JPS604608B2 - fm modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM modulator that linearizes modulation characteristics by controlling the amplitude ratio and phase of the fundamental wave and harmonics of the oscillation frequency, and compensates for changes in modulation characteristics due to temperature. It is something.

In an FM modulator using a variable capacitance diode, the linearity of the change in the input voltage of the modulator versus the oscillation frequency (hereinafter referred to as modulator linearity) is governed by the voltage versus capacitance characteristic of the variable capacitance diode.

Now, the voltage vs. capacitance characteristic of a variable capacitance diode is C=C.

V. -n '1} where Vo: operating voltage, Co=
Operating point capacitance n: When expressed as the capacitance change rate at the operating point, when this variable capacitance diode is used as part of the resonant circuit of a modulator, its oscillation frequency f is 1 ■ f=fusuku where L: Inductance formula of resonant circuit '1},'2
From 1, f=; direction v.

The wider the range that satisfies the condition n=2, the wider the linearity of the modulator will be.

However, when this variable capacitance diode is conventionally mounted in a modulator, the linearity of the modulator is affected by the operating voltage Vo, operating point capacitance Co, and capacitance change rate n of the variable capacitance diode, as shown in the above equation. However, it is difficult to satisfy n=2 over a wide band, and due to the non-uniformity of diode manufacturing characteristics, it is difficult to satisfy n = 2 over a wide band. Methods such as limiting the oscillation frequency band and performing capacitance compensation for the required oscillation frequency band have been explored, but it has been difficult to do so over a wide band because the circuit is complicated. On the other hand, in the original invention, Patent No. 1013758, the oscillation circuit of the modulator is provided with a harmonic generating means for generating harmonics of the oscillation frequency, and the amplitude ratio and phase of the fundamental wave and the harmonics of the oscillation frequency are is controlled so that the capacitance change rate of a variable capacitance diode provided in a part of the resonant circuit is 2, and the fundamental wave and harmonics are added to the variable capacitance diode to obtain linearity over a wide band. We offer FM modulators.

FIG. 1 is an explanatory diagram showing the configuration of the FM modulator of the original invention. FIG. 1 shows an FM modulator in which the capacitance of the resonant circuit of a Hartley type oscillator is a variable capacitance diode, and a modulation input is applied as the operating voltage.

That is, a series circuit of a variable capacitance diode 3 and a capacitor 4 and a parallel resonant circuit of an inductance 6 are connected between the collector of the transistor 2, which is supplied with power (110V), and the base via the capacitor 7 and ground. A bias (-1 skin) is fed back to the emitter via an inductance 6, a modulation input 1 is inserted between a variable capacitance diode 3 and a capacitor 4, and FM modulation is performed by the voltage vs. capacitance characteristic of the variable capacitance diode 3. Let's do it. In contrast to the configuration of the above-mentioned secondary FM modulator, the modulator of the original invention inserts a harmonic generator 8 in parallel to the resonant circuit as shown in the block, and branches the modulation input 1 through the DC amplifier 9. Controls the harmonic generator 8.

Further, an amplitude control circuit ID is inserted into the feedback circuit from the inductance 6 to the emitter, and an emitter current control circuit 11 is inserted into the bias power supply circuit of the emitter. With such a configuration, the amplitude and positive/negative phase of, for example, the second harmonic component generated by the harmonic generator 8 are controlled by the output level of the DC amplifier 9 branched from the modulation input 1,
This is sent to the amplitude control circuit 1 via the inductance 6, which further controls the amplitude of the second harmonic, while the emitter current control circuit 11 controls the amplitude of the oscillation frequency, thereby achieving linearity over a wide band. In the FM modulator of the original invention described above, the capacitance of the variable capacitance diode 3 is assumed to change depending on the modulation input voltage, and compensation for temperature is not performed.

