JP2000091845A - Colpitts oscillating circuit and radio communication terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate stably also after reaching a stationary state while reducing starting time after supplying power by providing a crystal oscillator and a switching means connecting one end of the crystal oscillator to a power supplying line before starting oscillation and connecting it to a ground potential point after starting oscillation. SOLUTION: This system is provided with MOS transistors SWp and SWn being a switching means selectively connecting one end of the crystal oscillator Xt to the power supplying line or the ground potential point. Then at the time of reaching the stationary state after supplying power, a switch control signal Vs is made a high level to switch the connection of the oscillator Xt from the side of a power source to a ground potential side. When one end of the oscillator Xt is connected to the side of the power supplying line after supplying power like this, the starting time of an oscillation circuit can be reduced. In addition by connecting one end of the oscillator Xt to the side of the ground potential point after starting oscillating operation, stable oscillating operation can be executed without receiving influence of noise, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Colpitts oscillation circuit and a radio communication terminal device, and more particularly, to a Colpitts oscillation circuit that includes a feedback capacitor and a crystal oscillator to generate a predetermined frequency signal, and a Colpitts oscillation circuit. The present invention relates to an improvement of a wireless communication terminal device using a Colpitts oscillation circuit.

[0002]

2. Description of the Related Art FIG. 16 is a diagram showing an example of a configuration of a conventional Colpitts oscillation circuit used for a portable telephone. In the drawing, R1 to R3 are bias resistors of the transistor Tr, R4 is an output resistor, and Xt is a crystal oscillator.
C1 and C2 are feedback capacitors for positively feeding back the output signal of the transistor Tr between the base and emitter terminals of the transistor Tr. C4 is a coupling capacitor for cutting off the output of the DC component, and C5 is a bypass capacitor for making the power supply line and the ground potential point equivalent in an AC manner. C5 may be arranged in a power supply circuit (not shown).

[0005] Cv1 is a variable capacitance diode called a varicap, the capacitance of which is changed by a frequency control signal Vf which is a voltage applied to the anode. C3 is a capacitor for cutting a DC component by the frequency control signal Vf. The series circuit of C3 and Cv1 functions as a voltage controlled variable capacitor controlled by the frequency control signal Vf to the connection point. Since the frequency of the output signal Vo of the oscillation circuit corresponds to the resonance frequency of the resonance circuit including C1, C2, C3, Cv1, and Xt, the frequency of the output signal Vo can be controlled by the frequency control signal Vf.

FIG. 17 is an equivalent circuit for explaining the operation of the oscillation circuit shown in FIG. 16 immediately after power is turned on. In the figure, Cbc is the capacitance between the base and collector terminals of the transistor Tr, and the influence of the crystal oscillator Xt is ignored. When power is supplied to the oscillation circuit, a steady state is reached after a transition period. The voltage Vx between the terminals of the crystal unit Xt in the steady state becomes equal to the voltage between the terminals of the resistor R2, and can be obtained from the voltage dividing ratio of the resistors R1 and R2. In the initial stage of the transition period up to the steady state, Vx represented by the following equation (1) is applied to the crystal resonator Xt.

[0005]

(Equation 1)

The values of C1 and C2 vary depending on the required oscillation frequency, but are generally on the order of tens of pF. On the other hand, the capacitance Cbc between the base and the collector of the transistor Tr is several pF. Therefore, Cn is Cbc
, The denominator of equation (1) is sufficiently larger than the numerator, and the crystal oscillator V
Only a voltage smaller than the power supply voltage Vcc could be applied to x.

The vibrator current immediately after the power is turned on is proportional to the voltage applied to the vibrator. For this reason, if only a small voltage can be applied, there is a problem that the time from power-on until the output signal Vo stabilizes (rise time) becomes long. In addition, when the equivalent resistance of the crystal unit is large, there is a problem that oscillation failure occurs easily.

Generally, a wireless communication terminal device such as a cellular phone is
Battery is used as power source. For this reason, it is required to reduce power consumption and operate the device for as long as possible. Therefore, in many cases, a sleep function for stopping power supply to the oscillation circuit during standby is provided. The wireless communication terminal device having such a sleep function turns on the power to the oscillation circuit at a predetermined time interval determined by the base station during standby. Then, after receiving the radio signal from the base station, the operation of interrupting the power supply to the oscillation circuit is repeated again to reduce the power consumption.

