JPH03283904A - piezoelectric oscillator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric oscillator suitable for application to a VCO (voltage controlled oscillator) or a DTCXO (digital temperature compensated crystal oscillator).

[Conventional technology]

Conventionally, as piezoelectric oscillators, crystal oscillators constructed by combining a crystal resonator and a CMOS inverter, and crystal oscillators constructed by combining a crystal resonator and a TTL inverter have been widely used.

FIG. 12 is a circuit configuration diagram showing an example of a crystal oscillator, in which a crystal resonator 2 and a feedback resistor R1 are connected between the input and output of the C-MOS inverter 1, and a capacitor 3 is connected between the input of the CMOS inverter 1 and the ground. and connect capacitor 4 between the output of C-MOS inverter and ground,
Constant voltage ■.

By applying , the power type @Icc is supplied to the C-MOS inverter 1.

[Problem to be solved by the invention]

However, in the crystal oscillator 10 configured in this way, the C-MOS
The loop gain of inverter 1 becomes smaller (see FIG. 13). This change in loop gain affects the negative resistance ρ of the circuit, and as the loop gain becomes smaller, the negative resistance ρ becomes shallower. That is, in the crystal oscillator 10, when the environmental temperature rises, the negative resistance ρ becomes shallow (see FIG. 14), and stable oscillation is inhibited.

That is, in general, in a crystal oscillator, the larger (deeper) the circuit resistance ρ is, the more stable the oscillation will be.

In terms of the characteristics shown in FIG. 15, the most stable oscillation occurs at the oscillation frequency fa where the negative resistance ρ is the deepest. On the other hand, when the negative resistance ρ becomes shallow, the oscillation becomes unstable.

Note that stable oscillation of a crystal oscillator using a TTL inverter is similarly inhibited by environmental temperature. However, in the case of a TTL inverter, the loop gain becomes small at low temperatures in a wide range of temperature environments (see FIG. 13). That is, in a crystal oscillator using a TTL inverter, when the environmental temperature decreases, the negative resistance ρ of the circuit becomes shallow (see FIG. 14), and oscillation becomes unstable.

[Means to solve the problem]

The present invention was proposed to solve these problems, and focuses on the fact that as the power supply current supplied to the inverter increases, the negative resistance ρ of the circuit increases. It is designed to change the power supply current.

[Effect]

Therefore, according to the present invention, in the case of a C-MOS inverter, the power supply current supplied to the inverter is increased in response to a rise in the environmental temperature, and in the case of a TTL inverter, the power supply current supplied to the inverter is increased in response to a decrease in the environmental temperature. By increasing the supplied power supply current, it becomes possible to correct the change in the negative resistance ρ in the shallow direction and maintain it constant.

〔Example〕

Hereinafter, the piezoelectric invention according to the present invention will be explained in detail.

FIG. 1 is a circuit diagram of a crystal oscillator showing an embodiment of the present invention. In this figure, the same reference numerals as in FIG. 12 indicate the same constituent elements, and the explanation thereof will be omitted. The difference between this crystal oscillator 11 and the crystal oscillator 10 is that a voltage control circuit 6 is added which substantially changes the power supply current of 1 cc according to the environmental temperature.

That is, an NPN transistor Q is inserted and connected to the supply path of 1 cc of power supply current, and a control voltage generated by the voltage control circuit 6 is applied to the base of this transistor Q. The voltage control circuit 6 includes an operational amplifier 6-1
, a feedback resistor R4, and a resistor R5, and the voltage generated at the connection point between the resistor R6 and the temperature detection circuit 7 is applied to the inverting input terminal of the operational amplifier 6-1. The temperature detection circuit 7 is constructed by connecting diodes D1 to D7 in series. In this embodiment, as the C-MOS inverter l, ICs of types such as 74HCUO4 and 4069UB are used.

In the crystal oscillator 11 configured in this manner, when the environmental temperature rises, the voltage generated at the connection point between the resistor R6 and the temperature detection circuit 7 rises. This voltage is applied to the inverting input terminal of the operational amplifier 6-1, amplified, and applied as a control voltage to the base of the transistor Q7. That is, a control voltage that increases in accordance with the temperature rise is applied to the base of transistor Q7. As a result, C-MOS inverter 1
The voltage applied to the C-MOS inverter 1 increases, that is, the power supply current 1 cc supplied to the C-MOS inverter 1 increases, and the negative resistance ρ of the circuit becomes deeper (see FIG. 2). As a result, the change in the negative resistance ρ in the shallow direction due to the rise in the environmental temperature is corrected, and by appropriately determining the amount of increase in the power supply current 1 cc, that is, the power supply current 1
By appropriately determining the change characteristics of cc, the negative resistance ρ
By maintaining a deep and constant value, stable oscillation can be maintained even if the environmental temperature rises.

In addition, in this example, C-MO
Although the voltage applied to the S inverter 1 is changed and the power supply current Icc is controlled as a result, the power supply current Iα may be directly controlled by providing a current mirror circuit or the like. In other words, the method of changing the voltage applied to the C-MOS inverter 1 can be considered to be included in the method of changing the power supply current ICe, and in this sense, the voltage control circuit 6 can be regarded as a current control circuit. can be done.

Further, in this embodiment, the change characteristics between the environmental temperature and the power supply current 1 cc, which keep the negative resistance ρ of the circuit constant, vary depending on the capacitance values of the connected capacitors 3 and 4.

That is, now the capacitance values of capacitors 3 and 4, that is, the capacitance value of the oscillation capacitor, are both C, and the change characteristic of the environmental temperature and power supply current Ice is the characteristic t1 shown in FIG.
Suppose that it is defined as In this state, if the capacitance values of capacitors 3 and 4 are changed to 02 and C5, the environmental temperature and power supply current will be the same. For example, the change characteristics must be defined as characteristics t2 and t3 shown in the same figure, or
It may be necessary to define the characteristics t4 and t5 shown in FIG. When the characteristics change as shown in FIG. 3, by adding a multiplier circuit to the voltage control circuit 6, the gain can be changed to cope with the change. When the characteristics change as shown in FIG. 4, that is, when the characteristics change parallel to the change in capacitance value, by adding an adder circuit to the voltage control circuit 6,
This can be handled by changing the gain.

Furthermore, although this embodiment has been described as an example of temperature compensation in a crystal oscillator using a C-MOS inverter, T
Temperature compensation can be similarly performed in a crystal oscillator using a TL inverter. However, TTL
In a crystal oscillator using an inverter, a drop in the environmental temperature is detected, and the power supply current supplied to the TTL inverter is increased according to the drop in the environmental temperature, and the negative resistance ρ is increased.
to correct changes in the direction of shallowness.

FIG. 5 shows an example in which an oscillation frequency changing function and a control voltage compensation function are added to the crystal oscillator 11 shown in FIG. 1.

That is, in this crystal oscillator 12, C-MOS
Connect Harikab 8 between the input of inverter 1 and the ground,
By applying a control voltage Vc to this Varicap 8 via a resistor R2, the oscillation frequency can be changed. A current control circuit 5 is provided to apply a control voltage Vc to the amplifier 51, and when the control voltage Vc becomes low, a high amplification voltage is applied, and when the control voltage Vc becomes high, a low amplification voltage is applied to the amplifier 5-1. It is assumed to be obtained as output. Then, the output of this amplifier 5-1 is connected to the FETQ
, and a power supply current I determined by the gain of the amplifier 5-1 and the ratio (1:1 in this case) in the current mirror circuit 5-2.
ce is supplied to the C-MOS inverter 1 via the transistor Q.

In the crystal oscillator 12 configured as above, when the control voltage Vc decreases, the capacitance C of the Varicap 8 increases (see Fig. 6), and when the capacitance C of the Varicap 8 increases, the negative resistance ρ of the circuit increases. becomes shallower (see Figure 7). That is, as the control voltage Vc becomes lower, the negative resistance ρ becomes shallower (see FIG. 8).

There is a risk that oscillation may become unstable or stop.

