JPH0231547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a circuit capable of removing a synchronization signal contained in a composite video signal.

First, FIG. 1 shows the configuration of a signal circuit of a conventional color television receiver. The luminance signal in the composite video signal is amplified by a first video amplification circuit 1, a second video amplification circuit 2, and a third video amplification circuit 3. On the other hand, after the carrier color signal is amplified by the first video amplification circuit 1,
The carrier color signal is applied to a first band amplification circuit 4, and the carrier color signal is input to a second band amplification circuit 5 and a burst amplification circuit 6. The carrier color signal amplified by the second band amplification circuit 5 is input to demodulation circuits 8, 9, and 10 for RY, GY, and BY. Burst amplification circuit 6
The burst signal amplified by the burst signal is input to the subcarrier generation circuit 7 which generates a subcarrier signal using the burst signal, and the subcarrier signal from the subcarrier generation circuit is also R-Y, G-Y, B-Y.
is input to demodulation circuits 8, 9, and 10. In demodulation circuits 8, 9, and 10, color difference signals RY, G-Y, and BY are demodulated from the two signals.

The luminance signal from the third video amplification circuit 3 and R-
The color difference signals from the Y, G-Y, B-Y demodulation circuits 8, 9, and 10 are mixed by the R, G, and B video output circuit, and demodulated into the R, G, and B primary color signals 14R, G, and B. is used to drive the cathode ray tube.

Next, FIG. 2 shows a configuration for explaining a circuit using a synchronization signal removal circuit according to an embodiment of the present invention. FIG. 2 shows R,
A circuit that demodulates G and B primary color signals (the first
The circuit configuration shown in the figure is intended to drive a cathode ray tube by switching between the R, G, and B signals from the circuit 15 and the R, G, and B signals from a camera and the like.

The primary color signals 14R, 14G, 14B and the primary color signals 17R, 17G, 17B from cameras, etc. are switched by a video switch circuit 16, and are connected to a video amplification circuit 18, a clamp circuit 19, and a video output circuit 2.
0 to the cathode ray tube.

Next, the circuit configuration of each block will be explained. The demodulation circuit 15 uses the same circuit configuration as explained in FIG. The first and second band amplifier circuits 4 and 5 are demodulation circuits for supplying a carrier color signal to the color difference demodulation circuits 8, 9, and 10, and this carrier color signal includes a 3.58MHz burst signal. . When the above-mentioned burst signals are included in the signals applied to the color difference demodulation circuits 8, 9, and 10 and are applied together, the burst signals are demodulated and output on the back porch of the primary color signals, as shown in FIG. 3a.

Now, considering removing the burst signal from the color difference demodulation input, a circuit is used that stops the operation of the second band amplifier circuit 5 during the burst signal period in order to remove the burst signal.

However, a circuit system that requires removing the burst signal from the output signal of the band amplification circuit 5 is a circuit that uses a DC blocking capacitor between the stages from the demodulation circuit connected to the band amplification output stage to the cathode ray tube. , when a so-called AC coupling circuit is used, and this circuit system corresponds to a color difference signal drive system. In the primary color signal drive system that is the mainstream of color television receivers, everything from the demodulation circuit to the cathode ray tube is DC coupled, so there is no need for a DC regeneration circuit for color difference signals, and therefore there is no need to remove burst signals. do not have.

On the other hand, due to improvements in IC technology, the circuit configuration shown in Figure 1 has been created using a single-chip IC. Furthermore, as mentioned above, due to the primary color signal drive system and the need to minimize the number of IC terminals, it has not been done recently to remove burst signals from band amplification circuits.

In this way, the R, G, B signals 14R, 14G, 14B having the demodulated output of the burst signal, and the R, G, B signals 17 of the camera etc. shown in FIG.
The R, 17G, and 17B primary color signals are switched by the video switch circuit 16 and sent to the video amplifier circuit 1.
8 and input to the clamp circuit 19.

