JP2013150238A - Radio communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a test cost in a radio communication apparatus by automatically correcting a phase difference and I/Q gain difference of an orthogonal demodulator in a radio receiver.SOLUTION: A radio communication apparatus includes an orthogonal modulator 110 and an orthogonal demodulator 210. The output of the orthogonal modulator 110 is input to a Fourier transformation circuit 660 in a reception base band circuit 600 via switches 202, 270. An I/Q phase difference and I/Q gain difference of the orthogonal modulator 110 are corrected based on the calculation result. Then, the orthogonal demodulator 210 is corrected. In the correction of the orthogonal demodulator 210, the output of the orthogonal modulator 110 is input to the orthogonal demodulator 210 via switches 202, 201. The output is input to the Fourier transformation circuit 660 via the switch 270. Then, an I/Q phase difference and I/Q gain difference of the orthogonal demodulator 210 are corrected based on the calculation result.

Description

  The present invention relates to a wireless communication apparatus that transmits and receives an OFDM signal and the like, and more particularly to a technique for correcting an error component generated in an orthogonal demodulator provided in a wireless transceiver such as a wireless LAN apparatus.

  For example, Patent Document 1 describes a technique for automatically adjusting an error component included in a transmission signal of a transceiver. Specifically, an encoder that outputs a pattern signal including a pseudo I / Q component from the transmission side, an adjuster that corrects an error component including an amplitude error and a DC offset of the pattern signal with an adjustment value, It has a quadrature modulator for converting a pattern signal output from the regulator into a radio modulated wave signal using a carrier wave signal output from a voltage controlled oscillator (VCO1) of the transmitter. Here, during the correction operation, the modulation signal obtained by the quadrature modulator is connected to the receiving side via the switch, not to the antenna output of the transceiver.

  The modulated signal input to the receiver is demodulated into a demodulated I / Q baseband signal using a carrier wave signal output from the voltage controlled oscillator (VCO2) of the receiver. In order to detect an error component including an amplitude error and a DC offset of the demodulated I / Q baseband signal, a processor that performs Fourier transform processing and an adjustment value for correcting the error component detected by the processor are obtained. And a control circuit for setting the adjustment value as a new adjustment value in the adjuster. The control circuit sets an adjustment value in the adjuster while the output destination of the transmission system is an antenna. At this time, the carrier frequency of the voltage controlled oscillator for transmitter (VCO1) and the voltage controlled oscillator for receiver (VCO2) are set to be the same or approximate.

  In order to detect an amplitude error component, a phase error component, and a DC offset component included in the I / Q baseband signal demodulated by the demodulator, the I / Q baseband signal is Fourier-transformed using a processor, and the I / Q The baseband signal is converted from the time axis to the frequency axis. At this time, the frequency axis value of the obtained carrier component represents the DC offset component of the transmitter, one of the +/− frequency axis components separated from the carrier component by the baseband frequency represents the main component of the output, and the other is the side It represents a band leak.

  Patent Document 2 describes means for adjusting an offset of an I / Q signal included in a transmission signal of a transmitter. Specifically, a transmission signal modulated at the I / Q baseband frequency (fb) is detected by a detection circuit, and an I / Q baseband frequency (fb) component is detected using a filter for the detected signal. A double frequency component (2fb) is detected, and an error between the DC offset component and the amplitude component included in the I / Q signal is adjusted.

  In Patent Document 3, the DC offset voltage of the differential baseband reception signal and the differential baseband transmission signal is reduced, and an undesired sideband component included in the high-frequency transmission signal output from the quadrature modulator of the transmitter is minimized. Techniques for adjusting are shown. Specifically, the sideband signal component included in the high-frequency transmission signal is calculated using the fast Fourier transform function installed in the receiver, and the transmitter I / Q is set so that the unwanted sideband component is minimized. Adjust to reduce phase imbalance and I / Q gain imbalance.

JP 2008-228043 A JP 2007-235463 A JP 2008-278120 A

  For example, many wireless LAN devices that employ an OFDM (Orthogonal Frequency Division Multiplexing) system employ an orthogonal modulator / demodulator in order to simplify the circuit configuration of the wireless unit. The quadrature modulator includes an I signal (In-Phase signal) that is an in-phase component of a transmission baseband signal, a Q signal (Quadrature signal) that is a quadrature component, and a voltage controlled oscillator (VCO) to obtain a necessary radio modulation wave. : Voltage Controlled Oscillator) and a carrier signal shifted by 90 degrees are input. As a result, the quadrature modulator outputs a radio modulated wave signal.

  When modulation is performed in the above quadrature modulator, the I / Q baseband signal created by the transmission baseband circuit is converted from a digital signal to an analog signal by a DA converter and input to the quadrature modulator. At this time, a direct current component (DC offset) or an amplitude error is often added to the I / Q baseband signal. In addition, the carrier wave from the voltage controlled oscillator (VCO) also generates an amplitude error or a quadrature phase error, which may cause a carrier leak in the transmission modulation wave signal or deteriorate the signal accuracy (Error Vector Magnitude) of the transmission modulation wave signal. There is.

  In order to prevent the deterioration of the transmission modulation wave signal described above, the modulator includes a circuit for correcting the amplitude error and DC component error of the I / Q baseband signal, and the phase error of the carrier signal of the voltage controlled oscillator (VCO). It is desirable to implement a phase correction circuit for correcting. In addition, since various problems in the modulator described above can occur in the demodulator as well, it is desirable that a correction circuit and a phase correction circuit be mounted in the demodulator. FIG. 10 is a block diagram showing an example of a method for adjusting the amplitude error and the phase error of the demodulated I / Q baseband signal in the quadrature demodulator in the radio communication apparatus studied as a premise of the present invention.

