Frequency converter

A frequency converter includes a transistor pair having a first transistor and a second transistor respectively having collector terminals commonly connected to each other and emitter terminals commonly connected to each other, the commonly-connected collector terminals of the transistor pair being connected to a power supply terminal by way of a first resistor, a third transistor having a collector terminal connected to the power supply terminal by way of a second resistor and an emitter terminal connected to the commonly-connected emitter terminals of the transistor pair, a third resistor having an end connected to the commonly-connected emitter terminals of the transistor pair, and another end grounded by way of a constant current source, and an output terminal connected to the commonly-connected collector terminals of the transistor pair. The frequency converter can exhibit an excellent saturation characteristic and an excellent distortion characteristic even when operating from a low voltage and/or a low current.

FIELD OF THE INVENTION

The present invention relates to a frequency converter that multiplies the frequency of a high-frequency signal, such as a UHF, microwave, or millimeter wave, by a certain factor, or mixes high-frequency signals with each other in a wideband communication terminal or the like that conforms to a communication system such as a WCDMA system.

BACKGROUND OF THE INVENTION

FIG. 1is a schematic circuit diagram showing the structure of a prior art frequency converter. In the figure, reference numeral1denotes a power supply terminal to which a DC voltage Vcc is applied, reference numerals2aand2bdenote transistors each used for input of a local oscillation (LO) signal, reference numeral3adenotes a reference transistor, reference numeral5denotes a constant current source, reference numerals6aand6bdenote load resistors, reference numeral7adenotes a radio frequency (RF) signal input terminal, reference numerals8aand8bdenote local oscillation (LO) signal input terminals, reference numeral9denotes a reference bias terminal, reference numerals10aand10bdenote output terminals, reference numeral11adenotes a transistor pair that consists of the LO signal input transistors2aand2b, and reference numeral14denotes a transistor for input of a radio frequency (RF) signal. As shown inFIG. 1, in the prior art frequency converter, an RF signal is applied to the emitter-grounded RF signal input transistor14.

Next, a description will be made as to an operation of the prior art frequency converter.

A DC voltage Vcc, which is applied to the power supply terminal1of the prior art frequency converter as shown inFIG. 1, is then applied to the transistor pair11athat consists of the two LO signal input transistors2aand2band the RF signal input transistor14, and the reference transistor3aby way of the two load resistors6aand6b, respectively. The constant current source5supplies a constant current to a parallel circuit that consists of the transistor pair11aand the reference transistor3aby way of the RF signal input transistor14. A bias current is supplied to the reference transistor3aby way of the reference bias terminal9.

The RF signal input transistor14amplifies an RF signal that is applied to the base terminal thereof by way of the RF signal input terminal7a. On the other hand, the LO signal input transistor2aamplifies an LO signal of positive phase that is applied to the base terminal thereof by way of the LO signal input terminal8a, and the other LO signal input transistor2bamplifies another LO signal of negative phase that is applied to the base terminal thereof by way of the other LO signal input terminal8b. Thus, because the LO signal of positive phase and the other LO signal of negative phase are applied to the base terminals of the LO signal input transistors2aand2b, respectively, the transistor pair11ain which the collector terminals of these transistors are commonly connected to each other and the emitter terminals of these transistors are commonly connected to each other generates a signal having a frequency that is two times as high as that of the LO signals.

The sum of an electric current that flows through the transistor pair11aand an electric current that flows through the reference transistor3ais equal to an electric current that flows through the RF signal input transistor14, and is therefore equal to an electric current output from the constant current source5connected to the emitter terminal of the RF signal input transistor14. Because while the signal generated by the transistor pair11aand having a frequency that is two times as high as that of the LO signals changes the electric current that flows through the transistor pair11a, the RF signal input transistor14operates from the constant current from the constant current source5, a signal having a phase opposite to that of a change in the electric current that flows through the transistor pair11aflows through the reference transistor3a. Therefore, the prior art frequency converter as shown inFIG. 1serves as an even order harmonics frequency converter having a gain, which mixes the RF signal amplified by the RF signal input transistor14, the signal generated by the transistor pair11aand having a frequency that is two times as high as that of the LO signals, and the negative-phase signal that flows through the reference transistor3a, and outputs the mixed signal as a differential signal by way of the output terminals10aand10brespectively connected to the load resistors10aand10b.

A problem with the prior art frequency converter constructed as previously mentioned is that the saturation and distortion characteristics of the frequency converter are determined by the large signal characteristic of the RF signal input transistor14that is an active element, and therefore the saturation and distortion characteristics cannot be easily improved and degrade remarkably when the prior art frequency converter operates from a low voltage and/or a low current.

