JP2000114875A - Oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a small piezoelectric oscillator excellent in frequency start characteristic by providing a switch circuit formed of a switch for controlling the band characteristic of a low frequency filter circuit and a switch control circuit controlling the switch circuit. SOLUTION: A compensation voltage generation circuit 2 outputs a temperature compensating voltage based on a temperature detecting signal supplied from a temperature sensing element 1. A low frequency filter 3 removes the noise signal superimposed to the temperature compensating voltage. The switch circuit 4 controls the operation of the filter 3. A processing circuit 5 amplifies and outputs the temperature compensating voltage. A crystal oscillator of a voltage controlled type (VCXO) 6 has its output frequency controlled based on the temperature compensating voltage supplied from the circuit 5. The switch control circuit 7 outputs a switch controlling signal for controlling the operation of the circuit 4 based on the level of the output signal of VCXO 6. Namely, the circuit 4 is controlled based on at least one of the output signal level of VCXO 6 or the time from the supply of a power voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric oscillator,
In particular, it relates to a piezoelectric oscillator having excellent phase noise characteristics and short-term frequency stability.

[0002]

2. Description of the Related Art In recent years, miniaturization of mobile communication devices such as portable telephones has been advanced, and accordingly, for example, a temperature-compensated crystal oscillator (hereinafter, TCXO) has been used as a piezoelectric oscillator used as a reference signal source. It is required that there be.
The TCXO includes a temperature-compensated voltage generation circuit composed of a temperature-sensitive element and a resistance network, and a voltage-controlled crystal oscillator (hereinafter, referred to as a TCXO).
VCXO), and supplies the temperature compensation voltage output from the temperature compensation circuit to the variable capacitance element provided in the VCXO, and the capacitance value of the variable capacitance element fluctuates with the temperature change of the crystal resonator. There is generally known a configuration in which a control is performed so as to cancel the noise and a highly stable frequency is obtained.

[0003] Such a TCXO is composed of an electric circuit including the temperature compensating voltage generating circuit and an oscillating circuit as a one-chip IC.
In this case, it is possible to cope with the above-mentioned demand for downsizing. In this case, a circuit configuration as shown in FIG. 5 is generally used. FIG. 3A is a block circuit diagram of the TCXO, and FIG.
(C) shows a configuration of a processing circuit described later. As shown in FIG. 2A, the TCXO includes a temperature-sensitive element 101,
After removing a compensation voltage generation circuit 102 that outputs a temperature compensation voltage based on a temperature detection signal supplied from the temperature sensing element 101 and a noise signal that overlaps the temperature compensation voltage,
A processing circuit 103 for amplifying and outputting the signal;
And a VCXO 104 whose frequency is controlled based on the supplied temperature compensation voltage.

The processing circuit 103 includes an operational amplifier 105 and an operational amplifier 1 as shown in FIG.
A resistor R1 connected between the inverting input terminal of the compensating voltage generation circuit 102 and the output of the compensation voltage generating circuit 102;
A resistor R2 connected between the non-inverting input terminal of
It comprises an inverting amplifier having a feedback resistor R3 connected between the output of the operational amplifier 105 and the inverting input terminal, and a capacitor C1 connected in parallel with the feedback resistor R3. FIG. 3C is a circuit diagram of the processing circuit 103 when the capacitor C1 is connected between the inverting input terminal and ground.

Here, the amplification of the temperature compensation voltage by the inverting amplifier is performed because the output range of the compensation voltage generation circuit 102 becomes narrow due to the integration of the circuit. belongs to. Further, in addition to the above, in order to compensate for the above-mentioned shortage of the temperature compensation voltage, the VC
The frequency change amount (hereinafter, frequency sensitivity) with respect to the voltage change of the XO 104 is set to be large. However, at this time,
In the process of amplifying the temperature compensation voltage, the level of the noise signal included therein is also amplified. When the noise signal is directly supplied to the VCXO 104 having high frequency sensitivity, the output frequency of the VCXO 104 is modulated based on the compensation voltage including the noise signal, and as a result, the phase noise characteristic of the TCXO deteriorates.