  In FIG. 10, adjustment of the amplitude error component output from the quadrature demodulator 210 of the radio reception circuit 200 is performed as follows, for example. First, the OFDM signal output from the signal generator 1 such as a vector signal generator is input to the quadrature demodulator 210 via the switches SW1 and SW2. The demodulated I / Q baseband signal demodulated by the quadrature demodulator 210 is measured for its signal accuracy (Error Vector Magnitude) using the measuring device 2 for OFDM signal analysis. The measurement result is input to the external control / measurement personal computer (PC) of the wireless transceiver (wireless communication apparatus). The personal computer (PC) receives a reception I / Q amplitude adjuster 230 for adjusting the amplitude of the demodulated I / Q baseband signal of the quadrature demodulator 210 with respect to the control unit (CPU) of the wireless transceiver if necessary. , 231 are written in the adjustment register, and the register value is controlled so that the signal accuracy is improved.

  Similarly, regarding the adjustment of the phase error component, the signal accuracy (Error Vector Magnitude) of the demodulated I / Q baseband signal is measured, and the measurement result is input to the external control / measurement personal computer (PC) of the wireless transceiver. Is done. If necessary, the personal computer (PC) writes the corrected value in the adjustment register of the phase shifter 310 that adjusts the phase error of the voltage controlled oscillator (VCO) to the control unit (CPU) of the wireless transceiver. Control register values to improve accuracy. Each adjustment value obtained by such a method is stored in a non-volatile memory (not shown) connected to the control unit (CPU) of the radio transceiver, and is stored in the radio transceiver before the operation of the radio transceiver starts. It is written in the adjustment register provided.

  However, since the adjustment method as shown in FIG. 10 is a manual adjustment method using an external device such as the measuring instrument 2 or a personal computer (PC), the cost associated with the installation of the external device and the adjustment work are accompanied. There is a risk that the time cost will increase. On the other hand, as methods for adjusting the phase error and amplitude error of the quadrature modulator, the methods described in Patent Document 1, Patent Document 2, and Patent Document 3 are known.

  However, Patent Document 1 does not particularly describe the characteristics of the demodulator of the receiving system. When the demodulator is not adjusted, the demodulated I / Q signal usually includes the amplitude error and phase error of the I / Q signal generated by the quadrature modulator of the transmitter, I / Q amplitude errors and phase error components generated in the demodulator of the receiver are also included. For this reason, in order to remove the error of the demodulator of the receiving system, before adjusting the amplitude error, phase error, and DC offset component of the I / Q baseband signal of the transmitter, a measuring instrument as shown in FIG. 10 is used. It is necessary to measure the amplitude error and phase error component of the I / Q signal included in the demodulator of the receiver, and to set the adjustment value in the adjuster provided in the demodulator so that these are minimized. In addition, when observing the carrier leak component, since the carrier leak is obtained by shifting the carrier frequency of the transmitter and the carrier frequency of the receiver, two voltage controlled oscillators (VCOs) are required. There is concern about the increase.

  Patent Document 2 describes an adjustment method related to a DC offset and an amplitude error of a modulator of a transmission system, but does not describe an adjustment method related to a phase error of a voltage controlled oscillator (VCO). It is not enough as a method of adjusting the machine. In addition to the detector, a filter for newly detecting the I / Q baseband signal frequency component (fb) and the second harmonic component (2fb) is required, and there is a concern about an increase in circuit area.

  On the other hand, in Patent Document 3, the DC offset component of the I / Q baseband signal of the transmitter and the DC component of the I / Q baseband signal of the receiver are level-compared by a DC level comparator and correspond to the comparison result. The DC offset correction is performed by storing the DC level correction value in the DC level correction register. Further, in order to detect an unnecessary sideband signal component included in the high-frequency modulation signal output from the quadrature modulator, a test signal having a fixed period is transmitted as an I / Q baseband signal of the transmitter. In order to avoid the influence of the error component included in the quadrature demodulator, a signal obtained by square detection of the high frequency modulation signal is subjected to frequency analysis by a Fourier transform circuit mounted in the receiving system. As a result, the carrier I / Q phase and I / Q gain of the transmitter can be corrected so as to reduce the second harmonic and the third harmonic of the test signal generated when there is an unnecessary sideband signal. However, since the function for adjusting the imbalance between the I / Q phase and I / Q gain included in the quadrature demodulator of the receiver is not installed, it is necessary to separately calibrate the receiver using a measuring instrument or the like. Become.

  An embodiment described later has been made in view of the above problems, and one of its purposes is to reduce costs associated with correction of an orthogonal modulator / demodulator in a wireless communication apparatus that transmits and receives OFDM signals and the like. . The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the means for solving the problems disclosed in the present application, the outline of typical ones will be briefly described as follows.

  A wireless communication apparatus according to an embodiment includes a quadrature modulator and a quadrature demodulator, an analog / digital converter and a Fourier transform circuit for digitally transforming and Fourier transforming an output of the quadrature demodulator, and a correction control unit. The correction control unit includes a transmission correction circuit unit that corrects a phase error and an I / Q gain error of the quadrature modulator, a first switch that transmits an output of the quadrature modulator to the quadrature demodulator, a reception correction circuit unit, Is provided. After the correction by the transmission correction circuit unit is performed, the reception correction circuit unit controls the phase error and I / Q gain of the quadrature demodulator while referring to the conversion result of the Fourier transform circuit with the first switch turned on. Correct the error.

  According to the embodiment, in the wireless communication device that transmits and receives an OFDM signal and the like, it is possible to reduce the cost associated with the correction of the orthogonal modulator / demodulator.

