JPH1168462A - Piezoelectric oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption and to improve stability in an output frequency and output amplitude over wide temperature range in an oscillation circuit of a piezoelectric oscillator, even in the case of low power supply voltage. SOLUTION: In this oscillation circuit, a transistor Q1 is provided, in series with a bias resistor R2 is its base bias circuit, with a transistor Q2 with a base/emitter voltage characteristic equivalent to that of a transistor Q1 against changes in temperatures, and furthermore, the transistor Q2 is formed by diode connection structure to connect the base and the collector. The stability in the output frequency and in the amplitude of an output signal and reduction of power consumption of the piezoelectric oscillator are improved by the above structure in which the base bias circuit is inserted to suppress the change of a current value of collector current and emitter current of the transistor Q1 against the changes in temperatures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a piezoelectric oscillator circuit, and more particularly, to a piezoelectric oscillator circuit operating at a low power supply voltage.

[0002]

2. Description of the Related Art In mobile communication devices using a battery as a power source, such as a mobile phone, a model in which the communicable time is long with a battery of the same capacity is strongly demanded by minimizing power consumption. I have. For this reason, the performance of batteries used in conventional mobile communication devices is being improved, and measures are being taken to reduce the power consumption of components used, including crystal oscillators. In other words, if the drive voltage can be set low, more current capacity can be supplied by batteries of the same capacity. On the other hand, indispensable important characteristics required for such a crystal oscillator include high frequency accuracy and stability of output amplitude over a wide temperature range.However, a crystal oscillator is composed of many components with temperature characteristics. Therefore, there are a plurality of factors that deteriorate the characteristics. As one of the factors mentioned above, it is known that the transconductance changes because the operating current of the transistor used in the oscillation circuit greatly changes due to the ambient temperature change, and as a result, the amplitude of the output signal And the output frequency fluctuates due to the change in the input capacitance of the transistor.

[0003] This will be described with reference to the drawings.
Is a Colpitts type crystal oscillation circuit generally known as a prior art. In the figure, R1, R2, R3, and R4 are DC bias resistors of transistors, and are C1, C2, and C4.
3, C4 is a capacitor, Q1 is a transistor, and Y1 is a crystal oscillator. In general, the value of the DC bias resistor is set so that the transistor Q1 performs a class A operation. As described above, the main factor of the change in the operating current of the transistor with respect to the temperature change is that the voltage between the base and the emitter of the transistor (hereinafter referred to as V _BE ) has a linear temperature characteristic. Conventionally, in order to solve such a problem, a setting is made so that a current several times to several tens times the base current flows through the DC bias resistor R2, thereby suppressing the fluctuation of the base voltage of the transistor due to the change of the V _BE . Was set. In addition, with respect to fluctuations in the amplitude of the output signal, a high output signal amplitude is previously set by flowing a sufficiently large collector current in the past, and a request is made even when the amplitude of the output signal decreases due to a temperature change. The characteristics were satisfied. When the emitter voltage is V _E and the base voltage is V _B , V _E ≒ V _B −
By setting the base voltage V _B higher than V _BE, V
To reduce the change in emitter voltage V _E for _BE changes in,
Settings have been made to suppress fluctuations in the emitter current and the collector current.

[0004]

However, in the conventional oscillation circuit shown in FIG. 6, the power supply voltage is sufficiently high to set the base voltage sufficiently higher than V _BE as described above. Therefore, it is not possible to employ such a circuit in an oscillating circuit which has recently required a low voltage. In addition, a method of obtaining a high-amplitude output signal by flowing a large amount of collector current in order to compensate for the amplitude fluctuation of the output signal due to a temperature change is contrary to the demand for low current consumption.
The solution was desired. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and is capable of driving at a low power supply voltage, has low current consumption, and has excellent oscillation frequency accuracy and excellent stability of output signal amplitude. It is intended to provide an oscillator.

