JP2659464B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus for a video signal, and more particularly to an FM carrier whose phase is reset every horizontal cycle corresponding to the leading edge of a horizontal synchronizing signal, The present invention relates to a magnetic recording / reproducing apparatus that corrects jitter of a reproduced signal by using a specific portion of a reproduced FM carrier as a reference burst signal.

[0002]

2. Description of the Related Art A video signal reproduced by a recording / reproducing apparatus usually has a fluctuation in a time axis of a waveform, that is, a jitter. Correcting this jitter is important for ensuring the stability of the reproduced image. Therefore, in the case of a magnetic recording / reproducing apparatus such as a VTR for broadcasting which employs a direct FM recording method for directly recording and reproducing an NTSC signal by FM modulation, a color burst inserted every horizontal scanning period of a video signal is used. The signal is used as a reference signal, and a jitter detection signal is formed from a time-base variation at a specific zero-cross point of the color burst signal to correct the jitter.

On the other hand, in the case of a magnetic recording / reproducing apparatus such as a home VTR adopting a low-frequency conversion recording method of a color signal, a color burst signal is not added to a video signal.
Usually, a specific portion at the rise or fall of the horizontal synchronization signal is detected to generate a jitter detection signal, and the jitter is corrected based on the jitter detection signal.

[0004] However, the horizontal synchronizing signal is also usually superimposed with random noise of phase and level, and this noise causes the accuracy of the jitter detection signal to decrease. This decrease in accuracy makes it difficult to sufficiently correct jitter, and thus causes a problem that the reproduced image becomes unstable.

Therefore, for example, Japanese Patent Application Laid-Open No. 63-274290
Japanese Patent Application Laid-Open Publication No. H11-163873 discloses a method capable of detecting jitter contained in a reproduced signal with high accuracy. That is, at the time of recording the video signal, the F / F modulated based on the video signal
The phase of the M carrier is reset for each horizontal cycle in correspondence with the leading edge of the horizontal synchronization signal. As a result, an FM carrier whose phase is synchronized with the leading edge of the horizontal synchronization signal is recorded. Also, at the time of reproducing the video signal, the F gate gated by the horizontal synchronization signal demodulated from the reproduced FM carrier.
The M carrier is used as a reference burst signal, so that a highly accurate jitter detection signal can be obtained.

Further, Japanese Patent Application Laid-Open No. Hei 1-264492 discloses a jitter detecting device capable of reducing the discontinuity of the FM carrier phase due to the above-described reset and preventing a demodulation error. I have. That is, the phase continuity compensation signal is added to the front porch portion immediately before the leading edge of the horizontal synchronization signal, and the level of the compensation signal is adjusted to shift the frequency of the FM carrier. As a result, the discontinuity of the phase of the FM carrier due to the reset is reduced.

As described above, the carrier reset methods disclosed in the above publications have high jitter correction accuracy and can contribute to stabilization of reproduced images.

[0008]

On the other hand, after a high-frequency carrier is FM-modulated based on a video signal to generate a primary FM carrier, the frequency is shifted to a low frequency to generate a low-frequency FM carrier. (Secondary FM carrier) recording method is known. According to this method, when a low-frequency carrier is directly FM-modulated and recorded (conventionally, the frequency of a carrier to be FM-modulated is 15
MHz), there is an advantage that unnecessary higher harmonic components are less likely to be included in the second FM carrier and the linearity is better. In particular, a high frequency carrier is transferred to an HDTV (High-D
This is effective when FM modulation is performed based on a wideband video signal such as a video signal of efinition television. However, a disadvantage is that during FM modulation, i.e.
Even if the above-described carrier reset is performed on the next FM carrier, the frequency is shifted and the phase is shifted at the same time, so that the phase of the secondary FM carrier is not synchronized with the horizontal synchronization signal. On the other hand, in the method of directly FM-modulating a low-frequency carrier, the FM carrier contains many unnecessary harmonic components, and also causes various problems described later.

