JP3824610B2 - Transmitter circuit - Google Patents

Description

  The present invention relates to a transmission circuit that wirelessly transmits a high-frequency signal.

  In general, in a modulation 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 requires a linear operation. . For this reason, class A or class AB has been used as the operation class of high-frequency power amplifiers.

  However, with the trend toward broadband communication, communication methods using subcarriers such as OFDM (Orthogonal Frequency Division Multiplex) have begun to be used, and high efficiency is expected for conventional Class A and Class AB high frequency power amplifiers. I can't. That is, in OFDM modulation, a large amount of power is instantaneously generated by superimposing subcarriers, and the ratio between the average power and 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 maximum. Especially in the case of OFDM modulation, since the PAPR is large, the peak voltage for compensating the peak power and the instantaneous voltage for compensating the instantaneous power at times other than when the peak power is output. The DC power given by multiplying the difference between the current and current is almost discarded as heat. The resulting efficiency is greatly reduced.

  For this reason, for example, in a portable radio device using a battery as a power source, the continuous usable time is shortened, causing a problem in practical use.

  In order to solve such a problem, a conventional EER method (Envelope Elimination and Restoration) known as Kahn's method has been proposed (see, for example, 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 which is a modulation signal detection means via a modulation signal wiring 410. Then, the detection circuit 402 detects the phase component and the amplitude component of the OFDM modulated wave separately. Specifically, the I and Q vector waves of the OFDM modulation wave generated by the modulation signal generation circuit 401 are divided into an amplitude component √ (I ² + Q ² ) and a phase component tan ⁻¹ (Q / I). Detected. Then, the phase component (complex phase modulation wave) is up-converted by the quadrature modulator 404 from the detection circuit 402 through the phase component wiring 411, and then in the form of high-frequency signal power, a high-frequency input terminal of the PA 405 (high-frequency power amplifier). Is input. 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 then input to the power supply voltage terminal of the PA 405.

  As an example of an OFDM modulated wave, in the case of IEEE802.11a, about 7 dB is required as a back-off amount (an amount representing how much the saturation power is operated). That is, since the high frequency output power is used only for 20% of the high frequency peak power, the efficiency deteriorates from 50% to 10%. In this way, in order to use a class A or class AB PA with high efficiency, it is necessary to sequentially supply the minimum power supply voltage necessary for outputting high-frequency power to the PA, and ideally set the backoff to 0 dB. desirable.

In order to solve this problem, in the EER method, a modulated wave obtained by orthogonally modulating the phase component obtained by polar-transforming the modulated signal is given as a modulated wave to be supplied to the PA 405. Since the modulated wave of the phase component becomes a sine wave whose phase changes with time having a constant amplitude, the PA 405 can operate with a back-off of 0 dB. Since the amplitude component input from the power supply terminal is multiplied by the phase component and the PA output, the same modulated wave as that obtained by orthogonal modulation of the original modulation signal can be obtained.
US Pat. No. 6,256,482 B1 (3 pages of drawings, FIG. 6)

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

  9A, 9 </ b> B, and 9 </ b> C are sequentially shown in order of the voltage amplitude (Vin) of the amplitude component input to the power supply voltage terminal (VDD) in the conventional PA 405 and the power supply voltage terminal (VDD) of the PA 405. It is a figure which shows the response characteristic of the output voltage (RFout) with respect to the input voltage, and the 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 accuracy and the amplitude component are multiplied by the output of the PA 405, and a modulation wave is generated. , The spectrum will deteriorate.

  An object of the present invention is to provide a transmission circuit having an EER method in which signal degradation does not occur even when a PA having a nonlinear 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 to provide an amplitude component wiring for transmitting the amplitude component, so that the amplitude value of the amplitude component of the modulation signal is A determination means for determining whether or not it is larger than the threshold value is provided in the amplitude component wiring.

  As a result, the transmission method can be changed according to the magnitude of the amplitude component of the modulation signal, and the malfunction of the normal class A operation and the malfunction when the EER method is used can be suppressed. In general, this threshold value may be set so as to correspond to the boundary between a region where a transmitted signal shows a linear response and a region where a nonlinear response is shown. Linear response means that when an appropriate offset voltage is given to the response and at the same time 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, the radio standard This is a region indicating the degree of linearity that satisfies the specified spectrum mask and modulation accuracy, and the non-linear response indicates a region that does not fall within the wireless standard when the same operation is performed. As a result, a low-loss method such as the EER method is used in a region where the transmitted signal falls within the wireless standard, and deterioration of the quality of the transmitted signal is suppressed in a region where the transmitted signal does not fall within the wireless standard. Can be adopted.