However, wireless communication with the base station must be performed after the oscillation circuit has reached a steady state. For this reason,
The longer the rise time of the oscillation circuit, the sooner it is necessary to turn on the power, and the shorter the sleep period. That is, even when the same battery is used, there is a problem that the longer the rise time of the oscillation circuit, the greater the power consumption during standby and the shorter the average standby time.

An example of a configuration of an oscillation circuit proposed to solve such a problem is disclosed in Japanese Patent Application Laid-Open No. 9-223930. FIG. 18 is a diagram showing a conventional oscillation circuit described in this publication. This oscillation circuit differs from the oscillation circuit shown in FIG. 16 in which one end of the crystal unit Xt is connected to the power supply line side and is connected to the ground potential point side. However, since the power supply line and the ground potential point are AC equivalent, the circuit in FIG. 18 also operates as an oscillation circuit similar to that in FIG.

FIG. 19 is an equivalent circuit for explaining the operation of the oscillation circuit shown in FIG. 18 immediately after power is turned on. Here, the effects of the crystal unit Xt and the variable capacitor Cv2 are ignored. A voltage Vx expressed by the following equation (2) is applied between the terminals of the crystal unit Xt in the initial stage of the transition period.

(Equation 2)

Since the crystal unit Xt is connected to the power supply line, the numerator of (2) is not Cbc but Cn. As described above, since Cn is sufficiently larger than Cbc, the denominator and the numerator of the expression (2) are substantially equal, and the power supply voltage Vcc is substantially applied to the crystal resonator Xt. Therefore, the rise time after turning on the power can be shortened as compared with the circuit of FIG.

However, in the oscillation circuit shown in FIG.
Since the crystal unit Xt is not connected to the ground potential point, it is easily affected by fluctuations in the output voltage from the battery, noise generated in the power supply regulator circuit, and various external noises. That is, although the rise time is short, there is a problem that the operation after reaching the steady state tends to be unstable.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and has a Colpitts oscillation which operates stably even after reaching a steady state while shortening a rise time after power is turned on. It is intended to provide a circuit.
It is another object of the present invention to provide a communication terminal device in which the power supply period to the oscillation circuit is shortened and power consumption is reduced without lowering the reliability of operation during wireless communication.

[0015]

A Colpitts oscillation circuit according to the present invention comprises a feedback capacitor for feeding an output signal of an amplifier circuit back to an input terminal of the amplifier circuit, and a crystal resonator which forms a resonance circuit together with the feedback capacitor. Switching means for connecting one end of the crystal unit to a power supply line before the start of oscillation and connecting to a ground potential point after the start of oscillation.

Further, the Colpitts oscillation circuit according to the present invention is constituted by connecting a capacitor between a connection point between the crystal oscillator and the switching means and a power supply line.

Further, a wireless communication terminal device according to the present invention comprises:
A receiving circuit that operates based on the output signal of the oscillation circuit;
A wireless communication terminal device that intermittently supplies power to an oscillation circuit and receives a radio signal by a reception circuit when power is supplied, wherein the oscillation circuit returns an output signal of the amplification circuit to an input terminal of the amplification circuit. A feedback capacitor, and a crystal unit that forms a resonance circuit with the feedback capacitor.
Switching means for connecting one end of the crystal unit to a power supply line before the start of oscillation and connecting to a ground potential point after the start of oscillation.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a diagram showing a configuration example of a Colpitts oscillation circuit according to the present invention.
SWp in the figure is a p-channel MOS transistor, SWn
Is an n-channel MOS transistor. The components corresponding to those of the conventional oscillation circuit are denoted by the same reference numerals, and description thereof is omitted.

SWp and SWn are switching means for selectively connecting one end of the crystal unit Xt to a power supply line or a ground potential point. That is, when the switching control signal Vs is at a low level, the transistor SWp is turned on and the transistor SWn is turned off.
The transistor SWn is turned on and the transistor SWp is turned off.

