JP2004289812A - Transmitting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitting circuit using an EER method without signal deterioration and having a high modulation precision. <P>SOLUTION: The transmitting circuit comprises a modulation signal generating circuit 101, wiring 120 of modulated signals in which an OFDM modulated waves are to be passed therethrough, a detecting circuit 102, wiring 121 of phase components for transmitting the phase components, wiring 122 of amplitude components for transmitting the amplitude components, a level deciding circuit 106 for making level decision of the amplitude components, wiring 111 for supplying a constant voltage, first and second selectors 103, 107, an orthogonal transformer 104, and a high-frequency power amplifier 105. An EER method or an approximated EER method is performed in an area where high-frequency input/output characteristics of the high-frequency power amplifier 105 indicates a linear response when executing a FER method, while a normal modulation is performed in an area indicating a non-linear response. A modulation method is switched by the level deciding circuit and the selector based on a threshold value of a boundary between the area indicating the linear response and the area indicating the non-linear response. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmission circuit for transmitting a high-frequency signal wirelessly.

  In general, in a modulated signal accompanied by amplitude modulation, particularly in multilevel modulation such as QAM (quadrature amplitude modulation), a high-frequency power amplifier arranged in a transmission circuit for transmitting power to an antenna needs a linear operation. . Therefore, as the operation class of the high-frequency power amplifier, class A or class AB has been used.

  However, with the use of broadband communication, communication systems using subcarriers such as OFDM (Orthogonal Frequency Division Multiplex) have begun to be used, and higher efficiency is expected in conventional class A and class AB high frequency power amplifiers. I can no longer do it. In other words, in the OFDM modulation, a large power is generated instantaneously and completely at random due to the superposition of subcarriers, and the ratio of the average power to the instantaneous maximum power, PAPR (Peak to Average Power Ratio) is large. Therefore, it is necessary to always maintain a large DC power so that a peak power considerably larger than the average power can be linearly amplified. In class A operation, the efficiency is only 50% at the maximum. Particularly in the case of OFDM modulation, the peak voltage for compensating for the peak power and the instantaneous voltage for compensating for the instantaneous power during periods other than when peak power is output due to the large PAPR. DC power obtained by multiplying the difference between the current and the current becomes almost heat and is discarded. The resulting efficiency is greatly reduced.

  For this reason, for example, in a portable wireless device using a battery as a power supply, the continuous usable time is short, and a practical problem occurs.

  In order to solve such a problem, a conventional EER method (Envelope Elimination and Restoration) known as Kahn's method has been proposed (for example, see Patent Document 1).

FIG. 8 is a block circuit diagram showing an outline of a conventionally known EER method. In the figure, an OFDM modulation wave (modulation signal) generated by a modulation signal generation circuit 401 is input to a detection circuit 402 as modulation signal detection means via a modulation signal wiring 410. Then, the detection circuit 402 detects the OFDM modulated wave by dividing it into a phase component and an amplitude component. Specifically, the I and Q vector waves of the OFDM modulated wave generated by the modulation signal generating circuit 401 are divided into an amplitude component √ (I ² + Q ² ) and a phase component tan ⁻¹ (Q / I). Is detected. Then, the phase component (complex phase modulated wave) is up-converted by the quadrature modulator 404 from the detection circuit 402 via the phase component wiring 411, and is then converted in the form of high-frequency signal power into a high-frequency input terminal of a PA 405 (high-frequency power amplifier). Is input to The amplitude component (amplitude modulated wave) is subjected to DC / DC conversion by the DC / DC converter 403 via the amplitude component wiring 412, and is then input to the power supply voltage terminal of the PA 405.

  As an example of the OFDM modulated wave, in the case of IEEE802.11a, the back-off amount (the amount indicating how low the operation is performed from the saturation power) is required to be about 7 dB. That is, since the high frequency output power is used only for 20% of the high frequency peak power, the efficiency is reduced from 50% to 10%. As described above, in order to use a class A or class AB operated PA with high efficiency, it is necessary to sequentially supply the minimum required power supply voltage to the PA to output high-frequency power to the PA and set the back-off ideally to 0 dB. desirable.

In order to solve this problem, in the EER method, a modulated wave obtained by orthogonally modulating a phase component obtained by performing a polar coordinate conversion on a modulated signal is provided as a modulated wave to be provided to the PA 405. Since the modulated wave of the phase component is a sine wave having a constant amplitude and a temporally changing phase, the PA 405 can operate with a backoff of almost 0 dB. Since the amplitude component input from the power supply terminal is multiplied by the phase component and the PA output, it is possible to obtain the same modulated wave obtained by orthogonally modulating the original modulation signal.
U.S. Pat. No. 6,256,482 B1 (3 page drawing, FIG. 6)

  However, according to the EER method of the related art, in the response of the output voltage to the power supply voltage of the PA 405 when a certain constant power is input to the PA 405, the resulting spectrum mask and EVM (modulation accuracy) do not fall within the wireless standard. However, there is a problem that the modulated wave cannot be restored correctly.

