JPH0454437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chroma signal recording and reproducing circuit for a video tape recorder, and particularly to a chroma signal recording and reproducing circuit for a video tape recorder, and particularly for recording and reproducing chroma signals recorded together with a luminance signal, a pilot signal, and an audio signal by frequency multiplexing on the same video track. Regarding circuits.

As conventional video tape recorder (hereinafter referred to as VTR) technology, it has been proposed to use a pilot signal to improve tracking performance, and to frequency-modulate the audio signal and record it on the video track by frequency multiplexing to further improve the sound quality. ing.

A spectrum diagram of a signal recorded on a video track in the above method is shown in FIG.

In FIG. 1, 1a is an FM luminance signal, 1b is a low frequency converted chroma signal, 1c is a tracking control pilot signal, and 1d is an FM audio signal.

The problem is that the pilot signal 1c and FM audio signal 1d are reproduced as sideband signals of the chroma signal 1b, causing beat disturbance on the screen, and that spurious c±2p ( c: chroma frequency, p: pilot frequency), which also causes beat disturbance on the screen.

The above interference is caused by (1) that the chroma signal is an AM recording, (2) that the pilot frequency and FM audio frequency are close to the chroma signal band, and (3) that the recording level of the pilot signal and FM audio signal is not low enough. This is due to this.

Therefore, it would be possible to record by separating the respective frequencies sufficiently or by converting the chroma signal to an FM signal, but in this case, a wide bandwidth would be required, which would reduce the recording density and make it impractical. It won't happen. Alternatively, it is possible to sufficiently lower the recording level of the pilot signal and FM audio signal, but this would cause problems with tracking control characteristics and sound quality, making it impractical.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a system that allows tracking control pilot signals and FM audio signals to be frequency-multiplexed and recorded together with chroma signals and FM brightness signals on a video track. An object of the present invention is to provide a chroma signal recording/reproducing circuit which is made less susceptible to interference from other sources.

In the present invention, sideband components of a chroma signal are nonlinearly emphasized and recorded, and conversely, during reproduction, they are nonlinearly de-emphasized. A conversion carrier generator that generates a conversion carrier for frequency converting a chroma signal has an oscillator that oscillates at the frequency of the chroma signal, and the oscillation output of this oscillator is a burst signal or a nonlinear signal in the recorded chroma signal before nonlinear emphasis. The phase is compared with the burst signal in the reproduced chroma signal after de-emphasis, and the phase of the conversion carrier is controlled according to the comparison result.

In FIG. 2, 2a is the frequency characteristic for the maximum amplitude signal (0 dB) of the chroma signal, and 2b is the frequency characteristic for the small amplitude chroma signal (-20 dB to -30 dB). The de-emphasis characteristics for this are shown in FIG. 5, where the characteristic for large amplitude chroma signals is 5a, and the characteristic for small amplitude chroma signals is 5b. The pilot signal and FM audio signal are small amplitude signals at the input of the dynamic de-emphasis circuit and are separated from c by 0.5 MHz or more, so they are suppressed by about 8 dB by the dynamic de-emphasis circuit. Spurious c±2p is also suppressed by about 3 dB if p is 0.1 MHz.

Figures 3 and 6 show characteristics that use both instantaneous companding characteristics and dynamic sideband characteristics, 3a,
6a is the characteristic for large amplitude signals, 3b and 6b are the characteristics for small amplitude signals, and effects similar to those in FIGS. 2 and 5 can be obtained. Further, FIGS. 4 and 7 show linear emphasis/de-emphasis characteristics.

FIG. 8 is a block diagram of a color signal processing circuit for a video tape recorder according to the present invention.

