JP2819034B2 - Voltage controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention is to arbitrarily switch and select one wave in a relatively wide frequency band of VHF band or UHF band (for example, 25 MHz to 33 MHz in a car telephone system). Wideband, low-noise, low-power voltage-controlled oscillator (VC) applied to radio equipment intended to obtain a transmitting carrier or a local oscillation source for transmission and reception
O).

(Prior art and its problems) VHF or UHF multi-channel access wireless devices (especially portable and in-vehicle types) switch and use one wave within a relatively wide frequency band. PLL (Phase Locked Loop) using VCO as described
Thus, a frequency synthesizer is widely used because a means for generating a carrier wave is extremely effective in terms of circuit configuration and frequency stability.

In a system that selects and uses an arbitrary wave of such a broadband frequency, a required noise characteristic (C / N
And S / N), increase the DC input power (voltage, current) to improve the low noise characteristics of the active device and raise the oscillation output level of the oscillator, or increase the The required noise characteristics are satisfied by increasing the Q (particularly the Q of the resonator). However, in the case of portable devices that are characterized by small size and light weight, the former requires an increase in power consumption and the battery life becomes extremely short, and the latter requires a relatively large resonator, and the The small size, light weight and prolonged battery life are severely hindered.

For this reason, many attempts have been made to use a small high-Q element for a resonator, and the use of a resonator such as a quartz oscillator or a surface acoustic wave has been studied. As shown in Table 1, a high dielectric resonator is used. Except for this, the conventional quartz resonator, surface acoustic wave resonator, and the like have an extremely large capacitance ratio (γ) of the resonator compared to the Love wave type surface acoustic wave resonator used in the present invention.
The frequency variable width of the VCO does not reach at most 1% even if various kinds of widening of the bandwidth are attempted, which greatly hinders the realization of a wideband VCO.

(Object of the Invention) The present invention has been made to overcome the drawbacks of the conventional method, and maintains excellent low power consumption characteristics.
In addition, low noise, that is, high purity of the VCO oscillation output,
To provide a voltage controlled oscillator realizing a high carrier wave.

(Structure and Operation of the Invention) A voltage controlled oscillator according to the present invention is provided with an oscillation circuit having at least one resonator and a capacitive element arranged in parallel with the resonator, and arranged in parallel with the resonator. A first one-port circuit having an inductive impedance, a second one-port circuit having a capacitive impedance having one terminal connected to one end of the first one-port circuit, and a control voltage terminal. A variable capacitance diode connected between the other end of the second one-port circuit and the other end of the first one-port circuit; and a variable capacitance diode connected in parallel to the variable capacitance diode. And a third one-port circuit having an inductive impedance to the diode, wherein the oscillation frequency is controlled by a control voltage applied to a control voltage terminal of the variable capacitance diode. The oscillator can also be constructed by using two of the resonators connected in series, wherein it is intended to be constructed using the Love wave type surface acoustic wave resonator as at least one resonator.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of a basic AC equivalent circuit of a broadband VCO using a surface acoustic wave resonator embodying the present invention. Symbols in parentheses in the figure indicate the element values of the capacitance of the capacitor or the variable capacitance diode as the corresponding passive element and the inductance of the coil.

In FIG. 1, reference numeral 1 denotes a transistor which is an oscillation active element;
And 3 are capacitors each having a capacitance C ₂ and C _3, are connected between the collector C and the emitter E of the transistor 1, and between the base B and emitter E.

4 is a capacitor having a capacitance C _4. 5
Is a resonator for example quartz oscillator, surface acoustic wave resonators has an equivalent inductance L _5, the capacitor 4 and the resonator 5
Are connected in series between the collector C and the base B of the transistor 1. Reference numeral 6 denotes a fixed coil or a composite reactance having an equivalent inductance L ₆ , which is connected in parallel to the resonator 5.

7 is a one-port circuit having a capacitive impedance at the oscillation frequency. Reference numeral 8 denotes a first variable capacitance diode having a variable capacitance C ₈ and a control voltage terminal M ₈ for controlling the value of C ₈ . This is a circuit having an impedance, and has both ends (C,
B ′) to form a branch circuit. 9 is a reactance circuit of the fixed or composite have an equivalent inductance L _9, are connected in parallel to the first variable capacitance diode 8.