  FIGS. 9A, 9B and 9C respectively show the voltage amplitude (Vin) of the amplitude component input to the power supply voltage terminal (VDD) of the conventional PA 405 and the power supply voltage terminal (VDD) of the PA 405, respectively. FIG. 4 is a diagram showing a response characteristic of an output voltage (RFout) with respect to an input voltage, and a voltage amplitude of the output voltage (RFout) with respect to Vin. As shown in FIG. 9B, since the response of the PA 405 is a non-linear response, when the EER method is executed, the phase component and the amplitude component are multiplied by the output of the PA 405, and when the modulated wave is generated, the modulation accuracy is reduced. , The spectrum is deteriorated.

  An object of the present invention is to provide a transmission circuit having an EER method that does not cause signal degradation even when a PA having a non-linear response is used.

  The basic configuration of the transmission circuit of the present invention is to detect at least an amplitude component of a modulation signal including a phase component and an amplitude component, and provide an amplitude component wiring for transmitting the amplitude component. A determination means for determining whether or not the value is larger than a threshold value is provided in the amplitude component wiring.

  This makes it possible to change the transmission method in accordance with the magnitude of the amplitude component of the modulated signal, thereby suppressing problems in normal class A operation and problems using the EER method. In general, the threshold may be set so as to correspond to a boundary between a region where a transmitted signal shows a linear response and a region where a transmitted signal shows a non-linear response. A linear response is defined as a radio standard when an appropriate offset voltage is applied to the response and the voltage amplitude component is proportionally multiplied so that the range of the response includes the voltage amplitude range in which the amplitude component of the modulation signal changes. This is a region showing the degree of linearity that satisfies the specified spectrum mask and modulation accuracy, and the non-linear response is a region that does not meet the wireless standard when the same operation is performed. Thus, in a region where a signal to be transmitted falls within the wireless standard, a low-loss method such as the EER method is used, and in a region where the signal to be transmitted does not fall within the wireless standard, deterioration of the quality of the transmitted signal is suppressed. Can be adopted.

  In the above basic configuration, not only the amplitude component but also the phase component is detected, and if the amplitude value of the amplitude component is equal to or smaller than the threshold value, the modulation signal is increased to the phase component wiring and the modulation signal wiring for transmitting the phase component. In this case, the first selection output means for outputting the phase component is provided, and the amplitude component wiring and the constant voltage supply wiring are provided with a constant voltage when the amplitude value of the amplitude component is equal to or less than the threshold value, and an amplitude component when the amplitude value is large. Is provided, the output of the first selection output means can be connected to the high-frequency input terminal of the high-frequency power amplifier, and the output of the second selection means can be connected to the power supply voltage terminal. Therefore, it is possible to perform the EER method only in a region where the response of the output amplitude from the high frequency output of the high frequency power amplifier falls within the wireless standard, and to linearly amplify a normal modulated wave in a region not meeting the wireless standard. That. Therefore, it is possible to prevent the deterioration of the transmission signal caused by performing the EER in a region where the response of the high-frequency power amplifier does not meet the wireless standard, and it is possible to realize a transmission circuit with high efficiency and no signal deterioration of the transmission signal.

  The apparatus may further include a DC / DC converter connected to the second selection output unit and converting the output signal of the second selection output unit into a voltage.

  By providing the modulation signal generation means with means for designating the output power level, the output power level to be output can be specified to the modulation signal generation means. Therefore, by setting the IQ level by the modulation signal generation means, the output power level can be reduced. Can be set freely.

  By providing the frequency conversion means between the first selection output means and the high-frequency power amplifier, it becomes possible to handle a high-frequency signal in a wider band. For example, since the bandwidth of a DA converter is at most several hundreds of megahertz, it cannot be processed if the carrier exceeds GHz, but the carrier can be easily converted by using a frequency conversion means such as a quadrature modulator. This is because the frequency can be up-converted.

  Further, according to the basic configuration, a constant voltage is output to the amplitude component wiring and the constant voltage supply wiring when the amplitude value of the amplitude component is equal to or less than the threshold value, and the amplitude component is output when the amplitude value is large, according to the determination result of the determination unit. Also, by providing the selective output means, the approximation EER method substantially equal to the EER method is performed only in a region where the response of the output amplitude from the high-frequency output of the high-frequency power amplifier falls within the wireless standard, and does not meet the wireless standard. In the region, a normal modulated wave can be linearly amplified. Therefore, it is possible to prevent the deterioration of the transmission signal which may be caused by performing the EER in a region where the response of the high-frequency power amplifier does not meet the linear standard, and it is possible to realize a transmission circuit with high efficiency and no signal deterioration of the transmission signal.

  Also in this case, by providing the frequency conversion means between the modulation signal generation means and the high-frequency power amplifier, it becomes possible to handle a high-frequency signal in a wider band. For example, since the bandwidth of a DA converter is at most several hundreds of megahertz, it cannot be processed if the carrier exceeds GHz, but the carrier can be easily converted by using a frequency conversion means such as a quadrature modulator. This is because the frequency can be up-converted.

  According to the transmission circuit of the present invention, when the normal EER method is used, even if the RF output response of the high-frequency power amplifier deviates from the linear standard with respect to the input from the power supply voltage terminal, deterioration of the modulation accuracy is suppressed. be able to.

(1st Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, an OFDM modulated wave is employed as a modulation signal. As a system using OFDM modulation, for example, there is a wireless LAN system of the IEEE802.11a standard. In the wireless LAN system, for example, modulation of 64 QAM is performed on each of the 52 orthogonal subcarriers, inverse discrete Fourier transform is performed, and this is multiplexed to obtain an OFDM modulated signal. The 52 carriers are separated by 312.5 kHz, and occupy 52 × 312.5 = 16.25 MHz.