In the radio | wireless communication apparatus by one embodiment of this invention, it is a block diagram which shows the example of the structure, and an example of the operation state at the time of transmission calibration. FIG. 2 is a block diagram illustrating an example of an operation state during reception calibration in the configuration example of FIG. 1. In FIG. 2, it is a figure which shows an example of the frequency spectrum contained in the output signal of a quadrature modulator. FIG. 3 is a graph showing an example of a frequency spectrum obtained by performing FFT processing on an output signal of the quadrature demodulator when the quadrature demodulator is ideal. FIG. 3 is a graph showing an example of a frequency spectrum obtained by performing FFT processing on an output signal of a quadrature demodulator when there is an I / Q amplitude error in the quadrature demodulator. FIG. 3 is a graph illustrating an example of a frequency spectrum obtained by performing FFT processing on an output signal of a quadrature demodulator when the quadrature demodulator has a quadrature phase error. In FIG. 2, it is a flowchart which shows an example of the adjustment procedure of a quadrature demodulator. It is explanatory drawing showing an example of the mode of operation | movement in the reception quadrature phase adjustment of FIG. FIG. 8 is an explanatory diagram illustrating an example of an operation state in reception I / Q amplitude adjustment of FIG. 7. FIG. 3 is a block diagram showing an example of a method for adjusting amplitude error and phase error of a demodulated I / Q baseband signal in the quadrature demodulator in the wireless communication apparatus studied as a premise of the present invention.

  In the following embodiment, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant, and one is the other. Some or all of the modifications, details, supplementary explanations, and the like are related. Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  The circuit elements constituting each functional block of the embodiment are not particularly limited, but are formed on a semiconductor substrate such as single crystal silicon by a known integrated circuit technology such as a CMOS (complementary MOS transistor). . Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

<< Outline of calibration method according to this embodiment >>
Here, the outline of the calibration method according to the present embodiment will be briefly described. First, as shown in FIG. 1, the transmission system of a wireless transceiver (wireless communication apparatus) is calibrated using a method using the technique of Patent Document 3. In the transmission calibration, the carrier wave output from the voltage controlled oscillator (VCO) 330 for both transmission and reception and the specific frequency from the SRAM (540) included in the transmission baseband circuit 500 are transmitted to the quadrature modulator 110. A Sin signal and a Cos signal are input. The upper sideband (USB) signal obtained from the quadrature modulator 110 is input to the square detector 260 provided on the radio reception circuit 200 side. The detection signal detected by the square detector 260 is input to a low-pass filter (LPF) 241 that removes out-of-band signal components of the demodulated I / Q baseband signal. The low-pass filter (LPF) 241 removes high-frequency components contained in the square detector output, and the detected signal is amplified by the variable amplifier 251 and then input to the reception baseband circuit 600. At this time, it is not necessary to input a detection signal to the other low-pass filter (LPF) 240.

  The detection signal input to the reception baseband circuit 600 is converted to a digital signal through one AD converter 611 that converts the demodulated I / Q baseband signal from an analog signal to a digital signal. A digital signal from the AD converter 611 is input to a digital low-pass filter (LPF) 621 and limited to a necessary signal band component. This band-limited detection signal is input to, for example, the I-side input of a Fourier transform circuit (FFT) 660 provided in the reception baseband circuit. The Fourier transform circuit converts the demodulated I / Q baseband signal, which is a time signal, into a frequency axis component, and performs the Fourier transform with the other Q-side input set to zero. At this time, in order to improve the calculation accuracy of the Fourier transform, it is desirable to keep the maximum amplitude of the analog signal input to the AD converter 611 within the maximum input range of the AD converter. Therefore, the digital value obtained from the AD converter 611 is input to the power measurement circuit 630 that measures the average power. The processor provided in the baseband circuit unit 700 variably controls the amplification degree of the variable amplifier 251 provided in the wireless reception circuit 200 based on the measured power.

  Also, the Fourier transform circuit 660 receives the digital value of the detection signal input to the I side and the zero value input to the Q side as a sample in units of a fixed number. For example, the Fourier transform circuit 660 performs Fourier transform every time 64 samples are input, and as a result, the specific power output from the transmission baseband circuit, the second harmonic of the specific frequency, and the average power of the third harmonic are observed. A control unit (processor) 400 in the baseband circuit unit 700 detects an error component of the quadrature modulator 110 based on the observation result of the average power of the frequency component, and adjusts to correct the detected error component. Calculate the value. The calculated adjustment values are used as new adjustment values, such as DC offset adjusters 140 and 141 provided on the I / Q input side of the quadrature modulator of the radio transmission circuit, and transmission I / Q amplitude adjusters 150 and 151. Or a phase shifter 320 that adjusts the quadrature phase error of the carrier wave output from the VCO. The control unit (processor) 400 searches for an adjustment value at which the power of the frequency component of the specific frequency obtained by the Fourier transform circuit 660 is equal to or less than a certain value while changing the adjustment value, and uses the adjustment value obtained as a result. The data is stored in an adjustment value storage register provided in the wireless circuit unit 300 and written to each adjustment circuit in the wireless transmission circuit 100. This completes the calibration of the transmission system.

  Next, as shown in FIG. 2, calibration of the reception system is performed. After the adjustment of the quadrature modulator 110 of the wireless transmission circuit is completed, the switches 201 and 202 are connected to the reception input of the quadrature demodulator 210 from the square wave detection circuit 260 of the wireless reception circuit 200 as the connection destination of the USB signal from the quadrature modulator. Can be switched through. The USB modulated wave signal is amplified by the variable low noise amplifier 220 and input to the quadrature demodulator 210. The quadrature demodulator 210 demodulates the USB modulated wave signal using the carrier wave output of the voltage controlled oscillator (VCO). The demodulated I / Q baseband signal is amplified to a constant value by the variable amplifiers 250 and 251 after signals outside the baseband are removed through low-pass filters (LPF) 240 and 241, and received baseband. Input to the circuit 600.

