JPS604609B2 - 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 high frequency of the oscillation frequency, and compensates for changes in modulation characteristics due to temperature. It is.

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 '11 where Vo: operating voltage Co: capacitance at operating point n: rate of change in capacitance at operating point When this variable capacitance diode is used as part of the resonant circuit of a modulator, its oscillation frequency f is 1
[2} f = Hiroki where L: Inductance of the resonant circuit From formula '11, ■, f = point V.

The value becomes '3', and the wider the range that satisfies the condition of n=2, the wider the linearity of the modulator becomes.

However, when this variable capacitance diode is conventionally mounted in a modulator, the linear curve of the modulator is affected by the variable capacitance diode's operating voltage Vo, operating point capacitance Co, and operating point capacitance change rate n, as shown in the above equation. However, it is difficult to satisfy n=2 over a wide band in terms of diode fabrication, and due to the non-uniformity of diode fabrication characteristics, it is difficult to satisfy n = 2 over a wide band. Methods such as limiting the oscillation frequency band or 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, the original invention, Japanese Patent No. 1013758, includes means for generating harmonics of the oscillation frequency in the oscillation circuit of the modulator;
a resonant circuit, comprising means for changing the amplitude ratio and phase of the fundamental wave and harmonics of the oscillation frequency; By controlling the capacitance change rate of the variable capacitance diode provided in a part of the variable capacitance diode to be 2, and adding the fundamental wave and harmonics to the variable capacitance diode', linearity over a wide band is obtained.
We offer M 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 (110 V), and the base via the capacitor 7 and ground. A bias (-10V) is fed back to the emitter via an inductance 6, and a modulation input 1 is inserted between a variable capacitance diode 3 and a capacitor 4, and FM modulation is performed by the voltage versus capacitance characteristic of the variable capacitance diode 3. In contrast to the configuration of the conventional FM modulator described above, 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 and passes it through the DC amplifier 9 to generate harmonics. The wave generator 8 is controlled.

Furthermore, an amplitude control circuit 10 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 101 via the inductance 6, while the emitter current control circuit 11 controls the amplitude of the oscillation frequency, and the amplitude control circuit 10' further controls the ratio of the amplitude of the harmonic to the fundamental wave. By controlling this, linearity over a wide band can be ensured.

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,
No compensation for temperature.

In reality, as shown in FIG. 2, the modulation characteristics vary significantly depending on the ambient temperature. In this figure, the horizontal axis shows the frequency, for example, 14 MHZ - 20 MHZ, and the vertical axis shows the modulation characteristics as a proportional characteristic.The temperature change is used as a parameter, -500 at low temperature, +25 °C at normal temperature, and +55 qo at high temperature. is plotted. In other words, as a result of the improvement by the harmonic component in the original invention, it shows almost flat characteristics near 250C, but at -5℃ it shows a characteristic of 120MHZ.
The differential gain near 120 MHz becomes high and the slope shows a descending characteristic, and conversely, at 155 pm, the differential gain near 120 MHz decreases but the slope changes to a rising characteristic. This deterioration in the linearity of the modulation characteristics due to temperature is dominated by the temperature characteristics of a variable capacitance diode, such as a varactor.In other words, at low temperatures, the oscillation amplitude increases due to an increase in the Q of the varactor; This is due to a decrease in the oscillation amplitude due to a decrease in Q.The purpose of the present invention is to linearize the modulation characteristics by controlling the amplitude ratio and phase of the fundamental wave and harmonics, and to achieve FM modulation that compensates for 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 changes the capacitance of the variable capacitance diode by an external voltage to generate oscillation. In an FM modulator that shifts the frequency, a harmonic generator that generates harmonics of the oscillation frequency in a feedback loop including a resonant circuit of the oscillation circuit, and a ratio and phase of the amplitude of the fundamental wave and the harmonics are controlled. an amplitude control circuit, 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 controlling the fundamental wave and the harmonics to the variable capacitance diode. In addition to this, the amplitude control circuit is characterized in that it includes a temperature compensator comprising a diode and a variable capacitance diode, each of which is operated by a bias voltage that changes with temperature.

The principle and embodiments of the present invention will be explained in detail below. Assume that the voltage vs. capacitance characteristic of the variable capacitance diode is expressed by the equation {1), and when this relational expression is expressed as a polynomial by the displacement voltage v from the operating point voltage Vo of the varactor, C=C.

