Mixer circuit and its mixing method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a mixer circuit and a mixing method thereof, for example, a mixer circuit for converting radio waves in a microwave band into a desired intermediate frequency signal, and a mixing method thereof.

【0002】

[Conventional technology]

Conventionally, in a transmitter / receiver that performs wireless communication, a mixer circuit (frequency conversion circuit) that mixes an RF (radio frequency) signal and a modulated signal has been used in order to generate an intermediate frequency signal that is easy to handle in a subsequent circuit. It is used.

【0003】

As such a mixer circuit, a so-called single mixer, a single-balanced mixer (hereinafter, SBM), and a double-balanced mixer (hereinafter, DBM) are generally used. Among them, a modulation signal can be obtained with a simple circuit configuration. Balanced mixers that can efficiently reduce leakage to the output side are widely used.

【0004】

[Problems to be Solved by the Invention]

Further, in recent years, there has been an increasing demand for high-speed communication in mobile wireless communication, that is, wireless communication capable of transmitting and receiving more information in a short time. In order to meet such a demand, when the RF signal of the microwave band such as 5.8 GHz band is converted by the above-mentioned conventional general balanced mixer using a wide band modulated signal of about several tens of MHz to 1 GHz, for example, In the output stage of the mixer circuit, not only the desired intermediate frequency signal does not appear, but also unnecessary radiation wave generation and modulation signal leakage appear prominently, and a mixed output that faithfully represents the waveform of the original RF signal is output. Difficult to obtain.

【0005】

Therefore, an object of the present invention is to provide a mixer circuit that performs good modulation on an RF signal in the microwave band and a mixing method thereof.

【0006】

[Means for solving problems]

In order to achieve the above object, the mixer circuit according to the present invention is characterized by the following configuration.

【0007】

That is, a mixer circuit that mixes an RF signal and a modulated signal, a divider that divides the RF signal into two RF signals, a delay circuit that delays the RF signal output from the divider by half a wavelength, and a modulated signal. Is output in the positive phase and inverted in the opposite phase, and the balun that outputs the inverted modulated signal and two single-balanced mixers having substantially the same frequency conversion characteristics are supplied from the divider. The first mixer that modulates the RF signal according to the positive-phase modulation signal supplied from the balun, and the anti-phase modulation supplied from the balun to the half-wavelength-delayed RF signal supplied from the delay circuit. By mixing the second mixer that modulates according to the signal and the modulated signals output from the first and second mixers, respectively, the leakage component caused by the RF signal contained in the modulated signals is offset. It is characterized in that it is provided with a mixer to be used.

【0008】

Alternatively, in order to achieve the above object, the mixing method of the mixer circuit according to the present invention is characterized by the following configuration.

【0009】

That is, it is a method of mixing an RF signal and a modulated signal in a mixer circuit, and two single-balanced mixers having substantially the same frequency conversion characteristics are prepared, and the first mixer, which is the single-balanced mixer, is RF. The signal is modulated according to the modulated signal of the positive phase, and the second mixer, which is the single-balanced mixer, modulates the RF signal delayed by half a wavelength according to the modulated signal inverted in the opposite phase, and the first and the first By mixing the modulated signals output from the second mixer with a mixer, the leakage component caused by the RF signal contained in the modulated signals is canceled out.

【0010】

The mixer circuit and the mixing method thereof are suitable for use, for example, when the RF signal is a microwave in a substantially 5.8 GHz band and the modulated signal changes in a range of several tens of MHz to 1 GHz.

【0011】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the mixer circuit according to the present invention will be described in detail with reference to the drawings as an embodiment for converting an RF signal in the 5.8 GHz band using a wideband modulated signal of several tens of MHz (about 20 MHz) to about 1 GHz. Explain to.

【0012】

FIG. 1 is a block diagram showing a circuit configuration of a mixer circuit according to an embodiment of the present invention.

【0013】

In the figure, 1 is a general divider that splits the RF signal in the 5.8 GHz band into two. One signal demultiplexed by the divider 1 is input to SBM1, and the other signal is input to the λ / 2 delay circuit 3. The λ / 2 delay circuit 3 is a general delay circuit that delays the output of the signal by half a wavelength by inverting the phase of the input signal.

【0014】

2 is a balun (balun:) that outputs a wideband modulated signal of several tens of MHz to 1 GHz with respect to SBM1 with the positive phase, and outputs a signal of opposite phase with the modulated signal inverted to SBM2. Balanced / unbalanced circuit).

【0015】

SBM1 and SBM2 are single-balanced mixers having a so-called rat race configuration, and both SMBs are general ones that do not include an isolation mechanism of an output port with respect to an input port, and have substantially the same frequency conversion characteristics. The SBM1 modulates the RF signal input from the divider 1 according to the positive phase modulation signal input from the balun 2, and inputs the modulated signal to the mixer 6. The SBM2 modulates the delayed RF signal input from the λ / 2 delay circuit 3 according to the opposite-phase modulation signal input from the balun 2, and inputs the modulated signal to the mixer 6.

【0016】

Reference numeral 6 denotes a mixer (coupler) that mixes the signals output from SBM1 and SBM2, respectively, and a desired intermediate frequency signal is output as a mixed output from an output port (not shown) of the mixer 6.

