DE2644465A1 - CIRCUIT FOR MONITORING THE LEVEL OF CHROMINANCE SIGNALS IN COLOR VIDEO SIGNALS OF DIFFERENT STANDARDS - Google Patents

Description

PATENT LAWYERS 2844465

TER MEER - MÜLLER - STEINMEISTER

D-SOOO Munich 22 D-4800 Bielefeld Triftstrasse 4 Siekerwall 7

^S76P132 'Oct. 1, 1976

SONY CORPORATION Tokyo / Japan

Circuit for monitoring the level of chrominance signals different in color image video signals

Standards

The invention is in the field of recording and / or reproducing devices for color image video signals according to the SECAM or PAL system and relates to a circuit for conditioning and processing the chrominance signal of a SECAM or PAL signal, to be recorded on and / or accessed from a video tape recorder. In particular, the invention relates to a Circuit according to the preamble of the claims.

In the PAL system, the color subcarrier is modulated in push-pull by two color signals (R-Y) and (B-Y) along two modulation axes, whereby the axes are offset from one another by 90 ° and

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cine Modu 1 at.ionsuchso in j ο dom horizontal interval reversed, i.e. pivoted by 180 °. As FIG. 1A shows, the PAL signal in the horizontal blanking interval is provided with a horizontal sync pulse or line pulse P, with a width of 4.7 jusec and a burst signal S, which is opposite the leading edge (time t.) Of the line pulse P _h is delayed by (5.6 t 0.1) lisec and has about 10 oscillation periods.

In the SECAM system, on the other hand, the color subcarrier is alternated with the (RY) or. the (BY) component of the chrominance signal is frequency-modulated and the signal modulated with (RY) or the signal modulated with (BY) are transmitted in line sequence. As can be seen from FIG. 1B, the SECAM signal in the horizontal blanking interval is also provided with the line pulse P, which also has a duration or width of 4.7 μsec, but on the other hand contains a non-modulated carrier signal S _f , which is delayed by (5.6 _ 0.3) usec compared to the time t. and lasts until the end of the horizontal blanking interval (time t ~). The carrier signal S- has a frequency f of 4.40625 MHz when the (RY) component occurs as the modulating signal and, on the other hand, has a frequency f of 4.250 MHz when the (BY) component is the modulating signal.

If a color video signal is to be recorded on or tapped from magnetic tape, it is generally necessary to the level of the chrominance signal component by an automatic color signal monitoring circuit (ACC circuit = Automatic C_olor C_ontrol) for a certain value to be monitored or closed rules.

In conventional recording and / or reproducing devices for PAL signals, the level monitoring for the chrominance signal carried out by sampling the level fluctuation of the burst signal, while in known recording and / or reproducing devices

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for SKCAM signals the level monitoring by sampling the mean value level of the chrominance signal is performed during a full horizontal interval.

For devices capable of recording and / or playback from both SECAM and PAL signals are suitable, it is disadvantageous to to provide an ACC circuit, the different signal intervals scans because the circuit structure becomes extremely complicated.

The invention is therefore based on the one hand on the object for such color video recording and reproducing devices To create a simple ACC circuit that is well suited for both SECAM and PAI signals.

In the case considered above with reference to FIG. 1B, it was assumed that the approach of the leading edges of the burst signal S, or of the non-modulated carrier signal S _f, lie in the middle of the specified norm or standard ranges. However, if the beginning of the burst signal S _b or the non-modulated carrier signal S _f - as shown in FIG. 3 - is shifted from the center or the predetermined reference value, an automatic chrominance signal control (ACC operation) cannot be performed with satisfactory accuracy reach. If, for example, the burst signal S (cf. FIG. 3) occurs with a time delay of 5.5 yusec compared to the time t .. and the non-modulated carrier signal S _f with a time delay of 6 μεβσ compared to the time t .., so If a burst signal S, ₂ ^{un (} ^ ^a carrier signal ^S f2 '^ - ^e are gated by a common key pulse P, their energy content is very much reduced, which _{applies in particular to the carrier signal S f2} . The consequence of this is that the level of the chrominance signal is sampled at a value lower than is the correct or inherently present value. as the standard regulations, particularly those of the carrier signal S _f are not especially strict, so

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Allow relatively large deviations, the beginning of the carrier signal S _f fluctuates considerably. For this reason, it is largely impossible or inexpedient to use the key pulse P, which is usually generated in PAL operation, for an advantageous ACC operation.

