DE1464497C - Circuit for electromagnetic line scanning in television technology Ge advises to linearize the current rise in the deflection coils - Google Patents

Description

running pulses obtained a sawtooth voltage and used to compensate for the non-linearities of the deflection current required type of change in the sawtooth voltage amplitude is by means of one of the Michtlinearity of the sawtooth deflection current derived control voltage made. To this end Addressing the disadvantages of the prior art negative feedback circuits uses a very complicated negative feedback circuit in which the deflection current is differentiated and the differentiated current is freed from the impulsive component adhering to it, in order to achieve a To obtain a sawtooth signal that is proportional to the non-linearity of the deflection current. After another Processing in a resonant circuit, this sawtooth signal controls a tube, which in turn is a sawtooth that changes the bias voltage of a linearizing diode. Disadvantage of this known Circuit is particularly the high component cost and the need for more extensive Adjustment work.

The invention is based on the object of providing a circuit of the type specified in the introduction create that .with little circuitry effort and without time-consuming adjustment work the non-linearities of the deflection current in the deflection coils of transistorized television equipment compensated.

This object is achieved according to the invention in that the coupling circuit has a constant gain for the sawtooth voltage resulting from the integration of the line retrace pulses, such that the sawtooth voltage added to the periodically interrupted DC voltage changes to their amplitude only by a constant factor of the amplitude of the respective generating Line retrace pulses are different.

The invention is based on the knowledge that the amplitude of the line return pulses is proportional to the non-linearity of the sawtooth deflection current and that therefore the deflection current curve determining DC voltage to compensate for the non-linearities one of the line return pulses Directly derived sawtooth voltage can be added when in derivation this sawtooth voltage is ensured that its existing non-linearity of the deflection current Amplitude proportionality is maintained.

The circuit according to the invention thus works as follows:

A deflection voltage obtained from the control voltage is applied to the deflection coil. The during The voltage pulse that occurs during the return line is used to generate a linear sawtooth voltage integrated and applied to the deflection coil. There the deflection voltage and the add up linear compensation sawtooth voltage for the corrected deflection voltage in the deflection coil, the one Generates deflection current of excellent linearity.

The particular advantage of the circuit according to the invention is that - starting from the above-mentioned knowledge of the basic relationships - the compensation of the non-linearities of the deflection current only a few additional Requires components and that the balancing of this circuit, i. H. the adjustment to the compensation, is easy to do.

According to a particularly advantageous embodiment of the circuit according to the invention, the Kpn- ^! capacitor of the integration circuit is connected to the controlled switch via a diode and supplies the linear compensation sawtooth voltage to the coupling circuit consisting of a transistor and a transformer, the output circuit. winding of the transformer forms the compensation current source.

ίο Another advantageous embodiment that is particularly suitable for a vidicon tube, is characterized in that between the terminals the operating voltage in series with the coupling circuit containing a transistor ■ operated in a collector circuit, the primary winding of the associated transformer, the primary winding of the deflection transformer and the controlled one consisting of a common emitter transistor .Switches are.

ao In the drawing is the circuit according to the invention illustrated in the form of a circuit diagram in two exemplary selected embodiments .. It shows .

F i g. 1 a greatly simplified circuit diagram for explanation the mode of action of the invention

Circuit,. . ...

^: F ig 2 the circuit diagram of an embodiment of the circuit according to the invention,

F i g. 3 shows a graphical representation of the time-dependent voltage or current curve at various circuit points of the circuit according to FIG . 2,, '

F i g. 4 shows the simplified circuit diagram of a further embodiment of the circuit according to the invention. In Fig. 1 shows a deflection coil 1 which can be electrically divided into an inductance L and a resistor R connected in series with it. If a constant voltage is applied to terminals A and B of the deflection coil Ϊ, the voltage increases. Amperage of the current i flowing through the coil increases exponentially after the switch / is closed. This exponential increase in current is due to the presence of the resistor R. Taking into account the voltage source v, the task of which will be explained later, the differential equation mathematically representing the behavior of the circuit can be written as follows:

"Ld / _ ' _f -

- German ,

If the coil were free of resistance, this equation would be:

German

ι =

namely - 1, is characteristic of a linear deflection

The solution to this differential equation, JE_

T current. ■. ■

Due to the. the resistance R. With the voltage drop Ri , the voltage u at the terminals of the inductance L changes as a function of time, since this voltage drop itself changes as a function of time, since the voltage E is constant.

