JP2020129779A - Transmitter - Google Patents

Abstract

To provide a transmitter capable of maximizing the intensity of a fundamental wave component of an intermediate frequency signal included in a transmission signal.SOLUTION: A transmitter (10) includes a modulation unit (11) that outputs a signal in which a baseband signal (BB) and a carrier signal (LO) are input and the carrier signal is superimposed on an intermediate frequency signal (IF) obtained by mixing the baseband signal and the carrier signal, and a frequency mixing unit (13) that is connected to the latter stage of the modulation unit and multiplies the output signal of the modulation unit, and the modulation unit is configured such that an amplitude voltage of the carrier signal superimposed on the intermediate frequency signal can be adjusted by an applied bias voltage (VB).SELECTED DRAWING: Figure 1

Description

The present invention relates to a transmitter, and more particularly to a transmitter that transmits a baseband signal on a carrier.

Conventionally, there has been developed a transmitter that multiplies an intermediate frequency signal obtained by mixing a baseband signal and a carrier signal by a frequency multiplier to generate a high frequency transmission signal. In such a transmitter, when the intermediate frequency signal is multiplied by the frequency multiplier, the amplitude of the baseband signal is raised to the power, and the linearity of the amplitude of the original baseband signal is lost. Therefore, there is known a transmitter that upconverts a baseband signal into a high-frequency transmission signal with good linearity by multiplying a signal obtained by superimposing a carrier signal on an intermediate frequency signal (see, for example, Patent Document 1).

JP, 2017-130804, A

In the transmitter, in addition to up-converting the baseband signal to a high-frequency transmission signal with good linearity, it is important to increase the strength of the fundamental wave component of the intermediate frequency signal among various signal components included in the transmission signal. This is one of the challenges.

Therefore, it is an object of the present invention to provide a transmitter capable of maximizing the intensity of the fundamental wave component of the intermediate frequency signal included in the transmission signal.

In a transmitter according to one aspect of the present invention, a baseband signal and a carrier signal are input, and the carrier signal is superimposed on an intermediate frequency signal obtained by mixing the baseband signal and the carrier signal. A modulation unit that outputs a signal, and a frequency mixing unit that is connected to the subsequent stage of the modulation unit and that multiplies the output signal of the modulation unit, and the modulation unit converts the intermediate frequency signal into the intermediate frequency signal by the applied bias voltage. The amplitude voltage of the carrier signals to be superimposed is adjustable.

The frequency mixer may include a squaring circuit that doubles the frequency of the output signal of the modulator, and the bias voltage may be the amplitude voltage of the carrier signal superimposed on the intermediate frequency signal. The value is preferably set to be equal to the amplitude voltage of the intermediate frequency signal.

Alternatively, the frequency mixing unit may include a cube circuit that triples the frequency of the output signal of the modulator, and the bias voltage is an amplitude voltage of the carrier signal that is superimposed on the intermediate frequency signal. Is preferably set to a value that is √2 times the amplitude voltage of the intermediate frequency signal.

For example, the modulation unit mixes the baseband signal and the carrier signal to generate the intermediate frequency signal, and outputs the inputted carrier signal as an amplitude voltage corresponding to the bias voltage and outputs the amplitude voltage. An amplitude adjuster and an adder for adding the output signal of the modulator and the output signal of the amplitude adjuster are included.

For example, the modulator is composed of a Gilbert cell, one of the differential input pairs of the Gilbert cell is connected to the baseband signal as a single-ended signal, and the other is connected to the bias voltage.

The baseband signal may be a quadrature phase amplitude modulated signal.

The intensity of the fundamental wave component of the intermediate frequency signal included in the transmission signal multiplied by the frequency mixing unit changes according to the amplitude voltage of the carrier signal superimposed on the intermediate frequency signal. According to the present invention, since the amplitude voltage of the carrier signal to be superimposed on the intermediate frequency signal can be adjusted by the bias voltage applied to the modulator, the bias voltage is optimized and the strength of the fundamental wave component of the intermediate frequency signal included in the transmission signal is adjusted. Can be maximized.

Block diagram of a transmitter according to an embodiment of the present invention Block diagram of a modulator according to an example Block diagram of a transmitter according to a first specific example Circuit diagram of a modulator in the transmitter according to the first example. A graph showing various signal intensities included in the modulator output when the bias voltage VB is set to 0V. A graph showing various signal intensities included in the output of the modulator when the bias voltage VB is set to 0.9V. Graph showing the relationship between LO signal strength and RF signal strength Block diagram of a transmitter according to a second specific example Circuit diagram of a modulator in a transmitter according to a second specific example. Modification of Gilbert cell shown in FIG.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed description of well-known matters and repeated description of substantially the same configuration may be omitted. This is for avoiding unnecessary redundancy in the following description and for facilitating understanding by those skilled in the art.

It is to be noted that the inventor provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present invention, and is not intended to limit the subject matter described in the claims by these. Absent.

<<Embodiment>>
FIG. 1 is a block diagram of a transmitter according to an embodiment of the present invention. The transmitter 10 according to the present embodiment includes a modulator 11, an amplifier 12, and a frequency mixer 13. The transmitter 10 up-converts a baseband signal (hereinafter referred to as a BB signal) output from a baseband unit (not shown) into a radio frequency signal (hereinafter referred to as an RF signal) of a high frequency (for example, 300 GHz band) and transmits the radio frequency signal. To do.