  FIG. 1 is a block circuit diagram of a transmission circuit for realizing the EER method according to the first embodiment of the present invention. As shown in the figure, the transmission circuit includes a modulation signal generation circuit 101 that is a modulation signal generation unit that generates an OFDM modulation wave (modulation signal) including an amplitude component and a phase component, and a modulation signal through which the OFDM modulation wave flows. A wiring 120, a detection circuit 102 which is a modulation signal detecting means for detecting an amplitude component and a phase component of the OFDM modulated wave, a phase component wiring 121 for transmitting a phase component of the OFDM modulated wave, and an amplitude component of the OFDM modulated wave. An amplitude component wiring 122 to be transmitted, a level determination circuit 106 as a determination means for determining the level of the amplitude component of the OFDM modulated wave, and a storage means for storing a threshold voltage serving as a reference for the level determination of the level determination circuit 106. A certain ROM 109, a constant voltage supply line 111 connected to a power supply voltage terminal receiving a voltage of 1.1 V and supplying a constant voltage of 1.1 V; A first selector 103 serving as first selection output means for selecting either the OFDM modulated wave from the modulation signal generation circuit 101 or a phase component from the detection circuit 102 in accordance with a result of the determination by the determination circuit 106; A second selection output for selecting one of an amplitude component input via the amplitude component wiring 122 and a constant voltage of 1.1 V supplied via the constant voltage wiring 111 in accordance with the determination result of the determination circuit 106 A signal selector 107, a DC / DC converter 108, a quadrature modulator 104 for quadrature-modulating an output from the first selector 103, and a high-frequency signal output from the quadrature modulator 104 to a high-frequency input terminal. PA 105 (high-frequency power amplifier) that receives the amplitude component from converter 108 at the power supply voltage terminal, and specifies the output power to modulation signal generation circuit 101 And an output power specifying unit 110 is an output power specifying unit that.

  The modulation signal generation circuit 101 generates the above-described OFDM modulation wave (modulation signal). The OFDM modulated wave generated by the modulation signal generation circuit 101 flows through the modulation signal wiring 120 and is input to the first selector 103.

The detection circuit 102 detects an OFDM modulated wave flowing through the modulated signal wiring 120 by dividing the OFDM modulated wave into a phase component (complex phase modulated wave) and an amplitude component (amplitude modulated wave). Specifically, the I and Q vector waves of the OFDM modulated wave generated by the modulation signal generation circuit 101 are divided into an amplitude component √ (I ² + Q ² ) and a phase component tan ⁻¹ (Q / I). Is detected. The phase component flows through the phase component wiring 121 as an IQ wave and is input to the first selector 103, and the amplitude component flows through the amplitude component wiring 122 and is input to the second selector 107.

  The level determination circuit 106 receives the threshold voltage level stored in the ROM 109 and the amplitude component flowing through the amplitude component wiring 122 and determines whether the voltage level of the amplitude component is greater than or less than the threshold voltage level.

  The first selector 103 selects one of the phase component of the OFDM modulated wave input through the phase component wiring 121 and the OFDM modulated wave input through the modulation signal wiring 120 based on the determination result of the level determination circuit 106. And output. At this time, if the voltage level of the amplitude component flowing through the amplitude component wiring 122 is equal to or lower than the threshold voltage level stored in the ROM 109, an OFDM modulated wave that is a modulation signal is selected and output, and the voltage level of the amplitude component becomes the threshold voltage. If it is larger than the level, the phase component from the detection circuit 102 is selected and output.

  The second selector 107 selects and outputs one of the constant voltage 1.1 V from the constant voltage supply wiring 111 and the amplitude component input through the amplitude component wiring 122 based on the determination result of the level determination circuit 106. I do. At this time, if the voltage level of the amplitude component flowing through the amplitude component wiring 122 is equal to or lower than the threshold voltage level stored in the ROM 109, a constant voltage 1.1V from the constant voltage supply wiring 111 is selected and output. The amplitude component from the detection circuit 102 is selected and output.

  The quadrature modulator 104 converts a complex phase modulated wave (quadrature component and in-phase component) output from the first selector 103 into a high-frequency signal.

  The DC / DC converter 108 amplifies the output from the second selector 107 and supplies an amplitude modulation signal having a desired voltage amplitude to the power supply voltage terminal of the PA 105.

  The PA 105, which is a high-frequency power amplifier, is of class A, and the high-frequency signal output from the quadrature modulator 104 is input to the high-frequency input terminal of the PA 105. When the system selects the EER method, the DC-DC converter 108 The converted amplitude component is input from the power supply voltage terminal. As a result, the high-frequency output terminal of PA 105 outputs a modulated wave in which both the phase and the amplitude are modulated, that is, the amplitude and the phase are multiplied. When the system selects the normal IQ quadrature modulation, PA 105 performs linear amplification by fixing the voltage supplied from the power supply voltage terminal to 1.1 V.

  The output power specifying unit 110 receives a specification regarding transmission power control from a MAC (Media Access Control) or the like.

-Example of signal change during processing-
FIG. 2 is a diagram illustrating an example of a change in a signal processed in the transmission circuit according to the present embodiment. 3A and 3B show the response characteristics of the voltage of the output signal (RFout) with respect to the input voltage to the power supply voltage terminals of the high-frequency amplifiers 405 and 105 of the conventional transmission circuit and the transmission circuit of the present embodiment, respectively. FIG.