First, the switching control signal Vs is set to a low level before the power is turned on, and the power is turned on in a state where the crystal oscillator Xt is connected to the power supply line side by turning on the power. FIG. 2 is an equivalent circuit for explaining the operation immediately after turning on the power. Here, the crystal oscillator Xt and the transistors SWp and SW
The effect of n is ignored. It is assumed that the Vf terminal at the time of power-on is in a high impedance state. A voltage Vx expressed by the following equation (3) is applied between the terminals of the crystal unit Xt in the early stage of the transition period.

[0021]

(Equation 3)

The numerator of the formula (3) is not Cbc but Cn + C
m, and Cn is sufficiently larger than Cbc, so that the denominator and the numerator of Expression (3) are substantially equal. Therefore,
The power supply voltage Vcc is applied to the crystal unit Xt immediately after the power is turned on.
Is applied, and the rise time after the power is turned on can be shortened similarly to the conventional circuit shown in FIG. This means that the capacitor C3 and the variable capacitance element Cv
If the influence of 1 is neglected, it can be understood from Expression (3) becomes equal to Expression (2).

Thereafter, when a steady state is reached and the oscillation operation is stabilized, the switching control signal Vs is set to a high level, and the crystal oscillator X
The connection of t is switched from the power supply side to the ground potential side. At this time, it is necessary to switch in a time sufficiently shorter than the oscillation cycle so that the oscillation operation does not stop. For example, in the case of oscillating at 20 MHz, the oscillation period is 50 ns, while the switching time by the MOS transistors SWp and SWn is several ns or less, so that the switching can be performed while maintaining the oscillation.

In this way, if one end of the crystal oscillator is connected to the power supply line side immediately after the power is turned on, the rise time of the oscillation circuit can be shortened, and the failure can be prevented and the oscillation circuit can be started. Can be performed stably. Also, by connecting one end of the crystal oscillator to the ground potential point side after starting the oscillation operation (preferably after stabilizing the oscillation operation), it is possible to perform a stable oscillation operation without being affected by noise or the like. it can.

Although FIG. 2 has been described assuming that the transistor SWp is an ideal switching means, FIG. 3 is an equivalent circuit in consideration of the capacitance of the crystal unit Xt and the transistor SWp. The operation immediately after will be further described.

In the figure, Cp is the capacitance between the source and drain terminals of the transistor SWp. Transistor SWp
Since it is considered that a capacitance (not shown) is further connected in series to the gate terminal, the effect of the capacitance between the gate terminal and the source or drain terminal is ignored. Crystal unit X
t is generally a coil Lo, a capacitor Co, and a resistor ro.
And a circuit in which a capacitor Cx and a series circuit (not shown) are connected in parallel. Capacitor Cx is 1-3pF
Here, only the capacitor Cx is considered as the equivalent capacitance of the crystal unit Xt. A voltage Vx expressed by the following equation (4) is applied between the terminals of the crystal unit Xt in the initial stage of the transition period.

[0027]

(Equation 4)

Since Cj is generally small, almost the power supply voltage Vcc is applied to Cbc as in the case of the equation (3).
The voltage Vx applied to the crystal unit Xt is determined by the ratio between Cp and Cx. That is, if Cp is about the same size as Cx, the applied voltage Vx becomes almost half of the power supply voltage Vcc,
If Cp is sufficiently larger than Cx, the applied voltage Vx becomes almost equal to the power supply voltage Vcc.

The MOS transistors SWp, SWn
Is preferably small. In the case of an oscillation circuit of a mobile phone, a crystal oscillator having an equivalent resistance of about several tens of ohms is often used. Therefore, a MOS transistor having an on-resistance sufficiently smaller than this, for example, an on-resistance of 1 ohm or less is used. If the one is used, the on-resistance does not matter.

In this embodiment, the variable capacitance diode C
Although the oscillation circuit in which the series circuit of v1 and C3 is connected in parallel to the crystal unit Xt has been described, the oscillation circuit may be configured without including such a circuit for frequency control, and furthermore, as in FIG. A capacitance element may be connected in series to the crystal unit Xt.

In this embodiment, the MOS transistors SWp and SWn have been described as switching means. However, if switching can be performed in a time sufficiently shorter than the oscillation cycle, other switching means can be used. For example, you may comprise using a bipolar transistor.

