JPS6223948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises: (a) a modulator for modulating a carrier signal derived from an oscillation signal supplied to an oscillation signal input section with a demodulated SECAM color information signal; (b) a method selection switch operable by a method selection signal for switching from processing the FM demodulated color information signal to quadrature demodulated color information signal, carrying a different frequency for each alternate scan line; The signal is FM modulated by different color difference signals
The present invention relates to a transcoding circuit that converts a SECAM color information signal into a combination of signals that can be demodulated by a demodulation circuit for quadrature demodulation.

Such a transcoding circuit is disclosed in European Patent Application No. 0003169. In this case, the carrier signal has the same frequency as the oscillation signal.

An object of the present invention is to make such a transcoding circuit suitable for use with an oscillation signal having a frequency twice that of the carrier signal.

According to the invention, in a transcoding circuit of the type described above, the input for the outgoing signal is connected to the modulator via a frequency divider, and the frequency divider includes two a stop signal input section connected to the output section of the difference generating circuit in the collector circuit of the transistor; further, the base of the transistor receives a voltage determined by the method selection signal, and the emitter are connected to different phase control terminals, and when the frequency divider is in an inaccurate frequency division state, the phase control terminals transmit a signal to stop the frequency divider via the difference generating circuit. terminals, while at the output for the first quadrature component of constant phase no color synchronization signal is generated, and at the output for the second quadrature component with phase varying from scan line to scan line. , only a color synchronization signal having a phase corresponding to the second quadrature component is generated every other horizontal retrace period.

Next, a transcoding circuit according to the present invention will be described with reference to a simplified block diagram in relation to a conventional demodulation circuit. Also, for clarity of illustration, details that are not important for understanding the invention have been omitted.

Even if the signal supplied to the input section 1 of the transcoding circuit 3 is of the SECAM format, it is PAL.
The color information signal may be of any type. In the case of this SECAM method, for each alternate scanning line,
One of the two types of color difference signals is
A carrier signal of one of the types of frequencies.
This is an FM modulation method. In addition, in the case of the PAL system, the color difference signal is modulated by each of the two types of orthogonal components of the carrier signal, and the phase of one of these two types of orthogonal components is inverted for each scanning line. It is a method.

This color information signal is supplied to the input section 5 of the FM demodulator 7, and the system selection switch 1
It is also supplied to the input section 9 of No. 1.

The output section 13 of the FM demodulator 7 is connected to the input section 15 of the system identification circuit 17. From the output section 19 of this system identification circuit 17, regarding this embodiment,
In the case of the PAL system, the system selection signal with a low value is
Further, in the case of the SECAM method, a high value method selection signal is generated. In this case, this mode selection signal is generated in a conventional manner, for example by means of a predetermined characteristic of the output signal of the FM demodulator 7.

The system selection signal is supplied to the system selection signal input section 21 of the system selection switch 11.
When processing SECAM color information signals,
This system selection switch 11 is located at the switching position shown in the drawing, and is located at the other switching position when processing color information signals of the PAL system.

The signal at the output 13 of the FM demodulator 7 is also supplied to the input 22 of the modulator 23 and the input 25 of the identification circuit 27 . When processing SECAM system signals, the output section 2 of this identification circuit 27
Obtain the identification signal from 9. Note that this identification signal is supplied to the input section 31 of the bistable multivibrator 33, and a frequency that is half the horizontal scanning frequency (hereinafter referred to as "1/2 horizontal scanning frequency") appearing at the output section 35 of this multivibrator 33 is obtained. The phase of the signal is coupled to the switching phase of a switch in the color television transmitter that determines the order in which the color difference signal modulates the carrier signal.

received from the input 39 of the transcoding circuit 3 and input to the input 37 of the multivibrator 33;
The state of the multivibrator 33 is switched line-sequentially by a pulse signal of horizontal scanning frequency _H supplied to the multivibrator 33.

A signal of 1/2 horizontal scanning frequency (1/2 _H ) is generated at the output section 35 of the multivibrator 33, and this signal is supplied to the input section 47 of the selection switch 45 to activate the selection switch 45. The carrier signal is sent from this output section 43 to the input section 4 of the modulator 23.
Supply to 1.