【0017】

In an actual mixer circuit, each block described above and the wiring pattern (copper foil) connecting the blocks have the best arrangement and length experimentally and empirically determined on the mounting substrate having a laminated structure. It is arranged.

【0018】

FIG. 2 is a diagram showing signal waveforms in each part of the mixer circuit according to the embodiment of the present invention.

【0019】

As shown in the figure, the RF signal input to the mixer circuit of FIG. 1 is a sine wave, and the modulated signal is a pulse signal that can take a wide frequency range of about several tens of MHz to 1 GHz. Moreover, since SBM1 and SBM2 employ a general single-balanced mixer that does not include an isolation mechanism, the modulation signal leaks from each of the modulation signals output from these mixers, and the leakage thereof. It can be seen that the reference level of the signal shifts to the + side in SBM1 and to the-side in SBM2 due to the influence of the components. However, in the present embodiment, as described above, SBM1 and SBM2 have substantially the same frequency conversion characteristics, and the modulation signal output from SBM2 is half that of the modulation signal output from SBM1. Since the modulation signals have a wavelength delay of the opposite phase, the leakage components contained in the modulated signals are canceled by mixing the modulated signals of the positive phase and the opposite phase in the mixer 6. Therefore, as shown in FIG. 2, from the output port (not shown) of the mixer 6, the RF signal input to the divider 1 is converted (modulated) by the modulated signal input to the balun 2 to obtain a faithful waveform. Can be output.

【0020】

FIG. 3 is a diagram showing the characteristics of the modulation frequency and the isolation by the mixer circuit according to the embodiment of the present invention, under the condition that the carrier wave of the RF signal is 0 dBm / 5.888 GHz and the level of the modulated wave is + 6 dBm. It shows the isolation characteristics for the modulation frequency measured for three samples (samples A, B, and C) with slightly different mounting conditions on the substrate, that is, the degree of reduction of modulation signal leakage in the output stage.

【0021】

When a general SBM is used alone, the isolation characteristics with respect to the modulation frequency are approximately -15 dB to -25 db, whereas the mixer circuit samples A, B, which have the circuit configuration shown in FIG. 1 described above. As shown in the figure, C shows good isolation characteristics over a wide band from about 5MHz to about 1GHz, and in particular, sample A realizes -40dB from about 5MHz to about 80MHz, and the isolation characteristics are good. It can be seen that even in the lowest frequency range around 500 MHz, it has better isolation characteristics of about -28 dB than when a general SBM is used alone.

【0022】

FIG. 4 is a diagram showing the signal characteristics of the lower first side wave band with respect to the carrier input to the mixer circuit according to the embodiment of the present invention, in which the carrier wave of the RF signal is 5.888 GHz and the modulated wave is + 6 dB / 150 MHz. The measurement was performed for the lower 1st sideband under the conditions of (Note that the description of the upper 1st sideband is omitted because the isolation characteristics are almost the same as those of the lower 1st sideband. To do).

【0023】

As is clear from the figure, in the mixer circuit according to the present embodiment, the lower first side wave band has a linear linear characteristic with respect to the input of the carrier wave (here, the broken line shown near + 5 dBm). (Due to the characteristics of the standard signal generator used to create the carrier signal in the experiment), which means that the mixed output signal generated by such a circuit can be easily handled in the subsequent circuit.

【0024】

Although the above-described embodiment has been described assuming an RF signal in the 5.8 GHz band, the description is not limited to this band, and the circuit configuration of the mixer circuit of FIG. 1 according to the present embodiment is, for example, 2.4. It can also be applied to RF signals in other bands such as the GHz band, and even in that case, the arrangement when configuring each block of the mixer circuit on the mounting board and the length and arrangement of the wiring pattern connecting the blocks can be determined. It may be designed in advance so that the modulation signal does not leak to the mixed output from the circuit.

【0025】

Further, in the present embodiment, the case where the RF signal in the microwave band is modulated by the configuration of the mixer circuit shown in FIG. 1 has been described, but the mixer circuit may be adopted as the demodulation circuit.

【0026】

[Effect of the invention]

As described above, according to the present invention, it is possible to provide a mixer circuit that performs good modulation on an RF signal in the microwave band and a mixing method thereof. If such a mixer circuit is adopted in a mobile wireless communication system, more information can be accurately transmitted and received in a short time.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram which shows the circuit structure of the mixer circuit in one Embodiment of this invention.

[Figure 2]

It is a figure which shows the signal waveform in each part of the mixer circuit which concerns on one Embodiment of this invention.

[Fig. 3]

It is a figure which shows the characteristic of the modulation frequency and isolation by the mixer circuit in one Embodiment of this invention.

[Fig. 4]

It is a figure which shows the signal characteristic of the lower 1st sideband with respect to the carrier input to the mixer circuit in one Embodiment of this invention.

[Explanation of symbols]

1: Divider, 2: Baran, 3: λ / 2 delay circuit, 4: Single balanced mixer (SBM) 1, 5: Single Balanced Mixer (SBM) 2, 6: Mixer,