A BB signal output from a baseband unit (not shown) and a carrier signal (hereinafter, referred to as LO signal) output from a local oscillator (not shown) are input to the modulator 11. The modulator 11 outputs a signal obtained by superimposing the LO signal on an intermediate frequency signal (hereinafter, referred to as an IF signal) obtained by mixing the BB signal and the LO signal. That is, the general modulator up-converts the BB signal using the LO signal and outputs the IF signal, whereas the modulator 11 leaks and outputs the LO signal as well as the IF signal.

Further, the bias voltage VB is applied to the modulator 11. The amplitude voltage of the LO signal and the superposed signal on the IF signal in the modulator 11 can be adjusted by the bias voltage VB applied to the modulator 11.

FIG. 2 is a block diagram of the modulator 11 according to an example. The modulator 11 includes a modulator 111, an amplitude adjuster 112, and an adder 113. The modulator 111 multiplies the BB signal by the LO signal to generate an IF signal. The amplitude adjuster 112 outputs the input LO signal as an amplitude voltage according to the bias voltage VB. The adder 113 adds the output signal of the modulator 111 and the output signal of the amplitude adjuster 112. As a result, the modulator 11 outputs a signal obtained by superimposing the LO signal on the IF signal. For convenience, this signal is referred to as “αLO+IF”. α represents that the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted.

Returning to FIG. 1, the amplification unit 12 amplifies the signal output from the modulation unit 11. The amplification unit 12 has a sufficient gain in the bands of the IF signal and the LO signal.

The frequency mixer 13 up-converts the signal output from the amplifier 12 to generate an RF signal. Specifically, the frequency mixing unit 13 can be configured by using a CMOS element like a general frequency multiplier, and can also be configured by another active element or passive element having a frequency multiplying characteristic. it can. However, unlike a general frequency multiplier, the frequency mixing unit 13 multiplies a signal (αLO+IF) in which the IF signal and the LO signal are superimposed. As will be described later, a square circuit or a cube circuit can be used as the frequency mixing unit 13.

Next, a more specific configuration example of the transmitter 10 according to the present embodiment will be described.

<<First Specific Example>>
FIG. 3 is a block diagram of a transmitter according to the first specific example. The transmitter 10A according to the first specific example embodies the modulator 11 in the transmitter 10 shown in FIG. 1 with an SDBM (Semi Double Balanced Mixer) 11A, and further embodies the frequency mixer 13 with a squaring circuit 13A. It was done. The SDBM is a circuit obtained by partially modifying a general DBM (Double Balanced Mixer) configured by using Gilbert cells, and the name SDBM is coined by the inventor.

FIG. 4 is a circuit diagram of the modulator (SDBM 11A) in the transmitter 10A according to the first specific example. As shown in the figure, the SDBM 11A can be composed of a Gilbert cell.

Generally, a Gilbert cell is configured by vertically stacking a circuit in which two differential switching transistor pairs are cross-connected (hereinafter referred to as a cross-connecting circuit) and a differential amplifier circuit, that is, connecting them in series. When the BB signal and the LO signal are mixed in the Gilbert cell, it is general to differentially input the LO signal to the cross-connect circuit and differentially input the BB signal to the differential amplifier circuit. On the other hand, in the SDBM 11A, the BB signal as a single end signal is connected to one of the differential input pairs and the bias voltage VB is connected to the other without inputting the BB signal differentially to the differential amplifier circuit in the Gilbert cell. Connected. That is, in the SDBM 11A, the BB signal is intentionally input unbalanced.

Generally, in a Gilbert cell, when the LO signal has a high frequency, the leakage of the LO signal to the output side (broken line arrow in the figure) increases due to the parasitic capacitance between the gate and drain of the transistor forming the cross-connect circuit. If the input signal is balanced, the leakage of the LO signal and the leakage of the inverted signal of the LO signal cancel each other and the LO signal superimposed on the IF signal is canceled. However, in the SDBM 11A, since the differential input of the differential amplifier circuit is unbalanced, the cancellation of the leakage of the LO signal and the leakage of the inverted signal of the LO signal is insufficient, and the LO signal is superimposed on the IF signal. That is, the SDBM 11A outputs a differential signal (αLO+IF) in which the LO signal is superimposed on the IF signal. Further, the coefficient α, that is, the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

Next, the simulation result of SDBM11A is shown. The LO signal was set to 136 GHz and the BB signal was changed in the range of 1 to 21 GHz to perform the simulation. FIG. 5A is a graph showing various signal intensities included in the output of the modulator (SDBM11A) when the bias voltage VB is set to 0V. FIG. 5B is a graph showing various signal intensities included in the modulator output when the bias voltage VB is set to 0.9V. The horizontal axis represents the frequency of the BB signal, and the vertical axis represents the intensity of various signals. In the graph, the intensities of the upper sideband (136-186 GHz) and the lower sideband (116-136 GHz) of the IF signal, the LO signal, and the image signal included in the output of the modulator are plotted.

