JPH09312524A - Frequency modulation circuit - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: I of satellite broadcasting receiver by digital transmission system
A Q-detector and a frequency modulation circuit with excellent phase noise characteristics that can be used in a channel selection section are realized. SOLUTION: First and second transistors 12 and 13 forming a differential circuit, and first and second capacitors 14 and 16 are connected between base and emitter terminals of the first and second transistors, The third capacitor 15 is connected between the emitter terminals of the first and second transistors, and the fourth and fifth capacitors 17 and 18 are connected to the base terminals of the first and second transistors, respectively, and one of them is connected. Of the balanced type negative resistance oscillation circuit configured with the respective terminals as input terminals, and an inductance is arranged between each input terminal of the balanced type negative resistance oscillation circuit and the ground. A resonance circuit including a capacitor and variable capacitance diodes 21 and 22 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency modulation circuit used in an IQ detector of a satellite broadcasting receiver using a digital transmission system.

[0002]

2. Description of the Related Art In satellite broadcasting, a video signal has been frequency-modulated and transmitted until now, but in recent years, a transmission system by phase modulation is being advanced using a communication satellite. In the case of conventional frequency modulation, a demodulation method using a PLL (Phase Lock Loop) in the 400 MHz band is general and is integrated into an IC. The demodulation is performed by providing a wide-band frequency modulator capable of producing a signal equivalent to the transmitted frequency-modulated signal, and forming the phase-locked loop of the output signal with a phase detector and a loop amplifier. It

The frequency modulator used for this is +/-
It is necessary that the frequency-modulation voltage has good linearity in the frequency bandwidth of 20 MHz or more. Therefore, in order to make a modulator that operates in such a wide band at a high frequency of 400 MHz into an IC, a patent registration number 184107
9: There is a circuit format as shown in "Frequency modulator".

This frequency modulator, as shown in FIG.
The base and collector of two transistors forming a differential circuit are connected by a series circuit of two capacitors so that positive feedback is applied to each other. A characteristic is that a resonance circuit is connected to the connection point of the two capacitors. When viewed from the middle point of the positive feedback circuit of the differential circuit, this resonant circuit can be regarded as a parallel resonant circuit for the oscillator that operates differentially.

Therefore, at the resonance frequency, the impedance at both ends of the resonance circuit becomes maximum, so that the positive feedback becomes maximum. Further, at a frequency away from the resonance frequency, its impedance becomes low, so the amount of positive feedback decreases. Therefore, oscillation occurs at this resonance frequency.

[0006]

As described above, in the conventional modulation circuit, the oscillation frequency range is wide because the positive feedback type oscillation circuit is used, and the oscillation signals are balanced because the differential circuit is used. Therefore, there is an advantage that it is suitable for IC. However, the collector load resistance and base resistance lowered the Q of the resonance circuit, and the purity of the oscillation signal (phase noise characteristic) was not very good. However, this is not a problematic level for demodulating a conventional FM satellite broadcast.

On the other hand, in the digital transmission method by phase modulation, in order to demodulate the QPSK signal, it is first detected by the regenerated carrier signal on the I and Q axes orthogonal to each other, and then transmitted by the regenerated clock signal. The data will be decrypted. The carrier signal is, for example, 480M
QP transmitted from an oscillator that oscillates in the Hz band
It is generated by extracting information from the SK signal and feeding it back. Therefore, this oscillator is a modulator, and its output must have excellent phase noise characteristics.

However, although the above-mentioned conventional type can obtain a sufficient wide band characteristic, it has a drawback that the phase noise characteristic is poor even if the resonance circuit has a narrow band.

[0009]

In order to solve the above problems, the frequency modulation circuit of the present invention comprises a first differential circuit.
A first capacitor is connected between the second transistor and the base-emitter terminal of the first transistor, and a second capacitor is connected between the base-emitter terminal of the second transistor; The third capacitor is connected between the emitter terminals of each of the transistors, and the fourth and fifth capacitors are connected to the base terminals of the first and second transistors, respectively, and one of these terminals is used as an input terminal. A balanced negative resistance oscillation circuit configured, and an inductance is arranged between each input terminal of the balanced negative resistance oscillation circuit and the ground, and the inductance, the capacitor, and the variable capacitance diode. It is characterized by having a resonance circuit composed of According to the present invention, it is possible to realize an IQ detector of a satellite broadcast receiver using a digital transmission system and a frequency modulation circuit having excellent phase noise characteristics that can be used in a channel selection unit.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a balanced-type negative resistance oscillation circuit composed of first and second transistors forming a differential circuit, and a base terminal of each of the transistors and ground. The placed inductance,
A resonant circuit composed of the inductance, the capacitor, and the variable capacitance diode is provided, and has an effect of realizing oscillation characteristics excellent in phase noise characteristics.

