JPH0325344Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a distortion reduction circuit for frequency modulated wave signals. It is an object of the present invention to provide a distortion reduction circuit that can reduce the second-order distortion of the information signal, and thus can suitably perform FM demodulation of a frequency modulated wave signal reproduced from, for example, an information signal recording disk with a good signal-to-noise ratio (SN ratio). do.

When a binary digital signal as shown in Figure 1A obtained by digital pulse modulation such as pulse code modulation (PCM) is applied to an information signal such as an audio signal or a video signal to a frequency modulator, the frequency modulator A frequency modulated wave signal (hereinafter also referred to as "FM signal") shown in FIG. When this FM signal is FM demodulated, it becomes the demodulated signal shown in FIG. 1C. However, if distortion (especially secondary distortion) occurs for some reason when the above-mentioned FM signal is transmitted through the transmission line, as shown in Figure 1D, the positive half cycle and negative half cycle of the FM signal waveform The symmetry with the half cycle is lost, and the output signal waveform of the FM demodulation circuit becomes as shown in Figure 1E, and a carrier component remains that cannot be removed by the filter.
Furthermore, the distortion component becomes an interference component and is FM demodulated, causing a code error. Therefore, it is necessary to reduce the second-order distortion of the FM signal before performing FM demodulation in order to reduce intersymbol interference.

The present invention satisfies the above requirements, and one embodiment thereof will be described below with reference to the drawings of FIGS. 2 to 4.

FIG. 1 shows a block system diagram of an embodiment in which the frequency modulated wave signal distortion reduction circuit according to the present invention is applied to an information signal recording disk reproducing apparatus previously proposed by the applicant. In the figure, 1 is an information signal recording disk (hereinafter referred to as "disc"), as previously disclosed by the applicant in Japanese Patent Application No. 52-25262 and others.
A main track is recorded as a series of intermittent pits in which a frequency modulated wave signal obtained by frequency modulating a single carrier wave with a main information signal, and a disc is located approximately in the middle between the track center lines of adjacent main tracks. Burst-shaped first and second tracking control reference signals f _P1 of a single frequency, which are in a band lower than the band of the frequency modulated wave signal, alternately every one rotation period.
and f _P2 are formed as a sub-track recorded as an intermittent pit row, and furthermore, f _P1 ,
A third tracking control reference signal f _P3 is recorded in the main track of the switching connection portion of f _P2 . Further, this disk 1 does not have a guide groove for tracking the regenerated needle, and has an electrode function.

Here, the main information signal is, for example, a signal obtained by digitally modulating a 4-channel information signal, divided into predetermined sections, and a synchronization signal, an error correction code, an error check code, and a synchronization signal, an error correction code, an error check code, and It is assumed that the digital signals added to the address signal and forming one frame are a digital signal sequence that is synthesized in time series in units of one frame.

The disk 1 on which the FM signal obtained by frequency modulating a carrier wave of, for example, about 7 MHz with this digital signal sequence and the tracking control reference signals f _P1 to f _P3 is mounted on a turntable (not shown).
It is placed on top and rotated synchronously at, for example, 900 rpm, and the bottom surface of the regeneration needle 2 shown in FIG. 1 slides on its surface. Regeneration needle 2 is cantilever 3
A permanent magnet 4 is fixed to the base side of the other end of the cantilever 3 . The portion of the cantilever 3 to which the permanent magnet 4 is fixed is surrounded by a tracking coil 5 and a jitter correction coil 6 which are fixed to the reproducing device. Since the left and right coil parts of the jitter correction coil 6 are wound in the same phase, the jitter correction coil 6 is simultaneously attracted to or repelled by the permanent magnet 4 depending on the polarity of the jitter correction signal input to the input terminal 7. Therefore, the cantilever 3 moves directly in the track tangential direction X of the disk 1, and can correct jitter caused by surface runout or eccentricity of the disk 1. Further, the tracking coil 5 generates a magnetic field in a direction perpendicular to the magnetic field direction of the permanent magnet 4, and moves the cantilever 3 to any position in the track width direction Y according to the polarity of the tracking error signal from the tracking servo circuit 8. Displace it in the direction and by the amount of displacement depending on its size.

