JP2785446B2 - Multi decoder circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulation circuit capable of supporting a plurality of color TV systems such as NTSC and PAL, and more particularly to a subcarrier generation circuit (APC circuit). is there.

2. Description of the Related Art The TV standard system in the world (hereinafter abbreviated as TV system) differs in the system adopted in each country of the world. The TV system is roughly classified into three systems, the NTSC (National Television System Committee) system used in Japan and the United States, and the PAL (Pase Alternat) mainly used in Western Europe.
ion by line) method, SECAM (Sequentiel Couleur 'a Memoire; adopted in France, USSR, Eastern European countries, etc.)
French). These TV systems differ from each other in the number of fields per second (field frequency), the number of scanning lines in one field, and the color signal modulation system.

For example, in the NTSC system, the field frequency is 59.94H
z While the number of scanning lines in one frame is 525 and the color signal is quadrature two-phase modulation with a subcarrier frequency of 3.579545 MHz, the PAL system has a field frequency of 50H
z The number of scanning lines in one frame is 625, the subcarrier frequency is 4.43361875 MHz, and the color signal is also modulated by inverting the polarity of one of the color difference signals line by line. In Brazil, the field frequency is 59.95H
z, 525 scanning lines, sub-carrier frequency 3.57561149
The PAL-M system of MHz is adopted. In Argentina and the like, the PAL-N system of a field frequency of 50 Hz, the number of scanning lines is 625, and the subcarrier frequency is 3.582056 MHz is adopted.

Since each TV system is different, TV receivers and VTRs
Are also compatible with each TV system. Therefore, in an area where a plurality of TV systems are mixed, a multi-system TV or VTR capable of supporting several TV systems is required.

In recent years, the number of overseas travelers and international students has increased,
With the internationalization of schools, corporations, government offices, etc., exchanges with countries (regions) with different TV formats have become active, and worldwide tape-based communication has been progressing. Appreciation of tapes (hereinafter abbreviated as video tapes) and exchange of video tapes with foreign countries have been occurring. Under these circumstances, TV standard system converters (hereinafter abbreviated as TV system converters) that convert between TV systems have been integrated into LSIs and cost reductions.
A VTR that is built into a multi-system VTR so that playback and creation (recording) of different-type video tapes can be done freely at home.
Are also being developed.

In this multi-system TV or TV system converter, it is necessary to cope with (1) the number of horizontal scanning lines, (2) the field frequency, and (3) the modulation system of the chroma signal, which differ for each TV system. In the processing, it is necessary to convert the number of horizontal scanning lines and the field frequency after converting them into color difference signals once.
Abbreviated as a multi-decoder).

FIGS. 2 and 3 show an example of a conventional multi-decoder circuit, which is compatible with NTSC and PAL systems (PAL, PAL-M, PAL-N). Hereinafter, the operation will be described with reference to these drawings.

First, the case of demodulating a chroma signal of the PAL system (PAL, PAL-M, PAL-N) will be described. In FIG.
The chroma signal input to the input terminal 1 is input to a 1H delay line (1HDL) 3 for delaying one horizontal scanning period after the chroma level is controlled to a predetermined level by ACC2.
The output of DL3 passes through the switch circuit 4 and subtracts the signal not passing through 1HDL28 and the output of the switch circuit 4 into a subtractor 5, and
Each of them is subtracted and added by the adder 6. PAL
As is well known, the signal has one R-Y signal component.
Since the modulation is performed by inverting the phase by 180 degrees for each scanning line, the output of the subtracter 5 does not have the phase inversion for each line.
The Y component is canceled and only the RY component is extracted. On the other hand, in the output of the adder 6, the RY component whose phase is inverted for each line is canceled, and only the BY component is extracted.

The chroma components in the RY and BY axes extracted in this way are multiplied (synchronous detection) with each of the subcarriers by the multiplying circuits 7 and 8, and the high-frequency components at the time of multiplication are converted to LPF9. After being removed at steps (10) and (10), the signals are extracted to the output terminals 11 and 12 of the multi-decoder as RY and BY color difference signals.

As is well known, the subcarriers at the time of multiplication are, as is well known, after a burst signal is extracted by a burst extraction circuit 13 and a subcarrier that is phase-locked to the burst signal is generated by a subcarrier generation circuit 14, which is used as a reference. Is synchronously detected. In other words, the BY component multiplier 8
A 0-degree sub-carrier in the Y-axis direction is generated, and the output sub-carriers of the 90-degree phase shifter 16 and the 180-degree phase shifter 17 are supplied to the RY component multiplier 8 by the line identification circuit 15. 1 of RY component
By alternately switching the switch circuit 18 in accordance with the phase inversion of each line, subcarriers corresponding to the phase inversion of each line of the RY axis are generated, and demodulation is performed using this.

