JPS61125207A - Temperature compensation surface acoustic wave oscillator - Google Patents

Abstract

PURPOSE:To attain miniaturization, mass-production and ease of adjustment with simple constitution by connecting a circuit of series connection of the 1st and 2nd transistors (TRs) in parallel with the 1st and 2nd capacitor to form a capacitance of a surface acoustic wave element and supplying a base voltage changed in response to temperature to the base of the 1st and 2nd TRs. CONSTITUTION:A base voltage is fed to a base of a TR26 via a resistor 19 and a thermister 28. A connecting npoint between the resistor 19 and the thermistor 28 is connected to common via a resistor 18. A base voltage is fed to a TR27 via a resistor 20 and the thermister 28. Further, a voltage fed to the thermistor 28 is kept to a constant voltage by a constant voltage diode 15 and the AC component is rejected by a capacitor 13. Since the termister 28 is a heat sensing element whose resistance is changed depending on ambient temperature, the base voltage or the TRs26, 27 is changed by temperature. Thus, the resistance value of the TRs26, 27 is changed by temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a temperature compensated surface acoustic wave oscillator, and particularly to an improvement of its temperature 1λ characteristic compensation circuit.

Prior Art Conventionally, this type of temperature-compensated surface acoustic wave oscillator has resistors 1 to 4, as shown in FIG. By applying the output voltage of a temperature-dependent voltage generating section consisting of a thermistor 8, 9, etc. to the variable six-stitch diode 14, the capacitance value is changed in accordance with the ambient temperature, and the capacitance value is changed by surface acoustic wave A surface acoustic wave oscillator having a configuration connected in parallel to the capacitor IO of the oscillator has a surface acoustic wave element 16. Capacitor 10-1
2. Resistors 5, 6. It is composed of transistors 17, etc., and oscillates at a frequency determined by these constants. Note that the oscillator includes a resistor 7. Constant voltage diode 1
5. A constant voltage is supplied by a capacitor 13 and the like.

The one-degree frequency characteristic of a surface acoustic wave oscillator without a compensation circuit is generally a characteristic close to a quadratic curve as shown in Figure 6, with the oscillation frequency reaching its highest at a certain temperature T1, and at a lower temperature T1. However, even at a high temperature T2, the oscillation frequency tends to decrease.

On the other hand, there is an inversely proportional relationship between the load capacity #CL of the surface acoustic wave resonance f and the oscillation frequency, and as the load capacity decreases, the oscillation frequency increases I:+jI. The frequency change rate Δf/f is generally expressed by the following equation (1).

Δf/f=1/2y(1+cL/co) --(+
) However, γ: Constant of the elastic surface wave resonator Co: Parallel capacitance of the Iil surface wave resonator CL: Load capacity (6 vertical lines between the resonator and ground) Therefore, in the circuit shown in Figure 5, the variable The temperature characteristics of the oscillation frequency can be compensated by making the voltage applied to the six-lance diode 14 lowest at temperature T1, and appropriately increasing the applied voltage at lower and higher temperatures.

However, in the conventional surface acoustic wave oscillator as shown in Fig. 5, complicated calculations are required to determine the values of elements such as the thermistor 8.9 and resistors 1 and 2.3. It takes a lot of effort and time. Furthermore, in order to obtain good frequency characteristics over a wide temperature range, it is necessary to use a large number of heat-sensitive resistors such as thermistors, and the variable capacitance diode 14 is required to have a high degree of linearity. For this reason, conventional oscillators have the disadvantage of being expensive.

OBJECTS OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional drawbacks, and to provide a temperature-compensated surface acoustic wave oscillator that is simple in construction, suitable for miniaturization and rapid production, easy to adjust, and inexpensive. .

Structure of the Invention The temperature-compensated surface acoustic wave oscillator of the present invention is a surface acoustic wave oscillator including a surface acoustic wave element and an amplifying section, in which a load capacitor is connected between the surface acoustic wave element and the ground. The load capacitance is formed by first and $2 capacitors and Ill and second transistors connected in series to the IR1 and second capacitors, respectively, and the first and second transistors are connected through a heat-sensitive resistor. It is characterized by supplying a temperature-dependent base voltage to the base.

Embodiments of the Invention Next, the present invention will be described in detail with reference to one drawing.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. That is, a capacitor 23 is connected between the surface acoustic wave oscillator 16 of the surface acoustic wave oscillator, which is composed of an amplifying section composed of capacitors II, 12, resistors 5 to 7, transistors 17, etc., and the surface acoustic wave element 16, and the ground. transistor 2
A series circuit of 6 and a series circuit of capacitor 24 and transistor 27 are connected to form a load capacitance. transistor 2
Resistors 21 and 22 are connected to the collectors of 8 and 27, respectively.
Collector voltage is supplied through. Further, a base voltage is supplied to the base of the transistor 26 via a resistor 19 and a thermistor 28, and a connection point between the resistor 18 and the thermistor 28 is grounded through the resistor 18. A base voltage is supplied to the transistor 27 through the resistor 20 and the thermistor 28. Note that the voltage supplied to the thermistor 28 is maintained at a constant voltage by the constant voltage diode 15, and the alternating current component is removed by the capacitor 13.

