JPH09130439A - Linear compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably operate a Cartesian feedback even when an amplifier having the characteristic whose phase characteristic is remarkably changed by an amplitude value is used and to improve a distortion improvement factor. SOLUTION: A modulation input - phase/conversion table 6 converts the common-mode modulation signal and the orthogonal modulation signal which are outputted from a distortion compensation circuit 1 into the converted amount of the phase characteristic of an amplifier 3 according to the amplifier-phase characteristic of the amplifier. A subtracter 8 subtracts the output of the modulation input - phase/conversion table 6 from phase adjustment amount adjusting phase rotational amount which does not depend on the modulation signal, the adjustment amount is inputted in an infinite phase converter 7 and the phase of the carrier wave of an quadrature modulator 2 is controlled. Because the phase characteristic of a feedback signal is compensated by changing the phase of the carrier wave of the quadrature modulator 2 according to the amplitude value of a modulation burst band signal, the phase margin of the feedback signal can be maintained even when the phase characteristic of the amplifier 3 is changed by an inputted amplitude value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear compensation circuit used in a transmitter equipped with a Cartesian feedback type distortion compensation circuit.

[0002]

2. Description of the Related Art In a transmitter for transmitting a linear modulation signal, if the linearity is poor, not only the modulation accuracy is deteriorated but also excessive out-of-band unwanted radiation is generated, which interferes with adjacent channels. There is a risk. Therefore, it is necessary to ensure linearity over the entire operating range of the transmitter.

Conventionally, so-called Cartesian feedback is one of the methods for improving the linearity of a transmitter.
This is a method of locally demodulating a part of the output of the transmitter into a quadrature baseband signal and applying negative feedback to the modulation baseband signal.It is possible to secure a phase margin, and if the loop gain can be set large, distortion The degree of improvement can also be increased.

This conventional example will be described with reference to FIG. 13. The in-phase modulation input signal I and the quadrature modulation input signal Q are input to the distortion compensation circuit 1. In the distortion compensation circuit 1, the in-phase modulation input signal I and the quadrature modulation input signal Q input
And a signal obtained by orthogonally demodulating the transmission signal by the orthogonal demodulator 5 performs distortion calculation. The modulation signal output from the distortion compensation circuit 1 is quadrature-modulated by the carrier wave from the oscillator 9 in the quadrature modulator 2, amplified by the amplifier 3, and input to the directional coupler 4. The output of the directional coupler 4 becomes a transmission output, and the branched output of the directional coupler 4 is input to the quadrature demodulator 5 and quadrature demodulated by the demodulation carrier wave input from the oscillator 9 through the infinite phase shifter 7.

[0005]

However, in general, the transfer phase characteristic of the power amplifier 3 varies depending on the pass frequency, the operating point and the environmental conditions. Therefore, the phase margin of the loop changes, the loop gain has an upper limit in order to ensure stable operation, and the amount of distortion improvement is also limited. Therefore, normally, before the actual signal transmission, the phase shift amount of one round of the loop is measured, and the phase of the carrier wave of the local demodulator 5 is rotated by the phase shifter 7. After that, it forms a closed loop. However, such pre-adjustment of the phase requires a long time, and the accuracy is not sufficient in the case of a modulation method in which the fluctuation of the envelope is large, or when the transmission frequency or the transmission power fluctuates greatly during a call. Therefore, there is a problem that the loop gain cannot be set large and the amount of distortion improvement cannot be set large.

The present invention solves the above-mentioned conventional problems, and can keep the fluctuation of the phase margin of the Cartesian loop small, and therefore has a characteristic that the phase characteristic largely changes depending on the amplitude value. Even when an amplifier is used, Cartesian feedback can be operated stably, and a large amount of feedback can be set.
Therefore, it is an object of the present invention to provide a linear compensation circuit capable of improving the degree of distortion improvement.

[0007]

In order to achieve the above object, the present invention provides an in-phase demodulation obtained by quadrature demodulating an in-phase modulation input signal and a quadrature modulation input signal with a distortion compensation circuit and a transmission signal with a quadrature demodulation circuit. Distortion compensation is calculated from the signal and the quadrature demodulation signal, the in-phase modulation signal and the quadrature modulation signal are input to the quadrature modulator, the output is amplified by an amplifier, and the signal is output as a transmission output. Cartesian feedback that demodulates the in-phase demodulation signal and the quadrature demodulation signal by the demodulation carrier wave input from the infinite phase shifter, inputs the demodulation signal to the distortion compensation circuit, and compensates the distortion in the baseband orthogonal coordinates. In the linear compensation circuit of the method, a modulation input-position for inputting the in-phase modulation signal and the quadrature modulation signal and outputting a phase rotation amount depending on the input of the quadrature modulator. - a conversion table, the modulation input - phase and
The output of the conversion table is subtracted from the phase shift adjustment amount that adjusts the phase rotation amount that does not depend on the modulation signal, the output is input to the infinite phase shifter, and the subtraction is performed to control the carrier phase of the quadrature modulator. It is characterized by having a container.

