JPS6230522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to temperature stabilization of a phase-shifted oscillator using a delay line, and particularly to a phase-shifted oscillator using a surface acoustic wave (hereinafter abbreviated as SAW) delay line. The present invention attempts to provide a simple phase-shifted oscillator by operating a voltage variable phase shifter in a part of the operating temperature range and performing temperature compensation.

A conventional example of a phase-shifted oscillator is shown in FIG. Figure 1 shows the document “TEMPERATURE COMPENSATION
OF CRYSTALS WITH PARABOLIC
TEMPERATURE COEFFICIENTS” 32nd
This is an oscillation circuit shown in the Annual Sym.on Freg Cont.1978 using an ST-cut crystal SAW delay line, and temperature compensated using two varactor diodes. In Fig. 1, 1 is an amplifier, 2 is a SAW delay line, 3, 4, 7 and 5, 6 are matching capacitors and inductances, 8 is a control voltage generation transistor, 9, 10
11 and 12 are collector and emitter resistors, respectively. 13 and 14 are high impedance resistors for applying control voltages to varactor diodes 17 and 18. 15 and 16 are bypass capacitors. In Figure 1, amplifier 1 and
A well-known phase shift oscillator is formed by a feedback loop with the SAW delay line 2, and the temperature compensation circuit 1
9 improves the temperature characteristics of the oscillation frequency. In this case, the characteristics without the temperature compensation circuit 19 are the second
As shown in the figure, it has an upwardly convex parabolic shape, and this is formed at 19 to form a downwardly convex voltage capacitance characteristic as shown in FIG.
The temperature characteristics of the oscillator are improved by utilizing the temperature characteristics of the transistor 8 to apply the voltage to the oscillator.

However, in the conventional example, as mentioned above, it is very delicate to match the temperature characteristics of the oscillator shown in Figure 2 with the convex shape at the top and the combined capacitance characteristics of the varactor diode with the convex shape below in Figure 3. For example, a slight change in the bias of a transistor causes the voltage at the center of the convex curve in FIG. 3 to deviate, so that the inverse correction for temperature changes may deviate, and in some cases, the compensation may become worse. In addition, since two varactor diodes are used, the correction curve may shift if the characteristics of the two varactor diodes vary, and since two varactors are used, the cost is high.

The present invention eliminates these drawbacks and provides a stabilized phase-shifted oscillator that is simple in construction and includes only one varactor diode for temperature correction.

An embodiment of the invention is shown in FIG. In FIG. 4, 20 is an oscillation transistor, 21 and 22 are the collector and bias resistor of the transistor 20, and 23
is a SAW delay line, 24, 25 and 26 are matching inductances and capacitors, 27 is a temperature variable voltage generation transistor, 28 and 29 are bias resistors, 30 is a bias variable resistor, 31 and 32 are emitter and collector resistors, 33 is a bypass capacitor, 34 is a high impedance resistor for voltage transmission,
35 is a varactor diode for phase shift circuit, 36,3
7 is an inductance and a capacitor for a fixed phase shifter, this capacitor 37 is a temperature compensation capacitor with a constant temperature gradient characteristic, and 38, 39, 4
0 is a coupling capacitor. 42 is a variable resistor for setting the initial voltage to the varactor diode 35.

This embodiment is similar to the conventional example in that oscillation is caused by feeding back the output of the oscillation transistor 20 through the SAW delay line 23, but the temperature compensation circuit 41 has this feature. In other words, in the phase shift circuits 36 and 37, by using a temperature correction capacitor with an almost linear temperature gradient characteristic as the capacitor 37, the temperature position of the flat part of the temperature characteristic of the SAW delay line 23 is shifted to the lower (or higher) side. direction),
Further, by operating the phase shift correction in the varactor diode 35 only at the higher (or lower) frequency near the flat portion, a stable phase shift oscillator is obtained.