  In the reception baseband circuit 600, the AD converters 610 and 611 convert the output signals from the variable amplifiers 250 and 251 into digital signals. The digital signal is limited to a necessary signal band component via digital low-pass filters (LPF) 620 and 621 and then input to the Fourier transform circuit 660, where Fourier transform is performed. At this time, the maximum amplitude of the analog signal input to the AD converters 610 and 611 is set to the maximum input of the AD converter in order to improve the calculation accuracy of the Fourier transform in the same manner as the adjustment of the quadrature modulator 110 of the wireless transmission circuit. It is desirable to be within the range. Therefore, digital values obtained from the AD converters 610 and 611 are input to the power measurement circuit 630 that measures the average power. The processor provided in the baseband circuit unit variably controls the amplification degree of the variable amplifiers 250 and 251 provided in the wireless reception circuit 200 based on the measured power.

  A digital signal input to the I side and a digital signal input to the Q side are sampled and input to the Fourier transform circuit 660 in units of a fixed number. For example, the Fourier transform circuit 660 performs a Fourier transform every time 64 samples are input, and as a result, the specific frequency on the upper side band (USB) side output from the transmission baseband circuit, the second harmonic of the specific frequency, and the third harmonic. Average power, and a specific frequency on the lower sideband (LSB) side, an average power of a second harmonic and a third harmonic of the specific frequency are observed. The processor included in the baseband circuit unit 700 detects an error component of the quadrature demodulator 210 based on the average power of each frequency component described above, and calculates an adjustment value for correcting the detected error component. . This calculated adjustment value is used as a new adjustment value for the reception I / Q amplitude adjusters 230 and 231 provided on the I / Q output side of the quadrature demodulator 210 of the radio reception circuit, and the carrier output from the VCO. The phase shifter 310 that adjusts the quadrature phase error is set. The control unit (processor) 400 searches for an adjustment value at which the power of the frequency component of the specific frequency obtained by the Fourier transform circuit 660 is equal to or less than a certain value while changing the adjustment value, and uses the adjustment value obtained as a result. The data is stored in an adjustment value storage register provided in the wireless circuit unit 300 and written to each adjustment circuit in the wireless reception circuit 200. This completes the calibration of the receiving system.

<< Main features and effects of calibration method according to this embodiment >>
As described above, the main feature of the calibration method according to this embodiment is that an SSB modulated wave from a transmitter is received in a receiver including a quadrature demodulator that shares a quadrature modulator and a voltage controlled oscillator (VCO). In addition to a path to be transmitted to the reception baseband circuit via the square detection circuit, a path for inputting the SSB modulated wave from the transmitter to the quadrature demodulator of the receiver is provided. Calibration can be performed for the transmitter using the former path, and calibration can be performed for the receiver using the latter path when the calibration is completed. In the latter path, the SSB signal demodulated by the quadrature demodulator is input to a Fourier transform circuit provided in the reception baseband circuit, and the frequency component power of the SSB signal obtained by the Fourier transform circuit is observed. As a result, an error component generated in the quadrature demodulator can be detected, and an amplitude error generated in the quadrature demodulator and a VCO quadrature phase error can be adjusted using the error component.

  Here, the Fourier transform circuit that converts the time waveform into frequency components is an essential circuit for the OFDM modulator / demodulator, and the mounted Fourier transform circuit can be used in the calibration. Further, by providing a switch for transmitting the output of the quadrature modulator to the receiving baseband circuit and a switch for transmitting the output of the quadrature modulator to the quadrature demodulator, the quadrature modulator and the quadrature demodulator can be corrected. it can. Therefore, in the wireless device, correction of the quadrature modulator / demodulator can be easily performed by automatic processing in a state where the circuit overhead associated with the correction is sufficiently suppressed. As a result, it is possible to reduce the cost associated with the correction of the quadrature modulator / demodulator.

<< Detailed Configuration and Detailed Operation of Wireless Communication Device (Wireless Transceiver) >>
FIG. 1 is a block diagram illustrating a configuration example and an example of an operation state during transmission calibration in a wireless communication apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of an operation state during reception calibration in the same configuration example as FIG. Here, a description will be given focusing on a circuit related to the realization of the calibration method according to the present embodiment, and a description on a circuit necessary for OFDM modulation / demodulation not related to the calibration will be omitted.

  A wireless communication device (wireless transmitter / receiver) 1000 illustrated in FIGS. 1 and 2 includes a baseband circuit unit 700 and a wireless circuit unit 300. The baseband circuit unit 700 includes a transmission baseband circuit 500 that converts transmission data into a transmission baseband signal, a reception baseband circuit 600 that decodes a demodulated baseband signal, and a control unit 400 that controls the entire wireless transceiver 1000, Is provided. The radio circuit unit 300 includes a radio transmission circuit 100 that converts a transmission baseband signal output from the transmission baseband circuit 500 into a radio signal, a radio reception circuit 200 that converts a received radio signal into a demodulated baseband signal, and a voltage A control oscillator (VCO) 330, phase shifters 310 and 320, and a radio control circuit 350 that controls the entire radio circuit unit are provided. The wireless transceiver 1000 of FIG. 1 is not particularly limited, and is configured by, for example, one semiconductor chip (LSI), and is used as a component such as a wireless LAN device, for example. A high-frequency transmission signal (TX Out) from the radio circuit unit 300 is transmitted to an external antenna (not shown), and a reception signal from the external antenna is input to the radio circuit unit 300 as a high-frequency reception signal (RX Input).

  The transmission baseband circuit 500 includes a Sin_ROM_Table (SROM) 540 for adjusting the quadrature modulator 110 of the radio transmission circuit 100 and the quadrature demodulator 210 of the radio reception circuit 200, a digital low-pass filter (LPF) 560, 561, a gain adjusting circuit 520, DA converters 510 and 511, and the like. The Sin_ROM_Table (SROM) 540 outputs a Sin wave and a Cos wave having a specific frequency instead of the I / Q baseband signal output from the OFDM modulation circuit 550. The reception baseband circuit 600 includes AD converters 610 and 611, digital low-pass filters (LPF) 620 and 621, a power measurement circuit 630, a Fourier transform circuit (FFT) 660, and a power measurement circuit for each subcarrier 670. And a subcarrier power averaging circuit 675 and the like.