It is desirable that the Vf terminal at the time of turning on the power supply be in a high impedance state as exemplified in this embodiment, but even in other states, for example, a state where a predetermined voltage is applied. Good.

Embodiment 2 FIG. FIG. 4 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention. This oscillation circuit is different from the oscillation circuit shown in FIG. 1 in that a capacitor Ca is provided. The capacitor Ca has one end connected to the transistors SWp and SWn side terminals of the crystal unit Xt, and the other end connected to a power supply line.
That is, it is connected between the source and drain terminals so as to be in parallel with the transistor SWp.

FIG. 5 is an equivalent circuit for explaining the operation immediately after the power is turned on. A voltage Vx expressed by the following equation (5) is applied between the terminals of the crystal unit Xt in the initial stage of the transition period. Here, the voltage applied to the capacitance Cbc between the base and collector terminals of the transistor Tr is V
It is simplified to approximate cc.

[0035]

(Equation 5)

Equation (5) is obtained by converting Cp in equation (4) to Cp + Ca
The voltage between the terminals of the crystal unit Xt is increased by the influence of Ca. That is, C
If p + Ca is approximately the same as Cx, the applied voltage Vx to the crystal unit Xt is almost half of the power supply voltage Vcc. If Cp + Ca is sufficiently larger than Cx, the applied voltage Vx is almost the same as the power supply voltage. Vcc. Therefore, even when the capacitance Cp of the transistor SWp is small, the rise time after turning on the power can be shortened by connecting the capacitor Ca having a relatively large capacitance in parallel.

Next, the effect of the capacitor Ca on the oscillating operation in the steady state in the oscillation circuit of FIG. 4 will be described. FIG. 6 shows the transistor SWp of the oscillation circuit of FIG.
Is an AC equivalent circuit in a state where is turned off and the transistor SWn is turned on. Cn in the figure is a transistor SW
n is the capacitance between the source and drain terminals.

Since the power supply line and the ground potential point are AC equivalent, a parallel circuit of Cn and Ca is connected in series to the crystal oscillator Xt as shown in FIG. Therefore, this oscillation circuit functions as a Colpitts oscillation circuit even if it has Cn and Ca, and Cn and Cn
a affects the oscillation frequency. Therefore, by appropriately selecting the capacitances of C1 to C3 and Cv1, a Colpitts oscillation circuit that obtains a desired oscillation frequency can be configured.

When the oscillation circuit of the first embodiment is similarly considered, it is desirable that the inter-terminal capacitance Csd of the transistor SWp be large, and the inter-terminal capacitance Cs of the transistor SWn be large.
It is understood that d is preferably smaller.

Embodiment 3 FIG. 7 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention. This oscillation circuit is a circuit in which switching means is provided in a cascode Colpitts oscillation circuit. Tr1 and Tr2 in the figure are cascode-connected NPN transistors, R11,
R21, R12 and R22 are the bias resistors, and C6 is a bypass capacitor for setting the transistor Tr2 to the base ground.

Since a large-capacity capacitor C6 is used between the base terminal of the transistor Tr2 and the ground potential point, when the power is turned on with one end of the crystal unit Xt connected to the ground potential point, Only a voltage lower than the power supply voltage Vcc can be applied to the crystal resonator Xt immediately after the power is turned on.

For this reason, as in the above embodiment, one end of the crystal oscillator Xt can be connected to the power supply line when the power is turned on by the switching control signal Vs, and the rise time can be shortened. Further, if one end of the crystal oscillator Xt is connected to the ground potential point after the start of the oscillation operation (preferably after the oscillation operation is stabilized), the crystal oscillator Xt can be operated stably without being affected by noise.

Embodiment 4 FIG. FIG. 8 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention. This oscillation circuit is a circuit in which switching means is provided in an overtone oscillation circuit, and differs from the oscillation circuit shown in FIG. 1 in that a parallel circuit of a capacitor C7 and a coil L1 is provided. The circuit composed of L1, C2 and C7 is a quartz oscillator X
The circuit becomes capacitive at a predetermined n (odd) overtone oscillation frequency of t and becomes inductive at an overtone oscillation frequency less than nth order including the fundamental oscillation frequency. Therefore, the circuit of FIG. 8 operates as a Colpitts oscillation circuit similar to that of FIG. 1 at the nth overtone frequency.

