JPS602710Y2 - automatic phase control device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an automatic phase control device that maintains a constant phase of a clock signal used when pulse-coding an information signal such as a television signal and converting it into a digital signal. This allows phase control to be carried out in immediate response to sudden changes in the reference phase used as a reference.

In general, when pulse-coding a television signal, the signal processing is facilitated and the reproduction of the encoded television signal is determined by the difference between the sampling frequency prior to encoding and the color subcarrier frequency of the television signal. In order to reduce the occurrence of beat disturbances in the picture, it is customary to choose the sampling frequency in such a way that the sampling pulse is synchronized with the horizontal synchronization signal of the television signal, and therefore the formation of the sampling pulse and Conventionally, when generating a lock signal required for encoding a television signal, horizontal synchronization was performed using a variable frequency oscillator equipped with an automatic phase control system, that is, an APC system, as shown in Figure 1. A clock signal was generated that was phase-synchronized with the signal.

That is, the oscillation output of the oscillator 2 whose oscillation frequency can be controlled is such that the oscillation output of the reference oscillation frequency is phase-locked with, for example, the horizontal synchronization signal, and the reference oscillation frequency has an integer relationship or the like with respect to the clock frequency. The wave is supplied to a counting circuit 3, which counts the wave number of the oscillation output wave for each cycle of the horizontal synchronizing signal, and supplies the counted output to a decoder 4.

In the decoder 4, each time the count value of the counter 3 reaches a predetermined wave number of the reference frequency oscillation output wave that matches the period length of the horizontal synchronization signal, the decoder 4 generates a count output pulse signal and sends a reset pulse to the counter 3. and reset the counter 3.

The count output pulse signal from the decoder 4 is supplied to the phase comparator 1 together with the horizontal synchronization signal used as a phase reference, and their mutual phases are compared. The count output pulse signal and the horizontal synchronization signal are controlled in phase so that the oscillation frequency is maintained at a predetermined reference oscillation frequency.

However, in the conventional automatic phase control system having such a configuration, for example, when the television signal to be encoded is switched to a television signal whose synchronization signals are not synchronized due to reasons such as program configuration, etc. Since the phase of the horizontal synchronization signal, which is used as a reference for phase control, changes rapidly, the response of the automatic phase control system can be immediately detected in response to such a sudden change in the reference phase. The drawback is that a stable clock signal cannot be obtained for a while, and during that time the encoded television signal is significantly disturbed.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional technology, and to enable the phase of the oscillation output to be controlled immediately even if a large sudden change in phase occurs in the signal used as the reference for phase control. An object of the present invention is to provide an automatic phase control device.

That is, the automatic phase control device of the present invention includes an oscillation circuit with a variable oscillation frequency, and a count output pulse signal that is reset every time a predetermined wave number is counted by counting the wave number of the oscillation output wave in the oscillation circuit. a counting circuit that makes
An automatic phase control device comprising: a phase comparison circuit that changes the oscillation frequency of the oscillation circuit according to a result of comparing the phases of the count output pulse signal and the reference synchronization signal;
A decoder circuit that generates a gate pulse corresponding to a period exceeding the phase controllable range of the counting circuit, an AND gate circuit that supplies the gate pulse and the reference synchronization signal, and a gate output signal of the AND gate circuit. and an OR gate circuit that supplies the counting output pulse signal and the gate output signal of the OR gate circuit.
The present invention is characterized in that the counting circuit is reset and the counting output pulse signal is generated.

The invention will be explained below by way of example with reference to the drawings.

First, an example of the configuration of the automatic phase control device of the present invention having the above-mentioned characteristics is shown in FIG. 2, and signal waveforms of each part thereof are shown in FIG. 3.

