 38), the conductive support frame 32 (grounded) with the record metal surface (grounded) for all operating positions (from the record edge to the record center) The low impedance path for RF signals modulated between -1 is evident. That is, the area of the record is overlaid by the frame even when the needle is at the record edge, and the area is large enough that the distribution capacitance between the metal surface and the frame provides a low impedance ground return path for the modulated RF signal for all operating positions.

In the above-described embodiment (about 13.66 mm as the distance from the groove edge of the opening 44 to the edge of the inner frame), the capacitor 48 in FIG. 4A has an equivalent capacitance of about 10PF. This capacitance should be about twice the size of capacitance 54 so that good performance can be achieved even when the distance between the record and the toe arm has changed by more than 25% due to the sound of the record. Increasing this capacitance increases pickup sensitivity, reduces radiation of RF signals, and minimizes pickup of drift RF signals. Also, since the capacitance depends on the distance between the two electrodes forming the capacitor, the distance between the record and the ton arm should keep the limit coefficient for the valley of the record as small as possible. The titration of the record edge overlap of the tow arm assembly is more easily achieved since the tow arm assembly has been simplified to the dual use of the conductive component 45 shown in FIGS. 3A and 3B. This can be observed by comparing the record part duplicated by the tow arm 32 in FIG. 2A with the record part duplicated by the tow arm 32-1 improved in FIG. 3A.

Claims (1)

As described in the text and shown in the drawings, an information reproducing dispute for reproducing information recorded on a record medium, comprising a first device for setting a reactance which is changeable according to the recorded information, and a conductive support frame or the like. A flexible mounted conductive component, comprising: first and second ends connected to the support frame such that the first end is movable, the second end having first and second ends connected to the first device. For electrically forming the transmission line having the support frame and mechanically supporting the first device to construct a tuning circuit containing the reactance represented by the reactance of the device. Pickup device.

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