  As shown in FIG. 2, for example, the output level specified by the MAC is input to the modulation signal generation circuit 101 via the output power specifying unit 110, and a constellation as shown in 2A of FIG. The IQ orthogonal signal of the OFDM modulated wave shown is generated. Then, the OFDM modulated wave is detected by the detection circuit 102 separately into an amplitude component as shown in 2B of FIG. 2 and a complex phase component (phase component) (not shown). The output amplitude component is compared by the level determination circuit 106 with a threshold voltage level set in the ROM 109.

  At this time, the threshold voltage level set in the ROM 109 is, for example, as shown in FIG. 3A, the lower limit value of a linear region showing a sufficiently linear response in the input voltage-output signal voltage response characteristic of the high-frequency power amplifier. , For example, 1V. Alternatively, the threshold voltage level may be set by a suitable mathematical operation. Here, the linear region means that the output spectrum or the output EVM is in a range that satisfies the wireless standard of the communication system, and does not mean that the response characteristic is a strict linear characteristic. Absent.

  Using the threshold voltage level 1V, the level determination circuit 106 determines whether the level of the amplitude component generated by the detection circuit 102 is higher than the threshold voltage A or lower than the threshold B. And outputs the determination result A or B to the selectors 107 and 103, respectively.

  When the determination A is input from the level determination circuit 106, that is, when the amplitude component is in the state shown in FIG. 2C, the second selector 107 outputs the amplitude component input from the detection circuit 102 via the amplitude component wiring 122. (See 2E in FIG. 2), and the first selector 103 selects a phase component (see 2F in FIG. 2) input from the detection circuit 102 via the phase component wiring 121.

  In this case, the EER method is used in the transmission circuit. Therefore, the PA 105 can be operated near the saturation point by the EER method, and can be operated at almost the theoretical maximum efficiency. Therefore, high efficiency can be realized by performing the EER method.

  On the other hand, when the judgment B is input from the level judgment circuit 106, that is, when the amplitude component is in the state shown in 2D in FIG. 2, the first selector 103 receives the input from the modulation signal generation circuit 101 through the modulation signal wiring 120. The selected OFDM modulated wave (modulated signal) is selected, and the second selector 107 selects a constant voltage of 1.1V.

  In this case, normal IQ quadrature modulation is performed in the transmission circuit. Therefore, the constant voltage to be supplied to the PA 105 is set to, for example, 1.1 V because the threshold voltage is set to 1 V, and a small margin is given to the threshold voltage. Assuming that the average voltage of the modulated wave having an amplitude of 1 V or less is 0.8 V, PA 105 operates with a back-off of 2 dB. At this time, the efficiency is 63%, which is 50% which is the theoretical efficiency of the class A operation, and is 31.5%. Assuming that the operation of the PA 105 in the EER method is a saturation operation, a theoretical efficiency of 50% is achieved. Therefore, the efficiency expected in the configuration of the present embodiment is 50 × 0.1 + 31.5 × 0.9 = 33.4% when the amplitude at the threshold voltage of 1 V or more is about 10%.

  In the case of only normal quadrature modulation, only an efficiency of 10% can be obtained, but by using the present invention, the efficiency can be greatly improved.

  Further, in the conventional transmission circuit, as shown in FIG. 3A, the response characteristic of the voltage amplitude at the high-frequency output terminal RFout with respect to the input voltage to the power supply voltage terminal of the high-frequency power amplifier does not conform to the wireless standard. Due to the existence of the nonlinear region, the output signal was distorted as shown on the left side of FIG. In contrast, in the present embodiment, the offset voltage applied to the amplitude component in the DC / DC converter is appropriately adjusted (in the present embodiment, the offset voltage is 0.5 V), and the voltage level of the amplitude component is equal to or lower than the threshold voltage level. In some cases, by performing normal quadrature modulation, it is possible to keep the entire response characteristics 3A and 3B of the voltage amplitude at RFout with respect to the input voltage within the wireless standard, as shown in FIG. Therefore, as shown on the left side of FIG. 3B, the amplitude component can be output without distortion. As described above, the linear region here also means that the spectrum output from the power amplifier or the output EVM is linear enough to satisfy the communication system standard, and the response characteristic is high. It does not mean that it is a perfectly linear characteristic.

(Second embodiment)
Also in the present embodiment, an OFDM modulated wave is employed as a modulation signal. FIG. 4 is a block circuit diagram schematically illustrating a configuration of a transmission circuit according to the second embodiment of the present invention. As shown in the figure, the transmission circuit includes a modulation signal generation circuit 201 that is a modulation signal generation unit that generates an OFDM modulation wave (modulation signal) including an amplitude component and a phase component, and a modulation signal through which the OFDM modulation wave flows. A wiring 220; a detection circuit 202 which is a modulation signal detecting means for detecting an amplitude component and a phase component of the OFDM modulated wave; an amplitude component wiring 222 transmitting the amplitude component of the OFDM modulated wave; A level determination circuit 206 that is a determination unit for performing a level determination, a ROM 209 that is a storage unit that stores a threshold voltage serving as a reference for the level determination of the level determination circuit 206, and an amplitude component wiring 222 are provided. A first DC / DC converter 208 for DC / DC conversion, a constant voltage supply line 211 for supplying a constant voltage, and a constant voltage supply line 211 The DC / DC converter 210 converts the constant voltage of 3V to DC / DC to output a constant voltage of 1.1V, and is supplied from the first DC / DC converter 208 according to the determination result of the level determination circuit 206. A signal selector 207, which is a selection output means for selecting any one of an amplitude component and a constant voltage of 1.1 V supplied from the second DC / DC converter 210, and an OFDM modulated wave transmitted through a modulation signal wiring 220 It includes a quadrature modulator 204 and a PA 205, which is a constant-saturation type high-frequency power amplifier that receives a high-frequency signal output from the quadrature modulator 204 at a high-frequency input terminal and receives an amplitude component from the selector 207 at a power supply voltage terminal. .

