JP2011035755A - High frequency band voltage controlled oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To making the frequency of an oscillating frequency high, even under a voltage reduction tendency of a logic circuit to be used for a PLL (Phase Locked Loop) circuit while reducing a tolerance of the oscillating frequency in a resonance circuit. <P>SOLUTION: In an LC tuning type voltage controlled oscillator for variably controlling an oscillating frequency, on an emitter side of an oscillation transistor 1, two short stubs P1 and P2 comprising microstrip lines of the same line length are formed between a pair of through-holes H1 and H2 which become a ground potential, and an emitter of the transistor 1 is connected between the short stubs P1 and P2. Namely, the short stubs P1 and P2 are connected in parallel at a position where they become symmetric around an emitter connecting point. Furthermore, a control voltage Vt of 0 to 5 V is applied to a cathode of a varactor Cv DC-cut by capacitors C1 and C2, and a reference voltage, for example, the reference voltage of -5V is applied from a reference voltage source 6 to an anode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-frequency band voltage controlled oscillator, and more particularly to a configuration of a voltage controlled oscillator that can be used as a component of a PLL circuit and can generate a high oscillation frequency exceeding an L-band microwave frequency.

  A voltage controlled oscillator (VCO) is used as a component of a PLL circuit that generates a local oscillation frequency of a converter for satellite communication. In this PLL circuit, a local oscillation frequency is directly oscillated using a high frequency resonator. Alternatively, there is a method of obtaining a desired high frequency by oscillating at a low frequency by a voltage controlled oscillator configured with an LC tuned circuit and multiplying the oscillation frequency. The above direct oscillation method has a high Q value, so it has high stability and low phase noise. On the other hand, the resonance frequency is high, so the peripheral circuit components are expensive and the mechanical structure has a large effect on the frequency. Therefore, the difficulty during production is high.

  On the other hand, in the voltage controlled oscillator of the multiplying method, the peripheral circuit components can be configured at low cost because it oscillates at about 1/5 to 1/2 of the local oscillation frequency, and it is difficult to be influenced by the mechanical structure, but compared with the direct oscillation method. Q value is low, and stability and phase noise performance are inferior. However, in recent years, with the advancement of frequency multiplying devices and circuit technology, more frequent VCOs that can construct inexpensive PLLs while satisfying required performance have been adopted. There is a growing need for higher accuracy.

  FIG. 4 shows an example of a resonance circuit of a conventional voltage controlled oscillator constituted by an LC tuned circuit including a microstrip line. In this circuit, a ground potential is provided on the emitter side of the oscillation transistor 1. A short stub P3 is connected between the through hole H4 and a varactor diode (hereinafter simply referred to as a varactor) Cv and a capacitor C3 are directly connected between the through hole H3 and the ground potential. Then, for example, a loop filter constituting a PLL (Phase Locked Loop) circuit is connected to the connection point between the varactor Cv and the capacitor C3 via the coil L3. According to the voltage controlled oscillator having such a resonance circuit, the control voltage Vt supplied from the loop filter of the PLL circuit is applied to the varactor Cv, and the capacitance value of the varactor Cv is changed, so that a desired oscillation frequency can be obtained. can get.

JP 2004-320664 A JP 2002-190709 A

  By the way, in order to increase the oscillation frequency in the voltage controlled oscillator constituting the PLL circuit, it is necessary to increase the resonance frequency of the resonance circuit, which reduces the circuit constants of the components constituting the circuit. Can be realized. However, when the circuit constant of a component is reduced, the actual value of the circuit constant is determined by the mechanical control resolution of the manufacturing apparatus for the component, and therefore the tolerance tends to be relatively larger than that of a component having a large circuit constant.

  The conventional resonance circuit shown in FIG. 4 has a capacitor C3, a varactor Cv, and a short stub P3. The capacitance tolerance of the capacitor C3 and the positional tolerance of the through hole H3 directly affect the resonance frequency of the short stub P3. Accordingly, these tolerances become oscillation frequency tolerances, and in the case of a PLL circuit, the result is a tolerance of the control applied voltage. Therefore, in order to set the oscillation frequency high, the modulation sensitivity (the control voltage for a certain modulation frequency width) The need to widen the width will increase.

