JPS6230521B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high frequency oscillator that can be frequency controlled or frequency modulated. In conventional frequency modulated oscillators, a variable capacitance diode is used as a part of the frequency determining element of the oscillation circuit, and the oscillation frequency is modulated by a control signal. Although this type of oscillator has a simple circuit configuration, the oscillation frequency tends to change due to the inherent temperature characteristics of the variable capacitance diode and fluctuations in the power supply voltage that provides the reference bias, and the variation in the capacitance value of the variable capacitance diode However, it has drawbacks such as frequency modulation sensitivity changes due to variations in capacitance change characteristics, and furthermore, the linearity of frequency variation is not very good. Furthermore, when attempting to configure an oscillator with 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 is difficult due to the stability issues mentioned above. Not only does this not solve the problem of variations in sensitivity, but it also becomes economically expensive. The present invention uses a surface acoustic wave element as a frequency-selective phase shift element to eliminate the above-mentioned drawbacks of the conventional example and to provide a frequency-modulated oscillator suitable for semiconductor integrated circuits. Hereinafter, the present invention will be explained based on illustrated embodiments. FIG. 1 is a basic block diagram of the present invention, and FIG. 2 is a characteristic diagram showing an example of the amplitude characteristics and phase characteristics of a surface acoustic wave element used in the present invention. In FIG. 1, reference numeral 1 denotes a surface acoustic wave element that outputs two outputs with the same amplitude characteristics and different phase characteristics to output terminals 7 and 8 in response to an input applied to an input terminal 6. It is supplied to the two input terminals 4a and 4b of the phase synthesizer 4 through amplifiers 2 and 3 having the same characteristics, respectively.
A positive feedback loop is formed by giving the output obtained from the output terminal 4c of the amplifier 5 to the input terminal 6 of the original surface acoustic wave element 1 through the amplifier 5 that can convert the impedance. It is configured to extract oscillation output. The phase synthesizer 4 vector-synthesizes a plurality of input signals having different phases, and has a control input terminal 9.
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. FIG. 2 shows the amplitude characteristics 11 and phase characteristics 12 of the surface acoustic wave element 1. This has an oscillation loop gain that allows oscillation, and performs stable oscillation at a frequency ₀ at a certain phase θ ₀ point such as positive feedback, and a phase synthesizer 5 in the oscillation loop changes the maximum phase θ ₁ to θ By adjusting the phase shift amount by ₂ , the oscillation frequency becomes
₁ to ₂ , and will be frequency modulated by the control input signal. Here, Δθ=θ ₂ −θ
₁ corresponds to the phase difference of the output of the surface acoustic wave element 1. Surface acoustic wave elements, which are frequency-selective phase-shifting elements, have the same amplitude characteristics but can easily extract outputs with different phases, and have good linearity in phase characteristics, so they can be used as oscillators as described above. With this structure, an oscillator with constant amplitude, wide variable frequency range, and good linearity can be realized. FIG. 3 is a diagram showing the main circuit configuration of the embodiment of the present invention based on FIG. 1, and shows in detail the portions corresponding to the phase synthesizer 4 and amplifier 5 in FIG. 1. In the figure, 13 is a surface acoustic wave element (corresponding to 1 in Figure 1) having the characteristics shown in Figure 2.
The input terminals 21 and 22 are balanced input terminals, and correspond to 6 in FIG. Further, the output terminals 23 and 24 correspond to 7 and 8 in FIG. 1, and two outputs having the same amplitude characteristics and a phase difference Δθ=θ ₁ −θ ₂ are obtained from these terminals. Reference numerals 14 and 15 designate amplifiers that are signal forming circuits that output equal amplitude signals of positive and negative two phases relative to the input signal, and the signal is outputted from 14 with a phase of θ ₁ '-θ ₁ , and from 15 with a phase of θ _2′−
It is output with a phase of θ ₂ . These correspond to amplifiers 2 and 3 in FIG. To explain the circuit part of the phase synthesizer, a signal of phase -θ ₁ is applied to the base electrode of transistor Q ₁ , a signal of +θ ₁ is applied to the base electrode of transistor Q ₂ , and a signal of phase -θ ₂ '+θ ₂ is applied to the base electrode of transistor Q 2. is applied to the base electrodes of transistors Q ₃ and Q ₄ . _Q1 ,
The emitter electrodes of Q ₂ are commonly connected, and Q ₃ ,
The emitter electrodes of Q ₄ are also commonly connected. Further, Q ₁ and Q ₃ of the collector electrode are commonly connected, and Q ₂ and Q ₄ are also commonly connected. With this connection configuration, 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 +θ ₁ and +θ
_{The two} inputs result in a vector-combined signal. The composite ratio is applied to differentially connected control transistors Q ₅ and Q ₆ . The current flowing through the transistors Q ₁ , Q ₂ , _{Q 3} , and _{Q 4 is} controlled by the control signal from the control input terminal ₂₅ corresponding to 9 in FIG. Considering the phase inversion of , it is clear that a signal with a phase of (θ ₁ to _{θ 2} )+π is generated. Similarly, a signal with a phase of (-θ ₁ to −θ ₂ )+π appears in R ₁ .