In reality, as shown in FIG. 2, the modulation characteristics vary significantly depending on the ambient temperature. The figure shows the modulation characteristic as a differential characteristic on the vertical axis, taking the frequency, for example, 14 MHZ and 20 MHZ, and plots -500 at low temperature, +2yo at normal temperature, and +55qC at high temperature with temperature change as a parameter. This is what I did. In other words, as a result of the improvement by the harmonic component in the original invention, the characteristic is almost flat near 25°C, whereas at -500, the differential gain near 120 MHz is high and the slope shows a falling characteristic, and conversely, the characteristic is not sufficiently high. For 55oo, the differential gain near 120MH2 decreases, but the slope changes to an increasing characteristic. The linearity deterioration of the modulation characteristics of the modulator due to temperature is dominated by the temperature characteristics of a variable capacitance diode, such as a paractor. That is, at low temperatures, the oscillation amplitude increases due to an increase in the Q of the parameter, and at high temperatures, the oscillation amplitude decreases due to a decrease in Q. An object of the present invention is to provide an FM modulator that linearizes modulation characteristics by controlling the amplitude ratio and phase of the fundamental wave and harmonics of the oscillation frequency and compensates for changes in the modulation characteristics due to temperature.

In order to achieve the above object, the FM modulator of the present invention includes a variable capacitance diode in a part of the resonant circuit of the oscillation circuit, and the capacitance of the variable capacitance diode is changed by an external voltage to shift the oscillation frequency. , a harmonic generator that generates harmonics of the oscillation frequency in a feedback loop including a resonant circuit of the oscillation circuit, and an amplitude control circuit that controls the amplitude ratio and phase of the fundamental wave and the harmonics of the oscillation frequency. ,
The fundamental wave and the harmonics are added to the variable capacitance diode by controlling the amplitude ratio and phase of the fundamental wave and harmonics of the oscillation frequency so that the capacitance change rate of the variable capacitance diode is 2, and The device is characterized by comprising a bias control circuit that changes a bias voltage at a feedback point to an oscillation element of an oscillation circuit in accordance with temperature, and further, the amplitude control circuit operates with a bias voltage that changes depending on temperature. The device is characterized in that it includes a temperature compensator made of a variable capacitance diode.

The principle and embodiments of the present invention will be explained in detail below.

Now, it is assumed that the voltage versus capacitance characteristic of the variable capacitance diode is expressed by the equation {1), and this relational expression is expressed by a polynomial from the operating point voltage Vo of the varactor to the displacement voltage v.

When a displacement voltage of v is applied to this variable capacitor diode, the current i that flows is i = maximum (VC) [51 When the capacitance C is constant and v = a, cos t, the current i is i - Cal Sin t
{6) (C constant) The capacitance value is.

Next, if the capacitance C is not constant, substitute formula '4} into formula [5}', and from formula '6r, when the displacement voltage v includes harmonics and the ap:p harmonic amplitude is here, the current is calculated by the formula It can be obtained by substituting ■ into formula ■.

Now, by simply using Equation '10 and considering up to the second harmonic, we can calculate the equation t (11
), the current is calculated as {from formula 91, I; a
;FalGin■t)X [1 one skin 2V.

・-1 ten good (a character + muyo) V. -2n(n+・)1go2
female a2 stern) V; 3n (n+1) (n 12)] 12 (S
in's t)
Stem) V62n (n+・)-Summer (Natsusantoa-tei a wife) V63
n(n11)(n+2)]13(t of Sin)X[1a
・V61n+Kiku a character ten dollar doll) V62nkun+. )−
Amount (a character a20a・a stalk) V53n x n1) (n+2
)] (12) If we focus only on the fundamental wave in equation (12), the capacitance value CI for the fundamental wave can be calculated from equation [61' to C
=Cy6n{・One na2V6・Jusaku (a character Juzo ≧) V;
2n (n11) - 1 (Kasa-tei - a20 $ stem) V63n (n
+1)(n+2)} (13) In other words, the capacitance value for the operating voltage when the voltage applied to the variable capacitance diode is only the fundamental wave is shown by equation 9), and the voltage applied to the variable capacitance diode is equal to the fundamental wave. The capacitance value with respect to the operating voltage when second harmonics are also included is shown by equation (13).
Generally, the capacitance change rate n' can be expressed as follows.

In this case, C=Cy center and n'=n
(15), and it can be seen that equation (14) is valid.