ι 4 ο 4

According to the invention, an additional voltage source ν is now connected in series with the power supply source E , and measures are taken to ensure that the instantaneous value of the additional voltage ν is equal to the voltage drop occurring in the resistor R at the same instant. Consequently the voltage applied to the terminals of the inductance remains constant, and the current intensity of the current flowing through it changes linearly as a function of time. As a result of this change, the voltage drop occurring at the terminals of the resistor R also changes linearly as a function of time. Accordingly, the additional voltage ν must have a linear change as a function of time. In other words, the corresponding additional voltage source must have a sawtooth voltage deliver a linear course of the sawtooth flanks.

A direct application of the above-described principle of the invention will now be based on an embodiment of a line tilt circle selected for example with reference to FIGS. 2 will be explained in detail. A transistor 7i operated in the emitter circuit is controlled by a train of positive pulses impinging on its base. These positive pulses, the frequency of which corresponds to the line frequency, have. a brief. Duration t of, for example, 20% of the period. During the two successive positive pulses separating time intervals Γ, a negative voltage is applied to the base of this transistor, which is negative enough to bring the transistor T ₁ into the saturation state. In the course of each positive pulse of the duration / the base is held at a positive potential and the transistor T _{1 is} blocked.

The lying at the circuit node A collector of the transistor T ₁ is connected to one terminal of the primary winding of Kipptransformators _Tr1 in series, the other, kept at the potential Vb end by the capacitor C ₃ decoupled from the mass and i via a resistor? _{4 is connected} to a power supply connection terminal with the negative potential - V ₀ . The secondary winding of the transformer Tr ₁ feeds the flyback coil, which is composed of the resistance R and the inductance L. In the shunt of the emitter-collector circuit of the transistor T ₁ are a capacitor C ₁ and a diode d _v ι

Seen from the side of the primary winding of the Kipptrans- \ formators Tr ₁ from whose Übersetzungsverhält- 'is nis assumed to be one, the deflection circuit is composed of a resistor and a lying in series with it inductance L. While \ every time interval T of the pulse during which j of the transistor T is saturated _1, because of the decision j coupling of the transformer in the circuit point C> through the capacitor C _3, a voltage Vb at the \ terminals of this resistance R and the series j inductance L. The current i flowing through this deflection circle therefore increases exponentially. It would increase linearly if the resistance part R were zero. i

When the transistor T ₁ by the positive pulse! the duration t is blocked, the current i in the < inductance L cannot stop immediately [point 1: in diagram (2) of FIG. 3] and charges the capacitor C ₁ . These circuit elements LR-C ₁ form an oscillating circuit that produces a free half-oscillation! carried out (points 1 to 2). The voltage in the circuit node A, which is zero during the saturation of the transistor T ₁ , becomes negative during its blocking (points 3 to 4) and then zero [point 5 in the diagram (3) in FIG. 3]; At this moment the current ί in the inductance L has changed direction because the capacitor C ₁ has discharged to the inductance L. The voltage in the circuit node A then tends to become positive and, when applied in the forward direction of the diode d _x , it is diverted to ground and consequently held at a value of approximately zero. The duration of the negative pulse in circuit node A [points 3, 4 and 5 in diagram (3)], which corresponds to a half period of the free oscillation of the circuit comprising inductance L and capacitor C ₁ [points 1 and 2 in diagram (2) ], is then equal to the duration of the line toggle return.

