JPH0551229B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal processing circuit, and particularly to a signal processing circuit used in a magnetic video recording and reproducing device.

[Conventional technology]

In general, consumer magnetic video recording and reproducing devices (hereinafter referred to as VTRs) employ various methods to reduce noise that affects image quality. There are several signal processing circuits.

FIG. 3 is a block diagram of an example of a conventional signal processing circuit.

In FIG. 3, 1 is a first demodulation circuit comprising a first limiter 11, a first demodulator 12, and a first reduction filter 13, 2 is a delay circuit, and 3' is a second demodulation circuit.
a second demodulation circuit comprising a limiter 31, a second demodulator 32', and a second low-pass filter 33, 4 a differential amplifier 41, a third limiter 42, and an adder 4;
3. The first and second demodulators 12 and 32' each include, for example, a multiplier using a balanced modulator consisting of an operating circuit and a monostable multivibrator that delays the input signal by an output pulse width corresponding to one horizontal scanning period. This is a well-known FM demodulator consisting of a phase shift circuit.

The signal processing circuit detects uncorrelated noise contained in the reproduced luminance signal and removes it.

That is, as shown in FIG. 3, the input read FM signal is demodulated by the demodulator 12 via the limiter 11 of the demodulation circuit 1 to obtain the first luminance signal, and the FM signal is transmitted through the glass delay line. After being delayed by one horizontal scanning period through the configured delay circuit 2,
The signal is demodulated by a demodulator 32' via a limiter 31 of a demodulating circuit 3' to obtain a second luminance signal.

Since the luminance signals between adjacent scanning lines, such as the first luminance signal and the second luminance signal, have a strong correlation, the operational amplifier 41 of the arithmetic circuit 4 calculates the difference between the first luminance signal and the second luminance signal. When the difference component is taken, a noise component with no correlation is obtained as an output.

The output of the operational amplifier 41 is further passed through a limiter 42 to remove components above a predetermined level, and then added to the first luminance signal in an adder 43 to produce a third luminance signal in which small amplitude noise components are canceled out.
A reproduced luminance signal as a luminance signal is obtained. On the other hand, during recording, a recording circuit including an FM modulator and a voltage-current conversion circuit that converts the video signal to be recorded into a current according to its voltage level is used. the above
The FM modulator is a well-known current-controlled oscillator circuit consisting of an emitter-coupled non-stable multivibrator whose oscillation frequency is controlled by an emitter current. The current is converted and supplied,
It oscillates at a frequency corresponding to this current value.

[Problem that the invention seeks to solve]

The conventional signal processing circuit described above is used only when reproducing magnetic video recording, and when recording, a recording circuit including an FM modulator is separately required.

Therefore, a VTR is equipped with a signal processing circuit that has two sets of demodulation circuits and a recording circuit that includes a modulator. When implemented using an integrated circuit, there is a problem in that the chip size and number of chips increase, leading to an increase in price.

Note that instead of using a glass delay line, a charge-coupled device delay line can be used to delay the demodulated luminance signal by one horizontal scanning period, thereby forming one set of demodulation circuits. Since it is expensive, an increase in price cannot be avoided.

An object of the present invention is to provide a signal processing circuit that can reduce the number of elements, reduce the chip size, and reduce the cost.

[Means for solving problems]

The signal processing circuit of the present invention includes a limiter that inputs an FM signal that is a reproduction signal of magnetic video recording and outputs an amplitude-limited FM signal obtained by limiting the amplitude of the F signal, the amplitude-limited FM signal, and the amplitude-limited FM signal. a multiplier that multiplies the signal by a phase-shifted FM signal delayed by a predetermined delay time, a low-pass filter that low-pass filters the output of the multiplier and outputs a demodulated signal, and a predetermined constant current source or constant current source. A fixed control signal source that supplies a fixed control signal that is a voltage source, a signal conversion circuit that converts a video signal into a variable control signal that is a variable current or variable voltage in a predetermined format, and a switching control signal that controls unstable operation. and monostable operation is selected, and when the monostable operation is selected, the phase shift is triggered by the amplitude limited FM signal and the delay time is set by the fixed control signal.
an oscillation circuit consisting of an unstable monostable dual-use multivibrator that generates an FM signal and generates an FM modulation signal whose oscillation frequency is controlled by the variable control signal during the unstable operation; and an oscillation circuit that performs recording and reproduction under external control. and a control section that supplies the switching control signal for switching.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The difference between the embodiment shown in FIG. 1 and the conventional example shown in FIG. a control unit 5 which is equipped with a function and further controls switching between the two functions using a recording/reproduction control signal R/P;
By adding a voltage-current conversion circuit 6 that converts the video signal to be recorded into voltage and current for FM modulation, and a recording signal processing circuit 7 that performs processing such as amplitude control on the FM modulation signal and generates a recording signal. be.