  In the above basic configuration, not only the amplitude component but also the phase component is detected, and when the amplitude value of the amplitude component is equal to or smaller than the threshold value, the modulation signal is increased in 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 respective phase components is arranged, while 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 when the amplitude component is large, the amplitude component 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, the EER method can be performed only in the region where the response of the output amplitude from the high frequency output of the high frequency power amplifier is in the wireless standard, and the normal modulated wave can be linearly amplified in the region not in the wireless standard. That. Therefore, it is possible to prevent deterioration of the transmission signal that can be caused by performing EER in a region where the response of the high-frequency power amplifier does not fall within the wireless standard, and it is possible to realize a transmission circuit that is highly efficient and has no signal deterioration of the transmission signal.

  A DC / DC conversion means connected to the second selection output means for converting the voltage of the output signal of the second selection output means can be further provided.

  By providing the modulation signal generation means with means for specifying the output power level, the output power level desired to be output can be specified for the modulation signal generation means. Therefore, by setting the IQ level with the modulation signal generation means, the output power level can be set. 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 the DA converter is several hundred mega at most, it cannot be processed when the carrier wave exceeds GHz. However, the carrier wave can be easily obtained by using a frequency conversion means such as a quadrature modulator. This is because the frequency can be up-converted.

  In addition, according to the above basic configuration, the amplitude component wiring and the constant voltage supply wiring output a constant voltage when the amplitude value of the amplitude component is equal to or smaller than the threshold value according to the determination result of the determination unit, and an amplitude component when the amplitude value is large Even when the selective output means is provided, the approximate EER method substantially equivalent to the EER method is performed only in the region where the response of the output amplitude from the high frequency output of the high frequency power amplifier is in the wireless standard, and the wireless standard is not entered. In the region, a normal modulation wave can be linearly amplified. Therefore, it is possible to prevent deterioration of the transmission signal that can be caused by performing EER in a region where the response of the high frequency power amplifier does not fall within the linear standard, and it is possible to realize a transmission circuit that is highly efficient and has no signal deterioration of the transmission signal.

  Even in that 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 the DA converter is several hundred mega at most, it cannot be processed when the carrier wave exceeds GHz. However, the carrier wave can be easily obtained 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, the deterioration of the modulation accuracy is suppressed. be able to.

(First 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 the 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, 64QAM modulation is performed on each of the 52 subcarriers orthogonal to each other, an inverse discrete Fourier transform is performed, and then multiplexed to obtain an OFDM modulated signal. The 52 carriers are each 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 in 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 that is a modulation signal detection means for detecting the amplitude component and phase component of the OFDM modulated wave, a phase component wiring 121 that transmits the 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 that is a determination unit that determines the level of the amplitude component of the OFDM modulated wave, and a storage unit that stores a threshold voltage that is a reference for level determination of the level determination circuit 106 A ROM 109, a constant voltage supply wiring 111 that is connected to a power supply voltage terminal that receives a voltage of 1.1V and supplies a constant voltage of 1.1V, and a level A first selector 103 which is a first selection output means for selecting either an OFDM modulated wave from the modulation signal generation circuit 101 or a phase component from the detection circuit 102 according to the determination result in the determination circuit 106; A second selection output for selecting either the amplitude component input via the amplitude component wiring 122 or the constant voltage of 1.1 V supplied via the constant voltage wiring 111 according to the determination result of the determination circuit 106. A signal selector 107, a DC / DC converter 108, a quadrature modulator 104 that performs quadrature modulation on the output from the first selector 103, and a high-frequency signal output from the quadrature modulator 104 as a high-frequency input terminal. PA105 (high frequency power amplifier) that receives the amplitude component from the converter 108 at the power supply voltage terminal, and the output power to the 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 modulation 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 the OFDM modulation wave flowing through the modulation signal wiring 120 by dividing it into a phase component (complex phase modulation wave) and an amplitude component (amplitude modulation wave). Specifically, the I and Q vector waves of the OFDM modulated wave generated by the modulation signal generation circuit 101 are divided into the amplitude component √ (I ² + Q ² ) and the phase component tan ⁻¹ (Q / I). Detected. The phase component flows as an IQ wave through the phase component wiring 121 and is input to the first selector 103, and the amplitude component flows through the amplitude component wiring 122 and 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 either the phase component of the OFDM modulated wave input via the phase component wiring 121 or the OFDM modulated wave input via 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, the OFDM modulated wave that is the modulation signal is selected and output, and the voltage level of the amplitude component is the threshold voltage. If it is greater than the level, the phase component from the detection circuit 102 is selected and output.