According to the present invention, first and second transistors forming a differential circuit, and a first capacitor connected between the base and emitter terminals of the first transistor,
A second capacitor connected between the base and emitter terminals of the second transistor; a third capacitor connected between the emitter terminals of each of the first and second transistors; Second and fifth capacitors respectively connected to the base terminals of the second transistor, a balanced negative resistance oscillation circuit configured by using one of these terminals as an input terminal, and the balanced negative resistance It is characterized by including an inductance arranged between each input terminal of the oscillation circuit and the ground, and a resonance circuit composed of the inductance, the capacitor and the variable capacitance diode. It has an effect of realizing oscillation characteristics excellent in noise characteristics.

According to the present invention, the inductance is arranged between each input terminal and the ground of the balanced type negative resistance oscillation circuit in the above invention, and the reverse polarity connected between the respective input terminals. It is characterized in that a resonance circuit composed of variable capacitance diodes connected in series is provided, and a control signal input terminal is provided at the midpoint of the variable capacitance diodes connected in series, and it has excellent phase noise characteristics. It has the effect of achieving excellent oscillation characteristics.

The present invention is characterized in that the inductance is a microstrip line in the above invention, and it is possible to realize an oscillation characteristic in which phase and frequency fluctuations due to mechanical vibration are relatively small.

According to the present invention, in the above-mentioned invention, the inductance is arranged between each input terminal and the ground of the balanced type negative resistance oscillation circuit, and the capacitor and the variable capacitance diode connected in parallel to the inductance. It is characterized in that a resonance circuit composed of circuits connected in series and a control signal input terminal is provided at one terminal of the variable capacitance diode, and it is possible to realize an oscillation characteristic excellent in phase noise characteristic. Have.

The present invention relates to the above-mentioned invention, in which the resonance circuit is composed of a series circuit of an inductance and a variable-capacitance diode which are respectively arranged between the input terminal and the ground of the balanced type negative resistance oscillation circuit. And a control signal input terminal is provided at one terminal of the variable capacitance diode, which has an effect of realizing oscillation characteristics excellent in phase noise characteristics in a high frequency band.

The present invention is characterized in that the inductance is a microstrip line in the above-mentioned invention, and can realize an oscillation characteristic in which the phase and frequency fluctuations due to mechanical vibration are relatively small.

According to the present invention, in the above invention, the inductance arranged between the respective input terminals of the balanced type negative resistance oscillation circuit and the variable capacitance diode connected in parallel to the inductance are connected in series in mutually opposite polarities. And a control signal input terminal is provided at the midpoint of the variable capacitance diode, and the Q value of the resonance circuit can be increased.
Since this resonance circuit has a symmetrical configuration with respect to the input of the balanced negative resistance oscillation circuit, it has a function of keeping the oscillation signal in a balanced state.

According to the present invention, in the above invention, a capacitor arranged between the input terminals of the balanced negative resistance oscillation circuit, a series connection circuit of the capacitor and the inductance, and a variable capacitance connected in parallel to the capacitor. A resonant circuit composed of a circuit in which diodes are connected in series with opposite polarities to each other, and a control signal input terminal is provided at the middle point of the variable capacitance diode, and the base terminal of the transistor is grounded. The Q value of the resonant circuit can be increased by increasing the resistance that is present sufficiently.

According to the present invention, first and second transistors forming a differential circuit are connected in series, and the collector terminal of the first transistor and the base terminal of the second transistor are connected in series. 2 capacitors,
A positive feedback oscillation circuit comprising third and fourth capacitors connected in series, which connects the collector terminal of the second transistor and the base terminal of the first transistor; and the positive feedback oscillation circuit of the balanced positive feedback oscillation circuit. A circuit in which an inductance arranged between a connection point of the first and second capacitors and a connection point of the third and fourth capacitors and a variable capacitance diode connected in parallel to the inductance are connected in series in mutually opposite polarities. And a control signal input terminal at the middle point of the variable capacitance diode.The resonance circuit is a target circuit for the input of a balanced negative resistance oscillation circuit. Since it has such a configuration, it has an effect of keeping the oscillation signal in a balanced state.

