DE1094818B - Transistor oscillator - Google Patents

Description

GERMAN

The invention relates to transistor oscillators and circuits having such oscillators, that respond to capacity changes.

Tube vibrators are known which have a bridge-connected resonant circuit, £ which consists of two capacitive and one inductive element in a closed current loop are connected in series, the common connection point of the capacitive elements and a tap on the inductive element, the ία output terminals of the bridge, and a tube is provided whose input circuit is between the output terminals of the bridge and whose Output circuit is connected to an element of the bridge so that when the bridge is off the equilibrium point is out of tune in one direction, vibrations are caused and, if the bridge is out of tune from the equilibrium point to the other side, no oscillations in Appearance.

Such a vibrator reaches the vibration threshold point, i. H. the state at which the vibrations are just starting when the positive feedback is on the input circuit the tube on a parallel path through the bridge between the output terminals of the bridge, the negative feedback on the input circuit of the tube on the other parallel path exceeds the bridge between the output terminals by a sufficient margin.

Vibrators of this type are used for the purpose of indicating when something is changing Element of the bridge has reached a predetermined size value, the oscillation generator being connected to the transistor oscillator

Applicant:

Fielden Electronics Limited,

Wythenshawe, Manchester, Lancashire

(Great Britain)

Representative: Dipl.-Ing. B. Weir,

Dipl.-Ing. H. Seiler, Berlin-Grunewald, Lynarstr. 1,

Dipl.-Ing. H. Stehmann and Dipl.-Ing. B. Judge,

Nuremberg 2, patent attorneys

Beanspiructite priority:
Great Britain 5 December 1957

Henryk Banasiewicz,
Wythenshawe, Manchester, Lancashire

(Great Britain),
has been named as the inventor

and the bridge grows, the oscillation threshold point comes into a more precise dependence on the size values of the elements of the bridge. The attenuation reduction However, this combination is due to the internal impedance of the bridge between their

is arranged so that it limits the oscillation threshold point measured 35 output terminals, whereby these

is sufficient if the variable element attains said predetermined size value.

It is now known that the electron tube with the known vibration impedance set forth above corresponds to the internal impedance of a generator, which is the input circuit of the transistor Excitation current supplies. The object of the invention is accordingly achieved by reducing the effect

generator can be replaced by a transistor. 40 of the internal impedance of the bridge is reached. If so, it has been found, however, that the starting point of the invention is in the present

Cases

Vibration threshold not only from the size value of the elements of the bridge, but also from the Temperature of the transistor and the potentials acting on the transistor electrodes is.

The object of the invention is hereinafter to provide a vibrator which uses a transistor as has amplifying element in which the entry em transistor oscillator, which is a bridge-connected Has resonant circuit, which consists of two capacitive and one inductive element, the are connected in series in a closed loop, with the common connection point being the capacitive elements and a tap on the inductive element, the connection terminals of the bridge form and a transistor is provided whose input

of the oscillation threshold point in an absolutely precise 50 output circuit between the output terminals of the

Relationship to the size values of the elements of the bridge.

It can now be shown that, as well as the attenuation reduction of the combination of the transistor Bridge is and its output circuit is connected to an element of the bridge, so that if the bridge is out of tune in one direction from the point of equilibrium, vibrations

009 678/380

be called and when the bridge is from the equilibrium point is out of tune to the other side, no vibrations appear. That The feature of the invention consists in the transistor of the aforementioned type in an additional inductive Element that connects via the output terminals of the bridge to the input circuit only of the transistor is connected, the reactance of the inductive element being essentially equal to the capacitive resistance of the bridge, measured at the output terminals.

In order to properly understand the invention, it is noted that it is in the field of tube vibrators is not applicable. There are two reasons for this. First, the oscillation threshold of a tube oscillator not affected by the ambient temperature and, secondly, could be reduced by reducing it the effect of the internal impedance of the bridge does not significantly reduce the damping of a tube vibrator caused because the input impedance of a tube is very high. In contrast the usefulness of the invention in the field of transistor oscillators is based on the fact that the impedance of the input circuit of a transistor is low.

In the following two embodiments according to the invention with reference to the drawing for example shown. In the drawing represents

1 shows a transistor oscillator,

FIG. 2 shows a capacitively excitable circuit using the transistor oscillator shown in FIG represent.

In the figures, switching elements that correspond to one another are indicated by the same reference symbols.