Secondly, the invention is based on the object of eliminating the influence on the ACC circuit resulting from any Shifts in the starting time of the non-modulated carrier signal S ^ in the SECAM system results.

This two-part technical problem is solved according to the invention according to the teaching of the claims.

With regard to the solution of the first sub-task, it is provided - as illustrated in FIG. 1 - to generate a key signal or a key pulse P derived from the line pulse P, the video signal. With the help of this key pulse P, a burst signal S, .. of the PAL signal or a non-modulated carrier signal S _f in the SECAM signal is gated and the respective level of the signals S _b1 and S _f1 are, for example, via a narrow band filter and an integration circuit detected in order to obtain the control or control signal for the ACC circuit therefrom.

To solve the second sub-task on which the invention is based - as illustrated in FIG. 4 - in the event that the burst signal S is to be obtained / provided, a key pulse or a key signal P ₁ is used, its spacing, width or duration from the trailing edge of the line pulse P. (time t ₃ ) to the end of the horizontal blanking interval (time t ₂ ), while on the other hand, for SECAM operation, _{i.e. when the non-modulated carrier signal S f is to be} gated, a key pulse P ₂ is generated (see. Also Fig. 4), which occurs near the end (time t ₂ ) of the horizontal blanking interval.

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With a circuit according to the invention, the burst signal S can be detected during its entire interval, which is indicated in FIG. 4 by the reference symbol S,. _{} is} shown, while other -Ht * il.s at SIiC ¹ AM-IJcI r i <> b the Trätjcrsiynal S _{f can} be gated correctly, i.e. in a clear energy level (reference symbol S _f3 in Fig. 4), even if the beginning or the start time for the carrier signal S _f fluctuates or even lies outside the prescribed normal range. If the level of the signals S. _ or S ^ -T is now queried, an exact indication of the level of the chrominance carrier signal can be derived from this.

The invention and advantageous details are described below with reference to the drawing in an exemplary embodiment explained in more detail. It showed:

1A, 1B and 2 to 4 already explained time-correlated

Signal curves to illustrate the starting point or the basic principle of the invention;

5 shows the block diagram representation of an example of a circuit part with features according to the invention in Recording system of a color signal tape recorder (VTR device) with two rotating magnetic heads;

6 shows the corresponding circuit in the playback mode;

7 shows the exemplary embodiment for a key pulse generator which is used in the circuits according to FIGS. 5 and 6 with the reference note 17 and

FIG. 8 shows the signal waveforms at various points in FIG Circuit according to FIG. 7.

In Fig. 5, reference 1 denotes an input terminal to which a color television signal according to the SECAM or PAL system to-

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Führbdr is. The input terminal 1 is connected on the one hand to a low-pass filter 3 and on the other hand to a band-pass filter 4. This circuit arrangement divides a F.irbl (* rn.si'h. * - ii <in «il into an I.uininunzsicfn.i 1 Y or oin chrominance carrier signal S. The luminance signal Y is converted into a modulated luminance signal by frequency modulation Y _pM converted, while the chrominance signal S is converted into a signal lying in a lower frequency band with a frequency of about 700 KHz in order to obtain a chrominance signal C _n lying in the lower frequency band. The signals Y_ _M and C_ are mixed and arrive the rotating magnetic heads 2a and 2b to be recorded on a magnetic tape (not shown).

The luminance signal Y separated by means of the low-pass filter 3 arrives at an FM modulator 5, the output signal of which is fed to a high-pass filter 6, at the output of which the modulated luminance signal Y "." On the other hand, the chrominance signal S _n separated by the bandpass filter 4 arrives via an ACC circuit 8 on a frequency converter 9 which is essentially formed by a level control circuit, for example an amplifier with a variable gain. The converter 9 is also acted upon by a carrier signal supplied, for example, by a rigid oscillator 10, so that a chrominance signal C_ in a lower frequency band is produced at the output of the converter 9, which signal reaches a low-pass filter 11. This low-pass filter 11 eliminates all unnecessary or disruptive signal components contained in the output signal of the converter 9. The signal appearing at the output of the low-pass filter 11 also feeds the adder circuit 7 and is mixed _{with the signal Y pM.} The output signal of the adder circuit 7 finally arrives at the rotating magnetic heads 2a and 2b via a recording amplifier 12.