According to the present invention, in the above invention, there is provided a resonance circuit composed of a series circuit of an inductance and a variable capacitance diode arranged between respective input terminals of a balanced type negative resistance oscillation circuit, A control signal input terminal is provided at one terminal of the variable capacitance diode, and it is possible to realize oscillation characteristics excellent in phase noise characteristics in a high frequency band.

(Embodiment 1) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numerals 12, 13 are transistors, 14, 15, 16, 17, 18 are capacitors, 1
Reference numerals 9 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, 23 and 24 are air core coils, 25 is a control terminal, and 26 is a power supply terminal.

First, the negative resistance oscillation circuit will be described. The collectors of the transistors 12 and 13 are power supply terminals 2 respectively.
It is connected to 6 and is grounded. Each transistor has capacitors 19 and 2 between the base and emitter.
Connected by 0. The constant current sources 21 and 22 are for biasing the transistors, and it is important not to lower the impedance of the emitter by the bias circuit in order to keep the negative resistance value larger.

The bias of the transistor and the capacitance value of the capacitor can be selected so that the impedance when the base of the transistor is viewed from the capacitors 18 to 19 becomes a negative resistance. Since the capacitor 15 is connected to the emitters of the transistors 12 and 13, each transistor forms a balanced negative resistance oscillation circuit, and the oscillation signal is balanced between the transistors, so that the power supply circuit has a high frequency signal. Does not flow. Therefore, it is less likely to interfere with other circuit blocks, which is suitable for an IC.
Further, when they oscillate, the phases are opposite to each other, so that fundamental wave oscillation can be performed.

The resonance circuit is composed of variable capacitance diodes 21, 2
2 and air core coils 23 and 24. Since the air-core coil 23 has a sufficiently low impedance at direct current or low frequency, most of the modulation signal input to the control terminal 25 is applied to the variable capacitance diode 21. Therefore, a modulator having good frequency characteristics from low frequencies can be constructed.

Since the control terminal 25 can be considered as a virtual ground point for a negative resistance circuit having a differential structure, the impedance at this point hardly affects oscillation. Therefore, it is possible to drive with a slightly lower impedance,
Suitable for modulators that require wideband characteristics. Further, since the base terminals of the transistors are grounded by the air core coils 21 and 22, respectively, there is an advantage that oscillation in an unnecessary mode other than the resonance frequency of the resonance circuit does not easily occur. Further, since this resonance circuit has a symmetrical structure with respect to the input of the balanced type negative resistance oscillation circuit, the oscillation signal is kept in a balanced state. Variable capacitance diode 2
1 and the air core coil 24 are replaced, and the variable capacitance diode 2
Even when the air core coil 23 and the air core coil 23 are exchanged, the resonance circuit has a symmetrical structure, so that the oscillation signal maintains a balanced state.

The inductances of the air-core coils 23 and 24 vary slightly depending on the density of the windings. Therefore, there is an advantage that the oscillation frequency can be finely adjusted by changing the winding interval.

(Embodiment 2) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, 12 and 13 are transistors, 14, 15, 16, 17 and 18 are capacitors,
Reference numerals 19 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, 34 and 35 are microstrip lines, 25 is a control terminal, and 26 is a power supply terminal.

The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit comprises variable capacitance diodes 21, 2
2 and microstrip lines 34 and 35. Since the microstrip lines 34 and 35 have sufficiently low impedance at direct current or low frequency, most of the modulation signal input to the control terminal 25 is applied to the variable capacitance diodes 21 and 22.

Therefore, a modulator having good frequency characteristics from low frequencies can be constructed. Since the control terminal 25 can be considered as a virtual ground point for the negative resistance circuit of the differential configuration, the impedance at this point hardly affects the oscillation. Therefore, it can be driven with a slightly low impedance, and is suitable for a modulator that requires wide band characteristics.