In the above technical means, the modulation input-phase / conversion table can be switched depending on the temperature, the transmission frequency, or the temperature and the transmission frequency.

The input of the modulation input-phase / conversion table can be the in-phase modulation input signal or the quadrature modulation input signal.

As described above, the degree of distortion improvement can be improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is an in-phase demodulation signal obtained by quadrature demodulating an in-phase modulation input signal and a quadrature modulation input signal in a distortion compensation circuit and a transmission signal in a quadrature demodulation circuit. Distortion compensation is calculated from the quadrature demodulation signal, the in-phase modulation signal and the quadrature modulation signal are input to the quadrature modulator, the output is amplified by an amplifier and output as a transmission output, and the signal is infinite by the quadrature demodulator. In the Cartesian feedback system that demodulates into the in-phase demodulation signal and the quadrature demodulation signal by the demodulation carrier wave input from the phase shifter, inputs the demodulation signal to the distortion compensation circuit, and compensates the distortion at the baseband orthogonal coordinates. In the linear compensation circuit, a modulation input-phase / conversion table that inputs the in-phase modulation signal and the quadrature modulation signal and outputs a phase rotation amount that depends on the quadrature modulator input, The output of this modulation input-phase / conversion table is subtracted from the amount of phase shift adjustment that adjusts the amount of phase rotation that does not depend on the modulation signal, and the output is input to the infinite phase shifter, and the carrier phase of the quadrature modulator is subtracted. It is equipped with a subtractor for controlling the power consumption.It measures the rough characteristics of the transmission modulator and power amplifier at the manufacturing stage, stores predictable phase shift data, and It is intended to adaptively absorb the fluctuation of the phase transition by shortening the phase adjustment time at the stage of transmitting the signal and dynamically changing the transition amount according to the envelope fluctuation during the call. , Even if the amplifier input amplitude becomes large and the phase characteristics change, the phase margin of the Cartesian loop is kept small by compensating for the phase of the carrier wave of the modulator regardless of the feedback effect. It can be. Further, in the configuration of the conventional example, the design was made with a margin for the change in the phase characteristic due to the input amplitude value of the amplifier.
By using the above configuration, the phase margin can be set smaller than in the conventional case, and therefore, the feedback amount can be set large. (Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
3 is a block diagram showing a linear compensation circuit in the embodiment of FIG.

As shown in FIG. 1, the in-phase modulated input signal I
(T) and the quadrature modulation input signal Q (t) are input to the distortion compensation circuit 1. In the distortion compensation circuit 1, the input in-phase modulation input signal I and quadrature modulation input signal Q, and the quadrature demodulator 5 are input.
The distortion compensation calculation is performed from the signal obtained by quadrature demodulation (detection) of the transmission signal. The in-phase modulation signal I ″ (t) and the quadrature modulation signal Q ″ (t) output from the distortion compensation circuit 1 are input to the quadrature modulator 2.

The in-phase modulation signal I ″ (t) and the quadrature modulation signal Q ″ (t) are input to the amplitude calculation circuit, and after the amplitude value I ″ × I ″ + Q ″ × Q ″ of the modulation input signal is calculated. , Is output. Amplitude calculation circuit output is modulation input-phase / conversion table 6
Is input to the amplifier 3 and converted into a change amount of the amplifier phase characteristic according to the amplitude-phase characteristic of the amplifier 3 and subtracted by the subtracter 8 from the phase shift adjustment amount θ that adjusts the phase rotation amount that does not depend on the modulation signal. It is input to the phase shifter 7. In the infinite phase shifter 7, the carrier wave is input to the quadrature modulator 2 from the inputs of the subtracter 8 and the oscillator 9, and the in-phase modulation signal I and the quadrature modulation symbol Q are quadrature-modulated. The output of the quadrature modulator is input to the amplifier 3, amplified, and input to the directional coupler 4. The output of the directional coupler 4 becomes a transmission output. The branch output of the directional coupler 4 is input to the quadrature demodulator 5 and quadrature demodulated by the carrier wave from the oscillator 9 to obtain the in-phase demodulation signal I ′ (t) and the quadrature demodulation signal Q ′ (t). The demodulated signals I ′ (t) and Q ′ (t) are input to the distortion compensation circuit 1 as described above, and distortion compensation calculation is performed with the separately input modulation input signals I (t) and Q (t).

