JP3276137B2 - Crystal oscillation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can operate with a low-voltage power supply, has good distortion characteristics, operates with high efficiency,
The present invention also relates to a crystal oscillation circuit in which the output level does not change much due to a load change.

[0002]

2. Description of the Related Art Conventionally, as a crystal oscillation circuit, for example, a Colpitts type crystal oscillation circuit as shown in FIG. 4 is known. In this crystal oscillation circuit, a Colpitts oscillation circuit using the crystal resonator 1 as a frequency source is constituted by the transistor 2. The transistor 2 operates as a common-emitter amplifier, and takes out the oscillation output 3 from the emitter.

However, in such a circuit configuration,
The bias voltage is relatively set as the operating point of the transistor 2,
A higher setting is performed. Therefore, there is a problem that the device operates as a so-called class A amplifier in which a collector current always flows, resulting in low operation efficiency and high current consumption.
In addition, in such a device, the influence of a load fluctuation or the like directly affects the transistor 2 in the oscillation stage, so that the stability is poor. In many cases, the oscillation output is received by the buffer circuit and supplied to the load. Is being done.

However, when a power supply having a low power supply voltage, for example, about 2.6 V, is used, if a buffer circuit is provided, a problem of voltage distribution between the oscillation stage and the buffer circuit occurs, and the operating voltage is reduced, and the oscillation output However, there is a problem that distortion is caused or the amplitude is reduced due to clipping.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can operate with a low-voltage power supply, can obtain an oscillation output with little distortion, and have good operation efficiency. It is another object of the present invention to provide a crystal oscillation circuit in which the output level does not fluctuate much due to a change in load resistance.

[0006]

According to the present invention, there is provided a class B in which the collector / emitter of a first NPN transistor and the emitter / collector of a second PNP transistor are connected in series between a power supply and a ground potential. In a crystal oscillator circuit in which a crystal resonator is connected to the input of an amplifier, one end of the crystal resonator is grounded, the other end of the crystal resonator is connected to the base of a PNP-type third transistor, the collector is grounded, and the emitter is grounded. A third transistor connected to a power supply via an emitter resistor, the other end of the crystal oscillator connected to the base of a fourth transistor of the NPN type, a collector connected to the power supply, and an emitter grounded via the emitter resistor; The base of the first transistor is connected to the emitter of the first transistor, the base of the second transistor is connected to the emitter of the fourth transistor, and the first and second transistors are connected. It derives the output terminal from the series connection point of the emitter of the transistor, the base of the third transistor
A first capacitor for increasing the positive peak value of the base voltage of the first transistor is connected between the emitters, and a first capacitor for decreasing the negative peak value of the base voltage of the second transistor is connected between the base and the emitter of the fourth transistor. A third capacitor between the bases of the third and fourth transistors and the output terminal, and a fourth capacitor having one end connected to the output terminal and the other end grounded. It is characterized by having.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the circuit diagram shown in FIG. Q1 is an NPN-type first transistor, and Q2 is a PNP-type second transistor. The collector of the first transistor Q1 is connected to the power supply Vcc, the collector of the second transistor Q2 is grounded, and the emitter is commonly connected to the output terminal Out.

[0008] The first and second transistors Q1, Q
2 form a so-called complementary class B output circuit. Q3 is a PNP-type third transistor having an emitter connected through an emitter resistor R1, for example, a voltage 2.
It is connected to a 6 V power supply Vcc and the collector is grounded.

Q4 is an NPN-type fourth transistor having a collector connected to the power supply Vcc, an emitter grounded via an emitter resistor R2, and a third end connected to the other end of the crystal resonator X having one end grounded. , The fourth transistor Q
3. The base of Q4 is connected.

The emitter of the third transistor Q3 is connected to the base of the first transistor Q1, and the emitter of the fourth transistor Q4 is connected to the base of the second transistor Q2. The second transistors Q1 and Q2 are driven.

The base of the third transistor Q3
The base voltage V of the first transistor Q1 is applied between the emitters.
a first capacitor C1 for raising the positive peak value of b1
Is interposed. Similarly, a second capacitor C2 for lowering the negative peak value of the base voltage Vb2 of the second transistor Q2 is interposed between the base and the emitter of the fourth transistor Q4.

The third and fourth transistors Q3,
The base of Q4 is connected to power supply Vcc via bias resistor R3.
, And grounded via a bias resistor R4 to apply a bias voltage to the bases of the third and fourth transistors Q3 and Q4.

