JPH0767048B2 - FM modulator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an FM modulator that frequency-modulates a carrier wave according to an input high-voice signal or an input video signal, and relates to an FM modulator having improved linearity performance. .

[Background of the Invention]

As a conventional FM modulator, for example, as described in JP-A-53-10249 and JP-A-50-106610, an emitter-coupled multi-type as shown in FIG. The vibrator was used. However, in the circuit shown in FIG. 1, the linearity of the change characteristic of the oscillation frequency with respect to the input voltage signal is poor. For example, in a magnetic recording / reproducing apparatus that FM-modulates an audio signal for recording, the linearity of the reproduced audio signal becomes However, there is a drawback that the strain rate deterioration depends on it.

Further, it will be described in detail with reference to the operation explanatory view shown in FIG. In FIG. 1, the current I _a flowing through the transistor 3 is switched by the differential switching circuit of the transistors 1 and 2. The current I _a flowing through the transistor 3 is the input voltage signal applied from the input terminal 4 converted into a current by the transistor 3 and the resistor 5, and the transistors 6 and 7 are
The emitters are connected by a capacitor 8 to form a so-called emitter-coupled multivibrator. Transistors 9 and 10 are somewhat lower voltage is applied from the power supply voltage V _cc to the base, and supplies a reference voltage transistor 6 and 7 prevents the saturation region and the multivibrator is inverted. The diode-connected transistor 11 is for temperature compensation of the transistors 9 and 10. resistance
Reference numerals 12 and 13 denote output load resistors, and the transistors 14 and 15 and the diodes 16 and 17 lower the DC level of the output signal and transmit the output signal to the switching circuit formed by the transistors 1 and 2.

In FIG. 2, (a) is the base of the transistor 6,
(B) shows the voltage waveforms of the base of the transistor 7, (c) shows the emitter of the transistor 6, and (d) shows the voltage waveforms of the emitter of the transistor 7. Considering the conduction state of the transistor 2 first, in this case, the transistors 6 and 9 are also in the conduction state, the transistors 1, 7 and 10 are in the cut-off state, and the current I _a is the transistor 9 and the resistor 12. Is the sum of the currents flowing to and, and also flows through the transistor 6, the capacitor 8 and the transistor 2. Therefore, if the base-emitter voltage of the transistors 6, 9 and 11 is V _BE , and the potential difference between the base of the transistor 9 and the power supply V _cc is V _c ,
The voltage of each part is as shown in the t ₁ period of FIGS. 2 (a) to 2 (d).

Next, when the current I _a flowing through the capacitor 8 causes the emitter voltage of the transistor 7 to drop and the transistor 7 starts to conduct, _a part of I _a passes through the transistor 7 and flows through the resistor 13 so that the base voltage of the transistor 6 is reduced. Or it drops sharply. Therefore, the collector current of the transistor 6 sharply decreases. However, since the base potential of the transistor 7 does not rise unless the transistor 9 is cut off, the collector current of the transistor 7 cannot be rapidly increased, and _a period in which the sum of the emitter currents of the transistors 6 and 7 is less than I _a occurs. , The collector capacitances of the transistors 1 and 2 are discharged, and the voltage across the capacitance 8 drops in a substantially similar manner. This period is the t ₂ period in FIG. ΔV is the base-emitter voltage of the transistor 6 or 7 at which the emitter voltage of the transistor 6 or 7 starts to rise
When V _BE ′ and transistor 6 or 7 start to conduct, t
_This is the difference between the base-emitter voltage just before the end of _two periods. Next, when the transistor 7 is turned on, the current I _a flows through the capacitor 8 and the transistor 1 contrary to the t ₁ period, and the emitter voltage of the transistor 6 decreases linearly. This period is the period t ₃ in FIG. Oscillation is connected by repeating the period t ₁ , t ₂ , t ₃ , t ₂ thereafter, and its frequency is Is represented. Here, it is clear that V _BE ′ and ΔV are affected by the positive feedback gain of the circuit shown in FIG. 1 and the hfe of the transistor, and their changes also change the t ₂ period. Therefore, the change of the oscillation frequency with respect to the current I _a becomes non-linear, and there is a drawback that the linearity deteriorates. Especially when FM modulation of audio signals is required, high linearity (0.1% or less in distortion of demodulated audio) is required, which is not suitable. The circuit shown in FIG. 1 can obtain only about 1 to 3% of the distortion rate of demodulated voice.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide an FM modulator having good linearity of the change characteristic of the oscillation frequency with respect to the input voltage signal.

[Outline of Invention]

In order to achieve the above-mentioned object, in the structure of the emitter-coupled multivibrator, the collector outputs of the transistors whose emitters are coupled by capacitance are connected through a diode, and the change of both collector outputs is made to have a mutual form. It eliminates the t ₂ period and improves the linearity of the FM modulator.