With respect to such an overtone oscillation circuit, similarly to the above embodiment, when the power is turned on, the crystal oscillator X
By connecting one end of t to the power supply line, the rise time can be shortened. Further, if one end of the crystal oscillator Xt is connected to the ground potential point after the start of the oscillation operation (preferably after the oscillation operation is stabilized), the crystal oscillator Xt can be operated stably without being affected by noise.

Embodiment 5 FIG. FIG. 9 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention. This oscillation circuit is obtained by providing a switching means in a Colpitts oscillation circuit using an inverter (inverting amplifier) as an amplification circuit. In the figure, INV is an inverter, Cin is an input capacitance of the inverter, and C1, C3 and Cv1 are feedback capacitors.

First, a description will be given of a case of an oscillation circuit in which the left end of the capacitor C1 is fixedly connected to the ground potential point without including the transistors SWp and SWn. There is no potential difference between the input and output terminals of the inverter INV before the power is turned on, and no voltage is applied to the crystal unit Xt. When the power is turned on, a potential difference is generated between the input and output terminals of the inverter INV, and the potential difference becomes a voltage applied to the crystal unit Xt. Therefore, a voltage cannot be applied to the crystal unit Xt until the inverter INV rises after the power is turned on.

Next, the operation of the oscillation circuit shown in FIG. 9 will be described. By setting the switching control signal Vs to a low level before turning on the power, the transistor SWp is turned on when the power is turned on, and one end of the crystal unit Xt is connected to the capacitor C.
1 and connected to a power supply line. Then, after the inverter INV rises and the oscillation operation starts (preferably after the oscillation operation is stabilized), the switching control signal Vs
Is changed to a high level, and the crystal oscillator Xt is connected to the ground potential point via the capacitor C1.

FIG. 10 is an equivalent circuit for explaining the operation immediately after turning on the power in this case. In the figure, Cx is the equivalent capacitance of the crystal oscillator, and Cin is the input capacitance of the inverter INV. Here, the influence of the output capacity of the inverter INV is ignored. Immediately after the power is turned on, a voltage Vx expressed by the following equation (6) is applied between the terminals of the crystal resonator Xt.

[0049]

(Equation 6)

The equivalent capacitance Cx of the crystal unit is about 1 to 3 pF, whereas the feedback capacitors C3 and Cv1 are about several tens of pF. Therefore, Cm is sufficiently larger than Cx. Therefore, the voltage Vx applied to the crystal unit Vt is C1
And (Cin + Ck). That is, if C1 is as large as (Cin + Ck), the applied voltage Vx becomes almost half of the power supply voltage Vcc, and C1 becomes (Ci + Ck).
If it is sufficiently higher than (n + Ck), the applied voltage Vx becomes almost the power supply voltage Vcc.

Therefore, by selecting appropriate capacitance values for C1, Cin, and Ck, the power supply can be reduced compared to a conventional oscillation circuit in which one end of the crystal oscillator Xt is fixedly connected to the ground potential point via the capacitor C1. The voltage applied to the crystal resonator Xt immediately after the application can be increased. If one end of the crystal unit Xt is connected to the ground potential point after the start of the oscillating operation, stable operation can be achieved as in the case of the conventional oscillating circuit.

Embodiment 5 FIG. FIG. 11 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention. This oscillation circuit is configured by providing switching means in a Colpitts oscillation circuit using an inverter, as in the circuit of FIG. 9. In the circuit of FIG. 9, switching means is provided on the input side of the inverter INV. The circuit 11 differs in that a switching means is provided on the output side of the inverter INV.

The operation of the oscillation circuit shown in FIG. 11 will be described. By setting the switching control signal Vs to a low level before turning on the power, the transistor SW can be turned on when the power is turned on.
p is turned on, and the crystal resonator Xt is connected to the power supply line via the capacitor C2. After that, the inverter IN
After V rises and the oscillation operation starts (preferably after the oscillation operation is stabilized), the switching control signal Vs is changed to a high level, and the crystal oscillator Xt is connected to the ground potential point via the capacitor C2.

