DE1005139B - Circuit arrangement with a demodulator and a transistor - Google Patents

Description

The invention relates to a circuit arrangement for coupling the output circuit of a demodulator with the input circuit of a transistor. The problem arises that, to a low demodulation distortion and a To ensure high efficiency, the demodulator preferably with relatively high voltages and relatively low currents, while the transistor is operated with relatively low voltages and relatively high currents, i.e. the demodulator has a high output resistance, and the transistor has a low input resistance.

It is known to avoid these difficulties in the output circuit of the demodulator Series connection of a resistor decoupled for the frequency of the demodulated signal and the Switch on the primary winding of a transformer, its into the input circuit of a following transistor switched-on secondary winding has a smaller number of turns than the primary winding, see above that although the demodulator works with relatively high voltage and low current, during the However, a strong alternating current is supplied to the following transistor at a correspondingly reduced voltage will. In this known circuit, the operating point of the transistor is from the supply voltage source, preferably with the help of a voltage divider. As a result, the transistor decreases In the absence of an input signal, energy is still available, which is therefore lost unused.

In a circuit arrangement with a demodulator, the output circuit of which is the series connection of the Primary winding of a voltage stepping down transformer and a resistor containing the is decoupled by a capacitor connected in parallel for the frequency of the demodulated signal, and in which the secondary winding of the transformer forms part of the input circuit of a transistor these disadvantages are avoided, and low-distortion demodulation and amplification are obtained with the lowest power consumption of the transistor amplifier, if according to the invention a setting current is also supplied to the input circuit of the transistor, that of the direct current component of the demodulated signal, and through which a power saving and / or control effect in Transistor is achieved.

The invention is explained in more detail with reference to the drawing, for example.

Fig. 1 shows an embodiment of the invention;

FIG. 2 shows an improved embodiment compared to FIG. 1.

Circuit arrangement

with a demodulator

and a transistor

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg I ₁ Mönckebergstr. 7th

Claimed priority:
Netherlands 10 May and 9 August 1954

Gerard Corneille Wolters, Jan Joost Rietveld

and Adrianus Johannes Wilhelmus

Marie van Overbeek, Eindhoven (Netherlands),

have been named as inventors

According to Fig. 1, the vibrations to be demodulated are fed to a tuned circuit 1, the with a rectifier 2, a capacitor 3 and a resistor 4, part of a demodulator forms so that the demodulated signal is generated across the demodulator output capacitor 3. Of the Resistor 4 is decoupled for the frequencies of the demodulated signal by means of a capacitor 5, while in series with the i? C element 4, 5 the primary winding a step-down transformer 6 is connected, the secondary winding of which a Forms part of the input circuit of a transistor amplifier 7.

The emitter of transistor 7 is connected to earth and its base is taken from the secondary winding of the Transformer 6 controlled with the demodulated oscillations. The collector that is on a terminal the amplified vibrations are taken from is via a working resistance to the negative pole connected to an otherwise earthed supply source. The capacitor 10 is initially disregarded and replaced by a direct connection.

In this circuit arrangement, on the one hand, the one generated across the capacitor 3 is demodulated

609 866/300

AC voltage is completely supplied to the transformer 6 via the capacitor 5, while on the other hand Demodulation distortion can easily be prevented by changing the input resistance of the Transistor 7 is adapted via the transformer 6 to the size of the resistor 4, in which case the low frequency AC impedance of the demodulation output filter 3, 4, 5, 6 is equal to the DC impedance of this filter, i.e. H. same as that Resistance 4. You can even increase the transformation ratio of the transformer 6 let this alternating current impedance exceed the mentioned direct current impedance. The resonance frequency of the series circuit formed by the capacitor 5 and the primary winding of the transformer 6 is formed, is so low that the currents corresponding to this frequency of the demodulated Signal are too low to cause demodulation distortion.

According to the invention, not only is the AC voltage component of the demodulated voltage via the demodulator output capacitor 3 via the decoupled resistor 4 to the transformer 6 and thus fed to the input circuit of the transistor 7, but also the DC voltage component the demodulated voltage on the capacitor 3 is determined by means of the circuit in the demodulator alternating circuit Capacitor 10 screened out and directly between the base electrode and the emitter electrode of the Transistor 7 made effective, since the capacitor 10 facing away from the emitter, in terms of alternating current grounded end of the secondary winding is connected, so that a direct current permeable connection exists between the demodulator circuit and the transistor input circuit. This changes the set current of the transistor 7 with the amplitude of the demodulated signal, which is not only for savings of energy, but z. B. also to generate a control current for automatic gain control can lead.

