JPH0531330B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention compensates for distortion in a transmitting amplifier of a wireless device by distorting an input signal, and compares the amount of compensation between the output of the transmitting amplifier and the input signal. The present invention relates to a transmitter with an adaptive predistorter that changes adaptively.

(Prior Art) In general, in radio equipment, particularly in radio equipment for mobile communication, it is common to operate a transmission amplifier in a saturation region in order to use power effectively. If an attempt is made to use a linear modulation method in which the amplitude changes, such as QAM, in such a radio device, distortion will occur due to the nonlinear characteristics of the transmission amplifier, and the spectrum will widen. As a countermeasure against this problem, there is a predistorter that distorts the input to the transmission amplifier in advance so that the output of the transmission amplifier is free of distortion. Furthermore, in order to compensate for fluctuations in characteristics due to temperature changes and time changes in the transmitting amplifier, an adaptive predistorter is installed that demodulates the output of the transmitting amplifier and compares it with the input to control the output of the transmitting amplifier so that it is always distortion-free. Proposed.

This adaptive pre-day stator is from the 1980s.
Volume 70 of the second volume of the 1985 IEICE Information and Systems Division National Conference Proceedings, a collection of papers published in 2005.
Familiar with the page.

(Problems to be Solved by the Invention) However, in the conventional adaptive predistorter, delay in a circuit including a modulator, a transmission amplifier, and a demodulator is not taken into account. Therefore, the input signal and the demodulator output at different times may be compared, and the adaptation may not be successful. Furthermore, this amount of delay differs depending on the frequency band, so if each call is transmitted on a different frequency, such as in a car phone, it is necessary to compensate for the different amount of delay each time, and to ensure proper adaptation. The drawback was that it was extremely difficult.

An object of the present invention is to provide a transmitter with a delay compensation type adaptive predistorter that eliminates the drawbacks of the conventional adaptive predistorter described above and also adaptively compensates for delay.

(Means for Solving the Problems) The present invention includes: a memory that stores the amount of distortion corresponding to each value of an input signal; an adder that adds the output of this memory and the input signal;
a modulator that modulates the output of the adder; a transmission amplifier that amplifies the output of the modulator; a demodulator that demodulates the output of the transmission amplifier; a variable length delay circuit that delays the input signal; a subtracter that takes the difference between the output of the long delay circuit and the output of the demodulator;
an adaptation circuit that updates the contents of the memory using the output of the subtracter; a differentiation circuit that time-differentiates the output of the variable length delay circuit; and a differentiation circuit that multiplies the sign of the output of the differentiation circuit by the output of the subtracter. a multiplier;
With a delay compensation type adaptive predistorter, comprising: a low-pass filter that integrates the output of the multiplier; and a delay control circuit that corrects the amount of delay of the variable-length delay circuit using the output of the low-pass filter. The above problem is solved by the transmitter.

(Operation) In order to adaptively compensate for the amount of delay, it is necessary to know whether the amount of delay at present is too advanced or too late. The device of the present invention must compensate for both the nonlinear distortion and delay of the transmitting amplifier using the demodulator output. For this purpose, it is necessary to consider the difference in the characteristics of distortion caused by nonlinear distortion and delay error.
Nonlinear distortion is a function of signal amplitude, and if the input signal amplitude is constant, the same distortion will always occur. On the other hand, distortion due to delay errors will vary if the time differential value at that point in time differs even if the amplitude of the input signal is constant. Figure 4 shows the situation. FIG. 4a shows a case where the input signal and the delayed demodulator output are compared. In this case, if the signal value is increasing, the input signal will be larger. On the other hand, an example in which too much delay is added to the input signal so that the input signal lags behind the output of the demodulator is shown in FIG. 4b. In this case, the input signal becomes smaller when the signal value is increasing. The opposite is true when the signal value is decreasing.
This phenomenon does not depend on the amplitude of the input signal. Therefore, by dividing the error signal by the time differential of the input signal, the delay time difference between the input signal and the demodulator output can be obtained. However, since the error between the input signal and the demodulator output also includes the distortion of the transmission amplifier, it is not possible to accurately determine the distortion from a single observed value. In order to eliminate the influence of distortion of the transmission amplifier, the output of the divider can be averaged with a low-pass filter and the amount of delay can be controlled to increase or decrease. As a practical matter, the circuit of the divider is complex and there is a problem that dividing by 0 will cause an overflow, so instead of dividing by the time differential value itself, divide by the sign of the time differential. This greatly simplifies the circuit because it is only necessary to change the sign of the error signal. Dividing only by the sign does not change the absolute value, so it is equivalent to multiplying by the sign. Therefore, the present invention adopts the expression of multiplying by signs.

