DE2254570A1 - DEMODULATION CIRCUIT FOR PAL COLOR TV RECEIVER - Google Patents

Description

Priority 16 «Ifoy» 1971 * ~ '^ "No. 92189/71 ί

The invention relates to a demodulation circuit for color television receivers (phase international line receivers) operating according to the PIL system, and in particular the invention relates to a circuit for demodulating the chrominance signal , which is represented by a modulated carrier wave modulated "the independent he gen with two ^spaced-1 Färbsignäien * a Demodulatiottsschaltung invention does not require the Inwenduiig a delay line for delaying the Chrominänzsignals.

, When transmitting color television signals, a Color synchronization signal (burst signal) and a line syn- " Chrqnisiersignal and the Chrotninanzsignal and the video signal (Brightness signal) transmitted. With the PIL transmission method is * as in the iiTSO transfer procedure,

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the chrominance signal by modulating a carrier wave modulated by two signals depending on the chrominance, and thereby becomes the phase of the chrominance signal from line to line on the transmitter side reversed between two values that symmetrical with respect to the modulation axis (B - Y) (Color difference axis for blue) lie. With the usual PAL Erapfängern this chrominance signal is delayed by a delay line for the duration of one line, and the delayed and the non-delayed chrominance

with
signal / combined with each other.

PAL receivers have also already become known that work without the use of an ultrasonic delay line; in this regard, reference should be made to gB-PS 1 066 798 . Here, the chrominance received signal is again switched in terms of phase in a switching stage, the switching stage being controlled by two color synchronizing signals, each of which has a phase of + 45 ° with respect to the demodulation axis (B - Y) in one line, and it becomes furthermore causes demodulation in the deraodulation stage with respect to the (R - Y) demodulation axis. The switching stage consists of a bistable multivibrator whose output signals are synchronized with the phase of the chrominance signal with respect to the (R - Y) axis.

For this reason, a phase discriminator must be provided - which is responsive to the phase of the color sync signal and provides a control signal characteristic of the detected phase of the color sync signal with respect to the (R - Y) axis. These control signals (pilot signals) then control the bistable multivibrator and switch it over.

309823/0686

The invention aims a demodulation for a color television working according to the PAL system which a phase discriminator is not required to control the multivibrator.

The following circumstances are relevant for the invention:

1) The invention uses a bistable multivibrator for switching, but the multivibrator is by the Line synchronizing signal and not by the color synchronizing signal controlled. So it is the multivibrator in the invention not by the output signal of a phase discriminator reversed.

2) The invention uses an APC circuit (automatic phase control circuit) to generate the color subcarrier (reference carrier), which is controlled by the color sync signal. .

3) In addition to the APC stage, a gate stage is provided, which fades out one of the two color synchronization signals, which are decisive for alternating lines, the faded out Color synchronization signals are synchronous with the change of the demodulation axis (R-Y) by 180 °. That, faded out The color synchronization signal is fed to a phase discriminator, to which the reference carrier supplied by the APC stage is also fed is supplied to the 'relative phase' of the color reference carrier in relation to the. F '^ synchronizing signals determine what has the consequence that the phase of the reference carrier either by 0 ° or -180 by means of a phase.ndrehstufe is rotated with respect to the demodulation axis.

4) In successive lines, the phase of the reference carrier is rotated by 180 °, and the chrominance signal (R-Y)

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is with respect to the phase-converted reference 1

carrier demodulated. \

Further features and advantages of the invention result _v

arise from the following claims and from the;

Description of preferred embodiments of the invention (

dung in connection with the figures. The figures show: j

Figure 1 is a block diagram of a first inventive j

according to demodulation circuit; [

Figure 2 is a vector diagram to explain the in i

Figure 1 shown circuit; '

Figure 3 shows the temporal relationships of the different

the signals that appear; ■ '

Figure 4 is a block diagram of a second embodiment (

form of invention; ι

FIG. 5 the associated vector diagram; ;

Figure 6 shows a phase discriminator with integration {

stage for use in the context of the invention; \

FIG. 7A are vector diagrams relevant to FIG. 6; and t

and 7B {

FIG. 8 shows a phase rotation circle provided within the scope of the invention.