The arrangement of the transistor oscillator shown in Fig. 1 consists of a transistor 1 of the pnp type and an oscillating circuit, consisting of a tapped in the middle coil 2 with a value of L Henry and two capacitors 3 and 4, each having a value owned by C Farad. The coil is constructed in such a way that the coupling factor between the two parts arranged on either side of the tapping point is practically the same. The mean potential of the base electrode 5 of the transistor 1 is kept at a suitable value in a known manner by connecting this electrode to the common connection between two resistors 6 and 7, which together represent a voltage divider, which in turn is between the negative pole 8 of a current source and the tapping point 9 of the coil 2 is arranged. One end of the coil 2 is connected to the positive pole 10 of the power source. The collector electrode 11 of the transistor 1 is connected to the negative pole 8 of the current source and the emitter electrode 12 is connected to the tapping point 9 via the resistor 13, which is bridged by the capacitor 14. The capacitor 14 means that the emitter electrode 12 is connected directly to the tapping point 9 with regard to the oscillating current. A capacitor 24, which is arranged between the poles 8 and 10 of the current source, requires that the collector electrode is connected directly to the end 23 of the coil 2, which is connected to the positive pole 10, with respect to the oscillating current. The resistor 13, together with the resistors 6 and 7, stabilizes the DC working position of the transistor in a known manner.

A coil 15 is between the common connection of the capacitors 3 and 4 and the base electrode 5 arranged.

During operation, any change in the flowing in the collector-emitter circuit of the transistor 1 becomes A change in the current flowing between the point 23 and the tapping point 9 of the coil 2 Result in electricity. Because the coupling factor between the two halves of the coil 2 is practical equals 1, induces this change in the flow of current between point 23 and the tapping point 9 in the two halves of the coil 2 an equal voltage. These voltages have the same phases with respect to the point 23 of the coil 2. These voltages are with respect to the tapping point 9 but in opposite phase. Since capacitors 3 and 4 are the same, the currents are the two parallel circles in the bridge branch between the tap point 9 and the connection of the capacitors 3 and 4 the same, but in opposite phase. The current of one circuit is in phase to provide positive feedback result, and the current of the other circuit is in phase to provide negative feedback to the To give the base electrode of the transistor. The oscillation starts as soon as the ratio of the capacitors 3 and 4 is changed enough and in a suitable direction starting from the value 1, so as to be positive Making the feedback bigger than the negative feedback. This amount by which the positive Feedback is greater than the negative feedback, must just be enough for the Circle has reached the threshold value for the use of vibrations.

It can be shown that when the attenuation reduction of the combination of the transistor 1 and the bridge 2, 3, 4 increases, the oscillation threshold in a more precise relation to the ratio the capacitance of the capacitors 3 and 4 occurs. The attenuation reduction of the combination becomes by reducing the effect of the internal reactance of the bridge, and this reduction reached by means of the coil 15.

Since the capacitors 3 and 4 are connected in series in the resonant circuit, they have the same effect in this circuit as a single capacitor of ¹ Zs C Farad. Furthermore, their combined reactance at the oscillation frequency is equal in size to that of L Henry's coil 2. The internal impedance of the bridge, measured between its output terminals, ie between the point where the capacitors 3 and 4 are connected to one another and the tap point 9, however, is 2 C Farads.

It follows from this that in order to switch off this damping at the oscillation frequency, the coil 15 must have a value of ¹ A L Henry. In practical implementation, the optimum value is somewhat above this stated, namely about 10 to 20% higher due to the fact that there is, among other things, a capacitance through the base-emitter connection.

The inclusion of the coil 15 has a further advantage in that it eliminates the effect of fluctuating the capacitance of the base-collector junction which results from a voltage fluctuation at the ends of this connection. As indicated above, due to the presence of capacitor 24, it is the collector electrode 11 is connected to point 23 of coil 2 with respect to the oscillation current. This results in that the base-collector connection for the alternating current between the base electrode 5 and the Point 23 is connected. Together with the coil 15, the base-collector connection is thus related

of the oscillating current connected in parallel with the capacitor 4. The oscillation voltage is generated by the coil 15 at the ends of the base-collector capacitance, however, with respect to the voltage between the capacitor 4 and the base-emitter connection decreased.

If the coil 2 were tapped at a point other than the center point, the capacitors would be 3 and 4 would be different and the value of coil 15 would have to be changed accordingly.

