JPH01211272A - magnetic recording and reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to
The present invention relates to a magnetic recording/reproducing device for M signals.

2. Description of the Related Art In recent years, the quality of audio recording using a fixed head has deteriorated due to a decrease in tape speed and recording speed due to longer recording times in video tape recorders. As a countermeasure to this problem, 7M recording of audio using a rotating head has started to be performed. (For example, "Introduction to New Video Technology Chapter 18" by Masumi Harada, Dempa Shimbunsha, 160 pages to 152 pages) In the FM audio recording method using rotating heads, multiple heads (usually 82 heads) alternate Since the playback signals from these heads are switched alternately during recording and playback, discontinuities inevitably occur at the switching points, and the generation of so-called switching noise is essentially unavoidable. This has become a problem.

FIG. 7 shows an example of a block diagram for one channel of a conventional FM audio recording system reproduction circuit.

In FIG. 7, 1.2 is a head forming a rotating head, 3 and 4 are reproduction RF amplifiers, 6 is a head switch circuit,
6 is a limiter, 7 is a voltage controlled oscillator (VCO) s, a phase comparator (PC) 9 and a low pass filter (LPF) 1o
11 is a hold circuit, 12 is a monostable multi-circuit that controls the hold circuit 11, 13 is an audio signal output terminal, and 14 is a head switch signal input terminal. .

The operation of the FM audio reproduction circuit configured as described above will be explained below.

First, the RF multiplied signal reproduced by the head 1.2 is amplified by the reproduction RF amplifiers 3 and 4, and then alternately switched by the head switch circuit 5 according to the head switch signal, and the amplitude is limited by the limiter 6, and the FM demodulation is performed. The signal is demodulated into an audio signal by the device 7, held for a certain period of time immediately after the head switch by the hold circuit 11, and outputted to the audio signal output terminal 13.

As shown in the above example, a PLL is usually used in the FM demodulator of the FM audio reproduction circuit. The PLL (as explained in the above document) is a VC controlled by the output of LPFlo.
Os, P(j9, which compares the phase of the output signal of this VCO, s, and limiter 6, and LPFlo, which extracts the low frequency component from the output signal of this pcs. pjh configured as above. In this case, the phase of the oscillation output of the VCO is always locked to the phase of the limiter output, and therefore its oscillation frequency always changes following the frequency of the limiter output, that is, the FM signal, so its control signal, that is, the LPF output signal, is It becomes equal to the audio signal modulating the FM signal, and therefore becomes the demodulated signal.

A specific example (conventional example) of the above-mentioned VCOa is shown in FIG. 8th
In the figure, 16 is a control input terminal, 17° and 18 are constant current sources whose current value is variable according to the control input, 19 is a switch that changes the direction of the current applied to the capacitor 2o by the output of the Schmitt trigger 21, and 22 is the vCO output It's the edge.

In the vCO configured as above, capacitor 2
The zero voltage reciprocates between two threshold levels determined by the Schmitt trigger 21, and the reciprocating speed is proportional to the current value of the constant current source 17,18. Therefore, the VCO
The oscillation frequency varies linearly with the control input signal.

Next, FIG. 9 shows the waveforms of each part of the FM audio reproduction circuit shown in FIGS. 7 and 8 above. In FIG. 9, a indicates the head switch signal, b and c indicate the RF amplifier 3.
4 output signal, d is the output signal of head switch circuit 5,
e is the output signal of limiter 6, f is the output signal of VCOa,
g is the voltage of capacitor 2°, h, , h2 is the threshold level of Schmitt trigger 21, i is the output signal of PCs, j is the waveform of the output signal of LPFlo, and t
is the time of the head switch point.

Problems to be Solved by the Invention In FIG. 9, for the head switch circuit output signal d, the RF multiplied signal on the head 1 side is selected before the time, and the RF multiplied signal on the head 2 side is selected after that time. , at time t, the phases of waveforms S and C do not necessarily match, and due to differences in tape tension during recording and playback, jitter of the rotating head, expansion and contraction of the tape, etc.
constantly changing. Therefore, the head switch circuit output signal d generally becomes discontinuous at time t.

For this discontinuous signal, the PLL has a delay element LPF in its loop, so it can immediately follow the phase of the vOO output signal, and it takes time to reach the phase lock state. It takes. During this time, an output corresponding to the phase error between the limiter output signal 0 and the VCO output signal f appears transiently in the PLL output as shown in waveform j. This is called switching noise.