Focusing on the other parts except for 6, 7, 8, and 9, the above connection constitutes a known Colpitts-type oscillation circuit or a clap-type oscillation circuit that is a modification of the Colpitts-type oscillation circuit. FIG. 1 shows a circuit as shown in FIG. 2 as an equivalent circuit relating to a general frequency which does not depend on the type of the oscillation circuit and focuses only on the element.

In FIG. 2, 5, 6, 7, 8, 9 are the same as in FIG.
0 is the transistor side (capacitor) from terminals C and B 'in FIG.
2, 3, 4) an equivalent capacitor having a total capacitance C ₁₀ when viewed, is connected in parallel to the resonator 5. It should be noted that the variable capacitance diode 8 in FIGS.
A control voltage terminal M ₈ for controlling the capacitance C ₈ (AC blocking, details of the DC bias circuit is shown omitted.) And a. In the known PLL circuit using the VCO shown in FIG. 1, applying a signal through a loop filter of a phase comparison output between the output frequency of the VCO and a reference frequency signal to the control voltage terminal as a feedback DC signal. Thereby, a stable oscillation frequency can be obtained. The one-port circuits 6, 7, and 9, which are the main parts of the present invention, use parameters specific to the resonator (C ₀ , L ₀ , r ₀ , C _{s in} FIG. 3) according to the frequency control voltage as described later. Overall, it has the function of changing reactance over a wide band.

The one-port circuit 6 is connected to C _{s of the} resonator equivalent circuit shown in FIG.
It acts as an inductance that acts to erase, those that act to increase the resonator-specific anti-resonance frequency (f _a). The one-port circuits 7 and 9 are independent or combined reactance circuits that are set to follow the change in capacitance caused by the variable capacitance diode 8 and to act in a direction in which the change in reactance further increases.

FIG. 3 is an equivalent circuit of the resonator 5 constituting the VCO,
As is well known, it has a resonance frequency (f _r ) determined by C ₀ , L ₀ , r ₀ and an anti-resonance frequency (f _a ) obtained by integrating C _s .

In order to realize the above-described characteristics, three types of configuration examples of the branch circuits of the one-port circuits 6, 7, and 9 constituting the main part of the present invention will be described with reference to FIGS. C). In the FIG. 4, FIG. 1, the AC cutting circuit of the control voltage terminal M ₈ in the case of Figure 2 similar to the variable capacitance diode 8,
Details of the DC bias circuit are omitted in the figure. or,
The portions surrounded by the dotted lines indicate the corresponding one-port circuit portions 6, 7, and 9 in FIG.

In FIG. 4A, the one-port circuits 6, 7, and 9 are individually arranged, and 9 is made infinite. 6 is a fixed inductance L ₆ , 71 is a second variable capacitance diode C ₇₁ connected in series with the first variable capacitance diode 8, and
It is connected in parallel with the fixed inductance 6 to form an anti-resonance circuit. The control voltage applied to the control voltage terminal M ₇₁ of the second variable capacitance diode 71 is controlled in the same direction as the control voltage applied to the control voltage terminal M ₈ of the first variable capacitance diode 8, and Sharply changes the combined reactance of

Figure 4 (B) and (C), by connecting the 9 in addition to the one-port circuit 6 and 7 in parallel with the variable capacitance diode 8 constitutes an anti-resonant circuit, the change amount of the actively variable capacitance C ₈ Is a configuration example for enlarging.

FIG. 5 is a characteristic example diagram of control voltage vs. oscillation frequency f ₀ and C / N in the case of the configuration shown in FIG. 4 (C). The operating conditions of the oscillator are a C / N value at a power supply voltage of 1.0 V, a collector current of 500 μA, and an output of −24 dBm. Further, the control voltage of the variable capacitance diode for controlling the frequency is limited to the range of 0.5V to 2.5V.

FIG. 6 is a graph showing one example of characteristics of the variable capacitance versus the oscillation frequency f ₀ and the C / N in the case of the configuration shown in FIG. 4 (C). .

