DE1224771B - Control amplifier for television signals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H04n

German class: 21 al-33/50

Number: 1224771

File number: F 25667 VIII a / 21 al

Filing date: May 2, 1958

Opening day: September 15, 1966

The invention relates to a control amplifier for television signals.

It is already known to change the gain of an electron tube by adjusting the grid bias is brought to different values. Since the grid voltage anode current characteristic in is generally curved and has a lower steepness at higher values of the lattice bias than at low values, the gain depends on the level of the grid bias and decreases with increasing negative bias. However, it is with this type of gain control it is inevitable that the working point on the characteristic curve of the tube will be in areas of strong curvature the characteristic shifted. Non-linear distortions then occur in the signal amplified by the tube on. In order to keep these distortions small, one is forced to choose the signal amplitude small, see above that only a small part of the characteristic curve in the vicinity of the operating point is controlled by the signal will.

The non-linear distortions have a particularly serious effect on a television signal, since they result in a change in the gradation of the brightness values, which is a distortion of the gradation in the reproduced image. It has therefore hitherto been necessary to feed the television signal to a regulated tube with such a small amplitude that the distortions that occur remain within permissible limits. For example, a type EF 43 tube could only _{be controlled with a television signal of 0.2 V ps} at the grid under normal operating conditions, so that the control by changing the grid bias did not cause excessive distortion due to the curvature of the characteristic. In the case of regulated amplifiers for television signals, this required an increased outlay on amplifier stages, since the input voltage of the regulated amplifier, even if it is greater than 0.2 V and, for example, has the standardized value of 1 V _pp , had to be attenuated before and after the regulated stage this had to be increased again to the desired starting value.

To avoid these deficiencies, a control amplifier for television signals has already been proposed, which contains two successive amplifier stages in which the signal with opposite Polarity and approximately the same amplitude occurs and in which the control voltage is caused by capacitors for direct current sealed control electrodes of both amplifier stages via electronic Switch is supplied, which only during the

Control amplifier for television signals

Applicant:
TV G. mb H.,
Darmstadt, Am Alten Bahnhof 6

Named as inventor:
Dr.-Ing. Wolfgang Dillenburger,
Lower Ramstadt near Darmstadt

Times are closed in which the television signal has the reference value.

In a control amplifier constructed according to this proposal with electron tubes, two Triode systems that are combined to form a double triode and have a common cathode resistor have used. The television signal is fed to the grid of the first system via a Coupling capacitor supplied. The grid of the second system is at zero potential via a capacitor placed. The control voltage is fed to the grids of the two tube systems via a clamping circuit each and the output signal is taken from the anode resistor of the second system. the The invention relates to an advantageous development of the proposed control amplifier.

In a control amplifier for television signals with two successive amplifier stages in which the signal with opposite polarity and approximately the same amplitude occurs at which the Control voltage to the control electrodes of both, sealed off by capacitors for direct current Amplifier stages are fed via electronic switches, which are only closed during the times in which the television signal has the reference value are, according to the invention, the control electrodes of the two amplifier stages facing away from the cathodes of the switching diodes, which are negatively directed Control pulses are supplied, and the two likewise to the control electrodes of the amplifier stages remote anodes of the switching diodes, to which positive control pulses are fed, in pairs Conductively connected to one another via one circuit point each, and these circuit points are either via a resistor each or with a simultaneous cross connection via a resistor via a further diode is connected to the control voltage line. In this way you avoid

609 660/275

separated leads and resistors for the second clamping circuit.

The circuit arrangement will now be based on FIGS. 1 and 2 showing the exemplary embodiments are explained in more detail.

Fig. 1 shows a regulated amplifier for television signals with two triode systems, which are combined with advantage to a double triode (z. B. E 88 CC). The grid of the first system 1 is fed via the coupling capacitor 5 (eg 0.25μΡ) ίο the television signal. The two systems 1 and 2 are coupled via the common cathode resistor 3. The regulated signal is picked up at the anode resistor 4 of the second system 2. The grid of the second system is blocked from ground by a capacitor 6 of the same size as the capacitor 5. The control voltage is fed to the grids of the two tube systems 1 and 2 via a clamping circuit each. According to the invention, the cathodes of the diodes 7, 8, to which the control voltage (via terminal 11) is supplied with negative polarity, and the anodes of the diodes 9, 10, to which the control voltage (via terminal 12) is supplied with positive polarity, conductively connected to one another in pairs, and the corresponding circuit points 13, 14 are connected via the resistors 15, 16 to terminal 17, via which the control voltage is fed to '. The clamping circuit is controlled in a known manner by means of anti-phase right-hand sleeves, which - as stated above - are supplied via terminals 11 and 12, respectively.

The clamping circuit shown in Fig. 1 can also be designed in a slightly modified form, as shown in FIG. The control voltage is via terminal 17 and the further diodes 18 and 19 to the circuit point 13 and 14, respectively, between which the resistor 20 is arranged.

Claims (1)

Claim: Control amplifier for television signals with two. successive amplifier stages in which the signal with opposite polarity and approximate same amplitude occurs at which the control voltage is determined by capacitors for Direct current sealed control electrodes of both amplifier stages via electronic switches is supplied, which are only closed during the times when the television signal is the Has reference value, characterized in that the, the control electrodes of the both amplifier stages (1, 2) facing away from Ka ^, methods of the switching diodes (7, 8), which negatively directed control pulses are supplied, and the both of the anodes of the, likewise facing away from the control electrodes of the amplifier stages (1, 2), Switching diodes (9, 10), to which the positively directed .- "-.- control pulses are supplied, in pairs via each a circuit point (13 or 14) are conductively connected to one another and that these Switching points (13 or 14) either via a resistor (15 or 16) or under equal, timely cross connection via a resistor (20) via a further diode (18 or 19) the control voltage line (17) are switched on. Legacy Patents Considered:
German Patent No. 1193 089. 1 sheet of drawings 609 660/275 9.66 © Bundesdruckerei Berlin