[0006] The low-pass filter 106 is arranged to prevent the deterioration of the phase noise characteristic caused by the above-mentioned causes, and functions to remove a noise signal superimposed on the temperature compensation voltage. The pole frequency (frequency at which the voltage gain starts decreasing) of the low-pass filter 106 is f = 1 / (2πR1C
It is represented by 1). Therefore, when the oscillator circuit is formed into an IC, by adopting the above-described configuration, it is possible to reduce the size of the TCXO without deteriorating the frequency temperature characteristics and the phase noise characteristics.

[0007]

[Problems to be solved by the present invention] However, FIG.
In the TCXO having the configuration shown in (1), there has been a problem that the time from when the supply of the power supply voltage is started to when the frequency is stabilized (hereinafter referred to as a frequency starting characteristic) becomes long. That is, when the supply of the power supply voltage is started, the processing circuit 103 and the
The VCXO 104 starts operating, and at the same time, the compensation voltage generating circuit 102 also operates.

The compensation voltage generation circuit 102 supplies a temperature compensation voltage based on the set conditions and the temperature detection result from the temperature sensing element 101 to the VCXO 104 via the processing circuit 103. At this time, when the temperature compensation voltage passes through the low-pass filter 106 provided in the processing circuit 103, the temperature compensation voltage is affected by power charging of the capacitor C1 and the like.
Supply to the VCXO 104 will be delayed. Therefore,
Due to the delay described above, the VCXO1
Since no voltage is supplied to the variable capacitance element of No. 04 and the output frequency becomes unstable, the TCXO has a problem that the frequency starting characteristic is deteriorated.

[0009] For example, some portable telephones operate intermittently in order to suppress the power consumption of the battery. However, due to the deterioration of the frequency starting characteristic of the TCXO, it takes time until the TCXO outputs a stable frequency. In some cases, it is necessary to set the standby time to a long time, so that sufficient power consumption may not be achieved.

The present invention has been made to solve the above-described problem, and has as its object to provide a small-sized piezoelectric oscillator having excellent frequency starting characteristics.

[0011]

According to a first aspect of the present invention, there is provided a voltage controlled piezoelectric oscillation circuit capable of controlling a frequency by a voltage signal, and a noise included in the voltage signal. A low-pass filter circuit for removing a signal, a switch circuit including a switch for controlling band characteristics of the low-pass filter circuit, and an output signal level or a power supply voltage of the voltage-controlled piezoelectric oscillator are supplied. And a switch control circuit for controlling the switch circuit based on at least one of the time from the switch.

According to a second aspect of the present invention, in addition to the first aspect, the low-pass filter circuit is a low-pass filter having a plurality of pass band characteristics, and the switch circuit is provided with a plurality of the low-pass filters. It is characterized by having a configuration provided with a plurality of switches corresponding to the filters.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 shows a TCXO according to the invention.
FIG. 3 is a circuit diagram showing one embodiment. The figure (a) shows TC
FIGS. 2B and 2C are block circuit diagrams of the XO, and FIGS. 2B and 2C are processing circuits to be described later, and FIG.

As shown in FIG. 1A, the TCXO comprises a temperature sensing element 1, a compensation voltage generating circuit 2 for outputting a temperature compensation voltage based on a temperature detection signal supplied from the temperature sensing element 1, A processing circuit 5 including a low-pass filter 3 for removing a noise signal superimposed on the compensation voltage, a switch circuit 4 for controlling the operation of the low-pass filter 3, and amplifying and outputting the temperature compensation voltage; A VCXO 6 whose output frequency is controlled based on the temperature compensation voltage supplied from the processing circuit 5,
The switch circuit 4 based on the level of the output signal of the VCXO 6
And a switch control circuit 7 for outputting a switch control signal for controlling the operation of the switch.

The processing circuit 5 comprises an operational amplifier 8, a resistor R1 connected between an inverting input terminal of the operational amplifier 8 and the output of the compensation voltage generating circuit 2, as shown in FIG. An inverting amplifier including a resistor R2 connected between the non-inverting input terminal of the operational amplifier 8 and ground and a feedback resistor R3 connected between the output of the operational amplifier 8 and the inverting input terminal; It comprises a feedback resistor R3 and a capacitor C1 connected in parallel via a switch SW1 constituting the switch circuit 4. The low-pass filter 3 is constituted by the resistor R1 and the capacitor C1, and the pole frequency is represented by f = 1 / (2πR1C1).

