RU2146415C1 - Flip-flop with three stable states and common output - Google Patents

Abstract

FIELD: pulse electronics for automatic control systems. SUBSTANCE: input trigger pulses build up potential across common output whose polarity depends on that of trigger pulse and zero potential set up across input interrupts output pulse and resets flip-flop to initial state with output voltage equal to zero. Flip-flop has two parallel- connected switches whose transistors 1,2 are of different polarity of conductivity and their collectors are combined and form common output with respect to ground point of two series-connected power supplies. Upon termination of trigger pulse action output voltage is saved due to positive feedback circuit connected in parallel with switches. It is set up of two amplifiers whose series-connected transistors 3 and 4 are of different polarity of conductivity and their interconnected emitters are grounded through low-value common resistor. EFFECT: provision for eliminating false information during turn-on period and indicating not only signal but also its polarity. 17 dwg

Description

 The invention relates to techniques for the automatic control of production processes and can be used to create pulsed devices as switching, counting, threshold and memory elements, as well as for storing and processing binary information in digital technology.

 Known trigger systems are electronic devices having two states of stable equilibrium, capable of being in one of them for a long time and alternating them under the influence of external control signals.

 Trigger systems are very diverse, but the differences are associated with the control circuits of the operation of the devices, and the trigger itself, which is the basis of the system, is an ordinary RS trigger with two inputs and two outputs. Its simplest option is a static RS-trigger [1], we will choose as a prototype. It consists of two transistor switches connected in parallel, covered by cross-positive feedback, so that if one transistor is in a conducting state and is saturated, the second transistor must be closed. This state is established under the action of triggering pulses at the input of the trigger: if a triggering pulse acts on one of the inputs, causing a high level voltage to appear on one of the outputs, then this input is called direct, unlike the reverse, a triggering pulse on which causes a high level voltage at the second (inverse) output. The appearance of a high level voltage at one of the outputs is necessarily accompanied by its disappearance at the other and therefore the voltage value at the second output does not carry any new information. Therefore, usually only one output is used, the voltage at which varies depending on which input the triggering pulse appears from from zero to the source voltage.

 At the end of the action of the trigger pulse, the trigger remains in the state that is caused by the trigger pulse. This ability to store received information is called memory. If one state is taken as 1, and the other as 0, then we can assume that the trigger stores information recorded in binary code.

 The presence of two separate inputs and two outputs complicates the electrical circuit of the trigger device and complicates the implementation of electrical connections with other elements of the device as a whole. But the main drawback of such a trigger is that it cannot be in a neutral state. Due to the asymmetry always present in the circuit, the trigger immediately after switching on rolls into one of two stable states and gives a false signal at the output without the action of a triggering pulse. Finally, the inputs and outputs are galvanically coupled to each other and electrical communication between them is possible.

 The purpose of the invention is to create a trigger that has three stable states and is able to alternate these states under the influence of zero voltage, triggering pulses of opposite polarity coming to one input so that zero voltage returns the trigger to its original state with an output voltage equal to zero, and trigger pulses opposite polarity cause the appearance of the same output voltage also opposite polarity.

 A trigger of this type does not give false information when it is turned on, it allows you to remove outdated information, it captures not only the fact that a signal appears at the input, but also its sign, for example, the sign (+) or (-).

 The circuit diagram of the trigger is shown in FIG. 1.

The trigger is formed by two parallel main branches ab and cd, each of which represents a transistor switch and contains a transistor and a collector resistor T ₁ R _k1 and T ₂ R _k2 . The branches are powered by two series-connected voltage sources E having a grounded common point O.

 Transistors of the main branches have different types of conductivity p-n-p and n-p-n. Their collectors are connected and form a common output of the device.

Parallel to the main branches, an additional branch of positive feedback MN is included. It consists of two series-connected amplifiers on transistors T ₃ and T _{4 of} different types of conductivity. Amplifiers emitters are interconnected and grounded through resistance R, the bases are interconnected and the common point of the collectors of transistors of the main branches. The collector loads of the amplifiers are formed by two series-connected resistors R ' ₃ R'' ₃ and R' ₄ R '' ₄ . Their common point is connected to the base of the transistor of the main circuit, which has the opposite type of conductivity with respect to the conductivity of the transistor forming the amplifier.

To describe the operation of the proposed device, we use its simplified scheme (Fig. 2). Unlike the circuit diagram (Fig. 1), it contains only the main branches, which are two parallel transistor switches with transistor collectors T ₁ and T ₂ connected at the point O '. For simplicity, we assume that the characteristics of the transistors T ₁ and T _{2 are} identical and differ only in the directions of current and voltage.

Транзисторные ключи принято рассматривать используя их нагрузочные прямые. Они представляют собой зависимость тока от напряжения при выбранных значениях напряжения источника питания и сопротивления коллекторного резистора [2], изображенную на поле статических характеристик транзистора. На фиг. За показана нагрузочная прямая для транзистора n-p-n, включенного как показано на фиг. 3в.In a symmetric system having R _k1 = R _k2 , at equilibrium I _k1 = I _k2 ; U _к1 = U _к2 and the potential at the point О is equal to zero, and the output voltage

Transistor switches are commonly considered using their load lines. They represent the dependence of current on voltage for selected values of the voltage of the power source and the resistance of the collector resistor [2], shown in the field of static characteristics of the transistor. In FIG. The load line for the npn transistor connected as shown in FIG. 3c.

