DE2310982A1 - LOW LIGHT TV SYSTEM - Google Patents

Description

Patent attorney Dipl.-Phys Leo Thul 23 10984

Stuttgart

M.M.Ramsay-A.I.McLennan Io - 1

INTERNATIONAL STANDARD ELECTRIC CORPORATION, New York

Low light television system

The invention relates to a low light television system having an image intensifier which is optically connected to the input of a television camera is coupled. In particular, the invention relates to a low light television system in which the operating voltage of the Image intensifier is generated by an oscillator via a rectifier voltage amplifier, and in which the television camera works with positive interlace.

Normally, a continuous feed would be used to feed the image intensifier operated sine wave oscillator can be used, but such an oscillator easily causes interference voltages that superimpose on the output video signal. One possible solution is given by using the oscillator only during the vertical Turn on blanking period; however, in many cases such oscillators have a response time that is in the The order of magnitude of the blanking period. If a vertical blanking pulse turns on the oscillator, this can result its response time feed the image intensifier only for a very small fraction of the vertical blanking period. A new development of oscillators with correspondingly short

February 28, 1973

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M.M. Ramsay -A.I.McLennan Io - 1

Response times would create other difficulties. It is therefore the object of the invention to provide a circuit which enables the video signal to be largely free of interference as well as perfect feeding of the image intensifier. The circuit according to the invention solves the problem in that a timing circuit ZS for generating a trigger pulse Il is connected to the television camera IVR, whose RUokflanke 2o the triggering of the vertical blanking pulse causes, and that the trigger pulse II to a voltage supply circuit SVS is applied, which at the time of arrival of the leading edge 21 of the trigger pulse II a Another pulse 111 of controllable duration is generated, which switches the downstream oscillator OSZ on and off.

The fact that the oscillator is switched on by the trigger pulse before the vertical blanking pulse is present its response time, in which not enough energy can be supplied to the image intensifier tube, also before the vertical Blanking pulse. The full power of the oscillator is then available for the duration of the blanking pulse, which enables optimal feeding of the image intensifier tube. A new development of oscillators with significantly shorter response times and the difficulties involved are avoided.

An embodiment of the circuit arrangement is characterized in that that the timing circuit ZS for generating the trigger pulse II from a crystal oscillator KO and a cascade of monostable frequency divider circuits (1-4), further characterized in that the voltage supply circuit SVS a Schmitt trigger VTl, VT2 to mark the rise

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M.M.Ramsay-A.I.McLennan Io - 1

Plank 21 of the trigger pulse II, and one of the Schmitt trigger VTl, VT2 controlled monostable multivibrator 951 for generating the pulse 111 to feed the oscillator OSZ contains.

The invention will now be explained with reference to figures, numerical data characterizing an exemplary embodiment. Show it:

Fig. 1 is a block diagram of a low light television system according to the invention;

FIG. 2 shows the temporal relationship of the pulses occurring, FIG. 5 shows the timing circuit and

4 shows the circuit of the oscillator, voltage supply and current limitation.

The block circuit according to FIG. 1 shows a television camera TVR with an optically coupled image intensifier BVR. The image intensifier BVR is powered by a rectifier voltage amplifier GBV fed by an oscillator OSZ. The oscillator OSZ in turn is supplied by a voltage supply circuit SVS switched on and off via a current limiter SB.

The television camera TVR is assigned a timing circuit ZS which generates the line frequency in a known manner, according to the Invention, however, additionally generates a trigger pulse II, from which both the vertical blanking pulse 112 is generated, as the oscillator OSZ is also switched on.

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M.M.Ramsay-A.I.McLennan Io - 1

The principle of operation of this circuit can best be seen by looking at FIGS. 1 and 2 at the same time clarify. The pulses II, 111, 112, Uli drawn next to the connecting lines in the block diagram are transmitted by these lines, FIG. 2 showing the temporal relationship of these pulses.

The timing circuit ZS generates the trigger pulse II at the field frequency. This pulse is initially used to generate the vertical blanking pulse I12j. This process is not explained here, but it is important that the falling edge 2o of the trigger pulse II at time T2 marks the beginning of the vertical blanking pulse triggers, which is indicated symbolically by the arrow B in FIG. However, the trigger pulse II is also passed on to the voltage supply circuit SVS. In this circuit, a pulse 111 of controllable duration rf is generated from the trigger pulse II, during which the oscillator OSZ is put into operation. In this process (in contrast to above) the rising edge 21 of the trigger pulse II is used to generate the pulse 111 at time T ₁ (arrow A), that is, the power supply pulse 111 of the oscillator is reduced by a period of </ "= Tp-T ₁ generated earlier than the vertical blanking pulse. This ensures that, taking into account the response time of the oscillator OSZ, its output signal Uli is already stationary when the vertical blanking pulse appears the parameters <i "and £ f , which can be varied in the circuit, are selected accordingly. In the example considered here, CT is approx. 5 msec.

