DE2529730A1 - DEMODULATOR CIRCUIT FOR COLOR TV SIGNALS - Google Patents

Description

Description of the patent application

from Indesit Industria Elettrodomestici Italiana

Spa.,

Rivaita (Torino, Italy), Strada Piossasco Km. 17

concerning

"Demodulator circuit for color television signal"

The invention relates to a circuit arrangement for demodulating a chrominance signal in one trained for receiving at least one color television signal, which television signal according to the PAL system is coded. The circuit arrangement includes, among other things, two synchronous demodulators and a switching voltage generator, which works with half the line frequency, but without identification of the switching phase.

A circuit arrangement of this type is disclosed, for example, in Italian patent specification 934,92ο. This document describes a circuit with which PAL signals are essentially converted into NTSC signals however, the advantages of the PAL system are lost. A circuit arrangement of the same type is also disclosed in the Italian patent specification 949, y5o, which different processes for the

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Decoding of the PAL signal describes without identification the phase of the switching voltage generator. Analog circuits are also disclosed in US Pat Italian patent applications 7o26o-A / 73 and 7o32o-A / 73.

All these circuits are similar to the Dekodierschaltkreisen from simple PAL type noticeably _f detected in the presence of phase errors introduced into the signal during transmission to introduce the undesirable so-called blind phenomenon in which the even numbered lines on the receiver screen one of the odd-numbered Lines have different color saturation.

The object of the present invention is to create a circuit arrangement that has the advantages of PAL type demodulation with a delay line, known for example from the Italian patent specification 7o5,469, combined with the advantages of the above-mentioned known circuit arrangements, the advantage that there is no need to identify the phase of the switching voltage generator so as to eliminate the disturbances caused due to the mentioned possible phase errors which are introduced in the transmitted signal can.

In a circuit arrangement in a device intended to receive at least one color television signal for the demodulation of a PAL chrominance signal, which contains alternating sequences of color information signals and reference signals and in which the color information signals are two relative to each other by 90 ° phase-shifted components, which circuit arrangement includes two synchronous demodulators and one with

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half line frequency operating switching voltage generator includes, this object is according to the invention solved in that the circuit arrangement comprises the combination of first circuits, which are arranged in front of the demodulators in the path of the signals for derivation, from the color information signals, at least the two components 90 out of phase with one another in separate form with second circuits which are controlled by the generator and are designed to feed the Synchronous demodulators with oscillations with the frequency of the reference signals are always essentially correct Phase position for the purpose of deriving the demodulated color information, whereby the primary switching voltage generator, which works at half the line frequency, is free of circuits for the identification of the phase the output voltage.

The object of the invention will be described in more detail below with reference to the accompanying drawings explained in more detail which embodiments represent.

Figure 1 shows a block diagram of a decoder circuit for color television signals of the PAL system, designed according to the present invention,

and

Figures 2 and 3 are block diagrams of second and third embodiments, respectively, of a color television signal decoder circuit according to the invention.

In Figure 1 there is a complete chrominance signal at input terminal 1 of the decoder circuit, which color information signals and reference signals

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(bursts). This complete signal should already be derived from the composite in a manner known per se Video signal or the received television signal have been derived. Terminal 1 is connected with the inputs of circuits 2, 3 and Io. Circuit 2 is a delay line, with which the chrominance signal can be delayed by a time interval substantially equal to that Duration of an odd multiple of scan lines (1,3,5 etc.), i.e. according to the Italian Norm around 64, 192 or 32o microseconds etc. The circuit 2 generally causes a Amplitude attenuation of the applied signal. Circuit 3 is a damping circuit that allows the Amplitude of the input signal is attenuated to the same extent as caused by the circuit 2. Circuit Io is explained below.

The delayed signal coming from circuit 2 and the direct signal from circuit 3 have the same amplitudes and are both sent to an adder circuit 4 and a subtracting circuit 5 is supplied. The output of the adder circuit 4 becomes the signal input dines first synchronous demodulator 6 supplied, while the output of the subtracting circuit 5 is connected to the signal input of a second Synchronous demodulator 7.

The two demodulated color difference signals are available at the outputs 8 and 9 of the demodulators 6 and 7, respectively.

Circuit Io is an electronic gate with a signal input, a control input and a Exit. The signal from terminal 1 is applied to the signal input; a line rate pulse, typically a return line pulse, which is derived in a manner known per se from the relevant deflection circuits.

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bar is applied to the control input from a terminal. The output of the gate Io is connected with the signal input of an electronic branch circuit 11, which has a control input and has two outputs.

