JP2005175633A - Temperature compensated saw oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a means for enhancing the frequency stability of a piezoelectric oscillator being employed in a remote key entry system, or the like. <P>SOLUTION: The temperature compensated piezoelectric oscillator comprises a piezoelectric oscillator, an amplifier circuit and a temperature compensating circuit. The temperature compensating circuit comprises a first differential amplifier having an input connected with a temperature detection diode and a first power supply for setting a predetermined temperature, a first current mirror circuit operating when the temperature is lower than a predetermined level, a second current mirror circuit, a second differential amplifier generating a current being supplied to the second current mirror circuit, and a second power supply for determining the minimum level of a voltage being generated from the second differential amplifier. The temperature compensated piezoelectric oscillator is arranged such that the output voltage from the temperature compensating circuit has V-shaped temperature characteristics. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a temperature-compensated SAW oscillator, and more particularly to a SAW oscillator provided with a circuit for compensating a secondary frequency temperature characteristic of a SAW vibrator.

In recent years, piezoelectric oscillators have been used in many fields of communication equipment and electronic equipment due to their frequency stability, small size, light weight, low price, etc. Among them, so-called temperature compensated piezoelectric oscillators that compensate the frequency temperature characteristics of piezoelectric vibrators It is indispensable for mobile phones and the like that require high stability. Recently, the remote keyless entry system, which has been remarkably popular, has been widely used because it makes it easy to open and close a car or a house key, and also has security by encrypting a transmission signal. Some remote keyless entry systems use a temperature-compensated piezoelectric oscillator in order to improve the accuracy of a transmission signal.

  FIG. 5 is a diagram showing a circuit configuration of the temperature compensated piezoelectric oscillator disclosed in Japanese Patent Application Laid-Open No. 2003-198250, and includes a tank circuit TU composed of a SAW vibrator Y1, a coil L, a capacitor C, and a thermistor Th. , An amplifier circuit AMP1, a phase circuit θ, and an amplifier circuit AMP2. A positive feedback loop is formed by the SAW vibrator Y1, the tank circuit TU, the amplifier circuit AMP1, and the phase circuit θ to start oscillation, and the oscillation frequency is output through the amplifier AMP2. The amplifier AMP2 is a buffer circuit provided to reduce the influence between the oscillation loop and the output.

  The feature of the temperature compensated piezoelectric oscillator shown in FIG. 5 is the operation of the tank circuit TU. As is well known, the resistance value of the thermistor Th has a characteristic of decreasing as the temperature rises. Therefore, when the temperature is low, the tank circuit TU has a small change amount of the transmission phase amount due to the temperature change. When the temperature is high, the change in the transmission phase amount due to the change in temperature becomes large. That is, it is described that by providing the tank circuit TU in the oscillation loop, the temperature change of the oscillation frequency can be reduced over a wide temperature range, but the temperature change particularly in a high temperature range can be significantly reduced. .

FIG. 6 is a diagram showing a circuit configuration of a temperature-compensated piezoelectric oscillator disclosed in Japanese Patent Application Laid-Open No. 2003-204260. A temperature-compensated piezoelectric oscillator circuit (TCXO), a phase comparison circuit, a low-pass filter, and a voltage control type A SAW oscillation circuit (VCSO) and a frequency dividing circuit are provided. The clock signal S1 is output from the TCXO and supplied to the phase comparison circuit. On the other hand, the frequency divider circuit divides the clock signal S4 output from the VCSO and outputs a frequency-divided signal S5. The frequency dividing ratio 1 / N of the frequency dividing circuit is set to a frequency dividing ratio at which the frequency of the frequency division signal S5 becomes equal to the frequency of the clock signal S1 output from the TCXO at the reference temperature. The phase comparison circuit outputs a phase difference signal S2 obtained by comparing the clock signal S1 and the clock signal S5. The low-pass filter supplies the smoothed phase difference signal S2 to the VCSO as the control signal S3. A so-called PLL circuit is configured by the circuit configuration of FIG. 6, and a temperature compensated piezoelectric oscillator satisfying high frequency stability in a high frequency band of several hundred MHz to several GHz can be configured.
JP 2003-198250 A JP 2003-204260 A

The problem to be solved is that the temperature compensated SAW oscillator configured using the circuit shown in FIG. 5 has insufficient frequency stability for use in a high-precision remote keyless entry system. A temperature-compensated SAW oscillator configured using a circuit has sufficient frequency stability, but is too expensive to be used in the above system and cannot be used.

