JP2002290151A - Temperature compensated quartz oscillator with afc - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature compensated oscillator which maintains variable voltage width and low noise by compensation voltage and exhibits proper AFC(automatic frequency control) operation. SOLUTION: The temperature compensated quartz oscillator is constituted of: a quartz oscillator which is constituted by using a quartz oscillator as an inductor components; a compensation voltage generation circuit for generating temperature compensated voltage corresponding to a temperature for compensating the frequency-temperature characteristics of the quartz oscillator; a first voltage variable capacitance element, which is inserted into the oscillation closed loop of the quartz oscillator and to which compensation voltage Vc is applied; a CR filter, arranged between the compensation voltage generation circuit and the first voltage variable capacitance element; a second voltage variable capacitance element is connected, in parallel with or in series with the first voltage variable capacitance element in terms of high frequency; and AFC control voltage from an automatic frequency control circuit is applied to the second voltage variable capacitance element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature-compensated crystal oscillator (hereinafter referred to as "temperature-compensated oscillator") as an industrial technical field, and particularly to a control voltage (AF) from an automatic frequency control (AFC) circuit.
AF for controlling the oscillation frequency by the C voltage VF)
The present invention relates to a temperature-compensated oscillator with C.

[0002]

2. Description of the Related Art A temperature-compensated oscillator flattens frequency-temperature characteristics caused by a quartz oscillator 3 and compensates for temperature. Therefore, a temperature-compensated oscillator is used especially in a dynamic environment such as a cellular phone. Used in equipment. On the other hand, the AFC circuit receives a communication frequency from a base station, for example, and causes the oscillation frequency to follow the communication frequency. These are all provided with a temperature compensation voltage Vc (compensation voltage Vc) in a voltage variable capacitance element provided in an oscillation closed loop.
And AFC voltage VF is applied to compensate for temperature and to control the oscillation frequency (see JP-A-2001-44758).

(Example of Prior Art) FIG. 3 is a block circuit diagram of a temperature-compensated oscillator schematically illustrating a conventional example.
The temperature-compensated oscillator generally includes a voltage-controlled crystal oscillator 1 and a compensation voltage generation circuit 2. The crystal oscillator 1
It comprises a crystal unit 3 and an oscillation circuit 4. The crystal resonator 3 is of a so-called Colpitts type in which a resonance circuit is formed as an inductor component with a not-shown divided capacitor in the oscillation circuit 4 and the resonance frequency is fed back by an amplifier. Then, a voltage variable capacitance element, in this case, a variable capacitance diode 5 is inserted into the oscillation closed loop of the crystal oscillator 1 to obtain a voltage control type shown by a dashed line frame. Then, the anode of the variable capacitance diode 5 is connected to the earth ground, and the cathode is connected to the crystal unit 3.

The compensation voltage generating circuit 2 obtains a detection voltage responsive to the ambient temperature by using, for example, the temperature characteristic of a resistor, and generates a compensation voltage Vc based on the detection voltage. The compensation voltage Vc is
A frequency-temperature characteristic of the crystal oscillator 1 of the crystal oscillator 1 mainly due to the crystal resonator 3, for example, a cubic curve (curve (a) in FIG. 4) is used to compensate for this. Then, a positive voltage, that is, a reverse voltage is applied to the cathode of the variable capacitance diode 5 in the oscillation closed loop. These (the crystal oscillator 1 and the compensation voltage generating circuit 2 excluding the crystal oscillator 3) are integrated into one chip LSI.
It is integrated in one body.

In such a device, when a compensation voltage Vc as a reverse voltage is applied to the cathode of the variable capacitance diode 5, only the capacitance between the terminals changes according to the level of the compensation voltage Vc. However, because of the reverse voltage, no current flows and only the capacity changes. Therefore, since the equivalent series capacitance including the variable capacitance diode 5 as viewed from the crystal unit 3 changes, the oscillation frequency changes. Then, by setting the compensation voltage Vc according to the frequency temperature characteristic, the frequency temperature characteristic is flattened within the standard temperature range and the temperature is compensated.

Reference numeral 6 in FIG. 3 denotes a low-pass filter (CR filter) comprising a capacitor 7 and a resistor 8.
Thus, the high frequency component contained in the constant voltage source is removed to improve the phase noise characteristic. Reference numeral 9 denotes a high-frequency blocking resistor that is separated from the crystal oscillator 1 in high frequency. Also, V in FIG.
co is a reference voltage at normal temperature.

Further, an AFC voltage VF from an automatic frequency control circuit (not shown) is applied to the anode of the variable capacitance diode 5 via the high frequency blocking resistor 10. Note that the AFC voltage VF is applied as a + voltage smaller than the compensation voltage Vc. Reference numeral 11 denotes a DC blocking capacitor. As a result, the applied voltage between the terminals of the variable capacitance diode 5 changes and the capacitance also changes, so that the oscillation frequency is controlled. From these facts, it is possible to supply a stable oscillation frequency whose temperature is compensated while controlling the oscillation frequency.

