JPH01248886A - Regenerative signal processing circuit - Google Patents

Abstract

PURPOSE:To eliminate a noise at a switching point and to prevent a level change at the switching point by detecting a low pass filter applied through a switching element to a reference voltage, and the pedestal level or synchronizing chip level of an output signal in an FM demodulating circuit and providing a reference voltage generating circuit given to the low pass filter as the reference voltage. CONSTITUTION:A control pulse Pb is formed by a control pulse generating circuit 19, and a low pass filter 11 is operated only in the period of the control pulse Pb. A video signal whose noise Sn is suppressed is taken off to an output terminal 18. A sampling pulse generating circuit 14 forms a sampling pulse Pa from a horizontal synchronizing signal. The Pa is supplied to a sample-and- hold circuit 12, and the pedestal level is sample-held. A sample-and-hold action is always executed, and since the output voltage of the sample-and-hold circuit 12 is made into the reference voltage of the low pass filter 11, the level change in the period of the control pulse Pb is prevented from being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reproduced signal processing circuit applied to processing reproduced signals of a rotary head type VTR.

[Summary of the invention]

In this invention, the output signal of the FM demodulation circuit is supplied to the reproduction signal processing circuit which converts the reproduction signals of a plurality of rotary heads into a single channel signal and demodulates the reproduction signal to FM, and the output signal of the FM demodulation circuit is supplied to the reproduction signal processing circuit which converts the reproduction signals of a plurality of rotary heads into a single channel signal and demodulates the reproduction signal to FM. A low-pass filter to which a reference voltage is applied via a switching element that is turned on, and a pedestal level or sync tip level of the output signal of the FM demodulation circuit are detected, and the detected pedestal level or sync tip level is applied to the low-pass filter as a reference voltage. A reference voltage generating circuit is provided to remove noise at the switching point and prevent level changes at the switching point.

[Conventional technology]

In a rotary two-head type VTR, output signals 4 from two rotary heads are converted into a one-channel reproduction signal by a reproduction switch circuit (referred to as an RFFM demodulation circuit). This regeneration switch circuit is controlled by RF switching pulses synchronized with the rotational phase of the rotary head. At the switching point where the output of one rotary head switches to the output of the other rotary head, the phase of the reproduced signal becomes discontinuous, and noise is generated when FM demodulated. This noise causes problems such as the synchronization separation circuit malfunctioning and the noise appearing in the middle of the screen.

For example, in order to solve such problems,
In Japanese Patent No. 174725, a pulse synchronized with the edge of the RF switching pulse is generated, this pulse is superimposed on the dropout detection pulse, and at the switching point, the reproduced video signal is changed to the video signal before IH (one horizontal period). A technique for removing noise by replacing the connector is described.

[Problems to be Solved by the Invention] In the reproduced signal processing circuit described in the above-mentioned document, since the signal before IH is superimposed, the switching point may be affected due to a shift in the lock phase of the servo during recording or reproduction. When the time number changes from the reference timing, the video signal or vertical synchronization signal is replaced, and the level changes at the switching point.

A problem arises in which this level change has the same negative effect as noise. - Therefore, it is an object of the present invention to provide a reproduced signal and signal processing circuit that can prevent the generation of noise at the switching point and that does not cause a level change in the signal after noise suppression.

[Means for Solving the Problems] - The present invention includes a reproduction switch circuit that combines reproduction signals of a plurality of rotary heads into one channel reproduction signal based on switching pulses, and an FM demodulation of the output signal of the reproduction switch circuit. an FM demodulation circuit; a low-pass filter to which the output signal of the FM demodulation circuit is supplied and a reference voltage is applied via a switching element that is turned on at a switching point by a switching pulse; and a pedestal level or sink of the output signal of the FM demodulation circuit. A reference voltage generation circuit is provided that detects the chip level and supplies the detected pedestal level or sync chip level to the low-pass filter as a reference voltage.

[Effect]

Switching point of output signal of rotating head (switching point)
In this case, noise is included in the FM demodulation output.

This noise is suppressed by a low-pass filter that operates only at the switching point. In this case, the reference voltage of the 6-bar filter is applied via a switching element that is turned on at a switching point, such as the pedestal level or sync tip level of the output signal of the FM demodulation circuit. Therefore, level changes caused by the operation of the low-pass filter are prevented.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.In FIG. 1, 1 and IB indicate a pair of rotating heads.
The zero-rotation drum is mounted on a rotating drum at an opposing interval of 18o and slides into contact with a magnetic tape that is wound around the circumferential surface of a rotary head at a winding angle slightly larger than 180°. One field is recorded as one diagonal track.

゛ □The signals reproduced by the rotary heads IA and IB are sent to the reproduction amplifier 2A via the rotary tragis (not shown).
and 2B. The output signals of the reproduction amplifiers 2A and 2B are converted into l-channel reproduction signals by a reproduction switch circuit including switch circuits 3A and 3B and an adder circuit 7. The switching circuit 3A has a transistor 4A, and the switch circuit 3B has a transistor 4B. The switching pulse Ps from the terminal 6 is supplied to the base of the transistor 4A, and the switching pulse Ps is inverted by the inverter 5 and supplied to the base of the transistor 4B. When transistor 4A is turned on, transmission of the output signal of rotary head IA is blocked and transistor 4A is turned on.
When B is turned on, transmission of the output signal of the rotary head IB is blocked.