An electrode (not shown) is fixed by vapor deposition on the end face of the regenerating needle 2 on the outlet side. The pick-up circuit 9 is a resonant circuit whose resonant frequency changes in response to changes in the capacitance formed between the electrode of the reproduction needle 2 and the disk 1 in accordance with the intermittent pit rows;
A circuit that applies a constant frequency to this resonant circuit, a circuit that detects the amplitude of the high frequency signal from the resonant circuit whose amplitude changes according to the change in capacitance, and a circuit that detects the amplitude of the high frequency signal that changes in amplitude according to the change in the capacitance. It consists of a preamplification circuit. This pick-up circuit 9
The high frequency signal extracted from the above, that is, the mixed signal of the frequency modulated wave signal and the first to third tracking control reference signals is supplied to the distortion reduction circuit 10 of the present invention, while a part of it is branched. The signal is then supplied to the tracking servo circuit 8.

The tracking servo circuit 8 selects and extracts the tracking control reference signals f _P1 to f _P3 from the reproduced mixed signal, respectively.
A tracking error signal obtained by differentially amplifying the envelope detection outputs of f _P1 and f _P2 is output to the tracking coil 5. However, f _P1 for the main track,
Since the recording position relationship of f _P2 changes every rotation period of disk 1, the tracking control reference signal
The tracking polarity is switched by a switching pulse generated based on the detection output of f _P3 . Note that when the tracking servo circuit 8 receives a kick instruction signal at the input terminal 11, the tracking polarity is switched accordingly, and at the same time, the reproducing needle 2 is forcibly moved by one track pitch or more in the track width direction. A signal for transferring to the tracking coil 5 is output to the tracking coil 5.

On the other hand, the frequency modulated wave signal in the reproduced mixed signal taken out from the pickup circuit 9 may have second-order distortion due to the following reasons.In order to reduce this, the reproduced frequency modulated wave signal The signal is supplied to the distortion reduction circuit 10 according to the present invention. here,
The frequency modulated wave signal and tracking control reference signal f _P3 are one modulated light beam obtained by modulating laser light with an optical modulator, while the tracking control reference signals f _P1 and f _P2 are obtained by modulating laser light with an optical modulator. The first modulated light beam is modulated by an optical modulator and is then modulated into a rectangular shape onto a disc-shaped recording master disc having a photosensitive agent layer formed on a glass substrate. The irradiation is focused on the area, and the position is 1/
A second modulated light beam is focused and irradiated in a circular shape at a position separated by about two track pitches. Thereafter, this recording master disk is subjected to a known development process and a disk making process to produce a stamper disk. Thus, the disk 1 was made by stamping this stamper board onto conductive plastic.

On the other hand, disk 1 uses the constant angular velocity method (CAV method)
Because the recording was formed at a certain frequency, the recording wavelength for a given frequency becomes shorter as you go from the outer circumference to the inner circumference of the disk. In particular, the recording wavelength near the innermost recording track becomes shorter when the recording frequency is high. Since the length is very short, close to the spot diameter of the first modulated light beam, a pit cannot be suitably formed. In particular, the frequencies of the frequency modulated wave signal are f ₀ and f ₁ corresponding to logic "0" and "1" of the digital signal series, respectively, but the spectrum of this digital signal series contains many high frequency components. Therefore, it is necessary to secure a predetermined signal-to-noise ratio for this high-frequency component, so a wider frequency shift is required than when the main information signal is a multiplexed signal of an analog video signal and an analog audio signal. .

Therefore, the frequency modulation wave signal recorded on the disk has a large frequency change, and especially on the disk inner recording track where the relative linear velocity between the playback needle 2 and the disk 1 is slow, this is due to the limitations of laser beam irradiation technology. Since the recording wavelength is close to the short wavelength, pits cannot be formed properly. Furthermore, the moldability of the disk using the stamp (differences in plating thickness, etc.) becomes worse as the inner recording track area approaches.

