JPH1023095A - Radio transmitting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress a nonlinear distortion generated in an amplifier, when transmission power is varied by previously adding a nonlinear reverse component to a transmitting signal, in accordance with a value which is calculated by a transmission power control signal and the transmitting signal. SOLUTION: Digital I data and digital Q data obtained at respective input terminals 11I and 11Q are supplied to a predistorter 30, through FIR filters 12I and 12Q so as to obtain digital I data and digital Q data where the reverse component of the nonlinear distortion which is generated by a variable power amplifier 16, where the amplification gain is decided by the transmission power control signal supplied from a transmission power controller 21, is superimposed. At this time, the transmission power control signal is supplied to the predistorter 30 from the transmission power controller 21 in addition to I data and Q data, the reverse component of the nonlinear distortion is calculated by an arithmetic processing, based on the transmission power control signal, I data and Q data and the calculated reverse component are superimposed on the I data and Q data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio transmission circuit suitable for application to, for example, a transmission system of a radio telephone device.

[0002]

2. Description of the Related Art Conventionally, as a radio transmission circuit, there is a circuit that performs transmission processing by using a circuit called a predistorter to compensate for nonlinear distortion of a transmission signal. FIG. 6 is a diagram showing an example of a transmission circuit using the predistorter circuit. In this example, the transmission signal is two-system data of digital I data and digital Q data. Data is input terminal 81I and 81Q
Is obtained. The digital I data and digital Q data obtained at the respective input terminals 81I and 81Q are FI
The signal is supplied to the predistorter 83 via the R filters 82I and 82Q, and the inverse component of the nonlinear distortion generated by the power amplifier 89 described later is superimposed.

[0003] Digital I data and digital Q data on which the inverse component of the nonlinear distortion is superimposed by the predistorter 83 are supplied to a digital / analog converter 84 to be converted into analog I signals and analog Q signals. The I signal and the Q signal are supplied to the modulator 85, and the I signal and the Q signal are quadrature-modulated using the modulated wave output from the oscillator 86. Then, the modulated transmission signal is supplied to a mixer 87, the frequency signal output from the frequency synthesizer 88 is mixed and frequency-converted to a predetermined transmission frequency, and the frequency-converted transmission signal is converted by a power amplifier 89. After amplifying the power, the power is supplied to the antenna 90 for wireless transmission.

Here, as the power amplifier 89, generally, an amplifier which causes nonlinear distortion is often used in order to perform efficient amplification. That is, although a low-distortion amplification operation is originally desirable, an amplifier that performs a class-A operation is required as a power amplifier that performs a low-distortion amplification operation, and a class-A operation is performed in terms of efficiency such as power consumption. It is not preferable to employ an amplifier.

Therefore, it is common to use an amplifier having high efficiency in the amplification operation itself but generating nonlinear distortion as the power amplifier 89. In this case, in the transmission circuit of FIG. 6, the non-linear distortion generated in the power amplifier 89 is compensated for by the predistorter 83 connected to the baseband unit, so that a linearized signal without distortion can be transmitted. It is like that.

Here, a state where distortion is compensated by the predistorter will be described with reference to FIG. FIG. 7 illustrates the distortion compensation state by the predistorter on the IQ vector plane.

In the figure, v is the baseband complex signal vector to be amplified on the IQ plane, and Av is the desired linear output of the power amplifier. The distortion generated by the nonlinear power amplifier is AM
Divided into an amplitude component causing AM modulation and a phase component causing AM-PM modulation. These distortions are expressed as complex gains on a complex plane by a polar coordinate to rectangular coordinate transformation. The principle equation of the predistorter is summarized below.

[0008]

G (| F (x) | · x) · F (x) · v = A · v

[0009]

X = | v | ²

Where A is a linear complex gain of the power amplifier,
F (•) is the complex gain of the predistorter, G (•) is the complex gain of the power amplifier, and x is the power of the signal input to the power amplifier.

