JP2000216633A - Voltage controlled crystal oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage controlled crystal oscillator VCXO that employs no coil and whose frequency control sensitivity is much more improved. SOLUTION: A capacitor C11 is connected between an input and an output of an amplifier 1, and a capacitor C12 is connected between the output terminal of the amplifier 1 and the ground. Furthermore, a crystal vibrator 2 is connected to the input terminal of the amplifier 1, an inductive reactance circuit 3 in place of an extension coil L is inserted between the crystal vibrator 2 and ground and a varactor diode CD is connected to a terminal A via a bias resistor RD whose resistance is comparatively higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled type crystal oscillator, and more particularly to a voltage controlled type crystal oscillator characterized in that a frequency variable amount can be further increased by using an inductive reactance circuit without using a coil. It relates to a crystal oscillator.

[0002]

2. Description of the Related Art In general, a voltage controlled crystal oscillator (hereinafter referred to as V
CXO), a variable capacitance diode such as a varicap is inserted into an oscillation loop, and the terminal voltage is controlled to change the capacitance value to obtain a desired frequency output. Conventionally, in such a VCXO, an extension coil is used to increase the frequency control sensitivity. That is, the frequency control sensitivity is a ratio of a change amount of the oscillation frequency obtained by a change in capacitance of the variable capacitance diode. As described later, the frequency control sensitivity increases as the load capacity increases.

FIG. 4 shows a VCX using a conventional extension coil.
In an example of a circuit diagram showing O, a capacitor C11 is connected between the input and output of the amplifier 1, and a capacitor C12 is connected between the output terminal of the amplifier 1 and the ground. Further, a crystal oscillator 2 is connected to the input terminal of the amplifier 1, and an extension coil L and a variable capacitance diode CD are connected between the crystal oscillator 2 and the ground. Terminal A is a control voltage input terminal, and has a relatively large bias resistor RD between the extension coil L and the variable capacitance diode. By changing the control voltage applied to the terminal A, the capacitance of the variable capacitance diode CD changes, and the amount of change in frequency can be expressed by equation (1). Δf / f = C0 / (2 · γ · (C0 + CL)) (1) where C0 is the equivalent parallel capacitance of the crystal unit, γ is the ratio between the equivalent parallel capacitance C0 of the crystal unit and the equivalent series capacitance C1, CL
Is the load capacity of the circuit. When the capacitance of the variable capacitance diode CD changes, the load capacitance of the circuit changes. Therefore, by changing the control voltage, the capacitance of the variable capacitance diode CD changes and the oscillation frequency can be changed.

FIG. 5 is an equivalent circuit diagram of a crystal unit,
1 is equivalent series inductance, C1 is equivalent series capacitance, R
1 is an equivalent series resistance, and C0 is an equivalent parallel capacitance.

FIG. 6 shows an equivalent circuit of a vibration loop when an extension coil is inserted. The left side of the broken line is a crystal oscillator, L1 is an equivalent series inductance, C1 is an equivalent series capacitance, R1 is an equivalent series resistance, C0 is an equivalent parallel capacitance.
On the right side of the broken line, the circuit-side inductance Lan excluding the crystal unit and the circuit-side capacitance Can excluding the crystal unit are connected.

In general, the frequency control sensitivity of a VCXO is expressed by equation (2). Δ (Δf / f) Can = − (1/2) (C1 / Can) (1−Ω) 2 (ΔCan / Can) (2) where Δ (Δf / f) Can is the frequency control sensitivity, C1 is the equivalent series capacitance of the crystal unit, Can is the capacitance on the circuit side, △
Can is the amount of change in capacitance on the circuit side, and Ω is C0 / (C0 + C
L). C0 is the equivalent parallel capacitance of the crystal unit, and CL is the load capacitance on the circuit side excluding the crystal unit. In the equation (2), since the load capacitance CL is generally larger than the equivalent parallel capacitance C0 of the crystal unit, Ω is a positive value smaller than 1.
Since Ω is a positive value smaller than 1, the frequency control sensitivity △ (△ f / f) Can increases as Ω further decreases.
That is, as the load capacitance CL on the circuit side excluding the crystal resonator increases, the frequency control sensitivity △ (△ f / f) Can increases. Here, in the circuit in which the inductance Lan is inserted in series with the variable reactance Can as shown in FIG. 6, the load capacitance CL on the circuit side is inevitably the inductance L.
An is taken into account, and the capacitance value is increased as shown in Expression (3) or Expression (4). 1 / (ωCL) = − ωLan + 1 / (ωCan) (3) CL = Can / (− ω2Lan + 1) (4) where ω is the oscillation angular frequency, CL is the load capacitance on the circuit side, and L
an is an inductance on the circuit side.