Although not shown, the switching pulse Ps is
It is formed from detection pulses synchronized with the rotations of A and IB, and in one field scanned by the rotating head IA,
It is a pulse signal that is at a low level and inverted for each field where it becomes a high level in the 1 field scanned by the rotary head IB.

One channel of the reproduced signal from the adder circuit 7 is FM demodulated by the FM demodulation circuit 8 . The output signal of the FM demodulation circuit 8 is supplied to a de-emphasis circuit 10 via a low-pass filter 9, and a reproduced video signal is obtained at the output of the de-emphasis circuit 10. This reproduced video signal is transmitted through a low-pass filter 11, a sample hold circuit 12,
The signal is supplied to the horizontal synchronization separation circuit 13.

A horizontal synchronization separation circuit 13 separates a horizontal synchronization signal from the reproduced video signal, and supplies this horizontal synchronization signal to a sampling pulse generation circuit 14 .

The sampling pulse generation circuit 14 generates a sampling pulse Pa having a phase that matches the back porch of the horizontal blanking period. -Second sampling pulse P
a is supplied to the sample and hold circuit 12. Therefore,
The sample and hold circuit 12 outputs the pedestal level of the reproduced video signal.

The low-pass filter 11 includes a resistor 15 and a capacitor 16.
It has a low-pass characteristic determined by A terminal of a transistor 17 is connected to one end of the capacitor 16, and a terminal of the transistor 17 is connected to an output terminal of the sample and hold circuit 12.

The output terminal of low-pass filter 11 is derived as output terminal 18. The low-pass filter 11 includes a transistor 1
7 is on, and when the register 17 is off, the reproduced video signal is directly output to the output terminal 18.

A control pulse Pb is supplied to the base of the transistor 17 from a control pulse generation circuit 19 . A switching pulse 'Ps' from the terminal 6 is supplied to the differentiating circuit 20 and the inverter 21 of the control pulse generating circuit 19. The output signal of the inverter 21 is supplied to the differentiating circuit 22.

The output signals of differentiating circuits 20 and -22 are supplied to waveform shaping circuits 23 and 24, respectively. These waveform shaping circuits 23
and 24 are positive differentials) A control pulse Pb signal is generated from the waveform shaping circuits 23 and 724. This 'control pulse pb is generated at the rising edge and falling edge of the switching pulse Ps.

FIG. 2 is a waveform diagram of the tinging pulse Ps at each part in an embodiment of the present invention. As shown in FIG. 2B, the video signal obtained as the output of the L% de-emphasis circuit 10 contains noise Sn at the edge timing of the switching pulse Ps, that is, at the switching point. The control pulse generation circuit 19 generates the control pulse PMI- shown in FIG. 2C, and the low-pass filter 11 operates only during the period of this control pulse -Pb:. As shown in the second diagram, the low-pass filter 11 outputs a video signal with the noise Sp suppressed to the output terminal 18. In the "-sampling pulse generation circuit 14, a sampling pulse Pa shown in FIG. 2E is generated from the horizontal open" period signal. This sampling pulse Pa is supplied to the sample and hold circuit 12, and the pedestal level is sampled and held. This sample and hold operation is always performed, and an output signal as shown in FIG. 2F is generated. The output voltage of the sample hold circuit 12 is passed through the low pass filter 11.
Since the reference voltage is set as the reference voltage, a level change is prevented from occurring during the period of the control pulse Pb.

Note that the sample and hold circuit 12 may detect the sync tip level, and a voltage shifted by a predetermined level with respect to the detected sync tip level is supplied to the low-pass filter 11 as a reference voltage.

〔Effect of the invention〕

According to this invention, it is possible to prevent noise from occurring at the switching point. This invention has the advantage that even if the switching point changes somewhat, no level change occurs at the switching point, compared to a method in which the noise period is replaced with a signal before IH.

Furthermore, in this invention, noise is not suppressed to a fixed potential by the low-pass filter, but to a potential of the pedestal level or sync chip level of the reproduced video signal, so that the APL (average video level) of the reproduced video signal is suppressed.
can be made to follow the output signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part of the embodiment of the invention. Explanation of main symbols in the drawings IA, IB: rotating head, 3A, 3B: switch circuit 8: FM demodulation circuit, 11: low pass filter, 12: sample hold circuit, 18: output terminal. Agent Patent Attorney Masatoshi Sugiura

Claims (1)

[Scope of Claims] A reproduction switch circuit that combines reproduction signals of a plurality of rotary heads into one channel reproduction signal based on switching pulses; an FM demodulation circuit that demodulates an output signal of the reproduction switch circuit into an FM signal; A low-pass filter to which the output signal of the demodulation circuit is supplied and a reference voltage is applied via a switching element that is turned on at a switching point by the switching pulse, and a pedestal level or sync tip level of the output signal of the FM demodulation circuit is detected. and a reference voltage generation circuit that supplies the detected pedestal level or sync tip level to the low-pass filter as the reference voltage.