The output signal of the ACC circuit 8 also acts on a

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Gate circuit 13 _f of a key pulse generator 17 supplies a key pulse. This tactile pulse is derived from the line pulse, which is separated by a line pulse separator circuit 18 and fed to the tactile pulse generator 17- In the case of the PAL system, the width of the generated tactile pulse P ... extends from the trailing edge of the line pulse P to the end of the horizontal blanking interval , while when switching to an operation for the SECAM system, the corresponding key pulse P ^{generated only} near the end of the horizontal blanking interval (see. Fig. 4) and the width of the pulse P "is chosen so that it is essentially the width of the Corresponds to burst signal.

An embodiment for the pulse generator 17 is explained below with reference to FIG. 7: With 18a an input terminal is designated, at which the line pulse separating circuit 18 obtained line pulse P. is applied, while 17a denotes an output terminal at which the key pulse can be tapped. The line pulse P, comes from the input terminal 18a on the one hand to a delay circuit 51, which like shown - consists of an inductance and capacitance and, on the other hand, an integration circuit that goes through a resistor 52 and a capacitor 53 are formed. The connection point between the resistor 52 and the capacitor 53 is grounded on the one hand via the collector-emitter path of a transistor 54 and on the other hand is connected to the base of a Transistor 55 connected. The transistor 54 can be switched over via a changeover switch 14 connected to its base in such a way that that in PAL operation of the movable arm 15a of the switch 14 rests against a fixed contact point 15p, whereby the Base of the transistor 54 is supplied from a DC voltage source 16 from a DC voltage, so that the transistor 54 in in this case is conductive. In the case of SECAM operation, on the other hand, this is the case movable arm 15a on the other fixed contact point 15s, whereby the base of the transistor 54 is connected to ground potential

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and this transistor blocks. The output signal of the delay circuit 51 is applied to the emitter of a transistor 56, its base or emitter by means of suitably selected voltage divider and bias resistors with a certain voltage derived from a voltage source + V are applied and its collector via a resistor is connected to the collector of transistor 55. The output terminal 17a is connected to the collector of the transistor 55.

If the line pulse P illustrated in FIG. 8a reaches the input terminal 18a, the output signal illustrated in FIG. 8B appears at the output of the delay circuit 51. If the level of this signal S ₁ exceeds a certain threshold voltage V ..., the transistor 56 becomes conductive, ie it switches through. In PAL operation - as mentioned - the transistor 5 4 is conductive, so that the transistor 55 blocks. Thus, at the collector of the transistor 56, ie at the output terminal 17a, a clock pulse P the base of the transistor 55 a illustrated in Fig. 8D voltage S ₂ occurs, which is produced by integration of the line pulse P i. During the interval in which the level of the voltage S ~ _{exceeds the threshold level V. 2} (which corresponds to the forward voltage of the base-emitter diode of the transistor 55), the transistor 55 is switched on. If the transistor 55 then blocks, the key pulse P ₂ illustrated in FIG. 8E occurs at the output terminal 17a. The pulse width of the probe pulse P ₂ is equal to the pulse width difference between the width of the probe pulse P ₁ and the time interval during which the transistor 55 is switched on. If the values of the elements of the delay circuit 51 and the integration circuit 52, 53 and also the threshold voltages V. ₁ and V ^ _{2 are} suitably selected, the pulse width or duration of the can

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Key pulse P .. can be set so that they are from the Trailing edge of the line pulse P, extends to the end of the horizontal blanking interval (time t "). The pulse width dos T.ihI impiilHPH ρ can be chosen to be about the width corresponds to the GeaamLintervalla of the burst signal.

Back to the circuit diagram of FIG. 5: The output signal of the Gate circuit 13 reaches a narrow band filter 19, the output signal of which feeds a rectifier circuit 20 for the purpose of level sensing. The sampled output signal the rectifier circuit 20 reaches the ACC circuit 8 as a control signal via an amplifier 21.

With the ACC control loop described so far, Fluctuations or shifts in the beginning of the burst signal

S. and especially with SECAM operation of the non-modulated b

Eliminate carrier signal S _f. In this way, the level of the chrominance carrier signal can be correctly detected both in the PAL and in the SECAM system without being influenced by fluctuations in the beginning of the signals S or S _f .

In the signal reproduction circuit according to FIG. 6, the structure of the ACC control loop essentially corresponds to that of Recording system, so that the corresponding parts are identified with the same references and their structure and their functionality does not require any further explanation.

