Two-band oscillating device

Abstract: Disclosed is a two-band oscillating device in which coupling between two oscillators is made loose so that an oscillation signal can be supplied to an amplifier without reducing the level of the signal. The two-band oscillating device comprises: a first oscillator (1) for outputting an oscillation signal in a first frequency band; a second oscillator (2) for outputting an oscillation signal in a second frequency band; an amplifier (4) for amplifying either the oscillation signal in the first frequency band or the oscillation signal in the second frequency band; a first switching diode (3a) for supplying the oscillation signal in the first frequency band to the amplifier; and a second switching diode (3b) for supplying the oscillation signal in the second frequency band to the amplifier. The first oscillator or the second oscillator is operation in an alternative way, the first switching diode is made conductive in association with the operation of the first oscillator, and the second switching diode is made conductive in association with the operation of the second oscillator.

Description: The present invention relates to a two-band oscillating device for use in a portable telephone, which is shared by two different systems. Fig. 5 shows the construction of a conventional two-band oscillating device comprising a first oscillator 21, a second oscillator 22, a coupled circuit 23, and an amplifier 24. The first oscillator 21 produces an oscillation signal in a low frequency band (Lf) of about 880 MHz to 940 MHz. The second oscillator 22 produces an oscillation signal in a higher frequency band (Hf) of about 1805 MHz to 1920 MHz. A power supply voltage (Vb) is applied to either the first oscillator 21 or second oscillator 22 by a change-over switch 25. The oscillator to which the power supply voltage is applied operates in an alternative way and outputs an oscillation signal. Each of the oscillation signals is supplied to the amplifier 24 via the coupled circuit 23. Each of the first and second oscillators 21 and 22 takes the form of a voltage-controlled collector-grounded Colpitts oscillator. The first oscillator 21 has a first oscillation transistor 21a, two feedback capacitors 21b and 21c, a first strip line 21d as an inductance device, and a first varactor diode 21e. Similarly, the second oscillator 22 has a second oscillation transistor 22a, two feedback capacitors 22b and 22c, a second strip line 22d as an inductance device, and a second varactor diode 22e. The oscillation frequency of each of the oscillators 21 and 22 is changed according to a control voltage (Vc) applied to each of the varactor diodes 21e and 22e. Oscillation signals are derived from the emitters of the oscillation transistors 21a and 22a. The coupled circuit 23 has two coupling capacitors 23a and 23b which are connected in series. One end of one of the coupling capacitors, 23a, is connected to the emitter of the first oscillation transistor 21a. One end of the other coupling capacitor 23b is connected to the emitter of the second oscillation transistor 22a. The amplifier 24 is an emitter-grounded aperiodic wide-band amplifier. A power supply voltage (Vb) is applied to the collector of a transistor 24a for amplification via a choke inductor 24b. The connection point of the coupling capacitors 23a and 23b is connected to the base of the transistor 24a for amplification. The power supply voltage is applied to either the collector of the first oscillation transistor 21a or the collector of the second oscillation transistor 22a by the change-over switch 25. When the power supply voltage is applied to the first oscillator 21 by the change-over switch 25, an oscillation signal appearing at the emitter of the first oscillation transistor 21a is supplied to the amplifier 24 via the coupling capacitor 23a. When the power supply voltage is applied to the second oscillator 22, an oscillation signal appearing at the emitter of the second oscillation transistor 22a is supplied to the amplifier 24 via the coupling capacitor 23b. The level of each of the oscillation signals supplied to the amplifier 24 is influenced by the capacitance value of the coupling capacitor 23a or 23b. The capacitance value is usually set to a few pF (2 to 5 pF). As described above, in the conventional two-band oscillating device, oscillation signals in two frequency bands are supplied to the amplifier via the corresponding coupling capacitors. Consequently, the two oscillators are coupled to each other via the coupling capacitors and each of the oscillators is a load on the other oscillator. It causes a problem such that the level of the oscillation signal supplied to the amplifier is reduced. In order to solve the problem (reduction in level), it is sufficient to increase the capacitance value of each of the coupling capacitors. In this case, however, the coupling of the oscillators becomes tight, the oscillators are influenced by each other, and a problem such that each of the oscillation frequencies changes arises. In order to reduce the coupling of the oscillators by decreasing the capacitance value of the coupling capacitors and increase the level of the oscillation signal, it