FIG. 3C shows the capacitor C1.
FIG. 9 is a circuit diagram of the processing circuit 5 when a series circuit including a switch SW1 is connected between the inverting input terminal and ground. On the other hand, the switch control circuit 7 shown in FIG.
For example, the output OUT of the VCXO 6 is connected to the base of a transistor constituting the switch SW1 via a rectifier circuit 9, and a resistor R4 is connected between the base and ground, and a resistor R4 is connected between the emitter of the transistor and ground. And a resistor R5. With such a configuration, the base voltage changes in accordance with the level of the output OUT, and the transistor performs a switching operation when the base voltage reaches a predetermined value.

Here, usually, the time required for the frequency of the output signal of the crystal oscillator to stabilize from the start of supply of the power supply voltage is shorter than the time required for the level of the output signal of the crystal oscillator to stabilize. Time. Therefore, the TCXO having the above configuration turns off the switch SW1 in the switch circuit 4 from when the supply of the power supply voltage is started until the level of the output signal of the VCXO 6 reaches a predetermined value. After the output signal level reaches a predetermined value, the switch circuit 4 is controlled by the switch control circuit 7 so that the switch SW1 is turned on, so that the switch SW1 is controlled after the output frequency is stabilized. Thus, a low-pass filter can be connected, and the frequency starting characteristic does not deteriorate due to the provision of the low-pass filter.

[0018] In other words, 0.5V output level of the TCXO is, for example, _{p - p}
When the output frequency is stable when the above is reached, when the output level is 0.7 V _pp or more, a DC current generated by rectifying the output level and the bases and emitters of the transistors generated by the resistors R4 and R5. If the voltage between the transistors is set to be 0.7 V or less, the transistor is operated (the switch is turned on) after the output frequency is sufficiently stabilized.
And the current flows between the collector and the emitter.
Therefore, since the filter circuit 4 is connected after the output frequency is stabilized by this, the frequency starting characteristic is not affected.

At this time, if the temperature compensation voltage changes abruptly due to the connection of the low-pass filter and the frequency fluctuates abruptly, it is desirable to use a processing circuit as shown in FIG.

FIGS. 2A and 2B are circuit diagrams showing another embodiment of the processing circuit 5 according to the present invention. 1A is different from FIG. 1A in that a plurality of series circuits each including a capacitor and a switch are provided, and these are connected in parallel with the feedback resistor R3. is there. At this time, the switch control circuit 7 connects the plurality of capacitors constituting the low-pass filter 3 to C1, C2, and C3.
… As Cn, switches connected in the same order as SW1 and S
When W2, SW3... SWn, and R3 / R1 = 1, the pole frequency of the low-pass filter 3
If you close from SW1 to SWn in order based on the output signal level of
Control can be performed in the range of f = 1 / (2πCR1) to f = 1 / (2πnCR1) (nC = C1 + C2 + C3 +... Cn). In this case, the configuration of the switch control circuit 7 is, for example, as shown in FIG.
The configuration shown in (d) may be a plurality of configurations.

That is, if the processing circuit 5 having such a configuration is used, it is possible to change the pole frequency of the low-pass filter 3 so as to gradually decrease, so that the temperature compensation voltage supplied to the VCXO 6 Can be prevented from rapidly changing. Therefore, it is possible to prevent rapid frequency fluctuation of TCXO. FIG. 2B shows a low-pass filter in which a series circuit of a plurality of capacitors and a switch is connected between the non-inverting input terminal of the operational amplifier 8 and the ground. Performs the same operation as that of FIG.