For example, a video tape recorder (hereinafter referred to as V
As shown in FIG. 5, an FM demodulator provided in the delay line driver 101 and the delay line driver 101
And a low-pass filter (LPF) 103 connected to the output of the full-wave rectifier circuit 102. The end of the delay line 104 is short-circuited. Now, FIG.
Assume that an ideal FM carrier free of unnecessary harmonic components as shown in FIG. 6B has been recorded and reproduced based on a video signal having a waveform as shown in FIG. The reproduced FM carrier is formed into a square wave via a high gain limiter circuit and the like, and then supplied to the delay line driver 101. The composite wave of the square wave and the square wave delayed and reflected by the delay line 104 is supplied to the full-wave rectifier circuit 102. In this way, from the full-wave rectifier circuit 102 to the LPF 103, FIG.
As shown in (c), a pulse signal whose rising edge is synchronized with the zero cross point of the FM carrier is supplied. This pulse signal has its carrier component removed by the LPF 103, and FIG.
As shown in (d), an ideal video signal without distortion is demodulated.

On the other hand, when a low-frequency carrier is directly FM-modulated, as shown in FIG. 6E, the FM carrier becomes a square wave due to the inclusion of many unnecessary harmonic components. In addition, since the frequency of the FM carrier shifts due to the superposition of the harmonic component, the zero cross point is shifted as shown in FIG. 6E as compared with the ideal FM carrier shown in FIG. 6C. . Full-wave rectifier circuit 1
02 to the LPF 103 as shown in FIG.
A pulse signal that detects a shifted zero-cross point of the FM carrier including a harmonic component is supplied. As a result, the video signal demodulated by removing the carrier component of the pulse signal by the LPF 103 has a problem that distortion occurs as shown in FIG.

The most problematic factor for increasing the distortion and moiré of the demodulated signal is the third harmonic component among the harmonic components contained in the FM carrier (the third harmonic component is the FM carrier component). Are the spectral components of
Its center frequency and modulation index are each three times the center frequency and modulation index of the FM carrier).
The third harmonic component will be described below with specific numerical values.

As shown in FIG. 7B, a carrier whose gray level frequency is 13 MHz is FM-modulated based on a MUSE signal having a frequency band of 9 MHz as shown in FIG. 7A. I do. However, the deviation after the FM modulation is ± 3.5 MHz, and the degree of pre-emphasis applied to the MUSE signal is 12 dB (about 4 times).

Since the frequency band of the FM carrier is considered to be 2 × (the deviation + the frequency band of the video signal), in this case, the upper limit of the frequency band of the FM carrier (shown in FIG. 7B) is 13+ ( 3.5 × 4 + 9) = 36 [MHz] (1) The center frequency (shown in FIG. 7C) of the third harmonic component of the FM carrier is 13 × 3 = 39 [MHz], and the upper limit value of the frequency band of the third harmonic component (FIG. 7).
13 (c)) and the lower limit (not shown) are respectively 13 × 3 + (3.5 × 4 × 3 + 9) = 90 [MHz] 13 × 3- (3.5 × 4 × 3 + 9) = − 12 [MHz]... (2) (note that the broken lines shown in FIGS. 7B and 7C indicate negative aliasing components, respectively).

As is apparent from FIGS. 7B and 7C while comparing the numerical values of the above (1) and (2), when the frequency of the carrier is low, the third harmonic component is reduced to the FM carrier. 7B, it cannot be separated even by the LPF 103 (FIG. 7D shows the FM to be recorded after the high-frequency cut by the LPF 103).
The frequency band of the carrier is shown, and the broken line in FIG.
Shows the second harmonic component). As a result, unnecessary third harmonic components and folded negative harmonic components adversely affect FM demodulation, resulting in increased distortion of the demodulated video signal and increased moiré. Furthermore, when the distortion of the video signal is large, demodulation may not be performed. Such a problem is caused by the usual VT
This also occurs in a pulse count type FM demodulator often used in R.

