DE2440149A1 - VIBRANT CIRCLE - Google Patents

Description

173 vol. Haussmann
Paris, France

Our sign; T 1637

Swing circle s

The invention relates to a resonant circuit with an induction coil, with a first variable capacitance, which is formed from capacitance diodes (varactors), and with a Biasing device for the capacitance diodes, which enables a change in capacitance to be achieved by changing the Allows preload.

Devices are already known in which the capacity change range is increased by successively a plurality of variable capacitance diodes formed Capacities can be connected in parallel. However, such a device, which is described in US Pat. No. 3,492,514, has the disadvantage that one or more varactor diodes are used in it, which in a large part of the Work with maximum capacity in the voltage change range; an additional change in voltage is therefore not possible

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achieving an additional change in the capacitance of the corresponding capacitance diodes. In addition, the Characteristic curve that indicates the capacity as a function of the bias / irregularities on which the Complicate calibration of such a capacity.

The invention aims to eliminate these disadvantages.

The problem solved to this end results in a device in which each varactor diode is in one area is used in which its capacitance remains sensitive to voltage changes.

According to the invention, in addition to the first variable capacitance, which changes from C to 2C when the bias voltage changes from V to V .., η (η integer, positive), the resonant circuit contains further variable capacitances, each of which is formed from capacitance diodes, which receive the same bias voltage as the varactor diodes of the first variable capacitance, the i-th (i = 1 ... n) further variable capacitance changing from 2 * C to 2 ¹ C when the bias voltage changes from V to V ₁ , and wherein a switching device makes it possible to successively and cumulatively connect the 1st, 2nd ... nth further variable capacitance to the first variable capacitance.

Further features and advantages of the invention emerge from the following description of exemplary embodiments Invention. In the drawings show:

Fig. 1 shows the basic circuit of the use of capacitance diodes for tuning a circuit, and

Fig. 2 shows an embodiment of an oscillating circuit of the invention, which is tunable in a wide frequency band.

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1 shows an oscillating circuit which consists of an induction coil L, to the terminals of which two capacitance diodes V ₁ and V ₂ connected to one another by their anodes are connected with their cathodes.

A bias voltage V, which is supplied by a variable voltage source S, is applied to the anode of these two capacitance diodes via a decoupling circuit, which consists of a resistor R ₁ in series with an induction coil L ₁ , which is connected to the positive terminal of the bias voltage source, and consists of a decoupling capacitance C. which is connected between the positive terminal and the circuit ground. The negative terminal of the bias source is also connected to circuit ground. The decoupling circuit has an impedance which is greater than 200 kilohms in the frequency band used.

When the bias voltage V changes from 30 V to 5 V, the capacitance of the varactor diodes V- and V- changes from 2C on 4C. The capacitance of the resonant circuit consequently changes from C to 2C (C is the minimum capacitance of the resonant circuit, which is taken as a reference value).

The frequency band in which the resonant circuit can be tuned is

= 1.41

where F and F- are the maximum and minimum frequencies, respectively

for which the resonant circuit can be tuned. An RF input voltage E is applied between the circuit ground and a tap on the induction coil L. The service voltage V is available at the terminals of the induction coil L.

The device according to the invention is shown in FIG.

The input voltage E is through a tap on the induction coil L applied, at the terminals of which two capacitance

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diodes V ₁ and V _{2 are connected} as in the device described with reference to Fig. 1, with the same bias circuit and the same characteristics. In addition, two further capacitance diodes V ₃ and V ₄ with the same characteristics as the capacitance diodes V and V _{3 are connected} to the terminals of the induction coil L and _{biased by means of a decoupling circuit R 3} , L ₂ , C ₂ , which is connected to the decoupling circuit of the capacitance diodes V .. and V ₂ is identical, but the capacitance diode V ₄ is connected to one terminal of the induction coil L by means of a switch K ₁ , while the capacitance diode V_ is directly connected to the other terminal of the induction coil L. Therefore the varactor diodes are V-. and V. always biased, but can _{be connected in parallel to the varactor diodes V 1} and V_ only if the capacitance of the varactor diodes V ₁ and V _? is no longer sufficient.