  The present invention is a temperature-compensated piezoelectric oscillator comprising a voltage-controlled piezoelectric oscillator and a temperature-compensated voltage generating circuit that supplies a voltage for temperature compensation to the voltage-controlled piezoelectric oscillator, the temperature-compensated voltage generating circuit Includes at least a temperature detection circuit whose voltage output fluctuates depending on temperature, first and second operational amplifiers, first and second current mirror circuits, and first and second constant voltage sources. The temperature detection circuit is connected to the positive input of the first operational amplifier, and the first constant voltage source is connected to the negative input of the first operational amplifier via a resistor. The output is connected to the input side circuit of the first and second current mirror circuits, the output side circuit of the first current mirror circuit is connected to the input side circuit of the second current mirror circuit, and the second Output side circuit of current mirror circuit The second constant voltage source is connected to the negative input of the second arithmetic circuit, the second constant voltage source is connected to the positive input of the second arithmetic circuit, and the output of the second operational amplifier is connected to the second through the resistor. This is a temperature compensated piezoelectric oscillator that is connected to the negative input of the operational amplifier, and that the output of the second operational amplifier is the output of the temperature correction voltage generation circuit.

  Since the temperature-compensated piezoelectric oscillator of the present invention includes a temperature-compensated voltage generation circuit having a V-shaped characteristic, the frequency temperature compensation can also be a V-shaped characteristic, and thus has a secondary frequency temperature characteristic. When used with a SAW resonator, an oscillator with high frequency stability can be configured, and the temperature compensated voltage generation circuit can be easily integrated into an IC, and the cost of the temperature compensated piezoelectric oscillator can be greatly reduced. is there.

FIG. 1 is a circuit diagram showing an embodiment of a temperature compensated SAW oscillator according to the present invention, in which a temperature compensation circuit α for converting a temperature change into a voltage change, and a voltage-capacitance conversion circuit for converting a generated voltage into a capacitor. β, a Colpitts oscillation circuit γ composed of a SAW vibrator and an amplifier, and a circuit for controlling (ON / OFF) the oscillation circuit γ. The Colpitts oscillation circuit γ shown in FIG. 1 uses a series connection element of a SAW vibrator Y1, a capacitor C3, and a varactor diode Dv between the base and the ground as an inductive element between the collector and the base of the transistor Tr. Further, a series connection element of capacitors C1 and C2 is connected between the base and the ground, and a resistor R2 is inserted between the emitter and the ground, and the midpoint of the capacitors C1 and C2 and the emitter are connected.
As shown in FIG. 1, the voltage-capacitance conversion circuit β is a π-type circuit in which one end of each of the varactor diode Dv and the capacitor C4 is connected to both terminals of the resistor R4 and the other terminal is grounded. The Colpitts oscillation circuit γ constitutes a voltage controlled oscillation circuit.

FIG. 2 is a diagram showing in detail the configuration of the temperature compensation circuit α (temperature compensation voltage generation circuit) shown in the block diagram of FIG. 1. The temperature compensation voltage generation circuit α is a temperature at which the voltage output varies depending on the temperature. The detection circuit includes first and second operational amplifiers U1 and U2, first and second current mirror circuits M1 and M2, and first and second constant voltage sources V1 and V2.
The positive input of the first differential amplifier U1 is connected to the other terminal of the resistor R2 having one terminal connected to the power supply Vcc, as shown in FIG. 2, and a composite diode D in which diodes D1 and D2 are connected in series. The other terminal of D is connected to a grounded temperature detection circuit. The negative input terminal of the first differential amplifier U1 is connected to the positive side of the first constant power source V1 via the resistor R1, and the negative side of the power source V1 is grounded. Then, the output of the first differential amplifier U1 and the base of the transistor Q1 are connected, and the emitter of the transistor Q1 and the negative input terminal of U1 are connected. The collector of the transistor Q3 of the first current mirror circuit M1 is connected to the transistor Q1, and the collector and base of the transistor Q3 are made conductive. The base of the transistor Q1 and the base of the transistor Q5 are connected, and the emitter and the negative input terminal of the first differential amplifier U1 are connected.