is necessary to pass a large current to the oscillation transistors. It however causes a problem such that the power savings cannot be achieved. JPO1173908 discloses a similar two-band oscillator using grounded gate oscillator transistors coupled to one output means of source follower transistors selected by switching a power supply. It is therefore an object of the invention to provide a two-band oscillating device which solves all of the problems, has loose coupling of two oscillators and can supply an oscillation signal to an amplifier without reducing the level of the signal. As means for solving the problems, according to the invention, there is provided a two-band oscillating device as claimed in claim 1 or in claim 3. Futher, preferable embodiments of the invention are defined in the dependent claims. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram showing the construction of a two-band oscillating device according to the invention. Fig. 2 is a circuit diagram showing another construction of a two-band oscillating device according to the invention. Fig. 3 is a circuit diagram showing further another construction of a two-band oscillating device according to the invention. Fig. 4 is a circuit diagram showing further another construction of a two-band oscillating device of the invention. Fig. 5 is a circuit diagram showing the construction of a conventional two-band oscillating device. Fig. 1 shows the construction of a two-band oscillating device of the invention, which comprises a first oscillator 1, a second oscillator 2, a coupled circuit 3 and an amplifier 4. The first oscillator 1 produces an oscillation signal in a first frequency band of low frequencies of 880 MHz to 940 MHz. The second oscillator 2 produces an oscillation signal in a second frequency band of 1805 MHz to 1920 MHz which is higher than the first frequency band. Each of the first and second oscillators 1 and 2 takes the form of a collector-grounded voltage-controlled Colpitts oscillator. A power supply voltage (Vb) is applied to either the first oscillator 1 or second oscillator 2 by a voltage switching means 5. The oscillator to which the power supply voltage is applied operates. The first oscillator 1 comprises a first oscillation transistor 1a, first feedback capacitors 1b and 1c, a first strip line 1d as an inductance device, and a first varactor diode 1e. The collector of the first oscillation transistor 1a is connected to the ground via a first grounding capacitor 1f so as to pass high frequencies. By a control voltage Vc applied to the first varactor diode 1e, the oscillation frequency in the first frequency band is changed and an oscillation signal is obtained from the emitter. The second oscillator 2 comprises a second oscillation transistor 2a, second feedback capacitors 2b and 2c, a second strip-line 2d as an inductance device, and a second varactor diode 2e. The collector of the second oscillation transistor 2a is connected to the ground via a second grounding capacitor 2f so as to pass high frequencies. By a control voltage Vc applied to the first varactor diode 2e, the oscillation frequency in the second frequency band is changed and an oscillation signal is obtained from the emitter. The coupled circuit 3 has: first and second switching diodes 3a and 3b whose cathodes are connected to each other; a first coupling capacitor 3c connected between the anode of the first switching diode 3a and the emitter of the first oscillation transistor 1a; a second coupling capacitor 3d connected between the anode of the second switching diode 3b and the emitter of the second oscillation transistor 2a; a first feeding resistor 3e for connecting the collector of the first oscillation transistor 1a and the anode of the first switching diode 3a so as to pass almost direct currents; a second feeding resistor 3f for connecting the collector of the second oscillation transistor 2a and the anode of the second switching diode 3b so as to pass almost direct currents; and a choke inductor 3g for connecting the cathodes of the switching diodes 3a and 3b to the ground so as to pass almost direct currents. The amplifier 4 takes the form of an emitter-grounded aperiodic wide-band amplifier. A power supply voltage is applied to the collector of a transistor 4a for amplification via a choke inductor 4b. The emitter is connected to the ground via a bias resistor 4c and a bypass capacitor 4d. The base as an input terminal of the amplifier 4 is connected to the cathodes of the first and second switching diodes 3a and 3b via a DC blocking capacitor 4e. For example, when the power supply voltage is applied to the collector of the first oscillation transistor 1a by the voltage switching means 5, the first oscillator 1 operates, a current is passed through the first feeding resistor 3e, the first switching diode 3a and the choke inductor 3g, and the first switching diode 3a is made conductive (ON). Then, the oscillation signal appearing at the emitter of the first oscillation transistor 1a is supplied to the base of the transistor 4a for amplification via the first coupling capacitor 3c, first switching diode 3a and DC blocking capacitor 4e. The amplified oscillation signal is outputted