Under the action of the control signal, the branch circuit 11 connects the signal input to the first or with the second output in an alternating manner.

A first output of branch circuit 11 is to a first subcarrier regenerator circuit 12, while the second output of the branch circuit 11 is connected to a second subcarrier regenerator circuit 13 is connected. The two circuits 12 and 13 are analogous to one another and can be of any type known per se. At their output they have to supply an oscillation with a subcarrier frequency, its phase and frequency is substantially coincident with the phase and frequency of the reference signal applied to its input is. In a preferred embodiment, circuits 12 and 13 comprise passive quartz crystal filters.

The outputs of the two regenerator circuits 12 and 13 are both provided with an adder circuit 14 and a subtraction circuit 15, of which the circuit 14 is analogous to circuit 4 and the circuit 15 can be designed analogously to circuit 5.

The output of the adder circuit 14 is applied to the subcarrier input of the demodulator 6,

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while the output of the subtracting circuit 15 to the signal input of an electronic periodic Phase inverter 16 is applied.

The inverter 16 also has a control input. Depending on the applied control signal, it inverts the Phase of the signal applied to the input or not. The output of inverter 16 becomes the subcarrier input of the demodulator 7 is supplied.

The line frequency pulses from terminal 18 also reach a circuit 17 in the form of a switching voltage generator, typically a bistable multivibrator or flip-flop; he delivers to his The output is a signal with half the line frequency, which is sent to the control inputs of the branch circuit 11 and the periodic inverter 16 is applied. The branch circuit 11 and the inverter 16 work accordingly in alternating synchronism and synchronously with the line deflection. However, since the The phase position of the generator 17 is indefinite, the phase of the circuits 11 and 16 is also absolute seen, redefined.

The circuit arrangement according to Figure 1 works as follows:

The PAL signal consists primarily to the two signal sequences, namely color information and reference information that are transmitted in alternating rows and differ from each other by the phase inversion of the RY component. However, the information of one sequence and that of the other are available at the same time because of the delay circuit. They are added in circuit 4 (and in this way the RY component, which is inverted in one sequence, is eliminated relative to the other)

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and subtracts in circuit 5 (which eliminates the B-Y component, the phase position of which is constant). As a result, only the B-Y component is at the output of the circuit 4, while at the output of the circuit 5 only the R-Y information is available, the phase of which is inverted in every line. The demodulator 6 is as a result the B-Y demodulator, and in order for it to work properly, it must have a subcarrier at the subcarrier input the phase B-Y obtained; the demodulator 7 is the R-Y demodulator and for it to work properly it must he received a subcarrier alternating with the R-Y phase.

The gate Io blocks the coloring information as it is during of the active portion of the rows is closed and only allows the reference signals to pass through Effect of the signals from terminal 18 with line frequency. The two sequences of the reference signals are by the branch circuit 11, which operates at half the line frequency, divided. The regenerator circuit 12 therefore always receives a sequence of the signals of the same phase and the regenerator circuit 13 always receives the other. However, it is not known which one because the switching phase is indefinite.

The two regenerated subcarrier oscillations are hence each in phase with a sequence of the reference signals. They are added in circuit 14 and, regardless of the switching phase of the generator 17, a subcarrier of constant phase is accordingly obtained, which is directed along the B-Y axis and is therefore suitable for controlling the demodulator 6.

The two subcarrier oscillations are also subtracted in the circuit 15 and one obtains accordingly a subcarrier whose phase is along the R-Y axis in the positive or negative direction, respectively

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After the phase of the generator 17, i.e., depending on whether the regenerator circuit 12 the straight Sequences or the odd sequences. The one obtainable from the subtracting circuit 15 Constant phase subcarriers (apart from the aforementioned uncertainty) are made alternating through the inverter 16 and is accordingly suitable for the control of the demodulator 7. Since the inverter circuit 16 is connected to the branch circuit 11, is the absolute phase position with which it work, meaningless. In this regard, if the phase is inverted, it will be inverted twice (im Circuit 16 and in branch circuit 11) and the effect is canceled. With the described Circuit arrangement one thus obtains the advantages of demodulation with a delay circuit (insensitive to any phase differences between the subcarrier oscillations and the color signal, because the R-Y and B-Y components are separated before synchronous demodulation), where These advantages are combined with the advantages of an automatic identification of the switching voltage generator (for identification is guaranteed for all signal conditions occurring).

