DE977479C - Circuit arrangement for frequency modulation - Google Patents

Description

ISSUED AUGUST 4, 1966

S 34873 IXd / 21a *

Transistors are used in amplifier arrangements in various types of circuit, the differ from each other in that the base, emitter or collector are each shared Electrode is used for an input and output circuit. The three circuit arrangements listed are briefly referred to below as base, emitter and collector circuits.

ίο It is known to use frequency modulation, i. H. to change the frequency of a voltage or a current in the rhythm of the frequency a modulation voltage to use circuit arrangements in which tubes, directional conductors or common base transistors form the essential elements.

In the present invention, the function of modulating takes over a transistor in the collector or emitter circuit, whereby this is not simply to the appropriate place in the known Circuit arrangements is set, which in itself would be possible, but not very advantageous, but rather, they are based on special properties that result from manufacturing, dimensioning, and forming and operation of the transistor can be achieved by the known circuit arrangements uses different arrangements that lead to various special advantages.

609 641/1

It has already been proposed a circuit arrangement for frequency modulation with a To use transistor arrangement that has a fixed impedance in a rhythm one fed to it Modulation frequency changeable impedance: transformed, with the transistor in collector circuit is operated and the transistor is thereby produced, formed and selected Working point has a very low dynamic ίο emitter resistance and / or a very high dynamic Has collector resistance.

Furthermore, it is known to select the operating point and the external resistances To operate the transistor so that its input or output impedance becomes zero. One has However, this has the disadvantage that the operating point is so unfavorably in the family of characteristics that the linear The control range of the transistor becomes so small that it can no longer be used in practice. The invention relates to a frequency modulation circuit using an in Emitter or collector circuit operated transistor, in which one at the output of the transistor switched on fixed admittance at the entrance with a transformed, in the rhythm of a the modulation quantity applied to the transistor, which is both zero and positive as can also be negative, appears. It is characterized in that a transistor is provided which has a working point through manufacture, dimensioning and formation, for which the one at the exit of the transistor measured open circuit resistance is exactly or approximately zero and that the on these Working point in the circuit set transistor by the modulation amount in such a way is controlled so that the measured at the output of the transistor open circuit resistance im The rhythm of the modulation quantity fluctuates around the value zero or approximately zero. Here can in particular the open circuit resistance of the transistor which appears at the output is known per se Stabilization measures made independent of supply voltage fluctuations and the transformed value of the admittance through Control of the direct current values of the transistor arrangement in the rhythm of the modulation frequency to be changed. The change in the transformed value of the admittance takes place either by controlling the emitter or collector current or by controlling the base current in the rhythm of the modulation frequency. The transistor can either be connected as a collector or operated in emitter circuit.

The arrangement according to the invention enables the operating point to be mapped into the characteristic curve can put that the transistor can be controlled linearly with sufficiently large amplitudes is.

In order to demonstrate that the no-load resistance measured at the output of the transistor can be made zero by manufacturing, dimensioning, forming and operating the transistor, this is shown using the generally known equivalent circuit diagram of a transistor shown in the drawing. In the case of the collector circuit on which the operating mode is based, B denotes the base electrode, K denotes the collector and B denotes the emitter electrode in the corresponding equivalent circuit diagram. R _a is the terminating resistor connected between the emitter and collector. Base, collector and emitter resistance are designated in the equivalent circuit with r _b , r _c and r _e , r _m i _e is the voltage source of the transistor controlled by the emitter current.

If R _{a is} infinitely large, ie if the transistor is idle, then, as can be readily seen, the output no-load resistance is

- γ Λ. γ -,

Since always r _e <^ r _c , f ₂ ι = 0, so to achieve an output no-load resistance of zero by creating a transistor in which by production, z. B. by appropriate choice of the semiconductor, in particular by the selection of germanium, by dimensioning, z. B. by suitable choice of the distances between the electrodes, and by forming for a specific working point located in the middle of the normal family of characteristics r _m = r _c . It is known that in the case of the otherwise commercially available tip transistors r _{m is} about two to three times as large as r _c and in the case of the commercially available flat transistors r _{m is} smaller than r _c .

If the operating point fluctuates around this point, be it that the modulation is carried out by changing the emitter, collector or base current, r ₂ i becomes the values of r _2t - <0 through r _2L = 0 to r _2L ^> 0 run through.