The circuits discussed below are '

Circuits that are currently as particularly cheap execution.

xungsformen of the invention are considered. It is however ^; it should be emphasized that these embodiments correspond to the general
The inventive concept does not limit the depicted
Rather, circuits only serve to explain the invention.

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SEC 3101 - 5 -. ,., ...,.

FIG. 1 shows the block diagram of a circuit according to the invention which serves the purpose of demodulating the chrominance signal contained in the composite PAL television signal. The circuit according to the invention has two automatic phase control APC chains 3, 4 »5 and 7, Qf 9 as well as a switching chain and two demodulators 13, 14. 15 is the matrix circuit provided for generating the color difference signals. The switching chain consists of a delay stage 16 ί a pulse shaping stage 17 j a switching stage 18, a differentiating stage 19, a Schmitt trigger stage 20 and two gate stages 2, 6.

The first APC chain, which is the output signal of the first disturbance stage 2 is supplied, consists of a phase discriminator 3 »a reactance stage 4 (retuning circuit) and one feedback oscillator 5 for generating the reference carrier. In the same way, the second APC chain consists of the Phase discriminator 7 »of the reactance stage 8 and the feedback generator 9. The generated by the two A ^ C chains Reference carriers are sent to the second demodulator 14 via an adding stage 10, a switching stage 11 and a phase rotation stage 12 fed *

The composite PAL television reception signal is fed from the image intensifier (not shown) to a bandpass amplifier : and the chrominance signal designated by 1 in FIG. 3 is fed to the two gate stages 2, 6. The line synchronization signal, denoted by 2 in FIG. 3, is fed to the delay stage 16 and to the pulse shaping stage 17, so that the signal denoted by 3 in FIG. So, unlike the well-known scarf

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device, as a control signal for the switching stage 18 not that Color synchronization signal, but the time-shifted line synchronization signal is used.

The pulses fed to the switching stage 18 as a control signal in accordance with the pulse series 3 in FIG. 3 produce square-wave signals in the output circuit of the switching stage 18, as shown in FIG. 3 _f line 7. A differentiating stage 19 generates differentiated pulses 8 therefrom, which are fed to the Schmitt trigger stage 20. In view of the control by the differentiated pulses, the Schmitt trigger stage 20 supplies 8 output pulses according to the line in FIG. 3f, which have a period of 2H of alternating lines.

Gate stage 2 immediately receives the control pulses according to line 3 and fades in successive lines (line period H) a color synchronization signal. The faded out color synchronization signal of gate stage 2 is shown in FIG. 3 reproduced in line 4. On the other hand, the gate stage 6 receives gate pulses 9 from the Schmitt trigger stage 20 and fades out a color synchronization signal of twice the pulse spacing

. the

2H off. The pulses shown in FIG. 3 in / lines 5 and 6 reproduce the impulses masked by gate step 6. Whether the gate stage 6 the color synchronization signal according to line 5 or the color synchronization signal according to line 6, depends on the conditions under which the Switching stage 18 is currently being operated.

The faded out color synchronization signal according to line 4 is fed to the first APC chain 1, which is formed by the phase discriminator 3, the reactance stage 4 and the reference carrier generator 5, and the two reference carriers f _QQt f ¹ Q ₀ since a phase

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difference of 90 ° to each other for demodulation in with reference to the demodulation axes (B- Y) or (E - Y), as will be shown, derived *

Similarly, the other faded out color synchronization signal 5 or 6 is fed to the second automatic phase control chain APC2, which feeds the second color reference carrier ^ 'B1 ^or ^' b2 '^ ^e ^ ^e ^ ^e * ^{n of the} ^ ^{nase utQ} 90 ° äen color ~' ~ Lagging the synchronization signals f _B - or f _B2 .