If the internal capacitance 17 of the primary winding of the transformer 6, indicated by dashed lines, is relatively is large, this capacitance can be used in cooperation with the capacitors 5 and 10 as a demodulator output capacitor be effective, so that the capacitor 3 may be unnecessary.

When using a germanium or selenium rectifier cell 2, it can be further advantageous to To achieve the highest possible output energy, a low reverse voltage source in the series circuit of the Equal to insert 2.

In a practical embodiment, the switching elements had the following values: Capacitor 3 = 100 pF; Resistor 4 == 500kOhm; capacitor 5 = 50,000 pF; Transformation ratio of transformer 6 = 20: 1; Input resistance of transistor 7 = 1200 ohms.

The invention can be carried out with both amplitude and frequency demodulators. When used with a conventional push-pull frequency demodulator with a tapped in the middle Low frequency output resistance can cause this output resistance through the primary winding of the Transformer 6 are replaced, which is then also provided with a center tap that is on the decoupled resistor 4 is connected to the input resonant circuit of the frequency demodulator.

When applied to a common type of asymmetrical ratio demodulator, the above-mentioned Demodulator output capacitor generated, demodulated voltage again via the decoupled resistor 4 is fed to the transformer 6.

The circuit arrangement of Fig. 1 still has the disadvantage that the alternating current amplitude in the The secondary winding of the transformer 6 is greater than the basic setting current generated in this way Transistor can be. Of course, you could again use the base electrode, not shown Connect the resistor to a suitably selected bias source and / or such Connect the source in series with the emitter electrode of transistor 7; but as a result, the In the absence of the input signal, more energy is unnecessarily lost in the transistor.

According to Fig. 2, the remaining disadvantage is eliminated in that with the help of an auxiliary demodulator 11,12, which is preferably an isolating resistor 13 and a decoupling capacitor 14 follow, the required current is generated. Resistance 13 must be chosen accordingly smaller than the resistor 4, while the demodulator 11,12 on a tap is connected to circuit 1, the tap ratio of which is of the same order of magnitude how the transformation ratio of the transformer 6 must be. By choosing the right The winding direction of the windings of the transformer 6 can then also bias direct current of the transformer core can be avoided. The obtained direct current component amplified in the transistor 7 can for automatic strength control a preceding transistor in a die present circuit containing receiving channel are supplied. Instead or in combination In this way, this component can also be amplified in the last-mentioned transistor and become automatic Strength control can be fed to one of the other transistors contained in the receiving channel.

Claims (5)

Patent claims: 1. Circuit arrangement with a demodulator, the output circuit of which is connected in series the primary winding of a step-down transformer and a resistor contains, by a capacitor connected in parallel for the frequency of the demodulated signal is decoupled, and in which the secondary winding of the transformer is part of the input circuit of a transistor, characterized in that the input circuit of the transistor in addition, an adjustment current is supplied which corresponds to the direct current component of the demodulated Signal corresponds and achieved by a power saving and / or a control effect in the transistor will. 2. Circuit arrangement according to claim 1, characterized in that said setting current is generated by means of an auxiliary demodulator (Fig. 2). 3. Circuit arrangement according to claim 2, characterized in that the auxiliary demodulator is connected to a tap of a circuit to which the demodulator is connected, wherein the tap ratio is of the same order of magnitude as the transformer ratio of the mentioned transformer. 4. Circuit arrangement according to claim 1, characterized in that by appropriate choice the VVickelsinnes of the transformer windings a direct current bias of the transformer core is avoided. 5. Circuit arrangement according to one of the preceding claims, in which the demodulator contains a rectifier cell, characterized in that to increase the demodulator output energy a low reverse voltage source is inserted in the rectifier circuit. Documents considered: German Patent No. 672 617; U.S. Patent No. 2,018,540; Electronics, Aug. 1953, p. 202. 1 sheet of drawings © 609 866/300 3.