JPH01155794A - Auxiliary carrier signal separation circuit device - Google Patents

Abstract

PURPOSE: To provide a circuit device surely in operation even when a video signal is faulty by introducing a binary subcarrier signal whose phase position decides uniquely a time error even in the case of a video signal with a deteriorated signal/noise interval. CONSTITUTION: A high definition television video signal fed to a terminal 1 is fed to a delay stage 3 and a switching low pass filter 4 via a buffer stage 2. In the switching low pass filter 4, a low pass filter is switched to a control signal fed from a terminal 5 for a subcarrier signal period and in this case, a signal component with higher frequency, especially the subcarrier is not transmitted. The cut-off frequency of the switching low pass filter 4 is increased so that the high definition television video signal fed to the input side is sent almost without any change for other periods than the subcarrier period. Outputs of buffer stages 6, 7 connecting to the delay stage 3 and the switching low pass filter 4 respectively as post-stages are connected to an input of a comparator 8 and the subcarrier separated from the high definition television video signal is extracted from an output (terminal 9) of the comparator 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The invention relates to a subcarrier signal separation circuit arrangement according to the preamble of claim 1.

Conventional technology West German patent publication number? A reference signal generator for a time base correction circuit arrangement for correcting time base errors in a color video signal reproduced by a magnetic recording/reproducing device is known from JP 730368. The reference signal generator is configured to track the time error of the reproduced color video signal. Typically, the reference signal generator is triggered by a color synchronization signal of the reproduced color video signal. For this purpose, the color video signal is first fed to a gate circuit, which conducts the color sync signal to a bandpass filter during the color sync signal period.The bandpass filter passes the color sync signal, so that from the output side of the bandpass filter A separate color synchronization signal is extracted from the video signal. The obtained color synchronization signal is supplied to a level detection device for subsequent signal processing. A disadvantage of this known circuit arrangement for separating the color synchronization signal from the color video signal is that its operation is not sufficiently stable against disturbances in the reproduced color video signal. If the signal/noise spacing of the color video signal is poor, the reproduced color synchronization signal will be out of phase. Since the phase position of the separated color synchronization signal substantially determines the actual value of the time error, the correction of the time error by the time error corrector may be insufficient or erroneous—furthermore, the phase distortion may e.g. This occurs in the transmission section due to DC voltage deviations caused by circuit stages or amplification stages that are not stable over temperature.

SUMMARY OF THE INVENTION It is an object of the invention to provide a circuit arrangement according to the opening paragraph, which operates reliably even in the presence of disturbances in the video signal.

Means for Solving the Problems The present invention is characterized in that the subcarrier signal separation circuit device comprises a switched filter for transmitting a video signal, and the subcarrier signal separation circuit device comprises a switched filter for transmitting a video signal. is switched to a low-pass filter during the subcarrier signal period and operates as an all-pass network outside the subcarrier signal period, further comprising a comparator, the first input of said comparator being connected to said switched filter; A second input of the comparator is connected to an output, and a second input of the comparator is supplied with the video signal, and from the output of the comparator the resolved subcarrier signal is taken off.

Effects of the Invention The advantage of the circuit arrangement according to the present invention is that even in the case of a video signal with a poor signal/noise interval, it is possible to derive a two-way side carrier signal whose phase position uniquely determines the time error. be.

Advantageous embodiments of the circuit arrangement according to claim 1 can be realized by the measures specified in the other claims. 2, with jitter-free zero-passing by using a comparator in conjunction with the cut-off frequency of a switched low-pass filter;
A roadside carrier signal can be derived. Furthermore, there is an advantage that an analog switch which is unstable with respect to temperature and which gate-controls the subcarrier signal is not required.

Example Next, the present invention will be explained based on an example using figures.

In the following embodiments, high definition television video signals are recorded and played back. High definition television video signals have a bandwidth of 0 to about 22 MH2. In the region of the front black level porch during the horizontal blanking period of a high definition television video signal processed by a magnetic recording/reproduction device, there is one subcarrier signal consisting of many oscillation periods. This subcarrier signal is used as a pilot signal for detecting time errors in the reproduced high-definition television video signal. The frequency of oscillation of the subcarrier signal is approximately 4 MHz. Other (lower) subcarriers
Frequencies can be used similarly.

In the block circuit diagram shown in FIG.
The high definition television video signal supplied to the buffer stage 2 is then supplied to the buffer stage 2.

The high definition television video signal taken at the output of the buffer stage 2 is applied to a delay stage 3 and a switched low-pass filter 4. A buffer stage 6 or 7 is respectively connected downstream of the delay stage 3 and the switched low-pass filter 4. The outputs of the buffer stages 6 and 7 are connected to the inputs of a comparator 8, from which the subcarriers separated from the high-definition television video signal are taken off (terminal 9).

