DE1001342B - Synchronizing circuit, especially for television receivers - Google Patents

Description

The invention relates to a synchronization circuit, in particular for television receivers, in which in a Phase comparison stage with an inherently asymmetrical structure through mutual modulation of the synchronization pulses with the oscillations of a generator to be synchronized, a control voltage for readjustment of the generator to be synchronized is obtained.

If a vibrator is to be synchronized by any other vibration, this is how known, possible through direct or indirect synchronization. With indirect synchronization, the Phase of the oscillation to be synchronized compared with the phase of the synchronizing oscillation. This is done in a phase comparison stage, which practically modulates the synchronizing caused with the oscillation to be synchronized. This comparison becomes a tension ζ. B. a DC voltage, the level of which depends on the mutual phase position of the to be compared Vibration is dependent. This voltage then regulates the generator so that synchronism is created.

The main advantage of indirect synchronization is that glitches or intermittent Failure of the synchronization oscillation or pulses can be bridged better than with direct synchronization. This is especially important with the line synchronization of televisions so that on the screen the smallest possible disturbance impression is created.

To explain the disturbing impression, reference is made to FIG. 1 of the drawing. Let f _{0 be} the setpoint frequency to which the generator is to be synchronized, e.g. B. the line frequency of the television broadcast. With precise synchronization, the generator will therefore always oscillate with the frequency f _0. If for some reason the synchronizing frequency (pulse train) remains out for a certain time, e.g. B. by an interference pulse (secondary interference in the amplitude filter or failure of the synchronization on the transmitter side), the frequency f _{Q of} the oscillator to be synchronized changes by a certain amount A f as a result of the lack of control voltage from the phase comparison circuit. The interference impression is now defined by the amount fodzAf. This interference impression becomes greater, the greater this frequency deviation A f is. The size of Af depends, among other things, mainly on the symmetrical operation of the phase comparison circuit. In this context, symmetry is to be understood as meaning that the oscillator, if it oscillates in a range between / Ί to f ₂ - the so-called capture range - without synchronization, can be drawn back to the setpoint frequency f _{0 when the synchronizing frequency is re-established and that the designation}

f ₀ = JjJph- applies. If now with fF the free frequency

Synchronizing circuit,
especially for television receivers

Applicant:

Blaupunkt-Werke GmbH,
Hildesheim, Hildesheimer Waldstr. 200

Dipl.-Ing. Johannes Backwinkel, Hildesheim,
has been named as the inventor

of the oscillator, ie the frequency with which the oscillator oscillates without synchronization, the interference impression is proportional to f ₀ - fF = Af. So it is the endeavor to reduce the frequency deviation in the event of failure

ao of the synchronization, ie Δ f, to be kept as small as possible. Keeping this frequency deviation amount A f small has hitherto only been possible with known symmetrically operating phase comparison circuits which, however, require a symmetry transformer or a phase rotation stage and are accordingly expensive.

If an asymmetrical phase comparison stage is used, as will be described in more detail later, in which the circuit for the oscillation of the generator to be synchronized becomes asymmetrical when the synchronization pulses fail, the frequency fF and thus the entire capture range f ₁ to f _{% of} the generator to be synchronized can be used Generator can be shifted very far from the setpoint frequency f ₀ , since the asymmetry of the phase comparison circuit in the event of failure of the synchronization creates a constant control voltage that greatly shifts the frequency of the generator to be synchronized. As a result, f ₀ - fF is significantly larger in this case than in the case of a symmetrical construction of the phase comparison stage.

In order to avoid these disadvantageous consequences, the synchronization circuit according to the invention is, in particular for television receivers, in which in a phase comparison stage with an inherently asymmetrical structure from the synchronizing vibrations and the vibrations of a generator to be synchronized a control voltage for readjustment of the generator to be synchronized is obtained, characterized in that that at or in front of the feed point of the symmetrizing oscillation or pulse train a additional oscillation or pulse train that is phase-locked with the oscillation or pulse train to be synchronized is connected, is coupled, which has such a size and shape that when the synchronizing Vibration all through right now

609 767/29 «

the additional control voltages caused by the asymmetrical structure are practically compensated and only a basic preload that is independent of the working state remains.

To explain the mode of operation of the invention, reference is made to the circuit structure in FIG. Here, G ₁ denotes the generator that supplies the synchronizing oscillation. The amplitude filter in a receiver, for example, can be regarded as a generator. R ₈ is the internal resistance of the generator. The capacitors C ₇ , C ₁ and C ₃ are used to isolate the DC voltage. G ₂ is the generator to be synchronized, for example the line oscillator or the line output stage of a television receiver. The phase comparison stage consists of a modulation bridge with the rectifiers GZ ₁ , GL ₂ , their load resistors Ji ₁ and R ₂ and the charging capacitor C ₂ .