For this reason, the frequency modulated wave signal reproduced from disk 1 often has second-order distortion, especially in the frequency modulated wave signal reproduced from the main track on the inner side of disk 1. Almost no second-order distortion occurs in the frequency modulated wave signal reproduced from the main track within most of the recording range where the relative linear velocity is above a predetermined value, excluding the inner circumferential side.)

The distortion reduction circuit 10 is a circuit for reducing secondary distortion contained in the frequency modulated wave signal reproduced from the above-mentioned inner recording track, and FIG. 3 shows a circuit diagram of one embodiment thereof. In FIG. 3, reference numeral 15 denotes a reproduction frequency modulated wave signal input terminal, which is connected to the base of an NPN transistor Q ₁ via a DC blocking capacitor C ₁ . The base of the transistor Q ₁ is connected to a power supply terminal via a resistor R ₁ and a variable impedance element VR in series, and is grounded via a resistor R ₂ . Also R ₃ is transistor Q ₁
The collector resistor _R4 is an emitter resistor, and _C2 is a bypass capacitor to compensate for the deterioration of high frequency characteristics that becomes a problem when operating in the nonlinear region, which will be described later. The above-mentioned transistor _Q1 and the like constitute a common emitter amplifier, and as will be described later, when reducing distortion, the value of the variable impedance element VR is varied to operate in a nonlinear region.

The collector output terminal of the transistor _Q1 is connected to a resistor via a coupling capacitor _C3 and a limiter 12, respectively.
It is connected to an integrating circuit consisting of R ₅ , capacitor C ₄ , and resistor R ₆ . This integrating circuit is connected via an amplifier 17 to an impedance control terminal of a variable impedance element VR. That is, the variable impedance element VR is configured to have its impedance varied according to the output signal level of the amplifier 17.

Next, the operation of the circuit shown in FIG. 3 will be explained.
When the frequency modulated wave signal reproduced from the main track where the reproducing needle 2 is located relatively on the outer circumferential side of the disk 1 enters the input terminal 15, the input frequency modulated wave signal reaches the operating point of normal class A operation. The signal is inverted and amplified by the set emitter grounded amplifier, taken out from the collector of the transistor _Q1 , and supplied to the limiter 12, where it is converted into a rectangular wave. This rectangular wave is supplied from the output terminal ₁₆ to the FM demodulation circuit ₁₃ shown in FIG _.
It is integrated by an integrating circuit consisting of: The time constant of this integrating circuit is selected to be sufficiently large so that changes in the average DC level of the input rectangular wave can be detected. When there is no second-order distortion in the reproduced frequency modulated wave signal, the symmetry of the waveform is maintained, so the average DC level of the rectangular wave is a substantially constant value. The output voltage of this integrator circuit is passed through an amplifier 17 as a control voltage for the variable impedance element VR to control the impedance of the variable impedance element VR, thereby maintaining the operating point of the common emitter amplifier consisting of the transistor _Q1 at the optimum value of that of the class A amplifier.

On the other hand, the frequency modulated wave signal reproduced from the main track on the inner side of the disk 1 is supplied from the input terminal 15 to a common emitter amplifier consisting of a transistor _Q1, etc., where it is amplified and then supplied to the limiter 12. , the average DC level of the output rectangular wave signal of the limiter 12 changes from before. In other words, the frequency modulated wave signal reproduced from the inner track has second-order distortion as shown in FIG. 1D or FIG. Since the half cycles are not symmetrical, the H level period and L level period of the output rectangular wave of the limiter 12, which had a duty cycle of about 50% when there was no secondary distortion, are now much larger than each other. In contrast, the average DC level changes compared to when there is no second-order distortion (Fig. 4C)
The average DC level of the rectangular wave output from the limiter 12 when the waveform enters the input terminal 15 is inverted and amplified by the transistor _Q1 and applied to the limiter 12. Since the H level period is shorter than the L level period, it becomes low. ).