On the other hand, it is known that the capacitance value of the varactor Cv changes with the applied voltage, but the equivalent resistance value also changes at the same time. As shown in FIG. 5, the varactors Cv, as the general reverse voltage V _R applied to increase the capacity decreases, as shown in FIG. 6, as the resistance r _s is also reverse voltage V _R becomes large, descend. In addition, it is convenient to increase the applied voltage to reduce the loss of the resonance circuit, but when the applied voltage is increased, the capacitance change ratio is decreased to sacrifice the modulation sensitivity. Therefore, when the oscillation frequency is set to be high due to such characteristics, it is necessary to increase the voltage applied to the varactor Cv and widen the range, and the control applied voltage to the voltage controlled oscillator in the PLL circuit is Must be satisfied.

  However, in recent years, logic circuit components such as LVTTL (Low Voltage Transistor Transistor Logic) tend to be low in voltage, and due to this low voltage tendency, the voltage applied to the varactor Cv increases as the oscillation frequency is set higher. However, it was difficult to widen the range.

  The present invention has been made in view of the above problems, and its object is to reduce the tolerance of the oscillation frequency in the resonance circuit, and to reduce the tolerance of the logic circuit used in the PLL circuit, as compared with the varactor diode. An object of the present invention is to provide a high frequency band voltage controlled oscillator capable of increasing the oscillation frequency by applying a high and wide applied voltage.

In order to achieve the above object, an invention according to claim 1 is provided with a resonance circuit composed of a varactor diode (voltage control element) and an inductor, and an oscillation frequency is variably controlled by applying a control voltage to the varactor diode. In a tuned high-frequency band voltage controlled oscillator, two inductance components of the same line length arranged between a pair of through-holes serving as a ground potential, at positions symmetrical to the connection point with the oscillation transistor Two arranged microstrip lines, a DC cut capacitor for DC-cutting both ends of the varactor diode connected to the oscillation transistor, and a control voltage for changing the oscillation frequency are applied to one end of the varactor diode In addition, the reference voltage from the reference voltage source is applied to the other end of the varactor diode. A control voltage applying circuit, characterized in that the provided.
According to a second aspect of the present invention, the control voltage application circuit applies a reference voltage of less than 0 V from a reference voltage source.

  According to the configuration of the present invention, two microstrip lines having the same line length are formed between a pair of through holes, and an oscillation transistor (for example, an emitter) is connected between the two microstrip lines. , Tolerances are reduced. That is, two microstrip lines between a pair of through holes (ground potential) are arranged symmetrically with respect to the connection point with the oscillation transistor and are connected in parallel (form an inductive element of a parallel resonant circuit). Since the error in the distance between a pair of through holes is small, for example, when one through hole is slightly displaced from the microstrip line by [+ ΔL (L: inductance)], the other through hole has the same length (− ΔL), and the tolerance is smaller than when one through hole is formed.

  According to the second aspect of the present invention, since a negative voltage is used as the reference voltage, the control voltage (voltage from one terminal) Vt + reference voltage (voltage from the other terminal) with respect to the varactor diode. ) A voltage of VRef can be applied, and a desired oscillation frequency with a higher frequency can be obtained by the capacitance value of the varactor diode that is higher than the conventional and controlled by a wider applied voltage.

  According to the present invention, the tolerance of the microstrip line constituting the inductance of the resonance circuit is reduced, and there is an effect that the oscillation frequency can be increased by the optimized inductance.

  According to the second aspect of the present invention, since the capacitance tolerance of the capacitor can be adjusted by the offset of the varactor diode applied voltage, the resonance frequency tolerance is adjusted to an optimum value by the capacitance optimized together with the inductance. Is possible. Furthermore, since the voltage applied to the varactor diode (control voltage) can be set high and wide while keeping the voltage for the logic circuit as it is, there is an effect that the PLL circuit can be lowered and the oscillation frequency can be increased simultaneously.