In order to remove this switching noise, conventionally, the seventh
As shown in the figure, a method is used in which a hold circuit 11 holds the PLL output signal for a certain period of time from the time of the head switch. In order to fully obtain the switching noise suppression effect of this hold, it is necessary to set the hold time to a time that sufficiently covers the switching noise. There is a problem in that large discontinuities occur in the audio signal, resulting in a sound that is difficult to hear.

In view of the above-mentioned problems, the present invention provides a magnetic recording/reproducing device that can extremely shorten the hold time or does not require a hold circuit by extremely reducing the width and magnitude of switching noise.

Means for Solving the Problems In order to solve the above problems, the magnetic recording and reproducing apparatus of the present invention includes a rotary head including a plurality of heads, a head switch means, a phase-locked loop means, and the head switch means. and a clamping means for clamping the operation of the voltage controlled oscillator in the phase-locked loop means.

According to the above-described structure, the clamping means clamps the operation of the voltage controlled oscillator at a predetermined phase at the time of the head switch, and thereafter or after a predetermined time has elapsed, the output of the polarity detecting means changes (at this point, the normal operation is stopped). by unclamping the voltage controlled oscillator (which corresponds to the clamped phase of the voltage controlled oscillator at
The operation can be immediately brought to a steady state, and as a result, switching noise can be suppressed to an extremely short period of time.

Embodiment Hereinafter, an FM magnetic recording/reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of a reproducing circuit for one channel of an FM magnetic recording and reproducing apparatus according to the first embodiment of the present invention, and each number from 1 to 14 is the same number as in FIG. The components are the same, and 16 is a clamping means.

The operations related to 1 to 14 of this embodiment are the same as those explained in FIG. 7, so the explanation will be omitted.
We will mainly explain the operations related to.

A block diagram of the clamping means section of this embodiment is shown in FIG. In FIG. 2, 8 to 22 are the same components as those with the same numbers in FIG. 8, 23 is a head switch signal input terminal, 24 is a limiter output signal input terminal, and 26 is a head switch signal and +J mitter output signal. 26 is a clamping section that clamps the capacitor 2o to a predetermined voltage, and 15 is a clamping means composed of the detection section 26 and the clamping section 26.

FIG. 3 shows waveforms at various parts in this example. Figure 3 a-
j is the waveform at the same point as that explained in FIG.

The operation of the clamping means 16 in this embodiment is as follows: First, the switching time t of the head switch signal a is detected, and the level of the vCO capacitor voltage determination (in the example shown in FIG. 3) is
Clamp at the midpoint between hl and hl). Next, the clamp is released by detecting the timing at which the output e of the limiter 6 is inverted from positive to negative. Then, the VCO capacitor voltage starts from the midpoint voltage between hl and hl, but since this phase matches the phase in which the limiter output reverses from positive to negative in the PLL lock state, it immediately enters a steady lock state. No time is required to enter the lock state. Therefore, the switching noise is also suppressed only during the clamp period, as shown in FIG. 3j, so that it can be made extremely short.

Incidentally, in the case of the operation shown in FIG. 3, at head switch time t, the capacitor voltage g of the VCO is on a downward slope, and is clamped at the midpoint of the downward slope. Therefore, the clamp may be released at the point corresponding to the midpoint of the downward slope, that is, at the point when the limiter output e is reversed from positive to negative.

However, if g is an upward slope at time t, then the clamp must be released when e reverses from negative to positive. In the example shown in FIG. 3, the upward slope of g corresponds to the H level of the VCO output f, and the downward slope corresponds to the L level. Therefore, the clamp may be released when f is at an H level and e is inverted from negative to positive, or when f is at an L level and 6 is inverted from positive to negative.

Therefore, if we pay attention to the PC output i, 1 is the product of e and f, so in any case, it is understood that the clamp should be released when i is reversed from negative to positive.

FIG. 4 shows a part of a block diagram of a magnetic recording/reproducing apparatus according to a second embodiment of the present invention, in which the clamp release point is detected by PC output. In FIG. 4, numerals 6 to 16 are the same components as those with the same numbers in FIG. In this embodiment, the input of the clamping means 16, which was connected to the output of the limiter 6 in the first embodiment, is connected to the output of PO2, and as in the first embodiment,
There is no need to determine whether to take the falling edge or the rising edge of the limiter output depending on whether the vCO output is at H level or L level as the clamp release point, which has the advantage of simplifying the circuit configuration.

By the way, in the first and second embodiments described above,
A maximum period of one wavelength is required from the time of the head switch until the clamp is released. Therefore, head switch time t
Depending on the polarity of the limiter output immediately after the VCO output, the third
In the example shown in the figure, if e is set to ff and L level when it is positive, and to H level when it is negative, the clamp can be released when the limiter output is inverted for the first time after that time. By doing so, the clamp period can be compressed to a maximum of half a wavelength, and switching noise can be reduced accordingly.