FIG. 12 is an equivalent circuit for explaining the operation immediately after turning on the power in this case. In the figure, Cx is the equivalent capacitance of the crystal oscillator, and Cot is the output capacitance of the inverter INV. Here, the influence of the input capacitance of the inverter INV is ignored. A voltage Vx expressed by the following equation (7) is applied between the terminals of the crystal oscillator Xt immediately after the power is turned on.

[0055]

(Equation 7)

As described above, since Cm is sufficiently larger than Cx, the voltage Vx applied to the crystal unit Vt is determined by the ratio of C2 to (Cot + Ck). That is, if C2 is about the same size as (Cot + Ck), the applied voltage Vx becomes almost half of the power supply voltage Vcc, and C2 becomes (Cot + Ck).
If it is sufficiently larger than (t + Ck), the applied voltage Vx becomes almost the power supply voltage Vcc.

Therefore, by selecting appropriate capacitance values for C2, Cot, and Ck, compared to an oscillator circuit in which one end of the crystal oscillator Xt is fixedly connected to the ground potential point via the capacitor C2, the power supply is immediately turned on. Crystal unit Xt
Can be increased. If one end of the crystal unit Xt is connected to the ground potential point after the start of the oscillating operation, stable operation can be achieved as in the case of the conventional oscillating circuit.

Embodiment 6 FIG. FIG. 13 is a block diagram showing one configuration example of the wireless communication terminal device according to the present invention.
In the figure, 1 is an antenna, 2 is an antenna duplexer, 3 is a receiving unit, 4 is a transmitting unit, 5 is a frequency synthesizer, and 6 is a baseband signal processing unit.

The signal received by the antenna 1 is input to the receiving section 3 via the antenna duplexer 2. The received signal is amplified by the high-frequency amplifier 30 in the receiving unit 3, mixed with the output signal Vc of the synthesizer 5 by the receiving mixer 31, and down-converted from a radio frequency to a baseband frequency. Then, filter 32
Thus, unnecessary frequency components are removed, demodulated by the demodulator 33, and output to the baseband signal processing unit 6.

On the other hand, the transmission signal from baseband processing section 6 is input to transmission section 4. This transmission signal is transmitted to the transmission unit 4
In, after being modulated by the modulator, it is mixed with the output signal Vc of the synthesizer 5 by the transmission mixer 41,
Upconverted from baseband frequency to radio frequency. Thereafter, the signal is amplified by the transmission power amplifier 40 and output to the antenna duplexer 2.

The baseband processing section 6 comprises a reception signal processing circuit 60, a control circuit 61 and a transmission signal processing circuit 62. The reception signal processing circuit 60 converts the output signal of the reception unit 3 into an audio signal and outputs the audio signal to the receiver. Further, the transmission signal processing circuit 62 converts a voice signal from the transmitter and outputs the signal to the transmission unit 4. Therefore, the receiving unit 3 and the received signal processing circuit 60 constitute a receiving circuit, and the transmitting unit 4 and the transmitted signal processing circuit 62 constitute a transmitting circuit. The control circuit 61 includes a microcomputer, a DSP, and the like, controls the reception signal processing circuit 60 and the transmission signal processing circuit 62, and controls the synthesizer 5.

FIG. 14 shows the synthesizer 5 shown in FIG.
FIG. 2 is a block diagram showing an example of the configuration. In the figure, reference numeral 50 denotes a voltage-controlled temperature-compensated crystal oscillator (VCTCXO), 51 denotes a phase comparator, 52 denotes a low-pass filter (LPF), 53 denotes a voltage-controlled oscillator (VCO), and 54 and 55 denote variable frequency dividers. The oscillator 50 is configured by the circuits shown in FIGS.

The oscillator 50 is constituted by the Colpitts oscillation circuit described in the above embodiment, and receives the switching control signal Vs and the frequency control signal Vf from the control circuit 61. As a method of performing temperature compensation in the oscillator 50, for example, a capacitor having a temperature characteristic such as a transistor Tr, a diode Cv1, or the like that cancels a change in capacitance can be used as C1, C2, or C3.