  Note that, also in the present embodiment, a circuit element having the same function as the output power specifying unit 110 for specifying the output power may be arranged in the modulation signal generation unit 101 in the first embodiment.

  Here, the constant voltage supply wiring 211 supplies the constant voltage 1.1 V converted by the second DC / DC converter 210.

  The detection circuit 202 obtains an amplitude component by performing an operation for obtaining an absolute value of a complex modulation vector of the modulation signal (OFDM modulation wave).

  The level determination circuit 206 receives the threshold voltage level stored in the ROM 209 serving as storage means and the amplitude component flowing through the amplitude component wiring 222, and determines whether the voltage level of the amplitude component is greater than or less than the threshold voltage level. Is determined.

  The first DC / DC converter 208 amplifies the amplitude component input from the detection circuit 202 via the amplitude component wiring 222 and supplies an amplitude component having a desired voltage amplitude to the power supply voltage terminal of the PA 205, and the PA 205 Supply the required DC power.

  The selector 207 selects and outputs one of a constant voltage of 1.1 V from the constant voltage supply wiring 211 and an amplitude component input via the amplitude component wiring 222 based on the determination result of the level determination circuit 206. At this time, when the voltage level of the amplitude component flowing through the amplitude component wiring 222 is equal to or lower than the threshold voltage level stored in the ROM 209, the output 1.1V of the constant voltage supply wiring 211 is selected and output. An amplitude component from the detection circuit 202 is selected and output via the DC / DC converter 208.

  The quadrature modulator 204 converts an OFDM modulated wave (modulated signal), which is a complex phase modulated wave (quadrature component and in-phase component) output from the detection circuit 202, into a high-frequency signal.

  The PA205, which is a high-frequency power amplifier, is of class A, and the high-frequency signal output from the quadrature modulator 204 is input to the high-frequency input terminal of the PA205 via the modulation signal wiring 220, and the system has substantially selected the EER method. At this time, the amplitude component DC-converted by the first DC-DC converter 208 is input from the power supply voltage terminal. As a result, the high-frequency output terminal of PA 205 outputs a modulated wave in which both the phase and the amplitude are modulated, that is, the amplitude and the phase are multiplied. When the system selects the normal IQ quadrature modulation, the voltage supplied from the power supply voltage terminal of PA 205 is fixed at a constant voltage of 1.1 V supplied from constant voltage supply line 211.

-Example of signal change during processing-
FIG. 6 is a diagram for explaining a change example of a signal processed in the transmission circuit of the present embodiment.

  As shown in FIG. 6, a detection circuit 202 converts an OFDM modulated wave (complex vector signal) having a constellation as shown in FIG. 6A generated in the modulation signal generation circuit 201 by a detection circuit 202 as shown in FIG. 6B. A large amplitude component is detected. The output amplitude component is compared by the level determination circuit 206 with a threshold voltage level set in the ROM 209.

  At this time, the threshold voltage level set in the ROM 209 is, for example, as shown in FIG. 3A, the lower limit value of the linear region showing a sufficiently linear response in the response characteristic of the input voltage-output signal voltage of the high-frequency power amplifier. , For example, 1V. Alternatively, the threshold voltage level may be set by a suitable mathematical operation. Here, the linear region means that the output spectrum or the output EVM is within a range that satisfies the linear standard of the communication system, and does not mean that the response characteristic is a strict linear characteristic. Absent.

  Using the threshold voltage level 1 V, the level determination circuit 206 determines whether the level of the amplitude component generated by the detection circuit 202 is higher than the threshold voltage C or lower than the threshold D. , And outputs the determination result C or D to the selector 207, respectively.

  Unlike the first embodiment, in the present embodiment, regardless of whether the determination of the level determination circuit 206 is the determination C or the determination D, the modulation signal generation circuit 201 The generated modulation signal (OFDM modulation wave) is input (see 6A in FIG. 6). Then, the OFDM modulated wave is detected by the detection circuit 202 into an amplitude component as shown in FIG. 6B and a complex phase component (phase component) (not shown). The output amplitude component is compared by the level determination circuit 206 with the threshold voltage level set in the ROM 209.

  When the determination C is input from the level determination circuit 206, the selector 207 selects an amplitude component (see 6C in FIG. 6) input from the detection circuit 202 via the amplitude component wiring 222.

  In this case, in this embodiment, since the input signal of the high-frequency power amplifier is not a phase component as in the first embodiment but a normal modulated wave having an amplitude component, the approximate EER method is used in the transmission circuit. Will be done. Therefore, the PA 205 can be operated near the saturation point by the approximate EER method, and can be operated with almost the theoretical maximum efficiency. The operation of the approximate EER method will be described later in detail.