[0007]

SUMMARY OF THE INVENTION As described above, VC
In order to increase the frequency control sensitivity △ (△ f / f) Can of the XO, it is necessary to increase the load capacitance CL on the circuit side excluding the crystal unit of the VCXO, and thus it is necessary to use an extension coil. However, in recent years, the use of ICs has been promoted in order to realize ultra-miniaturization of components used in response to the demand for miniaturization of electronic devices. The coil had to be an external component, which hindered complete IC implementation. SUMMARY OF THE INVENTION The present invention has been made to eliminate the above-mentioned drawbacks of a conventional VCXO using an extension coil, and achieves the same object without using a coil, and further improves the frequency control sensitivity. It is an object to provide an improved VCXO.

[0008]

To achieve the above object, a VCXO according to the present invention has the following arrangement. Claim 1
In the VCXO described above, at least a VCXO in which a piezoelectric vibrator, a variable capacitance element, and an amplification element are combined in a loop shape, an inductive reactance circuit including an amplification element, a resistance element, and a capacitance element is inserted into the loop. It is configured to The VCXO according to the second aspect is configured such that the capacitance element in the inductive reactance circuit is a variable capacitance element.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 is a circuit diagram showing one embodiment of a VCXO in which an inductive reactance circuit according to the present invention is inserted. Capacitor C1 between input and output of amplifier 1
1 and a capacitor C12 is connected between the output terminal of the amplifier 1 and the ground. Further, a crystal resonator 2 is connected to the input terminal of the amplifier 1, and an inductive reactance circuit 3 and a variable capacitance diode CD are connected between the crystal resonator 2 and the ground instead of the extension coil L.
A terminal A, which is a control voltage input terminal, is connected between the inductive reactance circuit 3 and the variable capacitance diode CD via a relatively large bias resistor RD. By changing the control voltage applied to the terminal A, the capacitance of the variable capacitance diode CD changes, and as can be seen from the above-mentioned equation (1) of the frequency change amount, the variable capacitance diode C
When the capacitance of D changes, the load capacitance CL of the circuit changes, so that the oscillation frequency can be changed. Further, by inserting the inductive reactance circuit 3 instead of the extension coil L, a VCXO can be configured without using the extension coil L, and it is easy to make an IC.

FIG. 2 is a diagram showing the basic configuration of an inductive reactance circuit. The transistor is biased so that the operating point is class A (omitted in the drawing). Reference numeral 4 denotes a field effect transistor of the amplifying element. A resistor R is connected between the drain terminal D and the gate terminal G, and a capacitor C is connected between the gate terminal G and the source terminal S. 5 is a bias resistor. When the inductive reactance circuit is configured as shown in FIG. 2, the distance between the drain terminal D and the source terminal S is equivalently represented by the inductance Leq represented by the equation (5). Leq = CR / gm (5) where C is a capacitor, R is a resistor, and gm is the transconductance of the transistor. From Equation (5), the inductance Leq of the inductive reactance circuit can be set to a desired value by adjusting the value of the capacitor C, the value of the resistor R, and the value of the transconductance gm of the transistor. If the inductance Leq of the inductive reactance circuit is increased, VCX can be calculated by the above-mentioned equation (2) of the frequency control sensitivity.
O frequency control sensitivity can be further improved.