  The second selector 107 selects and outputs either the constant voltage 1.1V from the constant voltage supply wiring 111 or the amplitude component input via the amplitude component wiring 122 based on the determination result of the level determination circuit 106. To do. At this time, when 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, the 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 the complex phase modulation wave (quadrature component (Quadrature) and in-phase component (In-phase)) 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 high-frequency power amplifier PA 105 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, and when the system selects the EER method, the DC / DC converter 108 performs direct current. The converted amplitude component is input from the power supply voltage terminal. As a result, the high frequency output terminal of the 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 normal IQ quadrature modulation, the PA 105 performs linear amplification by fixing the voltage supplied from the power supply voltage terminal to 1.1V.

  The output power designation unit 110 accepts designation regarding transmission power control from MAC (Media Access Control) or the like.

-Examples of signal changes during processing-
FIG. 2 is a diagram for explaining a change example of a signal processed in the transmission circuit of 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 this embodiment, respectively. FIG.

  As shown in FIG. 2, for example, the output level designated by the MAC is input to the modulation signal generation circuit 101 via the output power designation unit 110, and a constellation as shown in 2A of FIG. An IQ orthogonal signal of the OFDM modulation 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 in magnitude relation with the threshold voltage level set in the ROM 109 by the level determination circuit 106.

  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 the linear region showing a sufficiently linear response in the response characteristics of the input voltage-output signal voltage of the high-frequency power amplifier. For example, 1V is set. Alternatively, the threshold voltage level may be set by an appropriate mathematical operation. Here, the linear region means that the output spectrum or output EVM is in a range satisfying the wireless standard of the communication system, and does not mean that the response characteristic is a strict linear characteristic. Absent.

  The level determination circuit 106 uses this threshold voltage level 1V to determine whether the level of the amplitude component generated by the detection circuit 102 is determination A greater than the threshold voltage level or determination B below. The determination results A or B are output 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 2C of FIG. 2, the second selector 107 receives the amplitude component from the detection circuit 102 via the amplitude component wiring 122. (See 2E in FIG. 2) is selected, and the first selector 103 selects the 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 a theoretically maximum efficiency. Therefore, high efficiency can be realized by performing the EER method.

  On the other hand, when determination B is input from the level determination circuit 106, that is, when the amplitude component is in the state shown in 2D of FIG. 2, the first selector 103 inputs from the modulation signal generation circuit 101 through the modulation signal wiring 120. The modulated OFDM 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 supplied to the PA 105 is set to 1.1 V, for example, in order to give a slight margin to the threshold voltage set to 1 V here. Assuming that the average voltage of a modulated wave having an amplitude of 1 V or less is 0.8 V, the PA 105 operates with a 2 dB back-off. At this time, the efficiency is 63% of 50%, which is the theoretical efficiency of class A operation, and is 31.5%. If 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 of 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, whereas the efficiency can be greatly improved by using the present invention.

  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 fall within the wireless standard. Since a non-linear region existed, 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 this 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. Sometimes, by performing normal quadrature modulation, as shown in FIG. 3B, 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 radio standard. 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 standard of the communication system, and the response characteristic is It does not mean that it is a perfect linear characteristic.