As is clear from the comparison between the configuration of the device of the present invention shown in FIG. 2 and the configuration of the conventional device shown in FIG. 1, the automatic phase control device of the present invention has the configuration shown in FIG. Another decoder 5 separate from the conventionally connected decoder 4 is connected to the counting circuit 3 in the conventional device, and the decoder 5
The counting circuit 3 is reset by the AND of the output signal of the output signal and the horizontal synchronization signal used as the reference for phase control, and the above-mentioned count output pulse signal from the decoder 4. Similarly, the counting circuit 3 is reset in response to the counting output pulse signal from the decoder 4 to perform automatic phase control as in the past, and when the phase of the horizontal synchronizing signal used as the reference for such phase control changes significantly and suddenly. In this case, the counting circuit is reset by a horizontal synchronizing signal of a new phase without scattering, and then automatic phase control is performed by the conventional pull-in action.

Therefore, in order to facilitate the explanation of the mode of phase control when the phase of the horizontal synchronizing signal used as the reference for phase control changes significantly and suddenly as described above, we will give a specific numerical example as shown in Fig. 2. The operation of the automatic phase control device with the above configuration will be explained.

First, the center frequency of the oscillation frequency variable range of oscillator 2 is
For example, the color subcarrier frequency of a television signal is a clock frequency that has an integer relationship with its oscillation frequency.

When the color subcarrier frequency is selected to be three times 1. .

Since there is a relationship between f3° and horizontal synchronization frequency fH as follows: f3°=black f8, the center oscillation frequency of oscillator 2 is determined by counting the wave number in counting circuit 3 and stepping down to 1/(455×3). (455×3) fH so that the count output pulse signal can be synchronized with the horizontal synchronization signal in both frequency and phase.
be selected.

Therefore, when the oscillation frequency of the oscillator 2 is approximately equal to the center frequency of this value, as shown in FIG. is generated in the vicinity of the horizontal synchronizing pulse in almost phase synchronization with the horizontal synchronizing signal a.

That is, every time the horizontal synchronizing pulse a is applied, counting of the oscillation output pulse b is started, and the counted value becomes (455X3
) The phase of the counting output pulse C that appears when reaching ) is:
As shown in the figure, the phase almost matches the phase of the oscillation output pulse b near the horizontal synchronizing pulse a.

Therefore, the oscillator 2 oscillates at an oscillation frequency that deviates from the center frequency to such an extent that the count output pulse C appears in the vicinity of the horizontal synchronization pulse a, within a range of, for example, ±9 in terms of the number of oscillation output pulses. Since the phase comparison output level of the phase comparator 1 is maintained within the controllable range of the oscillation frequency of the oscillator 2, automatic phase control using the normal pull-in action is possible.

If the frequency precision of the horizontal synchronizing pulse a used as a reference for phase control is high and the phase is stable, the range in which automatic phase control is possible can be narrowed and the loop gain of the automatic phase control system can be increased. Automatic phase control with stable sensitivity can be performed.

However, the horizontal synchronizing pulse a used as a reference for phase control
The phase of the oscillator 2 changes significantly and the phase comparison output level changes within the phase shift range corresponding to the oscillation frequency controllable range of the oscillator 2, that is, the range of ±9 pulses expressed as the number of oscillation output pulses b. 10 (455 x 3) - counting from the position of the preceding horizontal synchronizing pulse a
When the position of the next horizontal synchronizing pulse a shifts within the range of up to 9 pulses, that is, 135ea, the phase relationship between the horizontal synchronizing pulse a and the counting output pulse C remains disturbed until they become close to each other. As described above, such clock frequency disturbances significantly degrade the reproduced image quality of the encoded television signal.

In the automatic phase control device of the present invention having the configuration shown in FIG. 2, in order to reduce the occurrence of such phase disturbance, the counting output of the counting circuit 3 is supplied to the decoder 5, and the preceding horizontal synchronizing pulse a Generates a decode output pulse d which becomes a high logic level 1 during a period in which the count value of the oscillation output pulse b started at the position is in the range 10 to 1356 mentioned above,
The decode output pulse d and the horizontal synchronizing pulse a are supplied to the AND gate circuit 6.

On the other hand, in the decoder 4 connected between the counting circuit 3 and the phase comparator 1 as in the conventional device, the count value of the counting circuit 3 starts at the position of the preceding horizontal synchronizing pulse a. Each time the count reaches 1364, which corresponds to (455X 3) -1, a count output pulse C is generated and supplied to the phase comparator 1 for phase comparison as well as to the OR gate circuit 7.