In the figure, a recording video signal is input to a terminal 1, and a chroma signal is selectively amplified by a BPF 2, an ACC amplifier 4, and an ACC detector 3. 5 is a burst emphasis circuit which normally enhances only the level of the burst signal by about 6 dB and records it. Reference numeral 35 denotes an emphasis circuit for a chroma signal including an emphasized chroma signal, and its input/output characteristics are as shown in FIG. 2, FIG. 3, or FIG. 4 as described above. The output of the emphasis circuit 35 is converted into a low frequency chroma signal by a frequency conversion circuit (hereinafter referred to as converter) 6, and mixed with an FM modulated luminance signal, an FM audio signal, and a tracking control pilot signal via an LPF 7. , are recorded on the magnetic tape 9 by the recording head 8. A low frequency converted chroma signal is selected by an LPF 11 from the signal reproduced by the reproduction head 10, and the low frequency chroma signal is amplified to a predetermined level by an ACC amplifier 12 and an ACC detector 13. 14 is a converter, converter 22
The output signal of the ACC 12 is converted into a chroma signal in a normal frequency band by being mixed with the converted carrier signal generated by the ACC 12 and the converted carrier signal selected by the BPF 21, and unnecessary spurious components are removed by the BPF 15. A comb filter circuit 16 removes crosstalk signals from adjacent tracks. Reference numeral 36 denotes a chroma signal de-emphasis circuit whose input/output characteristics are as shown in FIG. 5, FIG. 6, or FIG. A burst de-emphasis circuit 17 restores the level of the burst signal emphasized during recording. The reproduced chroma signal obtained at the output terminal 18 is mixed with the reproduced luminance signal and reproduced as a video signal.

On the other hand, the switches 19, 24, and 32 are switched to the illustrated positions during recording, and to the opposite positions during playback. The operation during recording will be explained. 20 is a burst gate circuit that extracts only the burst signal; during recording, the output signal of the ACC amplifier 4 is input to the phase detector 23 by a switch 19;
The phase detector 23 compares the phases of the burst signal from the burst gate 20 and the first carrier signal from the VCO 25, and controls the VCO 25 so that the oscillation frequency of the VCO 25 matches the carrier color signal frequency sc. A horizontal synchronizing signal or a signal equivalent thereto is input to the terminal 34 of the low-frequency carrier generating circuit 37, and the phase detector 30 receives this input signal and the oscillation of the VCO 31 whose frequency is divided by 1/n by the 1/n frequency dividing circuit 29. Compare the phase with the output. As a result, VCO3
Control is performed so that the oscillation frequency of 1 coincides with nH (H: horizontal scanning frequency). 28 is VCO
The phase shift circuit 26, which is a 1/8 frequency dividing circuit for the output signal of 31, generates a second carrier signal such that the recording color signal frequency has a predetermined frequency offset.

During playback, switches 19, 24 and 32 are switched to the switch positions indicated by black circles. The burst signal in the reproduced signal de-emphasized by the de-emphasis circuit 36 is transmitted to the burst gate 2.
0 and supplied to the phase detector 23. The output signal of the phase detector 23 is sent to the switch 2
4. Since it is supplied to the VCO 31 via the discriminator circuit 33 and the switch 32, the VCO
31 is controlled by the output signal of the phase detector 23. Further, the discriminator circuit 33 has a 1 value determined by the horizontal pulse supplied to the terminal 34.
The n pulses generated by the VCO 31 in each horizontal period are counted, and the VCO 31 is controlled to oscillate at nH in each horizontal period. Therefore, during reproduction, the VCO 31 is controlled by a signal corresponding to the phase difference between the first carrier signal and the burst signal generated by the freely oscillating VCO 25 and a signal corresponding to fluctuations in the oscillation frequency nH of the VCO 31. During both recording and playback, the sum signal of the output signal of the VCO 25 and the output signal of the phase shift circuit 26 is extracted by the BPF 21, and this sum signal is used as a conversion carrier to converter 6 (during recording) or converter 14 (playback). time). Thereby, the converters 6 and 14 convert the chroma signal into a predetermined frequency band.

Furthermore, in the NTSC system, the frequency of the low-band chroma signal must have an offset of an odd multiple of 1/2H between fields and an offset of 1/4H. For example, if the frequency of the low-frequency chroma signal, that is, the second carrier, is (47+1/
4) When set to H, the oscillation frequency of VCO31 is (47+
1/4)H×8=378H, and the frequency division ratio of the 1/n frequency dividing circuit 29 is selected to be n=378. Phase shift circuit 26 inverts the phase of the second carrier signal of one field by 180 degrees every horizontal period to generate a frequency offset between the fields.

