Cross-sectional mixer with distortion compensation function

Abstract

The objective is to provide an orthogonal mixer that has the function to perform distortion compensation independently on each of its two unit mixers. [Solution] A quadrature mixer comprising first and second unit mixers that use the mth order (m is a natural number) of the LO wave as a carrier wave, having an LO distribution unit that equally distributes the LO wave and outputs it to the first and second unit mixers with a phase difference of π / 2m, having a power combining unit that combines the output wave from the first unit mixer and the output wave from the second unit mixer, having a first compensation signal generation unit that generates a compensation signal to be input to the first unit mixer based on the quadrature transmission signal or its information, and a second compensation signal generation unit that generates a compensation signal to be input to the second unit mixer.

Description

Technical Field

[0001] The present invention relates to a quadrature mixer, and particularly to a quadrature mixer having a distortion compensation function.

Background Art

[0002] There is a quadrature mixer as a circuit for performing frequency conversion. As shown in FIG. 9(a), in the quadrature mixer, an IF signal or a baseband signal (hereinafter, referred to as an IF signal) orthogonal to two unit mixers 111 and 112 is input. The input IF signal is mixed with the LO wave, and an RF signal is output. However, when the input power of the IF signal increases, there is a problem that non-linear distortion increases and the signal quality deteriorates. As an index of non-linear distortion, as shown in FIG. 9(b), there is an intercept point (IP3), and the larger the value of IP3, the smaller the distortion. IP3 is indicated by the intersection of the output power of the desired wave (fundamental wave) and the output power of the third-order intermodulation distortion (IM3) (Non-Patent Document 1).

[0003] For example, Patent Document 1 discloses a balanced mixer circuit in which the amount of distortion is detected from the combined output of two mixers, the signals input to the two mixers are inverted so that the amounts of distortion of the two mixers cancel each other out by combination, and the signal level is adjusted by a gain variable circuit. On the other hand, as a result of studying distortion compensation as a quadrature mixer without adjusting the input signal level by an input signal phase inversion circuit or a gain variable circuit, the present inventors have arrived at the present invention.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-41129 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide an orthogonal mixer equipped with a function to independently perform distortion compensation on two unit mixers within the orthogonal mixer. [Means for solving the problem]

[0007] The quadrature mixer having a distortion compensation function according to the present invention is a quadrature mixer comprising a first and a second unit mixer whose carrier wave is the mth order (m is a natural number) of the LO wave, and has an LO distribution unit that equally distributes the LO wave and outputs it to the first and second unit mixers with a phase difference of π / 2m (for example, 90° when m=1, and 45° when m=2), and has a power combining unit that combines the output wave from the first unit mixer and the output wave from the second unit mixer, and is characterized by having a first compensation signal generation unit that generates a compensation signal to be input to the first unit mixer based on the quadrature transmission signal or its information, and a second compensation signal generation unit that generates a compensation signal to be input to the second unit mixer.

[0008] The present invention is characterized by the fact that separate compensation signal generation units are formed in each of the two unit mixers.

[0009] For example, the first and second compensation signal generation units each generate harmonics of the orthogonal transmission signals input to the first and second unit mixers, respectively. The first compensation signal generation unit controls the amplitude level of the harmonics generated based on the distortion occurring in the first unit mixer detected by applying the transmission signal only to the first unit mixer, and the second compensation signal generation unit controls the amplitude level of the harmonics generated based on the distortion occurring in the second unit mixer detected by applying the transmission signal only to the second unit mixer.

[0010] Furthermore, the device may have a signal level detection unit connected to the output terminal that takes a portion of the output signal power from the power combining unit as input, and a calculation unit that calculates the amplitude level coefficients in the first compensation signal generation unit and the second compensation signal generation unit based on the signal level information obtained by the signal level detection unit, and outputs first and second control signals to the first and second compensation signal generation units respectively based on the coefficients calculated by the calculation unit. These operational descriptions will be explained in detail in the descriptions of embodiments for carrying out the invention.

[0011] In the present invention, the first and second compensation signal generation units may include a digital circuit and a digital-to-analog converter.