Those caused by the rotating magnetic heads 2a and 2b in the reproducing operation sequentially generated signals reach a high-frequency switch via playback amplifiers 31a or 31b 32, which provides a continuous playback signal. This playback signal is on the one hand a high-pass filter 33 and on the other hand a low-pass filter 34 is supplied. The modulated separated by the high-pass filter 33 Luminance signal Y "arrives at an FM demodulator 35, whose output signal is passed through a low-pass filter 36,

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in order to eliminate unwanted and unnecessary signal components which are contained in the signal demodulated by the FM demodulator 35. On the other hand, it feeds through the low-pass I ι I l er 14 jbijtiLroniiLt! (Jiu omiiiaiizLrüi) "Jt" Hitjnal C the ACC circuit 8 to be brought to a constant level and then arrives at a frequency converter 37 in order to be converted to the original carrier frequency the output of which appears the original chrominance carrier signal S _c . This chrominance carrier signal S_ feeds an adder circuit 39 and is mixed there with the luminance signal Y supplied by the low-pass filter 36. A reproduced color television signal can thus be tapped off at an output terminal 40 of the adder circuit 39.

If signals are to be reproduced in the SECAM system, a movable arm is used in converter 37 for frequency conversion 42a of a changeover switch 41, so that it rests against a stationary contact 42s, so that the converter 37 a carrier signal is supplied from a known AFC circuit 43. On the other hand, to recover the PAL signal is the arm 42a on the other fixed contact 42p of the changeover switch 41, so that a carrier signal from a AFC and APC circuit 44 known in its structure reaches converter 37. One due to possible fluctuations Time base errors that have arisen in the V. -device or synchronization faults are thus eliminated In the playback system described so far, the same ACC control loop is used as in the recording mode .

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Claims (5)

Claims mJ Circuit for monitoring the level of chrominance signals which are contained in at least two different video color image signals which can be optionally fed to the circuit, the first of which is a burst signal in the horizontal blanking interval and the second of which is a non-modulated carrier signal in the horizontal blanking interval comprises, characterized by a circuit part (17) for generating a key signal (P _Λ or P _o .) derived from the line pulse (P.) for the time-different. g1 g2 Gating of the burst signal (S. \) on the one hand or the non-modulated carrier signal (S ^ -.) On the other hand during the duration of the blanking interval following the line pulse (p :) and by a generator part (13, 19, 20, 21) for generating a control signal as a function of the amplitude of the respective gated signal (Sv- or S _f3 ), which acts on the control input of a chrominance signal control circuit (ACC control circuit) (8). 2. Circuit for optional monitoring of the level of at least two different types of chrominance carrier signals, the first of which with two chrominance signals is modulated in push-pull and a burst signal in the horizontal blanking interval of a video image signal while the other with a chrominance signal is frequency-modulated and a non-modulated carrier in the horizontal blanking interval of a video image signal having, the level of the first and second chrominance carrier signals depending on the Amplitude of the burst signal or the non-modulated carrier signal is controllable, characterized 709815/0852 by a circuit part (17) for generating a first key pulse (P) for gating the burst signal (S,.,) when the first type of chrominance signals is applied to the circuit or for generating i'iacMi zwcili'ii T.ujI iinjju 1 ms icjrui 1 a (P. >) by Vcrzttyuruiuj of the first pulse signal for gating the non-modulated carrier signal (S ^.,) when the second type of chrominance signals is applied to the circuit. 3. A circuit according to claim 1 or 2, characterized by a delay circuit (51 optionally in conjunction with 52, 53) contained in the circuit part (17) for delaying the line pulse (Pi.) By a certain period of time and for generating and shaping the key signal for gating of the burst signal or the non-modulated carrier signal. 4. Circuit according to claim 1 or 2, characterized by a delay circuit (51) contained in the circuit part (17) for generation a first keying signal (P) intended for the keying of the burst signal by delaying the Line pulse (P,) and by an optional additional delay circuit (52, 52 in conjunction with 14, 54, 55) for generating a second key signal (P 2) for keying the non-modulated carrier signal near the end of the horizontal blanking interval by delaying the line pulse by a second predetermined period of time. 5. A circuit according to claim 4, characterized in that the supplementary delay circuit an integrating device that can optionally be effectively switched via a changeover switch (14 in conjunction with transistor 54) RC element (52, 53) contains the output of 70981 S / 0852 Threshold switch (transistor 55) is connected to the output (17a) of the circuit text (17). 70981b / 085 2