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M.M.Ramsay-A.I.McLennan Io - 1

Fig. 5 shows the timing circuit ZS in its structure. A crystal oscillator KO oscillates at a frequency of 31.25 kHz. These Frequency is halved by circuit 2 and at output 3. the line frequency of 15.625 kHz appears. In addition, the frequency of the crystal oscillator KO is divided by 5 four times by four monostable divider circuits 4, which are arranged as a cascade and at output 5 the 50 Hz trigger pulse II produce. The falling edge 2o is created by the transition of the output-side divider circuit 4 into its quasi-stable State, the rising edge 21 by reversing into the stable state. The generation of the vertical blanking pulse 112 from the falling edge 2o of the trigger pulse II is not shown here.

As already explained above, the trigger pulse II is passed to the voltage supply circuit SVS, in which the pulse 111 is generated. The common circuit of the modules SVS, SB and OSZ is shown in FIG.

The 50 Hz trigger pulse II is at the input 6 and controls a cut trigger VT1 and VT2, which is dimensioned such that it responds at a suitable point on the rising edge 21 of the trigger pulse II; in this case, the transistor VTl conducts and the transistor VT 2 blocks, whereby the collector voltage of the transistor VT2 increases; this turns on transistor VT3, which reaches saturation and turns on a monostable multivibrator 951 by feeding ground potential to its input. The resistor R13 and the capacitor C6 determine the time constant of the multivibrator 91β, which can be selected so that the desired shape of the pulse 111 is produced (FIG. 2). This pulse can in particular be chosen so that it encompasses the entire vertical blanking pulse 112, and under special circumstances,

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M.M.Ramsay-A.I.McLennan Io - 1

especially if the duration of the vertical blanking pulse is too short to provide sufficient BVR for the image intensifier during this time To supply energy, the pulse 111 can only stop a certain time after the vertical blanking pulse 112. The resulting oscillator interference, which is superimposed on the video signal, is limited to the first Lines of the television picture.

In the stable state of the multivibrator 91β + 5V are at the output Q, causing base current to flow to transistors VT5 and VT7 through resistors Rl6 and R17, respectively. These transistors are thus saturated and practically short the input of the oscillator OSZ, while the transistor ντο from the transistor VT5 is blocked. When the multivibrator 916 is in its quasi-stable State passes, the transistors VT5 and VTf are switched off and VT6 switched on, there is no short circuit more voltage is fed in at the oscillator input and via the current limiter SB. The required high starting current is provided by the capacitor C7 and at the output of the oscillator appears the signal Uli (Fig. 2), which over the Rectifier voltage amplifier GSV feeds the image intensifier BVR.

4 claims

3 sheets of drawings with 4 figures

309837/0940

Claims (3)

M.M.Ramsay-A.!. McLennan Io - 1 Patent claims: (T) Circuit arrangement for a low-light television system with a television camera, an image intensifier optically coupled to this and with an oscillator for feeding the image intensifier, characterized in that a timing circuit (ZS) for generating a trigger pulse (II) is connected to the television camera (TVR) whose trailing edge (2o) triggers the vertical blanking pulse (112) and that the trigger pulse (II) is applied to a voltage supply circuit (SVS) which, when the leading edge (21) of the trigger pulse (II) arrives, generates a further pulse (111) generates a controllable period of time that switches the downstream oscillator (OSZ) on and off. 2. Circuit arrangement according to claim 1, characterized in that the tent circuit (ZS) for generating the trigger pulse (II) consists of a crystal oscillator (KO) and a cascade of monostable frequency divider circuits (1-4). 3. Circuit arrangement according to claim 1, characterized in that the voltage supply circuit (SVS) has a Schmitt trigger (VTl, VT2) for marking the rising edge (21) of the trigger pulse (II), and one of the Schmitt trigger (VTl, VT2) controlled monostable multivibrator (951) for generating the pulse (II) to feed the oscillator (OSZ). k. Circuit arrangement according to Claims 1 and 3 *, characterized in that the voltage supply circuit (SVS) contains transistors (VT5 and VT7) which switch off the oscillator (OSZ). By shorting its input. 309837 / 09AO