Next, a case of demodulating an NTSC chroma signal will be described. In this case, according to a command from the mode control unit 19,
The switch circuit 4 selects the ground side in FIG.
Is not supplied to the adder 6 and the subtractor 5. This is because the phase of the RY component is not inverted for each line in the NTSC system as in the PAL system,
No need to perform addition and subtraction processing with the output of 3, directly ACC2
Is input to the multipliers 7 and 8. Further, the mode control unit 19 selects the mode of the subcarrier generation circuit 14 so that a 3.579545 MHz subcarrier of the NTSC system is generated, and the switch circuit 18 is fixed so as to select only the 90-degree phase shifter side. . Thus, a 90-degree phase subcarrier in the RY axis direction of the NTSC system is added to the multiplier circuit 7 and a 0-degree phase subcarrier in the BY axis direction is added to the multiplier circuit 8. Demodulated into a BY signal.

As described above, mode information indicating which TV system is to be demodulated is transmitted from the mode control unit 19, whereby the states of the subcarrier generation circuit 14, the switch circuits 4 and 18 are switched.

The subcarrier generating circuit 14 has a configuration as shown in FIG. 3, and one of the crystal oscillators 25, 26, 27, and 28 is selected by the switch circuit 40 according to the mode information of the mode control unit 19. It has become so. That is, in the subcarrier generation circuit 14, the subcarrier phase-locked to the burst signal input to the input terminal 20 is compared with the phase comparator 21, the loop filter 22, the voltage controlled crystal oscillator (VXO) 23, the frequency divider 2
Crystal oscillator 2 generated by 4 and connected to VXO23
By selecting 5, 26, 27, 28 with the switch circuit 40,
The output terminal 39 can take out a subcarrier corresponding to each TV system. In FIG. 3, reference numerals 29, 30, 31, and 32 denote trimmer capacitors for adjusting the free-run frequency of each crystal oscillator. Each of the capacitors is NTSC, PAL, PAL-M, PA
It is adjusted to oscillate at an integer multiple of the subcarrier frequency of the LN system.

As described above, NTSC, PAL, PAL-M, PAL-N
Can be demodulated.

However, in the subcarrier generation circuit 14 of the conventional multi-decoder circuit, it is necessary to select the crystal units 25, 26, 27, and 28 corresponding to each TV system by the switch circuit 40. For this reason, there has been a problem that oscillation of the selected crystal does not stably start at the time of mode switching of the TV system or the like.

That is, as shown in FIG.
Connection, the wiring pattern in this area is likely to be long, the stray capacitance in the wiring section between the crystal units 25, 26, 27, 28 and VXO23 increases, and the oscillation conditions of VXO23 and the crystal unit are sufficient. In some cases I was not satisfied. In particular, immediately after the crystal oscillator is switched by the switch circuit 40, the subcarrier generation circuit
Oscillation conditions cannot be satisfied during a transient such as immediately after a power supply voltage is applied to the power supply 14, causing oscillation at an odd multiple of the oscillation frequency of the crystal unit, or unnecessary oscillation in the high frequency range. Was. For this reason, conventionally, the oscillation conditions of the VXO23 and the crystal units 25, 26, 27, and 28 are matched, and
Great care was required in designing the wiring pattern.

An object of the present invention is to provide a multi-decoder circuit capable of stably oscillating a crystal unit and generating stable subcarriers even when switching the mode of a TV system, for example, in order to solve the above problem. It is an object.

Means for Solving the Problems The present invention provides NTSC, PAL, PAL-
In a multi-decoder circuit configured to demodulate a chroma signal of each color TV of M and PAL-N into a color difference signal,
A burst extracting circuit for extracting a burst signal in the chroma signal; and a desired color TV from each of the color TV systems.
Mode control means for selecting a system and generating a control signal, a subcarrier generating circuit for generating a subcarrier phase-synchronized with the burst signal extracted by the burst extracting circuit, and adapted to each of the color TV systems by the control signal And a demodulation circuit that demodulates the chroma signal into a color difference signal based on the output of the subcarrier generation circuit, and detects a change in the control signal. Immediately after the mode transition, the phase synchronization operation of the subcarrier generation circuit is low due to the mode transition detecting means for detecting that the mode has transitioned from the TV mode to the second color TV mode and the output of the mode transition detecting means. It has a configuration of an oscillation control circuit that controls the oscillation frequency so as to be performed from the frequency side.