Example of Invention

The present invention will be described below with reference to an example. FIG. 3 is a diagram showing an embodiment of the present invention, and FIG. 4 is a diagram explaining the operation of the embodiment shown in FIG. In FIG. 3, the input voltage signal 18 is input to the bases of the transistors 19 and 20, and the input voltage signal 18 is input by the transistors 19 and 20 and the resistors 21 and 22.
Is converted into a current signal I _b according to 18, and the transistors 19, 20
Flowing to the collector.

First, consider the case where the transistor 23 is conductive. In this case, the transistor 24 is in the cut-off state, and the collector current I _b of the transistor 20 is passed through by the capacitor 25.
23, and the collector current I _{b of the} transistor 19 also flows to the transistor 23. Therefore, if the base-emitter voltage of the diode-connected transistors 26 and 27 and the transistors 28 and 29 is V _BE, and the voltage at the connection point between the resistor 33 and the collector end of the transistor 24 is V _d , the resistor 32 and the transistor are connected. The voltage at the connection point with the collector end of 23 is V ₂ −V
_BE (the voltage between the base and emitter of the transistor 26) becomes, and the voltage of each part becomes as shown in the period t _{4 in} FIG. Note collector current 2 I _b flowing through the transistor 23 is the sum of the currents flowing current through resistor 33 and diode 26 resistor 32.

Next, when the current I _b flowing through the capacitor 25 lowers the emitter voltage of the transistor 24 and the transistor 24 starts to conduct, a part of I _b flows through the transistor 24 to the resistor 33, causing the base voltage of the transistor 23 to suddenly increase. Fall to. Therefore, the collector current of the transistor 23 sharply decreases. Moreover, when the base voltage of the transistor 23 drops sharply, the diode 27 starts to conduct and the collector voltage of the transistor 24 drops sharply. That is, the base inputs of the transistors 23 and 24 influence each other by the diodes 26 and 27, and the states are abruptly reversed, and the t ₂ period shown in the conventional example is greatly shortened, and it hardly exists. By setting the resistors 32 and 33 to the same value,
The waveform is as shown in the figure. In the next t ₅ period, the elements installed symmetrically with respect to the operation in the above t ₄ period perform the same operation, resulting in the t ₅ period shown in Fig. 4, and the above operation is repeated. Be done. At this time, the oscillation frequency is That is, the current signal I _b corresponding to the input voltage signal and the change in the oscillation frequency have a proportional relationship, and the linearity of the FM modulator is improved.

In addition, the dotted line portion 4 including the transistors 34 to 37 and the resistors 38 and 39
Reference numeral 0 is a circuit for removing the input voltage signal component generated in the FM modulation signal output to the emitters of the transistors 28 and 29. That is, as shown in FIG. 5, a signal corresponding to the current signal I _b is superimposed on the emitter outputs of the transistors 28 and 29, which easily causes interference with others and requires the HPF to remove this. There's a problem. It is possible to eliminate this problem and output only the FM modulation signal to the output terminal 43. That is, the output voltage signal from the transistor 28 is once converted into a current signal by the inverting circuit composed of the transistor 34, the resistor 38, and the transistors 36 and 37, and then converted into a voltage signal again by the resistor 39, and then from the transistor 28. An inverted voltage signal with respect to the output voltage signal of is obtained at the base of the transistor 41.

On the other hand, the output signal from the transistor 29 is
It is supplied to the base of the transistor 41 through the resistor 35 and the resistor 39, and is added to the inverted voltage signal from the inversion circuit, and the terminal 43 is connected to the terminal 43 as shown in FIG.
Only FM signals are output.

This point will be described in more detail. The voltage at the connection point between the resistor 33 and the collector terminal of the transistor 24 is V _a
The operation of the embodiment shown in the figure has been described as shown in FIG. 4, but in this case, the voltage V _a is obtained as follows.

That is, the respective input current signals I _b generated through the transistor 19 and the resistor 21 and the transistor 20 and the resistor 22 are supplied to the transistor 23 side or the transistor 24 side depending on the conduction / interruption state of the transistors 23 and 24. Via both,
It flows through resistors 32 and 33 and transistors 26 and 27. Therefore, the voltage at the center of operation of the collector terminals of the transistors 23 and 24 is the voltage when the currents flowing through the resistors 32 and 33 have the same value, that is, when the respective current values are I _b . Based on FIG. 4, the voltage V _a is a voltage when it is high as the voltage at the collector ends of the transistors 23 and 24, so V _a = V _cc −R ₃₂ × I _b + V _BE / Expressed as 2.

That is, V _a = (V _cc + V _BE / 2) −R ₃₂ × I _b , and the signal corresponding to the current signal I _b is superimposed.