Reference numerals 51 to 54 denote output signals Vo of the oscillator 50.
So-called PL that generates a signal Vc based on the frequency of
This is an L (Phase Locked Loop) circuit. That is, a signal obtained by dividing the output signal Vo of the oscillator 50 by the frequency divider 55 and a feedback signal obtained by dividing the output signal Vc of the oscillator 53 by the variable frequency divider 54 are input to the phase comparator 51. The output of the phase comparator 51 is smoothed by a low-pass filter 52 and input to the oscillator 53 as a control voltage. The output signal Vc of the PLL circuit is output to the receiving unit 3 and the transmitting unit 4.

The operation of the wireless communication terminal device during standby will be described. During standby, power is supplied to the synthesizer 5 intermittently. That is, the control circuit 61
Turns on the synthesizer 5 at predetermined time intervals, and after receiving a wireless communication signal from the base station, turns off the power again.

When receiving a wireless communication signal, the control circuit 61
Generates the frequency control signal Vf based on the error signal from the reception signal processing circuit 60 so that the error of the oscillation frequency of the synthesizer 5 is reduced. That is, when an error occurs in the frequency of the output signal Vc of the synthesizer 5, an error occurs in the frequency (baseband frequency) of the output signal of the receiving unit 3. This error is detected by the reception signal processing circuit 60 to generate an error signal. The control circuit 61 generates the frequency control signal Vf based on this error signal, whereby the oscillation frequency of the oscillation circuit 50 is adjusted, and the frequency error of the output signal of the synthesizer 5 can be reduced.

The control circuit 61 outputs the switching control signal Vs
Generate The switching control signal Vs is at a low level before the start of the oscillating operation of the synthesizer 5, that is, before, before or immediately after the power is turned on, and one end of the crystal resonator Xt immediately after the power is turned on is connected to the power supply line. Connected. Then, after the start of the oscillation operation (preferably, after the oscillation operation is stabilized) and before the start of the reception of the radio signal, the level changes to a high level. When the radio communication signal is received, one end of the crystal unit Xt is connected to the ground potential point. Connected to

FIG. 15 is a timing chart showing an example of the operation at the time of standby. (A) in the figure is the receiving unit 3
And the timing of the reception operation of the reception signal processing circuit 60,
(B) is the timing of power supply to the synthesizer 5,
(C) shows the output timing of the switching control signal Vs by the control unit 61. Here, the switching control signal Vs is changed to a low level (L) when the power is turned off, so that the oscillator 50 starts up in a short time regardless of the power-on time.

When the oscillator 50 starts stable oscillation,
The switching control signal Vs is changed to a high level, and thereafter, the receiving unit 3 starts receiving a wireless signal. The switching timing from the low level to the high level may be determined, for example, by previously obtaining the time from when the power is turned on until a stable oscillation state is reached, or based on an error in the output signal from the receiving unit 3. May be determined.

The start of the oscillating operation means the time when a desired frequency signal is output as the output signal Vo of the oscillating circuit, and the start of the receiving operation means that the receiving unit 3 and the received signal processing circuit 60 Operate together, and when transmission data from the base station is received.

In this embodiment, the case where the Colpitts oscillation circuit shown in the first to fifth embodiments is used for the oscillator 50 has been described. However, the same Colpitts oscillation circuit can be used for the oscillator 53.

[0072]

In the Colpitts oscillation circuit according to the present invention, a large voltage can be applied between the terminals of the crystal unit before the start of oscillation, and one end of the crystal unit after the start of oscillation is connected to the ground potential point. be able to. Therefore, it is possible to provide a Colpitts oscillation circuit that can reduce the rise time at power-on and operate stably thereafter.

The Colpitts oscillation circuit according to the present invention is constituted by connecting a capacitor between a connection point between the crystal oscillator and the switching means and a power supply line. For this reason, even when a switching means having a small capacity between the power supply line and the crystal oscillator is used, the rise time at power-on can be reduced.

Further, the wireless communication terminal device according to the present invention
By providing an oscillation circuit that operates stably while shortening the rise time at power-on, power supply time can be reduced and power consumption can be reduced without impairing the reliability of the reception operation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a Colpitts oscillation circuit according to the present invention.