  On the other hand, when the determination D is input from the level determination circuit 206, the selector 207 selects a constant voltage of 1.1V.

  In this case, normal IQ quadrature modulation is performed in the transmission circuit. Therefore, the constant voltage to be supplied to the PA 205 is set to, for example, 1.1 V because the threshold voltage is set to 1 V here and a margin is given to it. Assuming that the average voltage of a modulated wave having an amplitude of 1 V or less is 0.8 V, PA 205 operates with a 2 dB back-off. At this time, the efficiency is 63%, which is 50% which is the theoretical efficiency of the class A operation, and is 31.5%. Assuming that the operation of the PA 205 in the EER method is a saturation operation, a theoretical efficiency of 50% is achieved. Therefore, the efficiency expected in the configuration of the present embodiment is 50 × 0.1 + 31.5 × 0.9 = 33.4% when the amplitude at the threshold voltage of 1 V or more is about 10%.

  In the case of only normal quadrature modulation, only an efficiency of 10% can be obtained, but by using the present invention, the efficiency can be greatly improved.

  Furthermore, in the present embodiment, the EER method is substantially performed while the modulation signal is input to the high frequency input terminal of the PA 205 instead of the phase component as it is. Therefore, it is possible to avoid the deterioration of the modulation accuracy (Error Vector Magnitude: EVM) which cannot be avoided by the conventional EER method in which only the phase component is input to the high frequency input terminal of the high frequency power amplifier.

  In the conventional transmission circuit, as shown in FIG. 3A, the response characteristic of the voltage amplitude at the high-frequency output terminal RFout with respect to the input voltage to the power supply voltage terminal of the high-frequency power amplifier has a nonlinear region that does not fall within the linear standard. Was present, the output signal was distorted as shown on the left side of FIG. In contrast, in the present embodiment, the offset voltage applied to the amplitude component in the DC / DC converter is appropriately adjusted (in the present embodiment, the offset voltage is 0.5 V), and the voltage level of the amplitude component is equal to or lower than the threshold voltage level. In some cases, by performing normal quadrature modulation, it is possible to keep the entire response characteristics 3A and 3B of the voltage amplitude at RFout with respect to the input voltage within the linear standard as shown in FIG. 3B. Therefore, as shown on the left side of FIG. 3B, the amplitude component can be output without distortion. As described above, the linear region here also means that the spectrum output from the power amplifier or the output EVM is linear enough to satisfy the communication system standard, and the response characteristic is high. It does not mean that it is a perfectly linear characteristic.

  That is, when only the phase component is input to the high-frequency input terminal of the high-frequency power amplifier, the phase component is filtered within a range allowed by the digital-analog converter and to such an extent that the EVM is not affected. The resulting partial level drop of the phase component causes significant degradation of the EVM when the phase component is combined with the amplitude component at the output of the high frequency power amplifier. In addition, since the required bandwidth of the modulated signal is about 1/6 smaller than the phase component separated from the modulated signal, the bandwidth of a digital-to-analog converter or an anti-alias filter that suppresses spurious components generated by the digital-to-analog conversion is used. Can be narrowed. This is advantageous for reducing the power consumption of the digital-to-analog converter and for reducing the size and cost of the inductor used for the filter.

  Further, in the conventional transmission circuit, even when the amplitude component is 0, the output of the high-frequency power amplifier is determined by the coupling of the input power to the output, which is determined by the isolation characteristic between the input and output of the high-frequency power of the high-frequency power amplifier. Had an amplitude that caused an error. On the other hand, in the present embodiment, when the amplitude component applied to the power supply voltage terminal of the high-frequency power amplifier is 0, the power input to the high-frequency input terminal of the high-frequency power amplifier is also 0, and thus does not depend on the isolation characteristics. Thus, a correct modulated wave can be formed by the output of the high-frequency power amplifier.

  FIGS. 7A to 7D are diagrams for explaining a circuit operation for performing the approximate EER method using the constant envelope region.

  Here, for the sake of simplicity, the input wave (the OFDM modulated wave in the present embodiment) to the high-frequency power amplifier is a triangular wave whose amplitude envelope is triangular as shown in FIG. FIG. 7B shows the internal structure of the high-frequency power amplifier. The high-frequency power amplifier according to the present embodiment is a common-emitter bipolar transistor. An OFDM modulated wave, which is a modulation signal according to the present embodiment, is input to a base (high-frequency input terminal) of the bipolar transistor. Then, a choke inductor is inserted between the collector (power supply voltage terminal) of the bipolar transistor and the collector voltage Vc supply side, and the wiring from the collector to the high frequency output terminal is connected to the ground via the output load ZL. Is equivalently expressed as

  FIG. 7D is a diagram for explaining the input / output characteristics of the high-frequency power amplifier. The vertical axis represents the collector current Ic of the high-frequency power amplifier, and the horizontal axis represents the collector applied to the power supply voltage terminal of the high-frequency power amplifier. Represents the voltage Vc. FIG. 7D shows that the Ic-Vc characteristic changes with respect to the base-emitter voltage Vbe of the high-frequency power amplifier, and the DC base-emitter voltage Vbe, the DC collector voltage Vc, and the high-frequency It is shown that the load line determined by the output load ZL of the power amplifier determines the variable range of the base-emitter voltage Vbe, and further determines the variable range of the collector current Ic and the variable range of the collector voltage Vc.

