JP2007173896A - Offset correcting device, and radio device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct an IQ offset, and to reduce size and costs. <P>SOLUTION: There are provided an error detector 41 for adding a non-inverted signal and an inverted signal in a differential transmission signal for detecting the amount of offset from the added value, and an elimination means (subtraction and addition sections 43, 44) for eliminating the detected amount of offset. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an offset correction apparatus and a radio apparatus for correcting an offset (IQ offset) between an in-phase signal (I signal) and a quadrature signal (Q signal) in quadrature modulation or quadrature demodulation.

In the prior art described in Patent Document 1, as a method for deriving an adjustment value of an IQ offset of a quadrature modulator in a transmission circuit of a radio communication device, a quadrature modulator is used with a measuring instrument (spectrum analyzer) provided outside the radio communication device. The amount of carrier leakage of the output is measured, and the adjustment value of the offset between the I signal and the Q signal is derived from the measured value.
JP 2005-217911 A

  However, the above-described prior art has a problem in that the configuration such as a measuring device outside the wireless communication device is large and costly. In particular, in a portable wireless communication device such as a mobile phone used in mobile communication, it is not realistic to employ such a large-scale system as a correction device for IQ offset when used by a user.

  In mobile communications, OFDM (Orthogonal Frequency Division Multiplexing), which is one of the multicarrier schemes, is effective, but the transmission power per carrier in the multicarrier scheme is higher than that in the single carrier scheme. Therefore, there is a concern that the influence of the increase in the amount of carrier leak due to the IQ offset appears remarkably, leading to deterioration of communication quality. As shown in FIG. 4, in the case of the single carrier system (see FIG. 4A), the carrier leak power P2 when the IQ offset is present is larger than the carrier leak power P1 when the IQ offset is not present. Since the hit carrier wave power P3 is sufficiently large, the influence does not appear remarkably. On the other hand, in the case of the multicarrier system (see FIG. 4B), the carrier power P3 per carrier is smaller than that of the single carrier system, so that the influence of the carrier leak power P2 when the IQ offset is present becomes significant. Fear comes out. As a result, there arises a problem in communication quality such as a deviation of the IQ constellation pattern at the time of demodulation and a difficulty in correcting the IQ imbalance.

  For the reasons described above, it is desired to realize an IQ offset correction apparatus that can be easily employed in a portable wireless communication device for mobile communication.

  The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide an offset correction apparatus capable of correcting an IQ offset and reducing the size and cost. It is in.

  Another object of the present invention is to provide a radio apparatus provided with the offset correction apparatus of the present invention.

In order to solve the above problems, an offset correction apparatus according to the present invention is an offset correction apparatus that corrects an offset between an in-phase signal and an orthogonal signal in quadrature modulation or quadrature demodulation, and each of the in-phase signal and the orthogonal signal. And adding means for adding the non-inverted signal and the inverted signal of the differential transmission signal, detecting means for detecting the offset amount from the added value, and removing means for removing the detected offset amount. It is characterized by that.
This makes it possible to correct the IQ offset with a simple configuration without using an external measuring instrument.

The offset correction apparatus according to the present invention is characterized by comprising suppression means for suppressing fluctuations in the offset amount based on the fluctuation amounts of the in-phase signal and the quadrature signal.
As a result, it is possible to avoid instantaneous fluctuations in the offset amount caused by fluctuations in each of the I signal and the Q signal, and the detection accuracy of the offset amount is improved.

The offset correction apparatus according to the present invention is characterized in that unbalance-balance conversion means is provided and converted from unbalanced transmission to balanced transmission to obtain the differential transmission signal.
Thereby, it is possible to cope with a case where the I signal and the Q signal are transmitted unbalanced.

  A radio apparatus according to the present invention includes the above-described offset correction apparatus.

  According to the present invention, it is possible to correct the IQ offset, and it is possible to reduce the size and the cost.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram illustrating a configuration of a wireless device 1 according to an embodiment of the present invention. In FIG. 1, a wireless device 1 includes an antenna 2, a switch 3 that switches between transmission and reception, a transmission unit 10, a reception unit 20, and local oscillators 30a for frequency conversion in the transmission unit 10 and the reception unit 20. 30b.

  The transmission unit 10 includes a digital-analog converter (DAC) 11, an offset correction device 12 according to the present embodiment, a quadrature modulator 13, a variable gain amplifier (GCAMP) 14, a low-pass filter (LPF) 15, A mixer 16 and a power amplifier 17 are included. In the transmission unit 10, a digital signal (I signal, Q signal) to be transmitted is converted into an analog signal by the DAC 11 and input to the offset correction device 12. A reference signal A having a reference voltage is input from the DAC 11 to the offset correction device 12. The offset correction device 12 corrects the offset of the input I signal and Q signal, and outputs the corrected I signal and Q signal. The quadrature modulator 13 quadrature modulates the corrected I signal and Q signal and outputs a modulated signal. The modulated signal is amplified by the variable gain amplifier 14 and passes through the LPF 15, and then multiplied by the frequency signal from the primary local oscillator 30 b by the mixer 16, further amplified by the power amplifier 17, and from the antenna 2 via the switch 3. Sent.