(Second Embodiment)
Also in this embodiment, an OFDM modulated wave is adopted as a modulation signal. FIG. 4 is a block circuit diagram schematically showing the configuration of the transmission circuit in the second embodiment of the present invention. As shown in the figure, the transmission circuit includes a modulation signal generation circuit 201 which 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 that is a modulation signal detection means for detecting the amplitude component and phase component of the OFDM modulated wave, an amplitude component wiring 222 that transmits the amplitude component of the OFDM modulated wave, and an amplitude component of the OFDM modulated wave The level determination circuit 206 that is a determination unit that performs level determination, the ROM 209 that is a storage unit that stores a threshold voltage that serves as a reference for level determination of the level determination circuit 206, and the amplitude component wiring 222 are arranged. A first DC / DC converter 208 for DC / DC conversion, a constant voltage supply wiring 211 for supplying a constant voltage, and a constant voltage supply wiring 211 are provided. The second DC / DC converter 210 that converts the constant voltage of 3V to DC / DC and outputs the constant voltage of 1.1V is supplied from the first DC / DC converter 208 according to the determination result of the level determination circuit 206. An OFDM modulated wave transmitted via a signal selector 207 that is a selection output means for selecting either an amplitude component or a constant voltage of 1.1 V supplied from the second DC / DC converter 210 and the modulation signal wiring 220 A quadrature modulator 204; and a PA 205 that 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 an amplitude component from the selector 207 at a power supply voltage terminal. .

  Also in this embodiment, a circuit element having the same function as that of the output power specifying unit 110 that specifies the output power may be arranged in the modulation signal generating 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 that takes the absolute value of the complex modulation vector of the modulation signal (OFDM modulation wave).

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

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

  The selector 207 selects and outputs either the constant voltage 1.1V from the constant voltage supply wiring 211 or the 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. The 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) that is a complex phase modulated wave (quadrature component (Quadrature) and in-phase component (In-phase)) output from the detection circuit 202 into a high-frequency signal.

  The high-frequency power amplifier PA205 is class A, and the high-frequency signal output from the quadrature modulator 204 is input to the high-frequency input terminal of the PA 205 via the modulation signal wiring 220, and the system substantially selects the EER method. In some cases, 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 the 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 normal IQ quadrature modulation, the voltage supplied from the power supply voltage terminal of the PA 205 is fixed to the constant voltage 1.1 V supplied from the constant voltage supply wiring 211.

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

  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 characteristics of the input voltage-output signal voltage of the high-frequency power amplifier. For example, 1V is set. Alternatively, the threshold voltage level may be set by an appropriate mathematical operation. Here, the linear region means that the output spectrum or the output EVM is in a range satisfying the linear standard of the communication system, and does not mean that the response characteristic is a strict linear characteristic. Absent.

  The level determination circuit 206 uses the threshold voltage level 1V to determine whether the level of the amplitude component generated by the detection circuit 202 is a determination C that is greater than the threshold voltage level or a determination D that is the following. The determination result C or D is output to the selector 207, respectively.

  Unlike the first embodiment, in this embodiment, the modulation signal generation circuit 201 is connected to the high frequency input terminal of the PA 205 regardless of whether the determination of the level determination circuit 206 is determination C or determination D. The generated modulated signal (OFDM modulated wave) is input (see 6A in FIG. 6). Then, the OFDM modulated wave is detected by the detection circuit 202 by dividing it into an amplitude component as shown in 6B of FIG. 6 and a complex phase component (phase component) (not shown). The output amplitude component is compared by the level determination circuit 206 in magnitude relation with the threshold voltage level set in the ROM 209.

  When determination C is input from the level determination circuit 206, the selector 207 selects the 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 with an amplitude component, the approximate EER method is used in the transmission circuit. Will be. Therefore, by the approximate EER method, the PA 205 can be operated near the saturation point, and can be operated at almost the maximum theoretical 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 the constant voltage 1.1V.

  In this case, normal IQ quadrature modulation is performed in the transmission circuit. Therefore, the constant voltage supplied to the PA 205 is set to 1.1 V, for example, in order to give a slight margin to the threshold voltage set to 1 V here. Assuming that the average voltage of a modulated wave having an amplitude of 1 V or less is 0.8 V, the PA 205 operates with a back-off of 2 dB. At this time, the efficiency is 63% of 50%, which is the theoretical efficiency of 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 of 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, whereas the efficiency can be greatly improved by using the present invention.

  Further, in the present embodiment, the EER method is substantially performed while inputting the modulation signal, not the phase component, to the high frequency input terminal of the PA 205 as it is. Therefore, it is possible to avoid the deterioration of modulation accuracy (Error Vector Magnitude: EVM), which was unavoidable 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. 3 (a), 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. Therefore, 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 this 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. Sometimes, by performing normal quadrature modulation, as shown in FIG. 3B, 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. 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 standard of the communication system, and the response characteristic is It does not mean that it is a perfect 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 to the extent that the band of the digital-analog converter permits, and to the extent that does not affect the EVM. The resulting partial level drop of the phase component caused significant degradation of the EVM when the phase component was combined with the amplitude component at the output of the high frequency power amplifier. Also, since the required bandwidth of the modulation signal is about 1/6 smaller than the phase component separated from the modulation signal, the bandwidth of the anti-alias filter that suppresses spurious components generated by the digital-analog converter and digital-analog conversion Can be narrowed. Therefore, it is advantageous for reducing the power consumption of the digital-analog converter and reducing the size and cost of the inductor used in the filter.

  Further, in the conventional transmission circuit, even if the amplitude component is zero, the output of the high-frequency power amplifier is determined by coupling the input power to the output, which is determined by the isolation characteristics between the input and output of the high-frequency power of the high-frequency power amplifier. An amplitude causing an error appeared. 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, so that it does not depend on the isolation characteristics. A correct modulated wave can be formed at the output of the high frequency power amplifier.

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

  Here, in order to simplify the explanation, the input wave (OFDM modulated wave in this embodiment) to the high-frequency power amplifier is assumed to be 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 of this embodiment is a grounded-emitter bipolar transistor, and an OFDM modulated wave, which is a modulation signal in this embodiment, is input to the base (high-frequency input terminal) of the bipolar transistor. 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 connected from the collector to the high frequency output terminal is connected to the ground via the output load ZL. Is equivalent to

  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. The voltage Vc is represented. FIG. 7D shows that the Ic-Vc characteristic changes with respect to the base-emitter voltage Vbe of the high-frequency power amplifier. The DC base-emitter voltage Vbe, the DC collector voltage Vc, 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 the output voltage output as a result from the high frequency output terminal of the high frequency power amplifier, and the output power is determined from this 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 in which the amplitude is constant (constant envelope) occurs. Since the voltage amplitude is obtained by converting the collector current Ic by the load impedance ZL of the output, a constant (constant envelope) time region is also generated in the voltage amplitude Vout (= Ic · ZL). Since the signal having the constant envelope region is substantially equivalent to the phase component, the same processing is performed functionally as the EER that inputs 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. It will be. Therefore, in this specification, this processing is called an approximate EER method.

  In the present embodiment, in the time domain using the approximate EER method (area that enters 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 is set. The input power is adjusted so that a saturated output current is obtained during the time when the method is performed. As a result, when the amplitude component of the modulation signal is larger than the threshold voltage of the determination 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 in a modification of the second embodiment. This modification also includes a modulation signal generation circuit 201, a detection circuit 202, a quadrature modulator 204, PA205, a modulation signal wiring 220, and an amplitude component wiring 222, as in the transmission circuit of the second embodiment shown in FIG. 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 DA converter is interposed between the detection circuit 202 and the DC / DC converter 212, and a ROM 209 as a storage means. The threshold voltage level of 1.1 V is supplied to the high frequency input terminal of the selector 207 via the constant voltage supply wiring 251. In other words, in the present modification, the threshold voltage level that is the target of the magnitude comparison with the voltage level of the amplitude component in the level determination circuit 206 and the constant voltage supply wiring 251 are input to the power supply voltage terminal of the PA 205 via the selector 207. The constant voltage level is equal. That is, the ROM 209 serves as both means for storing the threshold voltage level and means for supplying a constant voltage to the power supply voltage terminal of the PA 205 in an area that does not fall within 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 exhibited. In addition, in the present modification, only one DC / DC converter is required, which is more advantageous than the second embodiment in terms of cost. Further, since the selector is arranged on the upstream side of the DC / DC converter, if the DC / DC converter also has an amplitude amplification function, there is an advantage that the pressure resistance may be relatively low.

  In particular, by using the approximate EER method of the second embodiment and its modifications, there is an advantage that high modulation accuracy can be maintained in a wider band than in the first embodiment. However, the method using the EER method of the first embodiment is easier to increase the efficiency than the second embodiment and its modifications.

  Here, a device for realizing the transmission circuit according to the first and second embodiments and the modification of the second embodiment will be described.

  One LSI chip on which the modulation signal generation circuit, the detection circuit, and the level determination circuit are mounted can be configured. In that case, the other circuit elements are provided in another LSI chip or discrete chip.

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

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

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

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

  The means for inputting the constant voltage to the constant voltage supply wiring may be a voltage generation 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 in the first embodiment. It is a figure for demonstrating the example of a change of the signal processed in the transmission circuit of 1st Embodiment. (A), (b) is a figure which shows the response characteristic of the voltage of an 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. 5 is a block circuit diagram of a transmission circuit in a second embodiment. It is a block circuit diagram of the transmission circuit in the modification of 2nd Embodiment. It is a figure for demonstrating the example of a change of the signal processed in the transmission circuit of 2nd 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), (c) are respectively the voltage amplitude (Vin) of the amplitude component input to the power supply voltage terminal in the conventional PA and the output voltage (RFout) with respect to the input voltage to the power supply voltage terminal. It is a figure which shows the response characteristic and the voltage amplitude of the output voltage (RFout) with respect to Vin.

Explanation of symbols

101 modulation 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
DESCRIPTION OF SYMBOLS 110 Output power designation | designated part 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 judgment 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 (9)

Modulation signal generation means for generating a modulation signal including a phase component and an amplitude component;
A modulation signal wiring connected to the modulation signal generating means for transmitting the modulation signal;
Modulation signal detection means connected to the modulation signal wiring for detecting the amplitude component and phase 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 the amplitude component of the modulation signal;
A phase component wiring connected to the modulation signal detecting means and transmitting a phase component of the modulation signal;
Threshold input means for inputting a threshold for switching the modulation method of the modulation signal;
A determination unit that is connected to the amplitude component wiring and determines 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 ;
A constant voltage supply wiring 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 less than or equal to the threshold value according to the determination result of the determination means, and outputs the phase component when large. First selection output means for outputting;
Connected to the amplitude component wiring and the constant voltage supply wiring, and according to the determination result of the determination means, outputs the constant voltage when the amplitude value of the amplitude component is not more than the threshold value, and outputs the amplitude when the amplitude value is large. Second selection output means for outputting the component;
DC / DC conversion means connected to the second selection output means for converting the voltage of the output signal of the second selection output means;
A transmission circuit 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 1,
The transmission circuit, wherein the threshold value 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 nonlinear response is shown. The transmission circuit according to claim 1 ,
A transmission circuit further comprising means for designating an output power level to the modulation signal generating means. The transmission circuit according to claim 1 ,
A transmission circuit further comprising frequency conversion means arranged between the first selection output means and the high-frequency power amplifier. Modulation signal generation means for generating a modulation signal including a phase component and an amplitude component;
A modulation signal wiring connected to the modulation signal generating means for transmitting the modulation signal;
Modulation signal detection means connected to the modulation signal wiring and detecting 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 the amplitude component of the modulation signal;
Threshold input means for inputting a threshold for switching the modulation method of the modulation signal;
A determination unit that is connected to the amplitude component wiring and determines 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;
A constant voltage supply wiring 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 less than or equal to the threshold value according to the determination result of the determination means, and when the amplitude value is large, the amplitude component and the selection output means for outputting,
A transmission circuit 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 5 , wherein
A first DC / DC converting means arranged between the modulation signal detecting means and the selective output means in the amplitude component wiring, for converting the amplitude component into a voltage;
A transmission circuit further comprising second DC / DC conversion means interposed in the constant voltage supply wiring. The transmission circuit according to claim 5 , wherein
A transmission circuit further comprising a DC / DC conversion means connected to the selection output means for converting a voltage of an output signal of the selection output means. The transmission circuit according to claim 5 , wherein
A transmission circuit further comprising frequency conversion means arranged between the modulation signal generating means and the high-frequency power amplifier and performing frequency conversion on the modulation signal . In the transmission circuit according to any one of claims 1 to 8 ,
The threshold value input means is a storage means for storing the threshold value,
The transmission circuit, wherein the determination means performs the determination by taking out a threshold value stored in the storage means.

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