The present invention is proposed to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a frequency converter that can exhibit an excellent saturation characteristic and an excellent distortion characteristic even when operating from a low voltage and/or a low current because of a resistor that is a passive element and is disposed in an RF signal input circuit instead of a transistor.

DISCLOSURE OF THE INVENTION

In accordance with the present invention, there is provided a frequency converter including: a transistor pair having a first transistor and a second transistor respectively having first terminals commonly connected to each other and second terminals commonly connected to each other, the commonly-connected first terminals (referred to as a first common terminal from here on) being connected to a power supply terminal by way of a first passive element; a third transistor having a first terminal connected to the power supply terminal by way of a second passive element, and a second terminal connected to the commonly-connected second terminals (referred to as a second common terminal from here on) of the first and second transistors of the transistor pair; a third passive element having an end connected to the second common terminal of the transistor pair, and another end directly or indirectly grounded; and an output terminal connected to the first common terminal of the transistor pair, a first signal being applied to a third terminal of the first transistor, a second signal having a phase opposite to that of the first signal being applied to a third terminal of the second transistor, a third signal being applied to the second common terminal of the transistor pair, and a reference signal being applied to a third terminal of the third transistor.

As a result, the frequency converter can exhibit an excellent saturation characteristic and an excellent distortion characteristic even when operating from a low voltage and/or a low current.

The frequency converter in accordance with the present invention can include another output terminal connected to the first terminal of the third transistor.

As a result, the frequency converter can remove the in-phase component included in unnecessary frequency components of the output signal.

In the frequency converter in accordance with the present invention, the first to third passive elements are resistors. In the frequency converter in accordance with the present invention, the first to third passive elements are inductors. As a result, each transistor included in the frequency converter can be made to operate in a linear region without increase in a voltage that appears between the first and second terminals of each transistor.

The frequency converter in accordance with the present invention can include a constant current source connected between the other end of the third passive element and a ground.

As a result, the frequency converter can have a voltage conversion gain.

In the frequency converter in accordance with the present invention, each of the first to third transistors is a bipolar junction transistor having a collector terminal as the first terminal, an emitter terminal as the second terminal, and a base terminal as the third terminal.

In the frequency converter in accordance with the present invention, each of the first to third transistors is a field effect transistor having a drain terminal as the first terminal, a source terminal as the second terminal, and a gate terminal as the third terminal.

In accordance with the present invention, there is provided a frequency converter including: a first transistor pair having a first transistor and a second transistor respectively having first terminals commonly connected to each other and second terminals commonly connected to each other, the commonly-connected first terminals (referred to as a first common terminal from here on) being connected to a power supply terminal by way of a first passive element; a third transistor having a first terminal directly or indirectly connected to the power supply terminal, and a second terminal connected to the commonly-connected second terminals (referred to as a second common terminal from here on) of the first and second transistors of the first transistor pair; a second passive element having an end connected to the second common terminal of the first transistor pair, and another end directly or indirectly grounded; a first output terminal connected to the first common terminal of the first transistor pair; a second transistor pair having a fourth transistor and a fifth transistor respectively having first terminals commonly connected to each other and second terminals commonly connected to each other, the commonly-connected first terminals (referred to as a first common terminal from here on) being connected to the power supply terminal by way of a third passive element; a sixth transistor having a first terminal directly or indirectly connected to the power supply terminal, and a second terminal connected to the commonly-connected second terminals (referred to as a second common terminal from here on) of the fourth and fifth transistors of the second transistor pair; a fourth passive element having an end connected to the second common terminal of the second transistor pair, and another end directly or indirectly grounded; and a second output terminal connected to the first common terminal of the second transistor pair, a first signal being applied to third terminals of the first and fifth transistors, a second signal having a phase opposite to that of the first signal being applied to third terminals of the second and fourth transistors, a third signal being applied to the second common terminal of the first transistor pair, a fourth signal having a phase opposite to that of the third signal being applied to the second common terminal of the second transistor pair, and a reference signal being applied to third terminals of the third and sixth transistors.

As a result, the frequency converter can exhibit an excellent saturation characteristic and an excellent distortion characteristic even when operating from a low voltage and/or a low current. The frequency converter can further suppress the odd order harmonics of the third signal, and a mixture of even order components of the first signal and even order components of the third signal.

In the frequency converter in accordance with the present invention can, the first terminal of the third transistor is connected to the power supply terminal by way of the fifth passive element, and the first terminal of the sixth transistor is connected to the power supply terminal by way of the sixth passive element.

