Mixer

Abstract

This mixer comprises: a transistor (Q101) to which a positive phase-side IF signal is input; a transistor (Q102) to which an opposite phase-side IF signal is input; a transistor (Q103) to which an LO signal is input; and a synthesizer (105) which synthesizes, in opposite phase, RF frequency components output from drain terminals of the transistors (Q101, Q102), and synthesizes, in phase, IF frequency components output from the drain terminals of the transistors (Q101, Q102).

Description

Technical Field

[0001] The present invention relates to a mixer that performs frequency conversion of an electrical signal.

Background Art

[0002] In circuits constituting a wireless communication transceiver, radar, etc., a mixer is an important circuit that plays a role in frequency conversion. Among mixers, as those with an easy configuration, there are generally three types: a single-ended mixer, a single-balanced mixer, and a double-balanced mixer.

[0003] FIG. 11 is a circuit diagram of a single-ended mixer disclosed in Non-Patent Document 1. The single-ended mixer includes a transistor Q100 having a gate terminal connected to an LO (Local Oscillator) signal terminal 101, a source terminal connected to ground, and a drain terminal connected to an IF (Intermediate Frequency) signal terminal 100 and an RF (Radio Frequency) signal terminal 102. In this circuit, when an IF signal is input to the IF signal terminal 100 and an LO signal is input to the LO signal terminal 101, an RF signal is output from the RF signal terminal 102.

[0004] FIG. 12 is a circuit diagram of a single-balanced mixer disclosed in Non-Patent Document 2. The single-balanced mixer includes a transistor Q101 having a gate terminal connected to a positive-phase IF signal terminal 100p, a transistor Q102 having a gate terminal connected to a negative-phase IF signal terminal 100n, a tail transistor Q103 having a gate terminal connected to an LO signal terminal 101, a source terminal connected to ground, and a drain terminal connected to the source terminals of the transistors Q101 and Q102, and a balun 103 that combines the outputs of the drain terminals of the transistors Q101 and Q102 in antiphase.

[0005] IFp is the IF signal on the positive phase side, and IFn is the IF signal on the negative phase side. In the circuit of FIG. 12, when the IF signal on the positive phase side is input to the IF signal terminal 100p, the IF signal on the negative phase side is input to the IF signal terminal 100n, and the LO signal is input to the LO signal terminal 101, an RF signal is output from the RF signal terminal 102.

[0006] FIG. 13 is a circuit diagram of a double-balanced mixer disclosed in Non-Patent Document 3. The double-balanced mixer includes a transistor Q104 whose gate terminal is connected to the IF signal terminal 100p on the positive phase side, a transistor Q105 whose gate terminal is connected to the IF signal terminal 100n on the negative phase side, a transistor Q106 whose gate terminal is connected to the LO signal terminal 101p on the positive phase side and whose source terminal is connected to the drain terminal of the transistor Q104, a transistor Q107 whose gate terminal is connected to the LO signal terminal 101n on the negative phase side and whose source terminal is connected to the drain terminal of the transistor Q104, a transistor Q108 whose gate terminal is connected to the LO signal terminal 101n on the negative phase side and whose source terminal is connected to the drain terminal of the transistor Q105, a transistor Q109 whose gate terminal is connected to the LO signal terminal 101p on the positive phase side and whose source terminal is connected to the drain terminal of the transistor Q105, a current source IS100 that supplies a constant current to the transistors Q104 and Q105, and a balun 104 that synthesizes the outputs of the drain terminals of the transistors Q106 and Q108 and the outputs of the drain terminals of the transistors Q107 and Q109 in opposite phases.

[0007] LOp is the LO signal on the positive phase side, and LOn is the LO signal on the negative phase side. In the circuit of FIG. 13, when the LO signal on the positive phase side is input to the LO signal terminal 101p, the LO signal on the negative phase side is input to the LO signal terminal 101n, the IF signal on the positive phase side is input to the IF signal terminal 100p, and the IF signal on the negative phase side is input to the IF signal terminal 100n, an RF signal is output from the RF signal terminal 102.

