DE1153802B - Frequency-modulated transistor oscillator - Google Patents

Description

The invention relates to frequency-modulated transistor oscillators with only one transistor.

The frequency modulation should be as simple as possible with good linearity and without disruptive Amplitude modulation take place.

It is known that the current amplification factor a of a transistor, that is to say the ratio between the change in the collector short-circuit current and the associated change in the emitter current in the basic basic circuit, is constant only for low frequencies. As the frequency increases, it drops rapidly above the so-called α limit frequency. This drop in the value of α is accompanied by a phase shift between the two currents.

As is known, the a-cutoff frequency of a transistor, in particular a peak transistor, changes with it the DC operating values of the transistor, being most evident on changes in the collector voltage and the emitter current reacts. The a-cutoff frequency increases with the collector voltage and falls with the emitter current.

By reducing the current amplifier factor α at higher frequencies, the application becomes possible a transistor as a gain element at frequencies above the a-cutoff frequency.

However, the reduction in α is not necessary for the use of a transistor as a vibration generator so important. Many high-frequency oscillators with feedback are known that are well above the a-cutoff frequency of their transistors oscillate.

It is known that compensation is then used to maintain the feedback conditions the phase shift caused by the transistor is necessary so that the oscillator also works these frequencies still vibrates. It is also already known that frequency modulation is used in such oscillators the vibrations can be achieved by changing the operating voltages.

The present invention seeks to provide a transistor oscillator in which a particularly effective Frequency modulation is possible without additional effort. In particular, the frequency change depend as linearly as possible on the modulation voltage, and there should only be a small additional Amplitude modulation occur.

The invention is based on a frequency-modulated, phase-compensated transistor oscillator with only one transistor and one oscillating circuit from which the feedback voltage is taken will. It recommends that its operating frequency be in a range near the a-cutoff frequency of the Frequency-modulated transistor oscillator

Applicant:

Western Electric Company, Incorporated,
New York, NY (V. St. A.)

Representative: Dipl.-Ing. H. Fecht, patent attorney,
Wiesbaden, Hohenlohestr. 21

Claimed priority:
V. St. v. America April 15, 1953 (No. 348 901)

Donald Edgar Thomas, Madison, NJ (V. St. Α.),
has been named as the inventor

Transistor is selected and that the resonant circuit is dimensioned so that the operating frequency on a substantially linear part of the phase-frequency characteristic of the resonant circuit.

Such an oscillator can be used as a frequency-modulated transmitter, the modulation voltage being supplied by a microphone, for example will. In addition to good electrical properties, such a transmitter is because of its simple structure robust and reliable and has only small size and small weight.

The oscillator can also be used in conjunction with a frequency control circuit. Under the influence of a slowly changing direct current signal which z. B. as an error signal from the Deviation of the operating frequency of the oscillator from a given nominal value can be derived, the operating frequency can then be brought back to the nominal value.

The invention will be explained in detail below with reference to the drawings; in the drawings shows

Fig. 1 is a schematic circuit diagram of an inventive FM transmitter with only one transistor, Fig. 1A simplified for the high frequencies Circuit diagram of the circuit according to Fig. 1,

IB shows the high-frequency equivalent circuit diagram of the circuit according to FIG.

309 670/228

is shifted in a substantially linear manner, and finally the frequency modulated output oscillation radiated from the coil 19 and the antenna 27. The DC voltage source 22 is like this 5 polarized that it biases the collector electrode of transistor 11 in the reverse direction. The varistor 18 and the resistor 17 cooperate to bias the emitter electrode in the direction of flow. The varistor 18 is a voltage-dependent resistor

1C shows the dependence of the size and phase position of the current amplification factor of a transistor on the frequency,

FIG. ID shows the dependence of the voltage and phase position of the resonant circuit of the one shown in FIG FM transmitter on the frequency

Fig. IE a simplified one for the low frequencies Circuit diagram of the circuit according to FIG. 1.

