JP2003283249A - Quartz oscillator circuit and electronic apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a quartz oscillator circuit and an electronic apparatus using it, wherein even when a capacitance is made variable, the oscillator circuit does not cause such problems that the voltage range in which the oscillator circuit can operate becomes smaller, the time required to start oscillation becomes longer, or the oscillator does not oscillate when the series equivalent resistance of the quartz oscillator is large, etc., and the current consumption in the circuit can be suppressed not to increase more than necessary. <P>SOLUTION: The quartz oscillator 7, an inverter 1 connected to the quartz oscillator 7 in series, a resistor R connected to the inverter 1 in parallel, one or more load capacitances C1-C7 connected to both ends of the quartz oscillator 7, and a programmable storage element 9 are provided, and the load capacitances C1 to C3, C6, C7 based on the content of the storage element 9 are made variable, and the gain of the inverter 1 is adjusted to carry out control. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator circuit technology using a crystal oscillator, and more particularly to a crystal oscillator circuit whose oscillation frequency can be adjusted by a load capacitance of the oscillator circuit and an electronic device using the crystal oscillator circuit. It is a thing.

[0002]

2. Description of the Related Art First, a conventional technique relating to a crystal oscillator circuit will be described. FIG. 4 is a diagram showing a general crystal oscillation circuit. This circuit will not oscillate when the gain of the circuit decreases, the operating voltage range of the oscillation circuit becomes narrow, the oscillation start time becomes long, or the series equivalent resistance value of the crystal unit is large (= oscillation allowance It is known to cause such problems (see Japanese Patent Application Laid-Open No. 4-165704).

On the other hand, as a method of adjusting the oscillation frequency with high accuracy based on the oscillation circuit of FIG. 4, in the crystal oscillation circuit including the crystal oscillator 31, the inverter 32, the resistor, the capacitance CG, and the capacitance CD, the capacitance CG, There is a method for making the capacity CD variable (see Japanese Patent Laid-Open No. 62-200804).

[0004]

However, when the crystal oscillation circuit is constructed by using the above conventional method, the capacitance C
When the gain of the oscillation circuit changes due to the values of G and the capacitance CD, and the gain of the oscillation circuit decreases, the operable voltage range of the oscillation circuit becomes narrow, the oscillation start time becomes long, or the crystal oscillator series If the equivalent resistance value is large, a problem such as no oscillation will occur. In order to avoid these effects, the gain of the oscillation circuit may be set sufficiently high so that the above-mentioned various characteristics are within the allowable range, but in this case, the current consumption of the oscillation circuit increases.

Therefore, the present invention does not cause the above-mentioned problems even when the capacitance is made variable, and it is possible to suppress the consumption current from increasing more than necessary. It is an object to provide an electronic device (claim 4) using a crystal oscillation circuit.

[0006]

In order to achieve the above object, the present invention provides a crystal resonator,
An inverter connected in series to the crystal unit, a resistor connected in parallel to the inverter, one or more load capacitors connected to both ends of the crystal unit, and a programmable storage element. , 1 based on the contents of the storage element
At least one of the load capacities described above is made variable, and the gain of the inverter is adjusted and controlled.

According to a second aspect of the present invention, in the configuration of the first aspect, the adjustment of the gain of the inverter is performed in the size (W / L).
Further, the invention is characterized in that a plurality of inverters having different thresholds are prepared and switched, and the invention according to claim 3 is the configuration of claim 1, wherein the gain of the inverter is adjusted by switching a constant voltage value to be operated. It is characterized by doing. A fourth aspect of the present invention is an electronic apparatus using the crystal oscillation circuit according to any one of the first to third aspects.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment) FIG. 1 is a diagram for explaining an embodiment of the present invention. In the figure, 1 is an inverting amplifier (inverter), 2 to 6 are inverters, 7 is a crystal oscillator, and 8 is a programmable storage element (EPROM, E).
A gain adjusting circuit for varying the gain of the inverter 1 according to the value of EPROM, fuse ROM, etc., SW1 to SW5 are transmission gates (analog switches), R1
Is a feedback resistor for bias for using the inverter 1 as an inverting amplifier, R2 is a stabilizing resistor for suppressing oscillation of the crystal unit at higher harmonics, and C1 to C4 are load capacitors on the gate side of the crystal unit (see FIG. 4 corresponds to CG), C4 is a fixed part, C1 to C3 are variable parts, C5 to C7 are drain side load capacitances of the crystal unit (corresponding to CD in FIG. 4), C5 is a fixed part, and C6 to C7. Is a variable part.