  Further, the collector of the transistor Q5, the collector of the transistor Q4 of the first current mirror circuit M1, and the collector of the transistor Q6 of the second current mirror circuit M2 are connected, and the collector and base of the transistor Q6 are made conductive. . The collector of the transistor Q7 of the second current mirror circuit M2 is connected to the negative input of the second differential amplifier U2, and the positive side of the second constant power supply V2 is connected to the positive input of the second differential amplifier U2. Then, the negative side of the power supply V2 is grounded. The output and second input of the second differential amplifier U2 are connected via a resistor R3.

The operation of the temperature compensation circuit α shown in FIG. 2 will be described in detail with reference to FIGS. As is well known, the temperature-frequency characteristic (also referred to as frequency temperature characteristic) of a SAW resonator formed using a piezoelectric crystal generally exhibits an upwardly inverted U-shaped curve. For example, a curve A (dashed line) in FIG. 3 is an example of a temperature-frequency characteristic of an oscillation circuit using a SAW resonator without a compensation circuit, and the frequency becomes lower as the apex temperature Tp becomes lower or as the temperature becomes higher. Becomes an inverted U-shaped curve with a curvilinear drop. Therefore, in the present invention, by controlling the frequency of the oscillation circuit to be V-shaped as shown by the broken line B in FIG. 3, the frequency variation of the curve A is canceled out, and the temperature as shown by the solid line C in FIG. The characteristic that the frequency fluctuation is reduced with respect to the change is obtained. 4A shows the temperature characteristics of the composite diode D in which the diodes D1 and D2 shown in FIG. 2 are connected in series. The horizontal axis indicates the temperature, and the vertical axis indicates the voltage Vd exhibited across the composite diode D. FIG. From this figure, as the temperature rises, the voltage Vd exhibited across the composite diode D decreases linearly. Here, Tp is the apex temperature Tp of the frequency temperature characteristic exhibited by the SAW vibrator Y1 shown in FIG. The value of the voltage Vd presented across the composite diode D at the temperature Tp is Vdp. Here, the voltage of the first constant power supply V1 is set equal to the voltage Vdp.
Assuming that the ambient temperature T of the temperature compensated SAW oscillator is lower than the temperature Tp, the voltage Vd, that is, V + is higher than Vdp. Then, according to the characteristics of the differential amplifier (when the amplification factor of the differential amplifier is infinite ∞, the positive input voltage V + and the negative input voltage V− operate to be equal), the first differential amplifier U1. V + = V− and V−> Vdp at the connection point between the resistor R1, the emitter of the transistor Q1 and the first input of the first operational amplifier, so that the current from the current mirror circuit M1 through the transistor Q1. _IL will be supplied. The same current I _L from the characteristic of the current mirror circuit through the transistor Q4 of the current mirror circuit M1, is supplied to the transistor Q6. Accordingly, so that also the current I _L flows through the transistor Q7 of the current mirror circuit M2. Since current I _L flowing through the transistor Q7 is supplied to the transistor Q7 through the resistor R3 of the second differential amplifier U2, the output voltage Vcont of the second differential amplifier U2 in response to the current I _L Will change.