This clamp circuit 19 is a circuit for reproducing the DC component, and prevents the same image from becoming a different color even if the DC level of the three primary color signals of R, G, and B changes and the image content changes. It is. This clamp circuit 9 conventionally performs clamping at the back porch of the synchronization part of the video signal to reproduce the DC component.

Here, even if an attempt is made to clamp the clamp pulse with the pulse shown in FIG. In FIG. 3a, the demodulated burst signal is output. Therefore, when clamping at this portion, the brightness of the cathode ray tube becomes brighter than when clamping the R, G, B primary color signals (FIG. 3b) from a camera or the like.

Although only the waveform shown in FIG. 3A has been described here, the amplitude and polarity of the burst portion of the demodulated signal change depending on the phase of the burst input to the color difference demodulation circuits 8, 9, and 10. If the clamp method described above is used, the white balance on the cathode ray tube will shift.

Therefore, the synchronization signal part of one horizontal period is shown in Fig. 3d.
If you clamp with a clamp pulse like
The waveforms shown in the output a of the demodulation circuit 15 and the output b of the camera or the like in the figure are clamped, and a brightness difference also appears on the screen. In other words, it becomes necessary to change the brightness adjustment each time the signal is switched. For example, if the brightness is adjusted in accordance with the signal shown in FIG. 3a and then switched to the signal shown in FIG. 3b, the brightness will become dark. (Screen with black spots) In the opposite case, it becomes brighter. (Black screen) 20 is a video output circuit, and this signal drives a cathode ray tube.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a synchronization signal removal circuit that solves the conventional problems as described above.

FIG. 4 shows a circuit configuration of an embodiment of the present invention.

First, the signal processing of the demodulation circuit 15 mentioned above will be explained. The composite video signal is separated into a luminance signal and a carrier color signal by a comb filter circuit 21.
The SYNC portion of the luminance signal is removed by a horizontal period and synchronization signal (hereinafter referred to as SYNC) removal circuit 22, and the signal is made equal to the pedestal level and amplified by a video amplification circuit 46. One carrier color signal is the first
The signal is input to the band amplification circuit 4. In the following, parts similar to the circuit operations shown in FIG. 1 described above will be omitted. Primary color signals 14R, 14 demodulated from the composite video signal
G, 14B and primary color signals 17R, 17 from cameras, etc.
G and 17B are switched by the video switch circuit 16, amplified by the video circuit 18 as explained in FIG. 2, a DC component is reproduced by the clamp circuit 19, and amplified by the video output circuit 20 to drive the cathode ray tube.

FIG. 5 shows a specific example of the synchronization signal removal circuit 22 of the present invention. FIG. 6 shows signal waveforms of various parts for explaining the present invention.

The composite video signal shown in FIG. 6i is inputted to the base of the transistor 23 from the input terminal shown in FIG. 5e. An emitter resistor 25 and a collector resistor 24 are connected to the transistor 23, and an inverted composite video signal is input from the collector to the base of the transistor 26. A resistor 27 is connected to the emitter of the transistor 26.
The impedance-converted composite video signal is connected to the connection point of the bias resistor 46, the base of the transistor 29, and the collector of the transistor 31 via the capacitor 28.

Transistor 31, bias resistor 32, resistor 3
3, diode 36, emitter resistor 37, resistor 3
4. The capacitor 35 constitutes a clamp circuit. The clamp pulse signal shown in FIG. 6 j is inputted to the base of the transistor 31 from the terminal f via a resistor 34 and a capacitor 35. During the period of this positive pulse j, the transistor 31 is turned on, and the resistor 32 and The pedestal level of the composite video signal is fixed to the DC level at the intersection of the diode 36 and the resistor 37.

The clamped composite video signal is transferred to transistor 2.
The impedance is converted by 9, and the signal is input to a differential amplifier circuit composed of transistors 38, 39, and 40. The aforementioned composite video signal is input to the base of the transistor 38 of the differential pair of transistors 38 and 39. A load resistor 41 is connected from the collector of the transistor 38 to the intersection of the collector of the transistor 23 and the base of the transistor 26.