Additional capacitance diodes can be connected in parallel to the induction coil L in the same way as the capacitance diodes V_ and V. However, they have values which are so different that the continuity of the change in capacitance is ensured. Therefore, two varactor diodes V ₁ . and V, may be provided with a capacitance 4C at 30 volts or with a capacitance 8C at 5 volts, which is generated by the decoupling circuit R ^, L_, C_ in the same way as the two groups of capacitance diodes V ₁ - V ₂ , V - V _{4 are biased, the capacitance diode V 1 being} connected to a terminal of the induction coil L via a switch K ", while the capacitance diode V 1. is directly connected to the other terminal of the induction coil L.

In this way the following areas of capacity change are obtained:

When switches K and K are open: the capacity of the The tuning circuit changes from C to 2C when the bias voltage goes from 30 volts to 5 volts.

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When switch K _{1 is} closed and switch K _{2 is} open: the capacitance of the tuning circuit changes from 2C to 4C when the bias voltage goes from 30 volts to 5 volts.

When switches K ₁ and K _{2 are} closed: the capacitance of the tuning circuit changes from 4C to 8C when the bias voltage goes from 30 volts to 5 volts.

There are thus three sub-ranges, each sub-range requiring a change in bias voltage from 30 volts to 5 volts.

The total frequency range is now (with C / C. = 8):

J = 2.83

min

this frequency range is divided into three sub-ranges.

Such a device enables the input stages of a receiver to be tuned as they change from 26 MHz to 72 MHz Frequency, the space requirement being considerably reduced with respect to the known devices.

In practice, when such a circuit is used to tune the input stages of a receiver, the biasing of the varactor diodes is the same as that used to power the oscillator of the frequency synthesizer of the receiver. This tension does not change continuously, but gradually in the various sub-areas. The voltage is supplied by a logic system made up of transistors and switching diodes. The steps can have as small a division as you like, so that good accuracy is achieved. The logic system can also work out information corresponding to the sub-areas of the device and used to trigger switches K ₁ and K «. These switches are, for example, bistable relays that do not consume any energy.

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The invention is not limited to the device described. In particular, it is possible / the tuning frequency band to increase by adding more capacitance diodes with their associated to the terminals of the induction coil L Switches can be connected. The total capacity of such an arrangement enables complete coverage of the tuning frequency band.

In addition, the groups of two capacitance diodes, such as, for example, the capacitance diodes V ₁ and V ₂ , can be replaced by several groups of two reversely connected capacitance diodes which are connected in series or in parallel. The bias voltage is now applied to the anodes of each group of two capacitance diodes via a decoupling circuit, the point common to the two groups being decoupled in the case of a series circuit by a decoupling circuit connected to the circuit ground.

The parallel connection of two groups of capacitance diodes enables the capacitance to be doubled. This circuit can be used in particular to replace the capacitance diodes V ₅ and V and in this way use capacitance diodes with the same characteristics for the entire circuit.

Incidentally, the RF input voltage became E in the above description applied to the induction coil L through a circuit connection. In practice this is the induction coil L is generally the secondary winding of an input transformer, at whose primary winding the input voltage E. the circuit is applied.

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Claims (4)

Patent claims: 1. / Resonant circuit with an induction coil, with a first variable capacitance, which is formed from capacitance diodes, and with a biasing device for the capacitance diodes, which enables a change in capacitance from C to 2C by changing the bias voltage V from V to V ₁ , thereby characterized in that the resonant circuit also contains η (η integer, positive) further variable capacitances, which are each formed from capacitance diodes, that the capacitance diodes of the η further variable capacitances receive the same bias voltage V, that the i-th (i = 1 ... n) further variable capacitance changes from 2 ¹ "C to 2 ¹ C when the bias voltage changes from V to V ₁ , and which enables a switching device to sequentially and cumulatively change the 1st, 2nd ... n- te connect further variable capacitance to the first variable capacitance. 2. Resonant circuit according to claim 1, characterized in that each variable capacitance has an even number of capacitance diodes contains. 3. resonant circuit according to claim 2, characterized in that, that the first variable capacitance is formed from two capacitance diodes which are connected to one another by their anodes are, while their cathodes are with one or the other of the two terminals of the induction coil are connected, and that the other variable capacitances in the same Way how the first variable capacitance are formed. 4. Receiver with input stages, which means at least a resonant circuit according to one of claims 1 to 3 are tuned. 509809/0909 Blank page