(V. 10v) 1o=Cow-n+OW-n-1(-n〉
V+Cow-.

-2n(n+,)V22! 10------+COW-n
-k(-・)k(nirak)! Vk(4)k! becomes.

When a displacement voltage of v is applied to this variable capacitance diode, the current i that flows is i = magazine (VC) [51 When the capacitance C is constant and v = a, cos t, the current i
is i=-Ca, ■sinwt
The side (C constant) capacitance value is C=-”-
'dt.

Next, if the capacitance C is not constant, substitute the formula ■ into the formula [5}' *i=group (C1V fort)'7} i=group k≧.

C. V. -n-k (-state n-10k)! ratio! )(n-
1)! (10k) vk From the side formula {6}', C = table.

Desk-n-ku elementary school 10k)! water! )(n-1)k (10k)vk (9r Displacement voltage v includes harmonics q v=p≧lapcosp t '10 where ap is the P-order harmonic amplitude, the current is expressed as can be obtained by substituting into equation '9}.

Now, we can easily convert the equation (■) to V by considering up to the second harmonic.
(2) Calculating the current when t of S+a2t of COS2 (11) From formula '9', -I;6;=(t of Sin)X[1-M2V.

→ Juzenkua-tei + Saemuro) V. }n (n11) - 1 (Kasa-tei a
20 powder stalks) V. pn(n+1)(n+2)]12(Si
n's t)X [a2 one trick・a≧-V. ” n + good (2 ≧ 10a grave) V. Zenn(n+1)-Hiroshimejuku≧)V. -3nkun+1)(n+2)] 13Gin t)X[-a・alsoV
. 1n+sa (a reed ten powder. a reference) V. ) n (n+.) - quantity (a to 20 to a stalk) V. -3n(n11)(n+2)] (12) In formula (12), if we focus only on the fundamental wave, the capacitance value C for the fundamental wave is calculated from the formula
.

10 good (a character + pine) V. -2nkuh11)-Poison (Kasa-tei-a20$ stem)V. Go n + (n + 1) ku n 12)} (
13) In other words, when the voltage applied to a variable capacitance diode is only the fundamental wave, the capacitance value for the operating voltage is expressed by the formula {9
}', and when the voltage applied to the variable capacitance diode includes a second harmonic in addition to the fundamental wave, the capacitance value with respect to the operating voltage is shown by equation (13). Generally, the capacitance change G rate n can be expressed as follows.

At this time, C=CoVm 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 fundamental wave and harmonics is applied to the variable capacitance diode can be obtained. That is, d=nXI−(n+1
) is 2Vo-1 ten (. ten,) (n+2) saze ten two. Season)
W-21-nQ2W-10n (n+・) recommendation+2be) last year 2・kun−. )(n+2)(n+3) units (4Q≧.2ju3&)en-3 0 phrase-n(nten・)(n+2) also (4Q
≧Q2130) W-3 Now, in order to see the change in n' with respect to the second harmonic, the characteristics of the varactor are set to n=2, a, /Vo
An example of how n' changes when a2/Vo is changed is shown in FIG. 3, assuming that =1/3.

From FIG. 3, when a2>0, baldness<nvo When a2<0, baldness>nvo Here, nvo represents the capacitance change rate 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, the ratio of the amplitude of the base fence and the second harmonic, and the positive/negative phase, the modulation characteristics can be linearized as in the case of the original invention. be able to. 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. As shown in Figure 2, changes in modulation characteristics (differential gain) due to temperature are caused by changes in the primary slope, which shows a decreasing characteristic at low temperatures and an increasing characteristic at high temperatures, and changes in the curvature on both sides of each characteristic. Can be divided.

This change in the primary slope can be controlled by connecting a temperature compensation diode in series with the amplitude control circuit 10 shown in FIG. The modulation characteristics when the variable capacitance diode in the circuit is kept at room temperature are shown in the second diagram as shown in Figure 4.
It is possible to have an inclination that is opposite to the primary obliquity shown in the figure. For example, at a low temperature of -5°C, a high bias resistance (440) will increase the characteristic, and at a room temperature of 125°C, an intermediate bias resistance (330
), it is possible to have a flat characteristic, and at a high temperature of +55 qo, it is possible to have a falling characteristic with a low bias resistance (220). On the other hand, the change in curvature is similarly compensated by connecting a variable capacitance diode, such as a varactor, in series with the amplitude control circuit 10', and applying a bias voltage to both ends of the variable capacitance diode through a temperature-sensitive variable resistance element.