from the collector of the transistor 4a for amplification via the DC blocking capacitor 4f. When the power supply voltage is applied to the collector of the second oscillation transistor 2a by the voltage switching means 5, the second oscillator 2 operates. Simultaneously, a current is passed through the second feeding resistor 3f, second switching diode 3b and choke inductor 3g, so that the second switching diode 3b is made conductive (ON). The oscillation signal appearing at the emitter of the second oscillation transistor 2a is supplied to the base of the transistor 4a for amplification via the second coupling capacitor 3d, second switching diode 3b and DC blocking capacitor 4e. Simultaneously, the amplified oscillation signal is outputted from the collector of the transistor 4a for amplification via the DC blocking capacitor 4f. As described above, in the two-band oscillating device, the oscillation signal in the first frequency band or the oscillation signal in the second frequency band is supplied to the amplifier 4 by the first switching diode 3a which is made conductive in association with the operating state of the first oscillator and the second switching diode 3b which is made conductive in association with the operating state of the second oscillator. Consequently, one of the switching diodes is certainly non-conducting and the first and second oscillators 1 and 2 are not coupled to each other. Therefore, one of the oscillators does not become a load on the other oscillator and the level of the oscillation signal supplied to the amplifier 4 is not reduced. Fig. 2 shows the construction of a modification of the two-band oscillating device of the invention. An inductor 3h is connected in series to the first coupling capacitor 3c connected to the first oscillator 1 for outputting the oscillation signal in the first frequency band which is low. A resistor 3i is connected in series to either the first coupling capacitor 3c or the second coupling capacitor 3d (the second coupling capacitor 3d in Fig. 2). Since the resistor 3i has the function of level adjustment, it is desirable to connect it to the coupling capacitor which is connected to the oscillator that produces the oscillation signal of a higher level. The other construction is similar to that shown in Fig. 1. The resonance frequency by the first coupling capacitor 3c and the inductor 3h is adjusted to an almost center frequency in the first frequency band. With the construction, the passage of higher harmonics of the oscillation signal in the first frequency band is checked by the inductor 3h, so that the level of the oscillation signal supplied to the amplifier 4 is reduced. Even when the amplifier 4 is of a wide band, the level of the higher harmonics to be outputted is reduced and the occurrence of an interference signal in a mixer (not shown) connected at the post stage of the amplifier 4 can be prevented. Even when the level of the oscillation signal in the second frequency band is higher than that of the oscillation signal in the first frequency band, the level of the oscillation signal in the second frequency band is reduced by the resistor 3i connected in series to the second coupling capacitor 3d. Consequently, the levels of two oscillation signals supplied to the amplifier 4 can be adjusted. Fig. 3 shows the construction of another modification of the two-band oscillating device. Either the first switching diode 3a or the second switching diode 3b in the coupled circuit 3 in Fig. 1 is replaced by the resistor 3i. In association with the replacement, either the first resistor 3e or the second resistor 3f for voltage supply is eliminated. In Fig. 3, the second switching diode 3b in Fig. 1 is replaced by the resistor 3i and the second feeding resistor 3f is eliminated. When the level of the oscillation signal in the second frequency band is higher than that of the oscillation signal in the first frequency band, by reducing the level of the oscillation signal in the second frequency band by the resistor 3i, the levels of the two oscillation signals to be supplied to the amplifier 4 can be adjusted. Since the coupling between the first and second oscillators 1 and 2 becomes loose by the resistor 3i, even when no switching diode (the second switching diode 3b in this case) is provided, reduction in level of the oscillation signal in the first frequency band is small. Fig. 4 shows the construction of further another modification of a two-band oscillating device. The first switching diode 3a in the coupled circuit 3 in Fig. 1 is replaced by the level adjusting resistor 3i. In association with the replacement, the resistor 3e for voltage supply is eliminated and the inductor 3h is connected in series to the first coupling capacitor 3c. The construction is suited to the case where the level of the oscillation signal in the first frequency band is higher than that of the oscillation signal in the second frequency band, and the frequency of the oscillation signal in the first frequency band is lower than that of the oscillation signal in the second frequency band. The other construction is the same as that of Fig. 1. In the construction, the level of the oscillation signal in the first frequency