In response to a signal at the input 47 of the selection switch 45, the output 4 of the selection switch 45
3 are alternately connected to the two outputs 49 and 51 of the frequency divider 53. An input section 55 of this frequency divider 53 receives an oscillation signal from an input section 57 of the transcoding circuit 3. The frequency of this oscillation signal is twice (2 _SUB ) the frequency ( _SUB ) of the carrier signal supplied to the input section 41 of the modulator 23 . Therefore, when this frequency divider 53 is in the correct frequency division state, the frequency of this oscillation signal is divided by half by the frequency divider 53, and this frequency-divided signal is sent to its output section 49. is generated at a phase of 0°, and the other output section 51
is generated with a phase of 90°.

If the frequency divider 53 is not performing correct frequency division operation, a difference generation circuit 61 is connected to the stop signal input section 58 of the frequency divider 53 in order to bring the frequency divider 53 into the correct frequency division state. A stop signal is supplied from the output section 59 of. This difference generating circuit 61 has two
It is included in the collector circuit of two transistors 63 and 65. The bases of these transistors 63 and 65 are connected to the output section 19 of the method identification circuit 17.
are connected, and when processing a PAL signal, both transistors 63 and 65 are made non-conductive, and when processing a SECAM signal, both transistors 63 and 65 are made conductive.

The emitters of the transistors 63 and 65 are respectively connected to terminals 67 and 69 for phase control signals. These phase control signals are generated at terminals 71 and 73 of the demodulation circuit 75, and these terminals 71 and 73 are connected to terminals 67 and 69 of the transcoding circuit 3.
In addition to connecting each, capacitors 76 and 77
It is grounded through each.

When processing SECAM system signals, the emitters of the two transistors 63 and 65 have the same potential according to the system selection signal at their bases. In this case, these transistors 63, 65
The current flowing through the demodulation circuit 75 is determined by the current flowing through the terminals 71 and 73 of the demodulation circuit 75. This state will return later. When receiving PAL signals, the transistors 63 and 65 are cut off and do not affect the voltages at the terminals 71 and 73 of the demodulation circuit 75.

In the demodulation circuit 75, the terminals 71 and 73
Phase control signal input sections 85 and 8 of the oscillator 89, respectively.
7, and also connected to the phase control signal output sections 79 and 81 of the phase detector 83, respectively. The output section 91 of this oscillator 89 is connected to the output section 93 of the demodulation circuit 75, and this output section 93 is connected to the oscillation signal input section 57 of the transcoding circuit 3, and also to the input section 97 of the frequency divider 99. Connecting.
Further, the output section 93 of the demodulation circuit 75 is connected to the input section 103 via the crystal 101, and this input section 103 is connected to the input section 105 of the oscillator 89. This oscillator 89 oscillates at a frequency twice the carrier frequency of the PAL color information signal, and in response to this oscillation, the frequency divider 99
The output parts 107, 109, and 111 each have a phase of 0.
, −90° and +90°, respectively. Output section 107 of this frequency divider 99
A signal with a phase of 0° generated at
The other input section 117 of the transcoding circuit 3 is connected to the input section 119 of the demodulation circuit 75, and this input section 119 is further connected to the output section 121 of the transcoding circuit 3.

If the circuit is in sync, SECAM and
No matter which of the PAL color information signals is being processed, the input section 119 inputs the blue color difference signal (B-
A carrier signal of phase 0° modulated by Y) is received. This signal is demodulated by a demodulator 115 and provides from its output 123 a blue color difference signal (B-Y) for further processing.

However, the input section 11 of the demodulation circuit 75
9, the two systems differ in the color synchronization signal transmitted during the horizontal retrace period,
When processing PAL signals, a color synchronization signal with a 180° phase is present in this input section 119,
In the case of signal processing using the SECAM method, there is no color synchronization signal.

Further, the input section 127 of the demodulation circuit 75 is connected to the output section 125 of the transcoding circuit 3. This input section 127 receives a red color difference signal ±(RY) when the circuit is in a synchronized state, regardless of whether the color information signal of SECAM or PAL is processed. A carrier signal having a modulated phase alternating between -90° and +90° is provided and is fed to an input 129 of a synchronous demodulator 131 where the phase is alternately between -90° and +90°. In response to the switching reference signal, the color difference signal ±
(RY) is demodulated and supplied from its output section 135 for subsequent processing. Note that the aforementioned reference signal is a signal supplied to the input section 133 of the demodulator 131.

When processing PAL signals, the input section 127 of the demodulation circuit 75 receives a color synchronization signal whose phase alternately switches between -90° and +90° during the horizontal retrace period. Supplied. On the other hand, when a SECAM signal is being processed, a color synchronization signal with a phase of +90° is supplied to the input section 127 for every other scanning line.

The reference signal at the input section 133 of the demodulator 131 is input to the output section 109, 1 of the frequency divider 99 by the selection switch 137 of 1/2 horizontal scanning frequency (1/2 _H ).
Obtained from 11. This 1/2 horizontal scanning frequency (1/2
The switching of the _selection switch 137 for 1/2 horizontal scanning frequency (1/2
This is done using the switching signal of _H ).

Further, the state of the multivibrator 143 is switched line-sequentially in response to a pulse signal of the horizontal scanning frequency _H supplied from the input section 147 of the demodulation circuit 75 to the input section 145.

The other input section 149 of this multivibrator 143 receives a signal from the output section 151 of the phase detector 83.
Provides an identification signal of 1/2 horizontal scanning frequency (1/2 _H ). For this purpose, when processing PAL signals, a color synchronization signal whose phase switches between -135° and +135°, and when processing SECAM signals, a circuit When in synchronization, a color synchronization signal that alternates between zero and +90° is applied to input 153 of phase detector 83 via switch 155 and adder 157.
In this case, this switch 155 is connected to the demodulation circuit 75.
The horizontal scanning frequency _H supplied to the input section 147 of
adder 157
The input parts of the demodulation circuit 75 are input to the input parts 119 and 127 of
It is connected to. In the asynchronous state, the color synchronization signal is always zero. In the case of either PAL or SECAM type signals, the phase detector 83 is connected to its input section 1.
In response to the 90° reference signal applied to 59, it produces at its output 151 a signal at 1/2 horizontal scan frequency (1/2 _H ). Multivibrator 1 with this signal
43 in the correct switching state, this signal can be used for color signal amplitude control circuitry and color cancellation circuitry, not shown.

When a PAL system signal is being processed, the phase of the oscillator 89 is controlled in a conventional manner using DC signals from the output sections 79 and 81 of the phase detector 83.
When processing SECAM signals, a DC component occurs at the outputs 79, 81 when the circuit is in a synchronous state. In this case, the transistors 63,
Since 65 operates as an emitter follower, this DC component cannot produce a DC voltage. Therefore, the phase of the oscillator 89 cannot be controlled.

When processing PAL signals, the asynchronous state occurs only when the multivibrator 143 is not in the correct switching state. In this case, this incorrect switching state is corrected by means of an identification signal at input 149 of multivibrator 143.

The reason why this asynchronous state occurs when processing SECAM signals is that the frequency divider 53 of the transcoding circuit 3 is not in the correct frequency division state, and the multivibrator 14 of the demodulation circuit 75
This is because the switching state of the transcoding circuit 3 is different from the switching state of the multivibrator 33 of the transcoding circuit 3.

Next, the operation of this transcoding circuit 3 will be explained in detail, and the multivibrator 143 will be explained in detail.
The effects of an incorrect or erroneous switching state of frequency divider 53 or an erroneous dividing state of frequency divider 53 will now be discussed.