When the generator 9 the second reference carriers f ¹ ^ supplies and also the first reference carrier f ^f _SQ and the second reference carriers f 'ηη 4 ^he adder 10 in DEID relative ratio "^" ^ ¹ I ^f * "οI ~ If * 3i, j zugefUlir- fc, the resulting reference carrier f ' _{sl has} a' phase which coincides with the demodulation axis (B - Y). In contrast, when the oscillator 9 the second reference carriers f _'B2 l ^{ie: fer' fc} * && ^d: * - ^e two reference carriers f ^f _B2> ^f so supplied ^'in el ^eicner way of the adder 10, so 10 provides the adder to the reference carrier f ' _s2 > whose phase coincides with the demodulation axis - (B - Y).

The reference carrier formed by vibration composition f, "the following Bezugsträgerumschaltstufe 11 is supplied, and it is the reference carrier f _'sl unchanged taken from the same, when the rectangular pulse 7 of the switching stage 18 for Zeit.t-, is positive, while f as the reference carrier ¹ O ₂ with reversed phase position is taken when the square pulse 7 is negative at time tp. Even if the reference carrier composition formed by f ^ ⁿ alternating phase position _'s2 of Bezugsträgerumschaltstufe, 11 is supplied, as in a similar manner, two reference carrier F'G-i »f'gp' are generated in successive lines.

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The resulting reference carriers f ' _sl f ^fl _S 2 ^{are fed to the} phase rotation stage 12 and a phase lead of 90 ° is brought about therein, so that the third reference carrier £ "-, on the + (R - Y) axis and the third reference carrier f _g2 on the - (R - Y) axis. In this way, in accordance with the switching of the color synchronization signals, third reference carriers are formed which define the demodulation axis (R - Y). Meanwhile, the chrominance signal is fed through the bandpass filter 1 to the (B-Y) demodulator 13, the reference signal of which is the fixed reference carrier frequency f " ₀ , and the (R - Y) demodulator 14 receives the reference carriers f" -, and f _g p supplied, each having phases offset by 180 ° during successive lines. The demodulators 13, 14 therefore supply the color difference signals S (B - Y), S (R - Y), which are fed to the matrix circuit 15 and there into the color difference signals S (R - Y), S corresponding to the red, green and blue signals (G - Y) and S (B - Y) are converted "] / The circuit for the chrominance signal can be designed in such a way that the polarity of the chrominance signal is reversed for one line and the demodulation is carried out using the reference carriers f _sl , fg ₂ instead of the switching stage 11 being provided for the reference carriers, such a possibility is not shown in FIG.

then
So / the chrominance signal of the bandpass amplifier 1 is fed to the (B - Y) demodulator 13 and a switching stage, not shown. The square pulse 7 from the switching stage 18 is fed to the switching stage provided for the phase reversal of the chrominance signal in such a way that the chrominance signal is reversed by 180 during the one line period when it enters the (R - Y) demodulator 14.

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At the same time, the reference carrier f _{ßQ of} the oscillator 5 is fed to the (B - Y) demodulator 13 for delivery of the color difference signal S (B - Y). The reference carrier f * or f *

ο is fed to the phase shift stage 12 causing a phase shift of 90, so that the color difference signal S (R - Y) is formed when the composite reference carriers f _{s: L} , fg _{2 are} fed from the phase shift stage 12 to the (RY) demodulator 14.

The same result can be achieved if you have one Push-pull demodulator, connected to an integration part, used by the square-wave pulses 7 of the switching stage 16 is activated, instead of one switching the chrominance signal Switch. '