By using a resonator having a small capacitance ratio (γ = C _s / C ₀ ), for example, a Love wave type surface acoustic wave resonator as the resonator 5 shown in FIGS. 1 and 2, the oscillation frequency variable width can be further increased. A wider band could be achieved, and according to experiments, a variable width of 5% or more could be obtained.

Further, as shown in FIG. 7, by connecting two resonators 5 in series between the connection terminals DD 'of the resonator 5 in FIG. 2, the frequency variable width can be expanded.

(Effects of the Invention) As described in detail above, according to the present invention, an oscillation frequency variable width of 1% or more is realized by a surface acoustic wave resonator, which has been conventionally difficult, despite its simple configuration. In addition, since a circuit having a relatively high Q value can be configured, a VCO with low noise characteristics can be realized.

In addition, by setting the effective Q of the oscillation circuit within a range that has little effect on the Q value inherent to the resonator, the conventional Q
A VCO that consumes about one digit less power than a VCO can be realized, and can be widely applied to portable and pocket-type wireless devices that require small size, low noise, and low power consumption. Since the size, weight and cost of the device can be reduced, there is an extremely large effect.

[Brief description of the drawings]

FIG. 1 is a structural example of a basic AC equivalent circuit of a broadband VCO embodying the present invention, FIG. 2 is an equivalent circuit relating to the frequency of FIG. 1, FIG. 3 is an equivalent circuit of a resonator, and FIG. 1 in Fig. 2
FIG. 5 is a diagram showing an example of the configuration of the branch circuits of the port circuits 6, 7, and 9, FIG. 5 is a diagram showing an example of characteristics of the control voltage vs. the oscillation frequency and C / N in the case of FIG. 4 (C), and FIG. FIG. 7 is a graph showing one example of characteristics of the variable capacitance versus the oscillation frequency and C / N in the case of (C).
It is a circuit diagram in which two resonators were connected in series between D '. 1 ... transistor, 2,3,4 ... capacitor, 5 ... resonator, 6,9 ... 1 port circuit of inductive impedance,
7: 1-port circuit with capacitive impedance, 8,71,73
…… variable capacitance diode, 10 …… composite equivalent capacitor,
M ₈ , M ₇₁ … Control voltage terminals.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kanemi Sasaki, Inventor 2-1-1 Shinmeidai, Hamura-cho, Nishitama-gun, Tokyo Inside the Hamura Plant of Kokusai Electric Co., Ltd. (72) Tadashi Kanda 2- Shinmeidai, Hamura-cho, Nishitama-gun, Tokyo 1-1 Inside the Hamura Plant of Kokusai Electric Inc. (72) Inventor Hiroshi Shimizu 1-22-12 Yagiyama Honcho, Aoba-ku, Aoba-ku, Sendai, Miyagi Prefecture (56) References JP-A-58-99008 (JP, A) 3-69203 (JP, A) Tadashi Kanda. Yuji Suzuki, Hiroshi Shimizu, "Wideband VCO Using Highly Coupled Lab-Type Surface Acoustic Wave Resonator", International Electrotechnical Report No. 19, (1992), p. 12-17 (58) Field surveyed (Int.Cl. ⁶ , DB name) H03B 5/30-5/42 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. An oscillation circuit having at least one resonator and a capacitance element arranged in parallel with the resonator, and a first element having an inductive impedance arranged in parallel with the resonator. A second one-port circuit having a capacitive impedance with one terminal connected to one end of the first one-port circuit; and a second one-port circuit having a control voltage terminal. A variable capacitance diode connected between the other end and the other end of the first one-port circuit; a variable capacitance diode connected in parallel to the variable capacitance diode and having an inductive impedance to the variable capacitance diode 3
A voltage-controlled oscillator comprising: a one-port circuit; and an oscillation frequency controlled by a control voltage applied to a control voltage terminal of the variable capacitance diode. 2. The voltage controlled oscillator according to claim 1, wherein said oscillator is constituted by using two said resonators connected in series. 3. The voltage controlled oscillator according to claim 1, wherein a Love wave type surface acoustic wave resonator is used as said at least one resonator.