DE1211292B - Oscillator switchable between two or more frequency values - Google Patents

Description

The oscillator can be switched between two or more frequency values The invention relates to an oscillator that can be switched between two or more frequency values, in which one or more reactances to or from the frequency-determining element of the oscillator with the help of one or more active components to or. switched off will.

In the frequency switchable oscillators are z. B. in telegraphy technology of interest. Here it is very important that the frequencies between which are switched will be adhered to with great accuracy. There are a number of them Circuits in which the required frequency accuracy is achieved. In these known circuits, the reactance to be switched on or off is used usually with the help of a controllable by the touch voltage resistor, z. B. one Transistor, switched on or off. This known method has the disadvantage that a so-called hard keying because of the resulting amplitude jumps can not be carried out and that above all the accuracy of the touch voltage in. Their amplitude must correspond to the required accuracy of the frequency. Through this such circuits are relatively complex.

The invention is based on the object, one between two or more frequency values to create a keyable oscillator that is relatively simple in its structure and in which the accuracy of the probe voltage is not high Requirements must be made.

This problem is solved in that each in series with the Active component lying on or off the reactance as a reactance stage is effective, the one opposite in the reactance to be switched on or off the voltage at the frequency-determining element by 90 ° in phase shifted reactive current generated and that this reactance stage is designed in such a way and the key voltage in such a way is measured that in one final state of the switchover (i.e. with one value of the Sensing voltage), at which the reactive current applied to the reactance generated voltage drop is equal to the voltage at the frequency-determining element, the DC resistance of the active component is largely zero, while in the other end state of the switchover (i.e. with the other value of the touch voltage) the active component is blocked in terms of direct current.

On the basis of the embodiment of FIG. 1 aims at the invention are explained in more detail. With 1 here is the oscillator, which switches in frequency- is to be, and designated with 2 its frequency-determining member. The reactance, which is to be added to or disconnected from this oscillating circuit 2 carries the reference number 3. This connection or disconnection is achieved by the transistor 4, which acts as a reactance stage (by means of phase-reversing capacitor 5). The capacity of the capacitor 6 is very large. It is only used for blocking. Also the inductance 7 is only used to separate direct and alternating current components. About the The touch voltage is applied to terminals 11, 12. The dimensioning of the resistances 8 and 10 is discussed below.

The circuit now works as follows: The state is to be assumed; in which the capacitance 3 does not affect the resonant circuit 2. If the sensing voltage at the terminals 11, 12 increases, the reactance stage 4 impresses a reactive current that is shifted by 90 ° in phase with respect to the resonant circuit voltage and flows through the capacitor 3. The amplitude of this current is proportional to the pulse DC voltage at terminals 11, 12. A growing voltage drop is generated on capacitor 3 by the reactive current that increases with increasing pulse voltage. This voltage drop is in phase with the voltage on the resonant circuit. Finally, a state is reached in which the AC voltage drop across the capacitor 3 is equal to the voltage across the resonant circuit. When this point is reached, the capacitor 3 has a low resistance to alternating voltage (capacity of 6 is large) connected to the base of the resonant circuit, that is to say is firmly coupled to it. The properties of the reactance stage no longer affect the size of the generated frequency. To this state (voltage equality between resonant circuit voltage and voltage drop. - at the capacitor 3) belongs a very specific collector direct current in the reactance stage 4. According to the invention the reactance stage is dimensioned in such a way that with this collector direct current the direct voltage drop between the emitter and the collector of the transistor 4: becomes almost zero, so that only the residual collector resistance RcER appears between these electrodes, which is known to be very, small. To achieve this state, the resistors 10 and 8 are dimensioned accordingly These two resistors are just large enough that the direct voltage between the emitter and collector of the transistor 4 is almost zero. where UB is the direct voltage applied to the transistor and l @ tl is the collector direct current for the one final state in which the frequency f results for the oscillator 1; represents. The current 1, [l includes a steepness of the transistor Sf :, (I cf 1 = cSf 1; c = constant) and thus a collector reactive current I @ f1, which in turn depends on the size of the capacitance C of the capacitor 5 and the resistor 9 resistance value R9) and the alternating current resistance between the base and emitter of the transistor 4 rBE depends.

This current I, fl flows through the capacitor 3 and causes a voltage on the capacitor 3 which, in terms of magnitude and phase, is opposite to the alternating voltage present on the resonant circuit. The relationship results from these conditions: where r is the resistance of the parallel connection of R9 and rBE. .

If the circuit is dimensioned as explained above, a further increase in the tactile voltage cannot change anything in terms of alternating current, since the residual resistance RcER of the transistor 4 no longer decreases with a further increase in the tactile voltage. Thus, one no longer needs great accuracy of the .Amplitude for the probe voltage. You choose that. The amplitude is somewhat larger in advance than necessary and thus ensures that the frequency f :, always remains the same even with fluctuations in the amplitudes. This means that stabilization circuits for the touch voltage can be dispensed with. Since the transistor 4 has no influence on the final frequency, germ frequency changes due to aging etc. can also occur. To resistor 10; which represents a DC negative feedback resistor, it should also be said that it is expediently chosen so large that in the final state the base-emitter DC voltage is small compared to the voltage drop across the resistor 10. This results in an I, linearization of the modulation characteristic between the two end states. This enables soft palpation.

