JPS5937632B2 - Signal reproduction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal reproduction method, and when reproducing a high frequency signal such as a video signal in which at least a portion of the high frequency signal is frequency modulated and recorded on a recording medium, the reproduced frequency By controlling the characteristics of circuits such as equalizing amplifiers, preamplifiers, and filters according to the modulated carrier frequency,
An object of the present invention is to provide a system capable of reproducing the above-mentioned high frequency signals such as video signals in a relatively narrow band with good /N.

In general, when a video signal is recorded and played back by a magnetic recording/playback device, in addition to the video signal, there is also modulation noise caused by the recording and playback process, amperes caused by passing the video signal through circuits such as amplifiers, and contact between the magnetic tape and the magnetic head. Noise such as contact noise that occurs depending on the situation is mixed into the reproduced signal.

However, in currently commercially available household magnetic recording and playback devices, the relative linear velocity between the magnetic tape and the video head is relatively high, and the playback output of the video head is also relatively large, so the amplifier noise mentioned above is almost eliminated. This is not the order in question. On the other hand, conventionally, in order to record and reproduce video signals in a narrow band, the relative linear velocity between the magnetic tape and the video head is relatively low, for example, about 10 times the normal linear velocity. The playback output of the head decreases (for example, in a home magnetic recording/playback device, the video head output of 7.5 V- at a relatively high normal linear velocity is
There is a drawback that the voltage decreases to 1.7V- at +P-P of the above linear velocity.
P.

Although the modulation noise decreases due to this reduction in the reproduction output, the amplifier noise hardly changes, so there is a drawback that the amplification noise becomes relatively large.

Further, the farther away the noise is from the frequency modulation (FM) carrier frequency, the larger the modulation index becomes, and the amplifier noise has a disadvantage in that it has an adverse effect on the demodulated video signal.
The present invention aims to eliminate the above-mentioned drawbacks, and embodiments thereof will be described below with reference to the drawings.

FIG. 1 shows a basic program diagram of a first embodiment of the system of the present invention.

In the figure, reference numeral 1 denotes a magnetic tape on which video signals are recorded using the same recording system as that of an ordinary household magnetic recording/reproducing device. That is, in the recording system, for example, a color video signal is supplied to a low pass filter with a cutoff frequency of 3 MHz and a band filter with a pass band width of 3 to 4 MHz, and
It is separated into a luminance signal component of ~3 MHz and a color signal component of 3~4 MHz. The luminance signal component is frequency modulated, and the chrominance signal component is frequency-converted to a frequency band lower than that of the frequency-modulated luminance signal, and then both are mixed and amplified by a recording amplifier. Recording is performed on the magnetic tape 1 by a rotary head using a known method. In this embodiment, in order to enable low linear velocity magnetic recording and playback, the Japan Electronics Industry Association unified standard,
Alternatively, the relative linear velocity is set to be the relative linear velocity of the magnetic tape 1 and the rotary head 2 of a general household magnetic recording/reproducing apparatus based on the unified standard for automatic tape loading type magnetic recording/reproducing apparatus of % inch.

Further, the frequency deviation of the carrier wave that is frequency-modulated by the luminance signal is set to a somewhat low frequency range (for example, 2.9 to 4.3 MHz) to provide a recordable frequency band. The relative linear velocity between the magnetic tape 1 and the rotary head 2 during reproduction is the same as that during recording, and the rotary head 2 is arranged to trace the video track on the magnetic tape 1.

The reproduced signal reproduced by the rotary head 2 passes through a rotary transformer, a slip ring, etc., and then is supplied to an equalizing amplifier 4 and a low-pass filter 9 through a preamplifier 3, respectively. The reproduced signal supplied to the equalization amplifier 4 is a control signal A, which is formed from the demodulated video signal supplied from the control signal generator 5 and has an opposite phase and the same voltage as shown in FIGS. 2A and B, respectively. , b (indirectly, depending on the carrier frequency of the reproduced FM luminance signal).

That is, since the equalizing amplifier 4 is composed of variable capacitance diodes Dl and D2 as shown in FIG. 1, by applying the control signals A and b, its equivalent circuit becomes as shown in FIG. 3A. The frequency characteristics change as shown in FIG. 3B. For example, when the carrier frequency of the reproduced FM signal is 3 MHz, the characteristics of the equalizing amplifier 4 are changed as shown by the solid line in FIG. 3B, and when it is 4 MHz, as shown by the broken line in FIG. 3B. Ru. FIG. 4A is a diagram showing an example of a noise distribution state when a signal obtained by frequency modulating (modulation index 1) a carrier wave of 3 MHz with a modulation signal of 1 MHz is recorded and reproduced.