By substituting equation (13) into equation (14), the capacitance change rate n' when a composite wave of the variable capacitance diode fundamental wave and harmonics is applied can be obtained. In other words, in order to see the change in n' with respect to the second harmonic, the characteristics of the varactor are set to n=2, al
n' when changing a2/Vo with /Vo=1/3
An example of the change in is shown in Fig. 3.

From Figure 3 When a2>0, n'<nvo When a2<0, n'>nv.

Here, nvo indicates the rate of change in capacitance at the operating voltage Vo point when no harmonics are applied to the variable capacitance diode.

That is, if the amplitude of the second harmonic is positive, the capacitance change rate decreases, and if it is negative, the capacitance change rate increases. Therefore, it can be seen that the capacitance change rate increases or decreases depending on the amplitude and phase of the second harmonic component. Therefore, by utilizing this principle and controlling the change in n due to temperature by controlling a2'Vo, that is, the ratio of the amplitudes of the fundamental wave and the secondary high frequency, or even the positive and negative phases, the modulation characteristics can be made linear as in the case of the original invention. can be converted into

In the present invention, a circuit that performs the control in response to temperature may be provided in addition to the circuit of the original invention. The change in modulation characteristics (differential characteristics) due to temperature is as shown in Figure 2.
It can be divided into a change in the primary forehead slope, which shows a downward characteristic at low temperatures and an upward characteristic at high temperatures, and a change in curvature on both sides of each characteristic.

To deal with changes in the primary slope, as shown in FIG. 4, by using a semiconductor temperature-sensitive variable resistance element such as a thermistor in the bias circuit of the oscillation element of the oscillation circuit shown in FIG. When the bias voltage at the feedback point to the oscillation element of the oscillation circuit is used as a parameter, the second
It is possible to provide a slope opposite to that of the modulation characteristic shown in the figure, that is, the frequency-differential characteristic.

For example, at a low temperature of -5℃, a low bias voltage (1.5Vr
ms), a rising characteristic at room temperature 125 qo, a flat characteristic at intermediate bias voltage (2.1 V ms), and a high temperature +55 qo.
In this case, it is possible to provide a falling characteristic with a high bias voltage (2. law plate s). In this case, the effect when the variable capacitance diode of the resonant circuit is maintained at approximately room temperature is shown. On the other hand, the change in curvature can be controlled by adding a variable capacitance diode, for example a varactor, for temperature compensation in series with the amplitude control circuit 101 of FIG. Compensation is performed by applying a bias voltage.

That is, as shown in FIG. 5, for example, at room temperature +25 oo
(capacity: 3F), exhibits flat characteristics at low temperature -5℃ (capacity: 3F),
3pF), the curvature on both sides increases, and the temperature rises to +55℃ (
With a capacitance of 47 pF), the curvature on both sides appears small. Therefore, by combining this with the compensation of the above-mentioned first-order slope, it is possible to always ensure the linearity of the modulation characteristics regardless of changes in the ambient temperature. However, if the change in the curvature on both sides of the modulation characteristic is not very large, a sufficiently flat wide band can be ensured only by compensating for the primary forehead slope. FIG. 6 is an explanatory diagram showing the configuration of an embodiment of the present invention according to the above principle.

This figure differs from FIG. 1 in that a bias control circuit 21 for temperature compensation is provided in place of the emitter current control circuit 11, and a temperature compensator 22 is added to the amplitude control circuit 10. As mentioned above, the bias control circuit 21 has a temperature-sensitive variable resistance element such as a thermistor inserted in series with the emitter bias circuit, and when the variable capacitance diode of the resonant circuit is kept at room temperature, it has the modulation characteristics as shown in Figure 4. 1 due to the temperature change shown in Figure 2.
Next, the slope can be compensated. The amplitude control circuit 10 in the original invention uses, for example, a variable capacitance diode and a diode connected in series, each of which is operated with a predetermined bias voltage.

