JPS6328394B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a still image color television signal demodulation device, and more particularly to a circuit for synchronizing a color signal demodulation signal with a subcarrier in an input signal.

In still image systems, band compression devices that drop frames or fields, etc.
A color television signal for one frame or one field is stored in a storage circuit, and is repeatedly read out from the storage circuit and displayed on a color television monitor. Therefore, the phase of the subcarrier in the color television signal becomes discontinuous at the start of a frame, so the phase synchronization oscillator performs synchronization at every frame start. Therefore, in a conventional demodulating device for a still picture color television signal, an input signal is input to a color demodulator, and a carrier color signal is demodulated in the color demodulator based on the output of the phase-locked oscillator, and a signal and a luminance signal are demodulated. When creating and outputting red, green, and blue signals from the signals, there is a drawback that the output of the phase-locked oscillator at the beginning of the frame is not accurate, and the demodulated color varies and deteriorates. That is, the color of the image deteriorates over several dozen lines at the top of the screen. In order to solve this drawback, the output voltage according to the phase difference between the phase of the phase synchronized oscillator and the subcarrier in the input signal is smoothed, and the time constant of the wave generator used to supply it to the phase oscillator is reduced. If the time is shortened, the disadvantage is that the stability of the oscillation frequency after the phase-locked oscillator is pulled in becomes poor.

The purpose of the present invention is to solve the above-mentioned conventional drawbacks and
An object of the present invention is to provide a still image color television signal demodulation device capable of faithfully and stably demodulating a still image signal in which one frame or one field of color television signal is repeatedly output.

The demodulation device of the present invention includes a sync separator that separates and outputs a sync signal from an input signal, an oscillator that outputs a color signal demodulation signal whose oscillation frequency phase is controlled by a control signal, and an output signal of the oscillator. a phase difference circuit that controls the phase of the oscillator by outputting a control signal according to a phase difference between the input signal and a subcarrier signal in the input signal; and a phase difference circuit that demodulates the input signal based on the output of the oscillator and outputs a color signal. a still image color television signal demodulating device comprising a color demodulator, one or more phase shifters for shifting the phase of the output signal of the oscillator, and selecting the output of the oscillator or the output of any of the phase shifters; a switch that uniformly selects and supplies the signal to the color demodulator; the output signal of the switch is supplied to the phase difference circuit, and the frame pulse, field pulse, etc. output from the sync separator is provided. The present invention is characterized in that the switching device is controlled to switch the phase of the output signal of the oscillator and output the signal.

In the above-mentioned apparatus, the output signal of the oscillator and the output signal of each phase shifter may be phase-compared with the subcarrier signal, and the phase shifter output that provides the smallest phase difference may be selectively output. For example, if the phase change of the input signal is not periodic,
For example, it is effective for signals in which the same frame signal is sometimes repeated in ordinary television signals.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In this embodiment, a still image is obtained by repeatedly inputting one frame of a color television signal based on the NTSC system. In other words, terminal 1 has
One frame of a color television signal based on the NTSC system is repeatedly input, and the sync separator 2
The frame synchronization signal at the beginning of one frame and other synchronization signals are synchronously separated and applied to a color demodulator 3 and a phase synchronization oscillator 4. The color demodulator 3 demodulates the carrier color signal in the input signal using a demodulation signal created based on the output of the phase synchronized oscillator 4,
Red, green, and blue color signals are created from this and the luminance signal and output from terminals 8, 9, and 10. Although various methods are known for demodulating color signals, this embodiment can be used with any conventionally known color demodulator. The phase synchronized oscillator 4 extracts a subcarrier signal from the color burst portion of the input signal 5, and outputs an oscillator output that is phase synchronized with this subcarrier signal or a signal whose phase is different by π from this subcarrier signal into the synchronization signal 7 outputted by the synchronization separator 2. The signal 6 alternately switched by the frame pulses is supplied to the color demodulator 3. Therefore, the phase of the color demodulation signal 6 input to the color demodulator 3 changes by π at the time of frame switching, and matches the phase of the subcarrier signal in the next frame. Therefore, unlike the conventional demodulator described above, the color of the image does not deteriorate until phase synchronization is established in the first part of the frame. That is, a stable demodulated signal of good quality can be output.