In the frequency converter in accordance with the present invention can, the first terminal of the third transistor is connected to the second output terminal and is also connected to the power supply terminal by way of the third passive element, and the first terminal of the sixth transistor is connected to the first output terminal and is also connected to the power supply terminal by way of the first passive element.

As a result, the circuit structure of the frequency converter can be simplified, and the second order component of the first signal can be further suppressed.

In the frequency converter in accordance with the present invention can, the first to fourth passive elements are resistors.

In the frequency converter in accordance with the present invention, the first to fourth passive elements are inductors.

As a result, each transistor included in the frequency converter can be made to operate in a linear region without increase in a voltage that appears between the first and second terminals of each transistor.

In the frequency converter in accordance with the present invention, the first to sixth passive elements are resistors. In the frequency converter in accordance with the present invention, the first to sixth passive elements are inductors. As a result, each transistor included in the frequency converter can be made to operate in a linear region without increase in a voltage that appears between the first and second terminals of each transistor.

The frequency converter in accordance with the present invention can include a constant current source connected between the other ends of the third and fourth passive element and a ground.

As a result, the frequency converter can have a voltage conversion gain.

The frequency converter in accordance with the present invention can include a resistor connected between the other ends of the third and fourth passive element and a ground. As a result, variations in the performance of the frequency converter due to temperature variations can be prevented because no constant current source is used.

In the frequency converter in accordance with the present invention, each of the first to sixth transistors is a bipolar junction transistor having a collector terminal as the first terminal, an emitter terminal as the second terminal, and a base terminal as the third terminal.

In the frequency converter in accordance with the present invention, each of the first to sixth transistors is a field effect transistor having a drain terminal as the first terminal, a source terminal as the second terminal, and a gate terminal as the third terminal.

PREFERRED EMBODIMENTS OF THE INVENTION

In order to explain the present invention in greater detail, the preferred embodiments will be described below with reference to the accompanying figures.

FIG. 2is a schematic circuit diagram showing the structure of a frequency converter in accordance with embodiment 1 of the present invention. In the figure, reference numeral1denotes a power supply terminal to which a DC voltage Vcc is applied, reference numerals2aand2bdenote transistors (i.e., first and second transistors) each used for input of a local oscillation (LO) signal, reference numeral3adenotes a reference transistor (i.e., a third transistor) used for input of a reference signal, reference numeral4adenotes a resistor (i.e., a third passive element) used for input of a radio frequency (RF) signal, reference numeral5denotes a constant current source, reference numerals6aand6bdenote load resistors (i.e., first and second passive elements), reference numeral7adenotes a radio frequency (RF) signal input terminal, reference numerals8aand8bdenote local oscillation (LO) signal input terminals, reference numeral9denotes a reference bias terminal to which the reference signal is applied, reference numeral1adenotes an output terminal, and reference numeral11adenotes a transistor pair that consists of the LO signal input transistors2aand2beach used for input of an LO signal.

As shown inFIG. 2, the LO signal input transistors2aand2b, which constitute the transistor pair11a, have collector terminals (i.e., first terminals) that are commonly connected to each other, and emitter terminals (i.e., second terminals) that are commonly connected to each other, respectively. The RF signal input terminal7a, one end of the RF signal input resistor4aand an emitter terminal of the reference transistor3aare connected to the emitter terminals (referred to as a common emitter terminal (i.e., a second common terminal) from here on) of the LO signal input transistors2aand2b, which are commonly connected to each other. Another end of the RF signal input resistor4ais connected to a ground by way of the constant current source5.

The collector terminals (referred to as a common collector terminal (i.e., a first common terminal) from here on) of the LO signal input transistors2aand2b, which are commonly connected to each other, are connected to the output terminal10aand one end of the load resistor6a, and another end of the load resistor6ais connected to the power supply terminal1. One end of the other load resistor6bis connected to the power supply terminal1, and another end of the other load resistor6bis connected to a collector terminal of the reference transistor3a. Furthermore, base terminals of the LO signal input transistors2aand2bare connected to the LO signal input terminals8aand8b, respectively, and a base terminal of the reference transistor3ais connected to the reference bias terminal9.

Next, a description will be made as to an operation of the frequency converter in accordance with embodiment 1 of the present invention.