[0008] On the one hand, in recent years, with the improvement of data rate, there has been a demand for a mixer that operates at high frequencies and has a wide bandwidth. Furthermore, for the mixer on the transmission side, it is required to have high performance in suppressing the component where the IF signal leaks to the RF signal terminal (IF rejection) and the component where the LO signal leaks to the RF signal terminal (LO rejection).

[0009] The single-ended mixer can be composed of only one diode or transistor, so it has excellent broadband characteristics, but there is a problem that the suppression performance of the IF signal and the LO signal is low. The double-balanced mixer can achieve high suppression performance for both the IF signal and the LO signal, but there is a problem that it is difficult to achieve a wide bandwidth because many signal wiring crossings that cause bandwidth degradation are required.

[0010] The single-balanced mixer has few signal wiring crossings and can achieve a relatively wide bandwidth, but there is a problem that it can only suppress either the IF signal or the LO signal. As described above, in the conventional technology, there has been a problem that it is difficult to realize a mixer that has a wide bandwidth and high suppression performance for both the IF signal and the LO signal.

Prior Art Documents

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

[0012] The present invention is made to solve the above problems, and an object thereof is to provide a mixer that is broadband and can significantly reduce the leakage to the RF signal terminals of the IF signal and the LO signal. [Means for Solving the Problems]

[0013] The mixer of the present invention includes: a first transistor to which an in-phase IF signal is input to a gate terminal; a second transistor to which an anti-phase IF signal is input to a gate terminal; a third transistor to which an LO signal is input to a gate terminal, a source terminal of which is connected to ground, and a drain terminal of which is connected to source terminals of the first and second transistors; and a synthesizer configured to synthesize components in an RF frequency band output from a drain terminal of the first transistor and components in an RF frequency band output from a drain terminal of the second transistor in anti-phase, and to synthesize components in an IF frequency band output from a drain terminal of the first transistor and components in an IF frequency band output from a drain terminal of the second transistor in in-phase.

[0014] In one configuration example of the mixer of the present invention, the synthesizer is a rat-race coupler, and includes: a first terminal connected to a drain terminal of the first transistor; a second terminal connected to a drain terminal of the second transistor; a third terminal that outputs an RF signal; a first transmission line having a length of λLO / 2 (λLO is a wavelength of the LO signal) that connects the first terminal and the second terminal; a second transmission line having a length of λLO / 4 that connects the first terminal and the third terminal; and a third transmission line having a length of 3λLO / 4 that connects the second terminal and the third terminal. In one configuration example of the mixer of the present invention, when a wavelength of a signal having the highest frequency in the IF signal is λIF and a wavelength of the LO signal is λLO, the relationship λLO = α × λIF (0 < α ≦ 0.12) is satisfied. In one configuration example of the mixer of the present invention, the first transmission line has a folded-back portion in the middle from the first terminal to the second terminal disposed near the first terminal. Also, one configuration example of the mixer of the present invention is characterized in that capacitors are further inserted between the drain terminal of the first transistor and the first terminal of the synthesizer, and between the drain terminal of the second transistor and the second terminal of the synthesizer, respectively.

Advantages of the Invention

[0015] According to the present invention, a synthesizer connected to the drain terminals of the first and second transistors is provided, and components in the RF frequency band output from the drain terminals of the first and second transistors are synthesized in antiphase, and components in the IF frequency band output from the drain terminals of the first and second transistors are synthesized in phase, thereby realizing a mixer capable of significantly reducing the leakage of the IF signal and the LO signal to the RF signal terminals in a wide band.

Brief Description of the Drawings

[0016]

Figure 1

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BEST MODE FOR CARRYING OUT THE INVENTION

[0017] [First Embodiment] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a mixer according to a first embodiment of the present invention. The mixer of this embodiment is a single-balanced mixer, and includes a transistor Q101 having a gate terminal connected to the positive-phase IF signal terminal 100p, a transistor Q102 having a gate terminal connected to the negative-phase IF signal terminal 100n, and a tail transistor Q103 having a gate terminal connected to the LO signal terminal 101, a source terminal connected to ground, and a drain terminal connected to the source terminals of the transistors Q101 and Q102.