Further, since the base terminals of the transistors are grounded by the microstrip lines 34 and 35, respectively, there is an advantage that oscillation in an unnecessary mode other than the resonance frequency of the resonance circuit is unlikely to occur. Furthermore, this resonance circuit is for the input of the balanced negative resistance oscillation circuit,
Since it has a symmetrical structure, the oscillating signal maintains a balanced state.

In the microstrip lines 34 and 35, the electromagnetic force tends to concentrate inside the dielectric of the printed circuit board, and the power radiation is smaller than that of the air core coil. Further, as compared with the air-core coil, mechanical vibration is less likely to occur in response to a mechanical shock from the outside, so that there is an advantage that frequency or phase noise at that time is less likely to occur.

The variable capacitance diode 21 and the microstrip line 35 are replaced with each other to replace the variable capacitance diode 2
Even if the 2 and the microstrip line 34 are exchanged, the resonance circuit has a symmetrical structure, and therefore the oscillation signal maintains a balanced state.

(Embodiment 3) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 3, 12 and 13 are transistors, 14, 15, 16, 17, 18, 30, and 31 are capacitors, 19 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, and 23 and 24 are empty. The core coil 25 is a control terminal, 26 is a power supply terminal, and 32 and 33 are resistors. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

As shown in FIG. 2, the resonance circuit includes resistors 32,
33, capacitors 30, 31, variable capacitance diode 2
1, 22 and air-core coils 23, 24. The capacitors 30 and 31 have a sufficiently low impedance with respect to the oscillating frequency and are short-circuited at high frequencies to cut off the DC bias. One resonance circuit is composed of a parallel resonance circuit including an air-core coil 23 and a variable capacitance diode 22. Further, a resonance circuit having the same structure is composed of the air-core coil 24 and the variable capacitance diode 21. By connecting them to the negative resistance circuit, it becomes possible to oscillate at high frequency. At that time, since the base terminals of the transistors are grounded by the air-core coils 21 and 22, respectively, there is an advantage that oscillation in an unnecessary mode other than the resonance frequency of the resonance circuit is unlikely to occur.

Further, since this resonance circuit has a symmetrical configuration with respect to the input of the balanced type negative resistance oscillation circuit, the oscillation signal is kept in a balanced state. The control terminal 25 is connected to the respective resonance circuits via the resistors 32 and 33. The control voltage is integrated with the sum of the capacitances of the capacitors 30 and 31 and the variable capacitance diodes 21 and 22 by the time constants of the resistors 32 and 33.
It cannot be expected to have such wide band characteristics.

The inductances of the air-core coils 23 and 24 vary slightly depending on the density of the windings. Therefore, there is an advantage that the oscillation frequency can be finely adjusted by changing the winding interval. Further, since the resonance circuit is a parallel resonance circuit, the Q value can be made higher than that of the series resonance circuit in a low frequency band where the inductance value is relatively large, which is suitable.

(Embodiment 4) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 4, 12 and 13 are transistors, 14, 15, 16, 17, and 18 are capacitors,
Reference numerals 19 and 20 are constant current sources, reference numerals 21 and 22 are variable capacitance diodes, reference numerals 23 and 24 are air core coils 25, control terminals, 26 are power supply terminals, and 32 and 33 are resistors. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit has resistors 32,
33, variable capacitance diodes 21 and 22, and air core coil 2
It is composed of 3 and 24. One resonance circuit is composed of a series resonance circuit of an air core coil 23 and a variable capacitance diode 22. Further, a resonance circuit having the same structure is composed of the air-core coil 24 and the variable capacitance diode 21. By connecting them to the negative resistance circuit, it becomes possible to oscillate at high frequency. Since this resonance circuit has a symmetrical configuration with respect to the input of the balanced negative resistance oscillation circuit, the oscillation signal is kept in a balanced state. The control terminal 25 is connected to the respective resonance circuits via the resistors 32 and 33.

Since the resonance circuit is a series resonance circuit, the Q value can be made higher than that of the parallel resonance circuit in a high frequency band where the inductance value is relatively small, which is suitable.