[0012] In this invention, m can be a natural number; for example, the mth order of the LO wave is m=2, and the first and second unit mixers may be even harmonic mixers. [Effects of the Invention]

[0013] The quadrature mixer according to the present invention can improve distortion, thereby contributing to improved signal quality, such as reducing error rates in communications and quantum computation errors in quantum computers. Furthermore, it contributes to miniaturizing the filters installed after the mixer, thereby contributing to the overall miniaturization of the device. [Brief explanation of the drawing]

[0014] [Figure 1]Shows a configuration example of the quadrature mixer of Example 1. [Figure 2] Shows the relationship between IM3 and the compensation coefficient. [Figure 3] Shows a configuration example of the quadrature mixer of Example 2. [Figure 4] (a) shows the output spectrum at the RF terminal of the quadrature mixer at the time of two-tone input, and (b) shows the input spectrum to the signal level detection unit. [Figure 5] Shows Example 3. [Figure 6] Shows Example 4. [Figure 7] Shows Example 5. [Figure 8] Shows the output spectrum at the RF terminal of the even harmonic quadrature mixer at the time of two-tone input. [Figure 9] (a) shows a configuration example of the quadrature mixer, and (b) shows the input / output characteristics.

Mode for Carrying Out the Invention

[0015] Fig. 1 shows a configuration example of the quadrature mixer of Example 1. The LO distribution unit 21 that equally distributes the LO wave having the frequency f1 is provided for the first unit mixer (I) 11 and the second unit mixer (Q) 12. As the quadrature transmission signals (f2, f3), the IF (I) signal having the frequency f2 is input to the first unit mixer (I) 11 via the first compensation signal generation unit 31, and the IF (Q) signal having the frequency f3 is input to the second unit mixer (Q) 12 via the second compensation signal generation unit 32. Also, the output signals from the first and second unit mixers 11 and 12 are combined by the power combining unit 41 and output as an RF signal.

[0016] Next, the operation will be described. For example, let the input / output function of the mixer be the following equation. TIFF2026049954000002.tif14166However, x is the input voltage, y is the output voltage, and a i is the coefficient of the i-th order. When x is sufficiently small, the output related to coefficients of order two or higher can be ignored, and from the input-output relationship, it can be considered as only a1x, thus being linear. As the input increases, the coefficients a2, a3, etc., of progressively lower order begin to have an effect, and the nonlinear characteristics become too significant to ignore, resulting in distortion. The voltage of IIP3 (Input IP3) is expressed by the following formula. Therefore, one way to suppress distortion is to reduce the cubic coefficient. Specifically, this involves applying a third harmonic of the opposite polarity to the input. If the input voltage is given by the following equation X, the output voltage Y is expressed by the following equation. TIFF2026049954000004.tif15166TIFF2026049954000005.tif33166In other words, in equation (3), x is the IF signal input to the compensation signal generation unit, and X is the compensation signal output from the compensation signal generation unit and input to the unit mixer, and in equation (4), it can be seen that the third-order coefficient disappears from the signal Y output from the unit mixer. This suppresses IM3. Although coefficients of the fourth order and above will be generated, their impact is considered small due to their high order. Alternatively, harmonics that cancel these out may be added to the input. Here, we have shown the case of the third degree, but the same procedure can be applied to other degrees as well.

[0017] As described above, distortion can be suppressed by adding a harmonic of opposite polarity to the input, but it is necessary to appropriately determine the amplitude of that harmonic. In the above case, it is necessary to determine the compensation coefficient a3 / a1. Furthermore, since the coefficients of the input / output functions differ for each unit mixer due to element variations, etc., each will have a different compensation coefficient. For example, as shown in Figure 2, the a3 / a1 at which the suppression amount of IM3 is maximized is the first unit mixer and It differs from the second unit, Mixa. Therefore, by providing a transmission signal to each unit mixer and determining IIP3, the optimal a3 / a1 for each unit mixer can be determined. By doing so, distortion in each unit mixer can be greatly suppressed, and as a result, the distortion of the quadrature mixer as a whole can be greatly reduced. This allows for the detection of different nonlinear coefficients for each unit mixer, improving the strain characteristics of the orthogonal mixer.

[0018] Figure 3 shows Example 2. The differences from Example 1 will be explained. It has a signal level detection unit 51 that takes a portion of the power of the output RF signal as input. The system includes a compensation signal control unit 52 that calculates a control signal based on the signal level information obtained by the signal level detection unit 51. This compensation signal control unit 52 has a calculation unit 52a that calculates the coefficient of the amplitude level of the harmonics in the first compensation signal generation unit and the coefficient of the amplitude level of the harmonics in the second compensation signal generation unit 32. This calculation unit 52a calculates the coefficient of the amplitude level of the harmonics and outputs control signals 52b and 52c to the first compensation signal generation unit 31 and the second compensation signal generation unit 32, respectively.

