JPS5912752Y2 - Recording/playback device - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a method for FM modulating a luminance signal and recording it on a recording medium.
The present invention relates to a recording/reproducing device that switches the frequency shift of modulation.

2. Description of the Related Art Some recording and reproducing apparatuses, such as VTRs, which record video signals on a magnetic tape and reproduce the video signals accordingly, are capable of switching the tape feeding speed during recording and reproducing into a binary format.

For example, using a cassette tape of the same length, a VT can be used to select between 1-hour recording and 2-hour recording.
R is known.

In such a VTR, when recording for 1 hour, there is a guard band (no signal band) between adjacent tracks on the tape, and when recording for 2 hours, there is a guard band between adjacent tracks. I try to record without a band.

Therefore, when reproducing a tape recorded for two hours, crosstalk from adjacent tracks increases and the quality of the reproduced screen deteriorates.

In order to eliminate such losstalk, two rotating magnetic heads are recorded with different azimuths (gap angles relative to the head scanning direction), and the azimuth between the magnetic head that is reproducing and the adjacent track is This difference reduces crosstalk.

In addition, in the above-mentioned VTR, the luminance signal is FM modulated and recorded, but it is known that crosstalk increases in proportion to the frequency difference of the FM modulation signals between adjacent tracks. .

For this reason, in one hour recording, for example, an FM frequency of 3 to 5 MHz is used.
For example, set the frequency deviation of modulation to 3 to 4 MHz, which is 3% of that for 2-hour recording, and reduce crosstalk by reducing the frequency difference in 2-hour recording compared to 1-hour recording. I try to let them do it.

FIG. 1A is a block circuit diagram of a recording system of a conventional VTR.

In FIG. 1A, a video signal Sa to be recorded is supplied to a low-pass filter 1, where unnecessary high-frequency components other than the luminance signal component are removed.

The separated brightness signal sb is supplied to the AGC/clamp circuit 2, where the amplitude of the brightness signal is made constant and clamped to a predetermined level.

And 1 hour record / 2 hour record (hereinafter simply I H/2
Connect the changeover switch 10 linked to the changeover operation lever or button (not shown) of the V
When the TR is set to the one-hour recording mode, the output signal Sc of the AGC/clamp circuit 2 is supplied to the emphasis circuit 4 via the level adjustment variable resistor 3 for adjusting the frequency deviation of the output of the FM modulator 11. Ru.

This emphasis circuit 4 is designed to emphasize the high frequency components of the video signal during recording in order to improve the decrease in the S/N ratio due to the specified upper limit of the frequency deviation of the FM modulator 11. be.

Note that during reproduction, this emphasized portion is attenuated together with the noise portion by a de-emphasis circuit.

The output signal Sd of the emphasis circuit 4 is transferred to the selector switch 10.
The signal is supplied to the FM modulator 11 through the 1B contact of the signal Sd, where an FM modulation signal Se having a frequency corresponding to the level of the signal Sd is formed.

This modulated signal Se is supplied to a mixer 12.

On the other hand, the video signal Sa to be recorded is transmitted to the chroma recording system circuit 15.
is also supplied to the chroma signal component (3,58M
Hz) is frequency-converted so that it becomes the lower frequency side of the FM modulation signal Se.

The frequency-converted low frequency converted chroma signal S is then supplied to the mixer 12 and mixed with the FM modulation signal Se.
The signal is supplied to the rotating magnetic heads 13a and 13b and recorded on the magnetic tape 14.

Next, when the changeover switch 10 is connected to the 2B contact side and the VTR is set to the 2-hour recording mode, the output signal Sc of the AGC/clamp circuit 2 is supplied to an emphasis circuit 5 similar to the emphasis circuit 4, where the brightness High frequency components of the signal are emphasized.

The output signal Sg of the emphasis circuit 5 is supplied to a compressor 6.

When the level of ttsg is high, this compressor 6 suppresses the high-frequency components and controls the emphasis circuit 5 in the previous stage.
When the signal level is low, the suppression function is lowered so that the signal Sg emphasized by the emphasis circuit 5 is recorded as is, and as a result, the reproduced signal is This is a circuit for improving the S/N ratio.