The oscillation to be synchronized and the synchronized oscillation are fed in a known manner to this phase comparison stage in such a way that a modulation of both oscillations is produced by separate rectification of the sum or the difference of the two oscillations to be compared. This sum or differential voltages result from rectification in GL ₁ or GL ₂ corresponding direct voltages, through which the capacitor C _{2 is} charged. The difference between these DC voltages is smoothed via the resistors R ₅ , R ₆ and R ₇ and the capacitors C ₄ , C ₅ and C ₆ , these elements simultaneously preventing control oscillations. The adjustable resistor R ₃ allows the basic bias voltage to be set and can represent the line frequency regulator. A ₄ and C ₂ form the pulse sequence supplied by the generator to be synchronized, for example the flyback pulses from the flyback transformer, into a form that is favorable for phase comparison, for example a sawtooth shape. The capacitor C ₂ should be as large as possible so that the pulses from G ₁ arrive _{at GZ 1} in the same size as at GL _2. If the synchronization is now interrupted, ie if the generator G ₁ no longer supplies a voltage or pulse sequence, the sawtooth voltage of the generator G _{2 is} rectified instead of a modulation of the voltages to be compared. Since the internal resistance of the generator G ₁ in this case represents a shunt to the rectifier GL ₂ , a differential voltage between GL ₁ and GL _{2 occurs} in the control line, the / Ί to f ₂ and thus the free frequency fF of the generator G ₂ due to the additional The control voltage shifts so that the capture range f _t to f ₂ and thus fF is shifted by a large amount A f from the setpoint frequency f _0. This means that there is a large amount of interference if the synchronization fails. To avoid this disadvantage, according to the invention, an oscillation or pulse sequence of suitable shape and size is fed to the input of the phase comparison stage _{via capacitor C 8 , which is connected to the comparison sawtooth from generator G 2 in a} phase-locked manner. As a result, an additional constant voltage is generated in the phase comparison stage, which counteracts the constant voltage resulting from the sole rectification of the oscillation of the generator to be synchronized. A phase comparison stage constructed in this way now has all the features of symmetry without the need for a symmetrically operating phase comparison stage. Since the oscillation additionally fed to the input of the phase comparison stage is phase-locked to the oscillation to be synchronized, ie in the exemplary embodiment it is _{taken directly from the generator G 2} , no control voltage is generated by this oscillation in the normal working case, ie when the synchronization pulses are present. If the synchronization pulses fail, however, a constant control voltage arises with the corresponding shape and size of the additionally supplied voltage, which counteracts all the various voltages resulting from the asymmetrical structure and thus the desired one

Shift f ₀ = ■ also in this per se

unbalanced circuit in the absence of synchronization pulses validated. The additional pulse train can, as shown, in the feed point of the symmetrizing oscillation or pulse train be coupled, but it can also be before the feed point of the symmetrizing oscillation in be coupled to the path of this vibration, z. B. in the amplitude sieve, and with this jointly to the Phase comparison stage can be created. However, the coupling of the additional pulse train must not be carried out on one Place where the path can be blocked by a disturbance. You may z. B. not the grid of the first Stage of the amplitude sieve or be fed beforehand. The additional pulse train can be the line oscillator a television set or the line output stage of the receiver. It is also possible that Additional pulse train of one of the existing or a special winding of the flyback output transformer refer to.

As is known per se, the control voltage obtained by the phase comparison stage is used to control the generator to be synchronized, that is to say in the example of the line oscillator of a television receiver. In the example, the control voltage controls the frequency of the generator G ₂ .

Claims (4)

PATENT CLAIMS: 1. Synchronizing circuit, especially for television receivers, in which in a phase comparison stage with an inherently asymmetrical structure from the synchronization pulses and the oscillation of the to synchronizing generator a control voltage for readjustment of the generator to be synchronized is obtained, characterized in that at or before the feed point of the symmetrizing Vibration or pulse train an additional vibration or pulse train that is synchronized with the Vibration or pulse sequence is connected in a phase-locked manner, is coupled in, which is such Size and shape has that when the synchronizing oscillation is suspended at that moment Additional control voltage caused by the asymmetrical structure is practically compensated for and only a basic preload that is independent of the working state remains. 2. Synchronizing circuit according to claim 1, characterized in that the additional oscillation or Pulse sequence is taken from the line oscillator of a television set. 3. Synchronizing circuit according to Ajisetztl, thereby characterized in that the additional oscillation or pulse sequence from the line output stage of a television receiver is removed. 4. Synchronizing circuit according to claim 1, characterized in that the additional oscillation or Pulse sequence of one of the existing or a special winding of the flyback output transformer taken from a television set. 1 sheet of drawings I 609 767/298 1.57