JPS60211664A - Recording circuit - Google Patents

Abstract

PURPOSE:To use effectively a dynamic range and to attain a recording current leaving a sufficient margin by minimizing the current consumption in each of recording, reproducing, and post recording modes in the range where the capacity is not degraded and adjusting the output potential of a buffer amplifier. CONSTITUTION:A recording signal A is supplied to a transistor (TR) Q30 and is outputted with the same phase as a recording signal supplied from the collector side of a TRQ31 and is supplied to an output terminal 30 through TRs Q35 and Q37 constituting an emitter follower. DC components of the recording signal obtained in the output terminal 30 are fed back by a capacitor C6, and its AC components are divided by resistances R62 and R63 and are fed back to the base of the TRQ31 through a terminal 31. The base potential of the TRQ30 and the DC potential of the terminal 31 coincide with each other by using the feedback- type buffer amplifier, and the DC potential of the output terminal 30 is adjusted by providing a resistance R61 between the terminal 31 and 9 power source. Thus, the recording current leaving a sufficient margin is flowed, and this circuit can cope easily with variation of the power source voltage.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magnetic recording and reproducing device using a two-head helical scanning system, and in particular, a magnetic recording and reproducing device in which a video signal and a PCM audio signal are supplied to the same rotating head. Regarding recording circuits.

[Background of the Invention] As is well known, most general video signal magnetic recording and reproducing apparatuses employ a two-head helical force scan system. That is, a cylinder is provided with two rotating heads, and a magnetic tape is wound around the cylinder by about 180 degrees and runs.These rotating heads alternately scan the tape, and each rotating head records or reproduces a video signal one field at a time. It is something. The video signal to be recorded or played back is F.
There is also a type that is M-modulated, and is further frequency-division multiplexed to this video transmitter so that audio signals, pilot signals for tracking the rotating head, etc. can be simultaneously recorded or reproduced.

In addition, some two-head heli force scan type magnetic recording and reproducing devices have an additional angle of 30 degrees to 4 degrees on the magnetic tape cylinder.
The time axis is compressed and PCM
A device that records encoded audio signals has also been proposed. Below, such recording method all overlap PC
This is called the M recording method. That is, in a magnetic recording/reproducing device using the overlap PCM recording method, in the approximately 180 degree winding portion of the magnetic tape wound around the cylinder,
As in the past, FM video signals, FM audio signals, pilot signals, etc. are recorded in frequency, and the remaining 30 to 40 degrees
A PCM audio signal and a piezo signal are frequency-multiplexed recorded on the magnetic tape.The video signal and the PCM audio signal are recorded at different locations on the magnetic tape. Recording only the PCM audio signal while leaving the video signal intact, that is, reproducing the video signal (hereinafter referred to as
This recording operation is called wpcy dubbing (after-recording).Also, since the pilot signal is frequency multiplexed to the pcy audio signal, the PCM audio signal remains, that is, the PCM audio signal is played back. It is also possible to re-record the sound of only the video signal (hereinafter referred to as a video insert for such recording operation).
Ru.

FIG. 1 is a pattern diagram showing recording tracks on a magnetic tape by such an overlap recording method, where 1 is the magnetic tape and 2 and 6 are partial tracks, respectively.

In the figure, one recording track is completely formed by one scan of a rotary head (not shown) using one partial track 2.3. The partial track 2 is formed by approximately 180 degrees of winding of the magnetic tape 1 around a cylinder (not shown), and has luminance signals (v), 5 chromaticity values (C), F
M audio signals (Ayht) and pilot signals ψ] are frequency-multiplexed and recorded. The partial track 3 is formed in the part where the magnetic tape 1 is further wound around the cylinder by 30 to 40 degrees, and the %PCM audio signal (Apcit) and the pilot signal ψ) are frequency-multiplexed and recorded. ing. PCM dubbing is a recording operation in which partial tracks are re-recorded while leaving partial track 2.
Video insert, on the contrary, is a recording operation in which partial track 2 is rerecorded while partial track 3 remains.

FIG. 2 is a circuit diagram showing an example of a conventional recording circuit,
R1-R24 are resistors, Q1-Q13 are transistors, C
1 to C5 are capacitors, Dl and Dl are diodes, L
1 to L3 are coils, 4 is a control signal input terminal, 5 is a recording signal input terminal, 6 is an output terminal of an integrated circuit (hereinafter referred to as IC), 7 is a bias power supply, 8 is a rotary transformer, and 9 is a video head. .

