JPH04290321A - Nonlinear distortion compensating method - Google Patents

Abstract

PURPOSE:To remarkably miniaturize a high frequency power amplifier to be used in a digital/micro radio equipment. CONSTITUTION:In a digital radio transmitter equipped with a modulation part 1 generating modulation wave by using an analog signal after converting a digital signal to be inputted into the analog signal in a digital/analog converter 11 and a transmission part 2 converting the inputted modulation wave frequency into the transmission frequency by using the output of internal transmission local part oscillator, and a high frequency power amplifier 3 transmitting the modulation wave of the inputted transmission frequency to the prescribed power after amplification, a digital filter 4 with a ROM storing compensating coefficient compensating the nonlinear component to be generated in the high frequency power amplifier is provided on the input of the digital/analog converter, and tone distortion compensating the nonlinear distortion component to be generated in the high frequency power amplifier is preliminarily applied to the digital signal to be inputted to the digital/analog converter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonlinear distortion compensation method used in digital micro radio equipment.

[0002] In recent years, the amount of backoff of high frequency power amplifiers has increased as modulation methods have become more multi-valued. For example, 16
In the case of QAM modulation method, it was about 8 dB, but 64Q
In the case of AM modulation method, it is approximately 10 dB, and further 256 dB.
In the case of QAM modulation, a backoff of 12 to 13 dB must be taken care of.

[0003] In response to this increase in backoff amount,
The power efficiency of the entire device decreases, and the power supply capacity must be increased, which increases costs, increases housing space, and requires more effective thermal design.

[0004] Therefore, by reducing the amount of back-off of the high frequency power amplifier, power efficiency can be improved, and
It is necessary to significantly downsize this amplifier.

[0005]

[Prior Art] FIG. 5 is a block diagram of a conventional example, and FIG. 6 is a block diagram of a conventional example.
FIG. 7 is a detailed block diagram of the transmitting side in FIG.

The operation of FIG. 5 will be explained below with reference to FIGS. 6 and 7. First, in FIG. 6, input to the modulation section 1,
For example, after the digital signals of I ch and Q ch are converted into analog signals by the digital/analog converter 11, the bandwidth is limited by the low pass filter 12 and the signal is applied to the quadrature modulator 13.

In the quadrature modulator, for example, carrier 1 in the intermediate frequency band is
4 is subjected to multi-value QAM modulation to generate a multi-value QAM modulated wave, which is sent to the frequency converter 21 in the transmitter 2. Since the frequency converter also receives the transmitting local oscillator signal from the transmitting local oscillator 22, the signal is frequency-converted into a multi-level QAM modulated wave in a high frequency band and then applied to the predistorter 31.

Here, since the high frequency power amplifier 32 operates in class A operation, the input/output characteristics change linearly until the input level approaches a certain level, as shown in (■) in FIG. However, when a certain level is exceeded, AM-AM conversion occurs and the signal deviates from the straight line and gradually approaches saturation.

Furthermore, when the input/output characteristics deviate from the linear portion, AM-PM conversion occurs, resulting in a phase characteristic as shown, for example, in FIG. 7. Therefore, the predistorter 31 applies distortions as shown in (1) and (2) in FIG. 7 to the output of the frequency converter 21 and sends it to the high frequency power amplifier 32. For this reason, the nonlinear distortion generated in the high-frequency power amplifier is compensated to some extent, and the linear portion of the input/output characteristics is slightly extended as shown in ■ and ■ in Figure 7, and the phase characteristic is within a certain range (as indicated by the dashed line in the figure). (pause). Note that the characteristics shown in (■) in FIG. 7 are formed by overlapping the nonlinear portions of the diodes.

Now, as shown in FIG. 5, the multi-level QAM modulated wave sent out from the high-frequency power amplifier 32 is frequency-converted into a multi-level QAM modulated wave in the intermediate frequency band by the receiving section 71 of the partner station, and then is converted into a multi-level QAM modulated wave in the intermediate frequency band. The signal is amplified to the level and applied to the demodulator 72.

In the demodulation section, a baseband signal is extracted from the multilevel QAM modulated wave, and then identified and converted into a digital signal.The transversal equalizer 73 equalizes the baseband signal to produce a digital signal with minimum intersymbol interference. can get.

0012

[Problem to be Solved by the Invention] Now, in order to significantly reduce the size of high-frequency power amplifiers, it is necessary to reduce the amount of backoff, but a predistorter with a simple circuit configuration as described above is generally used. There is.

However, although this method can compensate for the monotonous nonlinear distortion of the high-frequency power amplifier, it cannot compensate for other nonlinear distortions (regions that cannot be expressed by a monotone function).

Furthermore, due to the predistorter, it is not possible to completely compensate for fluctuations in the high frequency power amplifier.
Furthermore, since no feedback loop is configured, compensation for temperature and power supply fluctuations and aging is not possible.