Of the load capacitances (C1 to C7) of the crystal, the variable parts (C1 to C3, C6 to C7) are set to the state (value) of the storage element.
Accordingly, the switching of SW1 to SW5 adjusts the oscillation frequency, and at the same time, the gain of the inverting amplifier (oscillation inverter) is adjusted according to the state of the storage element at that time.

Here, as a method of changing the gain of the oscillation inverter, a plurality of oscillation inverters are prepared and switched. (Variable size W / L) Plural oscillation inverters with different Vth are prepared and switched. The oscillator circuit is operated at a constant voltage and the constant voltage value is switched. However, in any case, the current consumption increases due to the following reasons.

First, the above and the above will be described with reference to the drawings. These switch the oscillation inverter according to the value of the storage element. FIG. 2 is an example in which the value of the storage element is decoded into two codes and the oscillation inverter is switched according to the value of the storage element. As the inverter 1 (13) and the inverter 2 (14), those having different W / L sizes (above) or those having a different threshold Vth (above) are used.
When the inverter 2 (14) is used, the inverter 1 (13) is used when the oscillation condition is severe depending on the value of the storage element, and the inverter 2 (14) is used when the oscillation condition is loose.

Next, the above will be described with reference to the drawings. This is because when the oscillation circuit is operated at a constant voltage, the constant voltage value is switched according to the value of the storage element. Figure 3
Is an example in which the constant voltage value is switched by a DA converter.
Increase the output voltage of the converter and increase the gain of the inverter.

In the above case, the current consumption of the inverter is W
/ L ratio increases. In the above case, the current consumption increases by the square of the decrease in the threshold Vth. In the above case (W / L is the same), the current increases by the square of the increment of the power supply voltage.
It will be. Therefore, it is disadvantageous in terms of current consumption to always use the upper-order method, and therefore, in the present invention,
The current consumption is suppressed by switching the gain of the oscillation inverter according to the value of the storage element.

Similar to the above, by using the crystal oscillation circuit for varying the load capacitance based on the contents of the memory element and adjusting the gain of the inverter for control in the clock function section of various electronic devices. It is possible to realize an electronic device having the effect of.

[0015]

According to the present invention, even when the capacitance is made variable, the operable voltage range of the oscillation circuit becomes narrow, the oscillation start time becomes long, or the series equivalent resistance value of the crystal unit is large. Crystal oscillation circuit (claims 1 to 3) and electronic equipment using the crystal oscillation circuit (claims 1 to 3) capable of preventing the occurrence of problems such as no oscillation in the device and suppressing the consumption current from unnecessarily increasing. 4) can be realized.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing an example in which the value of a storage element is decoded into two codes and the oscillation inverter is switched according to the value of the storage element.

FIG. 3 is a diagram showing an example in which constant voltage values are switched by a DA converter.

FIG. 4 is a diagram showing a general crystal oscillation circuit.

[Explanation of symbols]

1: Inverting amplifier (inverter), 2 to 6: Inverter, 7: Crystal oscillator, 8: Gain adjusting circuit, 9, 11: Storage element, 12: Decoder, 13: Inverter 1, 14: Inverter 2, 21: Storage Element, 22: DA converter, 23: Inverter, 31: Crystal oscillator, 32: Inverter. SW1 to SW5: Transmission gate (analog switch), R1: Bias feedback resistor, R2: Stabilizing resistor, C1 to C4: Crystal oscillator gate side load capacitance, C5 to C7: Crystal oscillator drain side load capacitance, CD: capacity, CG: capacity.

Claims (4)

[Claims] 1. A crystal unit, an inverter connected in series to the crystal unit, a resistor connected in parallel to the inverter, and one or more load capacitors connected to both ends of the crystal unit. And a programmable storage element, wherein at least one of the one or more load capacitances is made variable based on the content of the storage element and the gain of the inverter is adjusted and controlled. circuit. 2. The crystal oscillating circuit according to claim 1, wherein the gain of the inverter is adjusted by preparing and switching a plurality of inverters having different (W / L) sizes or thresholds of their gates. 3. The crystal oscillator circuit according to claim 1, wherein the gain of the inverter is adjusted by switching a constant voltage value to be operated. 4. An electronic device using the crystal oscillating circuit according to claim 1.