JPS61139966A - Signal reproducing circuit of magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To eliminate the discontinuity of a phase in the switching time point, and to eliminate a pulsative noise generated in a reproducing signal by selecting and switching the respective waves to be modulated, after phases of the respective waves to be modulated, which are obtained from two rotary heads have coincides with each other. CONSTITUTION:A voice FM signal which has been brought to sound recording is reproduced by rotary heads 11a, 11b, amplified 12a, 12b, a signal of a prescribed band is fetched by BPFs 13a, 13b, and its amplitude is limited by limiters 14a, 14b, and signals F, G are outputted. when a phase difference of these signals F, G becomes below a prescribed value, a phase difference detector 15 is operated, and its output is provided to an OR gate 22. Also, a control signal for selecting an output of the heads 11a, 11b and obtaining a continuous signal is inputted to an input terminal 19, an output of rise and fall of its signal is provided to the gate 22, an output of the gate 22 is provided as a clock of a D latch 23, and the control signal is applied as a data. In this state, a switch 16 is controlled by an output signal J of the latch 23, the discontinuity of the time for switching the signals F, G is eliminated, and the signals F, G are reproduced by a demodulator 17.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a signal reproducing device for a magnetic recording and reproducing device, such as a video tape recorder, which reproduces a recorded audio signal by modulating it using rotation and attenuation. be.

2. Description of the Related Art In recent years, recording and reproduction of audio signals in video tape recorders has been achieved by frequency modulation (hereinafter referred to as FM) of high-frequency carrier waves.
This is done using a rotating head. An example of the signal reproducing circuit of the conventional video tape recorder mentioned above will be described below with reference to the drawings.

FIG. 3 is a block diagram of a conventional signal reproducing circuit, and FIG. 4 is a waveform diagram of each part thereof. In FIG. 3, 1a and 1b are rotary heads, and 2a and 2b are amplifiers for amplifying the signals reproduced by the rotary heads 1a and 1b provided with a rotary cylinder (not shown) K. Reference numeral 3 denotes an input terminal to which a control signal synchronized with the rotation of the rotary heads 1a, 1b is input. A switch 4 is controlled by a control signal input from the input terminal 3 and switches the outputs of the amplifiers 2a and 2b. Reference numeral 6 denotes a band pass filter (hereinafter referred to as BPF) that passes only a predetermined frequency band among the signals selected by the switch 4. 6 is a limiter that keeps the amplitude of the output signal of the BPF 5 at a constant level. A demodulator 7 demodulates the audio signal from the carrier wave output from the limiter 6. The operation of the video tape recorder signal reproducing circuit configured as described above will be explained below.

First, an audio FM signal recorded on a magnetic tape is reproduced by the rotary heads 1a and 1b, and then reproduced by the amplifier 2a.

2b is amplified. The magnetic tape is placed in a rotating cylinder with 18
The output waveforms of the amplifiers 2a and 2b are wrapped in a spiral at an angle slightly larger than 0 degrees, and the rotating beds 1a and 1b are attached to the rotating cylinder at a positional relationship of 180 degrees to form two rotating heads. becomes like signals A and B in FIG.

Then, the switch 4 selects the signal A or B.

The switch 4 is controlled by a control signal input from the input terminal 3. The control signal input to input terminal 3 is
This is shown in signal C in the figure. The output waveform of switch 4 controlled by control signal C is shown in Figure 4. The audio FM signal obtained in this way is extracted only in a predetermined frequency band by BPFs, and after the amplitude is made constant by +7 Mitsuta 6, it is sent to a demodulator consisting of a phase-locked loop (hereinafter referred to as PLL) etc. 7, demodulated into an audio signal, and outputted to an output terminal 8.

Problems to be Solved by the Invention However, in the above configuration, when the switch 4 is switched, if there is an effect such as expansion or contraction of the magnetic tape, the phase of the output signal of the switch 4 becomes discontinuous. When the phase becomes discontinuous, the demodulated output of the demodulator 7 has the problem of generating pulse-like noise as shown in FIG. 4E.

In view of the above-mentioned problems, the present invention provides a signal reproducing circuit that can reduce the generation of pulse-like noise even if the modulated waves obtained from two rotating heads are switched.

Means for Solving the Problems In order to solve the above problems, the signal regeneration circuit of the present invention comprises:
A phase detector that detects the phase difference between the respective modulated waves obtained from the two rotating heads and operates when the phases almost match, and selects each of the above-mentioned modulated waves by the operation of this phase detector. It is equipped with a switch.

Effect of the Invention According to the present invention, each modulated wave obtained from the two rotating heads is selected and switched after the phases of the modulated waves obtained from the two rotating heads coincide with each other by the above-described configuration, so that there is no phase discontinuity at the time of switching. , pulse-like noise does not occur in the demodulated audio signal.