In other words, a balanced output in which the amount of phase shift from θ ₁ to θ ₂ changes can be obtained through R ₁ and R ₂ . Note that 17 is a current source. The first effect of having such a circuit configuration is that the surface acoustic wave element outputs two signals with different phases based on the control signal, and furthermore, the control signal adjusts the synthesis ratio of these two signals. By providing a circuit in a positive feedback loop to perform frequency control, it is possible to perform frequency modulation without using a variable capacitance diode. The second effect is that by setting the input and output sides of the phase synthesizer to two phases, positive and negative, it becomes possible to connect the current paths in a complementary manner, and signal components 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 supplies, grounding, etc. That is, the currents flowing through the load resistors R ₁ and R ₂ are complementary regardless of the control input, and by connecting them in common, the current from the power supply terminal 27 does not include a signal component. Furthermore, the emitter currents of transistors Q ₁ and Q ₂ and the emitter currents of transistors Q ₃ 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. Next, an explanation will be given of an output amplification circuit section corresponding to the amplifier 5 in FIG. 1. The signal after phase synthesis mentioned above is
From R ₁ and R ₂ , as a balanced signal of positive and negative _phases , _the transistor Q ₇ , _Q8 ,
It is added to each base electrode of Q ₉ and Q ₁₀ . transistor
The emitter electrodes of Q ₇ and Q ₈ receive balanced signals that are approximately in phase with the input, and the collector electrodes of transistors Q ₉ and Q ₁₀ receive balanced signals that are approximately inverted with respect to the input. As shown in FIG. 3, the in-phase signals are connected to the input terminals 21 and 22 and the emitter electrodes of the transistors Q ₇ and Q ₈ via appropriate resistive loads R ₃ and R ₄ of equal value, respectively. Therefore, operationally, the transistors Q ₉ ,
The differential amplifier circuit composed of _Q10 further drives the active load which is driven in phase by transistors _Q7 and _Q8 . The amplified balanced signals are taken out from the emitter electrodes of transistors Q ₇ and Q ₈ and sent to input terminals 21 and 22 of surface acoustic wave element 13.
is connected to reduce matching loss and form a positive feedback loop. Furthermore, the configuration is such that the necessary oscillation output is taken out from the collector electrode of the transistor _Q9 through the amplifier 16 and from the output terminal 26 corresponding to 10 in FIG. Note that R ₅ and R ₆ are resistive loads, 1
8, 19, and 20 are constant current sources. The first effect of adopting the configuration shown in Figure 3 is that power efficiency can be increased by effectively utilizing the differential amplifier circuit configuration and integrating the positive feedback loop output stage and the oscillation output stage. It is possible. That is, constant current sources 19 and 20 are diodes.
This is for operating Q ₁₁ and Q ₁₂ in the forward direction, and since it requires a small amount of current, this circuit essentially operates only with the current from the constant current source 18. The second effect is that the transistor acting as an active load
Since the output impedance seen from the emitter electrodes of Q ₇ and Q ₈ is low, the gain is suppressed at low frequencies,
Since there is almost no attenuation at high frequencies, it has flat frequency characteristics, making it suitable for high frequency integrated circuits. The third effect, although complementary, is that three balanced outputs are taken out from the collector and emitter electrodes of transistors Q ₇ and Q ₈ and the collector electrodes of transistors Q ₉ and Q ₁₀ , and the output impedance and frequency Since they have different characteristics, they can be used effectively. Moreover, in this case, mutual interference between the positive feedback loop output and the oscillation output can be reduced due to the resistive loads R ₃ and R ₄ .