Figure 2 illustrates a modification of the circuit arrangement of Figure 1 and the analog blocks are therefore given the same reference numerals. Figure 2 differs from Figure 1 mainly in that the terminal 1 is only connected to the Inputs of the delay circuit 2 and the damping circuit 3, but not with the input of the gate circuit lo, which is accordingly missing here; the same applies to blocks 11, 12, 13, 14 and 15. The output of the adder circuit 4 is connected both with the signal input of the demodulator 6 as

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also with the input of a gate 2o, similar to gate from Figure 1. An electronic periodic phase inverter 24, similar to the inverter 16 of Figure 1, is connected between the output of the subtracting circuit 5 and the signal input of the demodulator 7.

The output of the inverter 24 is also at the input of a gate 21, which is similar to the gate 2o is. Terminal 18, to which line frequency pulses are applied, is connected to switching voltage generator 17 connected, the output of which is connected to the control input of the inverter 24, and also to the Control inputs of gates 2o and 21. The outputs of these two gates are at the inputs voj Subcarrier regenerator circuits 22 and 23, similar to the regenerators 12 and 13 from Figure 1, and the outputs of these regenerators 22 and 23 are to the subcarrier inputs of the demodulators 6 or 7 placed.

The circuit arrangement according to FIG. 2 operates as follows: The gate 2o only allows the passage of those Reference signals which, derived from the output of the adder circuit 4, have a phase which is the mean value corresponds to the phase of the signals of the two sequences, i.e. a phase in the direction of the B-Y axis. The circuit 22 accordingly generates an oscillation with this middle phase and is capable of the demodulator 6 to control, which applies the B-Y color difference information demodulated to terminal 8.

Gate 21 allows only those reference signals to pass through which are derived from the output of the subtracting circuit 5 and periodically inverted in phase by inverter 21, a fixed phase lengthways of the R-Y axis, but the direction remains indefinite. The circuit 23 generates accordingly

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an oscillation with this fixed phase which is suitable for controlling the demodulator 7, which applies the R-Y color difference information to terminal 9 in a demodulated manner. In this regard, the demodulator 7 receives the color information signals, which have passed through the inverter 24, by which one of the two information sequences has been inverted, and the information itself no longer alternates. As a result, the demodulator 7 operates correctly regardless of the phase of the generator 17,

The circuit arrangement according to FIG. 3 is a modification of the circuit arrangement according to FIG. 2, and consequently only the blocks that differ are described.

The outputs of the circuits 2 and 3 are connected to the two inputs of the adder circuit 4 and subtracter Circuit 5 after they have passed through a permutator, which is known per se Component in electronic design is, namely a double branch circuit, consisting for example from four diodes, with wwei inputs 31 and 32, two outputs 33 and 34 and a control input 35. The outputs of the delay circuit 2 and the attenuator 3 are connected to the two inputs 31 and 32 connected, the two outputs 33 and 34 are both connected to one input of the Circuits 4 and 5, while the output of the switching voltage generator 17 is applied to the control input 35 is. The inputs 31 and 32 are connected to the outputs 33 and 34, or to the outputs 34 and 34, respectively. 33, depending on the voltage phase of the circuit 17.

The output of the subtracting circuit 5 is also directly connected to the inputs of the demodulator 7 and the gate 21, and the inverter circuit 24

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is no longer provided.

The circuit arrangement according to Figure 3 works as follows:

At the output 33 of the permutator 3o are the signals from one of the two alternating signal sequences, where a line arrives directly via circuit 3 and the next line is delayed via circuit Similarly, the signals of the other sequence are at the other output 34. At the output of the Adding circuit 4 is obtained accordingly only the color information and reference signals of the phase, the are directed along the B-Y axis, while the signals with components along the R-Y axis derived from a sequence invert to the next, be eliminated. On the other hand, at the output of the subtracting circuit 5 only the color information and reference signals of the longitudinal Axis R-Y directed signals, which is indeterminate because it depends on the phase of the generator 17, but no longer alternieread is because of the permutator 3o,

The reference signals are then separated by the gate 2o and pass to the circuit 22, the one Subcarrier oscillation generated along axis B-Y, which, fed to the demodulator 6, is the derivative of the demodulated B-Y color difference information signal on terminal 8 allowed. The reference signals are also through the gate 21 is separated and are then fed to the circuit 23, the one subcarrier wave along R-Y axis generated. This subcarrier oscillation arrives at the demodulator 7, so that the demodulator 7 provides the color difference information R-Y can be demodulated, which is then applied to terminal 9. Since the reference signals, which reach the regenerator circuit 23 are derived from the same signal that is sent to the Demodulator 7 arrives, the phase of the subcarrier

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The oscillation for the demodulator 7 is always correct, regardless of the phase position of the generator 17.

