JP2004187153A - Radio equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a transmitting circuit capable of contriving lower distortion and stabilization of transmission output by using a distortion compensation circuit even when a transmission output level is drastically changed. <P>SOLUTION: A transmission signal generated and outputted by a radio control part 11 is inputted in a distortion compensation part 4, distortion compensation, modulation and frequency conversion, etc. are performed to the signal, its gain is adjusted and amplified by an AGC (automatic gain control) amplifier 5. After that, unnecessary waves are eliminated by a band-pass filter 6, voltage is amplified by a driver amplifier 7 and after that, power is amplified to prescribed transmission output by a power amplifier 8. The radio control part 11 changes the gain of the AGC amplifier 5 and adjusts a gain of a feedback system so that changes of the transmission output level are complemented by a level adjustment part 9 provided on a feedback path of the transmission output in the case of changing the transmission output level. Thus, a signal level of a feedback signal to be fed back to the distortion compensation part 4 is adjusted so that changed quantity of the signal level becomes smaller than changed quantity of the transmission output level and held within a prescribed range. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transmission circuit of a wireless device, and more particularly, to a wireless device including a distortion compensation circuit for stabilizing a transmission output level.
[0002]
[Prior art]
In a transmission circuit in wireless communication, stabilization of transmission output and low distortion are indispensable conditions for performing stable communication. Also, in a mobile communication system or the like that performs communication between a mobile station terminal and a fixed base station, the receiving circuit of the communication partner is autonomous so as not to be excessively input or forcibly based on a command from the communication partner. In some cases, the transmission output level is reduced at a constant rate.
[0003]
Conventionally, as a method for reducing the distortion of the transmission output, an envelope of the output of the power amplifier is compared with an envelope of the reference signal, and the difference signal is fed back to the input of the power amplifier (first conventional example). (For example, see Patent Document 1). In addition, an output of a power amplifier is detected by envelope detection using a diode, and a ratio of a peak value to an average value is detected as distortion, thereby controlling power supplied to the power amplifier (second conventional example). (For example, see Patent Document 2).
[0004]
Furthermore, a distortion compensation circuit used for narrowing the transmission spectrum is provided, and a part of the transmission output including the distortion component of the power amplifier is fed back to the distortion compensation circuit to correct the distortion and to reduce the transmission output level. Conventionally, a method for maintaining the stability has been known.
[0005]
FIG. 4 shows a configuration example of a transmission circuit including the above-described distortion compensation circuit. The baseband transmission signal generated by the radio controller 41 is added to the feedback signal by the distortion compensator 42, and then modulated and frequency-converted to become an RF transmission signal. An unnecessary wave is removed from the transmission signal by a band pass filter (BPF) 43, the voltage is amplified by a driver amplifier 44, and the power is amplified to a predetermined value by a power amplifier 45. After the transmission frequency band of the power-amplified transmission signal is limited by the filter 46, the transmission signal is supplied to the antenna 47 and radiated into space.
[0006]
A part of the transmission signal that has been power-amplified by the power amplifier 45 is linearly fed back to the distortion compensator 42 as a feedback signal, frequency-converted and demodulated to generate a baseband feedback signal. By adding this feedback signal in phase opposite to that of the transmission signal, distortion is compensated for, the fluctuation of the transmission output level is corrected, and the transmission output level is held at a predetermined value.
[0007]
[Patent Document 1]
JP-A-7-74552 (paragraph 0008, FIG. 1)
[Patent Document 2]
JP-A-2000-4173 (paragraphs 0025-0032, FIG. 2)
[0008]
[Problems to be solved by the invention]
However, in the configuration in which the transmission output is envelope-detected by a diode or the like to detect distortion as in the above-described conventional example, the level of the transmission output is significantly increased in order to prevent the reception level from being saturated in the receiving circuit of the communication partner. If it is lowered, it is difficult to stably detect a distortion component from a low-level signal due to characteristics of a detection element such as a diode.