The phase synchronized oscillator 4 is constructed as shown in FIG. That is, the input signal 5 is input to the phase difference circuit 41. The phase difference circuit 41 extracts the color burst portion of the input signal 5 using the color burst gate signal in the synchronization signal 7 supplied from the synchronization separator 2 (FIG. 1) to obtain a subcarrier signal. A control signal 49 corresponding to the phase difference between the output signal 6 and the output signal 6 of the switch 44, which will be described later, is output. The control signal 49
2 and then supplied to the oscillator 43. The oscillator 43 is an oscillator whose phase is controlled by the output signal of the wave generator 42, and is controlled so that the phase difference with the subcarrier signal is small. The output signal of the oscillator 43 is given a phase shift of 0 radian and π radian by phase shifters 45 and 46, respectively.
The outputs 47 and 48 are selectively outputted by the switch 44. The switch 44 switches the phase shifter 45 or 46 according to the frame synchronization pulse in the synchronization separation signal 7 (outputted from the synchronization separator 2 in FIG. 1).
Outputs are selected and output alternately. The output of the switch 44 is supplied to the color demodulator 3 (FIG. 1) as a signal 6 for color demodulation. The phase shifter 45 is 0
Since it provides a phase shift of radians, the output of the oscillator 43 may be simply provided to the switch 44 through a through connection without any special provision. Also, phase shifter 4
Since 6 is a π radian phase shifter, it can be obtained simply by an inverting connection. Therefore, by inverting the output of the oscillator 43 every frame using an inversion switch, the phase shifter 45, phase shifter 46, and switch 44 can be integrated. In this case, the reversing switch is the switch 4 and also the phase shifter 46.

In this embodiment, the switch 44 is configured as shown in FIG. This circuit is configured to prohibit the above-mentioned phase switching when an input signal in which there is no phase jump of the subcarrier signal at the time of frame switching, such as a normal television signal, is input. In this case, the control signal 49 output from the phase difference circuit 41 (FIG. 2) is input to the comparator 441 and compared with a constant reference value. Phase difference circuit 41 (Figure 2)
The output phase of the oscillator 43 (Fig. 2) is inverted and input for each frame, and this is compared with the subcarrier signal without jumps, so the value of the control signal 49 becomes large near the beginning of each frame. , the comparator 441 detects this, outputs a high level, and sends it to the counter 442. On the other hand, input the synchronization signal 7 to the frame pulse extraction circuit 444, input the extracted frame synchronization pulse to the counter 442,
A counter 442 samples and counts the output of the comparator 441 according to the frame synchronization pulse. In other words, control signal 4 is output at the beginning of the frame.
The number of frames in which 9 is increased is counted. Then, when the count value exceeds a certain value (for example, 16), a high level is output and the flip-flop 443 is inverted. The output of flip-flop 443 causes flip-flop 445
The operation of the flip-flop 445 is prohibited and the flip-flop 445 is kept in a constant state. That is, flip-flop 445 does not invert on every subsequent frame sync pulse, so switching circuit 446 causes phase shifter output 47 to
or 48 continuously. When a still image signal is input, the flip-flop 445 inverts each frame synchronization signal and switches the switching circuit 446.
The phase of the subcarrier signal in the input signal matches the phase of the subcarrier signal in the input signal. Therefore, the value of control signal 49 is small, flip-flop 443 does not invert, and flip-flop 445 continues to invert every frame synchronization pulse. According to this embodiment,
When a normal television signal is input, it is convenient because the operation of switching the phase of the demodulation signal for each frame is stopped and the normal demodulation operation is performed. However, the above-mentioned phase switching prohibition function is
It is not an essential component of the present invention.

FIG. 4 is a waveform diagram showing the signals of each main part in FIG. The demodulation signal 6 output from the switch 44 is shown. That is, the output phase is switched by the frame synchronization pulse, and the output phase changes from the first frame to the second frame.
The output phase is inverted at the time of conversion to a frame.

In the above embodiment, the switch 44 in FIG. 2 is switched by a frame synchronization pulse, but if the input signal is a field repetition, it is sufficient to switch by a field pulse, and the cycle corresponding to the format of the input signal can be changed. You can switch it with . Also, if the input signal
For PAL color television signals, 0,
It is sufficient to provide phase shifters of π/2, π, and 3/2π and to sequentially switch the outputs of these four phase shifters. In this case, the flip-flop 445 in FIG.
Four-state switching signals are periodically generated by a two-stage flip-flop.

Note that the oscillation frequency of the oscillator 43 in FIG. 2 is not the frequency of the subcarrier signal but its integer (n).
It is also possible to oscillate at twice the frequency and provide a 1/n frequency divider between the oscillator and the phase shifter.

