JPH07263962A - Linear compensation type amplitude modulating transmitter - Google Patents

Abstract

PURPOSE:To provide the linear compensation type amplitude modulating transmitter which compensates the nonlinear distortion brought about in a power amplifier and a synthesizer. CONSTITUTION:An A/D converter 2 converts an input analog signal to a digital signal, and a compensation table 11 compensates the inputted signal based on a compensation value, and a modulation encoder 3 makes N control signals of the input signal, and a power amplifier 4 amplifies a carrier signal based on N control signals, and a synthesizer 5 synthesizes N amplified carrier signals into one high frequency signal, and an output detector 7 detects it to obtain an output analog signal. AD A/D converter 8 converts the output analog signal to a digital signal, and the compensation value is calculated in accordance with this signal and the output of an A/D converter 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear compensation type amplitude modulation transmitter, and more particularly to a linear compensation type amplitude modulation transmitter in the long wave band, medium wave band and short wave band.

[0002]

2. Description of the Related Art Conventionally, an amplitude modulation transmitter has a circuit as shown in FIG. The conventional amplitude modulation transmitter shown in FIG. 2 includes an input terminal 1, an A / D converter 2, a modulation encoder 3, a plurality of power amplifiers 4, a combiner 5, and an output terminal 6. According to this configuration, the audio signal input from the input terminal 1 is converted from an analog signal to a digital signal by the A / D converter 2. The digitized audio signal is converted into a PA control signal for controlling the power amplifier by the modulation encoder 3, whereby the power amplifier 4 is turned on and off, and the high frequency signal from the power amplifier 4 is input to the combiner 5. . The combiner 5 combines the high frequency signals input from the power amplifier 4 in series. The combined high frequency signal is output from the output terminal 6.

[0003]

However, in the above-mentioned conventional amplitude modulation transmitter, the operating impedance of the power amplifier is the operating quantity of the power amplifier, that is, the input terminal 1.
Varies widely depending on the amplitude of the audio signal applied to the. For this reason, it becomes difficult to linearly modulate and amplify the audio signal in an ideal form due to the influence of the internal resistance of the amplifying element used in the power amplifier and the leakage current.

Further, the N power amplifiers (PA) are electrically connected in series in the combiner, and the PAs in operation are
Is added to the output amplitude and supplied to the output terminal. For this reason, it is difficult to linearly combine and transmit the output amplitude of the power amplifier in an ideal form due to electrical loss inside the combiner and structural influence of the combiner.

The above-mentioned non-linearity is accompanied by problems such as deterioration of the modulation distortion of the transmitter.

It is an object of the present invention to provide a linear compensation type amplitude modulation transmitter which can obtain an output signal with high linearity.

It is an object of the present invention to provide a linear compensation type amplitude modulation transmitter which efficiently corrects non-linear distortion generated in a power amplifier and a combiner.

[0008]

In order to achieve the above object, a linear compensation type amplitude modulation transmitter of the present invention is a first A / D converter for converting an input analog signal into a first digital signal and outputting the first digital signal. Means for correcting the first digital signal based on the compensation value to obtain a second digital signal;
Control means for converting the digital signal of the above into a plurality of control signals,
A plurality of power amplifying means for amplifying a carrier signal based on a plurality of respective control signals, and a synthesizing means for synthesizing the plurality of carrier signals amplified by the power amplifying means into one output analog signal 3rd output analog signal
Second A / D conversion means for converting into a digital signal and a calculation means for calculating a compensation value from the first digital signal and the third digital signal. It is characterized by compensating for linear distortion.

Further, the compensation value is a difference signal between the first digital signal and the third digital signal, the correction means has a storage table, and the compensation value may be stored in the storage table.

[0010]

Therefore, according to the linear compensation type amplitude modulation transmitter of the present invention, the input analog signal is converted into the first digital signal, the first digital signal is corrected based on the compensation value, and the corrected first digital signal is corrected. A carrier signal is amplified by using the two digital signals as a plurality of control signals, and the plurality of amplified carrier signals are combined into a single output analog signal. The output analog signal is further converted into a third digital signal, and the compensation value is calculated from the first digital signal and the third digital signal. Therefore, the correction value has a relationship between the input signal and the output signal, correction based on the closed loop of these input / output signals is possible, and the non-linear distortion generated in the power amplification means and the combining means can be compensated.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the linear compensation type amplitude modulation transmitter of the present invention will be explained with reference to FIG. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The input terminal 1 is an input terminal for a voice signal to the linear compensation type amplitude modulation transmitter. This input terminal 1 is
It is connected in parallel with the analog signal input terminals of the first A / D converter 2 and the second A / D converter 9. 2 A /
The D converters 2 and 9 are circuit elements that convert an analog signal into a digital signal together with a third A / D converter 8 described later.

The digital output signal A / D converted by the first A / D converter 2 is transmitted to the compensation table 11. The compensation table 11 is an input / output data conversion circuit unit having a storage element such as an electrically rewritable EE-PROM. Compensation values corresponding to the input signal are stored in a table form, and the input signal is compensated based on the stored compensation value. Data for performing compensation is stored in the compensation table 11. The compensation data can be changed at any time based on the output data of the arithmetic unit 10.

The output data of the compensation table 11 is input to the modulation encoder 3. The modulation encoder 3 is a circuit unit that converts an input digital signal into N switching signals and outputs the N switching signals to an output terminal.

The N output terminals of the modulation encoder 3 are connected to N power amplifiers (PA) 4, respectively, and the output of the power amplifier 4 is controlled. The control signal causes the power amplifier 4 to output a high frequency signal. The N high frequency signals output from the power amplifier 4 are connected in parallel to the input terminal of the combiner 5.

In the combiner 5, the high frequency signals input in parallel from the N input terminals are combined and output as a single signal. The high frequency signal output from the synthesizer 5 is input to the output detector 7. The output detector 7 is a circuit unit that demodulates a high frequency signal and converts it into an AM signal. Output detector 7
The output of is connected to the output terminal 6. The detection terminal of the output detector 7 is connected to the input terminal of the third A / D converter 8, and a part of the demodulated signal is included in the third A / D converter 8
Is output to.

The AM signal input from the output detector 7 is input to the third A / D converter 8 and converted into a digital signal. The output terminal of the third A / D converter 8 is connected to one input terminal of the arithmetic unit 10. The other one input terminal of the arithmetic unit 10 is connected to the second A / D converter 9. The calculator 10 calculates the difference ΔS between the digital signals So and Si from the two A / D converters 8 and 9. This difference ΔS corresponds to the difference between the input signal and the output signal to the linear compensation type amplitude modulation transmitter. The difference signal ΔS is input to the compensation table 11.

The operations of the arithmetic unit 10 and the compensation table 11 will be described in detail below. The output signal of the second A / D converter 9 is S
i, the output signal of the third A / D converter 8 is So, the input signal of the compensation table 11 is si, the output signal is so, and the correction coefficient is k.

The relationship between these signals Si, So, si, so and the correction coefficient k is as follows.
= So-Si is calculated. In the compensation table 11, the difference signal ΔS corresponding to the magnitude of the value of the input signal si is stored as table data. The compensation coefficient k is set empirically according to the value of the table data. The compensation coefficient k is simply set to 1. When these relationships are expressed as mathematical expressions, the following expression (1) is obtained.

So = k · (si + ΔS) (1) where ΔS = So−Si

When the transmitter is in the initial state, no data is stored in the storage circuit of the compensation table 11, the compensation value is "0", and the compensation is not substantially executed. In this state, the input signal si and the output signal so of the compensation table 11 are the same. When an audio signal is applied to the input terminal 1 in the initial state, the analog input signal is the first A / D converter 2
It becomes a digital signal in. The signal A / D converted by the A / D converter 2 is transmitted to the compensation table 11 and is added or subtracted in such a manner that the difference signal is canceled. However, in the initial state, the compensation in the compensation table 11 is not substantially executed. This compensated voice signal is converted by the modulation encoder 3 into a PA control signal suitable for the operation of the power amplifier 4.