For example, looking at the BB signal at 10 GHz, when the bias voltage VB is 0 V, the intensity of the LO signal contained in the modulator output is approximately -7 dBm (see FIG. 5A). On the other hand, when the bias voltage VB is 0.9 V, the intensity of the LO signal included in the modulator output is approximately -1.5 dBm (see FIG. 5B). From this result, it is understood that in the SDBM 11A, the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

Returning to FIG. 4, the differential signal (αLO+IF) output from the SDBM 11A is amplified by the amplification unit 12 and input to the squaring circuit 13A. The squaring circuit 13A doubles the frequency of the differential signal (αLO+IF) and outputs an RF signal. Since the squaring circuit 13A is a known circuit such as an active doubler (also referred to as a frequency doubler) including a pair of transistors, a detailed description of the circuit configuration will be omitted.

The squaring circuit 13A substantially executes the operation represented by the following expression (1).

(ΑLO+βIF) ² =α ² LO ² +2αβ·LO·IF+β ² IF ² (1)
However, in the formula (1), LO represents a LO signal and IF represents an IF signal. Further, α and β represent the amplitude voltage of the LO signal and the IF signal, respectively.

In this way, by squaring the signal obtained by superimposing the IF signal and the LO signal in the squaring circuit 13A, the first harmonic component (basic component) of the IF signal represented by the second term on the right side of the equation (1) (Also referred to as wave component) and the second harmonic component of the IF signal represented by the third term on the right side. Among these, the fundamental wave component of the IF signal is a signal to be output as an RF signal from the transmitter 10A. Therefore, a bandpass filter (not shown) that allows a signal in a desired band to pass therethrough may be provided at the subsequent stage of the squaring circuit 13A to allow the fundamental wave component of the IF signal to pass.

The coefficient of each term on the right side of the equation (1) represents the amplitude voltage of each component. That is, the amplitude voltage of the fundamental wave component (RF signal) of the IF signal is represented by 2αβ, and the amplitude voltage of the second harmonic component of the IF signal is represented by β ² . Here, consider the condition where the amplitude voltage of the RF signal, that is, the coefficient (2αβ) of the second term on the right side of the equation (1) becomes maximum. It is when α=β that the coefficient (2αβ) of the second term on the right side becomes maximum under the condition that the total signal intensity of the LO signal and the IF signal is constant, that is, α ² +β ² =1. That is, when the amplitude voltage of the LO signal is made equal to the amplitude voltage of the IF signal, the amplitude voltage of the RF signal can be maximized, and as a result, the strength of the RF signal is maximized.

FIG. 6 is a graph showing the relationship between LO signal strength and RF signal strength. Here, the frequency of the IF signal is 136 GHz and the intensity is -10 dBm. As can be seen from the graph, when the amplitude voltage of the LO signal and the amplitude voltage of the IF signal are the same, that is, when the strength of the LO signal is the same as the strength of the IF signal, ie, −10 dBm, the strength of the RF signal becomes maximum.

From the above knowledge, in order to maximize the strength of the RF signal output from the transmitter 10A, in the SDBM 11A, the bias voltage VB should be set to a value such that the amplitude voltage of the LO signal becomes equal to the amplitude voltage of the IF signal. It can be said that it is good.

<<Second Specific Example>>
FIG. 7 is a block diagram of a transmitter according to the second specific example. The transmitter 10B according to the second specific example is capable of modulating a BB signal that is quadrature-phase amplitude modulated. More specifically, the transmitter 10B embodies the modulator 11 in the transmitter 10 shown in FIG. 1 with an SDBQM (Semi Double Balanced Quadrature Mixer) 11B, and further embodies the frequency mixer 13 with a squaring circuit 13A. Is. The SDBQM is a circuit obtained by partially modifying a general DBQM (Double Balanced Quadrature Mixer) configured by using two Gilbert cells, and the name SDBQM is coined by the inventor.

FIG. 8 is a circuit diagram of the modulator (SDBQM11B) in the transmitter 10B according to the second specific example. As shown in the figure, the SDBQM 11B can be composed of two Gilbert cells. The first Gilbert cell (the Gilbert cell arranged on the left side of the figure) mixes the BB _I signal and the LO _I signal which are in-phase components of the BB signal and the LO signal. The second Gilbert cell (Gilbert cell arranged on the right side of the figure) mixes the BB _Q signal and the LO _Q signal, which are quadrature phase components of the BB signal and the LO signal.

In any of the Gilbert cell, as in the example of SDBM11A, BB _I signal without differential inputs the BB _I signal and the BB _Q signal in the differential amplifier circuit, as a single-ended signal to one of the differential input pair and connect the BB _Q signal, it connects the bias voltage VB to the other. That is, the SDBQM 11B intentionally inputs the BB _I signal and the BB _Q signal unbalanced.

Thus, LO cancellation of the leakage of the inverted signal of the leakage and LO _I signal of the _I signal, and LO _Q signal leakage and LO _Q signal LO signal to the IF signal becomes insufficient either cancel the leakage of the inverted signal of the Are overlaid. That is, the differential signal (αLO+IF) in which the LO signal is superimposed on the IF signal is output from the SDBQM 11B. Further, the coefficient α, that is, the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

In the transmitter 10B as well, as in the transmitter 10A, the bias voltage VB may be set to a value such that the amplitude voltage of the LO signal becomes equal to the amplitude voltage of the IF signal. Thereby, the strength of the RF signal output from the transmitter 10A can be maximized.