However, if the control voltage Vc becomes lower, the amplified voltage obtained as the output of the amplifier 5-1 becomes higher, and the power supply current 1 cc supplied to the C-MOS inverter 1 increases (see FIG. 9). Power supply current 1 to C-MOS inverter 1
As cc increases, the negative resistance ρ of the circuit becomes deeper. As a result, the above-mentioned shallow change in the negative resistance ρ is corrected, and by appropriately determining the amount of increase in the power supply current 1 cc, that is, the control voltage Vc and the power supply current I
By appropriately determining the change characteristics with ce, stable oscillation can be maintained even when the control voltage Vc becomes low.

In the above-mentioned embodiment, the current mirror circuit 5-2 was constructed using an FET, but FIG.
As shown in the figure, it may be constructed using transistors. Current mirror circuit 5- shown in Figure 10
3, a power supply current of 1 cc can be obtained at a ratio of 1:1, similar to the current mirror circuit 5-2. In the current mirror circuit 5-4 shown in FIG. 11, a power supply current of 1 cc can be obtained at a ratio of 1:2.

Furthermore, in the embodiment described above, the power supply current 1 cc is supplied to the C-MOS inverter 1 according to the control voltage VC.
However, depending on the control voltage Vc, C-
The voltage applied to the MOS inverter 1 may be changed. Even if a method of changing the voltage applied to the C-MO3 inverter 1 is adopted, the power supply current 1 eC supplied to the C-MOS inverter 1 will change as a result.

In other words, the method of changing the applied voltage also depends on the power supply current 1
This may be considered to be included in the method of changing eC.

It should be noted that this goes without saying, but the power supply current 1
When providing a current control means that changes cc according to control voltage Vc, the condition is that "a power supply current I cc that can maintain oscillation even if control voltage Vc becomes zero is supplied to C-MOS inverter 1". do.

〔Effect of the invention〕

As explained above, the piezoelectric oscillator according to the present invention focuses on the fact that the negative resistance ρ of the circuit increases as the power supply current supplied to the inverter increases, and changes the power supply current supplied to the inverter according to the environmental temperature. In the case of a C-MOS inverter, the power supply current supplied to the inverter is increased in response to a rise in the environmental temperature, and in the case of a TTL inverter, the power supply current supplied to the inverter is increased in response to a decrease in the environmental temperature. By increasing the power supply current, it is possible to correct the shallow change in negative resistance ρ and maintain it constant, making it possible to maintain stable oscillation even when the environmental temperature changes. Become.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a crystal oscillator showing an embodiment of the piezoelectric oscillator according to the present invention, and Fig. 2 shows the change characteristics of the negative resistance ρ with respect to the power supply current I Ct to the C=MOS inverter in this crystal oscillator. Figures 3 and 4 show a constant negative resistance ρ for changes in the capacitance value of the oscillation capacitor.
Fig. 5 is a circuit showing an example of the crystal oscillator shown in Fig. 1 with an oscillation frequency variation function and control voltage compensation function added. 6 is a characteristic diagram of the change in the capacitance C of the VARICARB with respect to the control voltage Vc, FIG. 7 is a characteristic diagram of the change in negative resistance ρ with respect to the capacity C of the VARICARB, and FIG. 8 is a characteristic diagram of the change in the negative resistance ρ with respect to the control voltage Vc. Is the change characteristic diagram, Figure 9, a control? I
10 and 11 are diagrams showing other configuration examples of the current mirror circuit in the crystal oscillator shown in FIG. 5, and FIG.
The figure is a circuit diagram showing a conventional crystal oscillator, and Figure 13 is a C
- Loop gain change characteristic diagram with respect to environmental temperature of MOS inverter and TTL inverter, Figure 14 is C-M
Chart of changes in negative resistance ρ with respect to environmental temperature in a crystal oscillator using an OS inverter and a TTL inverter,
Figure 15 shows the negative resistance ρ and the most stable oscillation frequency k ((fa
FIG. 1... C-MOS inverter, 2... Crystal oscillator,
3, 4...Oscillation capacitor, 6...Voltage control circuit, 7...Temperature detection circuit, ICC...Power supply current.

Claims (1)

[Claims] a piezoelectric vibrator connected between the input and output of the inverter, a first capacitor connected between the input of the inverter and ground, and a second capacitor connected between the output of the inverter and ground.
A piezoelectric oscillator comprising: a capacitor; further comprising current control means for changing a power supply current supplied to the inverter according to environmental temperature.