DE1591764B2 - OSCILLATOR CIRCUIT WITH A CAPACITIVELY TUNED PARALLEL RESONANCE CIRCUIT - Google Patents

Description

It is also of particular advantage that when using switch diodes for frequency range switching no special direct current path is required for supplying the bias voltage for the switch diodes becomes, as is necessary in the known circuits. In the case of the latter, the Reduction capacity a choke can be connected in parallel. This does not apply to the circuit structure according to the invention.

Further advantageous details of the invention are illustrated below with reference to one in the drawing Embodiment described.

F i g. 1 shows a known circuit of the type described in the opening paragraph and

F i g. 2 the circuit according to the invention.

It is assumed that the circuits are designed for the television frequency ranges Band I and Band III should be.

In Fig. 1, the oscillator parallel _{resonance circuit consists of the inductors L 1} and L ₂ in series with a shortening _{capacitor C 4} in a parallel branch and of the variable capacitor C ₂ and a shortening _{capacitor C 3} in the other parallel branch. The connection point 1 can be connected to ground by a switch 2, as a result of which the inductance L ₂ and the shortening capacitor C ₄ . be bridged. The high point 3 of the parallel resonant circuit is connected to the output _{electrode of an amplifier element 4, and at the same time a feedback capacitor C 1 is} provided between the high point 3 and the input electrode of the amplifier element 4, which is also included in the circular capacitance of the oscillator circuit.

The values of C ₂ and C ₃ are designed in such a way that when switch 2 is closed, a capacity variation of 1.24, ie in band III from 266 to 214 MHz, can be achieved. When switching to band I, ie by opening switch 2, C _{4 is switched on} in the circuit and this lowers the capacitance variation to 1.16 so that the oscillator for band I can be tuned between 101 and 87 MHz. The inductance L ₁ is designed for volume III and L ₁ + L ₂ for volume I in a known manner. As can be easily seen from FIG. 1, in band I operation the resonance resistance of the circuit is suppressed by the capacitor C ₄ , which can also be seen from the following equation:

The in F i g. The circuit according to the invention shown in FIG. 2 differs from that shown in FIG. 1 in that the capacitor C _{3 is} replaced by the capacitor C _{5 and the inductance L 3} connected in series with it and that the capacitor C ₄ is omitted. According to the invention, the shortening capacitor C ₅ is designed so that it generates the required frequency variation in band I. In this frequency range, the inductance L _{3 is} practically ineffective. It consists, for example, of only two turns of a wire. Small changes in the inductance of the coil L ₃ have practically no influence on the oscillator frequency. In band III, on the other hand, the inductance of coil L _{3 is} so high that the resonant circuit capacitance appears to be increased to such an extent that the frequency variation in band III has the required value of 1.24.

The capacitor C ₅ is to be selected so large that it _{corresponds to the value of the capacitors C 3} and C ₄ connected in series in FIG. 1, that is:

^ C ₃ -C ₄

The inductance L ₃ is to be dimensioned so that in band III operation the shortening capacitance _{corresponds to the value of the capacitor C 3} in FIG. 1, ie it must be:

^ 1 2 T Γ

I - CO Jb ₃ C ₅

The invention can be used particularly advantageously in two frequency ranges in which there is a different frequency variation. However, it can also be used for several frequency ranges, the inductances being increased or decreased in a known manner by switching, and additionally the coil L ₃ is dimensioned according to the invention so that it becomes effective or effective in several frequency ranges by connecting or disconnecting inductance parts . becomes ineffective. Although this requires a special switch for the coil L ₃ , this coil still has the advantage of synchronism adjustment in the individual bands, and the choke coils when using switch diodes are _{not required to bypass the capacitor C 4 of} the known circuits.