band outputted from the first oscillator 1 can be adjusted. The level of higher harmonics of the oscillation signal in the first frequency band supplied to the amplifier 4 can be reduced by the inductor 3h connected in series to the first coupling capacitor 3c. Obviously, voltage switching means for applying a power supply voltage to the first oscillator 1 or second oscillator 2 can be constructed by a switching diode or switching transistor. As described above, the two-band oscillating device of the invention comprises: the first switching diode connected in series between the first oscillator and the amplifier; and the second switching diode connected in series between the second oscillator and the amplifier. By the application of the power supply voltage, the first oscillator is operated and the first switching diode is made conductive, or the second oscillator is operated and the second switching diode is made conductive. Consequently, one of the switching diodes is certainly non-conducting and the first and second oscillators are not coupled to each other. Thus, one of the oscillators does not become a load on the other oscillator, and the level of an oscillation signal supplied to the amplifier is not reduced. According to the two-band oscillating device of the invention, the anode of the first switching diode is connected to the collector of the first oscillation transistor so as to pass almost direct currents and is connected to the emitter via the first coupling capacitor, the anode of the second switching diode is connected to the collector of the second oscillation transistor so as to pass almost direct currents and is connected to the emitter via the second coupling capacitor, each of cathodes of the first and second switching diodes is connected to an input terminal of the amplifier and is also connected to the ground so as to pass almost direct currents, and the power supply voltage is applied to either the collector of the first oscillation transistor or the collector of the second oscillation transistor by the voltage.switching means. Consequently, the operation of the oscillators and the conductive state of the switching diodes can be made associated with each other by the power source voltage applied to the collector of each of the oscillation transistors. According to the two-band oscillating device of the invention, a resistor is connected in series to either the first coupling capacitor or the second coupling capacitor. When the resistor is connected to the coupling capacitor through which an oscillation signal of a higher level passes, the level of the oscillation signal supplied to the amplifier can be reduced. Thus, the levels of the two oscillation signals supplied to the amplifier can be matched. The two-band oscillating device of the invention comprises: the switching diode connected in series between the first oscillator and the amplifier; and the resistor connected in series between the second oscillator and the amplifier. By the application of the power supply voltage, the first oscillator is operated and the switching diode is made conductive. Consequently, the two oscillators can be loosely coupled to each other by one switching diode and the resistor, so that the cost can be reduced. When the level of the oscillation signal in the second frequency band is higher tan that of the oscillation signal in the first frequency band, the level can be reduced by the resistor, thereby enabling the levels of the two oscillation signals supplied to the amplifier to be matched. According to the two-band oscillating device of the invention, the anode of the switching diode is connected to the collector of the first oscillation transistor so as to pass almost direct currents and is connected to the emitter via the first coupling capacitor. A resistor is connected in series between the cathode of the switching diode and the emitter of the second oscillation transistor, and the second coupling capacitor is connected in series to the resistor. The cathode of the switching diode is connected to the input terminal of the amplifier and is connected to the ground so as to pass almost direct currents. The power supply voltage is applied to either the collector of the first oscillation transistor or the collector of the second oscillation transistor by the voltage switching means. Thus, the switching diode can be made conductive in association with the operation of the first oscillator. In the two-band oscillating device of the invention, the frequency of the oscillation signal in the first frequency band is set to be lower than that of the oscillation signal in the second frequency band, an inductor is connected in series to the first coupling capacitor, and a resonance frequency by the first coupling capacitor and the inductor is set within the first frequency band. Consequently, passage of the higher harmonics of the oscillation signal in the first frequency band can be blocked by the inductor 3h. Even when the amplifier is an amplifier of a wide band, the level of higher harmonics to be outputted is reduced and the occurrence of an interference signal in a mixer or the like connected at the next stage of the amplifier can be prevented.