The figure shows a signal obtained by frequency modulating a 3 MHz carrier wave with a 1 MHz signal, recording it on a tape, and reproducing it, using a spectrum analyzer. 2, 3 in the figure,
The 4MHz peak is the first lower side wave, carrier wave,
This is the first upper side wave, and the noise is the remaining part excluding these. Note that in the figure, the frequency on the horizontal axis is a numerical value before the frequency modulated wave is demodulated. In the figure, the solid line 1 shows the noise distribution state at the output of the preamplifier 3 (input to the equalizing amplifier 4), and the dashed line shows the noise distribution state at the output of the equalizing amplifier 4, which has a peak value at 4.3 MHz. Also, the dashed line is 3MHz
The noise distribution state at the output of the equalizing amplifier 4 having a peak value is shown respectively. As is clear from FIG. 4A, the noise that is a problem in the present invention, such as amplification noise, is large and is distributed in a frequency range higher than the FM carrier frequency, and the noise distribution changes depending on the characteristics of the equalizing amplifier 4. I understand that. Here, in the conventional case, the characteristics of the equalizing amplifier were generally set near the upper limit of the deviation of the FM carrier frequency, that is, in the case of this embodiment, 4.3 MHz, and were fixed at a constant value. The noise distribution state at the output is always as shown by the dashed line in FIG. 4A.

On the other hand, in the present invention, the characteristics of the equalizing amplifier 4 are controlled according to the carrier frequency of the reproduced FM signal by using the control signals A,
Since the carrier frequency of the reproduced FM signal is 3 MHz, the noise distribution changes from the noise distribution state shown by the dashed line in Fig. 4A to the noise distribution state shown by the dashed line, as shown by the arrow. It can be seen that it is possible to reduce

In addition, in FIG. 4A, the output level (curve 1) of equalizing amplifier 4 is higher than the input side level (curve 1) in the vicinity of 2 MHz and 3 MHz, but this is due to the fact that the equalizing amplifier 4 This is because, as shown in FIG. 3B, the characteristic No. 4 has a peak in the high frequency range in order to correct the drop in the reproduced signal level in the high frequency range.

Therefore, if you compare before and after the equalizing amplifier 4, the noise level will increase on the output side, but at the same time (if a signal exists) the signal level will also increase, and the S/
When considering the effect of improving the N ratio, it is necessary to consider the signal after it has been equalized by an equalizing amplifier so that the signal can be demodulated normally, that is, the signal input to the demodulator 8. The reproduced signal whose characteristics have been corrected by the equalizing amplifier 4 is supplied to a high-pass filter 6, where the low-pass conversion carrier color signal component whose upper limit of the frequency band is selected to be about 1 MHz is removed, and
Control signals (for example, those of 1 MHz or less) included in the reproduced signal are also removed.

The reproduced FM signal generated by this high-pass filter 6 is
After the amplitude fluctuation is removed by the limiter 7, the signal is supplied to the demodulator 8, where it is FM demodulated. This demodulator 8
The noise distribution at the output of is shown in FIG. 4B. The curves in FIG. B correspond to the curves shown in FIG. A, respectively.

However, the curve indicates the signal to be demodulated and reproduced. Demodulator 8
The reproduced luminance signal demodulated and extracted is guided to a mixer 12, which will be described later, and is also supplied to the control signal generator 5 for controlling the equalization amplifier 4.

On the other hand, the reproduced signal supplied to the low-pass filter 9 is extracted here with only the low-pass converted carrier color signal component.

This low-pass converted carrier color signal is supplied to a frequency converter 10, frequency-converted by a reference signal from an input terminal 11, and returned to a carrier color signal having the original color subcarrier frequency. The reproduced carrier color signal extracted from the frequency converter 10 is supplied to the mixer 12, where it is added to the reproduced luminance signal. As a result, a reproduced color video signal with a good S/N ratio is taken out from the mixer 12 and guided to the output terminal 13. Note that since the control signal generator 5 supplies the equalizing amplifier 4 with the control signals A and b having opposite phases and the same voltage, the control signals A and b are canceled in the equalizing amplifier 4, and the control signals A and b are has a very small influence on the output of the equalizing amplifier 4, but the
If a low-pass filter (not shown) is provided between the control signal generator 5 and the control signal generator 5 so as to keep the output of the control signal generator 5 below a predetermined frequency (for example, 1 MHz), an equalizing amplifier Even if the control signals A and b are not completely canceled due to the relatively low performance of the control signals A and B, the influence caused by the mixing of the control signals A and b can be reduced.

