JP4649302B2 - Distortion compensator - Google Patents

Description

  The present invention relates to a distortion compensator that is used in transmission devices such as medium wave, short wave, terrestrial / satellite / cable television, and detects and compensates for distortion regardless of linear or non-linear.

  As is well known, the terrestrial digital broadcasting system employs the OFDM system. In this OFDM system, the linearity of the transmitter is important. Conventionally, non-linear distortion mainly generated in a power amplifier constituting a transmitter and linear distortion mainly generated in an output filter for band limitation are compensated by separate distortion compensators.

Examples of the nonlinear distortion compensator are described in Patent Documents 1 and 2.
Japanese Patent Laid-Open No. 2003-152459 JP 2004-112218 A

  As described above, in the past, in the situation where nonlinear distortion and linear distortion occurred at the same time, a distortion compensator was prepared separately, but in recent years both distortions have been developed for the purpose of circuit scale reduction and cost reduction. There is a demand for sharing the compensation circuit.

  The present invention has been made in view of the above circumstances, and provides a distortion compensator capable of reducing the circuit scale and realizing cost reduction by sharing circuits for linear distortion compensation and nonlinear distortion compensation. With the goal.

  In order to achieve the above object, the present invention provides a distortion compensator that performs distortion compensation on transmission signals sequentially processed by a first circuit device that generates nonlinear distortion and a second circuit device that generates linear distortion. , Linear distortion compensation means for receiving the transmission signal to compensate for linear distortion, nonlinear distortion compensation means for inputting the linear distortion compensation output to compensate for nonlinear distortion, and the nonlinear distortion compensation output to the first Output conversion means for converting into the input format of the circuit device, input switching means for selectively inputting the outputs of the first and second circuit devices, timing of the selection input of the input switching means and the transmission signal, and Input conversion means for matching frequencies, linear distortion detection means for detecting linear distortion from the selected input and transmission signal obtained by the input conversion means and outputting to the linear distortion compensation means, and obtained by the input conversion means Detecting a nonlinear distortion and a selection input and the transmission signal, and comprises a nonlinear distortion detecting means for outputting to said nonlinear distortion compensating means.

  According to the above-described invention, it is possible to provide a distortion compensator capable of simultaneously compensating for linear distortion and nonlinear distortion.

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

  FIG. 1 is a block diagram showing an embodiment in which a distortion compensator according to the present invention is applied to a transmitter of a digital terrestrial broadcasting system using the OFDM method.

  In FIG. 1, reference numeral 11 denotes a distortion compensator (also referred to as an exciter) that receives a transmitted IF signal (for example, ISDB-T / ATSC / DVB-T), compensates for linear / nonlinear distortion of a subsequent circuit, and converts it to an RF band. ), 12 is a power amplifier (PA) for amplifying the output signal of the distortion compensator 11, and 13 is an antenna (not shown) that excludes interference and spurious of adjacent channels in the transmission signal output from the power amplifier 12. Output band-pass filter (BPF) for transmission to the network.

  In the distortion compensator 11, the IF signal input from the terminal IF IN is converted from analog to digital by the sampling clock (CLK) generated by the clock generation circuit 11 J in the first A / D conversion circuit 111, 1 is sent to the linear distortion compensation circuit 112 and the delay circuit 11E.

  The first linear distortion compensation circuit 112 performs linear distortion compensation of the output BPF 13 based on the detection output of the linear distortion detection circuit 11F using the A / D conversion output as a main line signal. The output signal is sent to the nonlinear distortion compensation circuit 113.

  The nonlinear distortion compensation circuit 113 performs nonlinear compensation of the PA 12 based on the detection output of the nonlinear distortion detection circuit 11G using the first linear compensation output as the main line signal. The output signal is sent to the second linear distortion compensation circuit 114.

  The second linear distortion compensation circuit 114 performs linear distortion compensation of the up-converter (U / C) 117 and the PA 12 based on the detection output of the linear distortion detection circuit 11F using the nonlinear distortion compensation output as a main line signal. The output signal is sent to the first attenuator (ATT1) 115.

  The first attenuator 115 uses the second linear distortion compensation output as the main line signal, and varies the signal amplitude at the time of no compensation to adjust it to an appropriate level. The output signal is sent to the D / A conversion circuit 116 and converted into an analog signal by the sampling clock CLK. The output signal is output to an up converter (U / C) 117.

  The up-converter 117 converts the output converted into the analog signal into the main line input signal, and converts the IF band signal into the transmission frequency band (RF band) based on the local signal LO generated by the phase-locked oscillation circuit (PLO) 11I. The output signal is sent from the terminal RF OUT to the PA 12 and sent to the antenna via the output BPF 13.

  Both the output of the PA 12 and the output of the BPF 13 are distributed from the main line and fed back to the input terminals RF IN1 and RF IN2 of the distortion compensator 11, respectively.