On the other hand, the base of the differential pair transistor 39 is
The emitter of a transistor 31 constituting a clamp circuit is connected to the intersection of a diode 36 and a resistor 37. In order to make the base potential of the differential pair transistor 39 the same as the pedestal level potential of the composite video signal input to the transistor 38, the voltage V _BE between the base and emitter of the transistor 29 is corrected by a diode 36. has been added.

Next, the current source transistor 40 of the differential amplifier circuit
An emitter resistor 43 is connected to the emitter, and the base is grounded via a diode 44 and a resistor 45.

The positive SYNC shown in FIG. 6 k is input to the FIG. 5 terminal g. The transistor 40 is turned on only during the positive SYNC period, and the differential amplifier circuit operates. Here, the composite video signal shown in FIG. 6i is inverted by the transistor 23 and applied to the base of the transistor 38. As described above, the potential of the pedestal of the composite video signal input to the base of the transistor 38 of the differential pair of the differential amplifier circuit and the potential of the base of the transistor 39 of the differential pair are the same potential.

Next, since the SYNC portion of the base of transistor 38 is in a more positive direction than the pedestal, transistor 38 turns on. transistor 38 is on,
Transistor 39 is turned off, transistor 40 is turned on, current flows from the power supply to transistors 38 and 40 via resistor 24 and resistor 41, and the collector potential of transistor 23 decreases.

Conversely, when the SYNC at the base of the transistor 38 becomes smaller than the pedestal, the transistor 38 is turned off and the transistor 39 is turned on, and when the SYNC level at the base of the transistor 38 reaches the pedestal level, it becomes the same potential as the base potential of the transistor 39. The operation of the differential amplifier circuit stops.

SYNC in the composite video signal is removed by the method described above.

The video signal from which SYNC has been removed is taken out from the base of the transistor 38 of the differential pair.
The video signal shown in FIG. 6 l is taken out from the terminal h in FIG. 5 and input to the video amplification circuit 46 shown in FIG. 4. The primary color signals 14R, 14G, 1 are input to the video switch circuit 16 by the method described above.
4B and primary color signals 17R, 17G, 17 from cameras, etc.
The SYNC part of B is the same level as the pedestal part, and even if the SYNC part is clamped and the DC component is regenerated as explained in Figure 2, the brightness level on the screen will change when the signal is switched. can be improved.

As described above, according to the present invention, it is possible to obtain a useful circuit that can effectively remove a synchronization signal from a composite video signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a color television receiver, Fig. 2 is a block diagram of an example of a cathode ray tube drive circuit in which the sync signal removal circuit of the present invention is used, and Fig. 3 is a block diagram of a color television receiver.
4 is a circuit diagram of an example of a color television receiver in which the sync signal removal circuit of the present invention is used. FIG. 5 is a circuit diagram of a sync signal removal circuit in an embodiment of the present invention. 6 are waveform diagrams of each part. 15... Demodulation circuit, 16... Video switch,
18... Video amplification circuit, 19... Clamp circuit,
20...Video output circuit, 22...Synchronizing signal removal circuit, 28...Capacitor, 31...Transistor, 36...Diode, 37...Resistor, 29,
38, 39, 40...transistor.

Claims (1)

[Scope of Claims] 1. An input circuit into which a television composite video signal is input, a clamp circuit that clamps the input composite video signal, and a comparison circuit that compares the clamped composite video signal with a clamp level. and a feedback circuit that feeds back the output of the comparison circuit to the input circuit, and is configured to remove a synchronization signal from the composite video signal. 2. Claim 1, characterized in that the clamp circuit is one that clamps the back porch of the synchronization part in the composite video signal, and the comparison circuit is a differential amplifier that operates only during the synchronization signal period. The synchronization signal removal circuit described.