In this way, the demodulator 32 is used during recording and reproduction.
The same circuit can be used for multiple purposes by switching the operation to the modulation or demodulation required for each operation.

FIG. 2 is a detailed block diagram of the demodulator 32 which also serves as a modulator in the embodiment shown in FIG.

As shown in FIG. 2, the demodulator 32 includes an oscillation circuit 321 using an unstable monostable dual-purpose multivibrator as a current control type, a multiplier 322 similar to the multiplier of the conventional demodulator 32', and an oscillation circuit. A switch 32 that switches the control current of 321 under the control of the control unit 5
3 and a constant current source 324 that is connected to one side of the switch 323 and supplies a set current for the monostable operation of the oscillation circuit 321, thereby achieving dual FM modulation and demodulation functions.

The above non-stable monostable multivibrator is
Turn off the positive feedback path of the emitter-coupled unstable multivibrator explained in the conventional FM modulator,
FM signal from limiter 31 is used as trigger input,
The control section 5 can be easily realized by fixing the emitter current to the above-mentioned set current and operating the same as the monostable multivibrator that constitutes the phase shift circuit of the conventional demodulator 32'. Connecting/disconnecting the positive feedback path and connecting the above FM to the above trigger input
In addition to controlling the connection/disconnection of the signal, the switch 323
The control current is switched to select either the set current from the constant current source 324 or the control current value obtained by converting the video signal by the voltage-current conversion circuit 6. That is, during playback operation, the positive feedback path is turned off, and instead the FM signal via the limiter 31 is supplied to the oscillation circuit 321 as the trigger input, and the set current from the constant current source 324 is supplied as the control current. be done.

During recording operation, the above positive feedback path is turned on,
The FM signal is separated from the oscillation circuit 321, and the output current from the current-current conversion circuit 6 is supplied as a control current. At the same time, the output of the oscillation circuit 321 is supplied to the recording signal processing circuit 7.

〔Effect of the invention〕

As explained above, the signal processing circuit of the present invention has
By using at least one of the two sets of demodulators used for noise cancellation during playback as a modulator during recording operation, the number of elements can be reduced when applied to semiconductor integrated circuits that require high integration. Therefore, it is possible to reduce the chip size, which has the effect of reducing the cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
This figure is a detailed block diagram of a demodulator used as a modulator in the embodiment shown in FIG. 1, and FIG. 3 is a block diagram of an example of a conventional signal processing circuit. 1... Demodulation circuit, 2... Delay circuit, 3, 3'...
... Demodulation circuit, 4 ... Arithmetic circuit, 5 ... Control section, 6
... Voltage-current conversion circuit, 7 ... Recording signal processing circuit, 11 ... Limiter, 12 ... Demodulator, 13 ...
...low-pass filter, 31... limiter, 32,3
2'...Demodulator, 33...Low pass filter, 41...
... operational amplifier, 42 ... limiter, 43 ... adder, 321 ... oscillation circuit, 322 ... multiplier, 3
23...Switch, 324... Constant current source.

Claims (1)

[Claims] 1. An amplitude-limited FM that inputs an FM signal that is a reproduction signal of magnetic video recording and limits the amplitude of the FM signal.
a limiter that outputs a signal; a multiplier that multiplies the amplitude-limited FM signal by a transfer FM signal obtained by delaying the amplitude-limited FM signal by a predetermined delay time; and low-pass filters and demodulates the output of the multiplier. a low-pass filter that outputs a signal; a fixed control signal source that supplies a fixed control signal that is a predetermined constant current source or a constant voltage source; and a variable control signal that supplies a video signal that is a variable current or variable voltage in a predetermined manner. a signal conversion circuit for converting the signal into a signal; and a switching control signal selects either an astable operation or a monostable operation, the monostable operation is triggered by the amplitude limited FM signal, and the fixed control signal triggers the an oscillation circuit comprising an astable monostable dual-purpose multivibrator that generates the phase-shifted FM signal with a set delay time, and generates an FM modulation signal whose oscillation frequency is controlled by the variable control signal when in the astable operation; 1. A signal processing circuit comprising: a control section that supplies the switching control signal for switching recording/reproduction according to an external command.