JPH0534711U - Voltage controlled oscillator - Google Patents

Abstract

(57) [Abstract] [Purpose] To widen the variable range of the oscillation frequency without lowering the Q of the circuit. [Structure] An inductive impedance L ₁ is connected in parallel to a variable capacitance diode CR ₁ whose capacitance changes according to a control voltage Vc.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a voltage controlled oscillator used in communication equipment, and more particularly to a voltage controlled oscillator using a resonator.

[0002]

[Prior Art]

 FIG. 6 is a circuit diagram showing a configuration of an example of a conventional oscillator. Q in FIG.₁Is an NP N-type transistor, R₁Is the transistor Q₁Bias resistance, C connected between the base and collector of the₁, C₂Is a feedback capacitor connected between the base and emitter and between the emitter and ground, R₂Is a bias resistor connected between the emitter and ground, C₆Is a coupling capacitor connected to the emitter, and these form an oscillation circuit. Vcc is a power supply voltage. This oscillator circuit has a coupling capacitor C₃A SAW (abbreviation of Surface Acoustic Wave) resonator Z is connected in parallel to the resonator Z via a capacitor C._FourVariable capacitance CR via₁Are connected in parallel. R ₃ Is the input resistance, C_FiveIs a bypass capacitor, Vc is a control voltage input to the control voltage terminal Tc, and To is an output terminal.

In the above structure, when the control voltage Vc is applied to the control voltage terminal Tc, the capacitance of the variable capacitance diode CR ₁ is changed by the control voltage Vc and the frequency can be changed. The conventional FIG. 6 having such an operation can be rewritten as shown in FIG. 7 by removing the bias resistors R ₁ and R ₂ . When the circuit seen from the ab side in FIG. 7 is viewed from the transistor side as the capacitance Ca and the negative resistance −R, the result is as shown in FIG. 8. In FIG.

[Equation 1]

[Equation 2] In other words, the equivalent circuit of the SAW resonator Z can be represented in FIG. Therefore, the equivalent circuit of the conventional oscillator is the circuit shown in FIG. However,

[Equation 3] Is.

From the condition that the reactance of the circuit of FIG. 10 becomes zero, the oscillation frequency fosc is calculated by the following [Equation 4].

[Equation 4] Here, fr: series resonance frequency of SAW resonator γ: capacitance ratio of SAW resonator, Co / Co. Substituting [Expression 2] and [Expression 3] into [Expression 4],

[Equation 5] Is obtained. Therefore, when Co'is maximum and minimum, it is CR ₁ max and CR ₁ min.

[0005]

[Problems to be solved by the device]

In the above-mentioned conventional example, the variable range of the oscillation frequency that can be changed by the control voltage Vc is extremely narrow. When CR ₁ max = 43 pF, CR ₁ min = 11 pF, fr = 250 MHz, γ = 3.0, Ca ′ = 2.3 pF, Co = 8 pF, C ₄ = 33 pF, fosc min to fosc max is fmin = 286.5-fmax = 288. There was a problem that the variable width was 35 MHz and the variable width was as narrow as 0.64%.

[0006]

[Means for Solving the Problems]

In order to solve the above problems, the oscillator of the present invention has a resonator Z in parallel with an oscillator circuit using capacitive elements C ₁ and C ₂ and a variable capacitance diode CR ₁ to the resonator Z as shown in FIG. connected in parallel, the voltage controlled oscillator for controlling the oscillation frequency fosc by a control voltage Vc applied to the control voltage terminal Tc of variable capacitance diode CR _1, in parallel inductive impedance L ₁ to the variable capacitance diode CR ₁ Connected.

[0007]

[Work]

This invention oscillator comprises a conductive impedance L ₁ connected in parallel to the variable capacitance diode CR ₁ as this that you can increase the variable width of the variable capacitance diode CR _1, so that the voltage controlled oscillator frequency can significantly wider ..

[0008]

【Example】

 FIG. 1 is a circuit diagram showing the configuration of an embodiment of the oscillator of the invention. In Figure 1, Q₁ Is an NPN type transistor, R₁Is the transistor Q₁Bias resistance connected between the base and collector of C,₁, C₂Is a feedback capacitor connected between the base and emitter and between the emitter and ground, R₂Is a bias resistor connected between the emitter and ground, C₆Is a coupling capacitor connected to the emitter, and these form an oscillation circuit. Vcc is a power supply voltage. This oscillator circuit has a coupling capacitor C ₃ A SAW resonator Z in parallel via a capacitor C coupled to the resonator Z._FourVia variable capacitance diode CR₁Are connected in parallel. L₁Is a variable capacitance diode CR₁Expansion coil for increasing the variable width of_FiveIs a bypass capacitor, Vc is a control voltage input to the control voltage terminal Tc, and To is an output terminal.