[0005]

The cause of the above-mentioned problem in the conventional oscillation circuit is that the voltage V _BE between the base and the emitter of the transistor in the oscillation circuit varies with the temperature change. This is because the base voltage is fixed. Therefore, in the present invention, in order to solve the above problem, the invention according to claim 1 of the piezoelectric oscillation circuit according to the present invention uses a method in which the base bias circuit of the transistor in the oscillation circuit has the same voltage as the voltage between the base and the emitter of the transistor. The piezoelectric oscillation circuit according to claim 1, wherein a semiconductor element having temperature-voltage characteristics is provided to suppress a change in collector / emitter current due to a temperature change of the transistor. The invention according to claim 2 is characterized in that a transistor in which the semiconductor element is connected to a base and an emitter is inserted in a base bias circuit. The invention according to claim 3 adds to the invention according to claim 1,
The piezoelectric oscillation circuit is a Colpitts oscillation circuit including a cascode-type amplification circuit. Claim 4
The invention described in the present invention is characterized in that, in addition to the invention described in the above-mentioned claim 1, 2, or 3, the oscillation transistor is of the same type as the transistor in the base bias circuit.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a circuit diagram showing one embodiment of a crystal oscillation circuit using the present invention. The oscillation circuit shown in the figure has DC bias resistance elements R1, R2, R3, R4.
And capacitors C1, C2, C3, C4 and transistor Q
1 and Q2 and a crystal unit Y1 as shown in FIG.
Is different from the conventional Colpitts type crystal oscillation circuit in the following point of the base bias circuit of the transistor Q1.
That is, the DC bias resistor R2 of the base bias circuit
It connects the transistor Q2 connected diode connecting the base and collector in series, further, by the same type of the transistors Q1 and Q2, and the semiconductor element V _T constituted by the transistor Q2. As a result, the base voltage changes so as to follow the voltage change of V _BE of the transistor Q1 due to the temperature change, so that the change in the collector current and the emitter current accompanying the temperature change in the transistor Q1 is suppressed, A crystal oscillation circuit capable of outputting a stable signal amplitude can be realized.

Hereinafter, this will be described in detail using mathematical expressions. Now, in the oscillating circuit shown in FIG. 1, the collector current flows through I _C , the voltage between the base and the emitter of the transistor Q1 flows through V _BE1 , the voltage between the base and the emitter of the transistor Q2 flows through V _BE2 , and flows through the DC bias resistor R2. Current I
_R2 . The collector current is I _C is generally _{I C = (V BE2 + I} R2 × R2-V BE1) / R4 can be represented by the relational expression ···· (1), V due to a temperature change _BE1
And, when V _BE2 changes by + ΔV _BE1 and + ΔV _BE2 respectively, the collector current I _C + ΔI _C becomes I _C + _{ΔI C} = (V _BE2 + ΔV _BE2 + _{IR 2} × R2- (V _BE1 + ΔV _BE1 )) / R4... (2) As described above, since the transistors Q1 and Q2 use the same type of semiconductor device, V _BE1
And the amount of voltage change due to the temperature change of V _BE2 is equal to △ V _BE1 =
ΔV _BE2 . Therefore, the collector current I _C + △ I _C at the temperature change is represented by _{I C + △ I C = (} V BE2 + I R2 × R2-V BE1) / R4 ···· (3), which is the It is equal to I _{C in} equation (1). That is,
Since the voltage change between the base and the emitter of the transistor Q1 due to the temperature change is offset by the voltage change between the base and the emitter of the transistor Q2, the collector current I
_{Since a} constant current value flows through _C without being affected by a temperature change, stable oscillation frequency and amplitude of an output signal can be obtained.