It is a circuit block diagram which shows the structure of the high frequency band voltage control oscillator which concerns on the Example of this invention. It is a figure which shows the equivalent circuit of the resonance circuit in the high frequency band voltage controlled oscillator of an Example. It is a graph which shows control of the applied voltage with respect to the varactor diode of an Example compared with the past. It is a circuit block diagram which shows the structure of the conventional voltage controlled oscillator (resonance circuit). It is a graph which shows the relationship of the capacity | capacitance with respect to the applied voltage in a general varactor diode. It is a graph which shows the relationship of the resistance with respect to the applied voltage in a general varactor diode.

  FIG. 1 shows the configuration of a high-frequency band voltage controlled oscillator according to an embodiment of the present invention. As shown in the drawing, on the emitter side of the oscillation transistor 1, a microstrip having the same line length (same shape) is shown. Two short stubs P1 and P2 made of a line are connected in parallel at a symmetrical position with respect to the emitter connection point. That is, a pair of through holes H1 and H2 having the same diameter and being ground-connected to the ground surface on the back surface of the substrate are provided, and two short stubs P1 and P2 are provided between the through holes H1 and H2, for example. It is formed on a straight line, and the emitter of the oscillation transistor 1 is connected between the short stubs P1 and P2. The two short stubs P1 and P2 need only be in a symmetric state (point symmetry, line symmetry) when viewed from the emitter connection point between a pair of through holes H1 and H2, and are arranged in a square shape, for example. May be.

  A varactor diode (hereinafter simply referred to as a varactor) Cv is disposed between the oscillation transistor 1 and a through-hole H3 serving as a ground potential on the emitter side. A DC cut capacitor C1 is provided on the cathode side of the varactor Cv. A DC-cut capacitor C2 is connected to the anode side, and a PLL (Phase Locked Loop) circuit is configured via a coil L4 at the cathode of the DC-cut varactor Cv (a connection point with the capacitor C1). A loop filter 4 and a phase detector 5 are connected.

  On the other hand, a reference voltage source 6 is connected to the anode of the varactor Cv (a connection point with the capacitor C2) via a coil L5. In the embodiment, a voltage of 0 to 5 V, for example, is used as the control voltage Vt at the cathode of the varactor Cv, and −5 V is set as the reference voltage Vref at the anode, for example.

  The embodiment has the above-described configuration. As shown in FIG. 2, the equivalent circuit of the resonant circuit of the voltage controlled oscillator includes the inductance of the short stub P1, the inductance of the short stub P2, the capacitors C1, C2, and the variable capacitor Cv. In this resonant circuit, the tolerance of inductance (L) is reduced.

  That is, the short stubs P1 and P2 form a distributed constant determined by the distance from the ground point to the branch point, and become an inductance proportional to the electrical length. Since the distance from the ground point is determined by the position of the through hole, the inductance depends on the position tolerance of the through hole (H1, H2). The alignment tolerance between the circuit pattern on the board and the through hole at the time of manufacturing the oscillator is in-plane in the circuit (line) pattern generation process in addition to the alignment recognition error in the through hole drilling process. Due to variation, it becomes relatively large.

However, as in the embodiment, since the distance between two or more through holes (H1, H2) is determined by the mechanical control resolution of the manufacturing apparatus, it is generally compared with the case where one through hole is formed. It is known that the resolution is sufficiently small. In the embodiment, the short stubs P1 and P2 are arranged at positions where the microstrip lines having the same length are symmetric with respect to the emitter of the oscillation transistor 1 (in the reverse direction), so that the inductances of the short stubs P1 and P2 are L Then, this combined inductance La is expressed by a combination rule of parallel circuits (P1, P2).
1 / jωLa = (1 / jωL) + (1 / jωL)
= 2 / jωL (1)
However, (1 / jωL): Susceptance due to L.