On the other hand, the dotted line portion 40 shown in FIG. 3 solves this problem. The emitter output voltage signal of the transistor 28 is converted into a current signal through the transistor 34 and the resistor 38, and then the transistor It is transmitted to the resistor 39 as a current signal by 36 and 37. On the other hand, the emitter output voltage signal of the transistor 29 passes through the transistor 35, and then is reduced by the voltage of the product of the resistor 39 and the current signal and then the transistor 41.
Is supplied to. Therefore, since the output voltage signals V ₂₈ and V ₂₉ of the transistors ₂₈ and ₂₉ are signals in which the voltages V _a −V _BE and V _a −2V _BE are alternated, respectively. Is expressed as Therefore, the output V ₄₃ of the output terminal 43 is V ₄₃ = V ₂₈ −V ₂₉ × R ₃₉ / R ₃₈ where R ₃₈ and R ₃₉ are equal to The input voltage signal component is removed and the output terminal 43
Only the FM modulated signal can be output to.

Even in the conventional example shown in FIG. 1, the input current signal I _a flows through the resistor 12 or the resistor 13, but in this case, since the transistors 26 and 27 of FIG. 13
The voltage at the collector ends of the transistors 6 and 7 may or may not flow in only one side, and when it flows, V _cc −V _c
-V _BE , and if it does not flow, it will be fixed at V _cc -V _c . Therefore, at this time, a signal corresponding to the input current signal is not superimposed.

Also, the resistance for generating the voltage V _c is set to 0, that is, the voltage V _c
Even if 0 is set to 0, the same result as in the case of the conventional example shown in FIG. 1 is obtained.

Further, as shown in the equation (2), the oscillation fraction f has a temperature change characteristic depending on V _BE , but in FIG.
This is a circuit that has a temperature change characteristic that depends on V _BE , which can eliminate the temperature change characteristic of the oscillation frequency. That is, the sixth
In the amplifier shown in the figure, the gain G is And is dependent on V _BE . Since I _b = k _G V _in (k is a constant) is expressed here, Therefore, the temperature change characteristic can be eliminated.

In this embodiment, the number of transistor connections between the power supply voltage _Vcc and the ground is smaller than that of the circuit shown in FIG. 1, which is suitable for low voltage operation and low power consumption can be achieved.

〔The invention's effect〕

According to the present invention described above, an FM modulator having good linearity between an input voltage signal and an oscillation frequency can be realized with a simple configuration. For example, a reproduced audio signal such as a VTR that FM-modulates an audio signal and records it on a tape. The distortion rate can be significantly improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a conventional FM modulator, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a circuit diagram showing an embodiment of the present invention, FIGS. FIG. 6 is a waveform diagram for explaining the operation of FIG. 3, and FIG. 6 is a circuit diagram showing a part of the embodiment of the present invention. 18 …… Input voltage signal, 19,20,23,25,28,29 …… Transistor, 26,27 …… Diode-connected transistor, 40 …… Input signal component removal circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuuo Fukushima Inventor Yukio Fukushima 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Electric Appliance Research Institute, Hitachi, Ltd. (72) Kuji Watanabe 1410 Inada, Katsuta, Ibaraki Hitachi, Ltd. (72) Inventor Hideo Yoshida 1479, Kamimizuhonmachi, Kodaira-shi, Tokyo In-house Hitachi Mycro Computer Engineering Co., Ltd. (56) Reference JP-A-52-114251 (JP, A) JP-A-50-106610 (JP, A) JP-A-58-166817 (JP, A) JP-A-53-10249 (JP, A) JP-A-53-54948 (JP, A)

Claims (1)

[Claims] 1. The collector of the second transistor (24) is connected to the base of the third transistor (28), and the emitter of the third transistor (28) is connected to the base of the first transistor (23). And the collector of the first transistor (23) is connected to the base of the fourth transistor (29), and the emitter of the fourth transistor (29) is connected to the base of the second transistor (24). , A capacitor (2) provided between the first and second transistors (23, 24) and the emitters of these transistors (23, 24)
5) An emitter-coupled multivibrator having: and modulation signal supply means (18, 19, 20, 2) for applying a modulation signal to the emitters of the first and second transistors (23, 24).
1,22) and an FM modulator consisting of the first and second transistors (23,24), each of which is provided with a resistive load (32,33) and is connected in antiparallel between the collectors. Diode (26,2
7) is provided, and the bases of the output signals generated at the collectors of the first and second transistors (23, 24) are connected to the collectors of the first and second transistors (23, 24). And an inverting circuit (34, 38) for inverting the input signal and outputting the output signal of one of the third and fourth transistors (28, 29) which is taken out via the third and fourth transistors (28, 29). , 3
6, 37), and the output of the inverting circuit and the output signals of the other of the third and fourth transistors (28, 29) are added, whereby linearity is improved and the modulation signal component is removed. An FM modulator characterized by obtaining an FM modulated signal.