JPS5927486B2 - oscillation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oscillation circuit, and more particularly to an oscillation circuit using a vibrator whose frequency and voltage characteristics are inversely correlated.

AT-cut crystal resonators have less variation in oscillation frequency due to temperature changes than tuning fork-type crystal resonators, and are used in oscillation circuits that require high precision.

However, in an oscillation circuit using a solid-state resonator, the oscillation frequency of the oscillation circuit generally changes in response to changes in the voltage supplied to the circuit.

For example, the above AT whose frequency and voltage characteristics are inversely correlated
When a cut crystal resonator is used, as shown by the symbol A in Figure 1, the oscillation frequency decreases as the supply voltage VDD increases, and as the supply voltage VDD decreases, the oscillation frequency increases, making it difficult to oscillate with high precision. It becomes inconvenient for

In order to reduce such fluctuations in the oscillation frequency, for example, the voltage supplied to the oscillation circuit may be stabilized.

However, in order to stabilize the supply voltage, it is necessary to add a constant voltage circuit to the oscillation circuit, which leads to the complexity of the device.

Further, since there is power loss in a constant voltage circuit, it is extremely disadvantageous in terms of long-term use required for, for example, an electronic watch equipped with a built-in battery.

The present invention provides an oscillation circuit that uses a resonator whose frequency and voltage characteristics are inversely correlated, such as an AT-cut crystal resonator, in which a variable capacitance diode is installed on the same substrate as a MOS inverter constituting the oscillation circuit. A new oscillation circuit is created that eliminates the voltage dependence of the oscillation frequency of the oscillation circuit and does not unnecessarily complicate the circuit or increase power loss by connecting it in parallel to the capacitor in the oscillation circuit. Hereinafter, the details will be explained based on the illustrated embodiments.

In FIG. 2 showing an embodiment of the oscillation circuit according to the present invention, reference numeral 1 indicates a C-MOS inverter as a MOS inverter.

C-MOS inverter 1 is P channel MO8-FET
(hereinafter referred to as P-MO8T) 2 and N channel MO
8.FET (hereinafter referred to as N-MO8T) 3 are connected in a combinary manner.

An AT-cut crystal resonator 4 as a resonator and a feedback resistor 5 are connected between the input and output of the C-MOS Impark 1.

Furthermore, a capacitor 6 and a PN junction diode 7 as a variable capacitance diode are connected to the input side of the C-MOS Impark 1.

Furthermore, a capacitor 8 and a PN junction diode 9 as a variable capacitance diode are connected to the output side of the C-MOS impark 1.

Incidentally, the capacitor 6.8 is externally attached, and its capacitance value is about 20 to 40 PF.

In the oscillation circuit according to the present invention having such a configuration, the natural frequency of the AT-cut crystal resonator 4 exhibits an inverse correlation with the supplied voltage.

However, the PN junction diode 7.9 has a small capacitance value when the supply voltage is high, and a large capacitance value when the supply voltage is low.

Further, the natural frequency of the AT-cut crystal resonator 4 changes by about 2 to 3 degrees when changing from 1.57 volts to 1.2 volts when an AgO battery is used as a power source, for example.

On the other hand, by changing the ratio of the capacitance values of the capacitor 6 and the PN junction diode 7 and the capacitance values of the capacitor 8 and the PN junction diode 9 by IPF, the oscillation frequency can be changed by about 2 to 3 pIMn.

Therefore, by designing the capacitance of the PN junction diode 7.9 to be on the order of IPF, it is possible to change the capacitance value in accordance with changes in the natural frequency of the AT cut crystal resonator 4 due to fluctuations in the supplied voltage. can.

That is, when the supply voltage drops from a certain voltage, the natural frequency of the AT-cut crystal resonator 4 increases.

However, on the other hand, the capacitance of the PN junction diode 7.9 becomes large as the depletion layer shrinks due to a decrease in the supply voltage.

This increase in capacitance causes the oscillation frequency of the oscillation circuit to decrease.

Therefore, even if the supply voltage decreases, the apparent capacitance change of the oscillation circuit as a whole is canceled out, and the frequency of the oscillation output is held constant.

Note that when the supply voltage increases, the direction is opposite to that described above.

Further, as can be seen from FIG. 2, fluctuations in the oscillation frequency due to voltage changes can be prevented without complicating the circuit.

FIG. 3 shows P'-MO8T2, N-MOS T3 and P'-MO8T2, which constitute the C-MOS inverter 1 shown in FIG.
The N-junction diode 7.9 is connected to an N-type silicon semiconductor substrate (
FIG. 2 is a schematic diagram showing a state formed on a substrate 10 (hereinafter referred to as a substrate).

P-type impurity regions 11 and 12 of PN junction diode 7.9
is manufactured in the same process as the P type impurity region 13 which becomes the substrate of the N-MOS T3.

Also, the N-type impurity region 14 of the PN junction diode 7.9
, 15 are made in the manufacturing process of the source and drain regions 16 and 17 of the N-MOS T3.

Note that the N-type impurity regions indicated by numerals 18 and 19 are P-MO
These are the drain and source regions of 8T3.

In this way, the PN junction diode 7.9 is a C-MOS
It can be easily made in the process of manufacturing Impark 1.

Therefore, the process does not become complicated.

Further, since the PN junction diode 7.9 is formed on the same substrate as the C-MOS inverter 1, the device does not become larger.

Although the present invention has been described above in detail based on the illustrated embodiments, the present invention is not limited to the illustrated embodiments, and various changes and improvements can be made.

For example, in the embodiment, the MOS inverter is a C-MOS inverter, but it is also possible to impark only P-MO8 or N-MO8.

Furthermore, as a resonator, it is not limited to AT cut crystal resonators.
Any other vibrator may be used as long as its frequency-voltage characteristics have an inverse relationship.

Further, as the variable capacitance diode, a MOS diode can also be used in addition to a PN junction diode.

As mentioned above, the oscillation circuit according to the present invention has a variable capacitance diode connected in parallel with the ordinary external capacitor, so that the natural frequency of the oscillator changes as the supply voltage of the oscillation circuit changes. Since the capacitance value of the variable capacitance diode can be changed in accordance with the change in , an oscillation output with a constant frequency can be obtained regardless of changes in the supply voltage.

In addition, in order to stabilize the oscillation frequency, only the variable capacitance diode is simply formed on the same substrate as the MOS inverter, so there is no need to complicate the circuit or manufacturing process; It can be manufactured using the same manufacturing equipment and line, and the intended purpose can be fully achieved without causing an increase in the size of the equipment, resulting in great practical effects.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the characteristics of a resonator whose frequency and voltage characteristics are inversely correlated, FIG. 2 is a diagram showing an example of an oscillation circuit according to the present invention, and FIG. FIG. 2 is a schematic diagram showing the formation state of some circuit elements. 1...C-MOS inverter as a MOS inverter, 2...P-channel MO8-FET constituting the C-MOS inverter, 3...C-M
N-channel MO8-FET that constitutes the OS inverter. 4... AT-cut crystal resonator as a resonator whose frequency and voltage characteristics are inversely correlated, 6, 8...
... Capacitor, 7,9... PN junction diode as a variable capacitance diode.

Claims (1)

[Claims] An AT-cut crystal oscillation device comprising an I MOS inverter and capacitors connected to the input side and output side of the MOS inverter, and in which the oscillation frequency and voltage characteristics are inversely correlated in the oscillation circuit. In the oscillator circuit in which the capacitor is connected in parallel to the MOS inverter, a variable capacitance diode formed by a PN junction formed in a well on the same substrate as the MOS inverter is connected in parallel to the capacitor. Oscillation circuit. 2. The oscillation circuit according to claim 1, wherein the MOS impark is composed of a P-channel MO8-FET and an N-channel MO8-FET.