When the control voltage Vc is applied to the control voltage terminal Tc in the above configuration, the capacitance of the variable capacitance diode CR ₁ changes due to the control voltage Vc, but its variable width increases due to the inductive impedance L ₁ . The voltage control frequency can be made wider.

The reason will be described in detail below. The equivalent circuit of FIG. 1 is as shown in FIG. Considering that the variable frequency range is very small compared to the oscillation frequency fosc, the coil L ₁ is

[Equation 6] It can be considered that a negative capacitor (ω _c : central angular frequency of the variable range) is inserted. FIG. 2 can be rewritten as FIG. In FIG.

[Equation 7]

[Equation 8]

[Equation 9]

[Equation 10] Then, it becomes like FIG. The oscillation frequency fosc is calculated by the following [Equation 11] under the condition that the reactance in FIG. 4 becomes zero.

[Equation 11] FIG. 5 is a characteristic diagram of the oscillation frequency and the phase noise with respect to the control voltage in the present invention. This characteristic shows the characteristic of the equation of power supply voltage Vcc = 1V, current I = 600 μA, and electric power Po = −23 dBm.

The variable frequency range is, for example, L ₁ = 39 nH, CR ₁ max = 43 PF, CR ₁ min = 11 pF, fr = 250 MHz, γ = 3.0, C ₃ ′ = 2.3 pF, C _O = 8 pF , C ₄ = 33 pF, fmin = 282.55 MHz to fmax = 288.077 MHz, and the variable range is extremely wide at 1.94%. Therefore, by selecting L ₁ which can change C ₀ ′ to the maximum, the variable width can be maximized without lowering the Q of the SAW resonator Z.

[0012]

[Effect of the device]

As described above, according to the present invention, the resonator Z is connected in parallel to the oscillation circuit using the capacitance elements C ₁ and C ₂ , and the variable capacitance diode CR ₁ is connected in parallel to the resonator Z, and the variable capacitance is in the voltage controlled oscillator for controlling the oscillation frequency fosc by a control voltage Vc applied to the control voltage terminal Tc of the diode CR _1, since the inductive impedance L ₁ connected in parallel to the variable capacitance diode CR _1, circuit The variable width of the oscillating frequency can be significantly widened without lowering the Q, and the current consumption is small, and a voltage controlled oscillator with low noise characteristics can be realized.

[Brief description of drawings]

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

FIG. 2 is an equivalent circuit diagram of FIG.

FIG. 3 is an equivalent circuit diagram of the circuit of FIG.

FIG. 4 is an equivalent circuit diagram of the circuit of FIG.

FIG. 5 is a characteristic diagram of oscillation frequency and phase noise with respect to a control voltage in the present invention.

FIG. 6 is a circuit diagram showing a configuration of an example of a conventional oscillator.

FIG. 7 is a simplified circuit diagram of FIG.

FIG. 8 is an equivalent circuit diagram of FIG.

FIG. 9 is an equivalent circuit diagram of a resonator.

FIG. 10 is an equivalent circuit diagram of FIG.

[Explanation of symbols]

C ₁ capacitance element (feedback capacitor) C ₂ capacitance element (feedback capacitor) CR ₁ variable capacitance diode Tc control voltage terminal Vc control voltage fosc oscillation frequency L ₁ inductive impedance Z (SAW) resonator

Claims (1)

[Scope of utility model registration request] 1. A resonator (Z) is connected in parallel to an oscillation circuit using capacitive elements (C ₁ , C ₂ ), and a variable capacitance diode (CR ₁ ) is connected in parallel to the resonator (Z). in the variable capacitance diode (CR ₁₎ a voltage controlled oscillator for controlling the oscillation frequency (fosc) by a control voltage terminal (Tc) in the applied control voltage (Vc) of said inductive impedance to the variable capacitance diode (CR ₁₎ ( A voltage-controlled oscillator in which L ₁ ) are connected in parallel.