(Embodiment 5) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 5, 12 and 13 are transistors, 14, 15, 16, 17, and 18 are capacitors,
Reference numerals 19 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, 34 and 35 are microstrip lines, 25 is a control terminal, and 26 is a power supply terminal. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit is composed of variable capacitance diodes 21, 2
2 and microstrip lines 34 and 35. Since the microstrip lines 34 and 35 have sufficiently low impedance at direct current or low frequency, most of the modulation signal input to the control terminal 25 is applied to the variable capacitance diodes 21 and 22. Therefore, a modulator having good frequency characteristics from low frequencies can be constructed. Since the control terminal 25 can be considered as a virtual ground point for the negative resistance circuit of the differential configuration, the impedance at this point hardly affects the oscillation. Therefore, it can be driven with a slightly low impedance, and is suitable for a modulator that requires wide band characteristics.

Further, since the base terminals of the transistors are grounded by the microstrip lines 34 and 35, respectively, there is an advantage that oscillation in an unnecessary mode other than the resonance frequency of the resonance circuit is unlikely to occur. Furthermore, this resonance circuit is for the input of the balanced negative resistance oscillation circuit,
Since it has a symmetrical structure, the oscillating signal maintains a balanced state.

In the microstrip lines 34 and 35, electromagnetic force tends to concentrate inside the dielectric material of the printed circuit board, and the power radiation is smaller than that of the air core coil. Further, as compared with the air-core coil, mechanical vibration is less likely to occur in response to a mechanical shock from the outside, so that there is an advantage that frequency or phase noise at that time is less likely to occur.

The variable capacitance diode 21 and the microstrip line 35 are replaced with each other, and the variable capacitance diode 2 is replaced.
Even if the 2 and the microstrip line 34 are exchanged, the resonance circuit has a symmetrical structure, and therefore the oscillation signal maintains a balanced state.

(Embodiment 6) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 6, reference numerals 12 and 13 are transistors, 14, 15, 16, 17, and 18 are capacitors,
Reference numerals 19 and 20 denote constant current sources, 21 and 22 variable capacitance diodes, 23 and 24 air core coils, 25 control terminals, 26 power supply terminals, and 32 and 33 resistors. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit is composed of variable capacitance diodes 21, 2
This is a parallel resonance circuit composed of 2 and the air-core coil 23. The anode terminals of the variable capacitance diodes 21 and 22 are grounded by the resistors 32 and 33. The modulation signal input to the control terminal 25 is the variable capacitance diode 2
It is applied to the cathode side of Nos. 1 and 22, and its capacitance value changes depending on the control voltage. Since the control terminal 25 can be considered as a virtual ground point for the negative resistance circuit of the differential configuration, the impedance at this point hardly affects the oscillation. Therefore, driving with a slightly low impedance is possible. The Q value of the resonance circuit can be increased by sufficiently increasing the resistances 32 and 33 that ground the base terminals of the transistors. Further, since this resonance circuit has a symmetrical structure with respect to the input of the balanced type negative resistance oscillation circuit, the oscillation signal is kept in a balanced state.

The air-core coil 23 is
The inductance changes slightly. Therefore, there is an advantage that the oscillation frequency can be finely adjusted by changing the winding interval.

(Embodiment 7) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 7, reference numerals 12 and 13 are transistors, 14, 15, 16, 17, 18, 30, and 31 are capacitors, 19 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, and 23 is an air-core coil. , 25 are control terminals, 2
6 is a power supply terminal and 32 and 33 are resistors. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit is composed of variable capacitance diodes 21, 2
2 and the air-core coil 23, and the capacitors 30 and 31 are serial-parallel resonant circuits. Variable capacitance diode 2
The anode terminals of Nos. 1 and 22 are grounded by resistors 32 and 33, respectively. The modulation signal input to the control terminal 25 is applied to the cathode side of the variable capacitance diodes 21 and 22, and the capacitance value changes according to the control voltage. Since the control terminal 25 can be considered as a virtual ground point for the negative resistance circuit of the differential configuration, the impedance at this point hardly affects the oscillation. Therefore, driving with a slightly low impedance is possible. The Q value of the resonance circuit can be increased by sufficiently increasing the resistances 32 and 33 that ground the base terminals of the transistors.

Further, since this resonance circuit has a symmetrical structure with respect to the input of the balanced type negative resistance oscillation circuit, the oscillation signal is kept in a balanced state.

The air-core coil 23 is
The inductance changes slightly. Therefore, there is an advantage that the oscillation frequency can be finely adjusted by changing the winding interval.