A primary object of the present invention is to perform frequency conversion while maintaining the phase synchronization state of a primary FM carrier with respect to a horizontal synchronization signal, thereby achieving a low-frequency secondary FM carrier free from unnecessary harmonic components. Is to get

[0016]

A magnetic recording / reproducing apparatus according to the first aspect of the present invention includes the following means to solve the above-mentioned problems. That is, while oscillating the carrier having the first frequency,
The above carrier is FM-modulated based on the video signal,
FM modulation means (for example, an FM modulation circuit with an external reset function) for generating an M carrier, generates a pulse signal whose phase is synchronized with a horizontal synchronization signal included in a video signal,
By supplying the pulse signal to the modulation means, carrier reset means (for example, an FM modulation circuit with an external reset function and Carrier reset pulse generation circuit), reference signal generation means (for example, a clock generation circuit) for generating a frequency conversion signal having a first reference frequency and having a phase synchronized with the horizontal synchronization signal, the primary FM carrier and the frequency conversion signal (For example, a frequency shift circuit) that extracts only the component of the difference between the signals synthesized by the frequency converting means, and converts the center frequency of the primary FM carrier to the lower frequency side. Low-pass filter means (for example, a low-pass filter) for generating a second-order FM carrier having a center frequency set at the center

However, in the above configuration, the first frequency and the first reference frequency are set such that a lower limit of a frequency band of a sum component of the signals synthesized by the frequency conversion means is an upper limit of a frequency band of the difference component. It is set to exceed.

According to a second aspect of the present invention, there is provided a magnetic recording / reproducing apparatus which, in addition to the configuration of the first aspect, further comprises the reference signal generating means and the low-pass filter means having respective outputs. A second reference frequency included in the AFC reference frequency signal generated by the reference signal generation means and a frequency of a specific portion of the secondary FM carrier are compared every horizontal period, and a voltage corresponding to the frequency deviation is determined. An automatic frequency control circuit including frequency comparison means (for example, a frequency comparison circuit) for negatively feeding back a frequency error signal having a level to the input side of the FM modulation means is provided. Further, a magnetic recording / reproducing apparatus according to the invention of claim 3
Claim 1 or Claim 1
Item 2. In addition to the configuration of Item 2, the first frequency and the first
The quasi-frequency is further a third harmonic of the first FM carrier.
The lower limit of the frequency band of the wave component is
When converted to the low-frequency side by synthesis, the above difference component
Is set to exceed the upper limit of the frequency band of
It is characterized by.

[0019]

According to the first aspect of the present invention, the FM modulating means oscillates a carrier having a first frequency (for example, several times the frequency of a conventional carrier subjected to FM modulation) and converts the carrier into a video signal. FM modulation is performed on the basis of this to generate a primary FM carrier. It is desirable that the DC voltage level of this video signal is corrected to a constant value and pre-emphasis is performed.

The carrier reset means generates a pulse signal whose phase is synchronized with the horizontal synchronizing signal included in the video signal, and supplies the pulse signal to the FM modulating means, thereby shifting the phase of the primary FM carrier horizontally. Reset is performed every horizontal period corresponding to a specific portion of the synchronization signal. The specific portion of the horizontal synchronization signal may be the leading edge of the horizontal synchronization signal, or may be the specific portion of the horizontal synchronization signal corresponding to the convergence of the frequency shift of the FM carrier due to the pre-emphasis. .

The reference signal generating means has a first reference frequency, and as an important feature of the present invention, generates a frequency conversion signal whose phase is synchronized with the horizontal synchronization signal.

The frequency conversion means synthesizes the primary FM carrier input from the FM modulation means and the frequency conversion signal input from the reference signal generation means.

The low-pass filter means extracts only the difference component of the signal synthesized by the frequency conversion means,
A second FM carrier having a center frequency set to a second frequency obtained by converting the center frequency of the primary FM carrier to a lower frequency side is generated.

However, the first frequency and the second frequency are set such that the lower limit of the frequency band of the sum component of the signals synthesized by the frequency conversion means exceeds the upper limit of the frequency band of the difference component. Have been.

Since the phase of the primary FM carrier and the phase of the frequency conversion signal are both synchronized with the horizontal synchronization signal, the phase of the secondary FM carrier is also synchronized with the horizontal synchronization signal. This is explained as follows.