In other words, as shown in Figure 5, it exhibits a flat characteristic at room temperature of 25°C, and the curvature on both sides becomes large at low temperature of -5°C.
At 5500, the curvature on both sides appears small. If this curvature is combined with the above-mentioned primary slope, it is possible to sufficiently compensate for the change in the modulation characteristics shown in FIG. 2 due to temperature. FIG. 6 is an explanatory diagram showing the configuration of an embodiment of the present invention according to the above principle.

The difference between this figure and FIG. 1 is that a temperature compensator 21 is added to the amplitude control circuit 10, and the other configuration is
As shown in the figure. The amplitude control circuit 10 in the FM modulator of the nuclear power plant team shown in FIG. 1 has, for example, a variable capacitance diode and a diode connected in series, each of which is operated at a predetermined bias voltage.

On the other hand, the temperature compensator 21 of the present invention is connected in series, for example, as shown in FIG. A bias voltage is applied from both ends of the diode 31 via the choke coils 33, 332 and a temperature variable resistance element such as the thermistor 35 from the terminal 37, and similarly from both ends of the variable capacitance diode 32 via the choke coils 34, 342. thermistor 36
A bias voltage is applied from the terminal 38 through the terminal 38. In this way, the diode 31 and the variable capacitance diode 32
If the effects on the modulation characteristics due to temperature are made as shown in Figures 4 and 5, respectively, the changes in the modulation characteristics due to temperature in Figure 2, that is, the changes in the primary slope and the changes in curvature, will be effectively It becomes possible to compensate.

In this case, the temperature compensator 21 of the present invention has the same function as the amplitude control circuit 10, but the purpose of the latter is, for example, to linearize the characteristics with respect to room temperature, whereas the purpose of the former is to compensate for the temperature of the latter. The purpose is to provide a temperature variable resistance element separately for this purpose. Therefore, the variable capacitance diodes of the amplitude control circuit 10 and the temperature compensation section 21 are made common, and a bias resistance element for linearizing the modulation characteristics at room temperature and a temperature-sensitive variable resistance element for temperature compensation are connected in series. Then, an appropriate bias voltage may be applied or released. As explained above, the present invention not only linearizes the modulation characteristics of the fundamental wave and harmonic components at the head of a nuclear power plant, but also enables temperature compensation thereof.

In other words, changes in the primary slope and curvature of the modulation characteristic due to temperature changes can be effectively compensated for by the temperature compensating section each comprising a diode including a sensitive variable resistance element and a variable diode. Additional Relationship The present invention is an additional invention of Japanese Patent No. 1013758-55-5283.

In the original invention, the means for controlling the ratio of the amplitude of the fundamental wave and the harmonics of the oscillation frequency is provided with a temperature compensation section consisting of a diode and a variable capacitance diode each operated by a bias voltage that changes with temperature, and modulation characteristics based on temperature changes are provided. This effectively compensates for changes in primary slope and curvature.

[Brief explanation of the drawing]

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 inductor, 8 is a harmonic generator, 9 is a DC amplifier, 10 is an amplitude control circuit, 11 is an emitter current control circuit, and 21 is a temperature compensation section. Juice 1 figure Juice 2 figure, 3 figure O 4 figure O figure 5 O figure 6 off figure

Claims (1)

[Claims] 1. 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; and an amplitude control circuit that controls the amplitude ratio and phase of the fundamental wave and harmonics of the oscillation frequency; and the phase thereof are controlled so that the capacitance change rate of the variable capacitance diode is 2, and the fundamental wave and harmonics are applied to the variable capacitance diode, and the amplitude control circuit is provided with a bias voltage that changes depending on temperature. FM characterized by comprising a temperature compensating section formed by connecting in series a diode that changes the equivalent resistance and a variable capacitance diode that changes the equivalent capacitance by applying a bias voltage that changes depending on the temperature.
modulator.