A second preferred embodiment of the invention is; shown in FIG. In FIG. 4, the switching stages corresponding to FIG. 1 have the same reference symbols. In this further embodiment, only one APC chain 3 to 5 is used. The color synchronization signal 4 is taken from the gate stage 2 and fed to the provided APC stage, which is formed by the phase discriminator 3, the reactance stage 4 and the oscillator 5 and generates a first reference carrier fg, which generates a phase delayed by 90 ° with respect to the resulting phase of the two composite color synchronization signals f ^ _t Γ _β2 . This first reference carrier f ″, which is generated by the generator 5, lies in phase, as shown in FIG. 5, in the direction of the demodulation axis (R-Y). The supply of this first reference carrier f "to the 9Ö ⁰ -Phasendrehstufe 21 generates an N- second reference carrier £" ~ for the demodulation axis (B-Y). As part of the output of the generator

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2754570

is fed to the phase discriminator 3 via the feedback loop of the APG chain, the correct phase of the reference carrier f _{g is} maintained. The gate stage 6 fades out with twice the line period 2H Parbsynohronisiersignale. The faded out synchronization signal 5 and the reference carrier f _{g of} the oscillator 5 are fed to the phase discriminator 22 at the same time.

In FIG. 6, for example, an embodiment of a phase discriminator 22, connected to a subsequent integration stage, is shown. The color synchronization signal f _B1 is fed through the gate stage 6 to the primary winding L _{1 of} the transformer T ₁ . The color synchronization signals £ _B1 »- ^ b ₁ > ^d * ^ea ^ · ⁸ vectors are shown, are induced _{in the secondary winding L 2.} On the other hand, the reference carrier f _{g of} the oscillator 5 can also be fed to the primary winding L-, the reference carrier f “being shown as a vector in FIG. 7A. The voltage V ₁ at the phase discriminator diode D- corresponds to the voltage _{vector sum (f B1} + fg) »while the voltage V ₂ at the second phase discriminator diode D ₂ corresponds to the vector sum (f_, + (-f")). It can therefore be seen that the output signal is a direct voltage signal Δ., formed at the connection of the resistors H ₁ , IU, the integration circuit 23 being formed by the capacitances G ^, C ^ and the resistor R i. The DC voltage jZsS is positive, since JVJ> JY ^₂ I * ^Ven n the Farbsynchronielersignal f _B2 of the primary winding L, of the transformer T, is supplied, the Gleichspannungskompontnte ΔΕ becomes negative in the integration stage 23 because, for the voltages V and V _? at the phase discriminator diodes D ₁ . D ₂ according to FIG. 7B the relationship applies (vj <Jv ₂ |.

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In this way, the reference carrier f _{g of} the oscillator 5 and the DC voltage component Δ E of the integration stage 23 are fed to the phase shifter stage 24, and a third reference carrier fg- or f _{g2 is} formed, the phase of which lies on the demodulation axis (RY). The third reference carrier f ~ -, or f " _{2 also} corresponds to line 11 in Figure 3. ■"

According to Figure 8, the phase shifter stage 24 consists of the transistors Q ₁ , Q 2, Q ,. When the reference carrier f _{g is} fed to the primary winding L-, of the transformer T *, the reference carrier f n occurs at the collector of the transistor Q, and the phase-inverted voltage at the base electrode. The reference carrier f ~ of the collector electrode is fed to the interconnected emitter electrodes of the transistor pair Q- ,, Qp ..

The two transistors Q-,, Q ₂ are arranged so that the transistor Q- is switched on and the transistor Q _{2 is} switched off when a positive voltage ΔΕ of the integration stage 23 of the base electrode of the transistor Q- is supplied. In this way, the third loading. . tensile carrier f ", of the same phase as the first reference carrier fg occur on the secondary winding I _{2 of} the transformer T., which connects the two collectors of the transistors Q ₁ , Q ₂ . When the two transistors Q ₁ , Q ₂ are switched so that the first-mentioned transistor Q- is blocked and the second transistor Q ₂ is live. if a negative DC voltage signal -Δ.Ε the transistor Q- is fed, the third reference carrier fg _{2 is produced} with an inverted phase with respect to the reference carrier f _g at the secondary winding L _{2 of} the transformer T .. ~

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225457Π

In FIG. 4, the third reference carrier corresponding to line 11 and the square-wave pulses corresponding to line 7 of FIG. 3 are fed to the switching stage 25, which alternately supplies the fourth reference carriers f _gl , f _g2 , fg., ..., from line to Line of each of the fourth reference carriers mn 180 ° is inverted in phase.