<<Effect>>
As described above, the intensity of the fundamental wave component of the IF signal included in the RF signal multiplied by the frequency mixing unit 13 changes according to the amplitude voltage of the LO signal superimposed on the IF signal. In the transmitter 10 according to the present embodiment, the amplitude voltage of the LO signal to be superimposed on the IF signal can be adjusted by the bias voltage VB applied to the modulation unit 11, so that the bias voltage VB is set to an optimum value and the IF signal included in the RF signal is adjusted. The intensity of the fundamental wave component of can be maximized.

≪Modification≫
In the Gilbert cell shown in FIG. 4, the BB signal and the bias voltage VB are connected to the gates of the transistors in the differential amplifier circuit, but the BB signal and the bias voltage VB are directly connected to the common source of the pair transistors of the cross-connect circuit. May be. FIG. 9 shows a modification of the Gilbert cell shown in FIG. In the Gilbert cell shown in FIG. 9, the BB signal and the bias voltage VB are directly connected to the common source of the pair transistors of the cross-connection circuit. The Gilbert cell shown in FIG. 8 can be modified based on the same idea as in FIG.

The Gilbert cell shown in FIGS. 4, 8 and 9 as an example of the modulation unit 11 is composed of a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), but may be another type of transistor such as an NPN bipolar transistor. The Gilbert cell, that is, the modulation unit 11 may be configured.

A cube circuit may be used for the frequency mixing unit 13. Since the cube circuit is a known circuit such as a frequency tripler, detailed description of the circuit configuration will be omitted.

The frequency mixer 13 as a cube circuit substantially executes the operation represented by the following equation (2).

(ΑLO+βIF) ³ =α ³ LO ³ +3α ² β·LO ² ·IF
+3αβ ² ·LO·IF ² +β ³ IF ³ (2)
However, in the equation (2), LO represents the LO signal and IF represents the IF signal. Further, α and β represent the amplitude voltage of the LO signal and the IF signal, respectively.

In this way, the signal in which the IF signal and the LO signal are superposed is cubed in the cube circuit, so that the first harmonic component (fundamental wave component) of the IF signal represented by the second term on the right side of the equation (2) is expressed. (Also referred to as a component), the second harmonic component of the IF signal represented by the third term on the right side, and the third harmonic component of the IF signal represented by the fourth term on the right side. Among these, the fundamental wave component of the IF signal is a signal to be output as an RF signal from the transmitter 10. Therefore, a bandpass filter (not shown) that passes a signal in a desired band may be provided in the subsequent stage of the frequency mixer 13 as a cube circuit to pass the fundamental wave component of the IF signal.

The coefficient of each term on the right side of the equation (2) represents the amplitude voltage of each component. That is, the amplitude voltage of the fundamental wave component (RF signal) of the IF signal is 3α ² β, the amplitude voltage of the second harmonic component of the IF signal is 3αβ ² , and the amplitude voltage of the third harmonic component of the IF signal is β ³ . Represented respectively. Here, the condition that the amplitude voltage of the RF signal, that is, the coefficient (3α ² β) of the second term on the right side of the expression (2) becomes maximum will be considered. It is when α=√2β that the coefficient (3α ² β) of the second term on the right side becomes maximum under the condition that the total signal intensity of the LO signal and the IF signal is constant, that is, α ² +β ² =1. That is, when the amplitude voltage of the LO signal is √2 times the amplitude voltage of the IF signal, the amplitude voltage of the RF signal can be maximized, and as a result, the strength of the RF signal is maximized.

From the above knowledge, when the cube circuit is used as the frequency mixing unit 13, in order to maximize the strength of the RF signal output from the transmitter 10, the bias voltage VB is set to the amplitude voltage of the LO signal in the modulation unit 11. It can be said that the value should be set to a value that is √2 times the amplitude voltage of the IF signal.

As described above, the embodiment has been described as an example of the technique of the present invention. To that end, the accompanying drawings and detailed description are provided.

Therefore, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem but also the components not essential for solving the problem in order to exemplify the above technology Can also be included. Therefore, it should not be immediately recognized that the non-essential components are essential by the fact that the non-essential components are described in the accompanying drawings and the detailed description.

Further, since the above-described embodiment is for exemplifying the technique of the present invention, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the scope equivalent thereto.

10, 10A, 10B... Transmitter, 11... Modulation section, 11A... SDBM (specific example of modulation section), 11B... SDBQM (Specific example of modulation section), 13... Frequency mixing section, 13A... Square circuit (frequency mixing) Specific example), 111... Modulator, 112... Amplitude adjuster, 113... Adder, BB... Baseband signal, LO... Carrier signal, IF... Intermediate frequency signal, VB... Bias voltage

The present invention relates to a transmitter, and more particularly, to a transmitter that transmits a baseband signal on a carrier wave.

Conventionally, there has been developed a transmitter that multiplies an intermediate frequency signal obtained by mixing a baseband signal and a carrier signal by a frequency multiplier to generate a high frequency transmission signal. In such a transmitter, when the intermediate frequency signal is multiplied by the frequency multiplier, the amplitude of the baseband signal is raised, and the linearity of the amplitude of the original baseband signal is lost. Therefore, there is known a transmitter that upconverts a baseband signal into a high-frequency transmission signal with good linearity by multiplying a signal obtained by superimposing a carrier signal on an intermediate frequency signal (for example, refer to Patent Document 1).