The above consideration shows that in the collector circuit by manufacturing, dimensioning, forming and operating the transistor, the open circuit resistance r ₂ 1 measured at the output of the transistor can be made equal to zero. The input resistance does not become zero, however, since this resistance appears as a parallel-connected damping resistance of the resonant circuit, it must not be.

The input resistance is the parallel connection of the transformed admittance with the no-load input resistance of the transistor in a collector circuit, as the following considerations show. If r _{x is} the input resistance of the transistor and r _iL that at idle, then it is known that the following applies to every transistor

Ra ΐ 4 r ₂ L Ra

If the transistor is operated accordingly, z. B. in the collector circuit with suitable

neter choice of terminating resistor R _a , the

Short circuit stability δχ <ί— - made, so is

St.

Sx

SlL

Jk

Ra

= I + G _a T ₂ L

In the above equation, use was made of the possibility of setting the corresponding conductance g = - instead of a resistor,

z. B. the terminating resistor R _a - -x-.

If G _a = jY _{a is} chosen, that is, if the terminating resistor is a pure reactance and if the output idle resistance r _2L is controlled through zero, then the reactance jY _a r appears at the input of the transistor in parallel with g _{lL. z} Ig _{1 L} , which goes from negative values above zero to positive values. Since r _m = r _{c has been} selected, i.e. the transistor works stably, there is no tendency to oscillate.

In the already known modulation circuits which use a basic circuit, the Transistor, in order to achieve a noticeable control of the transformed admittance value, in be operated near an operating point where it becomes unstable, i.e. for self-excitation of Tends to vibrate. But to the extent that one can get the working point from the point of instability removed, the controllability of the transistor is reduced, while at the same time a growing, additional Damping conductance occurs, which is the frequency curve of the oscillating circuit to be controlled worsened. These disadvantages of the known circuit arrangements are alleviated by the circuit arrangement avoided according to the invention. In addition, the circuit arrangement according to the invention compared to the known Circuit arrangements for frequency modulation still have the following advantages:

The middle one, additionally connected to the frequency-determining resonant circuit by the transistor Admittance is zero or at least so small that the center frequency alone or at least practical is determined solely by the switching elements of the resonant circuit and therefore changes that the Transistor circuit z. B. shows as a result of temperature-dependent changes in its values that Not or not noticeably influencing the center frequency. Furthermore, through the circuit arrangement according to the invention a control with a relatively large frequency deviation with good linearity possible. Another advantage over the known circuit arrangements is based on the fact that a good stability of the transistor circuit is achieved. It also occurs as a damping resistor for the resonant circuit only the value of the input resistance, for example in a collector circuit between collector and base, measured with no load at the output.

Claims (8)

PATENT CLAIMS: i. Frequency modulation circuit using a transistor operated in an emitter or collector circuit, in which a fixed admittance connected to the output of the transistor has a transformed value at the input that changes in the rhythm of a modulation variable supplied to the transistor, which can be zero as well as positive or negative , appears, characterized in that a transistor is provided which has an operating point through manufacture, dimensioning and formation for which the open circuit resistance measured at the output of the transistor is exactly or approximately zero, and that the transistor set to this operating point in the circuit through the modulation variable is controlled in such a way that the no-load resistance measured at the output of the transistor fluctuates around the value zero or approximately zero in the rhythm of the modulation variable. 2. Circuit arrangement according to claim 1, characterized in that the appearing at the output No-load resistance of the transistor through stabilization measures for supply voltage fluctuations is made independent. 3. Circuit arrangement according to one of the preceding claims, characterized in that that the transformed value of the admittance by controlling the DC values of the Transistor arrangement is changed in the rhythm of the modulation frequency. 4. Circuit arrangement according to claim 3, characterized in that the transformed The value of the admittance is changed by controlling the emitter current in the rhythm of the modulation frequency. 5. Circuit arrangement according to claim 3, characterized in that the transformed The value of the admittance is changed by controlling the collector current in the rhythm of the modulation frequency. 6. Circuit arrangement according to claim 3, characterized in that the transformed The value of the admittance is changed by controlling the base current in the rhythm of the modulation frequency. 7. Circuit arrangement according to one of claims ι to 6, characterized in that the transistor is operated in collector circuit. 8. Circuit arrangement according to one of claims ι to 6, characterized in that the transistor is operated in the emitter circuit.