JPH0347007B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION The present invention relates to an oscillator capable of frequency control or frequency modulation. Conventional Structure and Problems Conventionally, as an oscillator capable of frequency modulation, a variable capacitance diode or the like is used as a part of the frequency determining element of an oscillation circuit, and the oscillation frequency is modulated by a control signal. Although the configuration of such a circuit is simple, due to the inherent temperature characteristics of the variable capacitance diode and fluctuations in the power supply that provides the reference bias,
The disadvantages include that the oscillation frequency changes easily, the frequency modulation sensitivity changes due to variations in the capacitance value and capacitance change characteristics of the variable capacitance diode, and the linearity of frequency variation is not very good. . Furthermore, when attempting to construct an oscillator using a semiconductor integrated circuit, it is difficult to integrate a variable capacitance diode at the same time as the circuit, and adding a variable capacitance diode to an integrated circuit oscillator may result in poor stability and sensitivity. Not only does this not solve the problem of variation, but it also becomes economically costly. Purpose of the Invention An object of the present invention is to eliminate the drawbacks of the conventional example by using a surface acoustic wave element as a frequency-selective phase shift element, and to provide a frequency-modulated oscillator suitable for semiconductor integrated circuits. It is something to do. Configuration of the Invention The present invention provides a surface acoustic wave element having two different output phases for a balanced input, a phase synthesizer that synthesizes a plurality of signals having different phases and controls a signal synthesis ratio, and a phase synthesizer that synthesizes a plurality of signals having different phases and controls a signal synthesis ratio. an output amplifier which inputs the output of the elastic converter and outputs a balanced output, and connects a tuned circuit type balanced/unbalanced converter including a capacitance element and an inductance element between two terminals of the balanced output; The two outputs of the surface wave element are connected to the two input sides of the phase synthesizer, and the balanced output of the output amplifier is connected to the balanced input of the surface acoustic wave element to form an oscillation loop, and the balanced・It is configured so that the oscillation output is taken out from the unbalanced terminal of the unbalanced converter. Description of Examples The examples will be described below. FIG. 1 is a basic block diagram of the present invention, and FIG. 2 shows the amplitude characteristic 11 and phase characteristic 12 of the elastic surface element. Reference numeral 1 denotes a surface acoustic wave element having two outputs with the same amplitude characteristic and different phase characteristics with respect to the input, and each output is connected to input terminals 4 and 5 of the phase synthesizer 2
The output after phase synthesis is connected to the balanced input of the original surface acoustic wave element at the two terminals 6 and 7 of the balanced output via the differential amplifier 3 having a balanced output for positive feedback. forming a loop. 8 is a balanced-unbalanced converter that converts signals input from balanced output terminals 6 and 7 into unbalanced signals, and 9 is its output terminal. The phase synthesizer 2 performs vector synthesis of a plurality of input signals having different phases, and has a control input terminal 10.
This is a phase shifter whose phase shift amount can be adjusted according to the level of a control signal provided by the phase shifter. In the characteristics of the surface acoustic wave element shown in Figure 2, the frequency at a certain phase θ ₀ point that has an oscillation loop gain that allows oscillation and positive feedback
The oscillation frequency changes from f 1 to f 2 by stably oscillating at f ₀ , and by adjusting the phase shift amount by a maximum of θ ₁ to θ 2 using the phase synthesizer ₂ in the oscillation loop, the oscillation frequency changes from f ₁ to f ₂ , and the control input signal This results in frequency modulation. Here, Δθ=θ ₂ −θ ₁ corresponds to the phase difference of the output of the surface acoustic wave element. Surface acoustic wave elements, which are frequency-selective phase-shifting elements, have the same amplitude characteristics, but it is easy to extract outputs with different phases, and the linearity of the phase characteristics is good. By configuring , an oscillator with a constant amplitude, a wide variable frequency range, and good linearity can be obtained. In addition, since the surface acoustic wave element is driven in a balanced manner for oscillation, the voltage gain is twice as high (6 dB) compared to when driven in an unbalanced manner.
