JPH0631211U - Voltage controlled oscillator - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a voltage controlled oscillator that is less susceptible to external noise by stabilizing the ground of a variable capacitance diode. [Structure] An inductance element 22 is connected in series to a capacitor 16 which grounds the variable capacitance diode 12, and the resonance frequency of a series resonance circuit constituted by the capacitor 16 and the inductance element 22 is set to the oscillation frequency of the voltage controlled oscillator. It is set in the vicinity.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a voltage controlled oscillator in which frequency modulation is performed using a variable capacitance diode, and more specifically to a means for making it less susceptible to noise externally applied to the voltage controlled oscillator.

[0002]

[Prior art]

 FIG. 4 is a circuit diagram showing an example of a conventional voltage controlled oscillator. This voltage controlled oscillator is an example of Colpitts type, and is provided with an oscillating transistor 2, a resonance circuit 6 connected to its base circuit via a coupling capacitor 4, and the like. In this example, the resonance circuit 6 is formed by connecting a variable capacitance diode 12 in series to a capacitor 10 in parallel with a coil 8, and a control voltage V applied to the variable capacitance diode 12 is used. _C The oscillation frequency is controlled by changing the capacitance of the variable capacitance diode 12. 14 is a choke coil.

FIG. 5 shows a voltage-controlled oscillator to which a modulation circuit is added. The frequency modulation of the output signal is usually performed by inputting the modulation signal V _M divided by the resistors 18 and 20 to the anode side of the variable capacitance diode 12 as in this example. By doing so, the capacity of the variable capacitance diode 12 can be changed by the modulation signal V _M , and therefore frequency modulation can be applied.

In order to apply the modulation signal V _M divided by the resistors 18 and 20 to the anode of the varactor diode 12, it is necessary to disconnect the anode side from the ground in a direct-current manner. It is grounded via 16.

The capacitor 16 uses a capacitance (electrostatic capacitance) that is sufficiently large with respect to the operating frequency (that is, the oscillation frequency of the voltage controlled oscillator), so that the impedance (Z = 1) with respect to the high frequency thereof is / JωC) becomes low, and the same effect as grounding the anode side of the variable capacitance diode 12 to ground is obtained for high frequencies.

[0006]

[Problems to be solved by the device]

 However, the above-mentioned capacitor 16 has a self-resonant frequency because an actual capacitor does not have an ideal electrostatic capacity but has an inductance component, and a frequency exceeding the self-resonant frequency is sufficient. Even with a large capacitance, it becomes inductive and loses its function as an electrostatic capacitance, and it becomes impossible to perform sufficient grounding on the node side of the variable capacitance diode 12.

As a result, the grounding of the variable-capacitance diode 12 becomes unstable, and it becomes easy to be affected by noise from the outside entering the grounding circuit. That is, a noise component appears strongly in the output of the voltage controlled oscillator.

As a countermeasure against this, conventionally, for example, by arranging the wiring of this voltage-controlled oscillator or other circuits that are assembled in the vicinity of the voltage-controlled oscillator, the ground circuit of the variable capacitance diode 12 can be protected from the outside. We tried to prevent noise from jumping in as much as possible, but such a method is very inconvenient because it not only limits the freedom of wiring but also requires a lot of time for its design.

Therefore, the main object of the present invention is to provide a voltage-controlled oscillator which is less susceptible to the influence of noise given from the outside by stabilizing the ground of the variable capacitance diode as described above.

[0010]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the voltage controlled oscillator of the present invention connects an inductance element in series with a capacitor that grounds the variable capacitance diode described above, and resonates a series resonance circuit composed of this capacitor and the inductance element. The frequency is set to be near the oscillation frequency of the voltage controlled oscillator.

[0011]

[Action]

 According to the above configuration, the series resonance circuit composed of the capacitor and the inductance element causes series resonance near the oscillation frequency of the voltage controlled oscillator to reduce the impedance, so that the variable capacitance near the oscillation frequency is reduced. Stabilizes the ground of the diode. As a result, this voltage controlled oscillator is less susceptible to the noise given from the outside.

[0012]

【Example】

 FIG. 1 is a circuit diagram showing a voltage controlled oscillator according to an embodiment of the present invention. The same or corresponding portions as those of the conventional example shown in FIG.

In this embodiment, an inductance element 22 is connected in series to a capacitor 16 whose ground is connected to the anode side of the variable capacitance diode 12 described above, and a series resonance circuit including the capacitor 16 and the inductance element 22 is connected. The resonance frequency is set to near the oscillation frequency of the voltage controlled oscillator by adjusting the values of the capacitor 16 and the inductance element 22.

More specifically, a capacitor 16 having a self-resonance frequency higher than the oscillation frequency of the voltage-controlled oscillator is used, and an inductance element 22 is combined with the capacitor 16 to cause series resonance, The impedance of the series resonance circuit near the oscillation frequency of the voltage controlled oscillator is smaller than that of the capacitor 16 alone.

Therefore, the resonance frequency of the series resonance circuit does not necessarily have to match the oscillation frequency of the voltage controlled oscillator, and the impedance of the series resonance circuit becomes smaller than that of the case of the capacitor 16 alone. The frequency should be close to the oscillation frequency.