  The radio transmission circuit 100 includes low-pass filters (LPF) 160 and 161, transmission I / Q amplitude adjusters 150 and 151, DC offset adjusters 140 and 141, a quadrature modulator 110, a variable amplifier 130, A power amplifier 120 and the like are provided. The radio reception circuit 200 includes a variable low noise amplifier (LNA) 220, a quadrature demodulator 210, reception I / Q amplitude adjusters 230 and 231, low pass filters (LPF) 240 and 241, variable amplifiers 250, 251 and a square detection circuit 260 and the like.

Here, details of the wireless reception circuit 200 will be described with reference to FIG. As a condition for explanation, it is assumed that calibration of the quadrature modulator 110 of the transmission system has been completed. First, the transmission baseband circuit 500 switches Sin wave and Cos wave modulation signals of specific frequencies from the Sin_ROM_Table (SROM) 540 through switches (SW) 530 and 531 instead of the I / Q baseband signal of the OFDM modulation circuit 550. To the digital low-pass filter (LPF) 560 and 561. The output signals of the digital low-pass filters (LPF) 560 and 561 are gain-adjusted by the gain adjusting circuit 520 and then converted into analog signals by the DA converters 510 and 511, and the radio transmitting circuit 100 of the radio circuit unit 300. Is input. The specific frequency output from the Sin_ROM_Table (SROM) 540 is a frequency that is X times the subcarrier frequency 0.3125 MHz defined by the IEEE 802.11g standard. For example, when the frequency is four times, the output Sin / Cos frequency is 1.25 MHz. The sampling frequencies of the DA converters 510 and 511 are ^2N times 0.3125 MHz in consideration of the transmission baseband signal band and the like. For example, when N = 7, the sampling frequency is 40 MHz. The number of bits of the DA converters 510 and 511 has a bit width of about 10 bits.

  The I / Q baseband signal output from the transmission baseband circuit 500 is freed of aliasing signal components generated by the DA converters 510 and 511 via the low-pass filters (LPF) 160 and 161 of the wireless transmission circuit 100. Then, it is input to the transmission I / Q amplitude adjusters 150 and 151. Transmission I / Q amplitude adjusters 150 and 151 finely adjust the amplitude of the I / Q baseband signal, and output the amplitude-adjusted I / Q baseband signal to DC offset adjusters 140 and 141. DC offset adjusters 140 and 141 remove the DC offset component included in the I / Q baseband signal and output the I / Q baseband signal from which the DC offset has been removed to quadrature modulator 110.

  The carrier wave output from the voltage controlled oscillator (VCO) 330 provided in the radio circuit unit 300 is input to the phase shifter 320. The phase shifter 320 performs phase adjustment based on the phase adjustment signal output from the radio control circuit 350 of the radio circuit unit 300, and outputs the quadrature carrier signal subjected to the phase adjustment to the quadrature modulator 110. The quadrature modulator 110 performs quadrature modulation using the I / Q baseband signal from which the DC offset described above is removed and the quadrature carrier signal from the phase shifter 310, and the modulation signal obtained thereby is variable amplifier. To 130.

  The variable amplifier 130 amplifies the input modulated wave signal with a predetermined gain based on an instruction from the radio control circuit 350, and then switches the connection destination of the signal to either the power amplifier 120 or the radio reception circuit 200 ( SW) 101. When the input signal is a modulated wave signal modulated with an OFDM signal (that is, in the normal operation mode), the switch (SW) 101 connects the modulated wave signal to the power amplifier 120 according to an instruction from the radio control circuit 350. The power amplifier 120 outputs the power-amplified modulated wave signal to the antenna side (not shown). On the other hand, when the input signal is a signal from the SRAM (540) (that is, in the calibration operation mode of the transmission system and the reception system), the switch (SW) 101 is in accordance with an instruction from the radio control circuit 350 and the quadrature modulator 110. The modulated signal modulated in step S1 is output to the switch (SW) 202 of the wireless reception circuit 200.

  In the calibration operation mode, when the modulation signal is “I side: Cosωbt, Q side: Sinωbt” and the carrier wave signal is “I side: Sinωct, Q side: Cosωct”, the modulated wave output from the quadrature modulator 110 As S (t), an upper sideband (USB) signal given by Equation (1) is obtained.

S (t) = Cosωbt · Sinωct + Sinωbt · Cosωct
= Sin (ωct + ωbt) (1)
FIG. 3 shows the frequency spectrum of the upper sideband (USB) signal obtained from the quadrature modulator when there is no error component of the quadrature modulator 110 based on the equation (1).

  In FIG. 2, a switch (SW) 202 of the wireless reception circuit 200 converts an upper side band (USB) signal (output of the switch (SW) 101) obtained from the orthogonal modulator 110 of the wireless transmission circuit 100 into an orthogonal modulator. 110 is output to the square detection circuit 260 of the radio reception circuit 200 when adjustment is performed, and is output to the switch (SW) 201 when adjustment of the quadrature demodulator 210 of the radio reception circuit 200 is performed. The switch (SW) 201 selects either the reception signal from the antenna side or the upper sideband (USB) signal from the wireless transmission circuit 100 in accordance with an instruction from the control unit (CPU) 400 (wireless control circuit 350). And output to the variable low noise amplifier (LNA) 220. The switch (SW) 201 outputs the upper sideband (USB) signal input from the wireless transmission circuit 100 to the variable low noise amplifier (LNA) 220 when adjusting the quadrature demodulator 210.