  FIG. 7C shows an output voltage output from the high-frequency output terminal of the high-frequency power amplifier, and the output power is determined from the output voltage and the output impedance ZL.

  Here, if the input voltage exceeds the variable range of the base-emitter voltage Vbe (Vbe4−Vbe2 in FIG. 7D), the collector current exceeds the variable range of the collector current Ic determined from the load line. A time domain occurs in which the amplitude is constant (constant envelope). Since the voltage amplitude is obtained by voltage conversion of the collector current Ic by the output load impedance ZL, a constant (constant envelope) time region also occurs in the voltage amplitude Vout (= Ic.ZL). Since the signal having the constant envelope region is substantially equivalent to the phase component, it performs the same processing as the EER for inputting the phase component and the amplitude component to the high frequency input terminal and the power supply voltage terminal of the high frequency power amplifier, respectively. Will be. Therefore, in this specification, this processing will be referred to as an approximate EER method.

  In the present embodiment, in the time domain using the approximate EER method (the area falling within the linear standard), the threshold voltage in the level determination circuit is set so that the output voltage has a constant envelope, or the approximate EER method is used. The input power is adjusted so that a saturated output current is obtained during the time when the method is performed. Thus, when the amplitude component of the modulation signal is larger than the threshold voltage of the decision level circuit, the power amplification operation by the approximate EER method is performed.

-Modification of the second embodiment-
FIG. 5 is a block circuit diagram schematically showing a configuration of a transmission circuit according to a modification of the second embodiment. Also in this modification, similarly to the transmission circuit of the second embodiment shown in FIG. 4, a modulation signal generation circuit 201, a detection circuit 202, a quadrature modulator 204, a PA 205, a modulation signal wiring 220, and an amplitude component wiring 222 are provided. The basic functions of these circuit elements are as described in the second embodiment.

  In this modification, one DC / DC converter 211 is provided, a selector 207 having a built-in DA converter is interposed between the detection circuit 202 and the DC / DC converter 212, and a ROM 209 serving as storage means is provided. Is supplied to the high-frequency input terminal of the selector 207 via the constant voltage supply line 251. That is, in the present modification, the threshold voltage level to be compared with the voltage level of the amplitude component in the level determination circuit 206 and the threshold voltage level which is input from the constant voltage supply wiring 251 to the power supply voltage terminal of the PA 205 via the selector 207. And the level of the constant voltage. In other words, the ROM 209 serves both as a means for storing the threshold voltage level and as a means for supplying a constant voltage to the power supply voltage terminal of the PA 205 in a region not conforming to the wireless standard.

  Since the modulation operation of this modification is basically the same as that of the second embodiment, the same effect as that of the second embodiment can be exerted. In addition, in the present modification, only one DC / DC converter is required, so that the cost is more advantageous than that of the second embodiment. Further, since the selector is arranged on the upstream side of the DC / DC converter, if the DC / DC converter also has the amplitude amplification function, there is an advantage that the withstand voltage may be relatively low.

  In particular, by using the approximate EER method of the second embodiment and its modification, there is an advantage that high modulation accuracy can be maintained in a wider band as compared with the first embodiment. However, the method using the EER method of the first embodiment can easily increase the efficiency compared to the second embodiment and its modified example.

  Here, a device for realizing the transmission circuit of the first, second and modified examples of the second embodiment will be described.

  One LSI chip on which a modulation signal generation circuit, a detection circuit, and a level determination circuit are mounted can be configured. In that case, another circuit element is provided on another LSI chip or discrete chip.

  The frequency converter (for example, the quadrature modulator 104 or 204) is not necessarily required, but the provision of the quadrature modulator 104 or 204 makes it possible to handle a high-frequency signal in a wider band. For example, since the bandwidth of a DA converter is at most several hundreds of megahertz, if the carrier exceeds GHz, it cannot be processed. However, by using the frequency conversion means, the carrier frequency can be easily up-converted. is there.

  The frequency converter such as a quadrature modulator is preferably provided on an LSI chip on which a modulation signal generation circuit, a detection circuit, and a level determination circuit are mounted.

  The DC / DC converter, the selector, the high-frequency power amplifier or the ROM may be individually arranged in the transmission circuit as a discrete chip, or may be provided as a system LSI in a chip common to the modulation signal generation circuit, the detection circuit, and the level determination circuit. Can be provided. In that case, one or more circuit elements of the DC / DC converter, the selector, the high-frequency power amplifier, or the ROM can be provided in a common chip with the modulation signal generation circuit, the detection circuit, and the level determination circuit.

  Further, a ROM for storing the threshold voltage level is not necessarily required, and a signal indicating the threshold voltage level can be input from outside.

  The means for inputting a constant voltage to the constant voltage supply wiring may be a voltage generating circuit in the LSI chip or a member for supplying a voltage to the power supply voltage terminal from the outside.

  The transmission circuit of the present invention can be used as a transmission unit of a wireless communication device such as a so-called mobile phone or wireless LAN.