The time when the carrier reset is performed is defined as time t _0.
It is assumed that the primary FM carrier C (t) at time t ₀ is represented by the following sine wave. C (t ₀ ) = sin (ω _c t ₀ + m _f × v (t ₀ )) (3) In the above formula, each symbol is: ω _c : the central angular frequency m _f of the primary FM carrier m _f : Modulation index v (t ₀ ): value v (t) = ∫v ^* (t) dt at time t ₀ of a function obtained by integrating video signal v ^* (t) with time t
(The integration constant is assumed to be 0). It is also assumed that the phase difference between the primary FM carrier and the horizontal synchronization signal at time t ₀ has become 0 [rad] due to the carrier reset.

The frequency conversion signal S (t) is also a sine wave, and is given by the following equation at time t ₀ . S (t ₀ ) = sin (ω _sh t ₀ + φ) (4) In the above formula, ω _sh : angular frequency of the frequency conversion signal φ: horizontal synchronization with the frequency conversion signal at time t ₀ It means the phase difference with the signal.

However, 1 which is considered to include the third harmonic component
Next FM carrier C ₃ (t) is expressed as _{C 3 (t) = sin (} ω c t + m f v (t)) + k · sin {3 × (ω c t + m f v (t))} You. The symbol k in the above equation is the amplitude coefficient of the third harmonic component.

From the above equations (3) and (4), the primary FM
FM carrier Cs of the carrier and the frequency-converted signal is synthesized (t) at time _{t 0, Cs (t 0)} = sin {(ω c t 0 + m f × v (t 0)) - (ω sh t _{0 + φ)} + sin {} (ω c t 0 + m f × v (t 0)) + ( expressed as _{ω sh t 0 + φ)}} .

The low-pass filter means takes out only the difference component of the synthesized FM carrier Cs (t) and outputs it as a secondary FM carrier. As a result, the resulting secondary FM carrier C ₂ (t ₀ ) is , C ₂ (t ₀ ) = sin ｛(ω _c t ₀ + m _f × v (t ₀ )) − (ω _sh t ₀ + φ)｝ = sin ｛(ω _c −ω _sh ) t ₀ + m _f × v ( t ₀ ) −φ)｝ (5)

Now, the phase difference φ is determined, for example, 0
Assuming that [rad] is set, the phase difference between the secondary FM carrier and the horizontal synchronization signal is also 0 from the above equation (5).
[Rad]. Thus, even if the frequency conversion is performed, the phase difference between the secondary FM carrier and the horizontal synchronizing signal becomes 0 [rad] every one horizontal cycle.

The first frequency of the carrier oscillated by the FM modulator and the second frequency which is the center frequency of the secondary FM carrier are the sum of the components of the FM carrier synthesized by the frequency converter. Since the lower limit of the frequency band is set so as to exceed the upper limit of the frequency band of the difference component, it is possible to separate a secondary FM carrier having a small unnecessary component. As a result, the reproduced F
By using the FM carrier gated by the horizontal synchronization signal demodulated from the M carrier as a reference burst signal, a highly accurate jitter detection signal can be obtained.

Further, since the unnecessary components contained in the secondary FM carrier are small, the accuracy of demodulation is improved,
Image quality is improved. Note that the carrier reset method has an advantage that a blanking period of a video signal can be shortened because it is not necessary to insert a burst signal for jitter detection into the video signal.

Next, according to the configuration of the second aspect, the frequency comparing means inputs the AFC reference frequency signal from the reference signal generating means, and inputs the secondary FM carrier from the low-pass filter means. The second reference frequency of the AFC reference frequency signal is compared with the frequency of a specific portion of the secondary FM carrier every one horizontal period, and a frequency error signal having a voltage level corresponding to the frequency deviation is converted to the FM modulation means. , For example, to a DC amplifier provided for correcting the DC voltage level of the video signal to a constant value.
As a result, an automatic frequency control circuit (AFC circuit) is configured, and the first frequency of the carrier oscillated by the FM modulator is stabilized without being affected by the temperature drift of the FM modulator and the frequency converter. Further, claim 3
According to the configuration, the third harmonic component of the primary FM carrier is
The frequency band is reduced by combining with the frequency conversion signal.
Being mixed with the above difference components when converted to the band side
Secondary carrier with less unnecessary components
Can be separated.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