JP, 2017-130804, A

In the transmitter, in addition to up-converting the baseband signal to a high-frequency transmission signal with good linearity, it is also important to increase the strength of the fundamental wave component of the intermediate frequency signal among various signal components included in the transmission signal. It is one of the challenges.

Therefore, it is an object of the present invention to provide a transmitter capable of maximizing the intensity of the fundamental wave component of the intermediate frequency signal included in the transmission signal.

In a transmitter according to one aspect of the present invention, a baseband signal and a carrier signal are input, and the carrier signal is superimposed on an intermediate frequency signal obtained by mixing the baseband signal and the carrier signal. A modulation unit that outputs a signal, and a frequency mixing unit that is connected to the subsequent stage of the modulation unit and that multiplies the output signal of the modulation unit, and the modulation unit converts the intermediate frequency signal into the intermediate frequency signal by the applied bias voltage. The amplitude voltage of the carrier signals to be superimposed is adjustable.

The frequency mixer may include a squaring circuit that doubles the frequency of the output signal of the modulator, and the bias voltage may be the amplitude voltage of the carrier signal superimposed on the intermediate frequency signal. The value is preferably set to be equal to the amplitude voltage of the intermediate frequency signal.

Alternatively, the frequency mixing unit may include a cube circuit that triples the frequency of the output signal of the modulator, and the bias voltage is an amplitude voltage of the carrier signal that is superimposed on the intermediate frequency signal. Is preferably set to a value that is √2 times the amplitude voltage of the intermediate frequency signal.

For example, the modulation unit mixes the baseband signal and the carrier signal to generate the intermediate frequency signal, and outputs the inputted carrier signal as an amplitude voltage corresponding to the bias voltage and outputs the amplitude voltage. An amplitude adjuster and an adder for adding the output signal of the modulator and the output signal of the amplitude adjuster are included.

For example, the modulator is composed of a Gilbert cell, one of the differential input pairs of the Gilbert cell is connected to the baseband signal as a single-ended signal, and the other is connected to the bias voltage.

The baseband signal may be a quadrature phase amplitude modulated signal.

The intensity of the fundamental wave component of the intermediate frequency signal included in the transmission signal multiplied by the frequency mixing unit changes according to the amplitude voltage of the carrier signal superimposed on the intermediate frequency signal. According to the present invention, since the amplitude voltage of the carrier signal to be superimposed on the intermediate frequency signal can be adjusted by the bias voltage applied to the modulator, the bias voltage is optimized and the strength of the fundamental wave component of the intermediate frequency signal included in the transmission signal is adjusted. Can be maximized.

Block diagram of a transmitter according to an embodiment of the present invention Block diagram of a modulator according to an example Block diagram of a transmitter according to a first specific example Circuit diagram of a modulator in the transmitter according to the first example. Block diagram of a transmitter according to a second specific example Circuit diagram of a modulator in a transmitter according to a second specific example. A graph showing various signal intensities included in the output of the modulator when the bias voltage VB is set to 0V. A graph showing various signal intensities included in the output of the modulator when the bias voltage VB is set to 0.9V. Graph showing the relationship between LO signal strength and RF signal strength Modification of Gilbert cell shown in FIG.

Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed description of well-known matters and repeated description of substantially the same configuration may be omitted. This is for avoiding unnecessary redundancy in the following description and for facilitating understanding by those skilled in the art.

It is to be noted that the inventor provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present invention, and is not intended to limit the subject matter described in the claims by these. Absent.

<<Embodiment>>
FIG. 1 is a block diagram of a transmitter according to an embodiment of the present invention. The transmitter 10 according to the present embodiment includes a modulator 11, an amplifier 12, and a frequency mixer 13. The transmitter 10 up-converts a baseband signal (hereinafter referred to as a BB signal) output from a baseband unit (not shown) into a radio frequency signal (hereinafter referred to as an RF signal) of a high frequency (for example, 300 GHz band) and transmits the radio frequency signal. To do.

A BB signal output from a baseband unit (not shown) and a carrier signal (hereinafter, referred to as LO signal) output from a local oscillator (not shown) are input to the modulator 11. The modulator 11 outputs a signal obtained by superimposing the LO signal on an intermediate frequency signal (hereinafter, referred to as an IF signal) obtained by mixing the BB signal and the LO signal. That is, the general modulator up-converts the BB signal using the LO signal and outputs the IF signal, whereas the modulator 11 leaks and outputs the LO signal as well as the IF signal.

Further, the bias voltage VB is applied to the modulator 11. The amplitude voltage of the LO signal and the superposition of the LO signal in the modulator 11 can be adjusted by the bias voltage VB applied to the modulator 11.

FIG. 2 is a block diagram of the modulator 11 according to an example. The modulator 11 includes a modulator 111, an amplitude adjuster 112, and an adder 113. The modulator 111 multiplies the BB signal by the LO signal to generate an IF signal. The amplitude adjuster 112 outputs the input LO signal as an amplitude voltage according to the bias voltage VB. The adder 113 adds the output signal of the modulator 111 and the output signal of the amplitude adjuster 112. As a result, the modulator 11 outputs a signal obtained by superimposing the LO signal on the IF signal. For convenience, this signal is referred to as “αLO+IF”. α represents that the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted.