  The variable low noise amplifier (LNA) 220 amplifies the input upper sideband (USB) signal with a constant amplification degree according to an instruction from the control unit 400 (radio control circuit 350), and then inputs the amplified signal to the quadrature demodulator 210. . The quadrature demodulator 210 demodulates the upper sideband (USB) signal from the variable low noise amplifier (LNA) 220 using the quadrature carrier wave output from the phase shifter 310, and receives the demodulated I / Q baseband signal. Output to the I / Q amplitude adjusters 230 and 231. At this time, the phase shifter 310 receives the carrier wave output from the voltage controlled oscillator (VCO) 330 and outputs a quadrature carrier wave. Thus, since the quadrature modulator 110 and the quadrature demodulator 210 use the carrier wave obtained from the same voltage controlled oscillator (VCO) 330, the demodulated demodulated I / Q baseband signal has no frequency error component. Not included.

  The reception I / Q amplitude adjusters 230 and 231 have a function of adjusting the amplitude of the demodulated I / Q baseband signal in accordance with a control signal from the control unit 400 (wireless control circuit 350). The amplitude adjustment value is given. Signal components outside the baseband are removed from the outputs of the reception I / Q amplitude adjusters 230 and 231 through low-pass filters (LPF) 240 and 241, and are input to the variable amplifier circuits 250 and 251. The low-pass filters (LPF) 240 and 241 also serve as anti-aliasing filters (AAF) of the AD converters 610 and 611 included in the reception baseband circuit 600. Further, between the reception I / Q amplitude adjuster 231 and the low-pass filter 241, the input of the low-pass filter 241 is the output of the square detection circuit 260 or the output of the reception I / Q amplitude adjuster 231. A switch (SW) 270 for switching between the two is provided. The variable amplifier circuits 250 and 251 amplify the input demodulated I / Q baseband signal according to the control signal of the control unit 400 (wireless control circuit 350) and output the amplified demodulated I / Q baseband signal to the reception baseband circuit 600.

  Here, in the demodulated I / Q baseband signal output from the quadrature demodulator 210, the carrier wave signal is “I side: Sinωct, Q side: Cosωct”, and the upper sideband (USB) signal from the quadrature modulator 110 is used. When Sin (ωct + ωbt) in the equation (1), it is as follows. First, the I-side baseband signal is expressed by Equation (2). Here, when signals other than the baseband signal component are removed by the low-pass filter (LPF) 241, the I-side baseband signal (after LPF) is expressed by Equation (3).

I-side baseband signal = Sin (ωct + ωbt) · Sinωct
= Sinωct · Sinωct · Cosωbt + Cosωct · Sinωct · Sinωbt (2)
I-side baseband signal (after LPF) = (1/2) · Cosωbt (3)
Similarly, the Q-side baseband signal is expressed by Equation (4). Here, when signals other than the baseband signal component are removed by the low-pass filter (LPF) 240, the Q-side baseband signal (after LPF) is expressed by Equation (5).

Q-side baseband signal = Sin (ωct + ωbt) · Cosωct
= Sinωct · Cosωct · Cosωbt + Cosωct · Cosωct · Sinωbt (4)
Q side baseband signal (after LPF) = (1/2) · Sinωbt (5)
The demodulated I / Q baseband signal input to the reception baseband circuit 600 is converted from an analog signal to a digital signal by AD converters (ADC) 610 and 611. The digital signal is input to a power measurement circuit 630 and a Fourier transform circuit (FFT) 660 after unnecessary signals outside the band are removed through low-pass filters (LPF) 620 and 621 composed of digital filters. Is done. The low-pass filters (LPF) 620 and 621 also have a decimation filter function.

  The power measurement circuit 630 measures the average power of the digital signals output from the low-pass filters 620 and 621, compares the average power with a power value held in advance in a register (not described) in the control unit 400, and determines a certain difference. The amplification degree of the variable amplifiers 250 and 251 in the radio reception circuit 200 is adjusted so as to be within the value. This adjustment is performed for the purpose of increasing the signal amplitude input to the AD converters 610 and 611 within a range not exceeding the maximum input range of the AD converters 610 and 611.

  After the adjustment of the input signal amplitude of the AD converters 610 and 611 is completed, the digital signals output from the low-pass filters (LPF) 620 and 621 are input to the Fourier transform circuit (FFT) 660. The Fourier transform circuit (FFT) 660 performs conversion from the time axis to the frequency axis for every fixed number of samples, and outputs the I / Q component of each subcarrier obtained thereby to the power measurement circuit 670 for each subcarrier. . In subcarrier-specific power measurement circuit 670, the result of squaring and adding the values of the I component and Q component of each subcarrier is used as the power of each subcarrier. At this time, the subcarrier frequency that needs to be calculated by the power measurement circuit 670 for each subcarrier is as follows.

  For example, when the modulation signal output from the transmission baseband circuit is an upper sideband (USB) signal, the frequency is 1.25 MHz, the Fourier transform circuit 660 has 64 points, and the sampling frequency is 20 MHz. Is assumed. In this case, the subcarrier number for which power calculation is required is the fundamental frequency of +4 (1.25 MHz / 0.3125 MHz), the fundamental frequency image frequency component of -4, and the subcarrier frequency is the fundamental frequency. Is +1.25 MHz, and the image frequency is -1.25 MHz.

  FIG. 4 shows a frequency spectrum when the output of the quadrature demodulator 210 when there is no error component is processed by the Fourier transform circuit (FFT) 660. In this case, powers of + fb, which is the fundamental component of the modulation signal, and +3 fb, which is the third harmonic component, are obtained. The + 3fb power is a harmonic component generated because the Sin wave and Cos wave are converted into digital values by the AD converters 610 and 611. 5 and 6 show the output of the quadrature demodulator 210 when the error component of the quadrature demodulator 210 includes the amplitude error of the demodulated I / Q baseband signal and the phase error component of the quadrature carrier signal as a Fourier transform circuit (FFT). The frequency spectrum when processed at 660 is shown. In these cases, large power is obtained at + fb, which is the fundamental wave component of the modulation signal, and at the image frequency -fb of the fundamental wave.