A carrier reset FM modulator (hereinafter referred to as an FM modulator) provided in the magnetic recording / reproducing apparatus according to the present invention.
As shown in FIG. 1, an input terminal 10 to which a video signal is supplied, and an output terminal 11 to output a carrier (hereinafter, referred to as an FM carrier) that is FM-modulated based on the video signal. . FM output from output terminal 11
The carrier is supplied to a recording circuit (not shown) at a subsequent stage and is recorded on a recording medium (not shown) such as a magnetic tape.

The FM modulator further includes a DC amplifier 1 connected to the input terminal 10. The DC amplifier 1 has a function of correcting the sync tip level and the pedestal level of the horizontal synchronization signal included in the video signal to a constant level regardless of the level of the video signal. The output of the DC amplifier 1 is connected to a pre-emphasis circuit 2 for enhancing the high-frequency amplitude of the video signal to improve the image quality.

The output of the pre-emphasis circuit 2 is connected to an FM modulation circuit 3 having an external reset function as a modulation means. In the FM modulation circuit 3 with the external reset function,
As will be described in detail later, a primary FM carrier a ₁ having a high center frequency and a phase reset corresponding to a specific portion of the horizontal synchronizing signal is generated and output to the frequency shift circuit 4 at the subsequent stage. It has become so. In addition, primary FM
The center frequency of the carrier a _1, from the center frequency of the conventional FM carrier is set several times higher.

The frequency shift circuit 4 is composed of, for example, an analog multiplier, by synthesizing the frequency shift signal d which will be described later in the primary FM carrier a _1, a low-pass center frequency of the primary FM carrier a ₁ Shift to the side.
A low-pass filter (hereinafter referred to as LPF) 5 is connected to the output of the frequency shift circuit 4.
Is connected to the output terminal 11 described above. LPF
5 are cut component of the sum of the primary FM carrier a ₁ and a frequency shift signal d, and a harmonic component, and generates and outputs a second FM carrier a _2.

On the other hand, the FM modulator further includes a synchronization separation circuit 9 connected to the input terminal 10 for extracting and separating a horizontal synchronization signal from a video signal. The clock generation circuit 8 is connected to the output of the synchronization separation circuit 9. The clock generation circuit 8 generates an original oscillation clock pulse whose phase is synchronized with the horizontal synchronization signal and whose frequency is stable.

The carrier reset pulse generating circuit 7 is connected to each output of the clock generating circuit 8 and the synchronizing separation circuit 9, and based on the horizontal synchronizing signal supplied from each of the circuits 8 and 9 and the original oscillation clock pulse, generates a carrier reset pulse. Generate b. The carrier reset pulse b is supplied from the carrier reset pulse generator circuit 7 to the external reset function with FM modulation circuit 3 is adapted to be used in the reset of the primary FM carrier a ₁ phase.

The clock generation circuit 8 generates the frequency shift signal d whose phase is synchronized with the horizontal synchronization signal. The frequency shift signal d is supplied from the clock generation circuit 8 to the frequency shift circuit 4.
Further, the clock generation circuit 8 generates an AFC (Automatic Frequency Control) reference frequency signal e based on the original oscillation clock pulse.

The frequency comparison circuit 6 outputs the above-mentioned secondary FM carrier output from the LPF 5, the above-mentioned AFC reference frequency signal e,
And a horizontal synchronizing signal output from the synchronizing separation circuit 9. The horizontal synchronizing signal supplied to the frequency comparing circuit 6 is a gate signal for allowing the frequency comparing circuit 6 to perform frequency comparison for one horizontal period from the fall of the horizontal synchronizing signal to the next fall. ing.

The frequency error signal c generated to have a predetermined voltage level based on the result of the frequency comparison in the frequency comparison circuit 6 is negatively fed back to the DC amplifier 1 and superimposed on the video signal. With this, F with external reset function
The instantaneous frequency of the carrier oscillated by the M modulation circuit 3 is AF
The frequency always coincides with the frequency of the C reference frequency signal e.