This means that stable oscillation is now possible. FIG. 4 is a circuit configuration diagram showing a specific embodiment of the present invention. As mentioned above, the surface acoustic wave element 13
The output terminals 23 and 24 have a phase difference Δθ=θ ₁ −
Two signals having θ ₂ =90° are taken out and inputted by constant voltage sources 32 and 33 to the respective emitter electrodes of transistors Q ₁₃ and Q ₁₇ which are of common base type. Here, the input stage is of a base-grounded type because it is suitable for impedance matching with the surface acoustic wave element in the embodiment, and is not particularly limited. The signal applied to the input terminal 23 is a transistor
Q ₁₃ , Q ₁₄ base-grounded type and transistor Q ₁₅ ,
It is amplified by a differential amplifier with a grounded-emitter composite connection of Q ₁₆ , and can be output as a balanced signal to load resistors R ₁₁ and R ₁₂ . Since the load resistances R ₉ and R ₁₀ of transistors Q ₁₃ and Q ₁₄ are connected to the collector electrodes of transistors Q ₁₅ and Q ₁₆ , negative feedback is applied at low frequencies, and the signal at high frequencies is not attenuated.
Balanced output with flat frequency characteristics. _C1 is the ground capacitance on one side of the unbalanced input, and since high frequency signals are handled here, the capacitance is small enough to be implemented in an integrated circuit. R ₇ and R ₈ are resistors, R ₁₃ is a collector voltage adjustment resistor, and 28 is a constant current source. Similarly, the signal applied to the input terminal 24 is also processed by a differential amplifier having exactly the same configuration as the input terminal 23 side.
A balanced signal with flat frequency characteristics can be extracted from the load resistors R ₁₈ and R ₁₉ . Here, Q ₁₇ , Q ₁₈ , Q ₁₉ , Q ₂₀
is a common base-grounded emitter differential amplifier transistor, R ₁₄ , R ₁₅ , R ₁₆ , R ₁₇ are load resistances, and R ₂₀
is a collector voltage adjustment resistor, _C2 is a small ground capacitor, 29 is a constant current source, and 33 is a constant voltage source. The two signals with different phases applied to the input terminals 23 and 24 in this way are amplified by differential amplifier circuits that are completely symmetrical and have the same characteristics, and the phase difference Δθ between the output signals of the surface acoustic wave elements is determined by the phase difference Δθ. =θ ₁ −θ ₂ =
It is input to the phase synthesizer as a balanced signal with the angle unchanged at 90°. Therefore, due to the operation of the phase synthesizer described above,
A balanced signal that allows a phase change of Δθ = 90° is extracted from the load resistors R ₁ and R ₂ , and the transistor
It is amplified by a differential amplifier composed of Q ₇ , Q ₈ , Q ₉ , and Q ₁₀ , and the positive feedback loop output is the balanced input of the surface acoustic wave element 13 with lower output impedance than the emitter electrodes of transistors Q ₇ and Q ₈ . It is connected to match the oscillator for stable oscillation. At the same time, the oscillation output is given from the collector electrode of transistor Q ₁₀ to the base electrode of transistor Q ₂₁ ,
The oscillation signal is amplified to the required oscillation level, and two outputs are taken out from output terminals 26 and 26'. The synthesis ratio of the phase synthesizer is changed by the control signal from the control input terminal 25, but the resistance R ₂₁ ,
R ₂₂ , R ₂₃ , R ₂₄ and constant current sources 30 and 31 are provided for setting the operating voltages of transistors Q ₅ and Q ₆ , adjusting control sensitivity, and DC balance. In order for this phase synthesizer to operate optimally,
It is desirable that the amplitude of the composite 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,
The gains of Q ₁ , Q ₂ , Q ₃ , and 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 as [Formula], and the amplitudes are equal. In order to realize this condition and stabilize the operation, resistors R ₂₅ , R ₂₆ , R ₂₇ , and R ₂₈ are connected to the emitter electrodes of each transistor Q ₁ , Q ₂ , Q ₃ , and Q _{4 ,} respectively. _R29 is a collector voltage adjustment resistor. Also, the resistances R ₃₀ and R ₃₁ of the output amplifier circuit are
By connecting R ₅ and R ₆ as shown in the figure, not only DC balance is achieved but also the positive feedback loop gain has a flat frequency characteristic. _C3 is a capacitor for grounding the emitter of transistor _Q21 . Also, L ₁ is
It is a load that acts as the output tuning coil of Q ₂₁ ,
A point with an appropriate turns ratio is set as the output terminal 26', and an output for a 50Ω termination value is taken out, and an output for an open value, which is not tuned, is taken out from the output terminal 26. In addition, 3
4 is a constant current source. Here, the surface acoustic wave element 13 mentioned above will be explained in more detail. FIG. 5 is a schematic diagram of a surface acoustic wave device, in which comb-shaped interdigital electrodes 35, 36, and 37 are generally provided on a Z _o O substrate or the like so as to intersect with each other. When a balanced input is applied from the input terminals 21 and 22, it is transmitted as a surface wave to the output electrodes 36 and 37 through the input electrode 35, and only signals near a certain frequency ₀ are extracted from the output terminals 23 and 24. 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 phases can be obtained. In an embodiment of the invention,