In the PAL system, "1/4H between fields
The conditions are "to have an offset of an odd multiple of" and "to have an offset of 1/8H". For example, if the frequency of the low-frequency chroma signal, that is, the second carrier, is (47-1/8)H, the oscillation frequency of the VCO 31 is (47-1/8)H x 8 = 375H,
Select n=375. The phase shift circuit 26 delays or advances the phase of the second carrier signal in one field by 90 degrees every horizontal period. Therefore, the second
By frequency offset of the carrier, the low frequency chroma signal is recorded and reproduced at a frequency that satisfies the conditions of the NTSC system and PAC system described above.

Next, the chroma signal emphasis circuit 35 and de-emphasis circuit 36 will be explained. FIG. 9 shows an example of the emphasis circuit 35.

53 is a circuit with a transfer characteristic H(W), 54 is an adder, and the transfer characteristic of this circuit is 1+H(W). 10 and 11 are examples of the de-emphasis circuit 36.

The transfer characteristic of FIG. 10 is 1/1+H(W), and is an inverse circuit to the circuit of FIG. 9 described above. Therefore the 9th
When the output signal of the emphasis circuit 35 in the figure is input to the de-emphasis circuit 36 in FIG. input signal is restored.

The transfer characteristic in FIG. 11 is 1-H(W),
The overall transfer characteristic when connected to the emphasis circuit 35 is 1+H(W)×1-H(W)=1-H(W) ²
Therefore, an error occurs with respect to the input signal, but this is not a problem in practice.

A specific circuit example of the circuit 53 having the transfer characteristic H(W) will be described below.

In FIG. 12a, the input signal input to the terminal 201 is amplified by the amplifier 58, and the color subcarrier frequency sc (3.58MHz for the NTSC system, 3.58MHz for the PAL system) is
Trap circuit 5 that blocks signals near 4.43MHz)
6 to the limiter circuit 57, and an output signal is obtained at the terminal 202. In FIG. 12b, the horizontal axis represents frequency, the vertical axis represents relative gain, and 62 is the frequency transfer characteristic of the trap circuit 56. When the input signal at the terminal 51 is large, the limiter circuit 57 causes the output signal at the terminal 202 to be at a constant level almost regardless of the frequency of the input signal, and the amplitude limit level of the limiter 57 is sufficiently smaller than the input signal. The output signal of adder 54 has almost no emphasis characteristic. On the other hand, even when the input signal is small, the input level of the limiter circuit 57 is kept above the amplitude limit range of the limiter circuit 57 by the amplifier 58, so the output signal of the adder 54 has an emphasis characteristic. In this case color subcarrier frequency sc
Since the nearby signal is always attenuated at the terminal 202 due to the characteristics of the trap circuit 56, the signal level near sc in the output signal of the adder 54 is approximately equal to the input signal level of the terminal 51, as shown in FIG. It is possible to realize the characteristic of emphasizing only the sideband of the color signal.

FIG. 13 shows a circuit 5 that provides a transfer characteristic H(W).
This is a more specific circuit example than 3. transistor 10
3 operates as a grounded emitter amplifier, and has a capacitor 106 and an inductor 1 connected to the collector terminal.
07 series resonant circuit to obtain trap characteristics.
The resonance frequency of capacitor 106 and inductor 107 is 3.58MHz in NTSC system and 3.58MHz in PAL system.
Select 4.43MHz. The diodes 109 and 109' are limiters and limit the amplitude of the signal generated at the output terminal 202 to the ON voltage of the diodes.

FIG. 14 is an example of a circuit that provides a transfer characteristic H(W) for obtaining the emphasis characteristic shown in FIG.

The difference from FIG. 13 is that a resistor 110 is further provided in series with the series resonant circuit of the capacitor 106 and the inductor 107. This resistor 110 causes a capacitor 106 and an inductor 10
An output signal is obtained at the terminal 202 for an input signal having a resonance frequency of 7, that is, a color subcarrier frequency, and is added to the input signal by an adder 54. Therefore, as shown in FIG. 3, it is possible to realize the characteristic of emphasizing both the signal band near the carrier and the side band of the color signal.

