JP2002290152A - Voltage-controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage-controlled oscillator which has improved non- linearity of frequency change characteristics with respect to control voltage. SOLUTION: In the voltage-controlled oscillator, where a voltage variable capacitance element is connected into the closed loop of an oscillation circuit and control voltage is applied to the voltage variable capacitance element for controlling the oscillation frequency of the oscillation circuit; a series circuit of a constant voltage source, a diode and a resistor is connected between the terminals of the voltage variable capacitance element; and control voltage is applied to the connection point of the voltage variable capacitance element and the series circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator as an industrial technical field, and more particularly to a voltage controlled oscillator having improved non-linear frequency characteristics with respect to a control voltage Vc caused by a voltage variable capacitor.

[0002]

2. Description of the Related Art A voltage controlled oscillator is a PLL.
(PHASE LOCKED LOOP) It is used as a temperature compensating mechanism of an oscillation circuit or the like, and is known to vary an oscillation frequency by a control voltage Vc. Normally, the control voltage Vc is applied to the voltage variable capacitance element inserted in the oscillation closed loop, and the oscillation frequency is varied by a change in capacitance between terminals.
In recent years, it has been desired to improve the linearity of a control voltage-frequency characteristic of an oscillation circuit using a voltage variable capacitance element.

FIG. 4 is a circuit diagram of a voltage controlled oscillator for explaining a conventional example. The voltage controlled oscillator has a voltage variable capacitance element 1 inserted in a closed loop of an oscillation circuit. The oscillation circuit forms a resonance circuit from, for example, the crystal resonator 2 having an inductor component, the capacitor 3, and the voltage variable capacitance element 1. Then, the resonance frequency is feedback-amplified by the inverter amplifying element 5 having the feedback resistor 4 connected in parallel to the crystal resonator 2. The voltage variable capacitance element 1 is a varicap diode (variable capacitance diode 1A)
Consists of Reference numeral 6 denotes a high-frequency blocking resistor, and reference numeral 7 denotes a DC blocking capacitor.

In such a device, when a control voltage Vc, which is a reverse voltage, is applied to the variable capacitance diode 1A via the high-frequency blocking resistor 6, the capacitance between the terminals of the variable capacitance diode 1A changes. Accordingly, the series equivalent capacitance on the circuit side as viewed from both terminals of the crystal unit 2 (the so-called load capacitance of the crystal unit 2) changes, so that the oscillation frequency changes.

[0005]

However, in the voltage controlled oscillator having the above structure, the voltage-capacitance characteristic of the variable capacitance diode 1A has an exponentially increasing capacitance with respect to the control voltage Vc as shown in FIG. Decrease. For this reason, the frequency characteristic of the oscillation frequency with respect to the control voltage Vc is not linear but non-linear. In other words, the oscillation frequency increases exponentially with respect to the control voltage Vc (the sixth characteristic).
In many cases, the sensitivity df / dVc of the oscillation frequency f to the control voltage Vc decreases as the control voltage Vc increases. This makes it difficult to control the oscillation frequency and complicates the design.

In particular, when applied to a temperature compensating mechanism (oscillator), a control voltage (temperature compensating voltage) is applied to a temperature change.
Although Vc changes, the control sensitivity (Δf / V) also changes due to the non-linearity of the variable capacitance diode 1A. Also,
When the AFC voltage by the automatic frequency control (AFC) circuit is applied to the variable capacitance diode 1A in common, the AF
The control sensitivity by the C voltage also changes.

[0007] From these, the temperature compensation voltage and AF
There is a problem that the C voltages are superimposed on each other, making it difficult to perform independent control in the non-linear portion, and deteriorating the frequency temperature characteristics after compensation. In particular, in reducing the power, non-linearity of the variable capacitance diode on the low frequency side becomes a problem.

(Object of the Invention) An object of the present invention is to provide a voltage controlled oscillator in which the nonlinearity of a frequency change characteristic with respect to a control voltage is improved.

[0009]

Means for Solving the Problems (Points of Interest) In the present invention,
The non-linearity of the frequency characteristic with respect to the control voltage Vc is caused by the non-linearity of the voltage-capacitance characteristic of the variable capacitance diode. As a result, attention has been paid to the point that the frequency characteristic with respect to the control voltage Vc has linearity.

(Solution) According to the present invention, a series circuit of a constant voltage source (voltage E), a diode and a resistor is connected between terminals of a voltage variable capacitance element to control a control voltage Vc of the voltage variable capacitance element and the series circuit. The application to the connection point is a basic solution.

[0011]

According to the present invention, when a control voltage Vc is applied between the terminals of a series circuit composed of a constant voltage source (voltage E), a diode and a resistor via a high-frequency blocking resistor, the voltage between the terminals of the series circuit, that is, the correction voltage Vc '. Becomes That is, almost no current flows through the diode when the applied voltage is about 0.7 V or less,
When the voltage exceeds 0.7 V, the current increases exponentially. Therefore, when the control voltage Vc falls below E-0.7 (V), the correction voltage Vc 'decreases exponentially. From these facts, even if the control voltage Vc is linear, the correction voltage Vc 'is changed to E-0.7.
(V) Since the curve is formed below, the voltage-capacitance characteristic and the frequency characteristic of the variable capacitance diode to which the correction voltage Vc 'is applied are linearized. Hereinafter, an embodiment of the present invention will be described.