 The load line of the p-n-p transistor differs only in the direction of currents and voltages. It is shown in FIG.

 For the case under consideration, when the keys are powered from two series-connected voltage sources E with a grounded common point, load lines are obtained by shifting the load lines by the value of E on the voltage axis and the value of E / 2R along the current axis, as shown in FIG. 3c and 3d.

 The load line of the entire device is obtained by combining the load lines of the main branches. The load straight lines of the branches ab and cd coincide and form a single load straight line, shown in figure 4. At each moment, the state of the device corresponds to a point lying on the load line. This point, depending on the voltage at the bases of the transistors, moves in the area between points B and C. For example, point A corresponds to equilibrium, the voltage at point O 'and the current are zero.

At the extreme points B and C, one transistor is in a saturation state, the other in a current cutoff state. For example, at point B, the transistor T ₁ conducts current and is saturated, and T _{2 is} closed. At point C, T ₂ is saturated, and T ₁ is in the cutoff state.

 All points on the load line BC are unstable and if, under the action of a short-term triggering pulse on the basis of one of the transistors, the device is in the state of one of these points, after the termination of the pulse, the state changes.

 To fix the state at points B and C, the positive feedback branch MN is used.

If, for example, under the action of a triggering pulse, the circuit is at point B, where the transistor T ₁ is saturated and the transistor T _{2 is} locked, the voltage at O 'exceeds zero, and at the bases of transistors T ₃ and T _{4 are} connected together, a positive voltage appears. It opens the transistor T ₃ and a current flows through its collector resistor R ₃ = R ' ₃ + R'' ₃ , creating a saturation voltage on R' ₃ based on T ₁ . This voltage exists for as long as you want, because as a result of positive feedback, the transistor T _{3 is} open due to a voltage drop on R _k1 , and the current through the resistor R _{k1 is} provided by a voltage on R ' ₃ .

B состоянии равновесия ток через резистор R не протекает и эмиттеры T₃T₄ имеют потенциал Земли.The transistor T ₂ , like the transistor T ₄ , is in the cut-off state during the operation of the transistors T ₁ and T ₃ . The emitters of transistors T ₃ and T _{4 are} connected to earth through a resistor R, the resistance of which is of the order of hundreds of ohms. It stabilizes the state, making it more stable, and limits the voltage at the bases of T ₃ and T ₄ , which is equal to

In equilibrium, no current flows through resistor R and emitters T ₃ T ₄ have Earth potential.

To transfer the device to the opposite state, to point C, it is necessary to apply a trigger pulse of negative polarity to the input. It locks the transistor T ₃ and simultaneously opens the transistors T ₄ and T ₂ . The process goes in reverse order.

In the state corresponding to point B, the output voltage U _o = U _{OO 'is} positive and its amplitude almost reaches (+ E), for point C this voltage is close to (-E).

Trigger triggering and its overturning can be carried out by supplying triggering pulses to the connected bases of transistors T ₃ and T ₄ or feeding them directly to the bases of transistors T ₁ and T ₂ . The second option performs a separate start, in which there is no connection between the input and output.

When the power is turned on, the voltage at the output of the trigger U _{OO 'is} set to zero and this equilibrium state is stable. It persists until the trigger pulse arrives at point O '. A positive trigger pulse causes a current to appear in the collector circuit of the transistor T ₃ . The flow of this current through the collector resistor R ' ₃ creates a voltage on it, supplied to the base T ₁ and opens it. The resulting current of the transistor T ₁ results in a voltage drop across R _k1 . This voltage is U _{OO '} and is the output.

A negative trigger pulse causes an output voltage of the opposite sign. If the point O 'is grounded when there is an output voltage, the current in the transistors T ₃ and T _{4 will} stop, the transistors T ₁ and T ₂ will also become non-conductive and the circuit will return to its original state.

 The trigger can also be used in devices of the ternary number system, but the common point of sources O must be isolated from the Earth of the entire device as a whole.

Sources of information
1. Zeldin B.A. Triggers - M.: Energoatomizdat, 1983, p. 6, Fig. 2a.

 2. Stepanenko I.P. Fundamentals of the theory of transistors and transistor circuits. - M.: Energy, 1977, p. 460.

Claims (1)

 A trigger with three stable states and a common output, formed by two parallel main branches, each of which is a transistor switch and contains a transistor with a collector resistor, powered by two series-connected voltage sources, the common point of which is grounded, characterized in that the main branches are used transistors with different types of conductivity, the collectors of which are connected and form a common trigger output with respect to the ground, a branch of n is connected in parallel with the main branches positive feedback, which is two series-connected amplifiers on transistors of different types of conductivity, the emitters of which are interconnected and grounded through a resistor, the bases are interconnected with a common point of the collectors of transistors of the main branches, their collector loads are formed by two series-connected resistors each, and the common the point of the resistors is connected to the base of the transistor of the main branches, which has the opposite type of conductivity compared to the conductivity of the trans Stora amplifier.

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