The function of this block circuit diagram will now be explained in detail with reference to the voltage-time diagram shown in FIG. The diagram at a in Figure 3 is a high-definition television digital video signal (terminal l).
A part of the horizontal blanking period area is shown. When this high-definition television digital video signal is transmitted, its frequency characteristics are not affected by the Bacher stage 2, the delay stage 3, and the Bacher stage 6. The high-definition television video signal taken at the output of the Bacher stage 6 is simply delayed in time with respect to the high-definition television video signal taken out at the terminal 1, and its amplitude is varied as the case may be. In the parallel branch, the high definition television video signal is passed from Bacher stage 2 to switched low pass filter 4 and then to Bacher stage 7.
and then to another input of comparator 8. In this case, the switchable low-pass filter 4 during the subcarrier signal period,
Under the control of the control signal (FIG. 3b) supplied from terminal 5, it is switched to a low-pass filter, in which case higher frequency signal components, in particular subcarriers, are not transmitted. Outside the subcarrier period, the cutoff frequency of the switching low-pass filter 4 is
The high definition television video signal applied to the input side is enhanced so that it is transmitted substantially unchanged. Outside the subcarrier signal period, the switched low-pass filter 4 therefore acts as an all-pass network. In FIG. 3a, a high definition television video signal processed by switched low pass filter 4 is shown.

d of FIG. 3 by dividing the low-pass filtered high-definition television video signal (FIG. 3C) from the direct high-definition television video signal (FIG. 3a'). The square binary subcarrier signal shown in is derived. By low-pass filtering during the subcarrier signal period, a DC voltage signal corresponding to the subcarrier is generated, which DC voltage signal is used as the dark value voltage for the comparator 8. Since only the bandwidth or corner frequency of the low-pass filter is switched, no build-up distortion in the form of over- or under-oscillations occurs in the separated subcarriers. Furthermore, the cutoff frequency of the switchable low-pass filter 4 is very low;
Advantageously, it can be chosen to be on the order of the scanning line frequency, so that disturbances, e.g. noise components, in the high-definition televised video signal are completely suppressed, so that the dark value voltage for the comparator 8 is equal to that of the subcarrier signal. Equal to the actual DC voltage level.

FIG. 2 shows a specific circuit arrangement of the block circuit diagram shown in FIG. Identical effects and functions are indicated by identical symbols in both figures. The high-definition television video signal supplied to terminal l is passed through differential amplifier 1.
0 to the voltage follower. The voltage follower corresponds to the Bacher stage 2 shown in FIG. The high definition television video signal taken from the low resistance output side of the voltage follower is fed via a resistor 11 to another differential amplifier 12.

The inverting input side and output side of the differential amplifier 12 are connected via a resistor 13. The non-inverting input side is connected to ground potential via a resistor I4.

In this resistor connection configuration, the differential amplifier 12 is connected as an inverting amplifier having an amplification effect. The function of this stage essentially corresponds to that of the delay stage 3 comprising the Bacher stage 6.

In the parallel branch, the high definition television video signal taken from the low resistance output of the voltage follower comprising the differential amplifier 10 is applied via a resistor 15 to the inverting input of the differential amplifier 16. In this differential amplifier 16 as well, the inverting input side and the output side are connected through a resistor 17, and the non-inverting input side of the differential amplifier 16 is connected through a resistor 18 to the ground potential. A high-definition television video signal is passed through a capacitor 19 and a resistor 20 to a differential amplifier 1.
6 is supplied to the non-inverting input side of 6. The control signal applied to the terminal 5 is applied to the gate electrode G of the field-effect transistor 21, to which a further capacitor 22 is connected in parallel to the capacitor 19 via the drain-source section of the field-effect transistor 21. Ru.

The outputs of the differential amplifiers 12 and 16 are each connected to one input of the comparator 8. A subcarrier signal is taken off from the output of comparator 8 via terminal 9.

The amplifier arrangement comprising the differential amplifier 16 also operates as an inverting amplifier. In contrast to the amplifier arrangement with the differential amplifier 16, on the non-inverting input side a high-definition television video signal which has been high-pass filtered by an RC element is supplied. During the subcarrier signal period, both capacitors 19
and 22 are connected in parallel to each other via the drain-source section of the field effect transistor 21. In this case, the time constant of the high-pass filter is expressed as Equation 1%. Outside the subcarrier spacing, the time constant is t2=(R18+R
20) It becomes C19. The magnitudes of the capacitances of both capacitors 19 and 22 and the resistance values of both resistors 18 and 20 shown in FIG. 2 have proven to be suitable in the case of a 4 MHz subcarrier of vibration. An inverting amplifier comprising a differential amplifier 16 cooperates with a high-pass filter consisting of an RC element to provide a signal which acts as a controlled reduction filter, such that the high definition television video signal taken from terminal 1 is , and is inverted by an inverting amplifier comprising a differential amplifier l2 and supplied to the comparator 8. Inversion is also performed with a switched low-pass filter comprising a differential amplifier 16. At the output of comparator 8, which has terminal 9, an inverted subcarrier signal is therefore tapped off.