(Embodiment 8) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numerals 12 and 13 denote transistors, 14, 15, 16, 17, and 18 denote capacitors, and 1
Reference numerals 9 and 20 are constant current sources, 21 and 22 are variable capacitance diodes, 23 and 24 are air core coils, 25 is a control terminal, and 26 is a power supply terminal.

First, the negative resistance oscillation circuit will be described. The collectors of the transistors 12 and 13 are power supply terminals 2 respectively.
It is connected to 6 and is grounded. Each transistor has capacitors 19 and 2 between the base and emitter.
Connected by 0. The constant current sources 21 and 22 are for biasing the transistors, and it is important not to lower the impedance of the emitter by the bias circuit in order to keep the negative resistance value larger. The bias of the transistor and the capacitance value of the capacitor can be selected so that the impedance when the base of the transistor is viewed from the capacitors 18 to 19 becomes a negative resistance. Since the capacitor 15 connects the emitters of the transistors 12 and 13, each transistor forms a balanced negative resistance oscillation circuit,
When they oscillate, they have opposite phases. Therefore, the fundamental wave can be oscillated.

The resonance circuit is composed of the variable capacitance diodes 21, 2
This is a parallel resonance circuit composed of 2 and the air-core coil 23. The anode terminals of the variable capacitance diodes 21 and 22 are grounded by the resistors 32 and 33. The modulation signal input to the control terminal 25 is the variable capacitance diode 2
It is applied to the cathode side of Nos. 1 and 22, and its capacitance value changes depending on the control voltage. Since the control terminal 25 can be considered as a virtual ground point for the negative resistance circuit of the differential configuration, the impedance at this point hardly affects the oscillation. Therefore, driving with a slightly low impedance is possible. The Q value of the resonance circuit can be increased by sufficiently increasing the resistances 32 and 33 that ground the base terminals of the transistors. Further, since this resonance circuit has a symmetrical structure with respect to the input of the balanced type negative resistance oscillation circuit, the oscillation signal is kept in a balanced state.

The inductances of the air-core coils 23 and 24 vary slightly depending on the density of the windings. Therefore, there is an advantage that the oscillation frequency can be finely adjusted by changing the winding interval.

(Embodiment 9) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 4, 12 and 13 are transistors, 14, 15, 16, 17, and 18 are capacitors,
Reference numerals 19 and 20 are constant current sources, reference numerals 21 and 22 are variable capacitance diodes, reference numerals 23 and 24 are air core coils 25, control terminals, 26 are power supply terminals, and 32 and 33 are resistors. The negative resistance oscillating circuit is the same as that shown in FIG. 1 in the first embodiment, and its explanation is omitted.

The resonance circuit has resistors 32,
33, variable capacitance diodes 21 and 22, and air core coil 2
It is composed of 3 and 24. Resonance circuit is air core coil 2
It is configured by a series resonance circuit of 3, 24 and variable capacitance diodes 21, 22. By connecting them to the negative resistance circuit, it becomes possible to oscillate at high frequency. Since this resonance circuit has a symmetrical configuration with respect to the input of the balanced negative resistance oscillation circuit, the oscillation signal is kept in a balanced state. The control terminal 25 is connected to the respective resonance circuits via the resistors 32 and 33. Further, since the resonance circuit is a series resonance circuit, the Q value can be made higher than that of the parallel resonance circuit in a high frequency band where the inductance value is relatively small, which is suitable.

As shown in FIG. 9, the inductance 2
Even if 3, 24 are replaced with microstrip lines 34, 35, oscillation can be similarly performed. In the case of the microstrip line, there is an advantage that the phase and frequency fluctuations are small against vibration. Further, the microstrip line does not necessarily have to be divided into two and may be one line.

[0069]

As described above, according to the present invention, it is possible to realize an IQ detector of a satellite broadcasting receiver by a digital transmission system and a frequency modulation circuit having excellent phase noise characteristics which can be used for a channel selection section.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a frequency modulation circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a frequency modulation circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a frequency modulation circuit according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a frequency modulation circuit according to a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram of a frequency modulation circuit according to a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram of a frequency modulation circuit according to a sixth embodiment of the present invention.

FIG. 7 is a circuit diagram of a frequency modulation circuit according to a seventh embodiment of the present invention.

FIG. 8 is a circuit diagram of a frequency modulation circuit according to an eighth embodiment of the present invention.

FIG. 9 is a circuit diagram of a frequency modulation circuit according to a ninth embodiment of the present invention.

