JP3619712B2 - Crystal oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystal oscillator, and more particularly to shortening of startup time.
[0002]
[Prior art]
In recent years, mobile communication devices such as mobile phones have been widely used, and electronic devices of this type are required to have various functions in addition to miniaturization.
For this reason, there are various demands for a crystal oscillator used as a communication frequency reference in such a communication device.
[0003]
For example, in a mobile phone, it is necessary to reduce the volume of a battery as a power source in order to reduce the size and weight. On the other hand, it is required that the operation time is extended even if the battery volume is reduced, and that long standby reception is possible.
[0004]
For this reason, in the standby state, it is considered to extend the battery life by checking the presence or absence of an incoming call by intermittently repeating the operation state and the suspension state.
2. Description of the Related Art Conventionally, some crystal oscillators that are used intermittently output an oscillation output via a gate circuit, for example.
[0005]
In this way, the output can be turned on and off by controlling the gate on and off.
However, in such a case, the oscillation output is cut off by using a gate circuit, and since the oscillation circuit operates continuously even when the output is cut off, the power consumption cannot be reduced.
[0006]
Therefore, in order to save power, a crystal oscillator that operates intermittently needs to be repeatedly operated and stopped. For this reason, it is necessary for the effective use of the battery power that the time required for the crystal oscillator to turn into a steady oscillation state, that is, the start-up time is as short as possible.
[0007]
Conventionally, in such a case, the startup time has been shortened by flowing a large current through the oscillation circuit at the time of startup.
However, in such a case, power consumption at the time of startup increases, which is not rational.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and provides a crystal oscillator that can significantly shorten the startup time and that is suitable for intermittent operation without particularly increasing power consumption during startup. It is intended.
[0009]
According to the present invention, in a crystal oscillation circuit having a varicap diode that varies a load capacity of a crystal resonator, an addition output from an addition circuit is applied to the varicap diode, and the addition circuit adjusts an oscillation frequency adjustment voltage V c. and immediately after power-on and configuration obtained by adding the generated voltage V k start generating circuit for applying a voltage higher than the steady state varicap diode.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to a circuit diagram shown in FIG.
Reference numeral 1 denotes an inverter. A feedback resistor 2 is connected between the input and output, and a crystal resonator 3 is connected to the feedback resistor 2 in parallel.
[0011]
The power source of the inverter 1 is supplied from VDD and the ground potential.
The output of the inverter 1 is connected to the output terminal (OUT) 4.
Capacitors 5 and 6 are inserted between the input terminal and output terminal of the inverter 1 and the ground potential so as to satisfy the phase condition.
[0012]
Further, series circuits of capacitors 7 and 8 and varicap diodes 9 and 10 are connected in parallel with the capacitors 5 and 6, respectively.
On the other hand, the addition output of the adder circuit using the operational amplifier 11 is given to the series connection point of the capacitors 7 and 8 and the varicap diodes 9 and 10 via the resistors 12 and 13 and the electrostatic capacitance of the varicap diodes 9 and 10 is applied. The capacity is controlled.
In the adder circuit, a separately adjusted adjustment voltage VC of the oscillation frequency and the generated voltage VK of the starting voltage generating circuit are added.
[0013]
In the startup voltage generating circuit, for example, a resistor 14 and a capacitor 15 are inserted in series between a power supply VDD and a ground potential.
The series connection point of the resistor 14 and the capacitor 15 is connected to the input of the inverter 16.
For example, if the start-up time of the oscillation circuit is 3 ms, the time constant of the series circuit of the resistor 14 and the capacitor 15 is set so that the time until the output of the inverter 16 is inverted from H to L is about 1 ms. Good.
[0014]
In this way, immediately after the power is turned on, the potential at the series connection point of the resistor 14 and the capacitor 15 is low, so the logic level of the input of the inverter 16 is L, so the logic level of the output is H, and the generated voltage VK is approximately the power supply potential VDD.
[0015]
Therefore, the adder circuit adds the adjustment voltage VC and the generated voltage VK and applies them to the varicap diodes 9 and 10.
Therefore, a higher voltage is applied to the varicap diodes 9 and 10 than when only the adjustment voltage VC is applied, so that the electrostatic capacity is reduced. When this is viewed from the inverter 1 of the oscillation circuit, the size of the load is reduced, so that the load is light.
[0016]
Therefore, the inverter 1 can be operated with a light load, whereby the time until the frequency and amplitude become steady after the power is turned on can be significantly reduced as compared with the case where the load and the load are kept constant. .
For example, in a conventional oscillation circuit using an inverter, it takes about 3 ms for the oscillation frequency and amplitude to reach a steady state after the power is turned on, but this time can be halved by reducing the load at startup. I was able to.
[0017]
After the power is turned on, when the charging voltage of the capacitor 15 gradually increases and exceeds the threshold voltage of the inverter 16, the output of the inverter 16 is inverted from H to L.
Therefore, the adjustment voltage VC is applied to the varicap diodes 9 and 10, and a steady operation state is obtained.
[0018]
The drain and source of a P-type FET 17 are connected in parallel with the capacitor 15, and the gate of the FET 17 is connected to the power supply VDD.
Accordingly, when the power supply VDD is cut off, the gate voltage of the FET 17 gradually decreases, and at a certain point in time, the drain and the source become conductive, and the charge of the capacitor 15 is discharged.
[0019]
The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, an oscillation circuit using an inverter has been described. However, the present invention can be similarly applied to a Colpitts-type oscillation circuit using a transistor, an FET, or the like. Of course.
[0020]
With such a configuration, the start-up time can be shortened with a simple configuration, thereby preventing an increase in power consumption.
Therefore, it is suitable for intermittent operation of mobile communication devices such as mobile phones, and can reduce power consumption by turning off the oscillator power for a certain period of time. It becomes an operation state. Therefore, it is possible to provide a crystal oscillator that can contribute to a reduction in power consumption of this type of electronic device.
[0021]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a crystal oscillator described in an intermittent operation without a short start-up time and an increase in power consumption at the time of start-up.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment of the present invention.
[Explanation of symbols]
1, 16 ··· Inverter 3 ··· Crystal resonator 9, 10 ·· Varicap diode

Claims (1)

In a crystal oscillator having a varicap diode that varies a load capacity of a crystal resonator, an addition output from an adder circuit is applied to the varicap diode, and the adder circuit adjusts an oscillation frequency adjustment voltage V c and immediately after power-on. A crystal oscillator characterized by adding a voltage V k generated by a start generation circuit that applies a voltage higher than a steady state to a varicap diode.

Images