Next, assuming that the ambient temperature T of the temperature compensated SAW oscillator is higher than the temperature Tp, the voltage Vd across the composite diode D falls below Vdp, and V + = Vd <V1. Since the voltage V− at the connection point between the resistor R1 and the emitter of the transistor Q1 is V− = V + <V1, the current _IH is supplied from the power supply V1 through the transistor Q5. When said current I _H flows through the transistor Q6, so that the current flows I _H through the transistor Q7 of the current mirror circuit M2. Current _{I H} flowing through the transistor Q7 is supplied to the transistor Q7 through the resistor R3 of the second differential amplifier U2. In order to supply this current, the output voltage Vcont of the second differential amplifier U2 increases. Here, when the temperature T is equal to Tp, no current flows through the current mirror circuits M1 and M2, so that the output voltage Vcont of the second differential amplifier U2 is output as it is as the voltage value of the second constant power supply V2. Will be. That is, the temperature characteristic of the output voltage Vcont of the temperature compensation circuit α shown in FIG. 2 is a V-shaped voltage characteristic that exhibits the minimum voltage V2 at the temperature Tp as shown in FIG. 4B.

The applied voltage (Vcont) -capacitance characteristic of the varactor diode Dv shown in FIG. 1 decreases as the voltage Vcont increases as shown in FIG. 3 (c). Now, assuming that the temperature of the Colpitts oscillation circuit γ is kept constant and only the ambient temperature T of the composite diode D is changed, the frequency temperature characteristic of the Colpitts oscillation circuit γ has a minimum temperature Tp as shown in FIG. It becomes V-shaped frequency characteristic as a value.
In FIG. 4, the frequency temperature characteristic C of the temperature compensated SAW oscillator of the present invention after temperature compensation is obtained by adding the frequency temperature characteristic B by the temperature compensation circuit α to the frequency temperature characteristic A of only the SAW vibrator.
Further, the circuit described above can be easily integrated, and has the advantage that the cost of the temperature compensated SAW oscillator can be significantly reduced.

It is the figure which showed the circuit structure of the temperature compensation type | mold piezoelectric oscillator which concerns on this invention. It is a circuit diagram which shows the detail of a temperature compensation circuit (temperature compensation voltage generation circuit). It is a figure which shows the frequency temperature characteristic of only a SAW vibrator, and the frequency temperature characteristic of a temperature compensation type piezoelectric oscillator. (A) is a diode voltage-temperature characteristic, (b) is an output voltage-temperature characteristic of a temperature compensation circuit (temperature compensation voltage generation circuit), (c) is a capacity-voltage characteristic of a varactor diode, and (d) is compensation. It is the frequency temperature characteristic of the circuit only. It is a circuit block diagram of a conventional temperature compensated piezoelectric oscillator. It is a circuit block diagram of a conventional temperature compensated piezoelectric oscillator with high frequency stability.

Explanation of symbols

Tr, Q1, Q3, Q4, Q5, Q6, Q7 Transistor
Y1 Piezoelectric vibrator
Dv Varactor diodes R1, R2, R3, R4 Resistors C1, C2, C3, C4, C5 Capacitance V1, V2 Power supply D1, D2 Diode U1, U2 Differential amplifier Vcont Output voltage Vcc of differential amplifier

Claims (2)

A temperature-compensated piezoelectric oscillator comprising a voltage-controlled piezoelectric oscillator and a temperature-compensated voltage generation circuit that supplies a temperature-compensated voltage to the voltage-controlled piezoelectric oscillator,
The temperature compensation voltage generation circuit includes a temperature detection circuit whose voltage output fluctuates according to temperature, first and second operational amplifiers, first and second current mirror circuits, and first and second constant voltage sources. And at least
A temperature detection circuit is connected to the positive input of the first operational amplifier, a first constant voltage source is connected to the negative input of the first operational amplifier via a resistor, and the output of the first operational amplifier Are connected to the input side circuits of the first and second current mirror circuits,
The output side circuit of the first current mirror circuit is connected to the input side circuit of the second current mirror circuit,
The output circuit of the second current mirror circuit is connected to the negative input of the second arithmetic circuit, the second constant voltage source is connected to the positive input of the second arithmetic circuit, A temperature compensation type characterized in that the output of the operational amplifier is connected to the negative input of the second operational amplifier through a resistor, and the output of the second operational amplifier becomes the output of the temperature correction voltage generation circuit Piezoelectric oscillator. The temperature compensated piezoelectric oscillator according to claim 1, wherein a SAW vibrator having a quadratic frequency frequency characteristic is used for the piezoelectric vibrator.

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