FIG. 6 shows a part of a block diagram of a magnetic recording/reproducing apparatus according to a third embodiment of the present invention in which the vCO output is set according to the polarity of the limiter output immediately after the head switch. 8 to 26 in FIG. 6 are the same components as those with the same numbers in FIG.

In this embodiment, depending on the polarity of the limiter output voltage 24 immediately after the head switch, the Schmitt trigger 21 during vCO
vOO is set by switching the threshold level from hl to h2.

FIG. 6 shows operating waveforms of each part in this embodiment. 6th
In the figure, 1l-j is the waveform at the same point as the one with the same symbol in FIG.

In the example shown in Fig. 6, the polarity of the limiter output e immediately after the head switch is negative, so the vCO output f is set to H level, and then the clamp is applied when e reverses from negative to positive. is released. In this way, the clamp is released within half a wavelength from the time of the head switch and the PLL enters the locked state, so switching noise can be made extremely small as shown in FIG. 6j.

In the above explanation, the standby state for clamp release is entered immediately after the head switch, and the clamp is released immediately when the limiter output reverses in a predetermined direction. However, in reality, the v00 capacitor 2 It takes some time to clamp it. Also, a bandpass filter may be inserted after the head switch circuit, but
In such a case, the effect of the discontinuity caused by the head switch will continue for some time. In order to eliminate the above effects,
In the clamping operation of the present invention, it is better not to enter the clamp release standby state immediately after the head switch, but to enter the clamp release standby state a certain period of time after the head switch. In that case, in a third embodiment of the invention:
At least after a certain period of time from the above head switch, vC
It is necessary to ensure that O is set.

Effects of the Invention As described above, the present invention clamps the vCO phase of the FM demodulation PLL using a head switch signal, and then releases the clamp at the timing when the polarity of the limiter output is reversed. This has the effect of greatly reducing switching noise generated by the switch.

Furthermore, the shift lamp circuit can be simplified by detecting the timing at which the polarity of the limiter output is reversed from the phase comparator output.

Furthermore, by setting the voltage controlled oscillator depending on the polarity of the limiter output at the time of clamping, the clamping time can be shortened and switching noise can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a magnetic recording/reproducing apparatus according to a first embodiment of the present invention, FIG. 2 is a block diagram of a specific example of a clamping means in the first embodiment, and FIG. FIG. 4 is a block diagram of a magnetic recording/reproducing apparatus according to a second embodiment of the present invention, FIG. 6 is a block diagram of a magnetic recording/reproducing apparatus according to a third embodiment of the present invention, FIG. 6 is a waveform diagram of the third embodiment, FIG. 7 is a block diagram of a conventional magnetic recording/reproducing device, and FIG. 8 is a 7-step diagram of the same device.
A block diagram of a specific example of the slotted loop means, and FIG. 9 is a waveform diagram of the same device. 1.2... Rotating head, 6... Head switch means, 6... Polarity detection means, 7...
... Phase-locked loop means, 8 ... Voltage controlled oscillator, 9 ... Phase comparator, 1o ...
...Low pass filter, 16... Clamping means. Name of agent: Patent attorney Toshio Nakao and one other person7.
2--Head 5-Head switch +4-function 10-m-low-pass filter 15--clamping means Fig. 2 Fig. 3 Fig. 4 Fig. 5 L-++ ++++J Fig. 6 Cutting Fig. 7 Fig. 9 figure

Claims (3)

[Claims] (1) A rotary head having a plurality of heads for reproducing FM signals recorded on tracks formed diagonally with respect to the longitudinal direction of the magnetic tape, and a reproduction output from each head of the rotary head. It consists of a head switch means for switching alternately or sequentially according to a head switch signal, a voltage controlled oscillator, a phase comparator and a low pass filter, and converts the output signal of the head switch means into FM.
phase-locked loop means for demodulating, polarity detection means for detecting the polarity of the output signal of the head switch means, and clamping the operation of the voltage controlled oscillator at a predetermined phase at the time of change of the head switch signal. , and clamping means that releases the clamping by a change in the output of the polarity detecting means thereafter or after a predetermined period of time has elapsed. (2) The magnetic recording and reproducing apparatus according to claim 1, wherein the phase comparator of the phase lock loop means also serves as polarity detection means. (3) After clamping or after a predetermined time has elapsed since clamping, the voltage controlled oscillator output of the phase lock loop means is set to a polarity corresponding to the output of the polarity detection means. The magnetic recording and reproducing device described in .