In the same figure, resistors R1 to R3, diodes D1゜Dl
The recording signal from the input terminal 5 is supplied to a differential amplifier consisting of transistors Q5 to QB, resistors R9, R11 to R15, and a bias power supply 7. The signal is amplified and outputted to the output terminal 6 of the rc through an emitter follower consisting of resistors R16 to R20 and transistors Q9 to Q11. Furthermore, the recording signal obtained at the output terminal 6 of the IC is transmitted through an emitter follower consisting of a transistor 012 and a resistor 7-21, and a recording amplifier circuit (hereinafter referred to as
REC amplifier]. Here, coil L
1 is the current flowing to the video head 9? The current flowing through the resistor R2S is generally very large, 10 to 20 mA, and in order to reduce the distortion rate of the recording current waveform, a transistor (? The direct current flowing through the REC amplifier must also be about 10 to 2 QmA.As described above, the current consumption in the REC amplifier is very large.

In other words, in general, ABC amplifiers are designed to reduce current consumption when not recording. In FIG. 2, the control signal supplied to input terminal 4 causes R
The current consumption of the EC amplifier can be increased or decreased.

That is, this control signal is not at a special high level for recording, but is at a low level except during recording. When the control signal goes low, transistor Q3 turns off, and along with this, transistors Q1 . Q4 turns on. When transistor Q1 turns on, transistor Q2, which constitutes the bias circuit, turns on.
is turned off, and the current source inside the IC becomes inactive. In addition, since transistor Q4 turns on, the collector voltage of transistor Q6 that constitutes the differential amplifier decreases, and the emitter voltage of transistor Q9 decreases, so that the potential at output terminal 6 of the IC decreases to a voltage at which transistor 012 does not turn on. do.

The entire configuration of the conventional recording circuit has been explained above. The REC amplifier of this recording circuit is designed to reduce power consumption of the magnetic recording/reproducing apparatus by reducing current consumption except during the recording mode.

However, if the above-mentioned REC amplifier is used in a magnetic recording/reproducing device using an overlap recording method, the current consumption of the REC amplifier is the same in each mode (recording, video insertion), and PCM dubbing, resulting in unnecessary power consumption. That means you are doing it.

As described above, in recent years, methods have been proposed for overlap PCM recording, but at present no specific circuit for implementing such a method has been proposed.

[Purpose of the invention]

In view of the above points, it is an object of the present invention to provide a recording circuit for an overlap recording type magnetic recording/reproducing device that is capable of setting the minimum current consumption that does not cause waveform distortion for each mode.

[Summary of the invention]

In order to achieve this objective, the present invention provides REC for each mode of recording, playback, video insert, and PCM dubbing.
Full switching of the amplifier's current consumption, minimizing current consumption in each mode.

The feature is that the output DC voltage of the buffer amplifier that fully drives the REC amplifier can be adjusted, and it is possible to drive with a low power supply voltage.

[Embodiments of the invention]

Hereinafter, all drawings of embodiments of the present invention will be described.

FIG. 3 is a circuit diagram showing an embodiment of the recording circuit according to the present invention, in which 10 is a selection switch, 11 is a control signal generation circuit, 12.13 is a changeover switch, 14 is a reproduction amplifier circuit,
15.1 (5 is a control signal input terminal, 17 to 20 are input terminals, 21.22 is a signal input terminal, and 23 is a control signal input terminal. Parts corresponding to those in Fig. 2 are given the same reference numerals. There is.

In FIG. 3, the signal input terminal 21 has a luminance signal (1
'), chromaticity signal CC), and FM audio signal (AFM) pilot signal ψ) are supplied with a first recording signal A that is frequency division multiplexed, and the signal input terminal 22 is supplied with a PCM
A second recording signal B is supplied in which the audio signal CApcx) and the pilot signal P) are frequency division multiplexed. The selection switch 10 is operated by a control signal from an input terminal 25.
Either the first recording signal A from the signal input terminal 21 or the second recording signal B from the signal input terminal 22 is fully selected. The changeover switches 12 and 13 perform all recording/reproduction switching, and during recording, the contacts are closed to the α side, as shown, and during reproduction, they are closed to the contact α side. The control signal circuit 11 receives a high level signal PR representing the playback mode from an input terminal 17, a high level signal REC representing the recording mode from the input terminal 18, and a high level signal REC representing the entire PCM dubbing mode from the input terminal 19. The signal Pαf is supplied from the input terminal 20, and the signal Vaf representing the entire video insert mode is supplied, respectively.
Control signals C+ and '2 are output at levels corresponding to these input signals.

Input signals REC, PEPa, f of the control signal generation circuit 11
, Vaf and the control signal C output by the logic circuit 11
1* The level relationship with C2 is shown in Figure 4.

Next, the operation of this embodiment will be explained with reference to FIG.

In the stop mode, all input signals of the control signal generation circuit 11 are at low level, and control signals '1 m' 7 are both at high level. Control signal CI is transistor Q
As a result, transistor Q2 is turned off and the current source becomes inactive.