Due to a change in the average DC level of the output rectangular wave of the limiter 12, the output voltage of the above-mentioned integrating circuit changes (in this case, becomes lower), so this output voltage is supplied via the amplifier 17 to the impedance of the variable impedance element VR. is variably controlled to a value larger than the previous value in accordance with the amount of change. As a result, the base bias of transistor Q ₁ is variably controlled, and the operating point of the common emitter amplifier made up of transistor _{Q 1 changes} . When a sine wave of
As shown in FIG. 2, the device operates in a nonlinear region in which a signal (collector voltage) having second-order distortion is outputted in a negative half-cycle period that is longer than a positive half-cycle period.

Therefore, at the base of transistor _Q1 of a common emitter amplifier operating in such a nonlinear region,
The polarity of the frequency modulated wave signal having second-order distortion reproduced from the inner track is changed in advance as shown in FIG. When selected and input, the second-order distortion components in the input frequency modulated wave signal are approximately canceled out, and the second-order distortion is reduced and the waveform becomes approximately symmetrical, as shown in Figure 4D, from the collector of transistor _Q1 . The resulting frequency modulated wave signal is extracted. Therefore, the average DC level of the output rectangular wave of the limiter 12 to which this frequency modulated wave signal is supplied is approximately the same value as when the outer track is reproduced.

The output rectangular wave of the limiter 12 is supplied from an output terminal 16 to an FM demodulation circuit 13 shown in FIG. 1, where it is FM demodulated and then output from an output terminal 14 to a decoder (not shown). According to this embodiment, a reproduced frequency modulated wave signal with no distortion regardless of the reproduction track position of the disk 1, or a reproduced frequency modulated wave signal with reduced second-order distortion if there is second-order distortion, is supplied to the limiter 12. Therefore, a rectangular wave with a substantially constant average DC level is always taken out from the limiter 12, and the demodulated signal output from the FM demodulation circuit 13 contains almost no carrier component or interference distortion component, and therefore is Even when decoding is performed by a decoder, accurate decoding can always be performed over the entire disk 1 without code errors due to intersymbol interference.

In the above embodiment, the impedance of the variable impedance element VR is variably controlled by the voltage obtained by integrating the output rectangular wave of the limiter 12, taking into account the variations in the disk 1, etc., and the operating point of the emitter grounded amplifier is varied. However, if there is no need to take into account variations in disk 1, the playback position of disk 1 of playback needle 2 is detected, and the detected position is where the second-order distortion becomes a problem. When the position is inner than the predetermined position, the grounded emitter amplifier may be operated in the nonlinear region described above. Furthermore, a common-base amplifier may be used instead of a common-emitter amplifier, and a differential amplifier may be used to control the current value of its constant current source to perform a similar second-order distortion reduction operation using nonlinear operation. You can also

Furthermore, in the above embodiment, the main information signal recorded on the disk 1 was explained as a digital signal sequence, but for example, a color video signal and a frequency modulated audio signal are each frequency division multiplexed and each carries a single carrier wave. When playing a disc on which FM signals obtained by frequency modulation are recorded, the playback FM
When second-order distortion occurs in the signal, the second-order distortion component of one of the color video signal and frequency modulated audio signal may mix into the band of the other, resulting in beat interference that may degrade image quality, etc. Therefore, it is also effective to use it to reduce distortion of FM signals reproduced from such disks.

In addition, for convenience of explanation, in the above embodiment, an example was explained in which the present invention was applied to a capacitance change reading type disc playback device proposed earlier by the applicant, but the present invention is not limited to this. It goes without saying that it can also be applied to playback devices for capacitance change reading type disks with tracking guide grooves, and playback devices that read recorded signals on disks using light beams. It can also be applied to transmission line systems that give second-order distortion to wave signals.