Therefore, improving the C/N of the oscillator is advantageous for reducing power consumption. Note that the area within the dotted line in FIG. 1 indicates the amplifier system of the oscillator. FIG. 3 shows a block diagram of an oscillator with higher performance than the oscillator having the basic configuration shown in FIG. 1. Elements having the same role as in FIG. 1 are designated by the same numbers. In addition to the configuration shown in FIG. 1, the configuration shown in FIG. and the two balanced output terminals of the differential amplifier 3 and the two balanced input terminals of the surface acoustic wave element.
The structure is such that output amplifiers 15 and 16 each having the same characteristics are connected between the two terminals. Normally, the amount of attenuation of a surface acoustic wave element is large, and by using the preamplifiers 13 and 14 and the output amplifiers 15 and 16, an oscillator with even better C/N can be realized. FIG. 4 shows the main circuit configuration of the block diagram of FIG. 3, showing the phase synthesizer 2 in detail.
Elements exhibiting effects similar to those described above are designated by similar symbols. Reference numeral 1 denotes a surface acoustic wave element having the characteristics as shown in FIG. 2, and the two outputs have the same amplitude characteristics but two different output phases with a phase difference Δθ=θ ₁ −θ ₂ . Reference numerals 13 and 14 are preamplifiers having the same characteristics, and the output is output at a phase of θ ₁ from 13 and at a phase of θ ₂ from 14. Next, the phase synthesizer 2 will be explained. A signal with phase θ ₁ is applied to the base electrode of transistor Q ₁ , with phase θ ₂
The signal is applied to the base electrode of Q ₂ , and the ground capacitors C ₁ and C ₂ are connected to the base electrodes of Q ₃ and Q ₄ , so the signals with phases of −θ ₁ and −θ _{2 are applied to the base electrode of Q 3 and Q 4} , respectively. It will be the same as if it were added. The same effect can be achieved even if the preamplifiers 13 and 14 are configured in advance with balanced outputs and are added directly to transistors Q ₁ and Q ₃ or Q ₂ and Q ₄ with balanced inputs. The emitter electrodes of Q ₁ and Q ₃ are commonly connected and connected to the collector electrode of Q ₅ .
Also, the emitter electrodes of Q ₂ and Q ₄ are commonly connected, and Q ₆
is connected to the collector electrode of. Q ₅ and Q ₆ have a differential amplification configuration, and each emitter electrode is connected to a current source 17. Further, the collector electrodes of Q ₁ and Q ₂ are also commonly connected, and the collector electrodes of Q ₃ and Q ₄ are also commonly connected and connected to the differential amplifier 3. With this kind of connection, the load resistor R ₁ receives a vector-combined signal from the inputs of −θ ₁ and −θ ₂ , and the load resistor R ₂ receives a vector-combined signal from the inputs of +θ ₁ and +θ ₂ . occurs. The combined ratio is applied to differentially connected control transistors Q ₅ and Q ₆ . A control signal from the control input terminal 10 controls the current flowing through the transistors Q ₁ , Q ₂ , Q ₃ , and Q ₄ , and for example, the phase inversion of the input signal by the transistors Q ₁ and Q ₂ is applied to the load resistor R ₂ . Considering, (θ ₁ ~ _{θ 2} ) + π
A signal with a phase of is generated. Similarly, R ₁ has (−θ ₁ −
A signal with a phase of θ ₂ )+π appears. That is, R ₁ , R ₂
Through this, a balanced output in which the amount of phase shift from θ ₁ to θ ₂ changes can be obtained. The first effect of using such a circuit is that the surface acoustic wave element outputs two signals with different phases, and a phase shift circuit is provided in the positive feedback loop to adjust the synthesis ratio of these two signals using a control signal. By performing frequency control using a variable capacitance diode, it is possible to perform frequency modulation without using a variable capacitance diode. The second effect is that by setting the signal path of the phase synthesizer to two phases, positive and negative, it becomes possible to connect the current paths in a complementary manner, and the signal components do not leak into the power supply and ground paths. This makes it possible to stably configure integrated circuits that tend to have high line impedance for power supply, grounding, etc. That is, load resistance R ₁ ,
The current flowing through R ₂ is complementary whatever the control inputs are, and by connecting them in common, the current from power supply terminal 18 does not include a signal component. Furthermore, the emitter currents of transistors Q ₁ and Q ₃ and the emitter currents of transistors Q ₂ and Q ₄ are complementary to each other, and by connecting them in common, the signal current flows through control transistors Q ₅ and Q ₆ . do not have. Therefore, the synthesis ratio can be controlled only by considering the direct current or modulation signal frequency. FIG. 5 shows a specific embodiment of the invention. Elements exhibiting effects similar to those described above are designated by similar symbols. Also, the bias circuit is omitted in the circuit diagram.