The other end state of the switchover, in which the higher frequency is generated in the given exemplary embodiment, is reached according to the invention when the transistor 4 is blocked in terms of direct current, i.e. when the direct current through the transistor is zero Reactive current zero, and the reactance stage also no longer has any influence on the frequency. In this state the capacitor 3 is switched off and the frequency of the oscillator 1 is determined solely by the oscillating circuit 2. In this final state, too, the accuracy of the amplitude of the direct voltage does not matter, since a further decrease below the value of the pulse direct voltage necessary to achieve this state cannot bring about any change in the magnitude of the direct current through the transistor 4 , since it cannot be less than zero. If one chooses the key DC voltage in advance to be too small for this switching state, it is ensured that the frequency f2 remains constant in this switching state even in the event of fluctuations in the key voltage.

The invention thus created a circuit which ensures exact frequencies in the two final states of the switchover, even if the key voltage amplitude fluctuates. In order to achieve this result, only a small amount of circuitry has to be made in the arrangement according to the invention. Soft keying is possible with the circuit according to the invention. But even with hard keying, there are no amplitude jumps or switching pulses. In FIG. 2 of the drawing, the curves of the collector-emitter direct voltage Ucg (curve 13) of the collector direct current IC (curve 14), the amount of the collector-emitter alternating voltage 1 (UCE) (curve 15) and the frequency f ( Curve 16) as a function of the pulse DC voltage UT.

The invention is of course not limited to switching between two frequencies. You can z. B. also switch between four frequencies if you have at least two circuits, such as the oscillator 1 and the circuit 2 according to F i g. 1 are switched on, provides. Such an arrangement is of interest for duoplex transmission in which the output frequency is reversed between four possible frequencies depending on the characters of two binary-coded signal channels. In the least expensive case, two reactance stages and two to or. disconnectable capacitors and two key voltages are used. In one end state there are both capacitors, in the second and third there is one of the two different capacitors and in the last case there is none. the capacitors are connected to the resonant circuit. The two keying voltage inputs receive keying voltage according to the desired frequency. In this embodiment, the size of the capacitors can be selected in such a way that the three highest frequencies have a slight distance from one another. The lowest frequency has, however, a different frequency difference compared to the next higher frequency. However, the difference is small with a small frequency stroke. However, a correction circuit for adjusting the frequency spacings can be provided, as shown in FIG. 3 shows. The oscillator is denoted by 1 and the resonant circuit is denoted by 2. The two switchable capacitors are labeled 3 and 3 '. 'In blocks 17 and 18 there is a reactance level as shown in FIG. 1 (items 4 to 10) is included. The inputs for the touch voltage are labeled 19 and 20. The correction circuit consists of the resistor 21 and the capacitance 23. At the output of the diodes 22a and 22b, which are connected to the key inputs 19 and 20, a drop in voltage only appears when both inputs have a hyphen. At the interconnection point of the diodes 22 a and 22 b , a voltage only appears when the lowest of the four possible frequencies is to be generated. As a result of this voltage, the capacitance diode 24, which is additionally connected at this point and which is parallel to the resonant circuit, is changed in its capacitance value in such a way that the frequency reaches its correct value (via the capacitor 23). Since the stroke is made small compared to the frequencies for reasons of non-linearity for this application, this capacitance diode only has the purpose of correcting the last few percent detuning on the circuit and therefore only has a very slight influence on the amplitude of the output voltage and when keying on the frequency accuracy.

Claims (3)

Claims: 1. Switchable between two or more frequency values Oscillator in which one or more reactances to or from the frequency-determining Link of the oscillator with the help of one or more active components. are switched off, characterized in that the each in series with the Active component lying or to be switched off reactance as a reactance stage is effective, the one opposite in the reactance to be switched on or off the voltage at the frequency-determining element by 90 ° in phase shifted reactive current generated and that this reactance stage is designed in such a way and the key voltage in such a way is dimensioned that in one final state of the switchover (i.e. with one value of the Sensing voltage), at which the reactive current is applied to the reactance by the impressed reactive current generated voltage drop is equal to the voltage at the frequency-determining element, the DC resistance of the active component is largely zero, while in the other end state of the switchover (i.e. with the other value of the touch voltage) the active component is blocked in terms of direct current. 2. oscillator according to claim 1, which is to be keyed between four frequencies, identified by the Use of two switchable capacitors and two dimensioned according to claim 1 Reactance levels that are controlled in such a way by two key voltages that either none, one or both capacitors for the frequency-determining Link are switched on. 3. oscillator according to claim 2, characterized in that that to achieve exactly the same frequency spacing of all four frequencies one Correction circuit is provided which is only effective when both capacitors are switched on.