1 sheet of drawings

Claims (2)

Patent claims: 1. oscillator circuit having a capacitively tunable parallel resonant circuit, in particular for use in tuning blocks for at least two frequency ranges, with a shortening capacitor for varying the capacitance variation of the variable oscillator circuit capacitance and a switch for the incremental change in the Oszillatorkreisinduktivität order frequency range conversion, characterized in that the padding capacitor (R ₅ ) is in series with the adjustable capacitance (C ₂ ) and is designed for the lowest frequency range (e.g. VHF band I) and an inductance (L ₃ ) is connected in series with this, which is practically ineffective in this frequency range , but the shortening capacitor (C ₅ ) in the higher frequency range (e.g. VHF band III) is transformed to a higher capacitance value required for this. 2. Oscillator circuit according to claim 1, characterized in that the variable oscillator circuit capacitance together with variable circuit capacitances, at least one input or band filter circuit can be set and as a changeable one Capacities voltage-dependent capacitors are used, which are adjustable on a common Voltage source. 35 The present invention relates to an oscillator circuit having a capacitively tunable Parallel resonance circuit, especially for use in tuning units for at least two Frequency ranges, with a shortening capacitor to change the capacitance variation of the adjustable oscillator circuit capacitance and with a switch for gradual change of the oscillator circuit inductance for the purpose of frequency range switching. In such a known circuit for long, medium and short wave in radio receivers are four inductors connected in series are provided, one each for medium, short and long wave and when the long waves are received all are switched on, with medium wave the long wave inductance is short-circuited and when receiving short waves, the medium wave inductance is also short-circuited. An inductance serves as a choke for the anode lead to the tube. The three frequency-determining inductors is a variable capacitor connected in series with a fixed capacitor in parallel. Furthermore, the long wave inductance is between and the variable capacitance switched on a shortening capacitor for long wave and a shortening capacitor for short wave, wherein the one for the long wave is short-circuited when receiving the short wave. With such circuits As is well known, the shortening capacitor in the oscillator circuit serves to reduce the capacitance variation of the To expand or reduce the variable capacitor for the individual areas in such a way that despite the necessary other capacitance variation ranges always the same in the individual frequency ranges Variable capacitor can be used. As usually the oscillator rotary capacitor with that If the HF-circles sit on one axis, this cannot be done more easily with a special drive device Way done. Corresponding circuits are also available when using capacitance-varying diodes for tuning purposes required because those of the input and oscillator circuit share a voltage divider can be set. The circuit just mentioned makes it possible to achieve these required variations in capacitance. However, by arranging the shorting capacitor to be short-circuited in series with the inductance for the lower frequency range the resonance resistance of the parallel resonant circuit scaled down. This can have the consequence that the lower tuning frequencies of the lower frequency range expose the oscillator vibrations. The object of the present invention is to be achieved, inter alia, "an oscillator circuit build so that the capacity variation of the oscillator circuit capacity can be switched without that the resonance resistance of the resonant circuit is reduced. Furthermore, to switch from two Frequency ranges only a single switch can be provided. This object is achieved in that the shortening capacitor in series with adjustable capacitance and is designed for the lowest frequency range (e.g. VHF band I) and is in An inductance is connected in series with this, which is practically ineffective in this frequency range, however, the shortening capacitor in the higher frequency range (e.g. VHF band III) on one for this purpose required higher capacitance value transformed. This circuit arrangement according to the invention ensures that when the lower Frequency range, d. i.e., when both frequency-determining inductors are switched on, the circuit acts as if only the changeable capacitor and the shortening capacity are present. To switch on the higher frequency range, only the frequency-determining inductance is required to be short-circuited in the lower frequency range. Since for the higher frequency range the the shortening capacitor in series inductance becomes effective, this has the effect of whether the shortening capacity is increased. This results in the desired increase in the capacity variation of the oscillator circuit. The invention can be used particularly advantageously, for example in the television frequency ranges Band I and Band III, since in these the oscillator frequency variation from Volume I must be changed from 1.16 to 1.24 Volume III. Another advantage of the invention is the fact that the series inductance according to the invention for The shortening capacitor enables synchronization in the higher frequency range. this comes about because there is a slight change in inductance predominantly at the lowest oscillator frequencies the higher frequency range is effective, while at the highest frequencies it is practical there is no influence.