At the same time, the chrominance signal is supplied from the bandpass amplifier 1 to the (B - Y) demodulator 13 and the (R - Y) demodulator 14. The (B - Y) demodulator 13 effects the (B - Y) demodulation according to the second reference carrier fg ₀ and thereby generates the color difference signal S (B - Y), while the (R - Y) demodulator 14 the (R - Y) demodulation using the third reference carrier ^f Sl ^ff S2 ' ^f Sl *** * J ^e ^ ^{ür e} * ^Jie causes the line duration and generates the color difference signal $ (R - Y). The two color difference signals S (B - Y), S (R - Y) are then converted in the matrix circuit 15 into the three color difference signals S (B - Y), S (GY) and S (R - Y).

In the circuit according to the invention, the switching means are simple and cheap, since the line synchronizing signal for Control of the bistable multivibrator is used. The time constant of the automatic phase locked loops APC can be chosen so that the reference carrier 12 of Figure 3 is properly generated even if by an interfering signal accidentally the bistable multivibrator switching stage is reversed.

Patent claims:

309823/0686

Claims (4)

HEC 3101 - ft- Pat ent, anapriiclie \ l) Demodulation circuit for a PAL color television receiver, characterized by a multivibrator switching stage (18) controlled by the line synchronization signal and by a first phase-controlled generator arrangement (APCl) for generating a first reference carrier (f _so »f ' _s0 ) from one of the composition of the two color synchronization signals (f _B1 , fg ₂ ) corresponding middle phase position and by a! Porstufe (j6) to mask out one of the two iarbsynchronisiersignale (f-ni or f *.?) » ^which is controlled by the aforementioned switching stage (18), and by a second, by the faded out Parbsynchronisiersignal (fgi or f-no) phase-regulated generator or arrangement (APG2) to generate a second reference carrier ^ 'b1 ^{0 (} * ^{er f 1} B ^ ¹ ^ * ^{durcl1 an} adder (10) for the vectorial addition of the two reference carriers formed and by a phase inversion stage (12) controlled by the multivibrator switching stage (18) for generating a third, from line to Z hurry the phase position changing by 180 ° reference carrier (f _gl »f _s2 > ^f gx ···) for the twos of the synchronization of a detnodulator serving to generate the iarbdifferenzssignal (S (S - Y)). (14) · 2. The circuit nachAnspruch.1, dadur eh ge ke η n z ö I et η that the third Bezügsträger (F'G-j ^ f ¹ Qp) ^ffli * iseilenweiser Phaaeninvertierung (11) your demodulator (14) is fed as reference frequency . 303823/0686 HEC 3101 - ♦ - ■ _Ä _ 3. Circuit according to claim 1, characterized that the chrominance signal with line-by-line phase inversion to the demodulator (14) is supplied. 4. Demodulation circuit for a PAL color television receiver, characterized by a multivibrator switching stage (18) controlled by the line synchronization signal and by a phase-controlled generator arrangement (APC) for generating a first reference carrier (f _g »fgn) ^from one of the composition of the two color synchronization signals (f-- ,, ^ -no) corresponding middle phase position and by a gate stage (6) for masking out one of the two color synchronization signals (f-οτ or f _B2 ) and by one of the first reference carrier (fg) and the output signal of said gate stage (6) controlled phase discriminator stage (22) with integration stage (23) and the phase of the first reference carrier (fg) controlled by the output signal of the integration stage (23) 0 ° or 180 ° shifting stage (24 »25) and by a phase inversion stage (25) controlled by the multivibrator level (18) to generate a third reference carrier (* ₃₁ ι fg ₂ » ^F gi ···)" ¹ ^ feeding of the same to the Deiiodulatora (14) serving the purpose of generating the fmrbdifferenzsignalB (S (R - Y)) 309823/0686 Blank page