The third and fourth transistors Q
3. A third capacitor C3 is connected between the base of Q4 and the output terminal Out. Further, a fourth capacitor C4 is connected between the output terminal Out and the ground potential.

With such a configuration, the base and emitter voltages Vbe of the first and second transistors Q1 and Q2 in the output stage are controlled by the third and fourth transistors Q3 and Q4.
And the occurrence of crossover distortion can be prevented. And the third and fourth transistors Q
3, the first and second transistors Q1 and Q2 in the output stage can be driven by the piezoelectric vibration of the crystal resonator X connected to the bases of Q4.

Here, when a sine wave signal as indicated by In in FIG. 2 is input to the first and second transistors Q1 and Q2 in the output stage, the base voltage V of the transistors Q1 and Q2
b1 and Vb2 change as shown by Vb1 and Vb2 in FIG. 2, respectively.

That is, the positive peak value of the transistor Q1 is raised by the charge of the capacitor C1,
Similarly, the negative peak value of transistor Q2 is
2, which is reduced by the charge.

The broken line in FIG. 2 shows how the positive and negative peak values are distorted when, for example, the power supply voltage is low and the first and second capacitors C1 and C2 are not provided. Thus, in the above embodiment, the oscillation output of the output terminal Out is as shown in FIG.
As shown by a solid line, a signal without distortion can be obtained. Note that the broken lines in FIG. 3 show the distortion of the output signal when the base voltages Vb1 and Vb2 are distorted as shown by the broken lines in FIG.

An oscillation circuit using a class B amplifier can obtain a large output as compared with a conventional Colpitts type crystal oscillation circuit as shown in FIG. 4, for example, and the output level fluctuation due to a load fluctuation is small. There is an advantage that it can be driven with a large amplitude even for a low resistance load.

The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, one end of the crystal unit is directly grounded, but the oscillation frequency can be reduced by inserting a capacitor here. Can be slightly variable. Therefore, if a variable capacitor is used here, the oscillation frequency can be continuously changed, and the oscillation frequency can be accurately adjusted.

[0020]

The present invention is embodied in the form described above and has the following effects.

Since a class B amplifier is used in the oscillation circuit, the operation efficiency is good, and a large amplitude output can be obtained without distortion even at a low voltage, for example, a power supply voltage of about 2.6 V. Therefore, it is possible to provide an output circuit in which the output level does not fluctuate due to the load fluctuation and the power consumption is small.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an oscillation circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing a change in a base voltage of a transistor in an output stage of the embodiment shown in FIG. 1;

FIG. 3 is a waveform chart showing an oscillation output of the embodiment shown in FIG.

FIG. 4 is a circuit diagram of a conventional Colpitts oscillation circuit.

[Explanation of symbols]

 Q1, Q2, Q3, Q4 Transistors C1, C2, C3, C4 Capacitors R1, R2, R3, R4 Resistance

Claims (3)

(57) [Claims] A crystal oscillator is provided at the input of a class B amplifier having a collector and emitter of an NPN type first transistor and an emitter and collector of a PNP type second transistor connected in series between a power supply and a ground potential. In the connected crystal oscillation circuit, a third PNP-type crystal resonator having one end grounded, and a base connected to the other end of the crystal resonator, the collector grounded, and the emitter connected to the power supply via an emitter resistor. A transistor, a fourth transistor of an NPN type having a base connected to the other end of the crystal unit, a collector connected to a power supply, and an emitter grounded via an emitter resistor; and a base connected to the emitter of the third transistor. A first transistor of NPN type connected to the transistor, and a second transistor of PNP type having a base connected to the emitter of the fourth transistor. An output terminal derived from a series connection point of the emitter of the first transistor and the emitter of the second transistor; a base voltage of the first transistor connected between the base and the emitter of the third transistor; A first capacitor connected between the base and the emitter of the fourth transistor, for reducing the negative peak value of the base voltage of the second transistor; and a third capacitor connected between the base and the emitter of the fourth transistor. A crystal comprising: a third capacitor interposed between a base of a fourth transistor and an output terminal; and a fourth capacitor having one end connected to the output terminal and the other end grounded. Oscillator circuit. 2. A crystal oscillation circuit according to claim 1, wherein a capacitor for adjusting the oscillation frequency is inserted at one end of the crystal resonator. 3. The crystal oscillation circuit according to claim 2, wherein the capacitor interposed at one end of the crystal unit is a variable capacitor.