Since the thermistor 28 is a heat-sensitive element whose resistance value changes depending on the ambient temperature, the base voltages of the transistors 2B and 27 change depending on the temperature. Therefore, the resistance values of transistor 26 and transistor 27 change depending on the temperature.

However, at temperatures above T1, the transistor 28 has a low resistance value with a saturated collector-to-emitter impedance and turns on, and when the transistor 27 turns on at temperatures below T1, the thermistor 28. Resistor 18 and resistor Ill.

It is assumed that a resistance value of 20 is set. Therefore, between temperatures T and T, the transistor 27 is in the on state,
The resistance value of the transistor 26 decreases as the temperature rises, and at the temperature T1, the transistor 26 and the transistor 27
Both are in an on state, and between temperatures T1 and T2, the transistor 26 is in an on state, and the transistor 27 increases its resistance value as the temperature rises.

Therefore, the load capacity of the surface acoustic wave element 1B is the temperature T,
At this temperature, the total capacitance of capacitor 23 and capacitor 24 becomes the maximum value, and at a temperature below that, transistor 2B
The capacitance value decreases due to an increase in the resistance value of the transistor 27, and the capacitance value decreases due to an increase in the resistance value of the transistor 27 at higher temperatures.

Generally, as shown in Fig. 2, when the load stage 1i1cL is configured with a circuit in which a fixed field iCI, a fixed coupling C2, and a resistance value R are connected in parallel, the load capacity CL is calculated by the formula 1, %. However, ω =2πf (f: oscillation frequency) Here, the frequency change Δ(Δf
/f) is expressed by equation (3).

Δ(Δf/f) −(1/ (1+ CL+ / Co ) −1/ (1
+CL2/Co) l/2γ・・・・・・・・・
...(3) However, rl 2+(1/C+ + 1/C2) 2/(1)2
Therefore, by changing the resistance value R depending on the temperature, it is possible to cause a frequency change depending on the ambient temperature.

In this embodiment, the frequency change is caused by changing the resistance value of the transistor 26 or the transistor 27 depending on the temperature. The characteristic shown by the solid line in FIG. 3 is an example of the frequency change-temperature characteristic of this embodiment, and is a characteristic that exactly cancels out the change in the oscillation frequency due to the temperature change of the surface acoustic wave element 16 shown by the dotted line.

By adjusting the resistors 18 to 22, various characteristics 1, 2, 3.4 as shown in FIG. 4 can be obtained. Therefore, it is possible to compensate for characteristic deviations of the components of the surface acoustic wave oscillator to some extent by adjusting the resistors 18-22.

This embodiment has a simple configuration, is suitable for miniaturization and mass production, and has the advantage of being easy to adjust.

Effects of the Invention As described above, in the present invention, a surface acoustic wave element of a surface acoustic wave oscillator is manufactured by connecting circuits in which first and second transistors are connected in series to first and second capacitors, respectively. Since the structure is configured to form a load capacitance of 7 and supply a base voltage that changes depending on temperature to the bases of the first and second transistors, the structure is simple and suitable for miniaturization and mass production. This has the advantage that the temperature characteristics of the surface acoustic wave element can be easily compensated for over a wide range.

[Brief explanation of drawings]

Figure 141 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a diagram for explaining the equivalent load density of the embodiment described above, Figure 3 is a diagram showing an example of the characteristics of the above embodiment, Figure 4 shows an example of adjusting the characteristics of the embodiment described in -. Figure 5 is a circuit diagram showing an example of a conventional temperature compensated surface acoustic wave oscillator. Figure 6 shows the characteristics of a surface acoustic wave oscillator without temperature compensation. It is a figure showing an example. In the figure, 1-7, 18-22: Resistor, 8°9.2
8: Thermistor, 10-13, 23, 24: Capacitor, 14: Variable capacitance diode, 15: Constant voltage diode, 16: Surface acoustic wave element, 17, 28.27: )
Ranjista.

Claims (1)

[Claims] In a surface acoustic wave oscillator including a surface acoustic wave element and an amplifying section, a load capacitor is connected between the surface acoustic wave element and the ground, and the load capacitor is connected to a first and a second
and first and second transistors connected in series to the first and second capacitors, respectively, and applying a temperature-dependent base voltage to the bases of the first and second transistors through a heat-sensitive resistor. A temperature compensated surface acoustic wave oscillator.