When processing a PAL system signal, the system selection switch 11 of the transcoding circuit 3 is at a different switching position from that shown. In this case,
The color information signal at the input section 1 is supplied to the output section 161 of the method selection switch 11 via the input section 9, and is further sent to the input section 163 of the delay line 165. The time is delayed by the scanning period. This delay line 165
The output section 167 of the balance circuit 171 is connected to the input section 169 of the balance circuit 171
and connect its output section 173 for a signal with a phase of 0° to the input section 175 of the method selection switch 11,
In this case, its input section 175 is connected to the output section 121 of the transcoding circuit 3. On the other hand,
The output 177 for the 180° phase output signal of the balancing circuit 171 is connected to the input 179 of the mode selection switch 11, whose input 175 is in this case connected to the output 125 of the transcoding circuit 3. Two output parts 173, 17 of the balance circuit 171
A resistor 181 is placed between
3 is connected to the input section 163 of the delay line 165 via the input section 185 of the method selection switch 11.

The quadrature component (B-Y) and ±(R-Y) are connected in a conventional manner to a delay line 165, a balance circuit 171 and a resistor 18.
1 and supplied to output sections 121 and 125 of the transcoding circuit 3, respectively, and processed by the demodulation circuit 75 in a conventional manner.

When processing SECAM signals, the method selection switch 11 is in the switching position shown. In this case, the signal obtained from the output section 187 of the modulator 23 is a modulated signal obtained by modulating the carrier signal. This carrier signal is supplied to the input section 41 of the modulator 23, and is the second carrier signal of the PAL system signal.
If the sign reversal of one of the two orthogonal components is ignored, different components of the two components are alternately switched in the scanning line sequence.

During the horizontal scanning period, the transcoding circuit 3
In response to a control signal at an input 191 connected to the input 39 of the horizontal scanning frequency _H selection switch 189 in the switching position shown,
This modulation signal is input to the input section 1 of the method selection switch 11.
93, and then this method selection switch 1
1 to the input section 1 of the delay line 165 via the output section 161 of the delay line 165.
63.

During retrace, selection switch 189 supplies the color synchronization signal from output 195 of selection switch 45 to input 193 of system selection switch 11. This color synchronization signal originates from the output 51 of the frequency divider 53, but because of the operation of the selection switch 45, it occurs only every other retrace interval. When the frequency divider 53 is operating correctly, the phase of the signal is +90°, and when it is not operating correctly, the phase is -90°.

Output section 121 of transcoding circuit 3
is input to the input section 19 via the method selection switch 11.
7 and further connected to the output section 35 of the multivibrator 33, the control signal input section 201
input section 163 of delay line 165 via selection switch 199 of 1/2 horizontal scanning frequency (1/2 _H ) having
and output section 167 alternately. Due to the operation of selection switch 45, selection switch 189 does not provide a color synchronization signal when selection switch 199 is in the illustrated switching position. Therefore, no color synchronization signal is generated at the output section 121 of the transcoding circuit 3. When the selection switch 199 is in a switching state (not shown), a delayed signal that does not contain a color synchronization signal appears at the output 121.

Output section 125 of transcoding circuit 3
During the horizontal scanning period, the 180° output section 1 of the balance circuit 171 is transmitted through the input section 203 of the method selection switch 11, the switch 205, and the selection switch 199.
77 and the input 163 of the delay line 165, so that the output 125 receives alternately a −90° or +90° carrier signal modulated by the red difference signal ±(RY). occurs in

Switch 205 is actuated by a control signal provided from AND gate 209 to input 207 of switch 205. The input part of the AND gate 209 is connected to the output part 35 of the multivibrator 33, and the input part 3 of the multivibrator 33 is
7 is connected to the horizontal scanning frequency _H pulse signal input section 39 of the transcoding circuit 3. In response to this control signal, the selection switch 199 prohibits passage of the color synchronization signal during the retrace period when the selection switch 199 is in a switching position (not shown), and the selection switch 199
Switch 205 is activated to pass the color synchronization signal during the retrace period when the switch is in the switched position shown.

In this case, the frequency divider 53 is connected to the output section 125 of the transcoding circuit 3 every other retrace period.
A correct division condition will result in a color sync signal having a phase of +90 degrees and an incorrect division condition will have a phase of -90 degrees.

As mentioned above, the transcoding circuit 3
No color synchronization signal is generated at the output section 121 of.