Returning to FIG. 1, the amplification unit 12 amplifies the signal output from the modulation unit 11. The amplification unit 12 has a sufficient gain in the bands of the IF signal and the LO signal.

The frequency mixer 13 up-converts the signal output from the amplifier 12 to generate an RF signal. Specifically, the frequency mixing unit 13 can be configured by using a CMOS element like a general frequency multiplier, and can also be configured by another active element or passive element having a frequency multiplying characteristic. it can. However, unlike a general frequency multiplier, the frequency mixing unit 13 multiplies a signal (αLO+IF) in which the IF signal and the LO signal are superimposed. As will be described later, a square circuit or a cube circuit can be used as the frequency mixing unit 13.

Next, a more specific configuration example of the transmitter 10 according to the present embodiment will be described.

<<First Specific Example>>
FIG. 3 is a block diagram of a transmitter according to the first specific example. The transmitter 10A according to the first specific example embodies the modulator 11 in the transmitter 10 shown in FIG. 1 with an SDBM (Semi Double Balanced Mixer) 11A, and further embodies the frequency mixer 13 with a squaring circuit 13A. It was done. The SDBM is a circuit obtained by partially modifying a general DBM (Double Balanced Mixer) configured using Gilbert cells, and the name SDBM is coined by the inventor.

FIG. 4 is a circuit diagram of the modulator (SDBM 11A) in the transmitter 10A according to the first specific example. As shown in the figure, the SDBM 11A can be composed of a Gilbert cell.

Generally, a Gilbert cell is configured by vertically stacking a circuit in which two differential switching transistor pairs are cross-connected (hereinafter referred to as a cross-connecting circuit) and a differential amplifier circuit, that is, connecting them in series. When the BB signal and the LO signal are mixed in the Gilbert cell, it is general that the LO signal is differentially input to the cross-connect circuit and the BB signal is differentially input to the differential amplifier circuit. On the other hand, in the SDBM 11A, the BB signal as a single end signal is connected to one of the differential input pairs and the bias voltage VB is connected to the other without inputting the BB signal differentially to the differential amplifier circuit in the Gilbert cell. Connected. That is, the SDBM 11A intentionally inputs the BB signal unbalanced.

Generally, in a Gilbert cell, when the LO signal has a high frequency, the leakage of the LO signal to the output side (broken line arrow in the figure) increases due to the parasitic capacitance between the gate and drain of the transistor forming the cross-connect circuit. If the input signal is balanced, the leakage of the LO signal and the leakage of the inverted signal of the LO signal cancel each other and the LO signal superimposed on the IF signal is canceled. However, in the SDBM 11A, since the differential input of the differential amplifier circuit is unbalanced, the cancellation of the leakage of the LO signal and the leakage of the inverted signal of the LO signal is insufficient, and the LO signal is superimposed on the IF signal. That is, the SDBM 11A outputs a differential signal (αLO+IF) in which the LO signal is superimposed on the IF signal. Further, the coefficient α, that is, the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

The differential signal (αLO+IF) output from the SDBM 11A is amplified by the amplification unit 12 and input to the squaring circuit 13A. The squaring circuit 13A doubles the frequency of the differential signal (αLO+IF) and outputs an RF signal. Since the squaring circuit 13A is a known circuit such as an active doubler (also referred to as a frequency doubler) including a pair of transistors, a detailed description of the circuit configuration will be omitted.

The squaring circuit 13A substantially executes the operation represented by the following expression (1).

(ΑLO+βIF) ² =α ² LO ² +2αβ·LO·IF+β ² IF ² (1)
However, in the formula (1), LO represents a LO signal and IF represents an IF signal. Further, α and β represent the amplitude voltage of the LO signal and the IF signal, respectively.

In this way, by squaring the signal obtained by superimposing the IF signal and the LO signal in the squaring circuit 13A, the first harmonic component (basic component) of the IF signal represented by the second term on the right side of the equation (1) (Also referred to as wave component) and the second harmonic component of the IF signal represented by the third term on the right side. Among these, the fundamental wave component of the IF signal is a signal to be output as an RF signal from the transmitter 10A. Therefore, a bandpass filter (not shown) that allows a signal in a desired band to pass therethrough may be provided at the subsequent stage of the squaring circuit 13A to allow the fundamental wave component of the IF signal to pass.

The coefficient of each term on the right side of the equation (1) represents the amplitude voltage of each component. That is, the amplitude voltage of the fundamental wave component (RF signal) of the IF signal is represented by 2αβ, and the amplitude voltage of the second harmonic component of the IF signal is represented by β ² . Here, consider the condition where the amplitude voltage of the RF signal, that is, the coefficient (2αβ) of the second term on the right side of the equation (1) becomes maximum. It is when α=β that the coefficient (2αβ) of the second term on the right side becomes maximum under the condition that the total signal intensity of the LO signal and the IF signal is constant, that is, α ² +β ² =1. That is, when the amplitude voltage of the LO signal is made equal to the amplitude voltage of the IF signal, the amplitude voltage of the RF signal can be maximized, and as a result, the strength of the RF signal is maximized.