(Example) Next, the present invention will be described in detail with reference to the drawings. First, a conventional adaptive predistorter will be explained. FIG. 2 shows this basic block diagram. A transmission signal is input as a digital signal from the input terminal 200. The RAM 201 stores the amount of distortion to be corrected. An example of this value is shown in FIG. In the first place, Preday Stotor is the third
In order to operate a transmission amplifier having saturation characteristics as shown in FIG. 3A like a transmission amplifier having characteristics as shown in FIG. For example, to obtain the linear amplified output corresponding to point A in Figure 3 using a transmitting amplifier with characteristics a, add ΔA to the input signal of A and input it to the transmitting amplifier, and the output of B (linear amplified output) is obtained and the distortion of the transmitting amplifier is removed. RAM201
The value of is added to the input signal by an adder 202 and input to a transmission amplifier 204 where it is modulated by a modulator 203. The output of transmission amplifier 204 is output from terminal 210 and demodulated by demodulator 205 . The output of the demodulator 205 is subtracted from the input signal by a subtracter 206, and when the output of the demodulator is too large,
The adaptation circuit 207 controls the content of the RAM 201 to be reduced, and conversely to increase the content of the RAM 201 if it is too small. This is an adder (adaptation circuit 20
In addition to 7), this can be easily achieved by writing to the RAM 201. When the input signal and the output of the demodulator 205 become equal, the output of the subtracter 206 becomes O and the RAM
The contents of 201 are constant values.

However, in an actual circuit, a delay occurs while the signal passes through the modulator 203, transmission amplifier 204, and demodulator 205. In this case, the distortion caused by the transmission amplifier 204 cannot be correctly compensated unless the input signal is delayed by the same amount and inputted to the subtracter 206. In the present invention, this problem is solved by adding a circuit that automatically delays the input signal by an optimum time using the configuration shown in FIG.

The signal input from input terminal 100 is sent to adder 1
At step 02, the correction amount from the RAM 101 is added to the signal, modulated by the modulator 103, and input to the transmission amplifier 104. The output of transmission amplifier 104 is output from terminal 120 and demodulated by demodulator 105 .
The output of demodulator 105 is applied to subtractor 106. Subtractor 106 subtracts the output of demodulator 105 from the input signal delayed by variable length delay circuit 112 and applies the subtracted value to adaptation circuit 107 . Adaptation circuit 107 operates to reduce the contents of RAM 101 when the output of demodulator 105 is too large, and to increase the contents of RAM 101 when it is too small. The adaptation circuit 107 consists of an adder, which adds the output of the subtracter 106 to the output of the RAM 101, and writes the result to the RAM 101. If the amount of delay in the variable length delay circuit 112 is incorrect, the output of the subtracter 106 will contain a mixture of distortion caused by the transmission amplifier 104 and distortion caused by the delay error. In order to remove delay errors, a differentiating circuit 108 differentiates the output of the variable length delay circuit 112, and a multiplier 109 multiplies the output of the subtracter 106 by the sign of the output of the differentiating circuit 108. By doing this, the output of the multiplier 109 becomes a positive value when the delay amount of the variable length delay circuit 112 is insufficient (the state shown in FIG. 4 a), and conversely, when it is too large (the state shown in FIG. 4 b) ) becomes a negative value. Therefore, in this embodiment, the low-pass filter 110 removes the influence of distortion of the transmission amplifier 104, and the delay control circuit 111 increases the delay amount of the variable length delay circuit 112 if the output of the low-pass filter 110 is positive, and increases the delay amount of the variable length delay circuit 112 if the output is negative. controlling the amount of delay of the variable length delay circuit 112 so as to reduce the amount of delay of the variable length delay circuit 112;
Automatically minimizes distortion due to delay errors. Differential circuit 108 is connected to variable length delay circuit 11 by register 121.
It is obtained by delaying the output of the variable length delay circuit 112 by a minute amount of time and taking the difference between the output of the variable length delay circuit 112 and the output of the variable length delay circuit 112. The variable length delay circuit 112 can be easily constructed by using several stages of shift registers. The register 121 is
If the variable length delay circuit 112 is a shift register, a circuit integrated with the shift register of the variable length delay circuit can be used.

(Effects of the Invention) As described in detail above, according to the present invention,
It is possible to provide a transmitter with a delay compensation type adaptive predistorter that automatically corrects linearity deterioration due to delay in a circuit including a modulator, a transmission amplifier, and a demodulator.

[Brief explanation of the drawing]

Fig. 1 is a circuit block diagram showing an embodiment of the present invention, Fig. 2 is a circuit block diagram showing a conventional adaptive predistorter, Fig. 3 is a diagram showing the principle of the predistorter, and Fig. 4. is a schematic waveform diagram showing the influence of delay error. 101...Memory, 102...Adder, 10
3...Modulator, 104...Transmission amplifier, 105...
... Demodulator, 106 ... Subtractor, 107 ... Adaptation circuit, 108 ... Differentiation circuit, 109 ... Multiplier,
110...Low pass filter, 111...Delay control circuit, 112...Variable length delay circuit.

Claims (1)

[Claims] 1. An adaptive predistorter that compensates for distortion in a transmitting amplifier of a radio device by distorting an input signal, and adaptively changes the amount of compensation by comparing the output of the transmitting amplifier with the input signal. a memory for storing an amount of distortion corresponding to each value of the input signal;
an adder that adds the output of this memory and the input signal; a modulator that modulates the output of the adder and applies it to the transmission amplifier; a demodulator that demodulates the output of the transmission amplifier; and a demodulator that delays the input signal. a subtracter that takes the difference between the output of the variable length delay circuit and the output of the demodulator, an adaptation circuit that updates the contents of the memory using the output of the subtracter; A differentiating circuit that time-differentiates the output of the long delay circuit, a multiplier that multiplies the sign of the output of this differentiating circuit by the output of the subtracter, a low-pass filter that integrates the output of this multiplier, and the output of this low-pass filter. A transmitter with a delay compensation type adaptive predistorter, comprising a delay control circuit that corrects the amount of delay of the variable length delay circuit.