As mentioned above, two signals with a phase of Δθ=θ ₁ −θ ₂ =90° are extracted from the output terminal of the surface acoustic wave element.
The grounded capacitances C ₇ and C ₈ provide input to the emitter electrodes of each of the transistors Q ₇ and Q ₈ which form a common base amplifier. The reason why the input stage is of a base-grounded type is because it is suitable for impedance matching with the surface acoustic wave element in the example.
It is not particularly limited. The two signals with different phases applied to the input terminals 4 and 5 are amplified by a grounded base type preamplifier having exactly the same characteristics, and the phase difference between the output signals of the surface acoustic wave element Δθ= With θ ₁ −θ ₂ =90°, the signal is input as an unbalanced signal to the phase synthesizer via coupling capacitances C ₃ and C ₄ . By the operation of the phase synthesizer described above, a balanced signal that allows a phase change of Δθ=90° is taken out to the load resistors R ₁ and R ₂ , and the transistors Q ₉ and
It is amplified by the differential amplifier constituted by _Q10 , and appears as a balanced signal at the resistors _R13 and _R14 . Then, _{the transistor}
It is connected in a balanced manner to the input side of the original surface acoustic wave element via a grounded emitter type amplifier with the same characteristics consisting of Q ₁₁ and Q ₁₂ , forming a positive feedback loop and oscillating. Then, a capacitor C ₁₃ and an inductance L ₁ are connected between the balanced output terminals 6 and 7 to form a parallel resonant load, and the signal is output via the inductance L ₂ . C ₁₁ and C ₁₂ are coupling capacitances. For the phase synthesizer to operate optimally, it is desirable that the amplitude of the combined output signal does not vary with the control signal, ie, with the output phase angle. This means that when Q ₅ and Q ₆ are in equilibrium, Q ₁ , Q ₂ , Q ₃ ,
The gain of Q ₄ may be 1/√2 of the maximum gain (which occurs in an unbalanced state). At this time, the composite output is

It is expressed by [Formula], and the amplitudes are equal. In order to realize this condition and stabilize the operation, resistors R ₃ , R ₄ , R ₅ , and R ₆ are connected to the emitter electrodes of each transistor Q ₁ , Q ₂ , Q ₃ , and Q ₄ , respectively. Also, resistors R ₇ and R ₈ adjust the amplification degree of the differential amplifier by transistors Q ₅ and Q ₆ , that is,
Adjust the modulation sensitivity. In addition, regarding the value of the ground capacitance coupling capacitance, when used in the VHF band, it normally operates at about 10 to 20 PF, so this is a value that can be realized even when integrated circuits are used. In addition, capacitance C ₁₃ and inductance L ₁ constitute a parallel resonant load.
Accordingly, it is possible to correct variations in the oscillation frequency due to variations in the surface acoustic wave element 1 and temperature characteristics. FIG. 6 shows a pin layout diagram when the oscillator of the present invention is integrated into an IC. Components exhibiting the same effects as those described above are indicated by the same reference numerals. The part inside the dotted line is a block diagram that is converted into an IC, and is housed in a DIL ₈ -pin package. The two input terminals of the amplifier system of the IC are the 1st pin P ₁ and the 8th pin P ₈ , and the two balanced output terminals are the 4th pin P ₄ and the 5th pin P ₅ , making them symmetrical. . Normally, the amount of attenuation of a surface acoustic wave element is large, and it is necessary to increase the amplification beyond that amount of attenuation. Therefore, as the frequency band becomes higher, abnormal oscillation phenomenon due to coupling between input and output of capacitance between pins becomes a problem. This problem can be solved by forming a balanced positive feedback loop with a parallel resonant load of capacitance C ₁₃ and inductance L ₁ .