FIG. 3 is a circuit diagram showing one embodiment of a VCXO in which an inductive reactance circuit according to the present invention is inserted.
This is an example in which a variable capacitance diode CD1 is inserted instead of the capacitor C of the inductive reactance circuit. A capacitor C11 is connected between the input and output of the amplifier 1, and a capacitor C12 is connected between the output terminal of the amplifier 1 and the ground. Further, one end of a crystal oscillator 2 is connected to the input terminal of the amplifier 1, and the other end of the crystal oscillator 2 is connected to one end of a variable capacitance diode CD and a relatively large bias resistor RD. The other end of the variable capacitance diode CD is a bias resistor RB
And the capacitor CP, the bias resistor R
The other end of B is connected to ground. The capacitor C
The other end of P is connected to a drain terminal of a field effect transistor 4 serving as an amplifying element. The purpose of insulation between the power supply between the drain terminal of the field effect transistor 4 and the power supply voltage V _CC, with high current mirror circuit 6 impedance, the between the drain terminal D and the gate terminal G of the field effect transistor 4 A resistor R is connected, and a capacitor CP and a variable capacitance diode CD1 for blocking DC current are connected between the gate terminal G and the ground. The connection point between the capacitor CP and the variable capacitance diode CD1 and the terminal V
A relatively large bias resistor RD is provided between the bias resistor RD and the con2. Vcon1 and Vcon2 are control voltage input terminals, and the capacitance of the variable capacitance diode CD changes by changing the control voltage Vcon1. From the equation (1) for the amount of change in the frequency, the variable capacitance diode C
When the capacitance of D changes, the load capacitance CL of the circuit changes. Therefore, the frequency can be changed by changing the control voltage Vcon1. Further, the capacitance of the variable capacitance diode CD1 changes by changing the control voltage Vcon2. Since the inductance Leq of the inductive reactance circuit is represented by Expression (5), when the capacitance of the variable capacitance diode CD1 changes, the inductance Leq of the inductive reactance circuit changes. When the inductance Leq of the inductive reactance circuit changes, the load capacitance CL of the circuit changes. Therefore, the frequency can be changed by changing the control voltage Vcon2. Therefore, the configuration as shown in FIG. 3 has two frequency control terminals, so that a wider frequency control range can be obtained.
Further, since an extension coil is not used, it is easy to make an IC.

Although the present invention has been described with reference to an example in which the present invention is applied to a VCXO, the present invention is not limited to this, and may be a VCO or a TCO or TCXO having a frequency control circuit.

[0013]

As described above, the present invention relates to a VCXO in which at least a piezoelectric vibrator, a variable capacitance element, and an amplification element are combined in a loop, wherein the loop includes an amplification element, a resistance element, and a capacitance element. The inductive reactance circuit to be configured is inserted, and the capacitance element in the inductive reactance circuit is, for example, a variable capacitance element.
With such a configuration, a VCXO that does not use an extension coil can be realized, and a remarkable effect can be exhibited when the circuit is formed into an IC.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a VCXO in which an inductive reactance circuit according to the present invention is inserted.

FIG. 2 is a diagram showing the basic configuration of an inductive reactance circuit.

FIG. 3 is a circuit diagram showing one embodiment of a VCXO in which an inductive reactance circuit according to the present invention is inserted.

FIG. 4 is an example of a circuit diagram showing a VCXO using a conventional extension coil.

FIG. 5 is an equivalent circuit diagram of the crystal unit.

FIG. 6 is an equivalent circuit diagram of VCXO.

[Description of Signs] 1 amplifier, 2 crystal oscillator, 3 inductive reactance circuit, 4 amplifying element, 5 bias resistor, 6 current mirror circuit, C, C11, C12, CP capacitor, CD, CD1 variable capacitance diode, R, RD, RB resistance, A, Vcon1, Vcon2 Control voltage input terminal, Vcc power supply voltage terminal, L extension coil, L1 Equivalent series inductance of crystal oscillator, C1 Equivalent series capacitance of crystal oscillator, R1 Equivalent series resistance of crystal oscillator , C0 Equivalent parallel capacitance of crystal unit, inductance on Lan circuit side, capacitance on Can circuit side

Claims (2)

[Claims] 1. A voltage-controlled crystal oscillator in which at least a piezoelectric vibrator, a variable capacitance element, and an amplification element are combined in a loop, wherein the loop includes an amplification element, a resistance element, and a capacitance element. A voltage controlled crystal oscillator characterized by inserting a reactance circuit. 2. The voltage controlled crystal oscillator according to claim 1, wherein the capacitive element in the inductive reactance circuit is a variable capacitive element.