  The power for each subcarrier frequency calculated by the subcarrier power measurement circuit 670 is input to the subcarrier power averaging circuit 675. The subcarrier power averaging circuit 675 integrates each subcarrier power calculated by the subcarrier power measurement circuit 670 for a certain period and outputs the average power of each subcarrier obtained as a result to the control unit 400. To do. The control unit 400 compares and confirms the powers of the subcarrier signals obtained from the power averaging circuit 675 for each subcarrier, and the power of the specific subcarrier (here, the image frequency of the fundamental wave -fb) is a certain value or less. Alternatively, the reception I / Q amplitude adjusters 230 and 231 provided in the wireless reception circuit 200 and the phase shifter 310 are adjusted so as to be minimized.

  FIG. 7 is a flowchart illustrating an example of the adjustment procedure of the quadrature demodulator. Step ST100 in the figure shows a procedure for generating the upper sideband (USB) signal described above and a signal path setting procedure for adjusting the quadrature demodulator 210. Specifically, the signal path for quadrature demodulator adjustment is set in the state shown in FIG. 2 (step ST101), and the upper sideband signal (fb = 1.25 MHz) generated using the SRAM (540). Are modulated and up-converted by the quadrature modulator 110 (steps ST102 and ST103). The USB signal (fc + fb) transmitted from the quadrature modulator 110 is demodulated and down-converted by the quadrature demodulator 210 and converted into a digital signal via the AD converters 610 and 611 (steps ST104 and ST105).

  Step ST200 in FIG. 7 shows a gain adjustment procedure for the variable amplifiers 250 and 251 in the wireless reception circuit 200 described above. Specifically, the control unit 400 refers to the power (Det_Power) of the demodulated I / Q baseband signal measured by the power measurement circuit 630 and brings the Det_Power closer to a predetermined comparison value (Ref_Power). In this manner, the gains of the variable amplifiers 250 and 251 are adjusted (steps ST201 to ST204). As a result, the amplitude of the demodulated I / Q baseband signal is within a certain amplitude range so as not to exceed the input range of the AD converters 610 and 611.

  Step ST300 in FIG. 7 shows an error adjustment procedure for the amplitude error component of the demodulated I / Q baseband signal output from the quadrature demodulator 210 and the phase error component of the quadrature carrier wave. In this step, first, the magnitude of the frequency component of each subcarrier included in the demodulated I / Q baseband signal is calculated by the Fourier transform circuit (FFT) 660 (step ST301), and the power averaging circuit 675 for each subcarrier is calculated. Thus, the average power for each subcarrier is detected (step ST302). The control unit 400 refers to the detection result of the power averaging circuit 675 for each subcarrier, and calculates the average power (fb_Pow) of the fundamental modulation wave component (fb) and the average power (−fb_Pow) of the image frequency component (−fb). The ratio (Diff_Pow2 (dB) = fb_Pow − (− fb_Pow)) is calculated (step ST303).

  Next, control section 400 adjusts the reception quadrature phase (step ST305). Specifically, referring to the ratio (Diff_Pow2 (dB)) calculated in step ST303, it becomes larger than a predetermined comparison value PrP (that is, the image frequency component (−fb) is the fundamental modulation wave component). The phase shifter 310 in FIG. 2 is adjusted until it becomes sufficiently smaller than (fb) (steps ST304 to ST306, ST309). At this time, the control unit 400 determines that the average power (−fb_Pow) of the image frequency component reaches the lowest point when the ratio (Diff_Pow2 (dB)) becomes larger than the comparison value PrP or before it becomes larger. If it has, the loop processing is exited as “reception quadrature phase adjustment complete” (steps ST304, ST307, ST308).

  Subsequently, control unit 400 adjusts the reception I / Q amplitude in a state in which the above-described reception quadrature phase adjustment result is reflected (step ST310). Specifically, similarly to the above-described adjustment of the reception quadrature phase, referring to the ratio (Diff_Pow2 (dB)) calculated in step ST303, until it becomes larger than a predetermined predetermined comparison value PtG, FIG. The reception I / Q amplitude adjusters 230 and 231 are adjusted (steps ST311, ST314, ST318). At this time, when the ratio (Diff_Pow2 (dB)) is larger than the comparison value PtG, the control unit 400 exits the loop process as “reception I / Q amplitude adjustment completion” (step ST312).

  On the other hand, when the average power (−fb_Pow) of the image frequency component reaches the lowest point before the ratio (Diff_Pow2 (dB)) becomes larger than the comparison value PtG, the control unit 400 receives the reception I The adjustment value of the reception quadrature phase described above is changed in a state where the adjustment result of / Q amplitude is reflected, and the adjustment is performed again from the adjustment of the reception quadrature phase (steps ST314 to ST316, ST309). However, the ratio (Diff_Pow2 (dB)) does not become larger than the comparison value PtG even if a series of loop processes including adjustment of reception quadrature phase and adjustment of reception I / Q amplitude are repeated within a predetermined number of times (K). In this case, the quadrature demodulator adjustment NG is set (step ST317). When the quadrature demodulator adjustment is completed (step ST312), the control unit 400 stores the obtained optimum adjustment value in a non-volatile memory provided in the control unit, and receives I / Q amplitude adjusters 230 and 231. And it writes in the phase shifter 310 as an adjustment value, and the adjustment of the quadrature demodulator 210 is completed (step ST313).