FIG. 2 is a block diagram showing an example of the distortion compensation circuit 1. As shown in FIG. 2, the in-phase modulation input signal I,
The in-phase demodulation signal I ′ input through the switch 18a is input to the subtraction circuit 19a, and the calculation result is in-phase modulation signal I ″.
Output as Similarly, the quadrature modulation input signal Q and the quadrature demodulation signal Q ′ input via the switch 18b are input to the subtraction circuit 19b, and the calculation result is output as the quadrature modulation signal Q ″. Negative feedback is done,
Distortion is improved.

FIG. 3 is a block diagram showing an example of the infinite phase shifter 7. As shown in FIG. 3, the phase adjustment amount θ is equal to the angle θ.
-Sin θ, cos θ conversion table 12 is input to the ROM, and sin θ and cos θ are output. Then each si
nθ and cosθ are input to the digital / analog converter 11, converted into analog values, and then input to the quadrature modulator 2. The output of the quadrature modulator 2 is the input signal cosωt
Then, cos θ × cos ωt−sin θ × sin ωt = cos
Since it is expressed as (ωt + θ), the output of the quadrature modulator 2 is
The phase rotates by θ and functions as an infinite phase shifter.

The modulation input-phase / conversion table 6 inputs the modulation signals I "and Q" and outputs the amount of change in the phase characteristics of the amplifier 3 and the quadrature modulator 2 when the inputs are applied.
Specifically, using a mathematical expression, the in-phase modulation signal is I ″,
When the quadrature modulation signal is Q ″, the in-phase demodulation signal is I ′, and the quadrature demodulation signal is Q ′, when the phase adjustment amount θ = 0, the following equation is obtained.

I ′ = A (I ″, Q ″) × (I ″ × cos θ1 + Q ″ × sin θ1) Q ′ = A (I ″, Q ″) × (−I ″ × sin θ1 + Q ″ × cos θ1) θ1 = θ2 + θ3 ( I ″, Q ″) θ3 (0, 0) = 0 where θ1 is the amount of phase rotation of the loop from the input of the quadrature modulator 2 to the output of the quadrature demodulator 5, and θ2 is the input of the modulator 2. Represents the amount of phase rotation independent of, and θ3 is
It represents the amount of phase rotation depending on the input of the modulator 2. θ3
(I ″, Q ″) is the phase rotation when the in-phase modulation signal is I ″ and the quadrature modulation signal is Q ″. A (I ", Q")
Represents the open loop amplitude characteristic of the loop including the quadrature modulator 2, the amplifier 3, the directional coupler 4 and the quadrature demodulator 5 when the in-phase modulation signal I ″ and the quadrature modulation signal Q ″ are added. The modulation input-phase / conversion table 6 is a table for inputting I ″ and Q ″ and outputting θ3.

FIG. 4 shows a block diagram of an example of the modulation input-phase / conversion table 6. Since the phase shift corresponding to the modulation input is proportional to the magnitude of the input vector, here, the square of the magnitude of the input vector is calculated and input to the table to obtain the phase shift. Since there is a one-to-one correspondence between the size of the input vector and the square of the size, a square root calculation is performed from the squared value, and instead of obtaining the size, the input of the table is squared and the square root calculation is performed. Has been reduced.
When the table is drawn by the square of the size of the modulation input as described above, the size of the table can be reduced as compared with the case where the modulation inputs I ″ and Q ″ are input to the table. However, in this case, an arithmetic circuit is required.

The flow of signals between the blocks will be described below. Since the in-phase modulation signal I ″ and the quadrature modulation signal Q ″ are analog values, the in-phase modulation signal I ″ and the quadrature modulation signal Q ″ are input to the analog / digital converters 14a and 14b to be converted into digital values, and thereafter, Multipliers 13a and 13b
Input and take the square of each signal. Further, the square of each signal is input to the adder 10, and I ″ × I ″ + Q ″ × Q ″ is calculated and input to the ROM which is the input amplitude-phase conversion table 15. As described above, the phase transition corresponding to the input is obtained.