The temperature compensator 22 of the present invention is connected in series with this, and an example thereof is shown in FIG. 322, a bias voltage is applied from the terminal 34 through the temperature-sensitive variable resistance element 33 such as a thermistor, and by providing the characteristics shown in FIG. 5 under the same conditions as in FIG. 4, both sides of the modulation characteristic are Curvature can be compensated. In this case, the variable capacitance diode 31 of the temperature compensator 22 of the present invention is connected to the amplitude control circuit 1.
These variable capacitance diodes have the same function as the variable capacitance diodes in 0, and also have a temperature compensation function, so these variable capacitance diodes can be used as a bias resistance element for linearizing the modulation characteristics at room temperature. , and a temperature-sensitive variable resistance element for temperature compensation may be connected in series to apply an appropriate bias voltage. As explained above, the present invention not only linearizes the modulation characteristics by controlling the amplitude ratio of the fundamental wave and harmonics of the oscillation frequency in the original invention, but also makes it possible to perform temperature compensation. .

In other words, changes in the primary slope of the modulation characteristic due to temperature changes are compensated for by a bias control circuit including a temperature-sensitive variable resistance element, and changes in curvature are compensated for by a temperature compensation fabric of an amplitude control circuit including a temperature-sensitive variable resistance element. Depending on the degree of change in modulation characteristics due to temperature change, only compensation for the primary forehead slope may be sufficient. Additional Relationship The present invention is an additional invention of Japanese Patent No. 1013758 No. 555283.

The invention comprises means for generating a fundamental wave and harmonics of an oscillation frequency, and means for controlling the amplitude ratio of the fundamental wave and harmonics of the oscillation frequency, which constitute the main part of the original invention. The fundamental wave and harmonics are added to the variable capacitance diode by controlling the amplitude ratio of the variable capacitance diode so that the capacitance change rate of the variable capacitance diode is 2. In addition, in the present invention, the feedback point to the oscillation element of the oscillation circuit is A bias control circuit was provided to change the bias voltage in response to temperature.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the FM modulator in the original invention, Fig. 2 is an explanatory diagram of changes in modulation characteristics with respect to temperature, Figs. An explanatory diagram showing the configuration of the embodiment. FIG. 7 is a detailed view of the main parts of the embodiment of FIG. , 6 is an inductance, 8 is a harmonic generator, 9 is a DC amplifier, 10' is an amplitude control circuit, 21 is a bias control circuit, and 22 is a temperature compensator. O figure O figure O 2 figure O figure 3 figure O figure O 4 figure O figure 5 figure O figure 6 off figure

Claims (1)

[Scope of Claims] 1. In an FM modulator in which a variable capacitance diode is provided in a part of a resonant circuit of an oscillation circuit and the capacitance of the variable capacitance diode is changed by an external voltage to shift the oscillation frequency, the resonant circuit of the oscillation circuit is a harmonic generator that generates harmonics of the oscillation frequency; an amplitude control circuit that controls the amplitude ratio and phase of the fundamental wave and the harmonics of the oscillation frequency; The fundamental wave and harmonics are added to the variable capacitance diode by controlling the amplitude ratio and phase of the harmonics so that the capacitance change rate of the variable capacitance diode is 2, and the feedback to the oscillation element of the oscillation circuit is An FM modulator comprising a bias control circuit that changes a bias voltage at a point in accordance with temperature. 2. In an FM modulator in which a variable capacitance diode is provided in a part of the resonant circuit of the oscillation circuit and the capacitance of the variable capacitance diode is changed by an external voltage to shift the oscillation frequency, the above-mentioned a harmonic generator that generates harmonics of an oscillation frequency; an amplitude control circuit that controls the ratio and phase of the amplitudes of the fundamental wave and harmonics of the oscillation frequency; The fundamental wave and harmonics are controlled to the variable capacitance diode so that the rate of change in capacitance of the variable capacitance diode is 2, and the bias voltage at the feedback point to the oscillation element of the oscillation circuit is controlled by changing the temperature. 1. An FM modulator, comprising: a bias control circuit that changes the bias voltage in accordance with the amplitude control circuit; and wherein the amplitude control circuit comprises a temperature compensator made of a variable capacitance diode that operates with a bias voltage that changes depending on temperature.