The frequency converter in accordance with this embodiment 1 mixes an RF signal (i.e., a third signal) applied thereto by way of the RF signal input terminal7aand a signal having a frequency that is two times as high as those of an LO signal of positive phase (i.e., a first signal) applied thereto by way of the LO signal input terminal8aand another LO signal of negative phase (i.e., a second signal) applied thereto by way of the other LO signal input terminal8b, the signal being generated by the transistor pair11afrom the LO signal of positive phase and the other LO signal of negative phase, so as to generate a mixed signal, and then outputs the mixed signal by way of the output terminal10a.

A DC voltage Vcc applied to the power supply terminal1of the frequency converter is then applied to both the transistor pair11a, which consists of the LO signal input transistors2aand2b, and the reference transistor3aby way of the two load resistors6aand6b. Constant currents are supplied from the constant current source5to the LO signal input transistors2aand2band the reference transistor3a, respectively. A bias current (i.e., a reference signal) is supplied to the base terminal of the reference transistor3aby way of the reference bias terminal9.

The LO signal input transistor2aamplifies the LO signal of positive phase applied to the base terminal thereof by way of the LO signal input terminal8a. Similarly, the LO signal input transistor2bamplifies the other LO signal of negative phase applied to the base terminal thereof by way of the LO input terminal8b. Thus, because the LO signal of positive phase and the other LO signal of negative phase are applied to the base terminals of the two LO signal input transistors2aand2b, respectively, the transistor pair11ain which the collector terminals of those transistors2aand2bare commonly connected to each other and the emitter terminals of those transistors2aand2bare also commonly connected to each other generates a signal having a frequency that is two times as high as that of the two LO signals.

The sum of an electric current that flows through the transistor pair11aand an electric current that flows through the reference transistor3ais equal to an electric current that flows through the RF signal input resistor4a, i.e., an electric current output from the constant current source5. Therefore, because the signal having a frequency that is two times as high as that of the LO signals and generated by the transistor pair11acauses a change in the electric current that flows through the transistor pair11awhile the electric current that flows in the entire parallel circuit consists of the transistor pair11aand the reference transistor3a, i.e., the electric current that flows through the RF signal input resistor4ais maintained constant by the constant current source5, a signal having a phase opposite to that of the change in the electric current that flows through the transistor pair11aflows through the reference transistor3a. Therefore, the frequency converter in accordance with this embodiment 1 serves as an even order harmonics frequency converter that outputs, as an intermediate frequency (IF) signal, a mixed signal (e.g., a signal having a frequency of (fRF−2fLO), where fRFis the frequency of the RF signal and fLOis the frequency of the LO signals), into which the RF signal, the positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the transistor pair11and the negative-phase signal flowing through the reference transistor3aare mixed, by way of the output terminal10aconnected between the load resistor6aand the common collector terminal of the transistor pair11a.

The frequency converter in accordance with this embodiment 1 can thus exhibit a high saturation characteristic and a high distortion characteristic because it does not use, as the RF signal input element, any transistor that is an active element. When the resistances of the load resistors6aand6bare suitably set and the electric current output from the constant current source5is suitably set, the frequency converter in accordance with this embodiment 1 can also have a voltage conversion gain.

The frequency converter in accordance with this embodiment 1 is not limited to the above-mentioned downconverter and can be alternatively an upconverter that outputs a mixed signal into which an IF signal applied to the RF signal input terminal instead of the RF signal, the positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the transistor pair11and the negative-phase signal flowing through the reference transistor3aare mixed, e.g., an RF signal having a frequency of (fIF+2fLO) (fIFis the frequency of the IF signal) by way of the output terminal10a.

As mentioned above, because the frequency converter in accordance with this embodiment 1 does not use, as the RF signal input element, any transistor that is an active element, this embodiment offers an advantage of being able to exhibit a high saturation characteristic and a high distortion characteristic.

Numerous variants can be made in this embodiment 1 mentioned above.FIG. 3is a schematic circuit diagram showing the structure of a frequency converter in accordance with a variant of embodiment 1. In this variant, the transistor pair11aconsists of two field-effect transistors20aand20b, and a reference field-effect transistor30aused for input of a reference signal is disposed instead of the reference transistor3a. In this case, the collector terminal, emitter terminal, and base terminal of each bipolar junction transistor ofFIG. 2are replaced by the drain terminal, source terminal, and gate terminal of each field-effect transistor.

FIG. 4is a schematic circuit diagram showing the structure of a frequency converter in accordance with another variant of embodiment 1. In this variant, the load resistors6aand6b, and the RF signal input resistor4aare replaced by inductors60a,60b, and40a, respectively. As a result, even though a DC bias electric current increases, each transistor included in the frequency converter can be made to operate in a linear region without increase in the collector-emitter voltage of each transistor. All the resistors of the frequency converter need not be replaced by inductors. For example, as shown inFIGS. 5 and 6, only either of the load resistors6aand6band the RF signal input resistor4amay be replaced by inductors.