[0019] For example, if a two-tone transmission signal (IF1, IF2) is input only to the first unit mixer, the output spectrum at the RF terminal will be as shown in Figure 4(a). Of these, the spectra of LO-IF1, which corresponds to the desired wave, and LO-(2IF1-IF2), which corresponds to IM3, are extracted using couplers and filters and input to the signal level detection unit, where the power of LO-IF1 and LO-(2IF1-IF2) is detected, respectively. For detection, for example, a detector that outputs a detection voltage according to the input power is used. Using this detection result, the compensation signal control unit calculates IIP3 and controls the compensation coefficient a3 / a1 that determines the amplitude level of harmonics in the first compensation signal generation unit based on the obtained IIP3. The calculation of IIP3 utilizes the fact that the desired wave increases with a slope of 10 dB / dec. in response to an increase in input power, while IM3 increases with a slope of 30 dB / dec. By varying the input power of the transmitted signals (IF1, IF2) and detecting the power of LO-IF1 and LO-(2IF1-IF2), and confirming whether the expected slope is obtained, IIP3 can be obtained more accurately. The same procedure is followed for the second unit mixer, and the compensation coefficient a3 / a1 that determines the amplitude level of the harmonics in the second compensation signal generation unit is controlled separately from the first compensation signal generation unit. By doing so, distortion in each unit mixer can be suppressed, and as a result, the distortion of the orthogonal mixer as a whole can be reduced.

[0020] Figure 5 shows Example 3. This embodiment 3 is equipped with a digital circuit and a digital-to-analog converter (31a, 32a) in addition to the first and second compensation signal generation units 31 and 32 in embodiment 1. The information of the quadrature transmission signal is provided to the digital signal processing circuit (DSP), and based on this, compensation signals are generated for each signal. The digital signal output from the DSP is converted to an analog signal by a digital-to-analog converter and input to the unit mixer. Figure 6 shows Example 4. This example, like Example 3, uses a compensation signal generation unit 31b, 32b equipped with a digital circuit and a digital-to-analog converter, in contrast to Example 2.

[0021] Figure 7 shows Example 5. This embodiment is an example where m=2, and is an example of an even-harmonic mixer using antiparallel diodes in the first and second unit mixers. Figure 8 shows the output spectrum at the RF terminal of the even-harmonic quadrature mixer when a two-tone input is used.

Claims

1. A quadrature mixer consisting of a first and a second unit mixer, the carrier wave being the mth order (m is a natural number) of the LO wave, It has an LO distribution unit that equally distributes the LO wave and outputs it to the first and second unit mixers with a phase difference of π / 2m, It has a power combining unit that combines the output wave from the first unit mixer and the output wave from the second unit mixer, A first compensation signal generation unit that generates a compensation signal to be input to the first unit mixer based on the orthogonal transmission signal or its information, A quadrature mixer having a distortion compensation function, characterized by having a second compensation signal generation unit that generates a compensation signal to be input to the second unit mixer.

2. The first and second compensation signal generation units each generate harmonics of the quadrature transmission signals input to the first and second unit mixers, respectively. Based on the distortion generated in the first unit mixer detected by applying the transmission signal only to the first unit mixer, the amplitude level of the harmonics generated by the first compensation signal generation unit is controlled. A quadrature mixer having a distortion compensation function according to claim 1, characterized in that it controls the amplitude level of harmonics generated by the second compensation signal generation unit based on the distortion generated in the second unit mixer detected by applying a transmission signal only to the second unit mixer.

3. It has a signal level detection unit connected to the output terminal that takes a portion of the output signal power from the power combining unit as input, The system includes a calculation unit that calculates the amplitude level coefficients in the first compensation signal generation unit and the second compensation signal generation unit based on the signal level information obtained by the signal level detection unit. A quadrature mixer having a distortion compensation function according to claim 1, characterized in that it outputs first and second control signals to the first and second compensation signal generation units, respectively, based on coefficients calculated by the calculation unit.

4. The quadrature mixer having any of the distortion compensation functions according to 1 to 3, characterized in that the first and second compensation signal generation units have a digital circuit and a digital-to-analog converter.

5. A quadrature mixer having any of the distortion compensation functions according to 1 to 3, characterized in that the m-th order of the LO wave is m = 2, and the first and second unit mixers are even harmonic mixers.

6. The quadrature mixer having a distortion compensation function according to claim 4, characterized in that the m-th order of the LO wave is m=2, and the first and second unit mixers are even-harmonic mixers.

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