From the above knowledge, in order to maximize the strength of the RF signal output from the transmitter 10A, in the SDBM 11A, the bias voltage VB should be set to a value such that the amplitude voltage of the LO signal becomes equal to the amplitude voltage of the IF signal. It can be said that it is good.

<<Second Specific Example>>
FIG. 5 is a block diagram of a transmitter according to the second specific example. The transmitter 10B according to the second specific example is capable of modulating a BB signal that is quadrature-phase amplitude modulated. More specifically, the transmitter 10B embodies the modulator 11 in the transmitter 10 shown in FIG. 1 with an SDBQM (Semi Double Balanced Quadrature Mixer) 11B and further embodies the frequency mixer 13 with a squaring circuit 13A. Is. The SDBQM is a circuit obtained by partially modifying a general DBQM (Double Balanced Quadrature Mixer) configured by using two Gilbert cells, and the name SDBQM is coined by the inventor.

FIG. 6 is a circuit diagram of the modulator (SDBQM11B) in the transmitter 10B according to the second specific example. As shown in the figure, the SDBQM 11B can be composed of two Gilbert cells. The first Gilbert cell (the Gilbert cell arranged on the left side of the figure) mixes the BB _I signal and the LO _I signal which are in-phase components of the BB signal and the LO signal. The second Gilbert cell (Gilbert cell arranged on the right side of the figure) mixes the BB _Q signal and the LO _Q signal, which are quadrature phase components of the BB signal and the LO signal.

In any of the Gilbert cell, as in the example of SDBM11A, BB _I signal without differential inputs the BB _I signal and the BB _Q signal in the differential amplifier circuit, as a single-ended signal to one of the differential input pair and connect the BB _Q signal, it connects the bias voltage VB to the other. That is, the SDBQM 11B intentionally inputs the BB _I signal and the BB _Q signal unbalanced.

Thus, LO cancellation of the leakage of the inverted signal of the leakage and LO _I signal of the _I signal, and LO _Q signal leakage and LO _Q signal LO signal to the IF signal becomes insufficient either cancel the leakage of the inverted signal of the Are overlaid. That is, the differential signal (αLO+IF) in which the LO signal is superimposed on the IF signal is output from the SDBQM 11B. Further, the coefficient α, that is, the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

In the transmitter 10B as well, as in the transmitter 10A, the bias voltage VB may be set to a value such that the amplitude voltage of the LO signal becomes equal to the amplitude voltage of the IF signal. Thereby, the strength of the RF signal output from the transmitter 10A can be maximized.

Next, the simulation result of SDBQM11B is shown. The LO signal was set to 136 GHz and the BB signal was changed in the range of 1 to 21 GHz to perform the simulation. FIG. 7A is a graph showing various signal intensities included in the output of the modulator ( SDBQM11B ) when the bias voltage VB is set to 0V. FIG. 7B is a graph showing various signal intensities included in the modulator output when the bias voltage VB is set to 0.9V. The horizontal axis represents the frequency of the BB signal, and the vertical axis represents the intensity of various signals. In the graph, the intensities of the upper sideband (136-186 GHz) and the lower sideband (116-136 GHz) of the IF signal, the LO signal, and the image signal included in the output of the modulator are plotted.

For example, looking at the BB signal at 10 GHz, when the bias voltage VB is 0 V, the intensity of the LO signal included in the modulator output is approximately −7 dBm (see FIG. 7A ). On the other hand, when the bias voltage VB is 0.9 V, the intensity of the LO signal included in the modulator output is approximately -1.5 dBm (see FIG. 7B ). From this result, it is understood that in the SDBQM 11B , the amplitude voltage of the LO signal superimposed on the IF signal can be adjusted by the bias voltage VB.

FIG. 8 is a graph showing the relationship between LO signal strength and RF signal strength. Here, the frequency of the IF signal is 136 GHz and the intensity is -10 dBm. As can be seen from the graph, when the amplitude voltage of the LO signal and the amplitude voltage of the IF signal are the same, that is, when the strength of the LO signal is the same as the strength of the IF signal, ie, −10 dBm, the strength of the RF signal becomes maximum.

<<Effect>>
As described above, the intensity of the fundamental wave component of the IF signal included in the RF signal multiplied by the frequency mixing unit 13 changes according to the amplitude voltage of the LO signal superimposed on the IF signal. In the transmitter 10 according to the present embodiment, the amplitude voltage of the LO signal to be superimposed on the IF signal can be adjusted by the bias voltage VB applied to the modulation unit 11, so that the bias voltage VB is set to an optimum value and the IF signal included in the RF signal is adjusted. The intensity of the fundamental wave component of can be maximized.

≪Modification≫
In the Gilbert cell shown in FIG. 4, the BB signal and the bias voltage VB are connected to the gates of the transistors in the differential amplifier circuit, but the BB signal and the bias voltage VB are directly connected to the common source of the pair transistors of the cross-connect circuit. May be. FIG. 9 shows a modification of the Gilbert cell shown in FIG. In the Gilbert cell shown in FIG. 9, the BB signal and the bias voltage VB are directly connected to the common source of the pair transistors of the cross-connection circuit. The Gilbert cell shown in FIG. 6 can be modified based on the same idea as in FIG.