The operating principle will be explained below. first
A method of shifting the temperature position of the flat part (top) of the temperature characteristic of the SAW delay line 23 will be explained with reference to FIG. Figure 5 shows the equivalent frequency change characteristic A of a fixed phase shifter consisting of an inductance 36 and a capacitor 37, the frequency characteristic B of a crystal substrate SAW phase shift oscillator (without temperature compensation), and the temperature characteristic C obtained by combining the two. It shows. In other words, the frequency characteristics of a fixed phase shifter change linearly with temperature,
By synthesizing the frequency characteristics of phase shifters that change in a quadratic manner (for example, a crystal substrate SAW delay line), it is possible to arbitrarily shift the temperature change center of the phase shifter that changes in a quadratic manner. . As an example, A is ∝-4T-4 (frequency, T temperature),
If B is ∝-T ² , the composite C is ∝-(T
+2) ² , which means that C has been shifted to a lower temperature than B.

Next, the above inductance 36 and capacitor 3
If the characteristics temperature-shifted to the lower range by the fixed phase shifter 7 are compensated for only in the higher range than the center of the temperature change using the variable phase shifter circuit composed of the varactor diode 35 and the inductance 24, then one varactor diode 35 This makes it possible to keep the oscillation frequency constant over a wide temperature range.

More specifically, the variable phase shift control voltage applied to the varactor diode 35 of the variable phase shift circuit changes the temperature characteristics of the base-emitter voltage V _BE of the transistor 27 (in silicon transistors, as the temperature rises, the V _BE voltage decreases). ) is obtained by converting the voltage into a temperature variable control voltage. The details of this temperature variable control voltage generation circuit are shown at ₄₁ in FIG. Transistor 27 can be cut off,
When T ₀ is exceeded, the transistor 27 becomes conductive due to a change in the temperature characteristics of the base-emitter voltage V _BE of the transistor 27, and the collector voltage increases with temperature. FIG. 6 shows how this voltage changes. By applying this voltage to the varactor diode 35, the characteristics of C are temperature compensated over a wide range from T ₀ to T ₁ ° C., like the characteristics of D, as shown in FIG. In Figs. 5, 6, and 7, V indicates the collector voltage, T indicates the temperature, ₀ indicates the set frequency, and V ₀ indicates the initial collector voltage.

As described above, according to this embodiment, a temperature fixed phase shifter is inserted in series in the crystal SAW delay line, and the temperature change characteristic of the phase delay characteristic in the oscillation system is adjusted to the center of the required temperature compensation range on the temperature axis. By shifting to a lower side than the temperature, only the high frequency side needs to be compensated for the temperature, so it is possible to realize a phase shift oscillator equipped with a simple variable phase shift circuit having only one varactor diode.

In the above embodiment, the temperature change characteristics were shifted to the lower side on the temperature axis by the fixed phase shifter including the inductance 36 and the capacitor 37, but this was shifted to the higher side.
If the variable phase shift circuit according to No. 5 is used to compensate for the temperature only on the low frequency side, the same effect as described above can be obtained.

Furthermore, by changing the temperature gradient characteristic of this temperature variable phase shifter, the flat portion of the temperature characteristic of the delay line phase shift oscillator can be brought to any desired temperature range as shown in FIG.

Furthermore, in the above embodiment, if the capacitor 26 for input matching of the SAW delay line 23 is a capacitor with constant temperature characteristics, the capacitance of the capacitor 26 does not change with temperature, so that Temperature changes in output impedance can be suppressed.

In the above embodiment, the capacitor 37 for output matching of the SAW delay line 23 is a capacitor with special temperature characteristics to constitute a fixed phase shifter for shifting. A fixed phase shifter for shifting can also be constructed by using the capacitor 26 as a capacitor having special temperature characteristics. The combination of this configuration and the variable phase shift circuit using the one varactor diode 35 also makes it possible to perform temperature compensation of the oscillation frequency. However, it is unavoidable that the output impedance seen from the capacitor 40 changes depending on the temperature.

On the other hand, the shift in the temperature range of the flat portion of the temperature characteristic explained in FIG. 5 can be realized not only by using the capacitor 37 but also by changing the temperature characteristic of the SAW delay line alone. For example, crystal SAW
In the case of a delay line, of course, it has better temperature characteristics than other crystal substrates, so it is possible to obtain fairly stable characteristics with that alone, but in order to obtain even higher temperature stability, it is necessary to change the cut angle of the crystal substrate. Since the center temperature position of the temperature characteristics differs depending on the difference in the temperature characteristics (the temperature characteristic curve is the same), by selecting a crystal substrate with the required center temperature position characteristics from among crystal substrates with different cut angles, C in Fig. 5 can be obtained. It is possible to obtain temperature characteristics shifted from the required temperature range position as shown in FIG. That is, the characteristics of C can be obtained without forming a fixed phase shifter for shifting using the characteristics of the capacitor 37. Therefore, by combining the variable phase shift circuit with the varactor diode 35, wide frequency temperature compensation similar to the above embodiment can be achieved. Of course, in this case, a fixed phase shift using the capacitor 37 may also be used as required.