As mentioned above, the frequency modulated wave signal distortion reduction circuit according to the present invention includes an amplifier that has a variable bias circuit and is supplied with the frequency modulated wave signal, and converts the output signal of this amplifier into a rectangular wave. a limiter that outputs the signal to the FM demodulation circuit, and a nonlinear region having input/output characteristics that variably controls the variable bias circuit of the amplifier to cancel the distortion when the frequency modulated wave signal contains distortion. Since the frequency modulated wave signal with reduced distortion can be extracted from the amplifier,
Therefore, when the frequencies of the modulated signal of the frequency modulated wave signal and the carrier wave are close to each other, and the frequency shift of the frequency modulated wave signal is large, it is possible to remove most of the carrier wave that could not be removed conventionally using a filter. Distortion, especially due to unwanted sidebands of second-order distortion
It is possible to almost eliminate intersymbol interference caused by interference components in the FM demodulated output and deterioration in image quality when the modulation signal of the frequency modulated wave signal is a multiplexed signal of a color video signal and a frequency modulated audio signal. Further, the control means includes an integrating circuit that integrates the output rectangular wave of the limiter to obtain its average DC level, and controls the variable bias circuit so that the amplifier operates in a nonlinear region based on the change in the average DC level with respect to a predetermined constant value. Therefore, it is possible to automatically detect the presence of second-order distortion in the frequency modulated wave signal and automatically perform a distortion reduction operation each time. It is a frequency modulated wave signal reproduced from a disc, and the control means is variable so that the amplifier operates in a nonlinear region when the recording disc reproduction track is a track on the inner circumference side of a predetermined constant diameter value. Since it is a means for controlling a bias circuit, it has a number of features such as being able to effectively reduce distortion only for the reproduced frequency modulated wave signal of the inner track where the occurrence of second-order distortion is a problem.

[Brief explanation of the drawing]

Figures 1A to 1E show examples of the waveforms of a modulated signal, a frequency modulated wave signal when there is no distortion, an FM demodulated output signal thereof, a frequency modulated wave signal when there is distortion, and an FM demodulated output signal, respectively. 2 is a block system diagram showing an embodiment of the circuit of the present invention applied to an information signal recording disk reproducing device previously proposed by the applicant, and FIG. 3 is a block system diagram showing an embodiment of the circuit of the present invention. The circuit diagrams shown in FIGS. 4A to 4D are signal waveform diagrams for explaining the operation of the circuit shown in FIG. 3, respectively. 1... Information signal recording disk (disc), 2...
Reproduction needle, 9... Pickup circuit, 10... Distortion reduction circuit, 12... Limiter, 13... FM demodulation circuit, 14... Demodulation signal output terminal, 15... Frequency modulation wave signal input terminal, 16... Rectangle wave output terminal,
Q ₁ ... NPN transistor for amplification, R ₁ , R ₂ ... Resistor for base bias, VR ... Variable impedance element for base bias, R ₅ , R ₆ ... Resistor for integration circuit, C ₄ ... Capacitor for integration .

Claims (1)

[Claims for Utility Model Registration] (1) An amplifier that has a variable bias circuit and is supplied with a frequency modulated wave signal, converts the output signal of the amplifier into a rectangular wave, and outputs the rectangular wave to an FM demodulation circuit. and a control that variably controls a variable bias circuit of the amplifier to operate the amplifier in a nonlinear region having input/output characteristics that cancel out the distortion when the frequency modulated wave signal includes distortion. A frequency modulated wave signal distortion reduction circuit comprising means for extracting a frequency modulated wave signal with reduced distortion from the amplifier. (2) The control means integrates the output rectangular wave of the limiter to obtain an average DC level of the rectangular wave, and controls the amplifier in the non-linear region by a change in the average DC level with respect to a predetermined constant value. The distortion reduction circuit for a frequency modulated wave signal according to claim 1, which is an integrating circuit that controls the variable bias circuit to operate. (3) The frequency modulated wave signal is a frequency modulated wave signal reproduced from a recording disk using a constant angular velocity method, and the control means controls the reproduction track of the recording disk to a track on the inner circumference side of a predetermined constant diameter value. 2. The frequency modulated wave signal distortion reduction circuit according to claim 1, which is means for controlling the variable bias circuit so that the amplifier operates in the non-linear region when .