FIG. 15 is a waveform diagram illustrating the waveform of the recording color signal emphasized by the aforementioned emphasis circuit 35.

a is the input signal of the emphasis circuit, b is the output signal of the trap circuit 56, c is the output signal of the limiter circuit 57, d is the output signal of the adder 54, and e is the burst gate pulse. The output signal of the adder 54, ie, the burst signal at the output end of the emphasis circuit 35, has a width expanded by the delay time generated in the circuit 53, as shown in FIG. 15d.

As explained in FIG. 8, the signal in FIG. 15d is frequency-converted and recorded and reproduced.
The output signals of the BPF 15 and the comb filter 16 are also substantially similar to the signals shown in FIG. 15d. In the embodiment shown in FIG. 8, the burst signal in the chroma signal after de-emphasizing the reproduced signal (FIG. 15 d) in the de-emphasis circuit 36 is extracted by the gate circuit 20 and supplied to the phase detector 23, and a carrier synchronized with the burst signal is extracted. Generating a signal. This is because, as mentioned above, the burst signal contained in the output signal of the comb filter 16 has distortion due to the emphasis as shown in FIG. 15d, so the burst signal cannot be extracted by the normal burst gate pulse shown in FIG. 15e. Because you can't. On the other hand, the output signal of the de-emphasis circuit 36 is similar to that shown in FIG. 15a, and only the burst signal can be extracted accurately by the burst gate pulse (FIG. 15e). Further, as mentioned above, since the distortion and width of the burst signal in the output signal of the emphasis circuit, that is, the reproduced chroma signal, differ depending on the configuration of the emphasis circuit 35, the burst signal of the output signal of the comb filter 16 is used to It is also undesirable to generate a carrier signal in terms of tape compatibility.
Furthermore, since the characteristics of the emphasis circuit 35 during recording change depending on the input level as described above, in FIG. ing. Also, since the characteristics of the de-emphasis circuit 36 during reproduction are similar, the burst signal level at the output end of the de-emphasis circuit 36 is made constant by the ACC detector 13 and the ACC amplifier 12.

16 to 24 show embodiments of the emphasis circuit of the present invention that can be easily integrated into an IC. Figure 16-2
Figure 0 is the characteristic of Figure 2, Figures 21 to 24 are the characteristics of Figure 3.
The characteristics of the figure are obtained.

In FIG. 16, a chroma signal supplied to an input terminal 201 is supplied via a transistor 203 to a differential amplifier consisting of transistors 204 and 205. Resistor 209 and capacitor 215 provide base bias for transistor 205;
08, the capacitor 220, and the inductor 219 provide the trap characteristic shown in FIG. 12b, and the load resistor 210 provides a chroma signal in which signals near the color subcarrier frequency are suppressed. transistor 20
6, 207 constitutes a limiter circuit. resistance 212
and capacitor 214 are for generating base bias of transistor 207, and resistor 211
is set to the same resistance value as the resistor 212, thereby balancing the voltage drops due to the base currents of the transistors 206 and 207, resulting in good limiter characteristics. A signal to the adder is obtained at the output terminal 202 via the load resistor 213. This circuit
When converting into an IC, the only pin required is the terminal 222, and the capacitors 215 and 214 are replaced by the resistors 209 and 222.
By choosing a value of 212, the IC is good at several tens of pF.
can be accumulated within

The difference between FIG. 17 and FIG. 16 is that the trap circuit is constructed from a parallel resonant circuit. At the color subcarrier number, capacitor 220 and inductor 2
Since the impedance of the resonant circuit No. 19 becomes large, the base voltages of the differential pair transistors 204 and 205 become equal, and no signal is generated at the load resistor 210.