[0018] Furthermore, the mixer of this embodiment includes a synthesizer 105 having a first terminal connected to the drain terminal of the transistor Q101, a second terminal connected to the drain terminal of the transistor Q102, synthesizing the components in the RF frequency band output from the drain terminals of the transistors Q101 and Q102 in antiphase, and synthesizing the components in the IF frequency band output from the drain terminals of the transistors Q101 and Q102 in phase, and outputting an RF signal from a third terminal (RF signal terminal 102).

[0019] The operation of the mixer in this embodiment will be described in detail below. In this embodiment, the frequency of the IF signal is defined as fIF, and the frequency of the LO signal is defined as fLO. The frequency spectrum of the in-phase IF signal (IFp) is shown in Fig. 2(a), the frequency spectrum of the anti-phase IF signal (IFn) is shown in Fig. 2(b), and the frequency spectrum of the LO signal is shown in Fig. 2(c). The frequency spectrum of the output RFp of the transistor Q101 is shown in Fig. 3(a), the frequency spectrum of the output RFn of the transistor Q102 is shown in Fig. 3(b), and the frequency spectrum of the output of the synthesizer 105 is shown in Fig. 3(c). BIF in Fig. 3 indicates the IF frequency band, and BRF indicates the RF frequency band.

[0020] When the in-phase IF signal is input to the transistor Q101, the anti-phase IF signal is input to the transistor Q102, and the LO signal is input to the tail transistor Q103, signals including components of frequencies fIF, fLO - fIF, fLO, and fLO + fIF are output to the differential outputs RFn and RFp of the differential pair transistors Q101 and Q102, respectively.

[0021] When the synthesizer 105 is connected to the drain terminals of the transistors Q101 and Q102, and the components in the RF frequency band of the differential outputs RFn and RFp are synthesized in anti-phase, and the components in the IF frequency band are synthesized in in-phase, both the LO suppression function and the IF suppression function can be realized as described below.

[0022] Since the components of the LO signal included in the differential outputs RFn and RFp exist in-phase in the RF frequency band respectively, they are synthesized in anti-phase by the synthesizer 105 and cancel each other out. Since the components of the IF signal included in the differential outputs RFn and RFp exist in anti-phase in the IF frequency band respectively, they are synthesized in in-phase by the synthesizer 105 and cancel each other out.

[0023] On the one hand, since the components of the frequency fLO - fIF included in the differential outputs RFn and RFp exist in opposite phases in the RF frequency band respectively, when they are combined in opposite phases by the synthesizer 105, the signal intensity doubles and is output to the RF signal terminal 102. Similarly, since the components of the frequency fLO + fIF included in the differential outputs RFn and RFp exist in opposite phases in the RF frequency band respectively, the signal intensity doubles and is output to the RF signal terminal 102.

[0024] To verify the effects of this embodiment, simulations of the conversion gain and the suppression performance of the IF signal and the LO signal were performed for the conventional single - ended mixer shown in FIG. 11 and the mixer of this embodiment. The conversion gain is a value obtained by normalizing the power of the RF signal after frequency conversion output from the mixer by the power of the IF signal before frequency conversion input to the mixer.

[0025] The simulation results of the conversion gain are shown in FIG. 4. 300 in FIG. 4 shows the conversion gain characteristic normalized by the conversion gain at the frequency 270 GHz of the LO signal for the conventional single - ended mixer. 301 shows the conversion gain characteristic normalized by the conversion gain at the frequency 270 GHz of the LO signal for the mixer of this embodiment. Assuming that the RF band is the band within - 3 dB of the conversion gain with reference to the conversion gain of the mixer at the frequency of the LO signal, it can be confirmed that the deterioration of the RF band due to changing from the conventional single - ended mixer to the single - balanced mixer of this embodiment is suppressed to a small extent.