This is prevented by making the IC pin arrangement symmetrical. Next, some explanation will be given regarding the above-mentioned surface acoustic wave element. FIG. 7 is a schematic diagram of a surface acoustic wave element used in the present invention, in which comb-shaped interdigital electrodes 24, 25, and 26 are generally provided on a ZnO substrate or the like so as to intersect with each other. Balanced input terminal 20, 2
When an input signal is applied from 1, the output electrodes 25,
26 as a surface wave, and only signals near a certain frequency f ₀ are extracted from the output terminals 22 and 23. At this time, if the distance between the electrode centers is set so that the delay times τ ₁ and τ ₂ have appropriate values, two outputs with the same amplitude characteristics and different output phases can be obtained. In the embodiment of the invention f ₀ =145MHz
The design is such that the phase difference Δθ≒90°. Effects of the Invention As is clear from the above explanation, the present invention has the following effects. (1) Surface acoustic wave elements with the same amplitude characteristics and different output phases are used as frequency-selective phase shift elements, and are equipped with a phase synthesizer and differential amplifier for two signals with phase differences, and are equipped with a phase synthesizer and a differential amplifier for two signals with phase differences. By forming a feedback loop and taking out the output via a balanced/unbalanced converter, the amplitude characteristics are constant, linearity is good,
It can be used as an FM oscillator or voltage-controlled oscillator with good C/N and low power consumption. (2) Since it is equipped with a balanced/unbalanced converter that connects a parallel resonant load made of capacitance and inductance between the balanced output terminals, the gain on the output amplification side that makes up the oscillation loop increases, resulting in a high impedance output load. Therefore, high C/N characteristics can be obtained, and variations in oscillation frequency due to variations in surface acoustic wave elements, temperature characteristics, etc. can be corrected by the LC load. (3) By connecting the input/output terminals of the amplifier system to both ends of the DIL package and implementing an IC with a symmetrical pin arrangement, abnormal oscillation phenomena due to inter-pin capacitance can be prevented. This is especially advantageous when implementing ICs in high frequency bands.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an oscillator according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of a surface acoustic wave element, and FIG.
The figure is a block diagram of another embodiment, FIG. 4 is a configuration diagram of the same essential circuit, FIG. 5 is a wiring diagram of a more specific embodiment of the present invention, and FIG. FIG. 7 is a schematic diagram of the surface acoustic wave element. 1... Surface acoustic wave element, 2... Phase synthesizer, 3... Differential amplifier, 13, 14... Preamplifier, 15, 16
...Output amplifier, Q ₁ , Q ₂ , Q ₃ , Q ₄ ... Phase synthesis transistor, Q ₅ , Q ₆ ... Phase synthesis control transistor.

Claims (1)

[Claims] 1. A surface acoustic wave element having two different output phases for a balanced input, a phase synthesizer that synthesizes a plurality of signals with different phases and controls a signal synthesis ratio, and the phase synthesizer. an output amplifier which inputs the output of the amplifier and outputs a balanced output, and has a tuned circuit type balanced-unbalanced converter connected between two terminals of the balanced output using a capacitance element and an inductance element; Connecting two outputs of the surface acoustic wave element to two input sides of the phase synthesizer, and connecting a balanced output of the output amplifier to the balanced input of the surface acoustic wave element to form an oscillation loop, An oscillator characterized in that an oscillation output is taken out from an unbalanced terminal of the balanced/unbalanced converter. 2 Connect the two input terminals and the two balanced output terminals of the phase synthesizer that make up the oscillation loop symmetrically using the pins at both ends of the IC-DIL package.
Claim 1 characterized in that it is integrated into an IC.
Oscillator mentioned in section.