  The RF IN1 input of the distortion compensator 11 is sent to the second attenuator (ATT2) 118. The second attenuator 118 adjusts the signal amplitude at the time of nonlinear distortion compensation to an appropriate level, and its output signal is sent to the switch 11A. Also, the RF IN2 input is sent to the third attenuator (ATT3) 119. The third attenuator 119 varies the signal amplitude at the time of linear distortion compensation and adjusts it to an appropriate level, and its output signal is sent to the switch 11A.

  The switch 11A selectively outputs the output signals of the attenuators 118 and 119 according to the control signal from the control circuit 11H, and the signal selected by the switching is sent to the down converter (D / C) 11B. The down converter 11B uses the output of the switch 11A as a main line input signal, mixes the RF (transmission frequency) band signal with the local signal LO, and converts the frequency into an IF (intermediate frequency) band signal. It is sent to the second A / D conversion circuit 11C.

  The second A / D conversion circuit 11C performs A / D conversion based on the sampling clock CLK using the output of the down converter 11B as a main line signal, and the output is sent to the temperature compensation circuit 11D.

  The temperature compensation circuit 11D is for compensating output fluctuations due to temperature changes of the down converter 11B and the A / D conversion circuit 11C. Since temperature fluctuations in this downconverter system lead to fluctuations in the output of broadcast waves, precise temperature compensation is required. The output signal is sent to the linear distortion detection circuit 11F and the nonlinear distortion detection circuit 11G.

  On the other hand, the delay circuit 11E adjusts the delay time of the IF IN signal with reference to the RF IN1 and RF IN2 signals. That is, since the RF IN1 signal and the RF IN2 signal have a delay time difference, they are controlled by the delay circuit 11E.

  The linear distortion detection circuit 11F uses the outputs of the delay circuit 11E and the temperature compensation circuit 11D as inputs, uses the IF IN signal as a reference signal, uses the RF IN2 signal to output the linear distortion of the output BPF 13, and uses a technique such as an LMS algorithm or FFT + IFFT. To detect. This linear distortion detection circuit 11F stops linear distortion detection and holds the distortion value under the control of the control circuit 11H.

  Here, an LMS (Least Mean Square) algorithm is often used for linear distortion detection. This LMS algorithm calculates an error component by feeding back its own output signal. However, since the transmitter's band-limited output signal must be fed back to the LMS here, it cannot be handled as it is. Therefore, when using the LMS, the peak component of the feedback is detected, and the feedback of the LMS itself is stopped at the detection timing to stop the linear distortion detection process. Thereby, the fall of the error detection accuracy of LMS can be suppressed.

  The nonlinear distortion detection circuit 11G receives the outputs of the delay circuit 11E and the temperature compensation circuit 11D as inputs, and detects the nonlinear distortion from the RF IN1 signal using the IF IN signal as a reference signal by using an algorithm shown in, for example, Patent Document 1. I do. Further, the nonlinear distortion detection is stopped by the control from the control circuit 11H, and the distortion value is held.

  The control circuit 11H performs switching control between linear distortion detection / compensation and nonlinear distortion detection / compensation. If nonlinear distortion detection / compensation is performed at the RF IN2 input, the compensator output deteriorates. However, if the degradation is acceptable, nonlinear distortion detection / compensation can be performed at the RF IN2 input.

  Further, the control circuit 11H is provided for each of the first linear distortion compensation circuit 112, the nonlinear distortion compensation circuit 113, the second linear distortion compensation circuit 114, the switch 11A, the linear distortion detection circuit 11F, and the nonlinear distortion detection circuit 11G. Load initialization data at power-on to improve startup speed.

  A phase-locked oscillation circuit (PLO) 11I generates a local signal LO by applying a PLL to an internal or external frequency reference signal. The clock generation circuit 11J generates a sampling clock CLK for A / D and D / A by TCXO (temperature compensated crystal oscillator).

  In the above configuration, linear / nonlinear compensation switching control in the control circuit 11H will be described.

  FIG. 2 shows a processing flow of the switching control. First, when a compensation start is instructed in step S1 (for example, when power is turned on), a temperature is detected from a temperature sensor disposed in the power amplifier 12 in step S2. Information is obtained, a temperature change amount Δθ ° is obtained in step S3, and it is determined in step S4 whether the temperature change amount Δθ ° is within an allowable range (threshold value ± TH). If it is within the allowable range, the nonlinear distortion compensation is preferentially executed in step S5, and then linear distortion compensation is also executed in step S6. On the other hand, if the allowable range is exceeded in step S4, only nonlinear compensation is executed in step S7. The above steps S2 to S7 are repeated until a compensation off instruction is received in step S8.