FIG. 5 is a block diagram showing another embodiment of the invention. In this case, the switch 44' is configured to compare the plurality of phase shifter outputs with the phase of the subcarrier signal of the input signal, and select and output the phase shifter output with the smallest phase difference. It is therefore suitable, for example, in cases where frame or field repetition occurs occasionally in ordinary television signals, ie where the phase changes of the input signal are not periodic. That is, in FIG. 5, input signal 5 is input to phase difference circuit 41 and also to auxiliary phase difference circuits 448 and 449. The output of the phase difference circuit 41 is smoothed by a wave generator 42 and used as a phase control signal for an oscillator 43. The output signal of the oscillator 43 is given a phase shift of 0 radian and π radian by phase shifters 45 and 46, respectively, and the output signals 47 and 48 are input to the switching circuit 446, and the auxiliary phase difference circuit 448, 4
49 as well. Auxiliary phase circuit 448, 44
9 inputs into the comparator 447 an output signal corresponding to the phase difference between the phase shifter outputs 47 and 48 and the subcarrier signal in the input signal 5, respectively. Comparator 447
compares both inputs and controls the switching circuit 446 to select the phase shifter output with the smaller value. The switching circuit 446 is operated by a frame synchronization pulse or the like in the synchronization signal 7, selects and outputs one of the phase shifter outputs 47 and 48, and outputs it as the demodulation signal 6. Also input.
Therefore, the phase difference circuit 41 compares the phase shifter output having a smaller phase difference with the subcarrier signal with the phase of the subcarrier signal, and controls the phase of the oscillator 43 according to the phase difference. . As a result, the oscillator 43 is quickly phase-controlled, and the output signal 6 of the switching circuit 446 is quickly brought into phase with the subcarrier signal in the frame. In other words, phase locking is quickly completed. phase shifter 45,
Of course, if more number 46 etc. are provided, the retraction time will be further shortened. Since the phase of the input subcarrier signal can be quickly followed even for a television signal in which the phase of the subcarrier signal of each frame or field is sometimes discontinuous, faithful color demodulation can be realized.

As described above, in the present invention, one or more phase shifters are connected to the oscillator output, and an appropriate phase shifter output (or oscillator output) is selected and output to obtain a signal for color demodulation. This configuration has the effect of preventing color deterioration of still images at the time of frame switching. For an input signal in which the phase of the input subcarrier signal changes periodically from frame to frame, the above effect can be obtained by switching the output of each phase shifter in a fixed order. Furthermore, for signals where the phase of the input subcarrier signal is sometimes discontinuous, the above effect can be obtained by selecting and outputting the phase shifter output that has the smallest phase difference with the input subcarrier signal. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram showing an example of the configuration of the phase-locked oscillator of the above embodiment, FIG. 3 is a block diagram showing an example of the configuration of the switch of the above embodiment, and FIG.
FIG. 5 is a waveform diagram showing signals of main parts of the phase synchronized oscillator shown in the figure, and FIG. 5 is a block diagram showing another embodiment of the present invention. In the figure, 1... input terminal, 2... synchronization separator, 3... color demodulator, 4... phase synchronized oscillator, 5... input signal, 6... signal for demodulation, 7...
...Sync signal, 8...Red signal, 9...Green signal,
10... Blue signal, 41... Phase difference circuit, 42...
... wave generator, 43 ... oscillator, 44, 44' ... switch, 45, 46 ... phase shifter, 47, 48 ... phase shifter output signal, 49 ... control signal output from phase difference circuit 41 , 441... Comparator, 442... Counter, 443, 445... Flip-flop, 4
44...Frame pulse extraction circuit, 446...Switching circuit, 447...Comparator, 448, 449...
Auxiliary phase difference circuit.

Claims (1)

[Claims] 1. A synchronous separator 2 that separates and outputs a synchronous signal from an input signal, a phase synchronized oscillator 4 whose phase of oscillation frequency is controlled, and demodulates the input signal based on the output of this phase synchronized oscillator. and a color demodulator 3 that outputs a color signal, and the phase synchronized oscillator has a phase synchronized oscillator that controls the phase of the oscillation output by a control signal according to a phase difference between its output signal and a subcarrier signal in the input signal. In a still image color television signal demodulation device including a phase difference circuit, the phase control oscillator includes one or more phase shifters through which the oscillation output passes, and selects one of the outputs of the phase shifters to perform the color demodulation. a switch for supplying signals to the synchronous separator, an output signal of the switch is supplied to the phase difference circuit, and the switch is controlled by a signal output from the synchronous separator. Demodulator for still image color television signals. 2. In the still picture color television signal demodulation device as set forth in claim 1, the switching device serves as an auxiliary device for phase comparing the output of the oscillator and the output signal of each of the phase shifters with a subcarrier signal in the input signal, respectively. The present invention is characterized in that it includes a phase difference circuit and selects and outputs the phase shifter output having the minimum phase difference with the subcarrier signal.