Embodiment Hereinafter, a signal reproducing circuit of a magnetic recording/reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a signal reproducing circuit according to the present invention. In Fig. 1, 11a and 11b are 180° to the cylinder (not shown).
a rotating head 12a mounted in the positional relationship of;
12b is an amplifier for amplifying the signal reproduced by the rotary heads 11a and 11b; 1&a and 13b are amplifiers 12a and 12b
This is a bandpass filter that extracts a signal in a predetermined frequency band from the output signal of the . 14a and 14b are limiters that keep the amplitude of the signal constant, and 16 is a limiter 14a.

A phase detector that operates when the phases of the output signals of 14b substantially match, 16 a switch that switches the output of the limiters 14a and 14b according to the operation of the phase detector 15, and 17 a frequency connected to the output terminal of the switch 16. A demodulator 18 demodulates the modulated wave, and 18 is an output terminal that outputs the demodulated signal. 19 is synchronized with the rotation of the rotating heads 11a and 11b;
Input terminal 2o is input terminal 19 for inputting a control signal for selecting and switching the playback signal of each rotary head.
An edge detector 21 detects the rising edge (change from low level to high level) and falling edge (change from y level to low level) of the control signal inputted to the edge detector 20. an excited monostable multivibrator; 22 is an OR gate that ORs the output of the phase detector 16 and the output of the monostable multivibrator 21;
23 is a D latch. FIG. 2 shows a waveform diagram at each part of the block diagram of FIG. 1.

The operation of the signal reproducing circuit configured as described above will be explained below with reference to FIGS. 1 and 2.

The audio FM signal, which is a modulated wave recorded on a magnetic tape, is reproduced by rotating heads 11a and 11b attached to cylinders, amplified by amplifiers 12a and 12b, and then converted to a predetermined frequency by bandpass filters 13a and 13b. A band signal is extracted. Thereafter, when the amplitude is made constant using limiters 14a and 14b, intermittent signals F and G are obtained. Signals 2 F and G are applied to a phase detector 15, and signals F and G
When the phase difference becomes less than a predetermined value (for example, less than 20'), the phase detector 16 is activated. Since the output of the phase detector 15 is applied to the clock terminal of the D latch 23 through the OR gate 22, it is applied to the input terminal 19 which selects the output of each rotary head which is an intermittent signal to obtain a continuous signal. After the rising or falling edge of the control signal is input and the phase difference between signals F and G becomes small, D
The Q output of latch 23 changes like signal I. Signal I
Since the switch 16 is switched in accordance with the change in , a signal H whose phase is substantially continuous is obtained at the output terminal of the switch 16. Therefore, no pulse noise is mixed into the demodulated signal of the demodulator 17, and a good audio signal is outputted to the output terminal 18.

Further, when there is a dropout in the reproduction signal of the rotary head 11a or 11b and the phase detector 15 does not operate, the edge detector 20 for detecting the rising and falling edges of the control signal is activated by the rotary head 1a.

11b were both set to a time slightly shorter than the period during which the signal was regenerated (for example, 250 microseconds).

Since the monostable multivibrator 21 is driven and its output signal K is applied to the OR gate 22, the rotary head on the side where the switch 16 is not switched and is not reproducing the signal will not be selected.

As described above, according to this embodiment, a switch is provided to detect the phase difference between the respective signals reproduced by the two rotary heads, match the phases, and switch the selection. . 2,
2. Yo, Ioya, you can construct a signal regeneration circuit.

Effects of the Invention As described above, the present invention provides a phase detector that detects the phase difference between the reproduction signals of two intermittent signals such as two rotating heads, and a By providing a switch that selects and switches the reproduced signal, it is possible to obtain a signal reproducing circuit for a magnetic recording and reproducing apparatus in which pulse noise does not occur in the audio signal demodulated from the reproduced signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a signal reproducing circuit of a magnetic recording/reproducing device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of each part of FIG. 1, and FIG. 3 is a signal reproducing circuit of a conventional magnetic recording/reproducing device. The block diagram '1lJ4 is a waveform diagram of each part in FIG. 11a, 11b - single rotation head, 12a, 12b... amplifier, 16... phase detector, 16... - switch, 17... demodulator, 20... edge circuit,
21... Monostable multivibrator, 22...
...or gate~, 23...D latch. Name of agent: Patent attorney Toshio Nakao and one other person1i
! Figure J1/l Figure 2 Sea M-Ichigo--1-1

Claims (1)

[Claims] first and second amplifiers that amplify first and second input signals that are intermittent signals; a phase detector that operates when the phases of the output signals of the first and second amplifiers substantially match; After the rising or falling edge of the control signal is input in synchronization with the intermittent period of the first and second input signals, the output signals of the first and second amplifiers are selected in synchronization with the output of the phase detector. 1. A signal reproducing circuit for a magnetic recording/reproducing device, comprising a switch circuit for switching.