FIG. 3 is a block circuit diagram of a transmission circuit according to the first embodiment. FIG. 7 is a diagram for describing an example of a change in a signal processed in the transmission circuit according to the first embodiment. (A), (b) is a figure which shows the response characteristic of the voltage of the output signal with respect to the input voltage to the power supply voltage terminal of the high frequency amplifier of the conventional transmission circuit and the transmission circuit of 1st Embodiment, respectively. FIG. 9 is a block circuit diagram of a transmission circuit according to a second embodiment. FIG. 14 is a block circuit diagram of a transmission circuit according to a modification of the second embodiment. FIG. 11 is a diagram for describing an example of a change in a signal processed in the transmission circuit according to the second embodiment. (A)-(d) is a figure for demonstrating the circuit operation | movement which performs an approximate EER method using a constant envelope area | region. It is a block circuit diagram showing the outline of the conventionally known EER method. (A), (b), and (c) respectively show the voltage amplitude (Vin) of the amplitude component input to the power supply voltage terminal and the output voltage (RFout) with respect to the input voltage to the power supply voltage terminal in the conventional PA. It is a figure which shows the response characteristic and the voltage amplitude of the output voltage (RFout) with respect to Vin.

Explanation of reference numerals

Reference Signs List 101 Modulated signal generation circuit 102 Detection circuit 103 First selector 104 Quadrature modulator 105 PA
106 Level judgment circuit 107 Second selector 108 DC / DC converter 109 ROM
Reference Signs List 110 output power specifying section 111 constant voltage supply wiring 120 modulation signal wiring 121 phase component wiring 122 amplitude component wiring 201 modulation signal generation circuit 202 detection circuit 204 quadrature modulator 205 PA
206 Level determination circuit 207 Selector 208 First DC / DC converter 209 ROM
210 second DC / DC converter 211 constant voltage supply wiring 212 DC / DC converter 220 modulation signal 222 amplitude component wiring

Claims (13)

Modulation signal generation means for generating a modulation signal including a phase component and an amplitude component,
A modulation signal line connected to the modulation signal generation means for transmitting a modulation signal;
Modulation signal detection means connected to the modulation signal wiring and detecting at least an amplitude component of the modulation signal generated by the modulation signal generation means,
An amplitude component wiring connected to the modulation signal detection means and transmitting an amplitude component of the modulation signal;
Threshold input means for inputting a threshold for switching the modulation method of the modulation signal,
A transmission circuit connected to the amplitude component wiring, the transmission circuit comprising: a determination unit configured to determine whether an amplitude value of an amplitude component of the modulation signal is larger than the threshold value input from the threshold value input unit. The transmission circuit according to claim 1,
The transmission circuit, wherein the threshold is set so as to correspond to a boundary between a region where a signal to be transmitted shows a linear response and a region where a signal to be transmitted shows a non-linear response. The transmission circuit according to claim 1, wherein
The modulation signal detection means also detects a phase component of the modulation signal,
A phase component wiring connected to the modulation signal detection means and transmitting a phase component of the modulation signal;
A constant voltage supply line for supplying a constant voltage,
Connected to the modulation signal wiring and the phase component wiring, and outputs the modulation signal when the amplitude value of the amplitude component is equal to or less than the threshold, and outputs the phase component when the amplitude value is large, according to the determination result of the determination unit. First selection output means for outputting;
Connected to the amplitude component wiring and the constant voltage supply wiring, and outputs the constant voltage when the amplitude value of the amplitude component is equal to or less than the threshold value, and outputs the constant voltage when the amplitude value is large, according to the determination result of the determination unit. And a second selection output means for outputting a signal. The transmission circuit according to claim 3,
A transmission circuit connected to the second selection output means and further comprising DC / DC conversion means for converting the output signal of the second selection output means into a voltage. The transmission circuit according to claim 4,
A transmission circuit further comprising a high-frequency power amplifier having a high-frequency input terminal connected to the first selection output means and a power supply voltage terminal connected to the DC / DC conversion means. The transmission circuit according to claim 5,
A transmission circuit further comprising means for designating an output power level to the modulation signal generation means. The transmission circuit according to claim 5,
A transmission circuit further comprising frequency conversion means disposed between the first selection output means and the high frequency power amplifier. The transmission circuit according to claim 1, wherein
A constant voltage supply line for supplying a constant voltage,
Connected to the amplitude component wiring and the constant voltage supply wiring, and outputs the constant voltage when the amplitude value of the amplitude component is equal to or less than the threshold value, and outputs the constant voltage when the amplitude value is large, according to the determination result of the determination unit. And a selection output means for outputting a signal. The transmission circuit according to claim 8,
First DC / DC converting means disposed between the modulation signal detecting means and the selection output means in the amplitude component wiring, and converting the amplitude component into a voltage;
And a second DC / DC converter provided on the constant voltage supply line. The transmission circuit according to claim 8,
A transmission circuit connected to the selection output means and further comprising DC / DC conversion means for voltage-converting an output signal of the selection output means. The transmission circuit according to claim 8,
A transmission circuit further comprising a high-frequency power amplifier having a high-frequency input terminal connected to the modulation signal wiring and a power supply voltage terminal connected to the selection output means. The transmission circuit according to claim 11,
A transmission circuit further comprising frequency conversion means disposed between the first selection output means and the high frequency power amplifier. The transmission circuit according to any one of claims 1 to 12,
The threshold value input unit is a storage unit that stores the threshold value,
A transmitting circuit for performing the determination by extracting the threshold value stored in the storage means;

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