If the change in L due to the positional tolerance of the through holes H1 and H2 is ΔL, and the distance error between the two through holes is approximately zero, the combined inductance La is
1 / jωLa = [1 / jω (L + ΔL)] + [1− / jω (L−ΔL)]
= (1 / jω) · [1 / (L + ΔL) + 1 / (L−ΔL)]
= (1 / jω) · [2L / (L ² −ΔL ² )]
Here, since L >> ΔL, 1 / jωLa≈2 / jωL (2)
It becomes.

  Therefore, by satisfying the distance error between two through holes ≈ 0 and L >> ΔL, (1) and (2) have the same result. That is, in the embodiment, since the distance error between the two through holes (H1, H2) becomes small, even if the positions of the short stubs P1, P2 are slightly deviated from the positions of the through holes H1, H2. Since the stubs P1 and P2 are parallel circuits, it is possible to reduce inductance tolerance.

  In the varactor Cv, the control voltage Vt of 0 to 5V is supplied to the cathode through the loop filter 4 while supplying the reference voltage Vref of −5V from the reference voltage source 6 to the anode, thereby supplying the varactor Cv with the control voltage Vt. On the other hand, an applied voltage of 5 to 10 V is applied, and the oscillation frequency is controlled by changing the capacitance value based on the applied voltage.

FIG. 3 shows control of the applied voltage to the varactor Cv of the embodiment. Conventionally, as shown by 103 in FIG. 3, the reverse voltage (Vr) to the varactor Cv is 0 to 5 V (control voltage Vt). In the embodiment, a reference voltage of, for example, −5V, which is less than 0V, is applied to the anode as in 101, so that the reverse voltage to the varactor Cv is 5 to 102 as in 102. It becomes a range of 10V, and it becomes possible to apply a voltage higher than the conventional voltage to the varactor Cv without changing the control voltage Vt. Therefore, if the applied voltage is increased, the capacity of the varactor Cv is reduced as shown in FIG. 3, and the high frequency can be promoted. As understood from FIG. 6, the series resistance (r _s ). As a result, the loss of the resonant circuit is also improved.

  Further, by changing the reference voltage Vref in a range of, for example, -5 to 0V, the voltage applied to the varactor Cv can be set to an arbitrary width in a wide range of 0 to 10V without changing the control voltage Vt. There are advantages.

  In the above embodiment, a pair of through holes (H1, H2) is provided. However, a plurality of through holes are provided, and two microstrip lines are provided in each of these through hole pairs. Also good.

  In the above embodiment, the case where the resonance circuit is connected to the emitter terminal of the bipolar transistor has been described. However, the present invention is not limited to this, and the base circuit and the collector terminal are connected depending on the grounding method. It can be configured. The oscillation transistor is not limited to a bipolar transistor, and may be a field effect transistor (FET).

1 ... Oscillation transistor, 4 ... Loop filter,
5 ... Phase detector, 6 ... Reference voltage source,
Cv: Varactor diode, H1 to H4: Through hole,
P1, P2 ... Short stub (microstrip line),
C1, C2 ... capacitors.

Claims (2)

In an LC-tuned high-frequency band voltage controlled oscillator that includes a resonance circuit composed of a varactor diode and an inductor, and variably controls the oscillation frequency by applying a control voltage to the varactor diode.
Two microstrip lines that are two inductance components of the same line length arranged between a pair of through-holes that become a ground potential, and that are arranged symmetrically with respect to the connection point with the oscillation transistor;
A DC-cut capacitor for DC-cutting both ends of the varactor diode connected to the oscillation transistor;
A control voltage application circuit for applying a control voltage for changing the oscillation frequency to one end of the varactor diode and applying a reference voltage from a reference voltage source to the other end of the varactor diode is provided. High frequency band voltage controlled oscillator.   2. The high frequency band voltage controlled oscillator according to claim 1, wherein the control voltage applying circuit applies a reference voltage of less than 0 V from a reference voltage source.

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