Although the present invention has been described above using the processing circuit 5 having an inverting amplifier, the present invention is not limited to this, and the processing circuit 5 is configured using a non-inverting amplifier as shown in FIG. Obviously, a series circuit of a capacitor and a switch may be connected between the non-inverting input terminal of the operational amplifier 8 and the ground. FIG. 7A is a circuit diagram when the number of low-pass filters is set to one, and FIG. 7B is a circuit diagram when the pole frequency of the low-pass filter is selectable. Further, the present invention has been described for the case where the switch control circuit operates based on the output signal level of the VCXO.However, the present invention is not limited to this, and uses a switch control circuit that operates based on the time from startup. And in this case,
As shown in FIG. 4, the switch control circuit 7 connects the base of the transistor constituting the switch to a connection intermediate point of a series circuit of the resistor R6 and the capacitor C connected between the power supply Vcc and the ground. The emitter of the transistor is connected, for example, via a resistor R7. Then, since the transistor operates as a switch following the delay of the supply of the power supply voltage due to the time constant of the capacitor C, the switch may operate after the output frequency of the TCXO becomes stable by selecting this time constant. It becomes possible.

Further, the present invention has been described by taking an oscillator using a quartz oscillator as an example. However, the present invention is not limited to this, and is applicable to an oscillator using a piezoelectric oscillator other than quartz. Obviously it is good.

[0024]

As described above, according to the first aspect of the present invention, the voltage signal is not passed through the low-pass filter by the switch until the piezoelectric oscillator reaches the specified frequency stability after receiving the supply of the power supply voltage. After that, after the specified frequency stability is obtained, the voltage signals are supplied to the voltage-controlled piezoelectric oscillators through the low-pass filters, respectively, so that the starting characteristics of the piezoelectric oscillators are prevented from deteriorating. This has the effect that it becomes possible. The invention according to claim 2 is:
In addition to the effect of the first aspect of the present invention, since it is possible to control the pole frequency of the low-pass filter so as not to change abruptly, there is an effect that a sudden frequency of the piezoelectric oscillator is not generated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a temperature compensated crystal oscillator according to the present invention. FIG. 1A is a block circuit diagram of a temperature-compensated crystal oscillator. (B) shows a circuit diagram of an embodiment of a processing circuit according to the present invention. (C) A circuit diagram of another embodiment of the processing circuit according to the present invention. (D) One embodiment of a switch control circuit according to the present invention.

FIG. 2 shows another embodiment of a processing circuit provided in the temperature compensated crystal oscillator according to the present invention. FIG. 3A is a circuit diagram illustrating a configuration of a low-pass filter capable of controlling a pole frequency according to the present invention. (B) is a circuit diagram showing a configuration of a low-pass filter capable of controlling a pole frequency according to the present invention.

FIG. 3 shows another embodiment of the processing circuit provided in the temperature-compensated crystal oscillator according to the present invention. (A) is a circuit diagram showing a configuration of a processing circuit using a non-inverting amplifier according to the present invention. (B) is a circuit diagram illustrating a configuration of a processing circuit including a low-pass filter capable of controlling a pole frequency using a non-inverting amplifier according to the present invention.

FIG. 4 shows another embodiment of the switch control circuit according to the present invention.

FIG. 5 is a circuit diagram showing a configuration of a conventional temperature-compensated crystal oscillator. (A) shows a configuration of a conventional temperature-compensated crystal oscillator using a block circuit. FIG. 3B is a circuit diagram of a processing circuit of a conventional temperature-compensated crystal oscillator. (C) shows a circuit diagram of a processing circuit of a conventional temperature-compensated crystal oscillator.

[Explanation of symbols]

1, 101 temperature sensing element, 2, 102 compensation voltage generation circuit,
3, 106 low-pass filter, 4 switch circuit, 5, 103
Processing circuit, 6, 104VCXO, 7 switch control circuit, 8,
105 operational amplifier, 9 rectifier circuit

Claims (2)

[Claims] 1. A voltage-controlled piezoelectric oscillation circuit capable of frequency control by a voltage signal, a low-pass filter circuit for removing a noise signal included in the voltage signal, and controlling a band characteristic of the low-pass filter circuit. And a switch control circuit that controls the switch circuit based on at least one of an output signal level of the voltage-controlled piezoelectric oscillator or a time period after a power supply voltage is supplied. A piezoelectric oscillator having a configuration. 2. The low-pass filter circuit is a low-pass filter having a plurality of pass band characteristics, and the switch circuit is provided with a plurality of switches corresponding to the plurality of low-pass filters. The piezoelectric oscillator according to claim 1, wherein: