JPH066594Y2 - Overtone crystal oscillator circuit - Google Patents

Description

Detailed Description of the Invention A. This invention relates to an overtone crystal oscillator circuit using a C-MOS inverter.

B. SUMMARY OF THE INVENTION The present invention is an overtone crystal oscillator circuit, in which a low impedance gate input bias element is connected to the gate input terminal of a C-MOS of a Colpitts type oscillator circuit using a C-MOS inverter, so that the configuration is simple. In addition, the stable overtone oscillation can be generated without being influenced by the surrounding environment.

C. 2. Description of the Related Art In recent years, as ICs have become faster, there has been an increasing demand for stable oscillators at high frequencies. In order to oscillate stably at high frequency, conventionally, a tuning circuit (LC tuning circuit) is connected to a crystal oscillating circuit using a transistor that can obtain a sufficient gain even at a high frequency as an amplifier to cause overtone oscillation. Means were the mainstream. The overtone oscillation circuit using this transistor as an amplifier has a problem that the circuit configuration becomes extremely complicated and that it is difficult to set a constant.
Incidentally, FIG. 8 shows a Colpitts type crystal oscillation circuit using a C-MOS inverter as an amplifier. In FIG. 8, 1 and 2 are C-MOS inverters, and C-MOS inverter 1 is used as an amplifier. The feedback high resistance R _f determines the amplification degree. X
tal is a crystal oscillator, C ₁ and C ₂ are capacitors, and the C-MOS inverter 2 is a buffer. As the resistance value of R _f, a resistance of the order of 10 ⁶ to 10 ⁷ (Ω) is usually used. Further, the C-MOS inverter 2 prevents the influence of the load from affecting the oscillation circuit when the load is connected to the oscillation circuit.

Even in the Colpitts type crystal oscillation circuit using the C-MOS inverter as an amplifier, although not shown, LC
A means for connecting a tuning circuit to cause overtone oscillation has also been considered.

D. Problems to be Solved by the Invention When an LC tuning circuit is connected to a Colpitts type crystal oscillation circuit using a C-MOS inverter as an amplifier to cause overtone oscillation, the following problems occur, which is not preferable. .

Even if the LC tuning circuit is connected, the Q value as the tuning circuit does not become a very large value, and the frequency fed back to the amplification stage becomes unstable. Therefore, the output frequency becomes unstable. Especially for the coil L, since the influence of temperature change is extremely large, the tuning frequency may change.

E. Means for Solving the Problems This invention is to connect a crystal oscillator and a feedback resistor between the input and output ends of a C-MOS inverter composed of complementary MOSFETs, and connect the input and output ends of the C-MOS inverter and ground. A Colpitts oscillator circuit with a capacitor connected is provided.
A series circuit composed of low-impedance gate input bias elements connected in series between the power supply and ground is provided, and the common connection point of this series circuit is connected to the input terminal of the C-MOS inverter of the oscillation circuit.

F. By applying a bias voltage to the input gate of the C-MOS inverter of the oscillator circuit by means of a low-impedance gate input bias element, the input impedance on the circuit side as seen from the crystal oscillator becomes small. Therefore, the crystal unit shifts to high-frequency excitation (higher-order overtone). That is, since the gain of the C-MOS inverter decreases at a high frequency, the negative resistance at the triple overtone frequency becomes larger than the negative resistance at the fundamental wave, so that oscillation occurs at the triple overtone.

G. Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a C-MOS inverter of an amplification stage,
2 is a buffer C-MOS inverter, which is a C-MO
A crystal oscillator Xtal is connected between the input and output ends of the S inverter 1, and capacitors C ₁ and C ₂ are connected between the input and output end of the C-MOS inverter 1 and the ground to form a Colpitts oscillator circuit.

R _A and R _B are low resistances connected in series as gate input bias elements, and the series circuit of these resistors R _A and R _B is connected between the power supply and ground. The common connection point of the series circuit of the low resistances R _A and R _B is C-
It is connected to the input terminal (input gate) of the MOS inverter 1. A resistance value is selected for the potential (bias voltage) of this common connection point, and the threshold voltage V _TH (= V _DD / 2)
Try to be. V _DD is the voltage of the power supply. In addition, R
_A, the resistance value of R _B is the value that it is possible to three-fold overtone oscillation, and and selected as R _A = R _B.

The operation of the embodiment configured as above will be described.

When a bias voltage is applied to the input gate of the C-MOS inverter 1 of the Colpitts type crystal oscillator circuit by the low resistances R _A and R _B , as shown in FIG. 2, the input impedance Z _{in of} the circuit side viewed from the crystal unit Xtal is obtained. Becomes smaller, the crystal unit Xtal shifts to high-frequency excitation (higher-order overtone). To activate overtone, use C-MO
Since the gain of the S inverter 1 at high frequencies decreases, the negative resistance at the triple overtone frequency becomes larger due to the negative resistance at the fundamental wave, so that oscillation occurs at the triple overtone.

FIG. 3 is a circuit diagram showing an embodiment in which the present invention is applied to a clock C-MOS inverter. In FIG. 3, a high resistance (gate-drain bias resistance) which is a feedback resistance R _f is built in. 1st in this embodiment even if
As in the figure, the bias is C-MOS by the low resistances R _A and R _B.
When applied to the input gate of the inverter 1, triple overtone oscillation becomes possible. Therefore, even with the C-MOS inverter with the built-in feedback resistor R _f, triple overtone oscillation is possible.

Here, a circuit diagram in which the low resistances R _A and R _B in FIG. 3 are Z _A and Z _B (gate input bias elements) is shown in FIG. In FIG. 4, the following equation is established to enable triple overtone oscillation. However, V _TH is a threshold voltage.

Z ₁₁ = same as _{Z A // Z B Z A ·} Z B / Z A + Z B ... (1) V TH = Z B · V DD / Z A + Z B ... (2) Then the equivalent circuit of FIG. 2 The equivalent circuit of FIG. 4 is shown in FIG. In FIG. 5, Z ₁ is the conventional C
-The circuit-side impedance of the Colpitts-type crystal oscillator circuit using a MOS inverter as seen from the crystal oscillator. Z _in
Is the circuit-side impedance seen from the crystal unit when the gate input bias elements Z _A and Z _B are connected.

Z _in = Z ₁₁ // Z ₁ = Z ₁₁ · Z ₁ / Z ₁₁ + Z ₁ (3) From the above, the relationship between the magnitude of Z ₁₁ , the oscillation angular frequency ω, and the negative resistance _RL is shown in the graph. It looks like Figure 6. In FIG. 6, when ω _C = ω (when R _L = 0) and ω _C satisfies ω ₁ <ω _C <3ω ₁ , 3 times overtone oscillation becomes possible and 3ω ₁ <ω _C < When 5ω ₁ is satisfied, 5 times overtone oscillation becomes possible. However, ω ₁ is the fundamental wave resonance angular frequency of the crystal unit.

For obtaining more the output of the high frequency from the characteristic diagram of FIG. 6 in the embodiment shown in FIG. 1 and FIG. 3, it is necessary to lower the resistance of R _A = R _B to a very small value. When R _A and R _B are set to extremely small values, the current flowing from the power source (V _DD ) to the ground becomes large. Therefore, the power consumption cannot be ignored. An example in which this power consumption is improved will be described below.

FIG. 7 shows an embodiment of a triple overtone crystal oscillator circuit using a low power consumption C-MOS inverter. In FIG. 7, a series circuit including a low resistance R _A and a Zener diode D _Z is provided at the input gate of the C-MOS inverter 1.
The common connection point of this series circuit is connected to the input gate of the C-MOS inverter 1. At this time, the bias voltage is C-
It is selected so as to be the threshold voltage V _TH of the MOS inverter. Since the impedance of the Zener diode D _Z is very large, no current flows even if the value of R _A is made small, and the determination of the oscillation frequency depends only on R _A. If the value of R _A to perform the triple overtone oscillation and R _A = R _2, Fig. 1, when compared with bias resistor value R _A = R _B = R ₁ in the case of FIG. 3, R ₂ And R ₁ are as follows.

R ₂ = 2R ₁ (4) In addition, the Zener voltage of the Zener diode D _Z to be used is such that the threshold voltage of the C-MOS inverter is used, or the threshold voltage matches the Zener voltage of the Zener diode. The power supply voltage V _DD may be adjusted as described above.

By using the embodiments shown in FIGS. 1, 3, and 7 described above, the overtone crystal oscillation circuit using the C-MOS inverter can be reliably oscillated. Therefore, it has become possible to sufficiently cope with the recent increase in the speed of C-MOS. Further, since it is not a complicated circuit like an overtone oscillation circuit using a transistor, it is easy to determine a circuit constant, and is excellent in miniaturization, mass production, and low cost. Furthermore, unlike when using an LC tuning circuit,
Since no coil is used, stable oscillation can be performed even with changes in the surrounding environment.

H. As described above, according to the present invention, in the Colpitts type crystal oscillation circuit using the C-MOS inverter as an amplifier, the bias voltage is applied to the input gate of the C-MOS inverter by using the bias element. , It is possible to generate stable overtone oscillation by reducing the circuit impedance seen from the crystal oscillator side.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, FIG. 3 is a circuit diagram showing a second embodiment of the present invention, and FIG. 4 is a gate input bias. FIG. 5 is an equivalent circuit diagram of FIG. 4, FIG. 6 is a frequency vs. negative resistance characteristic diagram, and FIG. 7 is a circuit diagram showing a third embodiment of the present invention. FIG. 8 is a circuit diagram of a conventional example. 1,2 ...... C-MOS inverter, R _A, R _B ...... low resistance, Xtal ...... crystal oscillator, C _1, C ₂ ...... capacitor,
R _f ... Feedback resistor.

Claims (2)

[Scope of utility model registration request] 1. A Colpitts oscillator circuit comprising a crystal oscillator connected between the input and output ends of a C-MOS inverter composed of complementary MOSFETs, and a capacitor connected between the input and output end of the C-MOS inverter and ground. A series circuit including a low-impedance gate input bias element connected in series between a power source and ground is provided, and a common connection point of the series circuit is connected to an input end of a C-MOS inverter of the oscillation circuit and the common circuit is provided. An overtone crystal oscillation circuit characterized in that the potential at the connection point is set to a threshold voltage. 2. The utility model registration claim characterized in that the series circuit comprises a Zener diode and a resistor.
The overtone crystal oscillator circuit according to the item.