[0009]
Further, in the configuration in which the transmission output level is stabilized by using the distortion compensation circuit shown in FIG. 4, since the level of the feedback signal is greatly reduced by greatly reducing the transmission output level, the distortion compensation circuit has a wide range. Therefore, a circuit with a wide dynamic range that secures linearity is required. For example, when the transmission output level is lowered by -20 dB, a linearity of 20 dB or more is required in the distortion compensation circuit. However, the linearity can be secured over a wide range so as to cope with such a large change in the transmission output level. It was difficult to implement a distortion compensation circuit. If the linearity of the distortion compensation circuit is lost, the feedback system may not function properly, and the transmission output level may fluctuate. Also, depending on the variation of the components, not only the transmission output level but also the distortion characteristics are deteriorated, and there is a problem that the original purpose of the distortion compensation circuit cannot be fulfilled.
[0010]
The present invention has been made in order to solve the above-mentioned problem, and an object of the present invention is to use a distortion compensation circuit to stably maintain a transmission output level without deteriorating distortion characteristics even when the transmission output level is largely changed. An object of the present invention is to provide a wireless device including a transmission circuit that can maintain the wireless device.
[0011]
[Means for Solving the Problems]
A wireless device according to the present invention is a wireless device having a distortion compensation circuit that compensates for a distortion component of a transmission signal based on a feedback signal of a transmission output output from a transmission circuit, wherein the feedback that feeds back to the distortion compensation circuit is provided. A level adjusting unit for adjusting a signal level of the signal, wherein the level adjusting unit is configured such that, when the level of the transmission output is changed, a change in the signal level of the feedback signal is small with respect to the amount of change in the transmission output level. It is characterized in that it is adjusted so that
[0012]
With the above configuration, when the transmission output level from the power amplifier or the like of the transmission circuit is changed, the signal level change of the feedback signal that is fed back to the distortion compensation circuit with respect to the change amount of the transmission output level is performed by the level adjustment unit. By making the adjustment to be small, the width of change of the signal level of the feedback signal input to the distortion compensation circuit becomes small. Therefore, when a distortion compensation circuit is used, a circuit with a wide dynamic range that secures linearity over a wide range is not required, the distortion component can be suppressed, the transmission output level can be stabilized, and high stability and distortion characteristics can be achieved. An excellent transmitting circuit can be realized at low cost.
[0013]
Further, when the level of the transmission output changes, the level adjusting means changes the gain of the feedback system to the distortion compensation circuit so as to compensate for the change in the signal level of the feedback signal accompanying the change in the transmission output level. I will make it.
[0014]
In the above configuration, the level adjuster changes the gain of the feedback system to the distortion compensating circuit so as to compensate for the change in the signal level of the feedback signal accompanying the change in the transmission output level. The signal level of the feedback signal fed back to the compensation circuit is adjusted to be small, and the input signal level to the distortion compensation circuit can be kept within a predetermined range.
[0015]
Further, when the level of the transmission output decreases, the level adjusting means increases a gain of a feedback system to the distortion compensation circuit so as to compensate for a decrease in the signal level of the feedback signal due to the decrease in the transmission output level. I will make it.
[0016]
In the above configuration, the level adjustment means increases the gain of the feedback system to the distortion compensating circuit so as to compensate for the decrease in the signal level of the feedback signal accompanying the decrease in the transmission output level, so that the amount of change in the transmission output level is reduced. The signal level of the feedback signal fed back to the compensation circuit is adjusted to be small, and the input signal level to the distortion compensation circuit can be kept within a predetermined range.
[0017]
Further, the level adjusting means changes the gain of the feedback system to the distortion compensation circuit stepwise by a predetermined amount according to the change of the transmission output level.
[0018]
With the above configuration, the signal level of the feedback signal is adjusted stepwise with respect to the change in the transmission output level, and the input signal level to the distortion compensation circuit can be maintained within a predetermined range with a simple configuration.
[0019]
In addition, control means for changing the level of the transmission output and controlling the amount of adjustment of the signal level of the feedback signal in the level adjusting means in accordance with the amount of change in the transmission output level is provided.
[0020]
According to the above configuration, the transmission output control for changing the transmission output level is performed by the control means, and the level adjustment is performed such that the signal level change of the feedback signal that is fed back to the distortion compensation circuit falls within a predetermined range. , The transmission output level can be changed stably without deteriorating the distortion characteristics, and the distortion component can be suppressed and the transmission output level can be stabilized using the distortion compensation circuit. In this case, the distortion compensating circuit does not require a circuit with a wide dynamic range that secures linearity over a wide range, and a transmission circuit with high stability and excellent distortion characteristics can be realized at low cost.
[0021]
A transmission output control method for a wireless device according to the present invention is a transmission output control method for a wireless device having a distortion compensation circuit that compensates for a distortion component of a transmission signal based on a feedback signal of a transmission output output from a transmission circuit. Changing the level of the transmission output by changing the gain of the transmission system of the transmission circuit; and changing the gain of the feedback system to the distortion compensation circuit according to the amount of change in the level of the transmission output. Adjusting the signal level of the feedback signal; and feeding back the adjusted feedback signal to the distortion compensation circuit to compensate for the distortion component of the transmission signal.
[0022]
According to the above procedure, the transmission output is controlled to change the level of the transmission output, and the level is adjusted such that the change in the signal level of the feedback signal fed back to the distortion compensation circuit falls within a predetermined range in response to the change in the transmission output level. As a result, the transmission output level can be changed stably without deteriorating the distortion characteristics, and the distortion component can be suppressed and the transmission output level can be stabilized using the distortion compensation circuit. In this case, the distortion compensating circuit does not require a circuit with a wide dynamic range that secures linearity over a wide range, and a transmission circuit with high stability and excellent distortion characteristics can be realized at low cost.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments 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 according to an embodiment of the present invention. In the present embodiment, a configuration example of a wireless device used for a mobile wireless communication terminal such as a mobile station terminal in a mobile communication system will be described.
[0024]
The wireless device according to the present embodiment includes an antenna 1, a filter 2, and an antenna duplexer 3, and a transmission unit corresponding to a transmission circuit and a reception unit 10 corresponding to a reception circuit are connected to the antenna duplexer 3. . The antenna duplexer 3 is configured by a filter, a switch element, or the like, and switches a path of a transmission signal and a path of a reception signal. The transmission unit includes a distortion compensation unit 4 corresponding to a distortion compensation circuit, an AGC (automatic gain control) amplifier 5, which is a variable gain amplifier, a band-pass filter (BPF) 6, a driver amplifier 7, a power amplifier 8, and a level adjustment unit. 9 is provided. In addition, a wireless control unit 11 that performs processing of a transmission signal and a reception signal, control of each unit, and the like is provided.
[0025]
The distortion compensator 4 removes the distortion component of the transmission signal and corrects the signal level, and has a configuration as shown in FIG. 2, for example. FIG. 2 is a block diagram illustrating a configuration example of a distortion compensating unit in the transmitting unit illustrated in FIG. The distortion compensator 4 includes an adder 21, a modulator 22, an up-convert mixer 23, a phase shifter 24, a down-convert mixer 25, an AGC amplifier 26, and a demodulator 27.
[0026]
The level adjuster 9 adjusts the signal level of a feedback signal that feeds back a part of the transmission signal, and is composed of a variable attenuator or the like. FIG. 3 is a block diagram illustrating a configuration example of a level adjustment unit in the transmission unit illustrated in FIG. The level adjuster 9 includes a plurality of attenuators 31a, 31b, and 31c connected in series, and switch circuits 32a, 32b, and 32c that are connected in parallel with the attenuators 31a, 31b, and 31c and that turn on and off the respective attenuators. It is configured to have. For example, three sets of −10 dB attenuators and switch circuits are connected in series, and a signal level that can be adjusted in four steps from 0 to −30 dB in steps of 10 dB is used.
[0027]
The switch circuits 32a, 32b, and 32c are independently turned on and off by an attenuation control signal from the wireless control unit 11, thereby switching the passage of the feedback signal in the attenuators 31a, 31b, and 31c. The level of the feedback signal input to the distortion compensator 4 is adjusted.
[0028]
For example, when the transmission output of the power amplifier 8 is a specified value (for example, 33 dBm, 2 W), the switch circuits 32 a, 32 b, and 32 c are all turned off, and the three attenuators 31 a, 31 b, and 31 c are operated, and -30 dB attenuation is performed. The returned feedback signal is fed back to the distortion compensator 4. On the other hand, when the transmission output of the power amplifier 8 drops by -30 dB from the specified value, the switch circuits 32a, 32b, and 32c are all turned on to pass through the three attenuators 31a, 31b, and 31c, and do not attenuate (0 dB attenuation). The feedback signal is fed back to the distortion compensator 4. As described above, by adjusting the signal level of the feedback signal according to the transmission output of the power amplifier 8 by the level adjustment unit 9, the level change of the feedback signal becomes smaller with respect to the change of the transmission output, for example, within 10 dB. Make it fit.
[0029]
As an operation of the wireless device configured as described above, first, a normal transmission operation at a specified transmission output level in the transmission unit will be described with reference to FIGS. 1 and 2.
[0030]
The transmission signal of the baseband generated by the wireless control unit 11 is input to the distortion compensating unit 4 where distortion compensation, modulation, frequency conversion, and the like are performed. In the distortion compensating unit 4, a feedback signal described later is added to the transmission signal by the adder 21, and the transmission signal is modulated by the modulator 22 into a signal of a predetermined modulation method. By mixing with the frequency signal, the frequency is converted and up-converted to a radio frequency, and becomes a transmission signal in the RF band.
[0031]
The transmission signal output from the distortion compensating unit 4 is amplified by the AGC amplifier 5 with the gain specified by the wireless control unit 11, and then the bandpass filter 6 passes only a predetermined frequency band to remove unnecessary waves. You. The transmission signal after passing through the band-pass filter 6 is voltage-amplified by the driver amplifier 7 and power-amplified by the power amplifier 8 to a predetermined value so as to have a specified transmission power. The transmission signal output from the power amplifier 8 is supplied to the antenna 1 after being limited in the transmission frequency band by the filter 2 via the antenna sharing device 3 and radiated into space.
[0032]
A part of the transmission signal output from the power amplifier 8 is input to the level adjustment unit 9 as a feedback signal to adjust the signal level, and then is linearly fed back to the distortion compensation unit 4. In the distortion compensator 4, after the feedback signal is phase-converted by the phase shifter 24, the frequency is converted by the down-conversion mixer 25 by mixing with the local frequency signal from the local frequency oscillator 29, and is down-converted to the baseband frequency. , A feedback signal in the baseband. The feedback signal is amplified while the gain is controlled stably by the AGC amplifier 26, and further demodulated by the demodulator 27 to become a feedback signal having a phase opposite to that of the previous transmission signal. The feedback signal thus obtained is input to the adder 21 and added to the transmission signal. This suppresses non-linear distortion components generated from input / output characteristics of the power amplifier 8 and the like of the transmission unit, corrects fluctuations in the transmission output level, and stabilizes the transmission output level so as to maintain the transmission output level at a predetermined value. Can be.
[0033]
Next, the operation when the transmission unit lowers the transmission output level at a fixed rate will be described. For example, in a mobile wireless device such as a mobile station terminal, when the mobile device moves and the distance to a communication partner such as a fixed base station approaches, an excessive input is generated in a receiving circuit of the communication partner and the reception level becomes high. In order to prevent the transmission power from being saturated, the transmission output control in the own device or the control to lower the transmission output level by the transmission output control instruction from the communication partner is performed.
[0034]
The received signal received by the antenna 1 is separated by the antenna duplexer 3, demodulated by the receiving unit 10, and transmitted to the wireless control unit 11. If there is a transmission output control command sent from the communication partner in the received signal, the wireless control unit 11 detects it. This transmission output control command includes, for example, a control level value (reduction level value) to be reduced with respect to the current transmission output level in the case of a command instructing a reduction in the transmission output level.
[0035]
The wireless control unit 11 outputs a gain control signal to the AGC amplifier 5 according to the detected control level value in the transmission output control command, and controls the amplification gain of the AGC amplifier 5. For example, when a communication partner requests to reduce the transmission output by 20 dB with respect to the current transmission output level, the wireless control unit 11 lowers the gain of the AGC amplifier 5 by -20 dB as compared with a normal case. As a result, the transmission signal output from the AGC amplifier 5 has a signal level lowered by 20 dB. Then, the transmission signal is power-amplified by the power amplifier 8 through the band-pass filter 6 and the driver amplifier 7, and is output from the power amplifier 8 as a transmission signal whose power is reduced by -20 dB as compared with the normal specified transmission power. The light is radiated from the antenna 1 to the space via the filter 2.
[0036]
A part of the transmission signal output from the power amplifier 8 is input to the level adjustment unit 9 as a feedback signal, and the signal level is adjusted. At this time, the feedback signal input to the level adjustment unit 9 is reduced by −20 dB in response to the decrease in the transmission output level from the power amplifier 8. The level adjuster 9 performs level adjustment so as to complement the signal level of the feedback signal thus reduced.
[0037]
That is, when the transmission output level decreases by -20 dB, the attenuation in the level adjustment unit 9 is increased by +20 dB from the normal time (before the transmission output level decreases), and the feedback signal having a signal level substantially similar to that in the normal state. Is fed back to the distortion compensator 4. As a result, the variation level of the signal level of the feedback signal input to the distortion compensator 4 is reduced, and the feedback signal having a substantially constant level is always fed back. When the adjustment width in the level adjustment unit 9 is in units of 10 dB as in the configuration of FIG. 3, the signal level of the feedback signal input to the distortion compensation unit 4 is adjusted within the range of 10 dB.
[0038]
When the level adjustment unit 9 is not provided, when the transmission output level decreases by -20 dB, the signal level of the feedback signal also decreases by -20 dB. Therefore, the distortion component removal and the transmission output level stabilization by the distortion compensation unit 4 function normally. In this case, it is necessary to ensure linearity up to −20 dB in the distortion compensating unit 4. On the other hand, by adjusting the signal level of the feedback signal by the level adjusting unit 9 as in the present embodiment, the range of the linearity required in the distortion compensating unit 4 can be reduced.
[0039]
Then, in the distortion compensating unit 4, the feedback signal is phase-converted by the phase shifter 24, frequency-converted by the down-convert mixer 25, demodulated by the demodulator 27 via the AGC amplifier 26, and returned in the opposite phase to the transmission signal. A signal is generated. By adding the feedback signal to the transmission signal by the adder 21, the nonlinear distortion component caused by the input / output characteristics of the power amplifier 8 and the like of the transmission section is suppressed, and the fluctuation of the transmission output level is corrected and Retained by value.
[0040]
In the above-described embodiment, in the transmission circuit for stabilizing the transmission output and reducing the distortion by feeding back the feedback signal from the transmission output of the power amplifier 8 to the distortion compensating unit 4, the level adjusting unit 9 is provided in the feedback path. When the transmission output level is reduced, the level of the feedback signal is adjusted so as to compensate for the reduction. As a result, a feedback signal having a substantially constant level within a predetermined range is always input to the distortion compensating unit 4, and the input signal level can be maintained within the predetermined range. A high-stable and low-distortion transmitting circuit can be configured at low cost without the need.
[0041]
It should be noted that the present invention is not limited to the above-described embodiment at all, and can be implemented in various modes without departing from the gist thereof. In the above-described embodiment, the configuration in which the plurality of attenuators are switched and interposed is used as the variable attenuator of the level adjustment unit 9. However, the present invention is not limited to this, and other means capable of adjusting the signal level may be used. Good. Further, in the level adjustment unit 9, a configuration is adopted in which three stages of −10 dB attenuators are connected in series and the gain of the feedback system is changed stepwise by −10 dB, but the number of attenuators is not limited to this. Also, a plurality of attenuators having different attenuation values can be used in combination. This allows finer level adjustment of the feedback signal.
[0042]
Further, in the above embodiment, when performing transmission output control such as lowering the transmission output level to prevent saturation of the reception level at the communication partner, the transmission output is adjusted by receiving a transmission output control command from the communication partner. An example has been described. Alternatively, it is possible to detect the reception level in the own device, determine that the communication partner is close when the reception level is high, and perform transmission output control so as to lower the transmission power by itself. It is equally applicable.
[0043]
As described above, according to the present embodiment, even when the transmission output level is largely changed, the distortion compensation circuit is provided by providing the level adjustment unit for adjusting the signal level of the feedback signal on the feedback path to the distortion compensation unit. , A transmission circuit capable of stably maintaining a transmission output level without deteriorating distortion characteristics can be realized. In this case, even if the transmission output level is largely changed, the change in the signal level of the feedback signal can be made small, so that a circuit with a wide dynamic range is not required for the distortion compensation circuit, and a highly stable and low distortion transmission circuit with an inexpensive configuration. Can be realized.
[0044]
【The invention's effect】
As described above, according to the present invention, even when the transmission output level is largely changed, a transmission circuit is provided which can maintain the transmission output level stably without impairing the distortion characteristics by using the distortion compensation circuit. Wireless device can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a wireless device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a configuration example of a distortion compensating unit in a transmitting unit of the present embodiment. FIG. 3 is a transmitting unit of the present embodiment. FIG. 4 is a block diagram showing a configuration example of a level adjustment unit in FIG. 4; FIG. 4 is a block diagram showing a configuration example of a transmission circuit including a conventional distortion compensation circuit;
REFERENCE SIGNS LIST 1 antenna 2 filter 3 antenna duplexer 4 distortion compensator 5 AGC amplifier 6 bandpass filter 7 driver amplifier 8 power amplifier 9 level adjuster 10 receiver 11 radio controller 21 adder 22 modulator 23 upconvert mixer 24 phase shifter 25 Down-converting mixer 26 AGC amplifier 27 Demodulators 31a, 31b, 31c Attenuators 32a, 32b, 32c Switch circuit

Claims (6)

A wireless device having a distortion compensation circuit that compensates for a distortion component of a transmission signal based on a feedback signal of a transmission output output from a transmission circuit,
A level adjusting unit that adjusts a signal level of a feedback signal that returns to the distortion compensation circuit,
The radio apparatus according to claim 1, wherein, when the level of the transmission output is changed, the level adjusting means adjusts the change in the signal level of the feedback signal to be smaller than the amount of change in the transmission output level. The level adjusting means, when the level of the transmission output changes, changes a gain of a feedback system to the distortion compensation circuit so as to compensate for a change in the signal level of the feedback signal accompanying the change in the transmission output level. The wireless device according to claim 1, wherein: When the level of the transmission output decreases, the level adjustment unit increases a gain of a feedback system to the distortion compensation circuit so as to compensate for a decrease in the signal level of the feedback signal due to the decrease in the transmission output level. The wireless device according to claim 1, wherein: The wireless device according to claim 2, wherein the level adjustment unit changes a gain of a feedback system to the distortion compensation circuit stepwise by a predetermined amount according to a change in the transmission output level. 2. A control means for changing a level of the transmission output and controlling an adjustment amount of a signal level of the feedback signal in the level adjustment means according to the change amount of the transmission output level. A wireless device according to any one of claims 1 to 4. A transmission output control method for a wireless device having a distortion compensation circuit that compensates for a distortion component of a transmission signal based on a feedback signal of a transmission output output from a transmission circuit,
Changing the level of the transmission output by changing the transmission system gain of the transmission circuit,
Adjusting the signal level of the feedback signal by changing the gain of the feedback system to the distortion compensation circuit according to the amount of change in the level of the transmission output;
A step of feeding back the feedback signal whose signal level is adjusted to the distortion compensation circuit to compensate for a distortion component of the transmission signal;
A transmission output control method for a wireless device, comprising:

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