DE1033255B - Circuit arrangement for separating the synchronization signals in television receivers - Google Patents

Description

GERMAN

The invention relates to a circuit arrangement for separating the synchronization signals in television receivers, in which the demodulated signal with positive-going synchronizing pulses is fed to the control grid of a tube for log demodulation.

As is well known, the synchronization signals are often separated in a television receiver by that the demoduKerte video signal with positive direction Synchronizing pulses is fed to the control grid circuit of a tube such that the black level falls outside the pass band of the anode current-grid voltage characteristic of the tube and the vertex of the synchronization pulses is almost cathode potential correspond. As a result, only part of the amplitude of the aforementioned discharge tube is generated the synchronizing pulses passed through.

The anode current-material voltage characteristic of the aforementioned discharge tubes is mainly determined by the screen grid voltage in these connection arrangements. In the case of a very weak video signal, part of the image signal can also fall within the pass band of the sync barrier separation circuit. To avoid this, a lower voltage is often applied to the screen grid of the synchronization separator tube so that the grid voltage range from the cut-off point to the cathode potential is small enough to prevent any part of the image signal from passing through even with the smallest expected video signal. Even in medium or large ^L video signals in which the noise has become proportionally larger, but then an unwanted part of the Synchronized · - separated pulse.

There are already circuit arrangements known in which this disadvantage is reduced in that the DC voltage at the control grid of the synchronizing separator tube, which is designed as a triode, is almost constant proportional to the amplitude changes of the synchronization pulses fed to the control grid changes.

The invention relates to a circuit arrangement for separating the synchronization signals in Television receivers, in which the demodulated signal is taken from the anode circuit of a first screen grid tube and with positively directed synchronizing pulses for log demodulation to the control grid a second lattice tube is fed and the contrast control of the receiver by regulation the screen grid wiring of the first tube takes place.

The circuit arrangement according to the invention is characterized in that the adjustable screen grid voltage of the first tube or one that changes proportionally with this screen grid spacing

Circuit arrangement for disconnection

the synchronization signals

in television receivers

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Netherlands 21 January 1956

Peter Johannes Hubertus Janssen,

Eindhoven (Netherlands),
has been named as the inventor

DC voltage is fed to the screen grid of the second tube.

The invention is based on the knowledge that the separation of the synchronization signals by the contrast control is affected.

An embodiment of the circuit arrangement according to the invention is explained in more detail with reference to the drawing explained.

In FIG. 1, the signal of the demodulator circuit resulting via the intermediate frequency circuit 1 is shown fed from the rectifier 2 and the parallel connection of the capacitor 3 and the resistor 4 exists. In the case of a television signal modulated onto a carrier wave in the negative sense and With the specified polarity of diode 2 there is a demudulated signal across resistor 4, whose synchronization pulses are directed negatively, as shown schematically at 5 eats.

For the sake of clarity, it should be noted that in a television receiver with known means an automatic Fading control is used in such a way that the vertices of the synchronization pulses of the aforementioned Signal 5 can be kept at an almost constant amplitude. The one resulting from the resistor 4 Signal is fed to the control grid circuit of the tube 6, which contains a resistor 7, which is in the cathode line of the tube 6 and above which the required negative grid voltage for the Tube 6 is generated.

809 559/143

There is a resistor in the anode circuit of the tube, from which the signal that is fed to the synchronization separation stage is taken, after which this Signal by means of the series connection of the capacitor 9 and the resistor 10 to the control grid circuit the tube 11 is fed.

The screen grid 12 of the tube 6 is connected to an adjustable tap 13 on the potentiometer 14, which forms a voltage divider with resistors 15 and 16. In the illustrated embodiment the controllable tap 13 is effective in a known manner as a contrast control.

At the control grid of the tube 11 there is now a signal as it is denoted by 17 in FIG. In This figure is also the anode current-grid bias voltage characteristic 18 of the tube 11, which for a certain screen grid voltage is shown. The apex of the sync pulses of the signal at the control grid almost completely match the cathode potential of the tube 11. The base these impulses, the so-called black level, has a more negative potential than the blocking point 19 of the Tube 11.

If the contrast control 13 is changed, the screen grid voltage of the tube 6 changes, as a result, the anode current of this tube and thus the amplitude of that supplied to the tube 11 are also increased Signal 17 changes. If the tube 11 has a fixed screen grid voltage, the blocking point 19 must be so be set so that even with the smallest possible signal 17, the black level is not yet allowed through will. For larger signals 17, the amplitude of the transmitted part is consequently the synchronization pulses are relatively very small, so that the synchronization separation circuit is not very effective is. The invention reduces this disadvantage in that the screen grid voltage of the tube is no longer fixed, but made controllable.

The screen grid 12 of the tube 6 is connected to the screen grid 22 of the tube by means of the resistor 20 11 connected, while the screen grid 22 of the tube 11 by means of the smoothing capacitor 21 with Earth is connected.

If now the amplitude of the signal 17 increases by the DC voltage on the screen grid 12 of the Tube 6 is increased, the DC voltage of the screen grid 22 of the tube 11 is increased, so that this Tube receives an anode current-grid voltage characteristic, as is designated by 23 in FIG. Of the larger amplitude of the synchronizing pulses of the correspondingly enlarged signal 17 is thus again an almost proportional part let through. Conversely, the result is a lower one Screen grid voltage on the tube 6 and thus also on the tube 11 an anode current-grid voltage characteristic curve 24, so that of the correspondingly reduced signal 17 with a smaller amplitude again an almost proportional part is let through.

In the anode circuit of the tube 11 there is a resistor 25 from which the synchronization signal 26 is taken.

Claims (1)

PATENT CLAIM: Circuit arrangement for separating the synchronization signals in television receivers, in which the demodulated signal is taken from the anode circuit of a first screen grid tube and with positively directed synchronizing pulses for log demodulation to the control grid of a second screen grid tube is fed and the contrast control of the receiver by regulation the screen grid voltage of the first tube takes place, characterized in that the adjustable Screen grid voltage of the first tube (6) or one that is proportional to this screen grid voltage changing DC voltage is fed to the screen grid of the second tube (11). Considered publications:
German patent specification No. 715 875. 1 sheet of drawings © 809 559/143 6.58