  That is, in the distortion compensator 11 having the above-described configuration, the common parts of the nonlinear distortion compensation and the linear distortion compensation are shared, and the situation where the nonlinear distortion compensation of the power amplifier 12 is required and the situation where the linear distortion compensation of the output BPF 13 is needed. Thus, processing is performed by selectively switching between nonlinear distortion compensation and linear distortion compensation. The above processing is normally executed at intervals of about 3 seconds.

  Therefore, according to the above configuration, the circuits of the nonlinear distortion compensation and the linear distortion compensation are shared without affecting the performance, so that the circuit scale can be reduced and the cost can be reduced.

  In the above embodiment, the case where the input signal is the OFDM signal has been described. However, the present invention is not limited to the OFDM signal, and the present invention can be similarly applied to other transmission signals.

  In the above embodiment, the compensation operation for linear distortion / non-linear distortion is switched in accordance with the detected temperature of the power amplifier 12. However, it is also possible to cope with a temperature change caused by a change in the signal level of the IF IN input. Good. This is particularly effective when the input signal is other than an OFDM signal (the OFDM signal is constant, so there is almost no signal level fluctuation).

  Further, 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 at 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 diagram which shows one Embodiment at the time of applying the distortion compensator which concerns on this invention to the transmitter of the terrestrial digital broadcasting system using an OFDM system. The flowchart for demonstrating the control processing of the linear distortion compensation and the nonlinear distortion compensation in the control circuit of the distortion compensator shown in FIG.

Explanation of symbols

11 ... distortion compensator,
111 ... 1st A / D conversion circuit,
112 ... 1st linear distortion compensation circuit,
113 ... Nonlinear distortion compensation circuit,
114 ... second linear distortion compensation circuit,
115 ... first attenuator (ATT1),
116: D / A conversion circuit,
117: Up-converter (U / C),
118 ... Second attenuator (ATT2),
119: Third attenuator (ATT3),
11A ... switching device,
11B: Down converter (D / C),
11C 2nd A / D conversion circuit,
11D ... temperature compensation circuit,
11E: delay circuit,
11F ... Linear distortion detection circuit,
11G ... Nonlinear distortion detection circuit,
11H: control circuit,
11I: Phase-locked oscillation circuit (PLO),
11J: Clock generation circuit,
12 ... Power amplifier (PA),
121 ... temperature sensor,
13: Output band pass filter (BPF).

Claims (7)

In a distortion compensator that performs respective distortion compensation on a transmission signal sequentially processed by a first circuit device that generates nonlinear distortion and a second circuit device that generates linear distortion,
Linear distortion compensation means for inputting the transmission signal and compensating for linear distortion;
Nonlinear distortion compensation means for inputting the linear distortion compensation output and compensating for nonlinear distortion;
Output conversion means for converting the compensation output of the nonlinear distortion into an input format of the first circuit device;
Input switching means for selectively inputting the outputs of the first and second circuit devices;
Input conversion means for matching the timing and frequency of the selection input of the input switching means and the transmission signal;
Linear distortion detection means for detecting linear distortion from the selection input and transmission signal obtained by the input conversion means and outputting to the linear distortion compensation means;
Non-linear distortion detection means for detecting non-linear distortion from the selection input and transmission signal obtained by the input conversion means and outputting to the non-linear distortion compensation means ,
Temperature detecting means for detecting the temperature of the first circuit device;
A distortion compensator comprising control means for performing switching control between the nonlinear distortion detection and compensation and the linear distortion detection and compensation based on a temperature detection result of the temperature detection means . Analog / digital conversion means for converting the transmission signal and the selection signal of the input conversion means into digital signals, and
Further comprising a clock generating means for generating a clock signal for the digitized,
The linear distortion compensation means, the nonlinear distortion compensation means, the linear distortion detection means, and the nonlinear distortion detection means shall perform each processing by digital processing,
Distortion compensator according to claim 1, wherein the sharing the clock signal to the digital processing of the linear distortion compensation and nonlinear distortion compensation.   2. The distortion compensator according to claim 1, further comprising a post-stage linear compensation unit that performs linear compensation on the compensation output of the nonlinear distortion compensation unit and outputs the result to the output conversion unit. Further, the output conversion means includes
Digital-to-analog conversion means for converting the compensation output digitally processed by the clock signal into an analog signal;
3. The distortion compensator according to claim 2, further comprising level adjusting means for performing level adjustment before and after conversion to the analog signal.   2. The linear distortion compensator according to claim 1, wherein the input conversion means further comprises temperature compensation means for compensating for a variation due to temperature.   2. The distortion compensator according to claim 1, wherein the nonlinear distortion detection means and the linear distortion detection means operate in cooperation with each other.   The control means determines whether or not the amount of change in temperature detected by the temperature detection means is within an allowable range, and if it is within the allowable range, performs processing for executing linear distortion compensation after execution of the nonlinear distortion compensation. 2. The distortion compensator according to claim 1, wherein the distortion compensator is repeatedly performed and only nonlinear distortion compensation is executed when it is out of an allowable range.

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