According to Fig. 1, the transistor has an emitter electrode 12, a collector electrode 13 and a base io stood in the form of a rectifier (z. B. a crystal electrode 14. In the symbol shown is the or copper oxide rectifier), which together with the emitter electrode through marked by an arrow, the resistor 17, the required bias which indicates the positive current direction. Since the emitter delivers to the emitter electrode,
A more detailed explanation of the body flowing from the emitter electrode into the body, the operation of the circuit shown in FIG IA to IE are given, aimed. In a transistor with a p-semiconductor Fig. 1A shows the circuit with only those for the high body, however, the emitter current flows reversely, frequency behavior important parts. The condensate and the arrow is then away from the base electrode sators24 and 25 act as high-frequency short-directional. For the sake of simplicity, these and 20 are closed, so that the bias circuits and the load in the following figures, the arrow of the transistor resistor 21, are excluded from consideration. The symbols are directed towards the base electrode, and all bat resistors 16 in the emitter-base circuit are eliminated. The polarities and rectifier polarities are selected for the feedback via the base circuit and prevent the given direction of the emitter current. The resulting reduction in the highest invention, however, is not restricted to such transistors as the oscillation frequency of the circuit is below the a limit. With an emitter current in the opposite frequency of the transistor as well as breakover oscillations. The direction of the battery and rectifier polarity, together with the interference capacitance 15, should be reversed. Resonant circuit in Fig. 1A a feedback circuit

The transistor in Fig. 1 has an interfering electrode for the transistor 11, so that it has natural oscillations electrode capacitance 15 between its emitter and KoI- 30 at a frequency above its a-cutoff frequency lector electrode. The emitter electrode is also produced. The equivalent circuit diagram of the resulting one resistor 16 is connected. The resistance 16 of the oscillator is indicated in FIG. 1B, if one disregards it, which is very large compared to the inner Emitterelek- resistance 16. There is the trantrode resistance of the transistor 11. The other sistor 11 by an equivalent T-network represent-side of the resistor 16 is provided via a resistor 35, which is connected from the inner emitter resistor r _e , 17 to ground. The base electrode 14 of the collector resistor r _c and the base resistor transistor 11 is connected to ground via a varistor 18, stood r _b and the equivalent generator r _m i _{t while} the collector electrode is on one side of a. In this case, r _{m is connected} to what is known as the continuity resonant circuit, which consists of a state of the transistor and I ₁ the emitter current. The ductility 19 and a parallel-connected capacitance 40 interfering emitter-collector capacitance 15 is composed of Z _g ity 20. The other side of the resonant circuit and the impedance of the resonant circuit through Z _L is connected to the negative via a load resistor 21
Terminal of a battery 22 connected. The positive one
Terminal of battery 22 is grounded. The varistor 18,
for a current to the base electrode of the Tran- 45

posed.

The gain of the feedback loop of the equivalent circuit shown in Fig. 1B is approximate

sistor 11 is polarized in the forward direction, is bridged by a capacitor 23 for audio frequency. Furthermore, two bypass capacitors 24 and 25 are from the connection point of the resistors 16

μβ Sa

1 +

Z _L '

and 17 to the base electrode of the transistor 11 and from 50 where Z _L ' consists of the parallel resistors Z _L there to the connection point of the resonant circuit with and r _e . As stated earlier, the current gain of transistors is generally essentially constant for low frequencies, er

however, drops rapidly with increasing frequency if

derivation of the phase. To a good approximation, this frequency dependence of α can be given by the expression being represented:

the resistor 21 placed. The audio-frequency input terminals are on the one hand via the coupling capacitor 26 to the connection point of the resistors 16 and 17 and on the other hand directly at 55 the a-limit frequency is exceeded. This change the Base electrode of transistor 11 connected. tion of the absolute size of α is determined by a change-on If desired, an antenna 27 can be connected to a tap on the inductance 19.