The difference in Fig. 18 from Fig. 16 is that the trap circuit is not a simple series resonant circuit, but a resistor 20
8', capacitor 220, 220', inductor 2
19 constitutes a so-called bridge-type trap. This purpose is to reduce the inductance 21
This prevents deterioration of trap characteristics due to the DC resistance of inductance 219.
Rr, resistor 208', R208, capacitor 220,2
20' is respectively C220=C220' and inductance 219 is L219, then R208=4Rr, L219 and 2
If the resonance frequency due to ×C220 is selected as the color subcarrier frequency, an infinite degree of attenuation can be theoretically obtained.
If the attenuation of the trap is small due to the DC resistance Rr of the inductance 219, the characteristics shown in Fig. 2 cannot be obtained, and as a result, when the input signal level is large, the output level near sc in Fig. 2 2a rises. The output level of the SC varies depending on the input signal level, which is undesirable.

The difference between FIGS. 19 and 20 from FIG. 16 is that a series resonant circuit constituting a trap circuit is connected to the collectors of differential pair transistors 204 and 205. Resistor 209 and capacitor 21
5 is for bias generation, and its characteristics are the same as in FIG. 16.

In the above description, the differential pair transistor 20
4,205 has been described with a configuration in which the emitters are directly coupled, but it goes without saying that a configuration in which a resistor is inserted into the emitter may be used as long as the necessary gain is obtained.

The difference between FIG. 21 and FIG. 16 is that a resistor 221 is inserted in series with the series resonant circuit of an inductor 219 and a capacitor 220. A signal near a resonance frequency selected to be equal to the color subcarrier frequency is taken out to an output terminal 202 via a differential amplifier made up of transistors 204 and 205 and a limiter circuit made up of transistors 206 and 207. Therefore, as shown in FIG. 3, a characteristic is obtained in which the signal level near sc at the output of the emphasis circuit 35 changes depending on the input signal level.

The difference in FIG. 22 from FIG. 17 is that a resistor 221 is inserted in parallel to the parallel resonant circuit of an inductor 219 and a capacitor 220.

In FIG. 22, the same characteristics as in FIG. 21 can be obtained.

The difference between FIGS. 23 and 24 from FIGS. 18 and 19 is that a resistor 221 is inserted into the series resonant circuit of an inductor 219 and a capacitor 220.

The same characteristics as in FIG. 21 are also obtained in FIGS. 23 and 24.

As explained above, the circuits shown in FIGS. 16 to 24 require only a small number of pins when implemented as an IC, and the effect of implementing the circuit as an IC is large.

The difference between FIG. 25 and FIG. 20 is that a diode 3 is used instead of transistors 206 and 207.
A limiter circuit consisting of 01 and 302 is added. In the figure, the output terminal 202 is
The signal level is constant, and trap circuits 219 and 220 act on the limited signals. Therefore, it has the characteristic that the effective Q of the emphasis characteristic does not change.

In this circuit configuration, in order to change the emphasis characteristic, it is sufficient to add an amplification stage before the terminal 201 or add a limiter circuit after the terminal 202.

FIG. 26 is a block diagram illustrating another embodiment of the present invention. The difference between Figure 26 and Figure 8 is that
A switch circuit 29 is added and the ACC detector 3 is used for both recording and playback, and switch circuits 28 and 30 are added and the ACC amplifier 4 and BPF
2) is used both during recording and during playback.

In FIG. 26, the reproduced chroma signal is supplied to the converter circuit 14 via the LPF 11, and the ACC is performed using the output signal of the converter circuit 14. Normally, the playback level changes for each track, so the output signal of LPF 11, as shown in Figure 8,
Although it is preferable to perform ACC, as long as the input dynamics range of the converter circuit 14 is ensured, there is no practical problem even with the configuration shown in FIG. 26.

In FIG. 26, the input signal of the ACC detector 3 is the input signal of the emphasis circuit 35 during recording, and the output signal of the de-emphasis circuit 36 during reproduction. The input signal of the phase detector 23 for generating the second carrier is the output signal of the ACC amplifier 4 during recording, and the output signal of the de-emphasis circuit 36 during reproduction. Therefore, the problem of delay time occurring in the emphasis circuit 35 can be solved.