The circuit arrangement according to the invention is not limited to the embodiment shown in FIG. Other embodiments, in particular embodiments for the switched low-pass filter, can be modified in various ways within the scope of the invention.

The block circuit diagram shown in FIG. 4 substantially corresponds to the block circuit diagram of FIG. 4th irta 23 and 24
The only difference is that they are inserted and connected. Both bandpass filters 23 and 24 are connected and disconnected by control signals shown in FIG. 3b. The band center frequency of the band pass filters 23 and 24 is approximately 4 MHz, that is, the frequency of the subcarrier signal. The function of these additional bandpass filters 23 and 24 is to symmetrize the signal fed to the comparator 8. Furthermore, bandpass filters 23 and 24
is used to suppress build-up vibration characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a circuit device of the present invention, FIG. 3 is a voltage-time diagram for explaining FIGS. 1 and 2, and FIG. FIG. 4 shows a block circuit diagram of one advantageous embodiment of the circuit arrangement according to the invention. l...terminal, 2...buffer stage, 3...delay stage,
4...Switchable low-pass filter, 5...Terminal, 6.7.
...Buffer stage, 8...Comparator, 9...Terminal, 11
...Resistor, 12...Differential amplifier, 13.14.15
...Resistor, 16...Differential amplifier, 17.18...
Resistor, 19... Capacitor, 20... Resistor, 21.
...Field effect transistor, 23.24... Bandpass filter. Dan FIG, 2 FIG, 3

Claims (1)

[Claims] 1. A subcarrier signal separation circuit device for transmitting a video signal during a blanking period, comprising a switching filter (4) for transmitting a video signal, the switching filter (4) ) is switched to a low-pass filter during the subcarrier signal period and operates as an all-pass network outside the subcarrier signal period, further comprising a comparator (8), the first of said comparators (8) The input side is connected to the output side of the switching filter (4), the second input side of the comparator (8) is supplied with the video signal, and from the output side of the comparator (8): A subcarrier signal separation circuit device characterized in that a separated subcarrier signal is extracted. 2. A delay device (3) for delaying the video signal, the delayed video signal being fed to the second input of the comparator (8), the delay time being determined by the switching filter (3) during the subcarrier signal period; 4. The subcarrier signal separation circuit device according to claim 1, wherein the signal transit time is equal to the signal transit time of item 4). 3. The first differential amplifier (1
6), a video signal is supplied to the inverting input side of the first differential amplifier (16) via a first resistor (15); The inverting input side of the differential amplifier (16) is connected to the output side of the first differential amplifier (16) via a second resistor (17). First capacitor (19) and third resistor (20) on the inverting input side
the video signal is supplied via the first differential amplifier (16), the non-inverting input side of the first differential amplifier (16) is connected to a fixed potential via a fourth resistor (18), and the first capacitor (19) ) via a switching transistor (21) in parallel with the second capacitor (2
Claim 1 or 2 characterized in that 2) is connected.
The subcarrier signal separation circuit device according to. 4. An amplification stage including a second differential amplifier (12) is provided in parallel with the switching filter (4), and a fifth amplifier is provided on the inverting input side of the second differential amplifier (12). A video signal is supplied via a resistor (11), and the inverting input side of the second differential amplifier (12) is connected to the second differential amplifier (1) via a sixth resistor (13).
2), and the non-inverting input side of the second differential amplifier (12) is connected to a fixed potential via a seventh resistor (14). 2. The subcarrier signal separation circuit device according to 2. 5. The subcarrier signal separation circuit according to claim 3 or 4, wherein the output sides of the first and second differential amplifiers (16 and 12) are connected to the input side of the comparator (8). Device. 6. The time constant of the switched filter (4) is substantially equal to the duration of the scan line during the subcarrier signal period, and the time constant of the switched filter (4) is substantially equal to the duration of the scan line during the subcarrier signal period; 2. Subcarrier signal separation circuit arrangement according to claim 1, characterized in that the subcarrier signal separation circuit arrangement is at least equal to the duration of the signal period of the signal. 7. One switched bandpass filter (23, 24) is connected upstream of each input side of the comparator (8), the band center frequency of said switched bandpass filter (23, 24) being equal to the frequency of the subcarrier signal. The subcarrier signal separation circuit device according to claim 1, characterized in that the subcarrier signal separation circuit device is equal to .