  The receiving unit 20 includes a low noise amplifier (LNA) 21, a mixer 22, a band limiting filter (BPF) 23, a GCAMP 24, a quadrature demodulator 25, the offset correction device 26 according to the present embodiment, and an analog-digital And a converter (ADC) 27. In the receiving unit 20, the signal received by the antenna 2 is input to the LNA 21 via the switch 3 and amplified, and then the frequency signal from the primary local oscillator 30 b is multiplied by the mixer 22 and further passes through the BPF 23. Amplified by the variable gain amplifier 24 and input to the quadrature demodulator 25. The quadrature demodulator 25 performs quadrature demodulation on the input signal and outputs an analog demodulated signal (I signal, Q signal) to the offset correction device 26. The offset correction device 26 corrects the offset of the input I signal and Q signal, and outputs the corrected I signal and Q signal. The ADC 27 converts the corrected I signal and Q signal into digital signals. A reference signal A having a reference voltage is input from the ADC 27 to the offset correction device 26.

  The offset correction apparatuses 12 and 26 have the same configuration in the transmission unit 10 and the reception unit 20.

FIG. 2 is a block diagram showing the configuration of the offset correction apparatuses 12 and 26 shown in FIG.
In FIG. 2, the offset correction devices 12 and 26 include error detection units 41 and 42, a subtraction unit 43, an addition unit 44, and a reference voltage generation unit 45. The offset correction devices 12 and 26 have a configuration for correcting the offset of the I signal and a configuration for correcting the offset of the Q signal, and the configurations of both are the same (the same reference numerals are assigned to the portions corresponding to both). Attached). The I signal and the Q signal are differential signals and are transmitted through a balanced transmission line. The uncorrected I signal and Q signal are input from the DAC 11 in the transmitter 10 and input from the quadrature demodulator 25 in the receiver 20. The corrected I signal and Q signal are output to the quadrature modulator 13 in the transmitter 10 and output to the ADC 27 in the receiver 20. The reference signal A is input from the DAC 11 in the transmission unit 10 and input from the ADC 27 in the reception unit 20.
Hereinafter, for convenience of explanation, a case where the offset of the I signal is corrected will be described as an example.

  The error detector 41 adds the non-inverted signal and the inverted signal of the pre-correction I signal (differential signal), and detects the offset amount from the added value. Here, the offset amount is detected based on the reference voltage generated by the reference voltage generator 45. Further, the error detector 41 is provided with an LPF, extracts a DC component from the added value of the non-inverted signal and the inverted signal, and detects it as an offset amount.

  The error detection unit 42 suppresses the fluctuation of the offset amount detected by the error detection unit 41 based on the fluctuation amount of the pre-correction I signal. Specifically, the fluctuation of the offset amount detected by the error detection unit 41 is suppressed when the fluctuation amount of the pre-correction I signal is larger than the standard. An example of the suppression method will be described. First, during a period in which the fluctuation amount of the pre-correction I signal is below the specified value, the offset amount detected by the error detection unit 41 is output. Next, the offset amount when the fluctuation amount of the pre-correction I signal reaches the specified value is held, and the held offset amount is output during the period when the fluctuation amount of the I signal before correction exceeds the specified value. Next, when the fluctuation amount of the pre-correction I signal falls below a specified value, the holding of the offset amount is canceled, and the output of the offset amount detected by the error detection unit 41 is resumed. This avoids instantaneous fluctuations in the offset amount caused by fluctuations in the pre-correction I signal and improves the detection accuracy of the offset quantity. Note that the input timing of the offset amount from the error detection unit 41 to the error detection unit 42 is delayed from the corresponding pre-correction I signal by the LPF provided in the error detection unit 41. Due to this timing difference, it is possible to accurately detect the fluctuation of the offset amount caused by the fluctuation of the pre-correction I signal and suppress the fluctuation.

  The subtracting unit 43 subtracts the offset amount output from the error detecting unit 42 from the reference signal A. The adder 44 adds the subtraction result signal to the pre-correction I signal, and outputs the addition result signal as a post-correction I signal. The offset component is removed from the pre-correction I signal by the processing of the subtracting unit 43 and the adding unit 44.

  FIG. 3 is a block diagram illustrating a specific circuit configuration example of the offset correction apparatuses 12 and 26 according to the present embodiment. FIG. 3 shows only the configuration for correcting the offset of the I signal.

  In FIG. 3, the non-inverted signal I and the inverted signal I * of the pre-correction I signal (differential signal) are input via the balanced buffer 51. The reference voltage V0 is input to the balanced buffer 51 from the reference voltage generator 53 as a reference voltage for the differential signal. This reference voltage V0 is also supplied to the output source of the pre-correction I signal.