[0026] The simulation results of the suppression performance of the LO signal are shown in FIG. 5. 400 in FIG. 5 shows the intensity of the LO signal leaking to the RF signal terminal 102 in the conventional single - ended mixer, and 401 shows the intensity of the LO signal leaking to the RF signal terminal 102 in the mixer of this embodiment. It can be confirmed that by using the configuration of this embodiment, the leakage of the LO signal to the RF signal terminal 102 can be improved by 25 dB or more compared with the conventional case.

[0027] The simulation results of the IF signal suppression performance are shown in FIG. 6. In FIG. 6, 500 indicates the intensity of the IF signal leaking to the RF signal terminal 102 in the conventional single-ended mixer, and 501 indicates the intensity of the IF signal leaking to the RF signal terminal 102 in the mixer of this embodiment. By using the configuration of this embodiment, it can be confirmed that the leakage of the IF signal to the RF signal terminal 102 can be improved by 40 dB or more compared with the conventional case.

[0028] [Second Embodiment] Next, a second embodiment of the present invention will be described. This embodiment shows a specific example of the synthesizer 105 of the first embodiment, and a rat-race coupler as shown in FIG. 7 is used as the synthesizer 105. The rat-race coupler is formed by annularly connecting a transmission line 203 having a length of λLO / 2 (λLO is the wavelength of the LO signal) between the first terminal 200 and the second terminal 201, a transmission line 204 having a length of λLO / 4 between the first terminal 200 and the third terminal 202, and a transmission line 205 having a length of 3λLO / 4 between the second terminal 201 and the third terminal 202.

[0029] When the first terminal 200 is connected to the drain terminal of the transistor Q101 and the second terminal 201 is connected to the drain terminal of the transistor Q102, the third terminal 202 becomes the RF signal terminal 102. By setting the lengths of the transmission lines 203 to 205 as described above, a synthesizer 105 can be realized that synthesizes the components in the RF frequency band of the differential outputs RFn and RFp of the differential pair transistors Q101 and Q102 in antiphase and synthesizes the components in the IF frequency band in phase.

[0030] In the mixer using the rat-race coupler of this embodiment as the synthesizer 105, even when the IF signal is a baseband signal including a DC component, it is possible to significantly reduce the leakage of the IF signal to the RF signal terminal 102. Further, in the mixer using the rat-race coupler as the synthesizer 105, since it is not necessary to insert a capacitor or a filter between the drain terminals of the differential pair transistors Q101 and Q102 and the synthesizer 105 as described later, miniaturization and low loss of the mixer are possible. Further, it is also possible to supply the voltages and currents necessary for the operations of the transistors Q101 to Q103 from the load connected to the RF signal terminal 102.

[0031] [Third Embodiment] In the rat-race coupler of the second embodiment, when the wavelength λIF of the signal having the highest frequency in the IF signal and the wavelength λLO of the LO signal satisfy the following relationship, it is possible to achieve high suppression performance for both the IF signal and the LO signal. λLO = α × λIF ···(1)

[0032] In Equation (1), the coefficient α takes a range of 0 ≦ α ≦ 0.12. The derivation process of Equation (1) will be described. Consider the IF signal having a wavelength λIF that propagates through the rat-race coupler of FIG. 7. When a signal cos(0) is input to terminal 200, the signal S1 that reaches terminal 202 is as shown in Equation (2). S1 = (1 / 2) × cos(απ / 2) + (1 / 2) × cos(5απ / 2) ···(2)

[0033] When a signal cos(π) is input to terminal 201, the signal S2 that reaches terminal 202 is as shown in Equation (3). S2 = cos(π + 3απ / 2) ···(3)

[0034] Therefore, the signal output from terminal 202 is as shown in Equation (4) as a result of adding the signals S1 and S2. S1 + S2 = (1 / 2) × cos(απ / 2) + (1 / 2) × cos(5απ / 2) + cos(π + 3απ / 2) ···(4)

[0035] Regarding Equation (4), FIG. 8 shows the intensity of signal S1+S2 (the intensity of the IF signal leaking to the RF signal terminal 102) when the coefficient α is changed from 0 to 0.5. If the coefficient α is in the range of 0≦α≦0.12, the leakage of the IF signal to the RF signal terminal 102 can be suppressed to -15 dB or less.