FIG. 8 shows an example of the oscillation frequency temperature characteristic of a crystal SAW oscillator having a center frequency of 900 MHz according to the present invention. In the figure, A shows a zero temperature coefficient of about -5 degrees before temperature compensation. B shows the characteristics after temperature compensation. As shown in the figure, good oscillation frequency characteristics of 0.35 ppm/°C are obtained over a wide temperature range of 90°C by the temperature compensation according to the present invention.

FIG. 9 shows another embodiment. This example is the fourth
As a means for increasing the temperature sensitivity of the temperature compensation circuit 41 shown in the figure, a configuration is adopted in which a capacitance control voltage is applied to the varactor diode for the voltage variable phase shifter from both the collector and emitter of the transistor 8. This means that if the emitter resistance and collector resistance of the transistor 27 are the same, and the collector current (or emitter current) increases or decreases depending on the temperature, the potential difference between the emitter and collector terminals of the transistor 27 will decrease by the sum of the voltage fluctuations at each terminal. less or enlarge. That is, assuming that the emitter and collector resistances are the same, for the same collector (or emitter) current change, twice as much variation is applied to the varactor diode in FIG. 9 as compared to the configuration in FIG. 4. This expands the control voltage to the varactor diode and increases the sensitivity to temperature. In the drawings, the same symbols as in Fig. 4 indicate the same things as in Fig. 4.
4 and 45 are bypass capacitors, and 46 and 47 are bias transmission resistors.

As described above, according to the present invention, a fixed phase shifter for shifting the temperature characteristics is provided before and after the delay line, or a crystal cut having a characteristic that the center temperature of the temperature flatness characteristic is moved away from the center of the operating temperature range is used. Using a substrate,
Furthermore, by providing a variable phase shifter with one varactor diode, a very stable phase-shifted oscillator can be obtained. Furthermore, since only one varactor diode is used, the configuration is simple and inexpensive. In addition, if a fixed phase shifter is inserted after the SAW delay line feedback as shown in Figure 4, the oscillator itself will be buffered to some extent, and even if the impedance of the fixed temperature phase shifter changes due to temperature changes, the impedance on the output side of the oscillator will change. is not affected significantly, so stable output can be obtained.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional phase-shifted oscillator.
2 and 3 are characteristic diagrams for explaining the same phase-shifting oscillator, FIG. 4 is a circuit diagram of a phase-shifting oscillator according to an embodiment of the present invention, and FIGS. 5, 6, and 7
8 are characteristic diagrams for explaining the phase-shifting oscillator, and FIG. 9 is a circuit diagram of the phase-shifting oscillator in another embodiment. 23... SAW delay line, 20... Oscillation transistor, 27... Control voltage generation transistor,
35... Varactor diode, 36, 37... Reactance and capacitor for temperature fixed phase shift circuit.

Claims (1)

[Claims] 1. An oscillation transistor, a surface acoustic wave delay line configured into a loop that feeds back part of the output of this transistor, and either the input side or the output side of this surface acoustic wave delay line. A voltage-controlled variable phase shifter provided on one side and a temperature-variable voltage generator for driving the variable phase shifter are provided, and a temperature-fixed shifter is provided on either the input side or the output side of the surface acoustic wave delay line. The temperature characteristic is shifted by providing phase shifters in series, and the variable phase shifter is operated by the temperature variable voltage generator only on either side above or below the top temperature of the shifted temperature characteristic. phase-shifted oscillator. 2. An oscillation transistor, a surface acoustic wave delay line configured into a loop that feeds back part of the output of this transistor, and a voltage control provided on either the input side or the output side of this surface acoustic wave delay line. The surface acoustic wave delay line is composed of a crystal substrate, and by selecting crystal substrates having different cut angles. A phase-shifted oscillator characterized in that a temperature characteristic is shifted, and the variable phase shifter is operated by the temperature-variable voltage generator only on either side above or below the top temperature of the shifted temperature characteristic.