The circuit described is an FM transmitter with
a transistor in which the transistor, preferred 60
wisely, a tip transistor works as a high-frequency oscillator, as an audio frequency amplifier and as a frequency modulator. In general his can
Operation can be described as follows: The
Transistor 11 generates natural oscillations at a predetermined _{frequency, where a 0 is} the value of α at low frequencies; furthermore, an audio frequency applied to the tone / frequency and / “is that frequency at frequency input terminals causes α to” 3 db below the value for low signal that the oscillation frequency is under its influence frequencies (ie the a-cutoff frequency).

a = -

5 6

Substituting (2) into (1) gives the expression emitter-collector capacitance 15 and the phase des

Oscillating circuit. The dimensioning of the resonant circuit

^a <L elements is chosen so that z. B. a stationary

,, -If] oscillation frequency f _{osc is} generated which is above the

I / o / \ ^a \ ®_ _m 5 a limit frequency / ₀ . As shown in Fig. IC,

/ ¹ P - Z ⁼ Z 'is then α below its value for low fre-

1 + y, 1 + -yr sequences. If it was accepted for explanation,

^{L h} that at this frequency the phase of α = 70 °

where Θ is the phase of α. carries the phase in the rest of the feedback

The feedback oscillator according to Fig. 1B oscillates in a circular manner, i.e. in the oscillatory circuit and in the parasitic capacitance

at the frequency at which the absolute value of 15 is about + 70 ° to generate vibrations

/ ι β one and the phase of μ β is zero. In Fig. IB. It was found that the interference capacitance

is the absolute value of α for the frequencies, at 15 then about 50 ° and the oscillating circuit the others

which vibrations occur, less than one. Da- 20 °. The oscillating circuit thus works under-

where η β is equal to or greater than one, it must also be half of its resonance, however, on an essentially

the absolute value of the denominator in (3) less than one borrowed linear part of its phase-frequency characteristic

_ ... z _s η j, .. "line, as indicated by point D in Fig. ID,

be. The value of - £ - therefore must have a negative real _{According to the previous En} ^ f _{mng ste lt Sc} HAL

Have component. Since Z _g is essentially purely a stable high-frequency potion capacitance in FIG. 1, this can only be realized, as shown in the sistor oscillator, which has a positive imaginary component above the a limit when Z _L '. frequency of the transistor is working. According to the invention, therefore, the oscillator oscillates at a frequency which is the oscillation frequency by changing the somewhat smaller than the resonance frequency of the oscillation a-cutoff frequency of the transistor under the influence circle. In fact, the oscillator oscillates changed according to an applied signal. In the embodiment of the invention shown in FIG. 1, FIG. 1 is 0.9 times the resonance frequency of the resonant circuit, this signal is an audio-frequency modulation signal,
is equivalent to. The function of the oscillator according to FIG. 1 can be changed on the emitter current of the transistor according to FIG explains 30 the a-cutoff frequency of the transistor relax. In Fig. IC shows the upper solid chend, and the high-curve generated by the transistor, the change in the current amplification factor frequency oscillation becomes under the influence of that of the transistor with frequency. The value of the incoming signal is frequency-modulated, as yet

should be explained in more detail.

20 log -— 35 For a consideration at audio frequencies and

^a o lower frequencies can be used by the circuit

,, ... / - τητ.Αί Fig. 1 combined in the form shown in Fig. IE

is dependent, g onj _; applied. In the shallow initial ^ _The \ _are ochfrequenten überbrückung-

Part of the curve, α has the value a ₀ for low fre-capacitors 24 and 25 places at these frequencies. If / is increased, α decreases with about 6 db 40 sequences practically infinitely large resistances and per octave. At the a-cutoff frequency / ₀ (points) the oscillation circuit is essentially a short α by 3 db below the value at low frequency. As a result, the circuit results in decreased frequencies. a low frequency amplifier. That about the resistance

The lower solid curve in Fig. 1C represents 17 sound signal is occurring through the transistor represents the change in phase of α with frequency, 45 11 amplifies and then harbors am in an amplified form