The breakover circuit just described is a common type of circuit. In order to improve the linearity, according to the invention, a sawtooth voltage is superimposed on the breakover voltage applied to the deflection coils, so that this additional voltage compensates for the voltage drop due to the ohmic internal resistance of these coils. For this purpose, the circuit that can achieve this sawtooth voltage is formed from a diode d _{2 and a capacitor C 2} in series with it, which is connected in series to the terminals of the emitter-collector circuit of the transistor T ₁ . The negative voltage pulse in the circuit node A is used to charge the capacitor ^ Cij via the diode d _{2 with its peak value.} The presence of this capacitor in no way noticeably disturbs the operation of the circuit, but with the proviso that its value is substantially less than that of the capacitor C ₁ . The capacitor C ₂ discharges through the resistor R ₁ to ground. One thus obtains a capacitive generator of a triangular voltage "which has a · exponential time dependence. When the time constant C ₂ S ₁ with respect to the time is the negative control pulses of the transistor T ₁ is very large, occur in the node B linear Sägezahnzeichen on. These characters are to The linearity of the tilting process does not change with the amplitude, since the sawtooth correction voltage is proportional to the tilting amplitude (per change A and 'the voltage at the terminals of A ₁ ). It is therefore important Take measures to ensure that the sawtooth characters of the signal point B are appropriately applied to the coil provided for the horizontal deflection. As already indicated above, this connection! Must be on the input side of the sawtooth characters (circuit; point-B ) have a high impedance and a low impedance on the side of the deflection coil. Accordingly, a collector-operated transistor T ₂ having this dual property is used.

: The linear occurring at node B; The sawtooth mark passes through the capacitor C ₅

on the basis of this operated in collector circuit

Transistor T ₂ , from there to the emitter of this transistor, and is connected via the resonant circuit R _i C _i

j is the primary winding of a step-down transformer Tr ₂

placed. This sawtooth voltage is then applied to the secondary side S of the transformer Tr _s and.

thereby reaches the deflection coils and is thus superimposed on the voltage occurring on the secondary winding of the breakdown transformer Tr _1. This superposition takes place in the sense that the voltage drop Ri due to the resistance R of the deflection coils is compensated.

So that the transformation ratio of the transformer Tr _{2 has} the value η , the voltage at the primary winding of this transformer, which is approximately equal to the voltage at the circuit point B , must have the value η · Ri , where i is the amplitude from peak to peak of the breakover current as this voltage is intended to compensate for the voltage drop across the terminals of resistor R of the deflection coil. On the other hand, the impedance fed back via the correction circuit in series with the breakover circuit is approximately equal to a capacitance value of β-η ² -C ₂ , where β is the current gain factor of transistor T ₂ .

The transformation ratio η of the transformer Tr ₂ is chosen such that η-Ri remains below twice the value of the useful supply voltage of the transistor T _{2 in} order to avoid saturation of the same. This voltage is equal to the usual supply potential V ₀ , reduced by the voltage drop in the resonant circuit Jl ₈ C _{4 of} the emitter electrode of the transistor T ₂ . The mean current in this transistor must be greater than ¹ J ₂ · i / n so that:. , the transistor T _{2 is} never blocked and always the ^1st :

The breakover current fed back into its emitter circuit by the transformer 7V _{2 offers a low impedance.}

The linearity of the sawtooth flanks can be changed or improved according to known methods. In the embodiment of FIG. 2, the sawtooth voltage coming from node B is made linear; For this purpose the resistor R ₁ provided for the discharge of the capacitor C ₂ and the resistor R _{3 of} the base of the transistor T _{2 are} connected via the capacitor C ₈ (or possibly directly) to the high-voltage connection of the primary winding of the transformer Tr ₂ , which is the corresponds to the usual type of circuit. It is possible to obtain sawtooth characters from an additional winding applied to the breakdown transformer Tr _{1 in} order to extract the minimum energy from the breakover voltage.

Another embodiment is possible in the case of using a vidicon picture tube. In this case, the breakover power is low, and the supply voltage V ₀ is usually much greater than the voltage Vb at the terminals of the breakdown transformer Tr ₁ . The circuit is then carried out according to the circuit diagram of FIG. The correction stage is fed by the voltage difference Vo-Vb , whereby any additional power consumption is avoided, since in this special case the transistor is fed in series with the transistor T _1. ^

1 sheet of drawings 309 629/442

Claims (5)