In a multi-decoder circuit configured to demodulate a chroma signal of each color TV system of NTSC, PAL, PAL-M, and PAL-N into a color difference signal, a burst extracting circuit for extracting a burst signal in the chroma signal is provided. A mode control means for selecting a desired color TV system from each of the color TV systems and generating a control signal, and a subcarrier generation circuit for generating a subcarrier phase-synchronized with the burst signal extracted by the burst extraction circuit, A demodulation circuit that selects a demodulation mode suitable for each color TV system by the control signal, demodulates the chroma signal into a color difference signal based on an output of the subcarrier generation circuit, and an output of the subcarrier generation circuit A discriminating circuit for discriminating whether or not the phase is synchronized with the burst signal, and oscillating at a period longer than a time constant required for discriminating by the discriminating circuit; An oscillation circuit, comprising a gate circuit that gates an output pulse of the oscillation circuit,
If the determination circuit determines that the output of the subcarrier generation circuit is not synchronized with the burst signal, the gate circuit is opened, and the output pulse of the oscillation circuit is sent to the subcarrier generation circuit. The phase synchronization operation can be repeated from the low frequency side in the oscillation cycle of the output pulse.

Effect of the Invention With the above configuration, when the crystal oscillator is switched, the mode transition is detected, and the control input voltage of the VXO is temporarily switched to the constant voltage source so that the VXO starts oscillating from a low frequency. Then, the pull-in operation is performed after fixing, so that the pull-in operation can be stably performed even when the mode of the TV system is switched (when the crystal oscillator is switched).

Also, the oscillation frequency of the subcarrier generation circuit and the subcarrier frequency of the input burst signal are compared by a killer detection circuit, and if the oscillation does not reach the desired frequency (the phase is not locked to the subcarrier frequency of the burst signal) In this case, the control voltage of VXO is fixed to a constant voltage source at a cycle of about 1 Hz, and the pull-in operation is started many times from a low frequency until the oscillation frequency of the subcarrier generation circuit reaches a desired frequency. This makes it possible to prevent oscillation at an unnecessary frequency of the crystal oscillator and phase lock at an unnecessary frequency of the subcarrier generation circuit.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a subcarrier generation circuit of a multi-decoder circuit according to an embodiment of the present invention, and FIG. 4 is an explanatory diagram for explaining the operation thereof. The operation of the multi-decoder circuit other than the subcarrier generation circuit is as described in the prior art.

In FIG. 1, as described in the conventional example, the phase comparator
21, Loop filter 22, VXO23, Divider 24
A subcarrier phase-locked to the subcarrier frequency of the burst signal input to 10 is generated and extracted from the output terminal 39. The VXO23 is connected to crystal oscillators 25, 26, 27, and 28, and trimmer capacitors 29, 30, 31, and 32 for adjusting the free-run frequency for each crystal oscillator, and a switch circuit 40. One of the four crystal units is selected by the switch circuit 40 according to the mode information of the unit 19. The oscillation frequency of the crystal unit 25, 26, 27, 28 is NTSC, PA
The subcarrier frequency of each system of L, PAL-M, and PAL-N is an integral multiple of the subcarrier frequency. In this embodiment, the frequency is twice the subcarrier frequency. Further, the frequency division ratio of the frequency divider 24 is set in accordance with the oscillation frequency of the crystal oscillator, and is 1/2 frequency division in the present embodiment.

The present embodiment differs from the conventional example in that a switch circuit 37 and a voltage source 36 are provided so that the input voltage of the VXO 23 can be fixed at a predetermined voltage for a desired period. The input voltage vs. oscillation frequency characteristics of the VXO23 are as shown in FIG. 4. When the oscillation loop (APC loop) is stabilized, it oscillates near the frequency f _O near A _{O in} FIG. It has become. Once stable point A _O higher voltage source input voltage of the VXO32 the mode transition or the like (v _H) 36 to the switch circuit
By forcibly fixing at 37, the oscillation frequency of VXO23 shifts to a frequency f _L (point A _{L in} FIG. 4) lower than the stable point A _O , and then the switch circuit 37 is opened to oscillate. The stable point of the loop shifts reliably from A _L to A _O in the figure, and it is possible to prevent oscillation at an unnecessary stable point in a high frequency range and oscillation at an odd multiple of the crystal oscillation frequency.

In this embodiment, the control of the switch circuit 23 is performed by two control signals. One of them is to input the mode information from the mode control unit 19 for selecting the mode of the TV system to the mode transition detecting unit 38, where the mode transition is detected, and the switch circuit 37 is switched to the voltage source only during the transition period of the mode transition. It is controlled so as to be connected to 36 so that the oscillation stably rises from the low frequency f _L when the crystal oscillator is switched at the time of mode transition.