With the Schaltungsanordnun gene according to the present invention, there is the advantage that the phase of the Switching voltage generator not identified too so that its phase position does not play a role in correct operation. Simultaneously one can use a delay circuit to detect conceivable phase errors in the demodulated color signals, avoid those obtained.

(Patent claims)

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Claims (13)

Claims / Iy circuit arrangement in one for reception at least one device intended for color television signal for demodulating a PAL chrominance signal, which contains alternating sequences of color information signals and reference signals, wherein the color information signals comprise two 90 ° phase-shifted components, which circuit arrangement has two synchronous demodulators and a switching voltage generator, which with half line frequency operates, characterized in that the circuit arrangement comprises the A combination of first circuits which are upstream of the demodulators in the path of the signals, for deriving at least the two 90 ° phase-shifted components in separate Form of the color information signals, as well as second circuits controlled by the generator are for supplying the synchronous demodulators with oscillations of the frequency of the reference signals, but always essentially more correct Phase position for deriving the demodulated color information, during the one with half the line frequency working switching voltage generator free of circuitry for phase identification the output voltage is formed. 2. Circuit arrangement according to claim 1, characterized in that that the phase of each of the oscillations at the reference signal frequency generated by the second Circuits, is essentially the same as the phase of the 90 ° phase-shifted component, which is the corresponding synchronous demodulator is supplied. -14- 50988A / 0880 3. Circuit arrangement according to claim 1 or 2, characterized in that the first circuits have a Delay circuits include for delaying the chrominance signal by a time interval that is substantially equal to an odd multiple of the duration of a line. 4. Circuit arrangement according to claim 3, characterized in that the first circuits have a Attenuation circuit includes for the introduction of an attenuation of the chrominance signal equal to that, which is introduced by the delay circuit. 5. Circuit arrangement according to claim 3 or 4, characterized in that the first circuits have a Adding circuit and a subtracting circuit, which at least the output signals from are fed to the delay circuit and which is designed so that it at least the two 9o ° emits phase-shifted components in separate form. 6. Circuit arrangement according to one of the preceding claims, characterized in that the second Circuits include an electronic branch circuit controlled by the switching voltage generator, for branching the two alternating frequencies of reference signals to these two subcarrier regenerators feed, each of which generates an oscillation with subcarrier frequency, and an adding circuit and a subtracting circuit for deriving the sum or the difference between the two generated vibrations with subcarrier frequency, and finally one periodic phase inverters, controlled by the generator, for alternating the 4/0880 Phase of the subcarrier frequency oscillation generated by the subtracting circuit. 7. Circuit arrangement according to one of claims 1-5, characterized in that the second Circuits include an electronic switch that is behind the first circuits and is arranged in front of the synchronous demodulators, and is controlled by the switching voltage generator and which, at half the line frequency, inverts the phase of one of the separate 9o phase-shifted components as well as the alternating phase of a combination of the reference signals derived from the first circuits, which combination of the reference signals behind the changeover switch constant Has phase and is fed to a subcarrier regenerator to deliver the oscillation Reference signal frequency to one of the synchronous demodulators. 8. Circuit arrangement according to one of claims 3-5, characterized in that the second Circuits comprise an electronic permutator controlled by the switching voltage generator, and with at least two outputs, which is designed so that it is the direct Chrominance signal and the signal to the delay circuit delayed by the delay Supplies outputs, the output assigned to one of the signals being switched in each line. 9. Circuit arrangement according to claim 8 when dependent on claim 5, characterized in that the permutator between the delay circuit on the one hand and the adding or subtracting circuits -16- 5098 8 4/0880 on the other hand is peeled. 10. Circuit arrangement according to claim 9, characterized in that that the adder circuit has the first synchronous demodulator and a first subcarrier regenerator controls and that the subtraction circuit controls the second synchronous demodulator and a second subcarrier regenerator. 11. Circuit arrangement according to one of claims 6, 7 or Io, characterized in that it comprises gate circuits, controlled by line frequency pulses, the separation of the reference signals or the combination of the signals from the chrominance signal to enable such that only the reference signals are fed to the subcarrier regenerators. 12. Circuit arrangement according to one of claims 6, 7, Io or 11, characterized in that the Subcarrier regenerators each include a passive crystal filter. 13. Circuit arrangement according to one of the preceding claims, characterized in that the switching voltage generator is a bistable multivibrator controlled by line frequency pulses. 509884/0880