The details of the operation will be described below. FIG. 9 shows a graph of an example of the input amplitude-loop gain characteristic. The loop gain characteristics are the magnitude of the modulation signal vector (I ″, Q ″) when the phase adjustment amount θ = 0 and the demodulation signal vector (I ′,
It is the ratio of the size of Q '). Hereinafter, the loop gain characteristic is represented by A (I ″, Q ″).

FIG. 10 is a graph showing an example of the input amplitude-loop phase characteristic. The loop phase characteristic is the difference between the phase of the modulation signal vector (I ″, Q ″) and the phase of the demodulation signal vector (I ′, Q ′) when the phase adjustment amount θ = 0. Below, the loop phase characteristic is represented by θ (II ″, Q ″).

First, at the time of starting the operation, there is a possibility of oscillation if the feedback phase is undetermined and the loop is closed as it is. Therefore, the switch 1 in the distortion compensation circuit 1 of FIG.
8a and 18b are opened so that the loop is not formed.

In this state, the modulation input signals I and Q are input up to the level of a in FIG. 10 where the phase characteristic does not change. At that time, the loop phase characteristic θ2 is measured, and the phase adjustment amount is θ =
Set to -θ2. Actually, (I ″, Q ″) = (a,
0) or the like is input, and θ is adjusted so that the demodulation vector has the same phase as the modulation vector, that is, I ′> 0 and Q′≈0. With the above adjustment, the phase adjustment amount is set so as to prevent oscillation when the signal is small, and θ = −θ2.

The output of the modulation input-phase conversion table 6 is set to θ in consideration of individual differences of the amplifier 3, etc., temperature changes, and errors such as frequency.
3 '(I ", Q"). θ3 ′ (I ″, Q ″) ≈θ
3. Therefore, the input of the infinite phase shifter 7 is -θ2-θ
3 '(I ", Q"). Quadrature modulator 2 by this angle
Since the phase of the carrier wave of is corrected, the in-phase demodulated signal I ′,
The quadrature demodulated signal Q ′ is I ′ = A (I ″, Q ″) × (I ″ × cos θ4 + Q ″ × sin θ4) Q ′ = A (I ″, Q ″) × (−I ″ × sin θ4 + Q ″ × cos θ4) θ4 = Θ1-θ2-θ3 ′ = (θ2 + θ3) −θ2−θ3 ′ = θ3 (I ″, Q ″) − θ3 ′ (I ″, Q ″) ≈0, cos θ4≈cos0 = 1, sin θ4≈si
Since n0 = 0, eventually I'≈A (I ″, Q ″) × I ″ Q′≈A (I ″, Q ″) × Q ″. From the above consideration, it can be seen that there is no phase around the demodulation output. (Embodiment 2) Next, a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing a linear compensation circuit according to the second embodiment of the present invention.

This embodiment is different from the first embodiment in that the modulation input-phase conversion table 6 is set to the temperature measuring means 16.
To switch by. (Third Embodiment) Next, a third embodiment of the present invention will be described. FIG. 6 is a block diagram showing a linear compensation circuit according to the third embodiment of the present invention.

The present embodiment differs from the above-described embodiments in that the amplifier 3 includes a frequency converter.
In the Cartesian feedback, not only the amplifier 3 but also a circuit including the amplifier 3 and the frequency converter 17a, a frequency converter having a frequency relationship opposite to that of the transmission is provided between the directional coupler 4 and the quadrature demodulator 5. 17b is provided and the frequencies of the quadrature modulator 2 and the quadrature demodulator 5 are the same, it is possible to operate as a linear compensation circuit. This embodiment shows that the present invention can be similarly applied to a circuit including the frequency converters 17a and 17b. (Fourth Embodiment) A fourth embodiment of the present invention will be described below. FIG. 7 is a block diagram showing a linear compensation circuit according to the fourth embodiment of the present invention.

The present embodiment differs from the first embodiment in that the modulation input-phase conversion table 6 uses the modulation input signals I, Q instead of the modulation signals I ", Q". Especially. Also in the case of the present embodiment, it is possible to change the amplitude-phase conversion table 15 depending on the temperature and the frequency, and to apply not only to the amplifier 3 but also to a circuit including the frequency converters 17a and 17b. It is clear that you can do it. (Fifth Embodiment) The fifth embodiment of the present invention will be described below. FIG. 8 is a block diagram showing a linear compensation circuit according to the fifth embodiment of the present invention.