The OR gate circuit includes the AND gate circuit 6 described above.
A gate output pulse is also supplied.

Therefore, the next horizontal synchronizing pulse a is counted from the previous horizontal synchronizing pulse a, and the number of oscillation output pulses b is 1365.
When it appears in the range of ±9, the counting output pulse C from the decoder 4 is applied to the reset terminal of the counting circuit 3 via the OR gate circuit 7, and automatic phase control is performed by the normal pull-in action as before. The phase of the next horizontal synchronizing pulse a is significantly shifted, and the count value of the oscillation output pulse b in the counting circuit 3 is within the normal controllable range (1).
When the next horizontal synchronization pulse a appears within the range of 10 to 1356 before reaching 365±9, the horizontal synchronization pulse a whose phase is shifted from the decode output pulse d described above
AND gate output pulse C that appears when superimposed with
', that is, the phase-shifted horizontal synchronizing pulse a' that has passed through the AND gate circuit 6 is applied to the reset terminal of the counting circuit 3 via the OR gate circuit 7, and reset as before by the counting output pulse C corresponding to the normal count value. The automatic phase control is forcibly reset by the phase-shifted horizontal synchronizing pulse a' before the changeover occurs, and from that point on, automatic phase control is performed by the normal pull-in action based on the horizontal synchronizing pulse a' by the new television signal after switching. will be newly started.

Therefore, in the automatic phase control device of the present invention having such a configuration, a normal automatic phase control operation is immediately performed regardless of the phase of the next horizontal synchronization pulse a' that appears following the preceding horizontal synchronization pulse a. Therefore, there is no possibility that the phase disturbance of the lock signal will continue for a long time as occurred in the conventional device.

In addition, as a variable frequency oscillator that performs this type of automatic phase control, a crystal controlled oscillator is usually used to make the frequency of the clock signal obtained from the oscillation output inherently stable and with little phase jitter. Since the oscillation frequency is changed by changing externally added circuit constants, the variable range of the oscillation frequency is generally narrow. Therefore, if the phase of the horizontal synchronization pulse, which is used as a reference for phase control, is significantly disturbed, it is difficult to leave it as it is. For example, it usually takes a considerable amount of time until automatic phase control is performed due to a normal retraction action.

Furthermore, the output-side counting circuit 3' in the automatic phase control device having the configuration shown in FIG.
455X3) Stepping down fH=1365fs to i, f
s o'' 3f for the color subcarrier frequency 18 and 18;

This is for forming a clock signal having a frequency of

As is clear from the above explanation, according to the present invention, the time width in which disturbances in reproduced images occur due to switching of encoded video signals handled in digital video equipment, which is expected to be widely used in the future, can be reduced compared to conventional methods. It is possible to significantly shorten the time, almost eliminate image disturbance, and make it almost equivalent to the conventional switching of analog video signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional automatic phase control device, FIG. 2 is a block diagram showing an example of the configuration of the automatic phase control device of the present invention, and FIG. 3 is a waveform diagram showing the signal waveforms of each part. It is. 1... Phase comparator, 2... Variable frequency oscillator, 3.3'... Counting circuit, 4, 5...
...Decoder, 6...And gate, 7...
...or gate.

Claims (1)

[Scope of utility model registration request] an oscillation circuit with a variable oscillation frequency; a counting circuit that counts the wave number of an oscillation output wave in the oscillation circuit and is reset each time a predetermined wave number is counted and generates a count output pulse signal; and the count output pulse signal. and a phase comparison circuit that changes the oscillation frequency of the oscillation circuit according to the result of comparing the phase of the oscillation circuit with a reference synchronization signal, and the automatic phase control device corresponds to a period exceeding the phase controllable range of the counting circuit. a decoder circuit that generates a gate pulse, an AND gate circuit that supplies the gate pulse and the reference synchronization signal, and an OR gate circuit that supplies the gate output signal of the AND gate circuit and the counting output pulse signal, An automatic phase control device characterized in that the counting circuit is reset and the counting output pulse signal is generated by a gate output signal of the OR gate circuit.