DE1930929C3 - Transistor oscillator - Google Patents

Description

The invention relates to a transistor oscillator for the field of higher frequencies, in particular including the transition frequency of the transistor at which the input resistance of the The transistor has a low-resistance, complex value in a manner known per se and in which the frequency-concerned resonant circuit is located between the collector and base electrode and also the feedback takes place via r! ', c emitter electrode.

For feedback circuits with transistors In contrast to tube circuits, they occur even at relatively low frequencies, complex sizes between the individual electrodes. This leads to that, especially over larger ones Tuning ranges a perfect function of the oscillators is not guaranteed. It became this already proposed, together with the tuning of the frequency-determining circuit, the feedback conditions to change. The above proposal is based on a circuit in which the frequency-determining, preferably as a series resonant circuit trained resonant circuit, located between the collector and the base electrode and where between The emitter and collector have a capacitance used for feedback purposes.

The invention is based on the object for an oscillator in three-point connection one dimensioning specify in which the oscillator in all cases beyond the cutoff frequency of the transistor shows optimal vibration properties.

This task is in a transistor oscillator for the range of higher frequencies, in particular including the transition frequency of the transistor at which the input resistance of the transistor in on

ίο known way a low-resistance complex Has value and in which the frequency-determining resonant circuit between collector and base electrode and furthermore the feedback takes place via the emitter electrode, according to the invention thereby üelöst that the load impedance between the emitter and collector is dimensioned such that the current in the output circuit of the oscillator, u! m; between collector and emitter, the same phase position like the current in the input circuit of the oscillator; -,

so between emitter and base, assumes.

When tuning the oscillator in a very large frequency range, it is advantageous if the Elements of the load circuit, in adaptation to the alteration of the input impedance /, of the transistor, with the Frequency changed ·> earth.

The ratio of the effective resistances is advantageous for the optimum efficiency of the oscillator circuit in the load circuit and in the input circuit of the oscillator roughly equal to the gain of the scarf dimensioned.

Should the oscillator over a larger frequency range without simultaneous change of the elements of the load circuit, it is advantageous to adjust the dimensioning of the load impedance / for the highest frequencies of the range optima! hold true.

Due to the compensation proposed according to the invention it is achieved that the oscillator in each case an exact setting with regard to the feedback conditions has, so that by appropriate choice of the load and this lying in series or parallel between the emitter and collector Compensation reactance, especially if this occurs simultaneously with voting on a very large frequency range are changed, the vibration conditions are always met.

The invention is explained in more detail below with reference to figures.

1 shows a conventional oscillator in three-point circuit, in which the switching elements for the power supply, which are not absolutely necessary for the high-frequency consideration, have been omitted. The oscillating circuit that determines the frequency lies between the collector and the base electrode and is designed as a parallel resonance circuit consisting of the inductance L and the variable capacitance C ₁ . The feedback takes place via the emitter electrode, which for this purpose is connected to a voltage partial point between the capacitances C ₂ and C 1, which are in series parallel to the resonant circuit. The choke Dr should, as usual, be dimensioned so that it has a high resistance to the high-frequency currents. This circuit is always correct with regard to the feedback phase when the input resistance of the oscillator circuit connected _{to C 3 is large compared to the reactance of C 3} .

In general, this condition applies to transistor

I 930

ren not fulfilled, especially not if these are operated up to the transit frequency or beyond. Most transistors have low-value complex input resistances, the reactive and real values of which are only a few ohms. An example of this is shown in FIG. 2, where the resistance values are plotted on the ordinate and the associated frequencies on the abscissa. In this figure, the curve /., The imaginary part and the curve R ₁ the real part of the input impedance appearing as a series circuit of the transistor. It turns out that the transistor, which is unsuccessful here, has a capacitive input resistance at frequencies below about 300 MHz. while he has about bci of the mentioned frequency, uncn purely ohmic bin, anus resistance. At even higher frequencies, the input resistance becomes inductive.

In Fig. 3, such a complex input resistance is shown, consisting of the parallel connection of C, and the effective opposing country R ₁ ,,. ao This parallel connection is the connection for the series input impedance shown in FIG. In order to achieve phase-pure feedback, according to the invention, a resistor R _n is connected in parallel with the capacitance C such that the current in the parallel circuit of C ₂ and A _1,. is in phase with the? on L flowing in the parallel connection. The power loss at R _1n . represents the input power of the oscillator circuit, while the power at R _{1 is} the useful power that is extracted. The ratio of Λ ,,. zu /? ", in order to achieve Sn optimized efficiency, must be dimensioned to be equal to the gain factor of the transistor in the relevant frequency range.

In FIG. 4, the transistor oscillator is shown with general designations for the relevant impedances. The input conductance of an oscillator circuit consists of a real component R _be (of the order of a few ohms) and a reactive component Λ ,,,. _{Between- +} "see the emitter and collector electrode there is the real resistance R _n , to which the reactance X" par-

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1 sheet of drawings

Claims (4)

Patent claims: 1. Transistor oscillator for the field of higher frequencies, especially including the Transit frequency of the transistor at which the input resistance of the transistor is known per se Way has a low-resistance complex value and where the frequency-determining value The resonant circuit is located between the collector and the base electrode and also the feedback via the Emitter electrode takes place, characterized in that that the load impedance between the emitter and collector is dimensioned in such a way is that the current in the output circuit of the oscillator, i.e. between collector and emitter, the same phase position as the current in the input circuit of the oscillator, i.e. between the emitter and base, assumes. 2. transistor oscillator according to claim 1, characterized in that when tuning of the oscillator in a larger frequency range the elements of the load circuit with the frequency can be changed according to the change in the input impedance of the transistor. 3. transistor oscillator according to claim 1 or 2, characterized in that the ratio of Resistances in the load circuit and in the input circuit of the oscillator roughly equal to the gain the circuit dimensioned i ^ t. 4. transistor oscillator according to one of claims 1 and 3, characterized gckv wzc'ichr.ct, dafi when tuning the oscillator over a larger frequency range there is no simultaneous change of the elements in the load circuit the dimensioning of the load impedance for the highest Frequencies of the range is taken optimally.