Claims: A two-band oscillating device comprising: a first oscillator (1) having a first oscillation transistor (1a) for outputting an oscillation signal in a first frequency band; a second oscillator (2) having a second oscillation transistor (2a) for outputting an oscillation signal in a second frequency band; voltage switching means (5) for applying a power supply voltage to either the first oscillator (1) or second oscillator (2) in an alternative way; and an amplifier (4) for amplifying either the oscillation signal in the first frequency band or the oscillation signal in the second frequency band, wherein an anode of a first switching diode (3a) is connected to a collector of the first oscillation transistor (1a) so as to pass almost direct currents; a first coupling capacitor (3c) is connected between an emitter of the first oscillation transistor (1a) and an anode of the first switching diode (3a); an anode of the second switching diode (3b) is connected to a collector of the second oscillation transistor (2a) so as to pass almost direct currents; and a second coupling capacitor (3d) is connected between an emitter of the second oscillation transistor (2a) and an anode of the second switching diode (3b); wherein each of the cathodes of the first switching diode (3a) and the second switching diode (3b) is connected to an input terminal of the amplifier (4) and is also connected to the ground so as to pass almost direct currents; when the power supply voltage is applied to the collector of the first oscillation transistor (1a) by the voltage switching means (5) the first oscillator (1) is operated to make the first switching diode (3a) conductive; and when the power supply voltage is applied to the collector of the second oscillation transistor (2a) by the voltage switching means (5) the second oscillator (2) is operated to make the second switching diode (3b) conductive. A two-band oscillating device according to claim 1, wherein a resistor (3i) is connected in series to either the first coupling capacitor or the second coupling capacitor. A two-band oscillating device comprising: a first oscillator (1) for outputting an oscillation signal in a first frequency band; a second oscillator (2) for outputting an oscillation signal in a second frequency band; voltage switching means (5) for applying a power supply voltage to either the first oscillator or the second oscillator in an alternative way; an amplifier (4) for amplifying either the oscillation signal in the first frequency band or the oscillation signal in the second frequency band; wherein a serially connected circuit of a first coupling capacitor (3c) and a switching diode (3a) for supplying an oscillation signal in the first frequency band to the amplifier is connected between the first oscillator (1) and the amplifier, and a serially connected circuit of a second coupling capacitor (3d) and a resistor (3i) for supplying the oscillation signal in the second frequency band to the amplifier is connected between the second oscillator (2) and the amplifier (4), and wherein by the voltage switching means (5), the first oscillator (1) is operated and the switching diode (3a) is made conductive, or by the voltage switching means (5), the second oscillator (2) is operated and at the same time the switching diode (3a) is made non-conductive. A two-band oscillating device according to claim 3, wherein the first oscillator has a first oscillation transistor (1a), the second oscillator has a second oscillation transistor (2a), the anode of the switching diode is connected to the collector of the first oscillation transistor so as to pass almost direct currents and is connected to the emitter via the first coupling capacitor, the resistor is connected in series between the cathode of the switching diode and the emitter of the second oscillation transistor, the second coupling capacitor is connected to the resistor in series, the cathode of the switching diode is connected to an input terminal of the amplifier and is also connected to the ground so as to pass almost direct currents, and the power supply voltage is applied to either the collector of the first oscillation transistor or the collector of the second oscillation transistor by the voltage switching means. A two-band oscillating device according to any preceding claim, wherein the frequency of the oscillation signal in the first frequency band is set to be lower than that of the oscillation signal in the second frequency band, and an inductor (3h) is connected in series to the first coupling capacitor, and a resonance frequency by the first coupling capacitor and the inductor is set within the first frequency band.

Inventors: IKARASHI YASUHIRO, TANEMURA TAKESHI, IKARASHI, YASUHIRO, TANEMURA, TAKESHI, Ikarashi, Yasuhiro, c/o Alps Electric Co., Ltd, Tanemura, Takeshi, c/o Alps Electric Co., Ltd
Applicants: ALPS ELECTRIC CO LTD, ALPS ELECTRIC CO., LTD.
Application year: 2000
Main classification: H03B5
IPC codes: H03B5, H04B1