FIG. 10 is a circuit diagram of a frequency modulation circuit in a conventional example.

[Explanation of symbols]

12, 13 Transistors 14, 15, 16, 17, 18, 30, 31 Capacitors 19, 20 Constant current sources 21, 22 Variable capacitance diodes 23, 24 Air core coil 25 Control terminals 26 Power supply terminals 32, 33 Resistors 34, 35 Micro Strip line

Front page continuation (72) Inventor Hiroshi Azagami 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] 1. A balanced negative resistance oscillation circuit including first and second transistors forming a differential circuit, and an inductance arranged between each base terminal of the transistor and ground. A frequency modulation circuit comprising a resonance circuit composed of the inductance, a capacitor, and a variable capacitance diode. 2. A first and second transistor forming a differential circuit, a first capacitor connected between a base and an emitter terminal of the first transistor, and the second transistor.
A second capacitor connected between the base and emitter terminals of the first transistor, a third capacitor connected between the respective emitter terminals of the first and second transistors, and the first and second transistors Of the fourth and fifth capacitors respectively connected to the base terminals of the balanced negative resistance oscillation circuit and one of these terminals as an input terminal; A frequency modulation circuit comprising: an inductance arranged between each input terminal and ground; and a resonance circuit composed of the inductance, a capacitor, and a variable capacitance diode. 3. An inductance arranged between each input terminal of the balanced type negative resistance oscillation circuit and the ground, and a series connected in reverse polarity connected to each other between the respective input terminals. 3. The frequency modulation circuit according to claim 2, wherein a resonance circuit composed of a variable capacitance diode and a control signal input terminal are provided at a midpoint of the variable capacitance diodes connected in series. 4. The frequency modulation circuit according to claim 2, wherein the inductance is a microstrip line. 5. A circuit in which an inductance arranged between an input terminal and a ground of a balanced type negative resistance oscillation circuit, respectively, and a capacitor and a variable capacitance diode connected in parallel to the inductance are connected in series. 3. The frequency modulation circuit according to claim 2, further comprising: a resonance circuit composed of the variable capacitance diode and a control signal input terminal provided at one terminal of the variable capacitance diode. 6. A resonance circuit composed of a series circuit of an inductance and a variable capacitance diode, each of which is arranged between an input terminal and a ground of a balanced negative resistance oscillation circuit, and the variable capacitance. The frequency modulation circuit according to claim 2, wherein a control signal input terminal is provided at one terminal of the diode. 7. The frequency modulation circuit according to claim 6, wherein the inductance is a microstrip line. 8. A circuit in which an inductance arranged between respective input terminals of a balanced negative resistance oscillation circuit and a variable capacitance diode connected in parallel to the inductance are connected in series in mutually opposite polarities. 3. The frequency modulation circuit according to claim 2, further comprising a resonance circuit and a control signal input terminal provided at a middle point of the variable capacitance diode. 9. A capacitor arranged between input terminals of a balanced type negative resistance oscillation circuit, a series connection circuit of the capacitor and an inductance, and a variable capacitance diode connected in parallel to the capacitor have opposite polarities. 3. The frequency modulation circuit according to claim 2, further comprising a resonance circuit including a circuit connected in series with the control circuit, and a control signal input terminal provided at a middle point of the variable capacitance diode. 10. A first and a second transistor, which are connected in series, connecting a first and a second transistor forming a differential circuit, and a collector terminal of the first transistor and a base terminal of the second transistor. A positive feedback oscillation circuit comprising a capacitor, and third and fourth capacitors connected in series to connect the collector terminal of the second transistor and the base terminal of the first transistor, and the balanced positive feedback oscillation circuit. An inductance arranged between a connection point of the first and second capacitors and a connection point of the third and fourth capacitors of the circuit, and a variable capacitance diode connected in parallel with the inductance are connected in series in mutually opposite polarities. And a resonance circuit composed of a controlled circuit and a control signal input terminal at the midpoint of the variable capacitance diode. Modulation circuit. 11. A resonance circuit composed of a series circuit of an inductance and a variable capacitance diode arranged between respective input terminals of a balanced type negative resistance oscillation circuit, and one of the variable capacitance diode. The frequency modulation circuit according to claim 2, wherein a control signal input terminal is provided at the terminal.