FIG. 2 is an equivalent circuit for explaining the operation of the oscillation circuit of FIG. 1 immediately after power is turned on.

FIG. 3 is an equivalent circuit in which capacitances of a crystal oscillator and a transistor are taken into consideration.

FIG. 4 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention.

FIG. 5 is an equivalent circuit for describing an operation of the oscillation circuit of FIG. 4 immediately after power is turned on.

6 is an AC equivalent circuit in a state where the transistor SWp of the oscillation circuit in FIG. 4 is turned off and the transistor SWn is turned on.

FIG. 7 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention.

FIG. 8 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention.

FIG. 9 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention.

10 is an equivalent circuit for explaining the operation of the oscillation circuit of FIG. 9 immediately after power-on.

FIG. 11 is a diagram showing another configuration example of the Colpitts oscillation circuit according to the present invention.

12 is an equivalent circuit for describing an operation of the oscillation circuit of FIG. 11 immediately after power is turned on.

FIG. 13 is a block diagram showing a configuration example of a wireless communication terminal device according to the present invention.

FIG. 14 is a block diagram showing one configuration example of a synthesizer 5 in FIG.

FIG. 15 is a timing chart showing an example of an operation at the time of standby.

FIG. 16 is a diagram illustrating a configuration example of a conventional Colpitts oscillation circuit used for a mobile phone.

FIG. 17 is an equivalent circuit for explaining the operation of the oscillation circuit of FIG. 16 immediately after power is turned on.

FIG. 18 is a diagram showing another configuration example of the conventional Colpitts oscillation circuit.

FIG. 19 is an equivalent circuit for explaining the operation of the oscillation circuit of FIG. 18 immediately after power is turned on.

[Explanation of symbols]

 C1, C2 Capacitor Tr Transistor Xt Crystal oscillator SWp, SWn Switching means 3, 60 Receiving circuit 50 Oscillation circuit Vo Output signal of oscillation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J079 AA04 BA22 BA41 DA13 FA02 FA05 FA13 FA14 FA21 FB03 FB25 FB29 FB35 FB48 GA02 GA04 GA09 KA05 KA08 5J081 AA03 BB01 BB10 CC04 CC44 DD03 DD15 EE05 EE18 FF21 KK23 KK23 KK23 KK23 KK23 KK23 KK21 FF23 LL08 MM01 5K061 AA00 AA02 BB12 CC02 CC08 CC13 CC15 CC25 JJ01 JJ02 JJ05 JJ09 JJ11 JJ12

Claims (7)

[Claims] 1. An amplifier circuit, a feedback capacitor for feeding back an output signal of the amplifier circuit to an input terminal, a crystal oscillator forming a resonance circuit together with the feedback capacitor, Switching means for connecting one end to a power supply line and connecting to a ground potential point after the start of oscillation. 2. The Colpitts oscillation circuit according to claim 1, wherein said switching means connects one end of said crystal unit to a power supply line based on power supply to a power supply line. 3. The switching means is connected to the crystal resonator via the feedback capacitor, and selectively connects one end of the crystal resonator to a power supply line or a ground potential point via the feedback capacitor. The Colpitts oscillation circuit according to claim 1, wherein the oscillation circuit is connected. 4. A Colpitts oscillation circuit according to claim 1, wherein a capacitor is connected between a connection point between said crystal oscillator and said switching means and a power supply line. 5. A wireless communication terminal device comprising a receiving circuit that operates based on an output signal of an oscillation circuit, intermittently supplying power to the oscillation circuit, and receiving a radio signal by the receiving circuit when power is supplied. The oscillation circuit is an amplification circuit,
A feedback capacitor for feeding back the output signal of the amplifier circuit to the input terminal, a crystal oscillator forming a resonance circuit together with the feedback capacitor, and one end of the crystal oscillator connected to a power supply line before oscillation starts, Switching means for connecting to a ground potential point after the start of oscillation. 6. The wireless communication terminal device according to claim 5, wherein said receiving circuit starts a receiving operation after one end of said crystal resonator is connected to a ground potential point. 7. The wireless communication terminal device according to claim 5, wherein a capacitor is connected between a connection point between the crystal oscillator and the switching means and the power supply line.