Further, the control signal C2 turns on the transistor Q4 and brings the transistor Q6 into a saturated state. The collector potential of transistor Q6 is determined by the division ratio of resistors R1A and R10. The potential of the output terminal 6 is lower than the collector potential of the transistor Q6 by the sum of the base-emitter currents VBH of the transistors Q9, 10, that is, 2 VBx.

At this time, since the current source transistor Q11 is turned off by the control signal C1, the emitter current of the transistor Q10 is not sucked into the transistor 011, but becomes the base current of the transistor Q12. As a result, a leakage current flows through the transistor Q12, and the potential V of the output terminal 6
6 is a non-zero ΔV as shown in FIG. However, ΔV is made equal to or less than the base-emitter voltage VBE by setting the resistance values of the resistors 7H4 and R20 to predetermined values.

In the reproduction mode, the control signal C0 from the control signal generation circuit 11 is at a low level, and the control signal C3 is at a high level. For this reason, as in the stop mode, transistor Q6 is saturated and its collector potential decreases, but since control signal C3 is at a low level, transistor Q
1 is off, the transistor Q2 is turned on, the current source transistor Q11 is turned on, and the emitter current of the transistor 010 is sucked into the transistor 011. As a result,
The potential of the output terminal 6 becomes zero.

In the recording mode, PCM dubbing mode, and video insert mode, the control signals C, , C, from the control signal generating circuit 11 are both at a low level, and the transistors Q1 . C4 are both cut off and operate in the same manner as the recording circuit shown in FIG.

FIG. 5 is a circuit diagram showing a specific example of the control signal generation circuit 11 in FIG. 3, in which R2O-R41 are resistors, Q14 to
721 is a transistor, 61 to G10 are I”L (Int
24 and 25 are output terminals, and parts corresponding to those in FIG. 3 are given the same reference numerals.

The control signal C1 is obtained at the output terminal 24, and the control signal C3 is obtained at the output terminal 25. The control signal C1 is formed by the logic of transistors 014 and C15, and the signal REC
, PB are both at low level, it becomes high level. The control signal C7 is transmitted through transistors Q16 and QlB, respectively.
, C17 inverted signal REC.

7' consisting of gates 01 to G1o using PB and PcJf
Formed with 2L logic. Hatched goo) G1-
G3 is the interface from the linear transistor to the FL gate. G10 is the opposite interface. The transistors Q19 to Q21 and the resistor R40 form a current source for the interface between the 12L gate and the linear transistor, and are set to a current value that can sufficiently drive all the linear transistors.

Note that in FIG. 5, the signal raf is connected to the transistor Q.
1. The input terminal 15. is not directly related to the control of C4. I
The changeover switches 12,13'ij (necessary for generating all control signals) are supplied from S and are therefore illustrated in FIG.

FIG. 6 is a circuit diagram showing another embodiment of the recording circuit according to the present invention, in which R50 to R67 are resistors, Q30 to 039 are transistors, Llo is a coil, and C6 is a capacitor, which corresponds to FIG. All parts are given the same sign.

This embodiment uses a feedback type buffer amplifier.

In FIG. 6, the recording signal A or B selected by the selection switch 10 is supplied to one transistor 030 of a differential amplifier having a feedback configuration, and
The transistor Q5 is output in phase with the recording signal supplied from the collector side of the transistor Q5, and each constitutes an emitter follower.
5. Q57 and then supplied to the output terminal 60. The recording signal obtained at the output terminal 30 is further fed back to the transistor Q7,1 by the capacitor C6, and the AC component is divided by the resistors R62, R63. It is returned to the base of 031. In this way, by using a feedback type buffer amplifier.

The base potential of the transistor Q30 and the DC potential of the terminal 31 match, and the resistor R (51" i terminal 31,
By connecting between the ground terminals, the DC potential of the output terminal 30 can be adjusted. In the former case, output terminal 3
In the latter case, the DC potential at output terminal 30 increases.

7 and 8 are waveform diagrams showing the signal levels at the base, emitter, and collector points of the transistor 39 in FIG. 6, and in both figures, the power supply voltage is set to 5 (1').

FIG. 7 shows that the DC potential of the output terminal 30 is 2.0 (1/),
AC signal is 1.5 CVp-p), transistor 039
The collector output signal of the transistor Q59 is 4 (Vp-p), the DC potential of the output terminal 30 is 1.64'l, the AC signal is 15 CVp-p), and the collector output signal of the transistor Q59 is 4 (Vp-p). -p), and the gains are all the same. Generally, the inductance of the video head 9 is 8μH when viewed from the secondary side of the rotary transformer.
The impedance at 5jlz is about 250 (
2), when the collector output signal of the transistor 39 is 4 CVp-p), the current flowing through the resistor R23 is 5 MIIz and 16 (mA).

In the case of FIG. 7, transistor 039 (D base
The recording current distortion deteriorates when the voltage difference between the collectors is 0.25 J), but there is still a margin of 0.55 r) between the emitter and the ground. On the other hand, as shown in FIG. 8, if the base potential of transistor Q39 is set to about 1.6F),
There is a margin of 0.65 (3) between the base and collector, the recording current distortion characteristics are improved, and the voltage between the emitter base and ground is 0.15 (7), which is sufficient for the entire dynamic range compared to Fig. 7. This means that it is being utilized.

The above case was when the power supply voltage was 5 V'), but if the power supply voltage was chosen to be around k 9 F), then if the DC potential of the output terminal 30 was chosen to be k 1.6 ('), the recording current would increase. In this case, the current waveform will not be distorted due to insufficient margin of the voltage between the emitter and ground of the transistor Q39, and on the contrary, it is necessary to increase the potential of the output terminal 30.

In this way, being able to adjust the DC potential of the IC output terminal 30 makes it possible to broadly follow changes in the power supply voltage, and in particular, as in this embodiment, one resistor R61
Alternatively, it is a very great advantage that the resistor R61' can be used.

Similarly to the embodiment shown in FIG. 3, the control @TJ signal CI*C! from the control signal generation circuit 11 is generated. by transistor Q1
, 034'i, the potential V9 of the output terminal 30 and the emitter potential Vak of the transistor 039 are shown in FIG. When transistor Q54 turns on, transistor Q3
The base potential of 5 is determined by the power supply voltage and the voltage division ratio of resistors R54 and R67, and the setting of the value is the same as in the embodiment shown in FIG. In Figure 6, the resistor R61 is 30 (kΩ), and the resistor R62
is 43 (kΩ), and the resistance R is 63 and 820 (2), and the potential relationships at this time are all shown in FIG. Vso' is connected to output terminal 30 with resistor R60? Since it is the potential of the output terminal 3o in the stop mode when not connected and is 13r),
At this time, the emitter potential V,' of the transistor QS9 is about 0.6n, and it is not possible to sufficiently cut off the entire DC current of the REC amplifier. On the other hand, 3.
6 (kΩ) resistance J? When 60K is connected, the potential of the output terminal 60 is 0. At F4'), the emitter potential Vg' of the transistor Q39 becomes completely 0 (1'), and the entire DC current of the REC amplifier when stopped can be completely reduced to zero.

36 (kΩ) resistor R60 between output terminal 30 and ground terminal
By connecting f, the current consumed by resistor R60 during p c pt dubbing, recording, and video insertion is 0.5
(+++J) This is the following, and there is a sufficient effect if the reduction in current consumption during stoppage is taken into account.

The above description has been made regarding a VTR using the sidetone overlap PCM recording system according to the present invention, but it goes without saying that the present invention is also fully applicable to conventional nohelical scan type V'l'H.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to switch the current consumption of each mode of recording, playback, dubbing, and video insert in the overlap recording method to the minimum without degrading the performance. Can the total current be reduced and also the output potential of the buffer amplifier before the recording amplifier? By making it adjustable, the entire dynamic range of the recording amplifier can be fully utilized, and a recording amplifier with a low voltage power supply can flow a recording current with sufficient margin to the video head, including variations in the power supply. It has excellent effects such as being able to easily deal with voltage changes.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the track pattern of a magnetic tape.
FIG. 2 is a circuit diagram showing an example of a conventional recording circuit, and FIG. 3 is an embodiment of the recording circuit according to the present invention. 4 is a timing chart showing the operation of FIG. 3, FIG. 5 is a circuit diagram showing a specific example of the logic circuit of FIG. 3, and FIG. 6 is another implementation of the recording circuit according to the present invention. Circuit diagram showing an example, No. 7
8 and 8 are waveform diagrams showing an example of the signal level relationship in FIG. 6, and FIG. 9 is a timing chart showing the operation of FIG. 6. 9... Video head 10... Selection switch 11.
...Control signal generation circuits 17 to 20...Mode signal input terminals 21,22...Record signal input terminals Patent attorney Akio Takahashi

Claims (1)

[Claims] Magnetic chi 1118 on a rotating cylinder equipped with a rotating head
The 0 degree angle is also wrapped extra, and the video signal, FM audio signal, and pilot signal for tracking control are all-frequency multiplexed recorded on the 180 degree wrap, and the time axis compressed PCM audio signal is recorded on the remaining wrap. With the PC'M signal? In a helical scan type magnetic recording and reproducing apparatus that performs frequency multiplex recording, there are two times when the PCM audio signal and the pilot signal are recorded while reproducing the video signal and the pilot signal, and when the entire PCM audio signal is recorded. At the time of video insertion, the video signal, the FM audio signal, and the pilot signal sound are recorded while being played; and at the time of recording;
Control signal generation circuit that switches all current consumption in 4 modes including playback mode? A recording circuit characterized in that the current consumption can be set to the minimum in each of the modes.