Therefore, if the frequency divider 53 of the transcoding circuit 3 is in an incorrect frequency division state, the input 159 of the phase detector 83 will receive the 90° reference signal and the input 153 will receive the color synchronization signal. Receive. This color synchronization signal is generated at a phase of -90° every other horizontal retrace period. In this case, DC signals are generated at the inputs 67, 69 of the transcoding circuit 3 and the outputs 79, 81 of the phase detector 83,
This DC signal causes transistors 63, 6
5. The frequency divider 53 is stopped via the difference generating circuit 61 and the stop signal input 58 of the frequency divider 53, so that the frequency divider 53 no longer produces an output signal;
The color synchronization signal and therefore the output signal of the phase detector 83 which causes the frequency divider 53 to restart is cancelled. This state continues until the color synchronization signal generated at the input section 153 of the phase detector 83 every other horizontal retrace period has a correct phase of 90 degrees.

The frequency divider 53 of the transcoding circuit 3 is then synchronized with the frequency divider 99 of the demodulation circuit 75, after which the multivibrator 143 of the demodulation circuit 75 is activated in response to the signal at the output 151 of the phase detector 83. It is synchronized with the multivibrator 33 of the coding circuit 3.

Instead of using the transistors 63, 65 described above, it is also possible to use a combination circuit of transistors having the same characteristics, for example forming a pair of Darlington connections. Because of this,
The present invention may also include other such combinational circuits.

In the embodiment described above, the transistors 63, 65
The base of the system is directly controlled by the method selection signal. However, some type of transfer circuit may be used to perform this control. When the system selection switch 11 is operated manually, it goes without saying that the voltages at the bases of these transistors 63 and 65 are properly controlled by this manual scanning.

Furthermore, when processing the SECAM signal, if the synchronization of the phase detector 83 or the multivibrator 143 is adapted, the selection switches 45, 189, 1
It is clear that the phase of the color synchronization signal produced at the output 125 of the transcoding circuit 3 every other horizontal retrace period via each of the 99 and 99 can be -90 DEG as desired.

[Brief explanation of the drawing]

The figure is a simple block diagram showing the transcoding circuit of the present invention together with a conventional demodulation circuit. 1, 39... Input section, 3... Transcoding circuit, 7... FM demodulator, 11... Method selection switch, 45, 137, 189, 199... Selection switch, 17, 27... Identification circuit, 23...
Modulator, 33,143... Bistable multivibrator, 155,205... Switch, 53,99
...Frequency divider, 61...Difference generating circuit, 63, 65...
...Transistor, 67, 69...Terminal, 75...
Demodulation circuit, 76, 77... Capacitor, 83...
Phase detector, 89... oscillator, 101... crystal,
115, 131...Synchronous demodulator, 157...Adder, 165...Delay line, 171...Balanced circuit, 1
81...Resistance, 209...And gate.

Claims (1)

[Claims] 1. (a) A modulator for modulating a carrier signal derived from an oscillation signal supplied to an oscillation signal input section with a demodulated SECAM color information signal; and (b) FM. A method selection switch actuatable by a method selection signal for switching from processing a demodulated color information signal to processing a quadrature demodulated color information signal, the carrier signal having a different frequency for each alternating scan line is provided with a different color difference. FM modulated by the signal
In a transcoding circuit that converts a SECAM color information signal into a combination of signals that can be demodulated by a demodulation circuit for quadrature demodulation, the oscillation signal input section is connected to the modulator via a frequency divider. In addition, the frequency divider has an input part for a stop signal connected to the output part of the difference generating circuit in the collector circuit of the two transistors, and the base of the transistor is connected to the output part of the difference generating circuit in the collector circuit of the two transistors. and the emitters of the transistors are respectively connected to different phase control terminals, and when the frequency divider is in an inaccurate frequency division state, the voltage is determined by the difference generating circuit. A signal for stopping the frequency generator is received from the phase control terminal, while the output for the first quadrature component with a constant phase does not generate any color synchronization signal and has a phase that changes from scan line to scan line. In the output section for the second quadrature component, the second quadrature component is output every other horizontal retrace period.
A transcoding circuit characterized in that only color synchronization signals having phases corresponding to quadrature components are generated.