The output signal sh of the compressor 6 is supplied to the emphasis circuit 8 via a level adjustment variable resistor 7 for adjusting the frequency deviation of the output of the FM modulator 11.

This emphasis circuit 8 emphasizes the frequency band (for example, around 2 MHz) of crosstalk mixed in the reproduced signal during recording, and attenuates the emphasized portion during reproduction, thereby improving the S/N ratio of the reproduced signal. It is something.

The output signal Si of this emphasis circuit 8 is supplied to a compressor 9.

This compressor 9 has the same function as the compressor 6, and is for suppressing the emphasis of the crosstalk band by the emphasis circuit 8 when the signal level is high.

The output signal Sj of this compressor 9 is transferred to the selector switch 10.
The signal is supplied to the FM modulator 11 through the 2H side contact point of the signal, and is recorded on the tape 14 in the same manner as in the IH mode.

FIG. 1B is a graph showing the frequency deviation of the output of the FM modulator 11 of FIG. 1A, in which the input current I is in IH mode.

Frequency deviation f relative to -11. -fl (e.g. 3-5M
Hz), and input current I when in 2H mode.

~ ■ Frequency deviation f for 2.

-f2 (for example, 3 to 4 MHz).

This frequency shift is determined by variable resistors 3 and 7 in FIG. 1A.
are set by adjusting the level of the signal current supplied to the FM modulator 11 to an appropriate value.

Furthermore, I. is a current value corresponding to the level (sync tip level) of the tip of the synchronization signal of the luminance signal clamped to a predetermined level, and I□ and ■2 are 1H and 2H, respectively.
This is the current value corresponding to the white peak of the luminance signal when .

As described above, conventional VTRs have a problem in that there are many parts to be adjusted during assembly, which increases the number of adjustment steps.

The present invention was devised in view of the above-mentioned problems.
The level adjustment means for adjusting a plurality of frequency deviations of the M signal can be made common to these plurality of frequency deviations, thereby making it possible to perform this adjustment operation easily.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a partial block circuit diagram of a recording system of a VTR to which the present invention is applied, and only the parts different from those in FIG. 1 are shown.

Further, FIG. 3 is a graph showing the frequency characteristics of the impedance circuit of FIG. 2.

In FIG. 2, the transistor 17 and the impedance circuit 24 connected to its emitter constitute the emphasis circuit 4 shown in FIG. 1A.

The transistor 18 and the impedance circuit 25 connected to its emitter constitute an emphasis circuit 8 shown in FIG. 1A.

Note that one end of each of these impedance circuits 24 and 25 is a switch 2 having movable contacts 23a and 23b that operate in conjunction with an IH/2H switching operation lever or button.
It is grounded via 3.

Note that the switch 23 may be a changeover switch whose movable contact is grounded.

Further, the collectors of each of the transistors 17 and 18 are connected in common, and are connected to the collector of the transistor 19.

A variable resistor 21 is connected to the emitter of this transistor 19, and its base and collector are commonly connected and also connected to the base of a transistor 20.

A resistor 22 is connected to the emitter of the transistor 20, and these transistors 19 and 20 constitute a current mirror circuit.

Next, the operation of the circuit shown in FIG. 2 will be explained.

First, when the IH/2H switching operation lever or button (not shown) is switched to the IH side and the VTR is placed in the 1-hour recording mode, the movable contact 23a of the switch 23 is closed in conjunction with this switching operation lever or button. , the transistor 17 becomes operational.

The base of this transistor 17 is supplied with the output signal Sc of the AGC/clamp circuit 2.

Therefore, assuming that the signal level of this signal Sc is eln and the impedance of the impedance circuit 24 connected to the emitter of the transistor 17 is 21, a collector current 12□ expressed as follows flows through the collector of the transistor 17.

Note that this impedance Z1 has a frequency characteristic represented by 21 in FIG.

That is, the impedance B decreases in the high frequency range of the luminance signal (a predetermined high frequency range larger than fL as shown in FIG. 3).

Since this impedance Z1 provides negative current feedback to the transistor 17, the signal current iZl flowing through the collector of the transistor 17 obtained in response to the output signal Sc of the AGC/clamp circuit 2 has its high frequency region enhanced. .