If the coupling factor between the two parts of the tapped coil deviates significantly from the value 1, the coil 15 would have to be modified in order to correct the dispersion of the coil 2. ¹ p

FIG. 2 shows a capacitively excitable circuit which contains the oscillator according to FIG. 1. at of this device is an electrode or probe 17 with the common connection between the capacitors 3 and 4 are connected so that it has the same effect in the circuit as an equivalent Capacitor 4 'connected in parallel with capacitor 4. A small trimmer capacitor 3 'is the capacitor 3 connected in parallel.

The coil 2 is inductively coupled to the coil 18, which is between the base and emitter electrodes of a second transistor 19 is connected. The collector electrode of this transistor is with the negative Pole 8 connected via a resistor 20 and a display or control device 21. If so the oscillating circuit oscillates, the oscillating current flowing in the coil 2 induces a corresponding one Current in coil 18, which is rectified and amplified by transistor 19. Thus flows in Direct current through the display or control device 21, the size of which depends on the oscillation amplitude in the oscillating circuit.

The arrangement shown in FIG. 2 can be used as a capacitively excitable self-capacitance switch will. The state of oscillation or the state of rest depends on the distance of an object from the electrode 17. A change in this distance changes the size of the capacitance value of the capacitor 4 '. The resulting Change in the oscillation amplitude in the resonant circuit causes a corresponding change in the through the display or control device 21 flowing direct current. The trimmer capacitor 3 ' is used to set the display or control device to the value 0.

In a modification of the arrangement shown in FIG. 2, relatively large capacitors can be used in series are switched with the coil 15 in order to transfer the DC potential of the base electrode 5 from the electrode 17 to remove.

In the arrangement described above, the transistor can also be switched so that its Base electrode 5 via the coil 15 with the tapping point 9 of the coil 2 and the emitter electrode 12 with respect to of the oscillating current with the common connection of the two capacitor branches 3, 3 'and 4, 4' of the resonant circuit is interconnected. In this case, however, appropriate measures must be taken for connection of the positive pole 10 of the power source can be provided with the common connection.

In the arrangements described above, the transistor is connected so that its emitter electrode is common to both the input and output circuits of the transistor. In modification the transistor can be connected in such a way that its base or collector electrode corresponds to this is common to both circuits, the circuit being adapted accordingly and the coil 15 is connected in series with the input circuit of the transistor, so that it can only benefit from the excitation current that flows between the output terminals of the bridge.

In the arrangement described above, the polarity direction of the power source is the same as that used adapted p-n-p transistor. For a transistor of the n-p-n type, the polarity of the current source must be reversed will.

When the attenuation of the current source connected to poles 8 and 10 at the oscillation frequency is sufficiently low, the capacitor 24 can be omitted.

Claims (5)

Patent claims: 1. Transistor oscillator, which has a bridge-connected resonant circuit, which consists of two capacitive and one inductive element, which are connected in series in a closed loop, the common connection point of the capacitive elements and a tap on the inductive element forming the connecting terminals of the bridge and a transistor is provided whose input circuit is between the output terminals of the bridge and whose output circuit is connected to an element of the bridge, so that when the bridge is detuned from the point of equilibrium in one direction, oscillations are produced and when the bridge from the point of equilibrium out of tune in the other direction, no oscillations appear, characterized by an additional inductive element, which is connected to the input circuit of the transistor only via the output terminals of the bridge, the reactance of the inductive element it is essentially equal to the capacitive reactance of the bridge measured at the output terminals. 2. transistor oscillator according to claim 1, characterized in that the tapping of the Resonant circuit coil is in the middle and the inductance of the additional coil is about a quarter the inductance of the resonant circuit coil. 3. transistor oscillator according to claim 1, characterized in that in the bridge branch The base-emitter path of the transistor is switched on. 4. transistor oscillator according to claims 1 to 3, characterized by its use in Connection to a downstream rectifier arrangement, its input circuit with is coupled to the resonant circuit of the transistor oscillator and to the output circuit of the rectifier arrangement a current is taken which depends on the amplitude of the oscillation in the said resonant circuit. 5. transistor oscillator according to claims 1 to 4, characterized in that its oscillation state is controlled by the existing to earth capacitance of a probe connected to the common connection of the capacitive elements of the resonant circuits is connected. 1 sheet of drawings © 009 678/380 12.60