FIG. 3 shows a crystal oscillation circuit showing another embodiment adopting the present invention. The circuit shown in this embodiment is a Colpitts oscillation circuit using a cascode type amplifier circuit. In the figure, Q1, Q2, Q3 are transistors and Q
2 is a diode connection structure, and the same transistors Q1 and Q2 are used. R in FIG.
1, R2, R3, R4, R5 are DC bias resistors of transistors, C1, C2, C3, C4, C5 are capacitors, and C1, C2 have capacitance values according to oscillator characteristics, C3, C4 and C5 are bypass capacitors. Further, Y1 in the figure is a crystal oscillator, and the oscillator output frequency is f ₀ = 15.3 in the embodiment.
A 6 MHz crystal oscillator is used. In the configuration of the oscillation circuit shown in the figure, one terminal of the resistor R1 is connected to the output terminal of the regulator U1, and the other terminal is connected to the base terminal of the transistor Q3 and the capacitor C4. The other terminal of C4 is grounded. One terminal of the R2 is an output terminal of the U1;
The other terminal is connected to the base terminal of the transistor Q1, one terminal of the crystal unit Y1, and one terminal of the capacitor C1. The other terminal of C1 is connected to the emitter terminal of Q1 and the capacitor C2 and R5, and the other terminals of C2 and R5 are grounded.
The R3 has one terminal connected to the base terminal of the Q1 and the R2 and the vibrator Y1, the other terminal connected to the collector and the base terminal of the transistor Q3, the emitter terminal of the Q3, The other terminal of the vibrator Y1 is grounded. One terminal of the R4 is connected to the power supply, the input terminal of the U1, and the capacitor C3, the other terminal is connected to the collector terminal of the Q2 and the capacitor C5, and the other terminal of the C5 is an oscillator. Connected to output terminal. The other terminal of C3 is grounded, and the collector terminal of Q1 and the emitter terminal of Q2 are connected.

In order to make the effects of the present invention easy to understand,
The Colpitts type oscillation circuit using the cascode connection type amplification circuit based on the prior art shown in FIG. 8 was also evaluated and the characteristics were compared. The oscillation circuit shown in FIG.
The difference is that the base bias circuit of the oscillation transistor Q1 'is connected only to the DC bias resistor R3'. Since the oscillation circuits shown in FIGS. 2 and 7 are driven by a low power supply voltage, the power supply voltage is set to +2.7 V.
The output of the regulator is + 1.7V. Further, the base potential of the transistors Q1 and Q1 'is about +
It is set to 0.8 V, and most of the setting is occupied by V _BE .

Hereinafter, the collector current I _{C with} respect to the temperature change of the oscillation circuit shown in FIG. 2 and the oscillation circuit shown in FIG. 7 will be described.
And the results of the evaluation of the change in the amplitude of the output signal will be described. FIG. 3 shows the results of measuring the change in the collector current I _C when the ambient temperature changes in the range of −30 ° C. to + 85 ° C. in each oscillation circuit. FIG. 4 shows an ambient temperature of −30 ° C. and +25 in the oscillation circuit shown in FIG.
The amplitude of the output signal of the oscillator at ° C and + 85 ° C is shown. FIG.
Are ambient temperature -30 ° C and +2 in the oscillation circuit shown in FIG.
The amplitude of the output signal of the oscillator at 5 ° C. and + 85 ° C. is shown.

[0011] As shown in FIG. 3, the collector current I _C in the conventional oscillation circuit changes at least a width of 400μA The amplitude of the output signal varies in width of about 0.9V _PP.
In contrast, the collector current I _C in the oscillation circuit according to the present invention will vary with the width of less than 100 .mu.A, the conventional oscillator circuit in the collector current I variation compared to the range of change in _C, for example, about 1 / The result is a narrow characteristic of 4.

Further, as shown in FIG. 6, the output amplitude changes in the oscillation circuit according to the present invention in a width of about 0.2 V _PP , and changes as compared with the output amplitude of the oscillation circuit according to the prior art. As a result, a characteristic having a narrow width of about 1/5 was obtained.

[0013]

According to the above results, the oscillator circuit according to the present invention shown in FIG. 2 has a constant collector current of the transistor with respect to a temperature change, as compared with the oscillator circuit according to the prior art shown in FIG. It can be seen that the input capacitance of the transistor does not change because it is kept, and the oscillation frequency of the oscillator is hardly changed. In addition, since the amplitude of the output signal of the oscillator is stable with respect to temperature changes, the amplitude of the output signal at the time of setting can be suppressed as compared with the related art, so that the oscillator can further reduce current consumption. It can be understood that it has a realizable effect. Therefore, according to the present invention, it is possible to realize a crystal piezoelectric oscillator having low power consumption, low current consumption, and small fluctuations in the amplitude of an output signal in a wide temperature range, while being driven by a low power supply voltage.