In the second control method, the killer detection circuit 35 detects whether or not the output subcarrier of the frequency divider 24 and the subcarrier of the input burst signal of the phase comparator 21 are phase-locked. When the phase is not locked, the gate of the gate circuit 35 is opened, and the switch circuit 37 is operated so as to open and close at a constant cycle (about 1 Hz cycle) by the oscillation output pulse of the oscillation circuit 33. As a result, the input of the VXO 23 is connected to the voltage source 36 at a constant cycle until the output subcarrier of the frequency divider 24 and the subcarrier of the input burst signal of the phase comparator 21 are phase-locked, and then released again. It will be repeated operation, repeatedly transition from a _L of FIG. 4 to a _O, the oscillation will be repeated this operation until the rising edge to the desired frequency. After the oscillation rises and the output subcarrier of the frequency divider 24 and the subcarrier of the input burst signal of the phase comparator 21 are phase-locked, the killer detection circuit 35
The gate of the gate circuit 34 is closed by the control signal to stop the output pulse of the oscillation circuit 33 from being sent to the switch circuit 37,
The switch circuit 37 is open, and operates as a normal APC loop.

As described above, according to the present embodiment, by providing the switch circuit 37 and the voltage source 36 at the input section of the VXO 23, when the mode shifts to switch the crystal oscillator, or when the oscillation does not rise to the desired frequency, once closing switch circuit 37 connects the input voltage of VXO23 the voltage source 36, thereby temporarily lower the oscillation frequency points the oscillation frequency (a _L in the figure)
, The oscillation loop (APC loop) can be stably started, and oscillation can be reliably performed at a desired frequency.

In this embodiment, the killer detection circuit 35 operates even when there is no input or when there is no black and white signal in which a burst signal does not exist. In this case, the output pulse of the oscillation circuit 33 is also switched through the gate circuit 34. The signal is supplied to a circuit 37, and an operation for starting oscillation is performed at a constant cycle. However, since there is no need to perform an operation to lock the APC loop when there is no input or in a signal having no burst signal, in this case, the gate circuit 34 may not be opened, and the operation of starting oscillation may be prohibited.

Further, in the present embodiment, the mode transition detecting unit 38 detects the time of the mode transition and closes the switch circuit 37 during that period. However, during the period when the oscillation is likely to be unstable (for example, the power supply of the subcarrier oscillation circuit 14). close the predetermined period switching circuit 37 also in the like) immediately after the voltage is turned on, connecting the voltage source 36 to the input of VXO23, forcibly fixed to the lower frequency of the oscillation point (a _L), the power supply voltage is sufficiently stable At this point, the switch circuit 37 can be opened to shift to a desired oscillation point (A _O ), and oscillation can be stably started.

In this embodiment, the oscillation frequency of the oscillation circuit 33 is about 1H.
Oscillation is performed at z, but this may be any frequency as long as the oscillation period has a time interval sufficiently larger than the detection time constant of the killer detection circuit 35.

Note, however, that if the oscillation cycle of the oscillation circuit 33 oscillates at a cycle shorter than the detection time constant of the killer detection circuit 35, the following problem occurs, so care must be taken. That is, immediately after the oscillation of the crystal oscillator starts to oscillate normally and the output subcarrier has phase-locked to the burst signal at the input terminal 20, the killer detection circuit 35 has not yet locked in phase due to the detection time constant. As a result, the gate circuit 34 remains open. If an oscillation pulse is output from the oscillation circuit 33 during this period, the switch circuit 37 closes again, so that VX
O23 would start again pull-operation from the frequency f _L corresponding to v _H of the constant voltage source 36. Therefore, the killer detection circuit
Before the detection of 35 is completed, the oscillation start-up operation (opening and closing of the switch circuit 37) is repeated, and the subcarrier generation circuit
No. 14 cannot be phase locked to the input burst signal.

As can be seen, the oscillation circuit 33 is a killer detection circuit
It is necessary to oscillate at a period sufficiently longer than the detection time constant of 35.In this embodiment, since the time constant of the killer detection circuit is about 10 Hz, the oscillation frequency of the oscillation circuit 33 is set to about 1 Hz. You have set.

As is clear from the above description, according to the present invention, when the crystal oscillator is switched in the subcarrier generation circuit of the multi-decoder circuit, the mode transition is detected, and the VXO is switched from low frequency. Once the VXO control input voltage is fixed to a constant voltage source with a switch circuit to start oscillating, and then the pull-in operation is performed, erroneous oscillation at unnecessary high frequency is prevented and the desired It can oscillate at a frequency.

Also, even if the oscillation does not start up properly and the APC loop does not lock in phase with the input burst signal, this is detected by the killer detection circuit, and the VXO input voltage is fixed to a constant voltage source with a cycle of about 1 Hz, Until the oscillation frequency of the subcarrier oscillation circuit reaches a desired frequency, the pull-in operation is repeated from a low frequency, whereby it is possible to perform the pull-in operation many times until the APC loop is phase locked. Oscillation at an unnecessary frequency and phase lock at an unnecessary frequency can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a subcarrier generation circuit of a multi-decoder circuit according to one embodiment of the present invention, FIG. 2 is a block diagram of a main part of a conventional multi-decoder circuit, and FIG. FIG. 4 is a block diagram of the circuit, and FIG. 4 is a characteristic diagram of the input voltage of the VXO versus the oscillation frequency. 2 ... ACC, 3 ... 1HDL, 4,18,37,40 ... Switch circuit, 7,8 ... Multiplier circuit, 13 ... Burst extraction circuit, 1
4 ... Subcarrier generation circuit, 15 ... Line identification circuit, 1
9 Mode controller, 21 Phase comparator, 22 Loop filter, 23 VXO, 24 frequency divider, 25, 26, 27, 28
... crystal oscillator, 29, 30, 31, 32 ... trimmer, 33 ... oscillation circuit, 34 ... gate circuit, 35 ... killer detection circuit, 36 ...
... voltage source, 38 ... mode shift detector.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 9/00 H04N 9/45 H04N 9/64-9/66

Claims (3)

(57) [Claims] In a multi-decoder circuit configured to demodulate a chroma signal of each color TV system of NTSC, PAL, PAL-M, and PAL-N into a color difference signal, a burst for extracting a burst signal from the chroma signal is provided. A sampling circuit, mode control means for selecting a desired color TV system from the respective color TV systems and generating a control signal, and subcarrier generation for generating a subcarrier phase-synchronized with the burst signal extracted by the burst sampling circuit A circuit, a demodulation circuit that selects a demodulation mode suitable for each color TV system by the control signal, and demodulates the chroma signal into a color difference signal based on an output of the subcarrier generation circuit; and a change in the control signal. And each color TV system is the first color TV
Mode transition detecting means for detecting that the mode has shifted from the system to the second color TV system, and the output of the mode transition detecting means allows the phase synchronization operation of the subcarrier generation circuit to be performed at a low frequency immediately after the mode transition. A multi-decoder circuit comprising: an oscillation control circuit that controls an oscillation frequency so as to be performed from the side. 2. A multi-decoder circuit configured to demodulate a chroma signal of each color TV system of NTSC, PAL, PAL-M, and PAL-N into a color difference signal, wherein a burst for extracting a burst signal from the chroma signal is provided. A sampling circuit, mode control means for selecting a desired color TV system from the respective color TV systems and generating a control signal, and subcarrier generation for generating a subcarrier phase-synchronized with the burst signal extracted by the burst sampling circuit A demodulation circuit for selecting a demodulation form suitable for each color TV system by the control signal, and demodulating the chroma signal into a color difference signal based on an output of the subcarrier generation circuit; and the subcarrier generation circuit A discriminating circuit for discriminating whether or not the output of the discriminator is in phase with the burst signal; An oscillation circuit for oscillating, and a gate circuit for applying a gate to an output pulse of the oscillation circuit, and when it is determined that the output of the subcarrier generation circuit is not phase-synchronized with the burst signal by the determination circuit, A multi-decoder circuit wherein the gate circuit is opened, an output pulse of the oscillation circuit is sent to the subcarrier generation circuit, and a phase synchronization operation can be repeated from a low frequency side in an oscillation cycle of the output pulse. 3. A sub-carrier generating circuit comprising: a crystal oscillator oscillating at an integer N times the sub-carrier frequency of each TV system; a voltage-controlled oscillator oscillated by the crystal oscillator; / N frequency divider for generating a subcarrier output of the subcarrier generation circuit, a phase comparator for comparing the phase of the subcarrier output of the frequency divider with the input burst signal, and the phase comparator A loop filter that integrates a comparison error voltage that is an output of the loop filter, and a subcarrier output that is phase-synchronized with the burst signal by applying an output voltage of the loop filter to the voltage-controlled oscillator. A switch circuit for fixing the applied voltage of the voltage-controlled oscillator for a desired period, and a constant voltage source connected to the switch circuit, wherein the desired period is By closing the switch circuit, the voltage-controlled oscillator oscillates at a lower frequency than the oscillation frequency when phase-locked to the burst signal. 3. The multi-decoder circuit according to claim 1, wherein the multi-decoder circuit operates.