FIG. 7is a schematic circuit diagram showing the structure of a frequency converter in accordance with another variant of embodiment 1. In this variant, the constant current source5is omitted, and the other end of the RF signal input resistor4ais connected directly with the ground. Thus, even when the frequency converter does not include the constant current source5, because the electric current flowing through the entire parallel circuit that consists of the transistor pair11aand the reference transistor3ais maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the RF signal input resistor4a, the same advantage is provided.

FIG. 8is a schematic circuit diagram showing the structure of a frequency converter in accordance with embodiment 2 of the present invention. In the figure, the same reference numerals as shown inFIG. 2denotes the same components as those of the frequency converter in accordance with above-mentioned embodiment 1 or like components, and therefore the explanation of those components will be omitted hereafter. Furthermore, inFIG. 8, reference numeral10bdenotes a second output terminal connected between a load resistor6band a collector terminal of a reference transistor3b.

Next, a description will be made as to an operation of the frequency converter in accordance with embodiment 2 of the present invention.

The frequency converter in accordance with this embodiment 2 operates basically in the same way that that in accordance with above-mentioned embodiment 1 does. Next, only a characterized operation of the frequency converter in accordance with this embodiment 2 will be explained.

The frequency converter in accordance with this embodiment 2 outputs, as an output signal, a differential signal by way of a differential terminal pair that consists of a first output terminal10aand the second output terminal10b. As a result, the frequency converter in accordance with this embodiment 2 can remove the in-phase component included in unnecessary frequency components of the output signal.

Numerous variants can be made in this embodiment 2, as in the case of above-mentioned embodiment 1. A transistor pair11aconsists of two field-effect transistors20aand20b, and a reference field-effect transistor30aused for input of a reference signal is disposed instead of a reference transistor3a, as in the case as shown inFIG. 3. In this case, the collector terminal, emitter terminal, and base terminal of each bipolar junction transistor ofFIG. 8are replaced by the drain terminal, source terminal, and gate terminal of each field-effect transistor.

In another variant, load resistors6aand6b, and an RF signal input resistor4aare replaced by inductors60a,60b, and40a, respectively, as in the case as shown inFIG. 4. As a result, even though a DC bias electric current increases, each transistor included in the frequency converter can be made to operate in a linear region without increase in the collector-emitter voltage of each transistor. All resistors of the frequency converter need not be replaced by inductors. For example, as in the cases as shown inFIGS. 5 and 6, only either of the load resistors6aand6band the RF signal input resistor4amay be replaced by inductors.

In another variant, a constant current source5is omitted, and an end of the RF signal input resistor4ais connected directly with a ground, as in the case as shown inFIG. 7. Thus, even when the frequency converter does not include the constant current source5, because an electric current flowing through an entire parallel circuit that consists of the transistor pair11aand the reference transistor3ais maintained constant by both a DC voltage Vcc applied to a power supply terminal1and the RF signal input resistor4a, the same advantage is provided.

FIG. 9is a schematic circuit diagram showing the structure of a frequency converter in accordance with embodiment 3 of the present invention. In the figure, the same reference numerals as shown inFIG. 8denotes the same components as those of the frequency converter in accordance with above-mentioned embodiment 2 or like components, and therefore the explanation of those components will be omitted hereafter. InFIG. 9, reference numerals2cand2ddenote LO signal input transistors (i.e., fourth and fifth transistors) each used for input of a local oscillation (LO) signal, reference numeral3bdenotes a second reference transistor (i.e., a sixth transistor) used for input of a reference signal, reference numeral4bdenotes a second RF signal input resistor (i.e., a fourth passive element) used for input of a radio frequency (RF) signal, reference numerals6cand6ddenote load resistors, reference numeral7bdenotes a second radio frequency (RF) signal input terminal, and reference numeral11bdenotes a second transistor pair that consists of the LO signal input transistors2cand2d.

