JP2003198256A - Crystal oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact sinusoidal wave output type crystal oscillator with low consumption current. <P>SOLUTION: A Colpitts type crystal oscillation circuit having a crystal resonator and an oscillating transistor, and a base-grounded amplifier type buffering transistor are provided. The oscillating transistor and the buffering transistor are connected in cascade via a resistor for cutting alternating current, one end of the crystal resonator is grounded through an interval between the base and the emitter of the buffering transistor, and the collector of the oscillating transistor is grounded in an alternating current way. As a direct current, since an oscillating transistor 2 and a buffering transistor 7 are connected in cascade (cascade connection), the collector currents of both the transistors can be commonly utilized, thereby enabling the compact sinusoidal wave output type crystal oscillator with low consumption current to be realized. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized, low-current-consumption type sine-wave output type crystal oscillator, and more particularly to a crystal oscillator with reduced output signal distortion. 2. Description of the Related Art Generally, in a digital PLL circuit provided with a level control type phase comparator, a duty ratio is required to prevent occurrence of jitter (synchronous deviation) between a reference input signal and an output signal. Is required to be 50%. For this reason, conventionally, a sine wave output type crystal oscillator as shown in FIG. 2 has been used as a reference signal source, and its output signal has been obtained in a pulse waveform with a duty ratio of 50% by, for example, an inverter circuit (the sine wave center potential is an Threshold level). A conventional sine wave output type crystal oscillator 100 shown in FIG. 2 includes a Colpitts type crystal oscillator having an oscillation amplifier circuit 101 and a crystal oscillator 102 and a grounded base type buffer circuit 103, for example. It is. That is, the oscillation amplifying circuit 101 inserts and connects a series circuit composed of a capacitor 105 and a capacitor 106, which are a part of the load capacitance, between the base of the oscillation transistor 104 and the ground. Connected to the emitter of the oscillating transistor 104, connected to the emitter resistor 107, and further inserted and connected between the collector of the oscillating transistor 104 and the power supply voltage Vcc line.
9 and a resistor 110, and a crystal oscillator 102 is inserted and connected between the base of the oscillation transistor 104 and the ground to function as an amplifier circuit for a Colpitts crystal oscillator. [0004] The crystal oscillator 100 operates so that a part of the excitation signal of the crystal oscillator 102 is used as an input signal.
The buffer circuit 103 is inserted and connected between one end of the output terminal OUT and the output terminal OUT. In the crystal oscillator 100 having such a configuration, the excitation signal of the crystal oscillator 102 has a sine wave because the crystal oscillator 102 has a high Q value.
If a signal is directly derived from one end of the second circuit 2, a sine wave signal (duty ratio 50%) can be output in a small configuration without requiring a complicated circuit configuration such as a tuning circuit. However, in the case of the crystal oscillator 100 having the above configuration, since the oscillation amplifying circuit 101 and the buffer circuit 103 have a parallel configuration,
Each of them has its own current consumption, which limits power saving. An object of the present invention is to provide a small-sized, low-current-consumption type sine-wave output type crystal oscillator by solving the above problems of the crystal oscillator. In order to solve the above-mentioned problems, the invention according to the first aspect of the present invention relates to a Colpitts type crystal oscillation circuit having a crystal oscillator and an oscillation transistor, and a grounded base amplifier. Type buffer transistor is connected vertically via a resistor for AC cut, one end of the crystal unit is connected to the emitter of the buffer transistor, and the collector of the oscillation transistor is AC grounded. It is characterized by the following. Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a circuit diagram showing an embodiment of a crystal oscillator according to the present invention. The crystal oscillator 1 shown in FIG. 1 is a Colpitts-type oscillation circuit, and a series circuit including a capacitor 3 and a capacitor 4 forming a part of a load capacitor is inserted and connected between the base of the oscillation transistor 2 and the ground. The connection midpoint of the series circuit is connected to the emitter of the oscillation transistor 2, the emitter resistor 5 is connected, the collector of the oscillation transistor 2 is grounded via the capacitor 6, and the collector of the oscillation transistor 2 is connected to the buffer. The emitter of the transistor 7 is connected via an AC cut resistor 8 and a resistor 9 is inserted and connected between the collector of the buffer transistor 7 and the power supply voltage Vcc line.
The resistor 10 is connected to the resistor 1 so that a base bias is appropriately applied to the oscillation transistor 2 and the buffer transistor 7.
2 and a base of the buffer transistor 7 is grounded via the capacitor 13 between the emitter and the ground. Further, a crystal oscillator 14 is connected to the base of the oscillation transistor 2, and the other end of the crystal oscillator 14 is connected to the base of the buffer transistor 7 via, for example, a capacitor 15. A capacitor 16 is inserted and connected to the ground, and the collector of the buffer transistor 7 and the output terminal OUT are connected via a DC cut capacitor 17. With such a configuration, in the crystal oscillator 1, the buffer circuit including the buffer transistor 7 is of a grounded base type, and the potential between the base and the emitter of the buffer transistor 7 fluctuates based on the amplitude of the excitation signal of the crystal oscillator 14. However, by setting a bias so that the buffer transistor is always in an active state, a bias current flows from the base of the buffer transistor 7 to the emitter. Since an oscillation loop is formed in which the capacitor 4 and the capacitor 13 are AC-connected via the ground, an oscillation operation can be obtained. Since the excitation signal of the crystal unit 14 having a high Q value is a sine wave signal, a sine wave signal is generated at the emitter and the collector of the buffer transistor 7, and as a result, a sine wave signal is output from the output terminal OUT. A signal can be output. Since the AC signal generated at the collector of the oscillating transistor 2 is grounded via the capacitor 6,
Is not transmitted to the buffer transistor 7. On the other hand, in the DC circuit, since the oscillation transistor 2 and the buffer transistor 7 are vertically connected (cascode connection), both transistors commonly use the collector current, thereby setting the current consumption of the crystal oscillator 1 small. be able to. For example, when the power supply voltage Vcc is 3.3 V, the emitter current of the transistor 2 is about 1.572 mA, the base current of the transistor 2 is about 14.11 μA, and the transistor 7
The DC bias is set so that the emitter current of the transistor 7 is about 1.557 mA and the base current of the transistor 7 is about 13.96 μA. Further, in order to suppress the level of the feedback signal to the crystal unit 14, the capacity 3 is set to 180 pF and the capacity 4 Is 390 pF, the oscillator current flowing through the quartz oscillator 14 is 1.3 mA (rms).
When it is set so that the value of the output load connected to the output terminal OUT is equivalent to a parallel circuit of RL = 10 kΩ and CL = 10 pF, about 1.2 Vp-p Sine wave output was able to be generated. As described above, the crystal oscillator according to the present invention includes a Colpitts crystal oscillation circuit having a crystal oscillator and an oscillation transistor, and a grounded base amplifier type buffer transistor. Wherein the oscillation transistor and the buffer transistor are vertically connected via an AC cut resistor, and one end of the crystal unit is connected to a base of the buffer transistor.
Since the emitter is grounded through the emitter and the collector of the oscillation transistor is grounded in an AC manner, the DC circuit
Since the oscillation transistor 2 and the buffer transistor 7 are connected vertically (cascode connection), it is possible to commonly use the collector currents of both transistors, thereby making it possible to use a small and low current consumption sine wave output type crystal oscillator. Can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing one embodiment of a crystal oscillator according to the present invention. FIG. 2 is a circuit diagram showing a conventional crystal oscillator. [Description of Signs] 1 crystal oscillator, 2 oscillation transistors, 3, 4, 6, 1
3, 15, 16, 17 capacity, 5, 8, 9, 10, 11,
12 resistor, 7 buffer transistor, 14 crystal oscillator, 100 crystal oscillator, 101 oscillation amplifier circuit, 102
Crystal oscillator, 103 buffer circuit, 104 oscillation transistor, 105, 106 capacitance, 107, 108, 10
9,110 resistance

Claims (1)

Claims: 1. A Colpitts type crystal oscillation circuit having a crystal oscillator and an oscillation transistor, and a grounded base amplifier type buffer transistor are longitudinally connected via an AC cut resistor, and A crystal oscillator wherein one end of a crystal oscillator is connected to an emitter of the buffer transistor, and a collector of the oscillation transistor is AC grounded.