  FIG. 8 is an explanatory diagram illustrating an example of operation in the reception quadrature phase adjustment of FIG. 7, and FIG. 9 is an explanatory diagram illustrating an example of operation in the reception I / Q amplitude adjustment of FIG. As shown in FIG. 8, in the reception quadrature phase adjustment, the phase shifter 310 in FIG. 2 averages the image frequency components while changing the phase difference between the quadrature carriers from the initial setting value (90 degrees) in the plus direction or the minus direction. A minimum point of power (-fb_Pow (dB)) (or a point smaller than a predetermined value) is searched. This ideally corrects the error from 90 degrees in the actual phase difference. Then, with the reception quadrature phase adjustment result reflected, reception I / Q amplitude adjustment is performed as shown in FIG. In the reception I / Q amplitude adjustment, the above-described reception I / Q amplitude adjusters 230 and 231 in FIG. 2 change the gain difference between I / Q from the initial setting value (zero) to the plus direction or the minus direction while changing the image. A minimum point (or a point smaller than a predetermined value) of the average power (−fb_Pow (dB)) of frequency components is searched. This ideally corrects the error from zero in the actual gain difference.

  As described above, the I / Q phase and I / Q gain adjustment of the quadrature demodulator can be automatically performed by the radio transceiver 1000 of FIG. 2 executing the loop processing described in FIG. become. Although an example in which reception I / Q amplitude adjustment is performed after reception quadrature phase adjustment has been described here, this order can be reversed.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Signal generator 100 Wireless transmission circuit 1000 Wireless transmitter / receiver 101 Switch 110 Quadrature modulator 120 Power amplifier 130 Variable amplifier 140,141 DC offset adjuster 150,151 Transmission I / Q amplitude adjuster 160,161 Low-pass filter 2 Measurement 200 Radio receiving circuit 201, 202, 270 Switch 210 Quadrature demodulator 220 Variable low noise amplifier (LNA)
230, 231 Reception I / Q amplitude adjuster 240, 241 Low pass filter 250, 251 Variable amplifier 260 Square detection circuit 300 Radio circuit unit 310, 320 Phase shifter 330 Voltage controlled oscillator (VCO)
340 Phase-locked loop (PLL)
350 Wireless Control Circuit 400 Control Unit (CPU)
500 Transmission Baseband Circuit 510,511 DA Converter 520 Gain Adjustment Circuit 530,531 Switch 540 Sin Rom Table (SROM)
550 OFDM modulation circuit 560,561 Digital low-pass filter 600 Reception baseband circuit 610,611 AD converter 620,621 Digital low-pass filter 630 Power measurement circuit 640 Switch 650 Zero data 660 Fourier transform circuit (FFT)
670 Power measurement circuit for each subcarrier 675 Power averaging circuit for each subcarrier 680 Decoding circuit 700 Baseband circuit section

Claims (3)

A transmitter, a receiver, and a correction controller;
The transmitter is
A voltage controlled oscillator for generating a carrier wave signal;
A first phase shifter for generating a first I / Q carrier signal from the carrier signal;
A quadrature modulator that outputs a high-frequency modulation signal by modulating a first I / Q baseband signal using the first I / Q carrier signal;
The correction control unit includes a first switch that selects whether to transmit the high-frequency modulation signal output from the quadrature modulator to the reception unit side,
The receiver is
A second phase shifter for generating a second I / Q carrier signal from the carrier signal generated by the voltage controlled oscillator;
A quadrature demodulator that outputs a second I / Q baseband signal by demodulating the high-frequency modulated signal input through the first switch using the second I / Q carrier signal;
A reception I / Q amplitude adjuster for adjusting a difference in I / Q gain in the second I / Q baseband signal;
A low-pass filter that removes harmonic components contained in the second I / Q baseband signal;
A variable amplifier that outputs a fourth I / Q baseband signal by amplifying a third I / Q baseband signal obtained through the reception I / Q amplitude adjuster and the low-pass filter with a specified gain;
An analog / digital converter for converting the fourth I / Q baseband signal into a digital signal;
A first power measurement circuit for measuring the power of the fourth I / Q baseband signal based on the output of the analog-to-digital converter;
A gain control circuit that specifies the gain of the variable amplifier so that the power of the fourth I / Q baseband signal becomes a predetermined value based on the measurement result of the first power measurement circuit;
A Fourier transform circuit for Fourier transforming the output of the analog-digital converter;
A second power measurement circuit that measures the power of the frequency component of the specific frequency obtained by the Fourier transform,
The transmitter further includes a baseband signal generation circuit that generates an I / Q baseband signal for correction of the quadrature demodulator as the first I / Q baseband signal.
The correction control unit further includes:
A transmission correction circuit for correcting a phase error of the quadrature modulator by controlling the first phase shifter, and correcting an I / Q gain error of the quadrature modulator by processing the first I / Q baseband signal;
After the correction by the transmission correction circuit unit, the baseband signal generation circuit generates the I / Q baseband signal for correction, and the high frequency modulation signal from the quadrature modulator is supplied to the first switch. The phase error of the quadrature demodulator is corrected through the control of the second phase shifter while referring to the measurement result in the second power measurement circuit in a state of being transmitted to the receiver via A radio communication apparatus comprising: a reception correction circuit unit that corrects an I / Q gain error of the quadrature demodulator through control of the reception I / Q amplitude adjuster. The wireless communication device according to claim 1, wherein
The transmission correction circuit unit includes:
A transmission I / Q amplitude adjuster for adjusting a difference in I / Q gain in the first I / Q baseband signal;
An offset adjuster for adjusting an offset component included in the first I / Q baseband signal;
A detection circuit that squarely detects the high-frequency modulation signal from the quadrature modulator;
And a second switch that outputs an output of the detection circuit toward the variable amplifier of the reception unit. The wireless communication device according to claim 1 or 2,
The baseband signal generation circuit generates a Sin signal as one of the correction I / Q baseband signals, and generates a Cos signal as the other.

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