The oscillation frequency of the voltage controlled oscillator is not one frequency but a frequency within a range that can be controlled by the control voltage V _C described above.

According to the above, the series resonance circuit formed of the capacitor 16 and the inductance element 22 causes series resonance near the oscillation frequency of the voltage controlled oscillator to reduce its impedance. In other words, the grounding of the variable-capacitance diode 12 in the vicinity of the used frequency is stabilized. As a result, even if noise with a frequency close to the oscillation frequency enters the grounding circuit of the variable capacitance diode 12 from the outside, the grounding is stable and the noise can be effectively dropped to the ground. it can. Therefore, this voltage controlled oscillator is less likely to be affected by noise given from the outside.

In addition, by making it less susceptible to noise in this way, the degree of freedom in routing the wiring of this voltage controlled oscillator or other circuits built in the vicinity thereof is improved, and the design thereof is also made. It will be easier.

Next, a more specific embodiment of the present invention will be described by taking the case where the oscillation frequency is in the 800 MHz band as an example.

When the oscillation frequency is in the 800 MHz band, in the conventional voltage controlled oscillator of FIG. 5, the capacitance of the capacitor 16 is usually selected to be 100 pF to 1000 pF. When the capacitor 16 is a multi-layer capacitor of 100 pF, it usually has a self-resonant frequency around 600 MHz, becomes inductive in the 800 MHz band, does not function as a capacitance, and the impedance in the 800 MHz band increases. Will end up.

On the other hand, in this embodiment, the capacitor 16 is composed of a laminated multilayer capacitor having a capacitance of 18 pF, and the inductance element 22 is composed of an electrode pattern having an inductance of 1 nH. The self-resonant frequency of the 18 pF capacitor 16 is around 1.1 GHz, and it works sufficiently as an electrostatic capacitance in the 800 MHz band. The resonance frequency of the series resonance circuit in which this is combined with the 1 nH inductance element 22 is around 840 MHz.

With respect to each of the voltage controlled oscillator of the conventional example and the voltage controlled oscillator of the embodiment as described above, an oscillation frequency is set to around 890 MHz, and a conductor through which a signal having an oscillation frequency of +100 KHz flows is connected to each voltage controlled oscillator. By bringing them close to each other, the signal of the above frequency component was forcibly input as noise to each voltage controlled oscillator as radiation from the conductor. An example of the measurement result of the frequency spectrum of the output of each voltage controlled oscillator in that case is shown in FIG. 2 (for the conventional example) and FIG. 3 (for the example), respectively.

In both figures, A is the original oscillation frequency component, B is the noise component, and C is the frequency component (oscillation frequency −100 KHz and oscillation frequency −200 KHz) in which both components are mixed.

The noise component B of the embodiment of FIG. 3 is smaller than that of the conventional example of FIG. 2 by 10 to 12 dB. Along with this, the mixed frequency component C is also reduced. Thus, it can be seen that the voltage controlled oscillator of this embodiment is very unlikely to be affected by externally applied noise.

It is to be noted that, in various cases, a signal (noise) having a frequency near the oscillation frequency is input to the voltage controlled oscillator as described above, for example, by using a voltage controlled oscillator, a PLL (phase locked loop) circuit is used. In such a case, if the countermeasure against noise of the voltage controlled oscillator is bad, the frequency of the PLL circuit becomes unstable. Even in such a case, if the voltage controlled oscillator of the present invention is used, a great effect can be obtained.

[0026]

[Effect of device]

 As described above, according to the present invention, the variable capacitance diode is grounded by the series resonance circuit composed of the capacitor and the inductance element as described above, and the series resonance circuit is the oscillation frequency of the voltage controlled oscillator. Since series resonance occurs in the vicinity and its impedance decreases, the grounding of the variable capacitance diode near the oscillation frequency is stabilized. As a result, the voltage controlled oscillator of the present invention is less susceptible to the noise given from the outside.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a voltage controlled oscillator according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a result of measuring a frequency spectrum of an output of a conventional voltage controlled oscillator when noise is forcibly input.

FIG. 3 is a diagram showing an example of a result of measuring a frequency spectrum of an output of the voltage controlled oscillator of the embodiment when noise is forcibly input.

FIG. 4 is a circuit diagram showing an example of a conventional voltage controlled oscillator.

FIG. 5 is a circuit diagram showing an example of a conventional voltage controlled oscillator to which a modulation circuit is added.

[Explanation of symbols]

2 Oscillation transistor 6 Resonance circuit 12 Variable capacitance diode 16 Capacitor 22 Inductance element V _C Control voltage V _M Modulation signal

Claims (1)

[Scope of utility model registration request] 1. A voltage-controlled oscillator having a variable capacitance diode in a resonance circuit, wherein an oscillation frequency is controlled by a control voltage applied to the variable capacitance diode, wherein one end side of the variable capacitance diode is provided. Is grounded via a capacitor, and a modulation signal is input to one end of the capacitor for frequency modulation, and an inductance element is connected in series to the capacitor,
A voltage-controlled oscillator characterized in that a resonance frequency of a series resonance circuit composed of this capacitor and an inductance element is set near an oscillation frequency of the voltage-controlled oscillator.