[0012]

FIG. 1 is a circuit diagram of a voltage controlled oscillator for explaining an embodiment of the present invention. The same parts as those in the prior art are denoted by the same reference numerals, and description thereof will be simplified or omitted. As described above, the voltage controlled oscillator includes the crystal resonator 1, the voltage variable capacitance element 1 (variable capacitance diode 1A), the capacitor 3 (ab), and the inverter amplification element 5 having the feedback resistor 4. Reference numeral 6 denotes a high-frequency blocking resistor, and reference numeral 7 denotes
Is a DC blocking resistance.

In this embodiment, between the terminals of the variable capacitance diode 1A, that is, between the cathode and the ground potential.
A constant voltage source (voltage E) 8, a diode 9, and a series circuit 11 including a resistor 10 are connected from the ground side.

In such a circuit, when the control voltage Vc is applied to the series circuit 11 via the high-frequency blocking resistor 6, the voltage Vc 'between terminals of the series circuit 11 becomes as follows. That is, when the control voltage Vc is equal to or higher than E-0.7 (V), the voltage applied between the terminals of the diode 9 is equal to or lower than 0.7 V, that is, the potential of the cathode is increased and almost no current flows, and Vc '≒ Vc.

When the control voltage Vc is equal to or lower than E-0.7 (V), the potential of the anode becomes high, and a current flows through the diode 9;
c ′> Vc. And the voltage between the terminals of the diode 9 is
When the voltage exceeds 0.7 V, the current increases exponentially. Therefore, when the control voltage Vc falls below E-0.7 (V) and the voltage between the terminals of the diode 9 becomes 0.7 V or more, the current increases exponentially and the terminal voltage (correction voltage) Vc 'becomes an exponential function. Decrease.

When Vc = 0, assuming that the resistance of the high-frequency blocking resistor 6 is R1 and the resistance of the resistor 10 in the series circuit 11 is R2, Vc '= (E−0.7) R2 / (R1 + R2) (V). Become. Therefore, as shown in FIG.
And the resistance value R1 and R2 of the resistor 10, the correction voltage V
The lower limit value of c 'is set, and the control voltage Vc becomes E-0.7 (V).
Hereinafter, the inter-terminal voltage Vc 'becomes a curve. However, E-
Above 0.7 (V), it becomes linear as in the prior art.

A voltage Vc 'between terminals of the series circuit 11, ie, a correction voltage Vc of the control voltage Vc is applied to the voltage variable capacitance element 1.
c 'is applied. The correction voltage Vc 'is equal to E-0.
Below 7 (V), it is curved.

From these facts, as shown in FIG. 3, the oscillation frequency f with respect to the control voltage Vc is E-0.7
(V) It becomes linear in the voltage range below. Therefore,
The change characteristic of the oscillation frequency f with respect to the control voltage Vc can be improved. In particular, as the power supply voltage due to the reduction in power becomes smaller (for example, 2 V or less), the effect becomes larger.

[0019]

[Other Matters] In the above embodiment, one of the capacitors forming the resonance circuit with the crystal resonator 2 is the variable capacitance diode 1. However, the other capacitor 3 is applied with the correction voltage Vc 'as the voltage variable capacitance element 1. You may. Further, the voltage variable capacitance element 1 is the variable capacitance diode 1A, but any semiconductor element whose capacitance between terminals substantially changes with respect to voltage can be applied.

[0020]

According to the present invention, a series circuit of a constant voltage source (voltage E), a diode and a resistor is connected between terminals of a voltage variable capacitance element, and a control voltage Vc is applied to a connection point between the voltage variable capacitance element and the series circuit. Applied to the control voltage Vc, it is possible to provide a voltage controlled oscillator with improved non-linearity of the frequency change characteristic with respect to the control voltage Vc.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage-controlled oscillator illustrating one embodiment of the present invention.

FIG. 2 is a characteristic diagram of a correction voltage Vc 'with respect to a control voltage Vc for explaining an embodiment of the present invention.

FIG. 3 is a graph showing a change characteristic of an oscillation frequency with respect to a control voltage for explaining an embodiment of the present invention;

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

FIG. 5 is a diagram illustrating capacitance characteristics of a voltage variable capacitance element with respect to a control voltage for explaining a conventional example.

FIG. 6 is a diagram illustrating a change characteristic of an oscillation frequency with respect to a control voltage for explaining a conventional example.

[Explanation of symbols]

1 voltage variable capacitance element, 2 crystal oscillator, 3 (ab)
Divided capacitor, 4 feedback resistor, 5 inverter amplifying element, 6 high frequency blocking resistor, 7 DC blocking capacitor, 8
Constant voltage source, 9 diode, 10 resistor, 11 series circuit.

Claims (1)

[Claims] A voltage controlled oscillator comprising a voltage variable capacitance element connected in a closed loop of an oscillation circuit, a control voltage applied to the voltage variable capacitance element via a high-frequency blocking resistor, and an oscillation frequency of the oscillation circuit controlled. Wherein a series circuit of a constant voltage source, a diode, and a resistor is connected between terminals of the voltage variable capacitance element, and the control voltage is applied to a connection point between the voltage variable capacitance element and the series circuit. Controlled oscillator.