As shown inFIG. 9, in the frequency converter in accordance with this embodiment 3, two parallel circuits, each of which is the same as that as shown inFIG. 8that constitutes the frequency converter in accordance with above-mentioned embodiment 2, are connected in parallel between a power supply terminal1and a ground. A first RF signal input terminal7ais connected between a first RF signal input resistor4a(i.e., a second passive element) and a common emitter terminal of a first transistor pair11a. On the other hand, the second RF signal input terminal7bis connected between the second RF signal input resistor4band a common emitter terminal of the second transistor pair11b. An LO signal input terminal8ais connected to a base terminal of an LO signal input transistor2aof the first transistor pair11aand a base terminal of the LO signal input transistor2dof the second transistor pair11b. On the other hand, another LO signal input terminal8bis connected to a base terminal of another LO signal input transistor2bof the first transistor pair11aand a base terminal of the other LO signal input transistor2cof the second transistor pair11b. A first output terminal10ais connected between a load resistor6a(i.e., a first passive element) and a common collector terminal of the first transistor pair11a. On the other hand, a second output terminal10bis connected between the load resistor6c(i.e., a third passive element) and a common collector terminal of the second transistor pair11b. Furthermore, a first reference transistor3aand the second reference transistor3bhave base terminals connected commonly with a reference bias terminal9, collector terminals connected to the power supply terminal1by way of the load resistors6band6d(i.e., fifth and sixth passive elements), respectively, and emitter terminals connected to the common emitter terminals of the first and second transistor pairs11aand11b, respectively.

Next, a description will be made as to an operation of the frequency converter in accordance with embodiment 3 of the present invention.

The frequency converter in accordance with this embodiment 3 operates basically in the same way that that in accordance with above-mentioned embodiment 2 does. Next, only a characterized operation of the frequency converter in accordance with this embodiment 3 will be explained.

An RF signal (i.e., a third signal) of positive phase is applied to the common emitter terminal of the first transistor pair11aby way of the first RF signal input terminal7a, and another RF signal (i.e., a fourth signal) of negative phase is applied to the common emitter terminal of the second transistor pair11bby way of the second RF signal input terminal7b. Therefore, the frequency converter in accordance with this embodiment 3 serves as an even order harmonics frequency converter that outputs, as an intermediate frequency (IF) signal, a differential signal consisting of both a mixed signal (e.g., a signal having a frequency of (fRF−2fLO), where fRFis the frequency of the RF signals and fLOis the frequency of the LO signals), into which the RF signal of positive phase, a positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the first transistor pair11aand a negative-phase signal flowing through the first reference transistor3aare mixed, and a mixed signal (e.g., a signal having a frequency of (fRF−2fLO), into which the other RF signal of negative phase, a positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the second transistor pair11band a negative-phase signal flowing through the second reference transistor3bare mixed, by way of the first and second output terminals10aand10b.

Because the frequency converter in accordance with this embodiment 3 thus has a balanced-type structure, receives the RF signal of positive phase and the other RF signal of negative phase, and outputs a differential signal that consists of mixed signals respectively including the RF signal of positive phase and the other RF signal of negative phase, the same advantage as offered by above-mentioned embodiment 1 is provided. The frequency converter in accordance with this embodiment 3 can further suppress the odd order harmonics of the RF signals, and a mixture of even order components of the LO signals and even order components of the RF signals, as compared with that of above-mentioned embodiment 1. Therefore, because the frequency converter in accordance with this embodiment 3 facilitates an output of a mixture wave of the second order components of the LO signals and the first order components of the RF signals, which can be general output signals from a harmonic mixer, and suppresses unnecessary spurious components, the structure of a filter circuit intended for reduction of spurious components and connected as an output stage of the frequency converter can be simplified.

The frequency converter in accordance with this embodiment 3 is not limited to the above-mentioned downconverter and can be alternatively an upconverter that outputs a differential signal consisting of both a mixed signal into which an IF signal of positive phase applied to the first RF signal input terminal instead of the RF signal of positive, the positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the first transistor pair11aand the negative-phase signal flowing through the first reference transistor3aare mixed, e.g., an RF signal having a frequency of (fIF+2fLO) (fIFis the frequency of the IF signal) and a mixed signal into which another IF signal of negative phase applied to the second RF signal input terminal instead of the other RF signal of negative phase, the positive-phase signal having a frequency that is two times as high as that of the LO signals and generated by the second transistor pair11band the negative-phase signal flowing through the second reference transistor3bare mixed, e.g., an RF signal having a frequency of (fIF+2fLO) by way of the first and second output terminals10aand10b, respectively.

Numerous variants can be made in this embodiment 3 mentioned above.FIG. 10is a schematic circuit diagram showing the structure of a frequency converter in accordance with a variant of embodiment 3. In this variant, the first transistor pair11aconsists of two field-effect transistors20aand20band the second transistor pair11bconsists of two field-effect transistors20cand20d, and reference field-effect transistors30aand30beach used for input of a reference signal are disposed instead of the first and second reference transistors3aand3b. In this case, the collector terminal, emitter terminal, and base terminal of each bipolar junction transistor ofFIG. 9are replaced by the drain terminal, source terminal, and gate terminal of each field-effect transistor.