,.,. ", ,, .... fr - ^ load resistance 21. As a result, the collector fluctuates

the phase being carried out depending on the. It _voltage ^ _the sound signal, and the «limit shows that the phase of α changes from about 0 ° at the frequency of the transistor correspondingly low frequencies to about -90 ° at high frequencies under the influence of the applied sound signal,
sequences changes, being at the a-cutoff frequency f _a 50 The way in which the operating frequency goes through - 45 °. Changes in the a-cutoff frequency is regulated

Figure ID shows the amplitude and phase relationships shown in Figures IC and ID. For the discussions of the resonant circuit as a function of the sion, it is assumed that the instantaneous amplitude frequency, the lower curve the change of the applied sound signal from zero to a nega-phase Θ _τ and the upper curve the change in the tive value is changed . This gives an increase in amplitude V ₇ represents. The phase of the resonant circuit of the a-cutoff frequency of the transistor. In fact, in the vicinity of the resonance frequency f _T, the curve which changes the absolute value -r 90 ° to about -90 °, where a phase of α represents the frequency, changes to the right from 0 ^c at the resonance frequency itself present pushed and now appears in the through the mind. The voltage on the resonant circuit, which position indicated for the dashed curve. The new a-borderline is plotted, reaches a maximum at the frequency at which α 3 db below its value for low-resonance frequency f _T. cherishes lower frequencies is correspondingly higher

The oscillator according to FIG. 1 or IA generates eigenvalues and denoted by f ₀ 'in FIG. IC. In the upper vibration at a frequency f _osc at which the curve of Fig. IC is the new a-limit frequency total phase shift in the feedback circuit 65 indicated by point E.
Is zero. The three main factors that lead to this phase- For the phase of α there is a corresponding one

shift are the phase of the current shift indicated by the dashed curve in the Gain factor α, the phase of the disturbing lower half of Fig. IC is shown. In order to

If the operating frequency is assumed, the phase of α also changes. Since the total phase shift in the feedback loop must remain zero, the phase shift in the other elements must change accordingly. By a shift in the operating frequency is required, which is designated in the lower part of FIG. ID with _f A. The new working point is designated by G. The transistor oscillator then oscillates at the new frequency until the a-cutoff frequency of the transistor is changed again.

As can be seen from the upper part of FIG. ID, the amplitude modulation accompanying this frequency modulation is amplitude modulation negligibly small.

In the manner described, the α cut-off frequency of the transistor 11 in FIG. 1 becomes for small input signals changed essentially linearly under the influence of the audio frequency modulation signal. The resulting changes in the a-cutoff frequency are accompanied by changes in the α-phase, which cause the oscillator to adopt a new operating frequency. The one generated by the oscillator The carrier frequency is thus frequency modulated in a linear manner under the influence of the modulation signal.

Another advantage results from the special arrangement for the bias, which the use a single battery, which also contributes to downsizing the transmitter. the Antenna 27 can be used as required. It has been found that the coil 19 even without the antenna 27 emits so much energy that reception is possible at a distance of about 100 m is possible.

It should be noted that the resistors 17 and 21, if desired, audio-frequency bridging coils can be connected in parallel to save battery power. However, this results the disadvantage that additional space is required for the coils.

In the case of some transistors, it has been found that the load resistor 21 has been removed from the circuit of FIG can be. The change in the emitter current caused by the modulation signal is then sufficient of its own accord without changing the collector voltage to reduce the a-cutoff frequency of the transistor in the desired way to change.

Claims (1)

PATENT CLAIM: Frequency-modulated, phase-compensated transistor oscillator with only one transistor and a resonant circuit from which the feedback voltage is taken, characterized in that its operating frequency is selected in a range near the a-cutoff frequency of the transistor and that the resonant circuit is dimensioned so that the operating frequency lies on an essentially linear part of the phase-frequency characteristic of the resonant circuit. Considered publications:
Swiss Patent No. 212 950;
U.S. Patent Nos. 2,556,296, 2,570,939;
»The BeU Syst. Techn. Journ. ”, July 1949, pp. 379 to 384; May 1952, pp. 415, 439, 440. 1 sheet of drawings © 309 670/228 8.