  The non-inverted signal I and the inverted signal I * after the output of the balanced buffer 51 are added by the adder 54. The signal resulting from this addition passes through the LPF 55, so that a DC component is extracted and detected as an offset amount.

  The signal after passing through the LPF 55 is inverted and input to the adder 57 via the hold circuit 56. The hold circuit 56 receives the inverted signal I * after the output of the balanced buffer 51. In the hold circuit 56, a threshold that is a condition for holding a signal is set. When the level of the inverted signal I * reaches the threshold value, the hold circuit 56 holds the level of the signal input from the LPF 55. Then, during the period in which the level of the inverted signal I * reaches the threshold value, the held level is inverted and continuously output to the adder 57. Then, when the level of the inverted signal I * falls below the threshold value, the holding of the signal level is canceled, and the inverted output of the signal input from the LPF 55 to the adder 57 is resumed.

  The adder 57 adds the signal after the inverted output of the hold circuit 56 to the reference signal A. The signal resulting from the addition is input to the balanced buffer 52 as a reference voltage for the differential signal. The balanced buffer 52 converts the level of the non-inverted signal I and the inverted signal I * after the output of the balanced buffer 51 with reference to the reference voltage, and outputs the non-inverted signal I and the inverted signal I * of the corrected I signal. Thereby, in the balanced buffer 52, the offset amount is removed from the reference voltage of the differential signal, and the corrected I signal from which the offset component is removed is generated by level conversion using the reference voltage.

  As described above, according to the present embodiment, for each of the I signal and the Q signal, the offset amount is detected from the addition value of the non-inverted signal and the inverted signal of the differential transmission signal (differential signal). Since the offset amount is removed, the IQ offset can be corrected with a simple configuration without using an external measuring instrument. As a result, it is possible to reduce the size and cost of the offset correction apparatus, and it can be easily adopted in a portable wireless communication device.

  Further, since the fluctuation of the offset amount is suppressed based on the fluctuation amount of each of the I signal and the Q signal, the instantaneous fluctuation of the offset amount caused by the fluctuation of each of the I signal and the Q signal can be avoided. Detection accuracy is improved.

  Further, since the feed forward offset correction is performed, the transmission data and the reception data themselves are corrected, so that communication can be performed without damaging the data.

  Moreover, according to this embodiment, an offset correction apparatus can be comprised with an analog circuit.

  In addition, when the operation of the transmission unit 10 or the reception unit 20 is stopped, the offset amount before the operation stop is held, so that the erroneous detection of the offset amount when the operation is stopped can be prevented.

  Further, the offset amount generated by the quadrature modulator 13 of the transmission unit 10 can be dealt with by measuring in advance and adjusting the amount corrected by the offset correction device from the measured value. This makes it possible to perform offset correction with higher accuracy.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like within a scope not departing from the gist of the present invention.
For example, in the above-described embodiment, the case of the differential signal in which the I signal and the Q signal are transmitted through the balanced transmission path is described as an example. However, the same applies to the case where the I signal and the Q signal are unbalanced. Can be applied to. In that case, unbalance-balance conversion means may be provided and converted to balanced transmission to obtain a differential transmission signal.

  Note that various wireless system devices are applicable as the wireless device according to the present invention. For example, the present invention can be applied to a base station device of a mobile communication system or a mobile station device (such as a mobile phone). In particular, as a mobile station device, it is possible to reduce the size and reduce the cost, which is very effective. Further, the present invention can greatly contribute to the adoption of the OFDM method in a mobile communication system.

It is a block diagram which shows the structure of the radio | wireless apparatus 1 which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the offset correction apparatuses 12 and 26 shown in FIG. FIG. 3 is a block diagram illustrating a specific circuit configuration example of the offset correction devices 12 and 26 illustrated in FIG. 2. It is a figure for demonstrating the influence of IQ offset in a multicarrier system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Radio | wireless apparatus, 12, 26 ... Offset correction apparatus, 13 ... Quadrature modulator, 25 ... Quadrature demodulator, 41, 42 ... Error detection part, 43 ... Subtraction part, 44 ... Addition part, 45, 53 ... Reference voltage generation , 51, 52 ... balanced buffer, 54, 57 ... adder, 55 ... low pass filter (LPF), 56 ... hold circuit

Claims (4)

An offset correction device that corrects an offset between an in-phase signal and an orthogonal signal in quadrature modulation or demodulation, and for each of the in-phase signal and the orthogonal signal,
Adding means for adding the non-inverted signal and the inverted signal of the differential transmission signal;
Detecting means for detecting an offset amount from the added value;
Removing means for removing the detected offset amount;
An offset correction apparatus comprising:   The offset correction apparatus according to claim 1, further comprising a suppression unit that suppresses a variation in the offset amount based on a variation amount of each of the in-phase signal and the quadrature signal.   3. The offset correction apparatus according to claim 1, wherein unbalance-balance conversion means is provided to convert the unbalanced transmission into balanced transmission to obtain the differential transmission signal. A radio apparatus comprising the offset correction apparatus according to any one of claims 1 to 3.

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