FIG. 11is a schematic circuit diagram showing the structure of a frequency converter in accordance with another variant of embodiment 3. In this variant, the load resistors6ato6d, and the RF signal input resistors4aand4bare replaced by inductors60ato60d, and40aand40b, respectively. As a result, even though a DC bias electric current increases, each transistor included in the frequency converter can be made to operate in a linear region without increase in the collector-emitter voltage of each transistor. All the resistors of the frequency converter need not be replaced by inductors. For example, as shown inFIGS. 12 and 13, only either of the load resistors6ato6dand the RF signal input resistors4aand4bmay be replaced by inductors.

FIG. 14is a schematic circuit diagram showing the structure of a frequency converter in accordance with another variant of embodiment 3. In this variant, a constant current source5is omitted, and the other ends of the RF signal input resistors4aand4bare connected directly with the ground. Thus, even when the frequency converter does not include the constant current source5, because an electric current flowing through a parallel circuit that consists of the first transistor pair11aand the first reference transistor3ais maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the first RF signal input resistor4aand an electric current flowing through another parallel circuit that consists of the second transistor pair11band the second reference transistor3bis maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the second RF signal input resistor4b, the same advantage is provided.

FIG. 15is a schematic circuit diagram showing the structure of a frequency converter in accordance with another variant of embodiment 3. In this variant, the constant current source5is replaced by a resistor12. As a result, variations in the performance of the frequency converter due to temperature variations of the constant current source5, which is usually constructed of a transistor, can be prevented.

FIG. 16is a schematic circuit diagram showing the structure of a frequency converter in accordance with embodiment 4 of the present invention. In the figure, the same reference numerals as shown inFIG. 9denotes the same components as those of the frequency converter in accordance with above-mentioned embodiment 3 or like components, and therefore the explanation of those components will be omitted hereafter.

The frequency converter in accordance with this embodiment 4 differs from that in accordance with above-mentioned embodiment 3 in that the load resistors6band6d(i.e., fifth and sixth passive elements) as shown inFIG. 9are omitted. In other words, the collector terminals of first and second reference transistors3aand3bare connected directly with a power supply terminal1.

Next, a description will be made as to an operation of the frequency converter in accordance with embodiment 4 of the present invention.

The frequency converter in accordance with this embodiment 4 operates in the same way that that in accordance with above-mentioned embodiment 3 does. In other words, the frequency converter in accordance with this embodiment 4 outputs a differential signal byway of first and second output terminals10aand10brespectively connected to load resistors6aand6c, like that in accordance with above-mentioned embodiment 3.

Therefore, even though the frequency converter does not include the load resistors6band6das shown inFIG. 9, this embodiment 4 can provide the same advantage as offered by above-mentioned embodiment 3, and the circuit structure of the frequency converter can be simplified.

Numerous variants can be made in this embodiment 4, as in above-mentioned embodiment 3. In a variant, each of first and second transistor pairs11aand11bconsists of two field-effect transistors, as in the case shown inFIG. 10, and reference field-effect transistors each used for input of a reference signal are disposed instead of the first and second reference transistors3aand3b. In this case, the collector terminal, emitter terminal, and base terminal of each bipolar junction transistor are replaced by the drain terminal, source terminal, and gate terminal of each field-effect transistor.

In another variant, as in the case shown inFIG. 11, the load resistors6ato6d, and RF signal input resistors4aand4bare replaced by inductors, respectively. As a result, even though a DC bias electric current increases, each transistor included in the frequency converter can be made to operate in a linear region without increase in the collector-emitter voltage of each transistor. All the resistors of the frequency converter need not be replaced by inductors, as in the cases shown inFIGS. 12 and 13, only either of the load resistors6ato6dand the RF signal input resistors4aand4bmay be replaced by inductors.

In a further variant, as in the case shown inFIG. 14, a constant current source5is omitted and other ends of the RF signal input resistors4aand4bare connected directly with a ground. Thus, even when the frequency converter does not include the constant current source5, because an electric current flowing through a parallel circuit that consists of the first transistor pair11aand the first reference transistor3ais maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the first RF signal input resistor4aand an electric current flowing through another parallel circuit that consists of the second transistor pair11band the second reference transistor3bis maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the second RF signal input resistor4b, the same advantage is provided.