[0008]

[Problems to be Solved by the Invention]
However, in the temperature-compensated oscillator with an AFC having the above configuration, the variable capacitance diode 5 is shared, and the AFC voltage VF, which is a positive voltage, is applied to the anode. Therefore, the potential of the anode is higher by the AFC voltage VF than in the case where the anode is grounded. Thus, when the compensation voltage Vc is applied, the voltage between the terminals of the variable capacitance diode 5 becomes (Vc-VF) V, and there is a problem that the variable voltage width due to the compensation voltage Vc is reduced. These become more problematic as IC operation progresses and, for example, operation at a low voltage of 2 V or less is performed.

In this example, in order to reduce noise,
A low-pass filter 6 made of CR is inserted. For this reason, there is a problem that the AFC operation does not immediately follow due to the CR time constant. Since the temperature compensation only needs to follow the ambient temperature gently, the CR time constant does not matter.

(Object of the Invention) It is an object of the present invention to provide a temperature-compensated oscillator having improved AFC operation while maintaining a variable voltage width and low noise by a compensation voltage.

[0011]

The present invention provides a compensation voltage Vc.
The basic solution is to connect a second voltage variable capacitance element in parallel or series in high frequency to the first voltage variable capacitance element to which is applied the AFC voltage VF to the second voltage variable capacitance element. .

[0012]

According to the present invention, the compensation voltage Vc and the AFC voltage VF are separately applied to the first and second variable capacitance diodes.
The variable voltage width of the first variable capacitance diode to which the compensation voltage Vc is applied is increased. Hereinafter, an embodiment of the present invention will be described.

FIG. 1 is a block circuit diagram of a temperature-compensated 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 temperature-compensated oscillator includes the crystal oscillator 1 of the voltage control type by inserting the first variable capacitance diode in the oscillation closed loop, and the compensation voltage generating circuit 2 for generating the compensation voltage Vc. Then, a series circuit of the DC blocking capacitor 11 and the second variable capacitance diode 12 is inserted into the oscillation closed loop in parallel with the first variable capacitance diode 5 in high frequency, that is, a series circuit of the second variable capacitance diode 12. Each of them connects the anode of each of the variable capacitance diodes 5 and 12 to ground. The compensation voltage Vc is applied to the cathode of the first variable capacitance diode 5.
And the cathode of the second variable capacitance diode 12 is
The voltage VF is applied.

With such a configuration, the compensation voltage Vc from the compensation voltage generating circuit 2 is independently applied to the first variable capacitance diode 5. Therefore, the variable voltage width of the compensation voltage Vc is larger than when the conventional AFC voltage VF is applied to the anode. This is suitable for lowering the voltage when promoting the IC.

The second AFC voltage VF is applied.
The variable capacitance diode 12 includes the first variable capacitance diode 5.
Is blocked by the DC blocking capacitor 11. Therefore, the delay of the AFC operation due to the time constant of the low-pass filter (CR filter) 6 is prevented, and the AFC operation is ensured.

[0016]

In the above embodiment, the AFC voltage VF is applied to the first variable capacitance diode 5 to which the compensation voltage Vc is applied.
Is connected in parallel at high frequency, but the first and second variable capacitance diodes 5 and 12 may be connected in series at high frequency as shown in FIG. . However, in this case, a high frequency blocking resistor 13 is provided on the anode side of the first variable capacitance diode 5 and grounded.

[0017]

According to the present invention, the second voltage variable capacitance element is connected in parallel to the first voltage variable capacitance element to which the compensation voltage Vc is applied, and the AFC voltage VF is applied to the second voltage variable capacitance element. It is possible to provide a temperature-compensated oscillator with improved AFC operation while maintaining a variable voltage width and low noise due to the compensation voltage.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a temperature-compensated oscillator explaining one embodiment of the present invention.

FIG. 2 is a block circuit diagram of a temperature compensated oscillator illustrating another embodiment of the present invention.

FIG. 3 is a block circuit diagram of a temperature compensated oscillator illustrating a conventional example.

FIG. 4 shows frequency temperature characteristics and voltage frequency characteristics of a crystal oscillator for explaining a conventional example.

[Explanation of symbols]

Reference Signs List 1 crystal oscillator, 2 compensation voltage generation circuit, 3 crystal oscillator, 4 oscillation circuit, 5, 12 variable capacitance diode, 6
Low-pass filter (CR filter), 7, 11 Capacitor, 8, 9, 10, 13 Resistance.

Claims (1)

[Claims] 1. A crystal oscillator having a crystal resonator as an inductor component, a compensation voltage generation circuit for generating a temperature compensation voltage responsive to temperature for compensating frequency temperature characteristics of the crystal oscillator, and an oscillation of the crystal oscillator. A temperature-compensated crystal oscillator comprising a first voltage variable capacitance element inserted into a closed loop to which the compensation voltage Vc is applied, and a CR filter provided between the compensation voltage generation circuit and the first voltage variable capacitance element In the above, a second voltage variable capacitance element is connected to the first voltage variable capacitance element in parallel or in series in a high frequency manner, and the second voltage variable capacitance element is connected to A from an automatic frequency control circuit.
A temperature-compensated crystal oscillator with an AFC, characterized by applying an FC control voltage.