It is designed to have a phase difference of Δθ≒90° at ₀ = 145MHz. As is clear from the above description, the oscillator of the present invention has the following excellent features. (1) Surface acoustic wave elements with the same amplitude characteristics but different output phases are used as frequency-selective phase shift elements,
By providing a phase synthesizer for two signals with a phase difference in a positive feedback loop, it is possible to realize an FM oscillator or voltage-controlled oscillator with constant amplitude characteristics and good linearity. (2) It is possible to realize a circuit configuration in which all signal paths are complementary and balanced in terms of direct current, which is suitable for integrated circuits. (3) The connection between the surface acoustic wave element and the input/output on the circuit side is a connection with low matching loss, and an effective differential amplifier that integrates the positive feedback loop output stage and the oscillation output stage is used, resulting in high power efficiency. good. (4) In addition, it is possible to cover almost the entire range of the phase shift amount of the phase shift circuit by simply changing the polarity of the input signal of the synthesizer (4 combinations), and The frequency characteristics become flat and suitable for high frequency integrated circuits.

[Brief explanation of the drawing]

Figure 1 is a basic block configuration diagram of the present invention, Figure 2 is a basic block configuration diagram of the present invention.
The figure is a characteristic example diagram of a surface acoustic wave element, Figure 3 is a circuit diagram of a main part of an embodiment of the present invention, Figure 4 is a circuit diagram of a specific embodiment of the present invention, and Figure 5 is a diagram of a surface acoustic wave element. It is a schematic diagram of an element. 1, 13...Surface acoustic wave element, 2, 3, 5, 1
4, 15, 16...Amplifier, 4...Phase synthesizer,
6...Input terminal, 7, 8...Output terminal, 18...
Constant current source, Q ₁ , Q ₂ , Q ₃ , Q ₄ ... Transistor for phase synthesis, Q ₅ , Q ₆ ... Transistor for phase synthesis control, Q ₇ , Q ₈ , Q ₉ , Q ₁₀ ... Transistors for output amplification, Q ₁₁ , Q ₁₂ ...diodes, R ₃ ,
R ₄ , R ₅ , R ₆ ...Resistive load.

Claims (1)

[Claims] 1. A surface acoustic wave element that outputs signals having different phases to first and second output terminals when a signal is input to an input terminal; A phase synthesizer capable of synthesizing signals obtained from output terminals and controlling the signal synthesis ratio, and amplifying the output signal of the phase synthesizer,
The phase synthesizer includes first and second transistors and third and fourth transistors whose emitters are connected in common, respectively. , and fifth and sixth transistors that are differentially connected with their emitters in common, and the first
and the collector of the third transistor and the second
and the collectors of the fourth transistor are connected in common, and the emitters of the first and second transistors and the emitters of the third and fourth transistors are connected to the collectors of the fifth and sixth transistors, respectively. , signals of different polarities belonging to the same phase are applied to the bases of the first and second transistors, and signals of different polarities belonging to a phase different from the phase are applied to the bases of the third and fourth transistors. is given, and the control signal for the phase synthesis ratio is given to the base of at least one of the fifth and sixth transistors, and the first and third transistors
An oscillator characterized in that the oscillator is configured to obtain a balanced phase composite signal from the collector of the transistor and the collectors of the second and fourth transistors. 2. In the statement of claim 1, the amplifier includes an emitter of a seventh transistor and an emitter of a tenth transistor.
Resistors of equal value are connected between the collectors of the transistors, and between the emitters of the eighth transistor and the collectors of the ninth transistor, and resistive loads are connected to the collectors of the seventh and eighth transistors, respectively. connecting the emitters of each of the ninth and tenth transistors to a common current path;
forward operating diodes are connected between the bases of the seventh and ninth transistors and between the bases of the eighth and tenth transistors, respectively;
and the base of the eighth transistor or the bases of the ninth and tenth transistors, and the emitter of each of the seventh and eighth transistors, the collector of each of the ninth and The collector of each of the tenth transistors is used as an output terminal, one set of output terminals is connected to each input terminal of the surface acoustic wave element, and an oscillation output signal is taken out from the remaining output terminals. An oscillator characterized by comprising: