JP4498189B2 - Distortion compensator - Google Patents

Description

  The present invention relates to a distortion compensator that compensates for a distortion component generated in a distortion compensation target device such as a power amplifier of a broadcast transmitter, for example, and more particularly to a technique for limiting the output level fluctuation within a predetermined range.

  As is well known, in a broadcasting transmitter, in order to suppress an increase in output characteristic fluctuation of a power amplifier, for example, linear / nonlinear characteristic fluctuation, phase noise, etc. A distortion compensator is added to cancel and suppress the distortion component.

  By the way, the conventional distortion compensator is provided with an output limiter circuit in order to prevent damage to the subsequent apparatus. This output limiter circuit monitors the compensator output level, stops the distortion compensation operation when the output characteristics of the transmitter in operation fluctuates and the monitoring level reaches the reference value, and sets the output level to a preset limit. It has a function to fix by value.

  However, since the conventional output limiter circuit as described above has a function of monitoring only the output level of the compensator, control information for canceling the distortion compensation operation once stopped cannot be obtained, and the characteristics of the power amplifier are stable. Even in this case, the distortion compensation operation could not be automatically restored.

In addition, about the distortion compensator applied to an amplifier, the conventional structure is shown by patent document 1,2.
JP 2003-110372 A JP 2002-043861 A

  As described above, in the conventional distortion compensator, when the output limiter circuit is activated due to the output fluctuation of the distortion compensation target device, the distortion compensation operation is stopped, and the output level is fixed at a preset limit value. Therefore, even when the output of the distortion compensation target device is stable, the distortion compensation operation cannot be automatically restored, and is currently restored manually.

  The present invention solves the above-described problem, and automatically performs stop control / stop release control of the distortion compensation operation, and can limit the output level fluctuation within the range, whereby stable compensation operation can be performed. An object is to provide a distortion compensator.

  In order to achieve the above object, a distortion compensator according to the present invention is configured as follows.

  (1) distortion detection means for capturing an input signal of a device to be compensated for distortion and an output monitor signal of the device to be compared, and detecting a distortion component generated in the device from the comparison result; and the distortion detection Compensating means for giving distortion compensation characteristics to the input signal of the target device based on the detection result of the means, and comparing the output of the compensating means with an allowable threshold value, and stopping the compensation processing of the compensating means when the threshold value is exceeded A compensation stop means for comparing the output monitor signal of the target device with a release threshold, and canceling the stop of the compensation process when the output monitor signal level exceeds the release threshold during the stop of the compensation process And a release means.

(2) The compensation stop means monitors the output level of the compensation means, and when it exceeds the upper limit threshold of the fluctuation allowable range, sends a control signal for stopping the compensation operation to the compensation means to stop the compensation operation. The output level of the compensation means is fixed to the upper threshold,
The compensation stop cancellation means monitors the input level of the output monitor signal, compares it with a cancellation upper limit threshold value, and sends a control signal for canceling the compensation operation stop to the compensation means when the threshold value is larger than this threshold value. The compensation operation is resumed.

  (3) The compensation stop means monitors the output level of the compensation means, and sends a control signal for stopping the compensation operation to the compensation means when the output level is smaller than the lower limit threshold of the fluctuation allowable range. The compensation stop canceling means monitors the input level of the output monitor signal and compares it with the canceling lower limit threshold, which is smaller than this threshold. In this case, a control signal for canceling the compensation operation stop is sent to the compensation means to resume the compensation operation.

  In the configuration of the distortion compensator according to the present invention, the output level fluctuation of the distortion compensator is limited within a range by monitoring the input / output level and automatically performing the distortion compensation operation stop control / stop release control. A stable compensation operation can be performed.

  As described above, according to the present invention, stop control / stop release control of the distortion compensation operation can be automatically performed, and the output level fluctuation can be limited within the range, whereby stable compensation operation can be performed. The distortion compensator which can be provided can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration when the present invention is applied to a distortion compensator of a digital terrestrial broadcasting transmitter using an OFDM (Orthogonal Frequency Division Multiplex) system as an embodiment according to the present invention. It is a block circuit diagram. In FIG. 1, an OFDM signal A1 in IF band output from an OFDM modulator 11 is given distortion compensation characteristics by a distortion compensator 12 according to the present invention, and converted to a transmission frequency by an up converter (U / C) 13. After that, the power is amplified by the power amplifier 14 and sent to an antenna device (not shown) as a transmitter output. The output level of the power amplifier 14 is monitored by a monitor device 15, and the monitor output is converted into an OFDM signal B 1 in the IF band by a down converter (D / C) 16 and then fed back to the distortion compensator 12. .

  In the distortion compensator 12, the distortion detection circuit 121 detects the distortion component of the input OFDM signal A 1 and the output OFDM signal B 1, generates compensation table data C 1, and outputs it to the distortion compensation circuit 122. The distortion compensation circuit 122 performs distortion compensation based on the input OFDM signal A1 and the compensation table data C1, and outputs a compensated OFDM signal D1. Further, the output level fluctuation range limiting circuit 123 monitors the signal level of the compensated OFDM signal D1, compares it with the limit value E1, generates the compensation table update stop control signal C2 based on the comparison result, and outputs the output OFDM signal. The signal level of B1 is monitored and compared with the limit value E2, and a compensation table update stop cancellation control signal C3 is generated based on the comparison result and output to the distortion compensation circuit 122, respectively.

  In the above configuration, the processing operation of the output level variation range limiting circuit 123 will be described with reference to FIG.

  First, as shown in FIG. 2A, for example, by using an RS flip-flop, the output level of the output signal D1 of the distortion compensation circuit 122 is monitored, and when the output level exceeds the upper limit threshold E1 of the fluctuation allowable range, A control signal C2 for stopping the compensation table update is sent to the distortion compensation circuit 122 to stop the compensation operation, and the output level of the distortion compensation circuit 122 is fixed to the upper limit threshold E1. Further, the input level of the monitor output signal B1 of the power amplifier 14 is monitored and compared with the release threshold E2, and when it becomes larger than the threshold E2, the control signal C3 for releasing the compensation table update stop is sent to the distortion compensation circuit 122. To resume the compensation operation.

  On the other hand, as shown in FIG. 2B, the output level of the output signal D1 of the distortion compensation circuit 122 is monitored using, for example, an RS flip-flop, and compensation is performed when the output level is smaller than the lower limit threshold E1 ′ of the fluctuation allowable range. A control signal C2 for stopping the table update is sent to the distortion compensation circuit 122 to stop the compensation operation, and the output level of the distortion compensation circuit 122 is fixed to the lower limit threshold E1 ′. Further, the input level of the monitor output signal B1 of the power amplifier 14 is monitored and compared with the release threshold value E2 ′. When the input level becomes smaller than the threshold value E2 ′, the control signal C3 for releasing the compensation table update stop is compensated for distortion. It is sent to the circuit 122 to resume the compensation operation.

  FIG. 3 is a waveform diagram showing the timing relationship between compensation operation stop and compensation operation stop release (vertical axis is level, horizontal axis is time), (a) is compensation operation stop side (set operation), (b) is The compensation operation stop release side (reset operation) is shown. The signal change of each waveform will be described step by step.

  (1) First, it is assumed that the characteristic variation of the device subsequent to the compensator, for example, the failure of the power amplifier 14 occurs. At this time, since the feedback signal (distortion signal) level B1 decreases, the compensator output D1 increases so as to suppress the level decrease.

  (2) When the compensator output D1 continues to rise and reaches the compensation operation stop threshold (upper limit) E1, compensation operation stop control is executed. At this time, the compensator output D1 is fixed to the upper limit value E1 based on the stop threshold, and the input of the power amplifier 14 is limited regardless of its characteristics.

  (3) It is assumed that the characteristic variation of the device subsequent to the compensator, for example, the power amplifier 14 is restored. At this time, the feedback signal (distortion signal) level B1 increases.

  (4) When the feedback signal B1 exceeds the stop cancellation threshold value E2, the compensation operation stop is canceled. After the compensation operation is stopped, the compensator output level D1 approaches the rated value and the feedback signal (distortion signal) level B1 approaches the rated value by the compensation operation return.

  (5) By the above processing, normal operation is performed.

  Therefore, the distortion compensator having the above configuration monitors the input / output level and automatically performs the distortion compensation operation stop control / stop release control, thereby limiting the fluctuation of the distortion compensation output level within an allowable range, Automatic recovery is possible, and stable compensation operation can be performed.

  In the above-described embodiment, the case of the distortion compensator used in the terrestrial digital broadcast transmitter has been described. Of course, the present invention can be similarly applied to other distortion-compensated devices.

  As described above, the present invention is not limited to the above-described embodiments as they are, and various modifications can be made to the constituent elements without departing from the spirit of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements according to different embodiments may be appropriately combined.

The block circuit diagram which shows the structure at the time of applying this invention to the distortion compensator of the transmitter for digital terrestrial broadcasting using OFDM system as one Embodiment which concerns on invention. The figure for demonstrating the processing operation of the output level fluctuation | variation range limitation circuit 123 of the embodiment. The wave form diagram which shows the timing relationship of compensation operation stop and compensation operation stop cancellation of the same execution form.

Explanation of symbols

11: OFDM modulator,
12 ... distortion compensator,
121. Distortion detection circuit,
122 ... distortion compensation circuit,
123 ... Output level fluctuation range limiting circuit,
13: Upconverter (U / C),
14: Power amplifier,
15 ... Monitor device,
16: Down converter (D / C).

Claims (3)

A distortion detection unit that takes in an input signal of a device to be compensated for distortion and an output monitor signal of the target device and compares both, and detects a distortion component generated in the target device from the comparison result;
Compensation means for giving distortion compensation characteristics to the input signal of the target device based on the detection result of the distortion detection means;
Compensation stop means for comparing the output of the compensation means with a threshold value of an allowable range, and stopping compensation processing of the compensation means when the threshold value is exceeded;
Compensation stop release means for comparing the output monitor signal of the target device with a release threshold and releasing the stop of the compensation processing when the output monitor signal level exceeds the release threshold during the stop of the compensation processing. A distortion compensator characterized by that. The compensation stop means monitors the output level of the compensation means, and when it exceeds the upper limit threshold of the fluctuation allowable range, sends a control signal for stopping the compensation operation to the compensation means to stop the compensation operation, The output level of the compensation means is fixed to the upper threshold value,
The compensation stop cancellation means monitors the input level of the output monitor signal, compares it with a cancellation upper limit threshold value, and sends a control signal for canceling the compensation operation stop to the compensation means when the threshold value is larger than this threshold value. The distortion compensator according to claim 1, wherein the compensation operation is resumed. The compensation stop means monitors the output level of the compensation means, and when it becomes less than the lower limit threshold of the allowable fluctuation range, sends a control signal for stopping the compensation operation to the compensation means to stop the compensation operation, The output level of the compensation means is fixed to the lower threshold,
The compensation stop canceling means monitors the input level of the output monitor signal, compares it with a cancellation lower limit threshold value, and sends a control signal for canceling the compensation operation stop to the compensation means when it becomes smaller than this threshold value. The distortion compensator according to claim 1, wherein the compensation operation is resumed.

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