[0036] For example, when the frequency of the LO signal is 270 GHz, if the frequency of the IF signal is 32.4 GHz (270 GHz×0.12) or less, high suppression performance of the IF signal can be obtained.

[0037] [Fourth Embodiment] Generally, for a differential configuration wiring that transmits a differential signal, in order to maintain differential balance characteristics, it is desirable to arrange them as close as possible. Therefore, it is desirable that the first terminal 200 and the second terminal 201 of the rat-race type coupler connected to the drain terminals of the differential pair transistors Q101 and Q102 be as close as possible.

[0038] Therefore, as shown in FIG. 9, a folding portion 206 is provided in the middle of the transmission line 203 from the first terminal 200 to the second terminal 201 arranged in the vicinity of the first terminal 200. By using a folded transmission line as the transmission line 203, the first terminal 200 and the second terminal 201 can be arranged close to each other. The lengths of the transmission lines 203 to 205 are the same as the values shown in the second embodiment.

[0039] By using the configuration of this embodiment, a mixer with good balance characteristics of differential signals, wide bandwidth, and high suppression performance of IF signals and LO signals can be realized.

[0040] [Fifth Embodiment] FIG. 10 is a circuit diagram of a mixer according to a fifth embodiment of the present invention. In the mixer of this embodiment, a capacitor C100 is inserted between the drain terminal of transistor Q101 and the first terminal of synthesizer 105, and a capacitor C101 is inserted between the drain terminal of transistor Q102 and the second terminal of synthesizer 105. According to the configuration of this embodiment, it is possible to improve the suppression performance of the IF signal.

Industrial Applicability

[0041] The present invention can be applied to a mixer that performs frequency conversion of a signal.

Explanation of Reference Numerals

[0042] Q101 to Q103... transistors, C100, C101... capacitors, 105... synthesizer, 203 to 205... transmission lines, 206... folding section.

Claims

1. a first transistor to which an IF signal on the positive phase side is input to a gate terminal; a second transistor to which an IF signal on the negative phase side is input to a gate terminal; a third transistor to which an LO signal is input to a gate terminal, a source terminal of which is connected to ground, and a drain terminal of which is connected to source terminals of the first and second transistors; a mixer comprising: a synthesizer configured to synthesize components in an RF frequency band output from a drain terminal of the first transistor and components in an RF frequency band output from a drain terminal of the second transistor in antiphase, and to synthesize components in an IF frequency band output from the drain terminal of the first transistor and components in an IF frequency band output from the drain terminal of the second transistor in phase.

2. The mixer according to claim 1, wherein the synthesizer is a rat-race coupler, a first terminal connected to the drain terminal of the first transistor, a second terminal connected to the drain terminal of the second transistor, a third terminal for outputting an RF signal, a first transmission line having a length of λLO / 2 (λLO is the wavelength of the LO signal) connecting the first terminal and the second terminal, a second transmission line having a length of λLO / 4 connecting the first terminal and the third terminal, a third transmission line having a length of 3λLO / 4 connecting the second terminal and the third terminal.

3. The mixer according to claim 2, wherein when the wavelength of the signal having the highest frequency in the IF signal is λIF and the wavelength of the LO signal is λLO, a relationship of λLO = α × λIF (0 < α ≤ 0.12) is satisfied.

4. The mixer according to claim 2 or 3, wherein the first transmission line has a folded portion in the middle from the first terminal to the second terminal disposed near the first terminal.

5. The mixer according to claim 1, further comprising capacitors respectively inserted between the drain terminal of the first transistor and the first terminal of the synthesizer, and between the drain terminal of the second transistor and the second terminal of the synthesizer.

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