Patent claims: 1. Circuit for electromagnetic line scanning in television equipment to linearize the rise in current in the deflection coils, to which a DC voltage, periodically interrupted by an electronic switch controlled by switching pulses, is coupled in a transformer and in which an integration ίο circuit of high time constant to generate a linear sawtooth voltage the line retrace pulses and a coupling circuit is provided which applies the linear sawtooth voltage in series with the transformer-coupled, periodically interrupted DC charging voltage to the deflection coils in such a way that the former compensates for the ohmic voltage drop occurring when the current increases in the deflection coils, characterized in that the coupling circuit (T ₂ , Tr ₂ ) has a constant gain for the sawtooth voltage resulting from the integration of the line return pulses, such that the. The sawtooth voltage added to periodically interrupted DC voltage differs in its amplitude only by a constant factor from the amplitude of the line retraction pulses which it generates. , Z. circuit according to claim 1, characterized in that the capacitor (C ₂₎ of the ^integration: tion circuit (C _2, R ₁₎ is connected via a diode (J ₂₎ (at A) to the controlled switch (T ₁₎ and the linear compensation ~ sawtooth voltage (at B) reaches the coupling circuit consisting of a transistor (T ₂ ) and a transformer (Tr ₂ ), the output winding (S) of the transformer (7V ₂ ) forming the compensation current source (F i g . 2). 3. A circuit according to claim 1 or 2, characterized in that it contains a known flip-flop circuit in which the secondary winding of the constant voltage (E) delivering deflection transformer (Tr ₁ ) forming a closed loop with the deflection coils (L) and the output winding (S) of the transformer (7V ₂ ) of the coupling circuit is connected in series (FIG. 2). 4. Circuit according to one of claims 1 to 3, characterized in that one by a S-shaped curve representable change in the current as a function of time is achieved by that a voltage of the sawtooth correction voltage that can be represented as a function of time by a parabolic curve is superimposed. 5. Circuit according to one of the preceding claims for use in an image pickup tube, e.g. B. a Vidicon, characterized in that between the terminals of the operating voltage in series the one operated in the collector circuit transistor (T ₂ ) containing coupling circuit, the primary winding of the associated transformer (Tr ₂ ), the primary winding of the deflection transformer (Tr ₁ ) and the controlled , consisting of a transistor ^{/ ri} ji) operated in emitter circuit (Fig. 4). The invention relates to a circuit for electromagnetic line scanning in television technology Devices for linearizing the rise in current in the deflection coils, to which one is connected via an electronic switch controlled by switching pulses, periodically interrupted DC voltage is coupled by a transformer and in which an integration circuit of high time constant for generation a linear sawtooth voltage from the line retrace pulses and a coupling circuit is provided that the linear sawtooth voltage in series with the transformer coupled, periodically interrupted DC charging voltage to the deflection coils in such a way that the former applies the ohmic voltage drop occurring in the deflection coils when the current increases. Deflection coils cannot be made arbitrarily large for reasons of space and weight and because of the electrical energy converted into heat in them. The ratio of the inductance L of these coils to their intrinsic resistance /? is then usually too low for a constant voltage at its terminals to generate a current that increases in a sufficiently linear manner as a function of time. This is particularly true for the deflection coils of vidicon tubes, which are very small in size. It is therefore necessary to carry out the required linearization of the current flow in the deflection coils to produce additional circuits or circuit measures. For example, it is from the German Patent specification 915 944 known to counter-couple the deflection amplifier so that it is connected to the deflection coil supplies a current proportional to its input voltage. Because the negative feedback voltage in the coil circuit is removed, not only the distortion of the amplifier itself, but also the linearity deviations of the current rise in the deflection coil compensated within certain limits. Furthermore, a leakage voltage generator is already known, which is connected to a high-resistance consumer, for example an amplifier with a downstream deflection coil that supplies a sawtooth voltage. Included a transistor with two time constant circuits is provided in the emitter and collector circuit, which exert an opposite effect on the curvature of the sawtooth voltage generated, so that a Linearization is obtained. However, this known circuit is not suitable for low-resistance loads usable. ■ <. A circuit for linearizing the Course of the deflection current of a transformer flip-flop with low resistance, through switching pulses controlled switch proposed in which in the deflection circuit in series with the deflection coils an oscillating circuit of adjustable damping and resonance frequency is inductively coupled and this Resonant circuit energy is supplied from the flip-flop circuit via a phase-rotating coupling. ; In the proposed circuit, the approximately linear deflection current is thus matched by means of the Correction current generated by the dimensioned resonant circuit. This circuit is particular relatively complex in terms of comparison. In contrast, a circuit is introduced in the introduction specified genus from the German Auslegeschrift 1027721 known. There the line returns