As shown in FIG. 4, the FM modulation circuit 3 with the external reset function has a pair of monostable multivibrators 12 and 13. The inverted outputs of the monostable multivibrators 12 and 13 are connected to the other monostable multivibrators 12 and 13, respectively. Further, both poles of capacitors C1 and C2 are connected to the monostable multivibrators 12 and 13, respectively, and one ends of resistors R1 and R2 are connected to the capacitors C1 and C2, respectively. The other ends of these resistors R1 and R2 are connected to the output of the pre-emphasis circuit 2 described above.

As a result, the FM modulation circuit 3 with the external reset function oscillates a carrier having a frequency having a time constant determined by the resistors R1 and R2 and the capacitors C1 and C2, and inputs the carrier from the pre-emphasis circuit 2. Primary FM carrier a ₁ whose carrier frequency is modulated by a video signal
Is output.

The monostable multivibrator 12.1
A diode D is connected to each input side to which the inverted outputs of the three are connected.
The cathode side of 1 · D2 is connected. These diodes D1 and D2 have their anode sides connected to each other, and a carrier reset pulse b is supplied from the carrier reset pulse generation circuit 7 to these anode sides.

In the above configuration, when a video signal as shown in FIG. 2A is supplied to the synchronization separation circuit 9 via the input terminal 10, the horizontal synchronization signal is separated from the video signal in the synchronization separation circuit 9. You. At the same time, the video signal is supplied to the DC amplifier 1 via the input terminal 10, and the frequency error signal c transmitted from the frequency comparison circuit 6 is superimposed,
Further, the high frequency is emphasized by the pre-emphasis circuit 2.

For example, as shown in FIG. 2B, an overshoot appears at the falling edge and the rising edge of the horizontal synchronizing signal included in the video signal. Therefore, the carrier reset pulse generation circuit 7 sets the primary FM carrier at a stage where the frequency change of the primary FM carrier falls within a predetermined range so that a phase error due to the overshoot of the falling and rising of the horizontal synchronization signal does not occur. , A carrier reset pulse b for resetting the phase is generated. Note that the carrier reset pulse b is generated from an original oscillation clock pulse whose phase is synchronized with the horizontal synchronization signal.

In this manner, the FM modulation circuit 3 with the external reset function supplies the primary FM carrier a ₁ whose phase has been reset by the carrier reset pulse b to the frequency shift circuit 4 as shown in FIG. . Further, the clock generation circuit 8 supplies a frequency shift signal d represented by, for example, a sine wave to the frequency shift circuit 4. The frequency shift circuit 4 synthesizes the primary FM carrier a ₁ whose phase has been reset and the frequency shift signal d.

As a result, the LPF 5 extracts the component of the difference between the frequency of the primary FM carrier a _{1 and} the frequency of the frequency shift signal d, that is, the secondary FM carrier a ₂ . Since both the phase of the primary FM carrier and the phase of the frequency shift signal are synchronized with the horizontal synchronizing signal, FIG.
As shown in (e), as an important feature of the present invention, 2
The phase of the next FM carrier is also synchronized with the horizontal synchronization signal.

Here, as shown in FIG. 3A, the video signal has a MUSE (Multiple S) having a frequency band of 9 MHz.
ub-Nyquist Sampling Encoding), for example, the gray level frequency f _ch of the primary FM carrier a ₁ is 47 MHz, the deviation is ± 3.5 MHz,
The degree of pre-emphasis for the MUSE signal is set to 12
dB (about 4 times), the frequency f _sh of the frequency shift signal d is set to 34
MHz.

It is assumed that the frequency band of the FM carrier is 2 × (the deviation + the frequency band of the video signal). Based on this, the upper limit B of the frequency band of the primary FM carrier a ₁
As shown in FIG. 3B, W ₊₁ and lower limit BW ₋₁ are respectively BW ₊₁ = 47 + (3.5 × 4 + 9) = 70 [MHz] BW ₋₁ = 47− (3.5 × 4 + 9) = 24 [MHz].

The gray level frequency f _cd of the difference component of the signal obtained by combining the primary FM carrier a ₁ and the frequency shift signal d and the gray level frequency f _cs of the sum component are f _cd = 47− 34 = 13 [MHz] _fcs = 47 + 34 = 81 [MHz] Also, the upper limit BW of the frequency band of the difference component
_{d + 1} is BW _{d + 1} = 13 + (3.5 × 4 + 9) = 36 [MHz] (1), and the lower limit BW _s−1 of the sum component frequency band is BW _s−1 = 81. − (3.5 × 4 + 9) = 58 [MHz] (2) Therefore, from the values of (1) and (2) above, 1
If the gray-level frequency f _ch of the next FM carrier a ₁ and the frequency f _sh of the frequency shift signal d are set as described above, the difference component and the sum component do not mix into each other's frequency bands. It is possible to separate and extract only the difference components.

Next, the lower limit BW- ₃ of the frequency band of the third harmonic component of the first-order FM carrier is BW- ₃ = 47.times.3- (3.5.times.4.times.3 + 9) = 141-51 = 90 MHz. (3), and the lower limit BW _d-3 of the frequency band of the third harmonic component included in the difference component is: BW _d−3 = (47 × 3-34) − (3.5 × 4 × 3 + 9) = 56 MHz (4) Therefore, from the values of (3) and (4) above, the difference component and the third harmonic component contained in the difference component do not mix into each other's frequency bands, and are similarly separated by the LPF 5 to obtain the difference component. Is removed.

Note that, depending on the method of performing the carrier reset, it may take several cycles of the FM carrier until the phase of the FM carrier converges to the phase of the horizontal synchronization signal. In this case, performing the carrier reset at a high frequency requires less time than the carrier reset at a low frequency, even though the FM carrier wave number required until the phase converges is the same. That is, the FM modulator according to the present invention also has an advantage that the flaw after FM demodulation caused by discontinuity of the phase of the FM carrier before and after the carrier reset can be reduced.

[0057]

As described above, the magnetic recording / reproducing apparatus according to the first aspect of the present invention oscillates the carrier having the first frequency, and FM-modulates the carrier based on the video signal to perform the primary FM carrier. And a pulse signal whose phase is synchronized with a horizontal synchronizing signal included in the video signal, and the pulse signal is supplied to the FM modulating means, thereby making the phase of the primary FM carrier horizontal. Carrier reset means for resetting every horizontal period corresponding to a specific portion of the synchronization signal, reference signal generation means having a first reference frequency, and generating a frequency conversion signal whose phase is synchronized with the horizontal synchronization signal; Frequency conversion means for synthesizing the primary FM carrier and the frequency conversion signal, and extracting only the difference component of the signal synthesized by the frequency conversion means, And a low-pass filter means the center frequency of the M carriers to generate a second FM carrier center frequency is set to a second frequency which is converted to the low frequency side, the first frequency and the first reference frequency, the The configuration is such that the lower limit of the frequency band of the sum component of the signals synthesized by the frequency conversion means exceeds the upper limit of the frequency band of the difference component.

Therefore, a carrier reset is performed on the primary FM carrier having a high frequency, and the frequency of the primary FM carrier is converted into a low frequency, thereby generating a secondary FM carrier having a small unnecessary harmonic component. be able to. As a result, a highly accurate jitter detection signal can be obtained by using the FM carrier gated by the horizontal synchronization signal demodulated from the reproduced FM carrier as a reference burst signal. Further, since the number of unnecessary components contained in the secondary FM carrier is small, there is an effect that demodulation accuracy is improved and image quality is improved.

A magnetic recording / reproducing apparatus according to a second aspect of the present invention, as described above, is connected to each output of the reference signal generating means and the low-pass filter means, and generates an AFC reference frequency signal generated by the reference signal generating means. Is compared with the frequency of the specific part of the secondary FM carrier every horizontal period, and a frequency error signal having a voltage level corresponding to the frequency deviation is input to the input side of the FM modulation means. This is a configuration including an automatic frequency control circuit including a frequency comparison unit that performs negative feedback.

Therefore, the first frequency of the carrier oscillated by the FM modulating means is stabilized without being affected by the temperature drift of the FM modulating means and the frequency converting means. This has the effect of improving image quality. Magnetic recording and reproduction according to the invention of claim 3
As described above, the apparatus is configured according to claim 1 or claim 2.
And the first frequency and the first reference frequency
Is the third harmonic component of the first FM carrier.
The lower limit of the frequency band is determined by synthesis with the frequency conversion signal.
When converted to the low frequency side, the frequency of the difference component
The configuration is set to exceed the upper limit of the bandwidth.
You. Therefore, the frequency of the third harmonic component of the first FM carrier
The wave number band is reduced to a low band by combining with the frequency conversion signal.
When converted to the side, it can be mixed into the above difference component
No secondary FM carrier with less unnecessary components
Claim 1 or Claim 3
This is achieved in addition to the effect of the configuration of claim 2.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a carrier reset FM modulator included in a magnetic recording / reproducing apparatus according to the present invention.

FIG. 2 is a waveform diagram illustrating a reset state of a phase of a primary FM carrier and a synchronous state of a phase of a secondary FM carrier after frequency conversion.

FIG. 3 is an explanatory diagram showing frequency bands of various signals input and output in the carrier reset FM modulator.

FIG. 4 is a circuit diagram of an FM modulation circuit with an external reset function using a monostable multivibrator.

FIG. 5 is a block diagram showing a configuration of an FM demodulator using a delay line provided in a conventional VTR.

FIG. 6 is a waveform diagram illustrating an operation of the FM demodulator for an ideal FM carrier and an FM carrier including unnecessary harmonic components.

FIG. 7 shows a conventional FM that does not convert the frequency of an FM carrier.
FIG. 3 is an explanatory diagram illustrating frequency bands of various signals input / output in a modulator.

[Explanation of symbols]

3 FM modulation circuit with external reset function (FM modulation means and carrier reset means) 4 Frequency shift circuit (frequency conversion means) 5 LPF (low-pass filter means) 6 Frequency comparison circuit (frequency comparison means) 7 Carrier reset pulse generation circuit (carrier) resetting means) 8 clock generator circuit (reference signal generating means) a ₁ 1-order FM carrier a ₂ 2-order FM carrier b carrier reset pulse c frequency error signal d frequency shift signals (frequency-converted signal) e AFC reference frequency signal

Claims (3)

(57) [Claims] 1. A carrier having a first frequency is oscillated, and the carrier is FM-modulated based on a video signal.
FM modulation means for generating a primary FM carrier; generating a pulse signal whose phase is synchronized with a horizontal synchronizing signal included in a video signal; and supplying the pulse signal to the FM modulation means, thereby providing the primary FM carrier. Carrier reset means for resetting the phase of the horizontal synchronization signal every one horizontal period in accordance with a specific portion of the horizontal synchronization signal; Means, frequency conversion means for synthesizing the primary FM carrier and the frequency conversion signal, and taking out only a difference component of the signal synthesized by the frequency conversion means, wherein the center frequency of the primary FM carrier is low. Low-pass filter means for generating a second-order FM carrier in which the center frequency is set to the second frequency converted to the first frequency; The first reference frequency is set such that the lower limit of the frequency band of the sum component of the signals synthesized by the frequency conversion means exceeds the upper limit of the frequency band of the difference component. Recording and playback device. 2. A second reference frequency which is connected to each output of said reference signal generation means and said low-pass filter means and has an AFC reference frequency signal generated by said reference signal generation means, and a specific part of said secondary FM carrier. And an automatic frequency control circuit including frequency comparison means for negatively feeding back a frequency error signal having a voltage level corresponding to the frequency deviation to the input side of the FM modulation means. The magnetic recording / reproducing apparatus according to claim 1, wherein: 3. The first frequency and the first reference frequency.
Is the third harmonic component of the first FM carrier.
The lower limit of the frequency band is determined by synthesis with the frequency conversion signal.
When converted to the low frequency side, the frequency of the difference component
It is set to exceed the upper limit of the bandwidth
Magnetic recording instrumentation of claim 1 or claim 2,
Place.