Further, in one embodiment of the present invention, a Colpitts oscillation circuit using a cascode type amplifier circuit has been described. However, the present invention is not limited to this, and can be applied to any oscillation amplifier circuit of a crystal oscillator. Needless to say, the same effects as those of the embodiment can be obtained.

In one embodiment of the present invention, a quartz oscillator and a specific frequency are used as the piezoelectric element. However, the present invention is not limited to this, and can be applied to all piezoelectric elements and frequencies. It goes without saying that the same effect as in the example can be obtained.

In one embodiment of the present invention, the transistors Q1 and Q1 'for oscillation and the transistors Q3 and Q3' in the base bias circuit are of the same type. However, the present invention is not limited to this. Alternatively, a combination of different types of transistors may be used as long as the output amplitude of the piezoelectric oscillator is stable.

[0017]

[Brief description of the drawings]

FIG. 1 shows an embodiment according to the invention.

FIG. 2 shows another embodiment according to the present invention.

FIG. 3 shows a change in collector current with a change in temperature.

FIG. 4 shows an output waveform temperature change of an oscillation circuit based on the prior art.

FIG. 5 shows an output waveform temperature change of the oscillation circuit according to the present invention.

FIG. 6 shows a Colpitts oscillator using a cascode amplifier based on the prior art.

FIG. 7 is a Colpitts oscillation circuit using a cascode amplification circuit based on the prior art.

[0018]

[Explanation of symbols]

U1, U1 '... Regulator R1, R2, R3, R4, R5, R1', R2 ', R
3 ', R4', R5 '... resistance elements C1, C2, C3, C4, C5, C1', C2 ', C
3 ', C4', C5 '... capacitors Q1, Q2, Q3, Q1', Q2 ', Q3' ... transistors Y1, Y1 '... crystal oscillator

Claims (4)

[Claims] In a piezoelectric oscillation circuit having an oscillation amplifier circuit and a piezoelectric element, the oscillation amplifier circuit includes an NPN connection type semiconductor element (hereinafter, referred to as a transistor) to which the piezoelectric vibrator is connected. Further, the base bias circuit of the transistor includes a semiconductor element having a temperature-voltage characteristic equivalent to the voltage between the base and the emitter of the transistor, so that a change in the collector / emitter current due to a change in the temperature of the transistor is prevented. The piezoelectric oscillation circuit, wherein the piezoelectric oscillation circuit is configured to be suppressed. 2. A piezoelectric oscillation circuit having an oscillation amplifier circuit and a piezoelectric element, wherein the oscillation amplifier circuit includes a transistor connected to the piezoelectric vibrator, and further includes a base bias circuit of the transistor. , The temperature between the base and the emitter which is equivalent to the temperature between the base and the emitter of the transistor.
The transistor in the base bias circuit includes a transistor having a voltage characteristic, and the transistor in the base bias circuit has a diode connection structure in which a base and a collector are connected, so that a change in the collector-emitter current of the transistor connected to the piezoelectric element can be suppressed. 2. The piezoelectric oscillation circuit according to claim 1, wherein the piezoelectric oscillation circuit is configured to suppress the oscillation. 3. The piezoelectric oscillation circuit according to claim 1, wherein said piezoelectric oscillation circuit is a Colpitts oscillation circuit including a cascode-type amplifier circuit. 2. A cascode amplification circuit having a Colpitts oscillation circuit.
And the piezoelectric oscillation circuit according to claim 2. 4. A transistor to which said piezoelectric element is connected,
4. The piezoelectric oscillation circuit according to claim 1, wherein the other transistor provided in the base bias circuit of the transistor is a semiconductor element of the same type.