That is, since the control signal (for example, one of 1 MHz or less) mixed into the reproduced signal in the equalization amplifier 4 is blocked by the high-pass filter 6 in the next stage, it has little effect on the reproduced luminance signal. Furthermore, when using an equalizing amplifier 4 that has relatively high performance (well-balanced) and can almost completely cancel out the control signals A and b, it is necessary to cut off the high-frequency components of the demodulated luminance signal. (without providing the above-mentioned low-pass filter (not shown) in the control signal generator 5 or between the demodulator 8 and the control signal generator 5), the reproduced luminance signal is mixed with the control signals A and b. It is possible to reduce the influence of

FIG. 5 shows a circuit diagram of a main part of a second embodiment of the system of the present invention. In the same figure, the same parts as in Figure 1 are given the same reference numerals.
The explanation will be omitted. In FIG. 5, reference numeral 14 denotes an input terminal, through which a high-frequency signal recorded at high density in a narrow band with a relatively low relative linear velocity between the video head and the recording medium is reproduced at the same linear velocity as when it was recorded. The input signal is amplified by an amplifier (not shown). The reproduced signal that has entered this input terminal 14 is supplied to an equalizing amplifier 4', which will be described later, while
The signal is supplied to a low-pass filter 9. The carrier color signal which has been frequency-converted to a low frequency band and extracted from the low-pass filter 9 is supplied to the color processing circuit 15, where it is frequency-converted to a carrier color signal having the original color subcarrier frequency. At the same time, time axis fluctuations caused by recording and reproduction are removed by the automatic phase control circuit. The output signal of the color processing circuit 15 is supplied to the mixer 12 as a reproduced carrier color signal after signal components of 3 MHz or less are removed by a bandpass filter 16. 17 is 3MHz from the demodulated video signal
A low-pass filter is used to remove the above-mentioned frequency components, and the reproduced luminance signal extracted from this low-pass filter 17 is supplied to the mixer 12, and is also supplied to the input terminal 18 of the control signal generator 5'. Ru.

The reproduced luminance signal supplied to this input terminal 18 is a video signal of negative polarity, and is applied to the base of the NPN transistor Q3, and from the collector of this transistor Q3 is used to set the characteristic deviation width of the equalizing amplifier 4'. It is applied to the base of NPN transistor Q4 through variable resistor R1.
The reproduced luminance signal taken out from the collector of this transistor Q4 is applied to the base of a PNP transistor Q6 through an NPN transistor Q5 and a capacitor. Here, the resistor R2 is a variable resistor for setting the clamp level for clamping the sync chip (the tip of the sync signal), and the reproduction brightness is a negative video signal supplied to the base (point O) of the PNP transistor Q6. The sync chip level of the signal is clamped to a constant level. The reproduced luminance signal taken out from the emitter of the transistor Q6 is attenuated by a capacitor C2 etc. to remove high frequency components in the demodulated luminance signal which cannot be controlled by the control signal generator 5'. , and NPN transistor Q8, and are supplied to the base of the PNP transistor Q, respectively. A Zener diode ZD in the direction shown is connected between the emitter of this PNP transistor Q and the positive DC power supply terminal. This results in transistor Q
The signal taken out from the emitter 9 is shifted by a predetermined voltage by the Zener diode ZD and applied to the base of the PNP transistor QlO. The resistor R3 connected between the emitter of the transistor QlO and the power supply terminal is a semi-fixed resistor for balancing with the resistor R4 connected between the collector of the transistor QlO and the ground, and is also connected in parallel to the resistor R3. capacitor C1
is a trimmer capacitor for high frequency phase compensation. Signals taken out from the collector and emitter of transistor QlO are applied to the bases of NPN transistor Qll and PNP transistor Ql2, respectively. Here, the signal waveforms (signal waveforms at points [F] and [F]) applied to the bases of the transistors Qll and Ql2 have opposite phases and the same voltage. Therefore, a signal a is applied as a control signal to the variable capacitance diode D1 from the collector of the transistor Qll through the PNP transistor Ql3, and a signal a is applied as a control signal to the variable capacitance diode D1 from the collector of the transistor Ql2.
The signal b applied to the variable capacitance diode D2 through l4 has opposite phases to each other, as shown in FIG. 2A and B, respectively.
and the same voltage. As a result, the capacitances of the variable capacitance diodes Dl and D2 change depending on the levels of the control signals A and b. Therefore, the NPN transistor Q1 amplifies the NP
The reproduced signal from the input terminal 14 taken out from the emitter of the N transistor Q2 is processed by the equalizing amplifier 4' according to the level of the demodulated luminance signal reproduced by the control signals A and b from the control signal generator 5'. The high-pass filter 2 is given a transmission characteristic that varies in the range shown from the curve V in Figure 6.
It leads to 0.