[0015] Moreover, it is necessary to make individual settings for combinations with high-frequency power amplifiers, and adjustments must be made for each unit. In other words, it is impossible to compensate for distortion caused by areas where nonlinear distortion cannot be expressed as a monotonic function, fluctuations in environmental conditions, changes over time, etc., so there is a problem that it is impossible to significantly reduce the amount of backoff. .

[0016] The present invention greatly reduces the amount of backoff,
The aim is to significantly reduce the size of high-frequency power amplifiers.

[0017]

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the first to third aspects of the present invention. 1 is a modulation section that converts an input digital signal into an analog signal using a digital/analog converter, and then generates a modulated wave using the analog signal; 2 is a modulation section that uses the output of an internal transmitting local oscillator to convert an input digital signal into an analog signal; This is a transmitter that converts the frequency of the modulated wave into a transmission frequency.

Further, 3 is a high frequency power amplifier that amplifies the power of the input modulated wave of the transmission frequency and sends it out, and 4 is a ROM that stores compensation coefficients for compensating for nonlinear distortion generated in the high frequency power amplifier. This is an added digital filter.

Further, 5 is a receiving/demodulating section which converts the frequency of the modulated wave sent out from the high frequency power amplifier using an internally generated receiving station oscillation signal and extracts a demodulated signal.
6 is a control unit that generates a control signal using the demodulated signal.

In the first aspect of the present invention, a digital filter is provided on the input side of the digital/analog converter, and the digital filter filters the nonlinear signal generated in the high frequency power amplifier into the digital signal input to the digital/analog converter. Distortion to compensate for the distortion was given in advance.

[0021] The second aspect of the present invention is provided with a receiving/demodulating section and a control section that generates a control signal using the demodulated signal, and the control section is configured to detect codes generated due to fluctuations in operating conditions of the high frequency power amplifier. The control signal is used to control the operation of the digital filter so that interference between the filters is minimized.

The third aspect of the invention synchronizes the receiving station oscillator signal with the output of the transmitting local oscillator.

[0023]

[Operation] The present invention is directed to the A
M-AM conversion and AM-PM conversion are converted into amplitude characteristics and delay characteristics of this amplifier. On the other hand, since a linear digital filter can compensate for the amplitude characteristics and delay characteristics, the nonlinear distortion (AM-AM conversion, AM-PM conversion) that occurs within a certain region within the dynamic range of the high-frequency power amplifier can be compensated for by the above-mentioned digital filter. It is based on the idea that it can be compensated.

In order to achieve this, the first aspect of the present invention uses a digital filter to apply distortion to the digital signal input to the digital/analog converter in advance so as to compensate for the nonlinear distortion generated in the high frequency power amplifier. I did it like that.

In the second aspect of the invention, a simplified reception/demodulation section and a control section are provided on the transmitting side, and a digital filter is provided on the input side of the digital/analog converter to form a feedback loop. Further, the third aspect of the present invention synchronizes the receiving station oscillation signal with the output of the transmitting local oscillator.

By forming the feedback loop described above, the operation of the digital filter is controlled using the control signal from the control section so that the nonlinear distortion of the high frequency power amplifier is minimized.

[0027] As a result, the amount of backoff of the high frequency power amplifier is significantly reduced, and the deterioration of the bit error rate due to parameter fluctuations of the high frequency power amplifier itself due to changes in power supply, temperature, and aging is minimized.

In other words, the high frequency power amplifier can be significantly downsized.

[0029]

[Embodiment] FIG. 2 is a block diagram of main parts of the first to third embodiments of the present invention, FIG. 3 is an example of the control unit/digital filter configuration diagram of FIG. 2, and FIG. 4 is an in-phase and quadrature An example of a configuration diagram of a tap section, (A) is a basic configuration diagram, and (B) is a configuration diagram of the present invention.

Here, the receiving section 51 and the demodulating section 52 are the constituent parts of the receiving/demodulating section 5, and the correlator 61 and the integrator 62 are the constituent parts of the control section 6. Note that the same reference numerals indicate the same objects throughout the figures.

The operation of FIG. 2 will be explained below with reference to FIGS. 3 and 4. First, input, for example, I ch, Q
The digital signal of channel is subjected to a predetermined distortion as described later by a digital filter 4, and then converted into an analog signal by a digital/analog converter 11. Then, a quadrature modulator (not shown) uses this analog signal to generate, for example, a multilevel QAM modulated wave.

This multi-level QAM modulated wave is frequency-converted in the transmitting section 2 using a transmitting station oscillator signal from the transmitting local oscillator 21, power amplified in the high-frequency power amplifier 3, and sent to the outside. is the receiving section 51, and the built-in receiving local oscillator 5
11 using the receiving station oscillation signal from the intermediate frequency band.
Frequency conversion to AM modulated wave.