The Gilbert cell shown in FIGS . 4, 6 and 9 as an example of the modulator 11 is composed of a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), but it may be another type of transistor such as an NPN bipolar transistor. The Gilbert cell, that is, the modulation unit 11 may be configured.

A cube circuit may be used for the frequency mixing unit 13. Since the cube circuit is a known circuit such as a frequency tripler, detailed description of the circuit configuration will be omitted.

The frequency mixer 13 as a cube circuit substantially executes the operation represented by the following equation (2).

(ΑLO+βIF) ³ =α ³ LO ³ +3α ² β·LO ² ·IF
+3αβ ² ·LO·IF ² +β ³ IF ³ (2)
However, in the equation (2), LO represents the LO signal and IF represents the IF signal. Further, α and β represent the amplitude voltage of the LO signal and the IF signal, respectively.

In this way, the signal in which the IF signal and the LO signal are superposed is cubed in the cube circuit, so that the first harmonic component (fundamental wave component) of the IF signal represented by the second term on the right side of the equation (2). Component), the second harmonic component of the IF signal represented by the third term on the right side, and the third harmonic component of the IF signal represented by the fourth term on the right side. Among these, the fundamental wave component of the IF signal is a signal to be output as an RF signal from the transmitter 10. Therefore, a bandpass filter (not shown) that allows signals in a desired band to pass therethrough may be provided in the subsequent stage of the frequency mixer 13 as a cube circuit to allow the fundamental wave component of the IF signal to pass.

The coefficient of each term on the right side of the equation (2) represents the amplitude voltage of each component. That is, the amplitude voltage of the fundamental wave component (RF signal) of the IF signal is 3α ² β, the amplitude voltage of the second harmonic component of the IF signal is 3αβ ² , and the amplitude voltage of the third harmonic component of the IF signal is β ³ . Represented respectively. Here, the condition that the amplitude voltage of the RF signal, that is, the coefficient (3α ² β) of the second term on the right side of the expression (2) becomes maximum will be considered. It is when α=√2β that the coefficient (3α ² β) of the second term on the right side becomes maximum under the condition that the total signal intensity of the LO signal and the IF signal is constant, that is, α ² +β ² =1. That is, when the amplitude voltage of the LO signal is √2 times the amplitude voltage of the IF signal, the amplitude voltage of the RF signal can be maximized, and as a result, the strength of the RF signal is maximized.

From the above knowledge, when the cube circuit is used as the frequency mixing unit 13, in order to maximize the strength of the RF signal output from the transmitter 10, the bias voltage VB is set to the amplitude voltage of the LO signal in the modulation unit 11. It can be said that the value should be set to a value that is √2 times the amplitude voltage of the IF signal.

As described above, the embodiment has been described as an example of the technique of the present invention. To that end, the accompanying drawings and detailed description are provided.

Therefore, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem but also the components not essential for solving the problem in order to exemplify the above technology Can also be included. Therefore, it should not be immediately recognized that the non-essential components are essential by the fact that the non-essential components are described in the accompanying drawings and the detailed description.

Further, since the above-described embodiment is for exemplifying the technique of the present invention, various changes, replacements, additions, omissions, etc. can be made within the scope of the claims or the scope equivalent thereto.

10, 10A, 10B... Transmitter, 11... Modulation section, 11A... SDBM (specific example of modulation section), 11B... SDBQM (Specific example of modulation section), 13... Frequency mixing section, 13A... Square circuit (frequency mixing) Specific examples), 111... Modulator, 112... Amplitude adjuster, 113... Adder, BB... Baseband signal, LO... Carrier signal, IF... Intermediate frequency signal, VB... Bias voltage

Claims (6)

A baseband signal and a carrier signal are input, and a modulator that outputs a signal in which the carrier signal is superimposed on an intermediate frequency signal obtained by mixing the baseband signal and the carrier signal,
A frequency mixing unit connected to the latter stage of the modulation unit and multiplying an output signal of the modulation unit,
The transmitter is configured such that an amplitude voltage of the carrier signal to be superimposed on the intermediate frequency signal can be adjusted by the applied bias voltage in the modulator. The frequency mixing section has a squaring circuit that doubles the frequency of the output signal of the modulation section,
The transmitter according to claim 1, wherein the bias voltage is set to a value such that an amplitude voltage of the carrier signal superimposed on the intermediate frequency signal becomes equal to an amplitude voltage of the intermediate frequency signal. The frequency mixing section has a cube circuit that triples the frequency of the output signal of the modulation section,
The transmitter according to claim 1, wherein the bias voltage is set to a value such that the amplitude voltage of the carrier signal superimposed on the intermediate frequency signal is √2 times the amplitude voltage of the intermediate frequency signal. .. A modulator in which the modulator mixes the baseband signal and the carrier signal to generate the intermediate frequency signal, and an amplitude adjustment for outputting the inputted carrier signal as an amplitude voltage according to the bias voltage. The transmitter according to any one of claims 1 to 3, further comprising: an adder for adding an output signal of the modulator and an output signal of the amplitude adjuster. The modulator is composed of a Gilbert cell,
The transmitter according to claim 1, wherein the baseband signal as a single-ended signal is connected to one of the differential input pairs of the Gilbert cell, and the bias voltage is connected to the other. .. The transmitter according to claim 1, wherein the baseband signal is a quadrature phase amplitude modulated signal.

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