Note that R5 is equalization amplifier 4! This is a variable resistor for explaining the characteristic compensation level (indicated by G in FIG. 6). The reproduced FM signal from which low-frequency noise has been removed by the high-pass filter 20 is supplied to the limiter 7. By the way, in a low-pass filter that is generally supplied with a demodulated luminance signal, 3
A relatively large amount of delay is provided in order to remove noise components of MHz or higher and to synchronize the time with the reproduced conveyed color signal supplied to the mixer 12 through the color processing circuit 15.

In such a case, the control signal A formed from the demodulated luminance signal
, b are delayed in time. If a problem occurs in such a case, the demodulated luminance signal that is the output of the demodulator 8 should be passed through the low-pass filter 21 shown in FIG. 5, which has a small delay time.
and this output is input to input terminal 1 of the control signal generator 5'.
8, the delay amount of the control signals A and b can be reduced. In addition, this low-pass filter 2
By selecting the cutoff frequency of 1 lower than the cutoff frequency of the high-pass filter 20, even if the video signal is mixed into the FM signal at the equalization amplifier 4', it is removed by the high-pass filter 20. 5/ can be configured more easily.

In the above embodiment, the relative linear velocity between the magnetic tape and the video head is relatively low to record signals in a narrow band and at high density.
We have explained the case of reproducing at the same relative linear velocity as during recording, but below we will explain normal recording and reproducing with a relatively high linear velocity and high density in a narrow band with a relatively low linear velocity using the same magnetic recording and reproducing device. The case where recording and reproduction are switched will be explained. In Fig. 5, SWl is a changeover switch for switching between normal playback and high-density playback, and when playing back a normally recorded magnetic tape, it is closed and connected to the fixed contact N, and high-density recording is performed. When reproducing a magnetic tape, it is switched and connected to the fixed contact L. R6 is equalization amplifier 4 during normal reproduction
This is a variable resistor for setting the characteristic of ' to a predetermined value.
In addition, in the figure, the broken line part including the changeover switch SWl and the variable resistor R6 is inserted in place of the solid line between the connection points of the broken line part and the solid line part when such switching is necessary. In a device capable of such switching, the solid line between the connection point of the broken line section and the solid line section is deleted. With the above configuration, when reproducing a magnetic tape recorded at high density, the characteristics of the equalizing amplifier 4' are controlled according to the carrier frequency of the reproduced FM signal in the same manner as described above, reducing amplification noise etc. A reproduced image can be obtained.

In addition, for normal playback (at this time, the magnetic tape drive system and head rotation drive system are controlled so that the relative linear velocity between the tape and the head is naturally high), the selector switch S
By switching Wl to the fixed contact N, only the predetermined voltage from the variable resistor R6 is applied to the base of the transistor Q9, so that the characteristics of the equalizing amplifier 4' can be set to the predetermined characteristics (as described above). At linear velocities of the level used in general household magnetic recording and reproducing devices on the market, amplification and the like can be ignored.

In each of the above embodiments, a demodulated luminance signal is used as a signal corresponding to the carrier frequency of the reproduced FM signal, but the present invention is not limited to this. Then other signals can be used.