[0033] In the third aspect of the present invention, the receiving station oscillation signal is synchronized with the transmitting station oscillation signal by using, for example, an internally provided PLL circuit (not shown). Now, the demodulator 52 demodulates the input multi-level QAM modulated wave in the intermediate frequency band and extracts a demodulated signal, of which a polar signal and an error signal are added to the controller 6.

Therefore, the control section shown in FIG.
The integrator 62 calculates the correlation between the polarity signal and the error signal, and the integrator 62 integrates the correlation result for a predetermined time using an up/down counter (not shown) and sends it to the digital filter 4 as a control signal.

Digital filter 4 has I ch, Q
In-phase tap portion 41 for compensating the in-phase component of ch.
44, I ch →Q ch, Q ch→ I
orthogonal tap portion 42 for compensating the orthogonal component of ch.
43, and each tap portion is comprised of a shift register composed of FF1 to FF4, multipliers M1 to M3, and an adder, as shown in FIG. 4(A). Note that the shift register has four stages.

Therefore, each time the I channel data passes through one FF (flip-flop), it is multiplied by a control signal in a multiplier and added in an adder.
The control signal is controlled so that intersymbol interference is minimized at each time from .

Here, as shown in FIG. 4(B), the FF
ROM1~ in which the value of the control signal that compensates for the nonlinear component of the high frequency power amplifier is written on the output side of FF1~FF3
ROM3 is provided. Then, when the power is turned on, the digital signal of this written value is added to the adder as an initial value through the multiplier. From this point on, the feedback loop begins to compensate for changes in the high-frequency power amplifier, which widens the dynamic range of this loop.

Note that ROM1 to ROM3 and multipliers M1 to
By writing the functions of M3 into the respective ROMs, it is possible to replace the ROM and the multiplier with one ROM. In other words, originally, no distortion should occur from the digital/analog converter 11 to the transmitter 2 in FIG. is input, the control unit 6 controls the value of the control signal applied to the multiplier of the digital filter so that the intersymbol interference is minimized.

Control at this time may be slow. because,
This is because nonlinear distortion occurs slowly, and power supply fluctuations and temperature fluctuations also occur slowly. Therefore, the demodulation section, the control section,
If the operating speed of the digital filter is also made slower (by thinning out the clocks supplied to these parts), the power consumption of these parts will be reduced.

However, in response to analog fluctuations such as nonlinear distortion in a high-frequency power amplifier, sampling is performed at n times the speed of the main signal (oversampling method) to operate the digital filter in a fractional manner. ,
If the main signal is thinned out by 1/n and configured to pass the signal, it is possible to more precisely guarantee the nonlinearity.

[0041]

As described above in detail, according to the present invention, the amount of backoff of the high frequency power amplifier can be reduced, so that the high frequency power amplifier can be significantly downsized.

[Brief explanation of the drawing]

FIG. 1 is a principle block diagram of first to third aspects of the present invention.

FIG. 2 is a block diagram of main parts of first to third embodiments of the present invention.

FIG. 3 is an example of a configuration diagram of a control unit and digital filter in FIG. 2;

[Figure 4] An example of a configuration diagram of the in-phase and quadrature tap sections in Figure 3.
(A) is a basic configuration diagram, and (B) is a configuration diagram of the present invention.

FIG. 5 is a block diagram of a conventional example.

FIG. 6 is a detailed block diagram of the transmitting side in FIG. 5;

FIG. 7 is an explanatory diagram of high frequency power amplifier operation.

[Explanation of symbols]

1 Modulation section
2 Transmitter 3 High frequency power amplifier 4 Digital filter

Claims (3)

[Claims] 1. A modulator (1) that converts an input digital signal into an analog signal by a digital/analog converter (11) and then generates a modulated wave using the analog signal.
) and a transmitter (2) that converts the frequency of the input modulated wave into a transmit frequency using the output of an internal transmit local oscillator.
) and a high-frequency power amplifier (3) that amplifies the power of an input modulated wave of the transmission frequency and transmits the same, a compensation coefficient for compensating for nonlinear distortion generated in the high-frequency power amplifier is provided. Stored RO
A digital filter (4) to which M is added is provided on the input side of the digital/analog converter, and the digital filter applies nonlinear distortion generated in the high-frequency power amplifier to the digital signal input to the digital/analog converter. A nonlinear distortion compensation method characterized by providing distortion to be compensated in advance. 2. A receiving/demodulating section (5) that frequency-converts the modulated wave sent out from the high-frequency power amplifier using an internally generated receiving station oscillation signal and then extracts the demodulated signal, and utilizes the demodulated signal. A control unit (6) that generates a control signal by
and the controller is configured to minimize intersymbol interference caused by fluctuations in the operating conditions of the high frequency power amplifier.
2. The nonlinear distortion compensation method according to claim 1, wherein the control signal is used to control the operation of the digital filter. 3. The nonlinear distortion compensation method according to claim 2, wherein the receiving station oscillator signal is synchronized with the output of the transmitting local oscillator.