As a result, emphasis is applied to the high range of the luminance signal.

The collector current 12□ of the transistor 17 is the variable resistor 2
1 and transistor 19 (substantially a PN junction diode since the base and collector are short-circuited).

Therefore, this collector current is the resistance value R2□ due to 121
The voltage drop across the variable resistor 21 and transistor 19 is ■
.

=R2□iz□+Vbe.

This voltage V. is given to the base of the transistor 20, so if the signal current flowing through the transistor 20 is 11 and the resistance value of the resistor 22 is R2□, ■o=R22i1-)
-Vbe.

Therefore, a signal current 11 determined by , flows through the transistor 20 .

This signal current 11 passes through a compressor 9 to an FM modulator 1.
1, and an FM modulation signal Se corresponding to the current value is formed.

This FM modulation signal Se is recorded on the magnetic tape 14 after being mixed with the low frequency converted chroma signal as described above.

The frequency shift of this FM modulation signal Se is f shown in FIG. 1A.

-fl (for example, 3 to 5 MHz), the variable resistor 21 in FIG. 2 is adjusted.

That is, by changing R2□ in the second equation, R2 is set so that the change in the signal current 11 at the collector of the transistor 20 is from L to ■1.

Note that during one hour recording, the compressor 9 operates as a white clip circuit (white peak value limiter).

Next, when setting the VTR to 2-hour recording mode, switch 23
The movable contact 23 a is opened, and the movable contact 23 a is opened.
b is closed and the transistor 18 becomes operational.

The output signal Sc of the AGC/clamp circuit 2 is supplied to the base of the transistor 18 via an emphasis circuit 5 and a compressor 6 similar to those shown in FIG. 1A.

Note that in a frequency range other than the high frequency range in which this emphasis circuit 5 and compressor 6 operate, the signal Sc
is supplied to the base of transistor 18 with its level eln hardly changing.

Therefore, assuming that the impedance of the impedance circuit 25 connected to the emitter of the transistor 18 is 22, a collector current 12□ expressed as follows flows through the collector of the transistor 17.

Note that this impedance Z2 has a frequency characteristic represented by 22 in FIG.

Therefore, as in the case of one-hour recording, the signal current 12° flowing through the collector of the transistor 18 is enhanced in a predetermined high frequency range greater than the frequency fL as shown in FIG.

Further, in a band below the frequency fL where this emphasis is applied, I2 is set in advance to be approximately twice Zo.

In this case, similarly to the second equation, a signal current 12 determined by follows flows through the transistor 20, and this current 12 is supplied to the FM modulator 11 via the compressor 9.

In this case, as mentioned above, below the frequency fL in FIG. 3, ゛ is Z2=2Z1...■. 4. From formula 5, 12 = Kei 11...■.

As mentioned above, the 11 changes in the 1-hour recording mode are I in Figure 3.

-11, so a change of 12 is I.

/2 to 11/2.

Therefore, during the current change, it becomes '2 (L ~ IO) and becomes 1.
Especially when in time recording mode, the FM modulator 11
The frequency deviation of the output is also %.

In addition, in the 2-hour recording mode, the change in the signal current 12 in the FM modulator 11 is Io = Iz in FIG. 1B.
After the current is corrected so that (I2IO=+(11-Io)), FM modulation is performed.

In this current correction, the signal current 12 remains at ±(11Io) while the signal current 12 is changing, and the lower limit of the change is I, which is the same as the lower limit of the change in 11 in the 1-hour recording mode.

For example, a constant current may be added to the signal current i2 so that.

In this way, the frequency shift during the 1-hour recording mode is f as shown in FIG. 1B.

If it is set to -fl, the frequency shift in the 2-hour recording mode is dynamically determined by the ratio of Zl and 22, and becomes f.

-It becomes I2.

Therefore, since the frequency shift of the FM modulator 11 can be adjusted by simply adjusting the variable resistor 21, the number of adjustment steps when assembling the VTR can be reduced.

In the above-described embodiment, the variable resistor 21 may be a fixed resistor, and a variable resistor for level adjustment may be provided at the output of the AGC/clamp circuit.

Further, the switch 23 may be provided on the base side of the transistors 17 and 18.

Furthermore, in the above embodiment, the impedance circuit 2
4.25 is given a frequency characteristic in order to perform emphasis, but these may be pure resistance elements each having a resistance value corresponding to the frequency shift ratio of I H/2 H.

In this case, circuits similar to emphasis circuits 4 and 8 of FIG. 1A are provided in front of transistors 17 and 18, respectively.

Further, the impedance circuit 25 may also serve as the compressor circuit 9.

In this case, contrary to FIG. 3, it is sufficient to give the impedance Z2 a frequency characteristic that increases in the high range, and in this case, the impedance Z1 may be a pure resistance.

Next, FIG. 4 is a partial circuit diagram showing a modification of the circuit for setting the frequency shift shown in FIG. 2, and only the parts different from the case of FIG. 2 are shown.

The circuit of FIG. 4 has a similar configuration to the circuit for setting the frequency deviation shown in FIG. It is connected to the.

An output signal is obtained from one end of this variable resistor 21.

In this case, impedance Z1. Voltage output V1. according to the ratio of Z2. v2 is obtained, the FM modulator 11 in FIG.
If configured, the frequency deviation of L H/2 H can be set according to the ratio of the impedance factor and Z2.

Note that the present invention can also be applied to a recording/reproducing apparatus in which the tape running speed can be switched between three or more types.

In this case, a circuit having the same configuration as the transistor 17.18 and the impedance circuit 24.25, and the movable contact 23a
, 23b and a similar movable contact may be further added.

As described above, the present invention provides first and second recording media whose gain ratio is set to a ratio of first and second frequency deviations corresponding to at least two types of first and second recording medium moving speeds. When the moving speed of the recording medium is set to the first speed, the first amplifier said first
and a common level adjustment means for the second amplifier, and in this adjustment state, when the moving speed of the recording medium is switched to the second speed, the output signal is adjusted according to the output signal obtained from the second amplifier. The FM signal has a second frequency shift.

Therefore, F is switched according to multiple moving speeds of the recording medium.
The level adjustment means for adjusting a plurality of frequency deviations of the M signal can be made common to these plurality of frequency deviations, and therefore this adjustment operation can be performed easily.

[Brief explanation of the drawing]

FIG. 1A is a block circuit diagram of a recording system of a conventional VTR, and FIG. 1B is a graph showing the frequency shift of the output of the FM modulator shown in FIG. 1A. Figure 2 is a partial block circuit diagram of the recording system of a VTR to which the present invention is applied, Figure 3 is a graph showing the frequency characteristics of the impedance circuit in Figure 2, and Figure 4 is a graph showing the frequency characteristics of the impedance circuit in Figure 2. FIG. 7 is a partial circuit diagram showing a modification of the circuit for setting. In addition, in the symbols used in the drawings, 11 is an FM modulator, 17 and 18 are transistors, 21 is a variable resistor, and 2
3 is a switch, and 24.25 is an impedance circuit.

Claims (1)

[Claims for Utility Model Registration] An FM modulator for modulating a luminance signal into an FM signal and recording the same, and a speed switch capable of switching the moving speed of a recording medium to at least two types of first and second speeds. and means for switching the frequency shift of the FM signal to first and second frequency shifts corresponding to the first and second speeds in response to the operation of the speed switching means. In the reproducing device, (a) the luminance signal is used as a common input signal, the gain ratio thereof is set to the ratio of the first and second frequency deviations, and the signal is supplied to the FM modulator from a common output terminal. (b) common level adjustment means for adjusting the level of said output signals of said first and second amplifiers; (C) said a changeover switch for switching the operation of the first and second amplifiers in conjunction with the operation of the speed switching means, and operating the speed switching means to change the moving speed of the recording medium to the first speed. the frequency deviation of the FM signal according to the output signal obtained from the first amplifier is adjusted by the level adjustment means to become the first frequency deviation, and In this state, when the moving speed of the recording medium is switched to the second speed, the frequency shift of the FM signal according to the output signal obtained from the second amplifier is changed to the first and second amplifiers. A recording/reproducing apparatus configured to automatically achieve the second frequency shift based on a gain ratio of.