As described above, the signal reproduction method of the present invention frequency-modulates the luminance signal of a color video signal, converts the carrier color signal to a lower frequency band than the frequency-modulated luminance signal, and mixes and multiplexes both signals. a reproduction head for reproducing the obtained multiplexed signal from a recording medium on which it has been recorded; a preamplifier for amplifying the signal reproduced by the reproduction head; and a signal from the preamplifier is supplied and reproduced. an equalizing amplifier whose frequency giving a peak value response is changed according to the carrier frequency of the frequency modulated luminance signal to match the carrier frequency; a frequency-modulated luminance signal from the high-pass filter; a limiter for removing amplitude fluctuations of the frequency-modulated luminance signal from the high-pass filter; a demodulator for demodulating the frequency-modulated luminance signal from the limiter to obtain a reproduced luminance signal; a control signal generator that supplies a control signal of the same voltage with opposite polarity to the equalizing amplifier in response to the reproduced luminance signal; and a low-pass filter that generates a low-pass converted carrier chrominance signal from the signal from the preamplifier. , a frequency converter that returns the low-pass converted carrier color signal from the low-pass filter to a reproduced carrier color signal having the original color subcarrier frequency, a reproduced luminance signal from the demodulator, and a reproduced luminance signal from the frequency converter. Since it consists of a mixer that mixes carrier color signals to obtain a reproduced color video signal, it is possible to obtain a reproduced signal with a good S/N ratio with less influence of amplification noise etc.
Compared to the case where the resonant point frequency of the reproducing head is controlled to match the carrier frequency of the reproducing frequency modulation signal, the circuit for controlling the transmission characteristics of the above transmission circuit can have a relatively simple configuration, and the resonant frequency is amplified by the preamplifier. Since the frequency characteristics of the signal after the signal is varied, the level of the control signal for variation is relatively small compared to the level of the amplified reproduced signal, and the control signal with the same voltage and opposite phase is used as the control signal. Because the control signals are used to cancel each other,
These factors combine to reduce the influence of the control signal on the reproduced signal, and since the control signal passes through a high-pass filter for filtering the luminance signal after frequency characteristics are controlled, the control signal also has a smaller influence on the reproduced signal. As the frequency characteristics are controlled by the equalizing amplifier, the response in the low range is improved compared to when the resonant frequency of the playback head is changed. There is little change in characteristics, making design and manufacturing easier, especially for consumer equipment that mainly uses the lower sideband of frequency modulated waves, and comparing the relative linear velocity between the recording medium and the reproducing head with a relatively high one. In the method of reproducing the multiplexed signal by switching when the relative linear velocity is relatively high, the characteristic of the equalizing amplifier is set to a constant predetermined characteristic when the relative linear velocity is relatively high; When the frequency is low, the characteristics of the equalizing amplifier are changed according to the carrier frequency of the reproduced frequency-modulated luminance signal so that the frequency that gives the peak value response matches the carrier frequency, so that the relative linear velocity is S/ that was able to reduce ampf noise etc. even with a low reproduction method
It has many features such as being able to obtain a good reproduction signal of N.

[Brief explanation of the drawing]

FIG. 1 is a basic program diagram of the first embodiment of the method of the present invention, FIGS. 2A and B are waveform diagrams for explaining the operation of FIG. An equalization circuit diagram for explaining the operation of the main part and a characteristic diagram for explaining the operation, FIGS. 4A and 4B are diagrams each showing an example of noise distribution for explaining the present invention, and FIG. FIG. 6 is a circuit system diagram of the main part of the second embodiment, and is a characteristic diagram for explaining the operation of FIG. 5. 3...1 preamplifier, 4,4t...equalizing amplifier, 5,5t...control signal generator, 6,20...
...High-pass filter, 8...Demodulator, 9,
17...Low pass filter, 10...Frequency converter, 12...Mixer, 16...
Bandwidth filter, Dl, D2...variable capacitance diode, SW pi...changeover switch.

Claims (1)

[Claims] 1. Frequency modulation of the luminance signal of the color video signal, frequency conversion of the carrier color signal to a lower frequency band than the frequency modulated luminance signal, and recording of a multiplexed signal obtained by mixing and multiplexing both signals. a reproducing head for reproducing the multiplexed signal from a recorded recording medium; a preamplifier for amplifying the signal reproduced by the reproducing head; and a preamplifier for amplifying the signal reproduced by the reproducing head; an equalizing amplifier whose frequency giving a peak value response is changed according to the carrier frequency to match the carrier frequency; a high-pass filter that filters a frequency-modulated luminance signal from the output of the equalizing amplifier; a limiter for removing amplitude fluctuations of the frequency modulated luminance signal from the filter; a demodulator for demodulating the frequency modulated luminance signal from the limiter to obtain a reproduced luminance signal; a control signal generator that supplies a control signal of opposite polarity and the same voltage to the equalizing amplifier; a low-pass filter that filters a carrier color signal that is lower-pass converted than the signal from the preamplifier; A frequency converter that returns the range-converted carrier color signal to a reproduced carrier color signal having the original color subcarrier frequency, and a reproduced luminance signal from the demodulator and the reproduced carrier color signal from the frequency converter are mixed and reproduced. A signal reproduction method characterized by comprising a mixer for obtaining a color video signal. 2. In a method of reproducing the multiplexed signal by switching the relative linear velocity between the recording medium and the reproducing head between relatively high and relatively low times, when the relative linear velocity is relatively high, the equalization is performed. The characteristics of the amplifier are set to constant predetermined characteristics, and when the relative linear velocity is relatively low, the frequency that gives a peak value response according to the carrier frequency of the reproduced frequency modulated luminance signal is made to match the carrier frequency. 2. The signal regeneration system according to claim 1, wherein characteristics of said equalizing amplifier are changed.