In another variant, as in the case shown inFIG. 15, the constant current source5is replaced by a resistor. As a result, variations in the performance of the frequency converter due to temperature variations of the constant cur-rent source5, which is usually constructed of a transistor, can be prevented.

FIG. 17is a schematic circuit diagram showing the structure of a frequency converter in accordance with embodiment 5 of the present invention. In the figure, the same reference numerals as shown inFIG. 16denotes the same components as those of the frequency converter in accordance with above-mentioned embodiment 4 or like components, and therefore the explanation of those components will be omitted hereafter.

Though the frequency converter in accordance with this embodiment 5 has a circuit structure similar to that of the frequency converter in accordance with above-mentioned embodiment 4, the frequency converter in accordance with this embodiment 5 differs from that in accordance with embodiment 4 in that a collector terminal of a first reference transistor3ais connected to a second output terminal10b, i.e., between a load resistor6cand a common collector terminal of a second transistor pair11b, and a collector terminal of a second reference transistor3bis connected to a first output terminal10a, i.e., between a load resistor6aand a common collector terminal of a first transistor pair11a.

Next, a description will be made as to an operation of the frequency converter in accordance with embodiment 5 of the present invention.

The frequency converter in accordance with this embodiment 5 operates basically in the same way that that in accordance with above-mentioned embodiment 4 does. Next, only a characterized operation of the frequency converter in accordance with this embodiment 5 will be explained.

In the frequency converter in accordance with above-mentioned embodiment 3 shown inFIG. 9, although the first and second reference transistors3aand3bsuppress the second order components of LO signals, voltages that respectively appear at the collector terminals of the first and second reference transistors3aand3bvary according to electric currents that respectively flow through the resistors6band6d. As a result, the second order components of the LO signals cannot be sufficiently suppressed. In contrast, in the frequency converter in accordance with this embodiment 5, because a voltage that appears at a common collector terminal of the first transistor pair11ais equal to a voltage that appears at a collector terminal of the second reference transistor3bregardless of an electric current that flows through the resistor6aand a voltage that appears at a common collector terminal of the second transistor pair11bis equal to a voltage that appears at a collector terminal of the first reference transistor3aregardless of an electric current that flows through the resistor6c, the appearance of the second order components of the LO signals at the first and second output terminals10aand10bcan be further suppressed.

As mentioned above, this embodiment 5 provides the same advantage as offered by above-mentioned embodiment 4, and an advantage of further suppressing the appearance of the second order components of the LO signals at the first and second output terminals10aand10b.

Numerous variants can be made in this embodiment 5, as in above-mentioned embodiment 3. In a variant, each of first and second transistor pairs11aand11bconsists of two field-effect transistors, as in the case shown inFIG. 10, and reference field-effect transistors each used for input of a reference signal are disposed instead of the first and second reference transistors3aand3b. In this case, the collector terminal, emitter terminal, and base terminal of each bipolar junction transistor are replaced by the drain terminal, source terminal, and gate terminal of each field-effect transistor.

In another variant, as in the case shown inFIG. 11, the load resistors6ato6d, and RF signal input resistors4aand4bare replaced by inductors, respectively. As a result, even though the DC bias electric current increases, each transistor included in the frequency converter can be made to operate in a linear region without increase in the collector-emitter voltage of each transistor. All the resistors of the frequency converter need not be replaced by inductors, as in the cases shown inFIGS. 12 and 13, only either of the load resistors6ato6dand the RF signal input resistors4aand4bmay be replaced by inductors.

In a further variant, as in the case shown inFIG. 14, a constant current source5is omitted and other ends of the RF signal input resistors4aand4bare connected directly with a ground. Thus, even when the frequency converter does not include the constant current source5, because an electric current flowing through an entire parallel circuit that consists of the first transistor pair11aand the first reference transistor3ais maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the first RF signal input resistor4aand an electric current flowing through an entire parallel circuit that consists of the second transistor pair11band the second reference transistor3bis maintained constant by both the DC voltage Vcc applied to the power supply terminal1and the second RF signal input resistor4b, the same advantage is provided.

In another variant, as in the case shown inFIG. 15, the constant current source5is replaced by a resistor. As a result, variations in the performance of the frequency converter due to temperature variations of the constant current source5, which is usually constructed of a transistor, can be prevented.

INDUSTRIAL APPLICABILITY

As mentioned above, the frequency converter in accordance with the present invention is suitable for multiplying the frequency of a high-frequency signal, such as a UHF, microwave, or millimeter wave, by a certain factor, or mixing high-frequency signals with each other in a wideband communication terminal or the like that conforms to a communication system such as a WCDMA system.