DE1591764A1 - Oscillator circuit with a capacitively tunable parallel resonance circuit - Google Patents

Description

Oscillator circuit with a capacitively tunable parallel resonance circuit. The present invention relates to an oscillator circuit with a capacitively tunable parallel resonance circuit, in particular for use in tuning units for at least two frequency ranges, with a shortening capacitor for changing the capacitance variation of the adjustable oscillator circuit capacitance and with a switch for gradually changing the oscillator circuit inductance for the purpose of frequency range switching.

In such a known circuit for long, medium and short wave radio receivers have four inductors connected in series, whereby one is provided for medium, short and long wave and when receiving the Long waves are all switched on, with medium wave the long wave inductance is short-circuited is short-circuited and when receiving short waves, the medium wave inductance is also short-circuited is. An inductance serves as a choke for the anode lead to the tube. The three frequency-determining inductances is a va.rabler capacitor in series connected in parallel with a fixed capacitor. Furthermore, the long wave inductance is between and the variable capacitance is a long wave shortening capacitor and a shortening capacitor switched on for the shortwave, the one for the longwave when receiving the short wave is short-circuited with.

It is known that the shortening capacitor is used in such circuits in the oscillator circuit, the capacitance variation of the variable capacitor for each To expand or reduce areas in such a way that despite the need for others Capacity variation ranges in the individual frequency ranges always the same Variable capacitor can be used. As usually the oscillator rotary capacitor sit on the same axis with that of the HF circuits, this cannot be achieved by a special drive device done in a simple manner. Appropriate Circuits si: dd even when using capacity variation «Uoden for tuning purposes required, since those of the input and oscillator circuit share one Voltage divider can be set.

The circuit just mentioned makes it possible to make this necessary To achieve capacity variations. However, the arrangement of the short-circuited Kurzungskondensa.tors in series with the inductance for the lower frequency range the resonance resistance of the parallel sowing circuit is reduced. This can result have that at the lower tuning frequencies of the lower frequency range the Expose oscillator vibrations.

The aim of the present invention is to achieve the object, among other things be to build an oscillator circuit so that the Kapa.zitätsvariation of Oscillator circuit capacitance can be switched without affecting the resonance resistance of the resonant circuit is reduced. Furthermore, to switch between two frequency ranges only a single switch can be provided.

According to the invention, this object is achieved in that the shortening capacitor in series with the adjustable capacitance and for the lowest frequency range (e.g. VHF Band I), and an inductance connected in series with it is, which is practically ineffective in this frequency range, but the shortening capacitor in the higher frequency range (e.g. VHF Band III) to one required for this higher capacity value transformed.

This circuit arrangement according to the invention ensures that when the lower frequency range is switched on, ie when both frequency-determining inductances are switched on, the circuit acts as if only the variable capacitor and the shortening capacitance were present. To switch on the higher frequency range, only the frequency-determining inductance of the lower frequency range needs to be short-circuited. Since the inductivity connected in series to the shortening capacitor becomes effective for the higher frequency range, this has the effect of increasing the shortening capacitance. This results in the desired increase in the capacity variation of the oscillator circuit. The invention can, for example, be used particularly advantageously in the television frequency ranges band * I and band III, since in these the oscillator frequency variation from band 1 has to be changed from 1t16 to 1.24 band III.

Another advantage of the invention can be seen in the fact that the inventive Series inductance to the shortening capacitor a synchronization in the higher Frequency range possible. This is due to the fact that there is a low Change in inductance mainly at the lowest oscillator frequencies of the higher Frequency range is effective, while at the highest frequencies practically none Influence is present. It is also of particular advantage that when using of switch diodes for frequency range switching for the supply of the bias voltage no special DC path is required for the switch diodes like this is necessary in the known circuits. For the latter, namely, the shortening capacity must a choke can be switched in parallel. This does not apply to the invention Circuit design.

Further advantageous details of the invention are described below using an exemplary embodiment illustrated in the drawing.

Fig. 1 shows a known circuit of the type described at the beginning and Fig. 2 shows the circuit according to the invention.

It is assumed that the circuits for the television frequency ranges Volume I and Volume III should be interpreted.

In Fig. 1 , the oscillator parallel resonance circuit consists of the inductors L 1 'and L 2 in series with a shortening capacitor 0 4- in a Para.llelzweig 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 are bridged. The high point 3 deu 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.

DI. (! Values of (11, and C 7) are 0, o designed so that when switch 2 is closed, a capacity variation of 1.24, ie in band III from 266 to P14 MHz, can be achieved. When switching to band Ig do That is, by opening switch 2, 0 4 is switched into the circuit and this lowers the capacitance variation to 1.16 so that the oscillator can be tuned between 101 and 87 MHz for band I. The inductance L 1 is in a known manner designed for band III and L, + L2 for band 1. As can be easily seen from Fig. 1 , the resonance resistance of the circuit is suppressed by the capacitor 0 4 in band I operation, which can also be seen from the following equation: The circuit according to the invention shown in FIG. 2 differs from that shown in FIG. 1 in that the capacitor 0 3 is replaced by the capacitor 0 5 and the inductance L 3 connected in series with it and that the capacitor 04 is omitted. According to the invention, the shortening capacitor 0 5 is designed so that it generates the required frequency variation in band I. In this frequency range the inductance L i 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 0 5 is to be chosen so large that it corresponds to the value of the capacitors 0 and 0 4 connected in series in Fig. 1 , i.e.: The inductance L 3 is to be dimensioned in such a way that in band III operation the shortening capacitance corresponds to the value of the capacitor 0 3 in FIG. 1 , ie it must be: 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 manner known per se by switching and, in addition, according to the invention, the coil L 3 is dimensioned in such a way that it is effective or disconnected 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 synchronizing the individual bands and the choke coils when using switch diodes are not required to bypass the capacitor 0 4 of the known circuits.

Claims (2)

Patent claim: 1. Oscillator circuit with a capacitively tunable parallel resonance circuit, in particular for use in tuning units for at least two frequency ranges, with a shortening capacitor for changing the capacitance variation of the adjustable oscillator circuit capacitance and with a switch for gradually changing the oscillator circuit inductance for the purpose of switching the frequency range, characterized in that Shortening capacitor (C 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 is, however, the shortening capacitor (0 5) in the higher frequency range (e.g. VEF 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 is adjustable together with variable circuit capacitances at least one input or band filter circuit and voltage-dependent capacitors which are connected to a common adjustable voltage source serve as variable capacitances.