Further, in the above description, it is assumed that a chroma signal that has been emphasized in advance during recording is de-emphasized during playback, but the present invention is not necessarily limited to this. For example, by performing only de-emphasis during playback without emphasizing during recording, interference with the chroma signal caused by the pilot signal and FM audio signal described above can be reduced. However, in this case, the bandwidth of the low-level chroma signal will become narrower, and the transient characteristics of the chroma signal will be slightly degraded, but by optimizing the de-emphasis characteristics, this will hardly be a problem visually. In this case, the above-mentioned optimization can be achieved if the preferable de-emphasis characteristic is one in which the input chroma signal does not have much frequency characteristic in the vicinity of 0 dB to -10 dB, but has a frequency characteristic for signals below about -10 dB.

According to the present invention, even if a pilot signal or an FM audio signal is recorded on a track by frequency multiplexing, the chroma image quality is not impaired. It is possible to eliminate the influence of delay time distortion that occurs in the chroma signal emphasis circuit, and realize a carrier generation circuit with excellent compatibility. Additionally, the emphasis circuit can be integrated into an IC with a small number of pins, which has great advantages in terms of economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a spectrum diagram showing an example of the spectrum of a signal written on a video track, FIGS. 2, 3, and 4 are characteristic diagrams showing examples of emphasis characteristics used in the present invention, and FIGS. 6 and 7 are characteristic diagrams showing an example of de-emphasis characteristics used in the present invention, FIGS. 8 and 26 are block diagrams showing an embodiment of the present invention, and FIG. 9 is a diagram showing an example of the configuration of an emphasis circuit. 10 and 11 are block diagrams showing an example of the configuration of a de-emphasis circuit, and FIGS. 12a and 12b are block diagrams showing an example of an emphasis circuit, and a frequency characteristic diagram showing characteristics of a trap circuit. Figures 13 and 14 are circuit diagrams showing examples of circuits that provide predetermined transfer characteristics;
The figure is a waveform diagram explaining the operation of the emphasis circuit.
Figure 16, Figure 17, Figure 18, Figure 19, Figure 2
Figure 0 is a circuit diagram showing a specific circuit example exhibiting the characteristics of Figure 2, Figures 21, 22, 23, 2
4 and 25 are circuit diagrams showing specific examples of circuits exhibiting the characteristics shown in FIG. 3. 35... Emphasis circuit, 6... Converter circuit, 14... Converter circuit, 36... De-emphasis circuit, 20... Burst gate circuit,
23... Phase detector, 25... VCO, 31...
VCO, 56...Trap, 57...Limiter, 5
4...Adder.

Claims (1)

[Claims] 1. An ACC circuit that controls the signal level of the chroma signal to be recorded, and a chroma signal whose level has been controlled by mixing the output of the ACC circuit and a carrier signal to the lower frequency side of the frequency modulated luminance signal. A frequency conversion circuit that converts the frequency, a recording means that records the frequency-converted chroma signal on a recording medium, and a level-controlled chroma signal provided in the path from the output of the ACC circuit to the input of the recording means. A nonlinear emphasis circuit that emphasizes sideband components as they move away from the center frequency and emphasizes the lower the level of the sideband components, and a chroma signal included in the above path that is after the output of the ACC circuit and before the input of the nonlinear emphasis circuit. 1. A chroma signal recording circuit comprising: a conversion carrier generation circuit which extracts a burst signal from a stream and generates the carrier signal based on the burst signal. 2. ACC means for controlling the level of the chroma signal;
non-linear emphasis means for emphasizing the sideband components of the recorded chroma signal outputted from the ACC means as the distance from the center frequency increases and as the level of the sideband components decreases;
It includes a nonlinear de-emphasis means that performs de-emphasis with a characteristic opposite to the emphasis characteristic of the non-linear emphasis means, and an oscillator that oscillates at the frequency of the chroma signal,
Conversion carrier generation means for generating a conversion carrier signal for converting the frequency of a chroma signal; and during recording, extracts a burst signal from the recorded chroma signal after the output of the ACC means and before input to the nonlinear emphasis means, and outputs it from the nonlinear de-emphasis means during playback. burst extraction means for extracting a burst signal from the reproduced chroma signal; and a phase comparison for controlling the phase of the converted carrier signal by comparing the phases of the burst signal from the burst extraction means and the oscillation output from the oscillator. A chroma signal recording/reproducing circuit comprising: means;