In the present embodiment, the case where the amplitude calculation circuit 20, the amplitude-phase conversion table 15, and the subtracter 8 are configured by software is shown. In this case, all the parts newly added in the present invention can be configured by software, and it is not necessary to add new hardware.

[0029]

As described above, according to the present invention,
Since the phase characteristic of the feedback signal is compensated by changing the carrier phase of the quadrature modulator according to the amplitude value of the modulation baseband signal, even when the phase characteristic of the amplifier changes according to the input amplitude value, the feedback signal The phase margin can be maintained. Therefore, even when using an amplifier whose phase characteristic changes significantly depending on the input amplitude value,
The Cartesian feedback can be operated stably. Further, in the past, the change in the phase characteristic due to the input amplitude of the amplifier was designed with a margin, but by using the configuration of the present invention, it is not necessary to take a margin for the change in the phase characteristic, and feedback is performed. Can be applied more, and the degree of distortion improvement can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a linear compensation circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a distortion compensation circuit forming the linear compensation circuit.

FIG. 3 is a block diagram showing an example of an infinite phase shifter forming the same linear compensation circuit.

FIG. 4 is a block diagram showing an example of a modulation input-phase / conversion table constituting the linear compensation circuit.

FIG. 5 is a block diagram showing a linear compensation circuit according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a linear compensation circuit according to a third embodiment of the present invention.

FIG. 7 is a block diagram showing a linear compensation circuit according to a fourth embodiment of the present invention.

FIG. 8 is a block diagram showing a linear compensation circuit according to a fifth embodiment of the present invention.

FIG. 9 is a diagram for explaining the operation of the embodiment of the present invention, where the input amplitude is −
Schematic diagram showing an example of loop gain characteristics

FIG. 10 is a schematic diagram showing an example of input amplitude-loop phase characteristics for explaining the operation of the embodiment of the present invention.

FIG. 11 is a schematic diagram showing an example of characteristics of a modulation input-phase conversion table for explaining the operation of the embodiment of the present invention.

FIG. 12 is a schematic diagram showing a signal input to an infinite phase shifter for explaining the operation of the embodiment of the present invention.

FIG. 13 is a block diagram showing an example of a conventional linear compensation circuit.

[Explanation of symbols]

 1 Distortion Compensation Circuit 2 Quadrature Modulator 3 Amplifier 4 Directional Coupler 5 Quadrature Demodulator 6 Modulation Input-Phase / Conversion Table 7 Infinite Phase Shifter 8 Subtractor 9 Oscillator 10 Adder 11 Digital / Analog Converter 12 Angle-sin , Cos conversion table (ROM) 13 multiplier 14 analog-digital converter 15 input amplitude-phase conversion table (ROM) 16 temperature measuring means 17 frequency converter 18 switch

Claims (5)

[Claims] 1. A distortion compensation circuit calculates distortion compensation from an in-phase modulation input signal and a quadrature modulation input signal and an in-phase demodulation signal and a quadrature demodulation signal obtained by quadrature demodulation of a transmission signal by a quadrature demodulation circuit, and an in-phase modulation signal. And the quadrature modulation signal are input to the quadrature modulator, the output is amplified by the amplifier and output as a transmission output, and the signal is in-phase demodulated by the demodulation carrier input from the infinite phase shifter by the quadrature demodulator. And a quadrature demodulated signal, and the demodulated signal is input to the distortion compensation circuit, and in the Cartesian feedback linear compensation circuit that compensates for distortion at the baseband quadrature coordinates, the in-phase modulated signal and the quadrature modulated signal are A modulation input-phase / conversion table for inputting and outputting the amount of phase rotation depending on the input of the quadrature modulator, and this modulation input-phase / phase conversion table.
The output of the conversion table is subtracted from the phase shift adjustment amount that adjusts the phase rotation amount that does not depend on the modulation signal, the output is input to the infinite phase shifter, and the subtraction is performed to control the carrier phase of the quadrature modulator. And a linear compensation circuit. 2. The linear compensation circuit according to claim 1, wherein the modulation input-phase / conversion table is switched according to temperature. 3. The linear compensation circuit according to claim 1, wherein the modulation input-phase / conversion table is switched according to the transmission frequency. 4. The modulation input-phase / conversion table is switched according to temperature and transmission frequency.
The described linear compensation circuit. 5. The linear compensation circuit according to claim 1, wherein the input of the modulation input-phase / conversion table is an in-phase modulation input signal and a quadrature modulation input signal.