The power amplifier 4 is turned on and off by the PA control signal, and the high frequency signal from the power amplifier 4 is input to the combiner 5. The combiner 5 combines the high frequency signals from the power amplifier 4. The combined high frequency signal is output from the output terminal 6 through the output detector 7. Output detector 7
A part of the analog signal detected by is input to the third A / D converter 8 to be a digital signal.

The digital signal of the input signal and the output signal to the linear compensation type amplitude modulation transmitter is converted into a differential signal by the arithmetic unit 10 and input to the compensation table 11. Compensation table 10
When the difference signal ΔS input to is 0, the compensation data stored in the compensation table 11 is 0. The compensation coefficient k when the compensation data is “0” is, for example, k = 1, and the input signal si and the output signal so in the compensation table 11 are the same, si = so.

Difference signal Δ input to the compensation table 11
When S is other than "0", for example, when So <Si, the input signal si
Is corrected, and if So> Si, the input signal si
Is corrected by subtracting from. This correction ensures the linearity of the amplitude modulation transmitter. The data stored in the compensation table 11 is updated at any time.

By the above procedure, the error data can be canceled by detecting the non-linear distortion generated in the power amplifier 4 and the combiner 5 and writing and accumulating it as data in advance. By this compensation, an AM signal having a low distortion modulation characteristic can be obtained.

Although the above-described embodiment is an example of a preferred embodiment of the present invention, the present invention is not limited to this and various modifications can be made without departing from the gist of the present invention. For example, in the embodiment, two AD converters 2 and 9 are used for A / D conversion of the input signal, but they are commonly used as 1
Good as an individual.

[0027]

As is apparent from the above description, the linear compensation type amplitude modulation transmitter according to the present invention receives the input analog signal as the first analog signal.
Is converted into a digital signal, corrected based on the compensation value, and the carrier signal is amplified based on the corrected second digital signal to be an output analog signal. The output analog signal is the third
Converted into a digital signal of the first digital signal and the third digital signal
The compensation value is calculated from the digital signal and the correction is performed based on the relationship between the input signal and the output signal. By performing the correction based on the closed loop with these input / output signals, the non-linear distortion can be compensated and the linearity of the output signal is compensated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a linear compensation type amplitude modulation transmitter of the present invention.

FIG. 2 is a block diagram showing an embodiment of a conventional amplitude modulation transmitter.

[Explanation of symbols]

 1 Input Terminals 2, 8, 9 A / D Converter 3 Modulation Encoder 4 Power Amplifier (PA) 5 Combiner 6 Output Terminal 7 Output Detector 10 Arithmetic Unit 11 Compensation Table

Claims (4)

[Claims] 1. A first A / D conversion means for converting an input analog signal into a first digital signal and outputting the first digital signal, and correcting the first digital signal based on a compensation value.
Correction means for converting the second digital signal into a plurality of control signals, and a plurality of power amplifying means for amplifying a carrier signal based on each of the plurality of control signals. Combining means for combining a plurality of carrier signals amplified by the power amplifying means into one output analog signal, and second A / D converting means for converting the output analog signal into a third digital signal And a calculating means for calculating the compensation value from the first digital signal and the third digital signal, and compensating for the non-linear distortion generated in the power amplifying means and the combining means. Linear compensation type amplitude modulation transmitter. 2. The linear compensation type amplitude modulation transmitter according to claim 1, wherein the compensation value is a difference signal between the first digital signal and the third digital signal. 3. The linear compensation type amplitude modulation transmitter according to claim 1, wherein the correction means has a storage table, and the compensation value is stored in the storage table. 4. The linear compensation type amplitude modulation transmitter according to claim 3, wherein the storage table is a storage element capable of being electrically rewritten, and the predetermined numerical value is rewritten and updated at any time.