The reason why the argument of G (•) has only a real component is that the nonlinear characteristic of the amplifier depends only on the level of the input signal and does not relate to the phase. In advance [Equation 1]
A predistorter characteristic F (·) that satisfies the equation is calculated and stored. The upper limit of the linear output is the saturation output of the power amplifier. [Equation 1] expresses the real part of G (•) as Gr (•),
The imaginary part is Gi (•), the real part of F (•) is F1 (•),
The imaginary part is F2 (•), the real part of A is Ar, and the imaginary part is Ai
Then

[0012]

## EQU3 ## Gr (x '). F1 (x) -Gi (x'). F
2 (x) = Ar

[0013]

## EQU4 ## Gr (x '). F2 (x) -Gi (x'). F
1 (x) = Ai

[0014]

X ¹ = sqrt {F1 ² (x) + F2 ² (x)} · x

As described above, it can be decomposed into a real part and an imaginary part. Obtaining the characteristics of the predistorter means F1 (x), F2
(X). F1 (x) and F2 (x) are stored in a memory using the value of x as an address.

[0016]

Since the reverse distortion characteristic of the predistorter is determined by calculating the input level of the power amplifier in reverse, the conversion gain between the predistorter and the power amplifier must always be constant. Therefore, in the case of a transmission circuit using a conventional predistorter, the amplification gain in the power amplifier is set to be constant, and when performing distortion compensation in the predistorter, the amplification gain in the power amplifier varies. It was difficult to do.

However, in a radio communication system such as a radio telephone system, there are many systems that require variable transmission power. Even when the transmission power is varied, it is necessary to suppress the nonlinear distortion generated in the amplifier. Is required to do so.

In view of the foregoing, it is an object of the present invention to effectively suppress nonlinear distortion generated in an amplifier when varying transmission power.

[0019]

According to the present invention, a power amplifier whose transmission power is controlled by a transmission power control signal is used as a power amplifier, and the inverse of nonlinear distortion is determined in accordance with the transmission power control signal and a value calculated from the transmission signal. A predistorter for adding a component to a transmission signal in advance is provided in a transmission circuit.

According to this configuration, the state of the nonlinear distortion in the power amplifier can be determined by determining the transmission power control state and the state of the transmission signal by the predistorter. Based on this, the inverse component of the nonlinear distortion can be generated, and the inverse component can suppress the nonlinear distortion in the power amplifier.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIG.
This will be described with reference to FIGS.

In this embodiment, the present invention is applied to a transmission circuit of a wireless telephone device. FIG. 1 is a diagram showing the circuit configuration of a wireless transmission circuit according to the present embodiment. In this example, a transmission signal is composed of two systems of digital I data and digital Q data, and the digital I data and digital Q data are supplied to input terminals. 1
1I and 11Q. Each input terminal 11I
I data and digital Q obtained in 11Q and 11Q
The data is supplied to the predistorter 30 via the FIR filters 12I and 12Q, and digital I data and digital Q data (hereinafter, referred to as the nonlinear distortion) on which the inverse component of the nonlinear distortion generated in the variable power amplifier 16 described later is superimposed. The data on which the inverse component is superimposed is referred to as I 'data and Q' data). Here, this predistorter 30
Is supplied with a transmission power control signal from a transmission power controller 21, which will be described later, in addition to the I data and Q data. Is calculated, and the calculated inverse component is superimposed on the I data and the Q data. In addition,
Details of the configuration of the predistorter 30 of this example will be described later.

The I 'data and Q' data output from the predistorter 30 are supplied to a digital / analog converter 13 to be converted into analog I signals and analog Q signals. 14 and quadrature-modulate the I signal and the Q signal using the modulated wave output from the oscillator 15. Further, in the case of the present example, a CDMA system (Code Division Multiple Access: code division multiple access system) is applied as a transmission system, and the modulator 14 performs spread modulation for the CDMA system. .

The spread modulated transmission signal is supplied to a variable power amplifier 16. This variable power amplifier 16
Is a variable amplifier whose amplification gain is determined by the transmission power control signal supplied from the transmission power controller 21. The variable amplifier is an amplifier in which nonlinear distortion is caused by the amplification gain. For example, the gain is adjusted to about 80 dB. Then, the transmission signal amplified by the variable power amplifier 16 with a predetermined gain is supplied to the mixer 17, and the frequency signal output from the frequency synthesizer 18 is mixed and frequency-converted to a predetermined transmission frequency. The transmitted signal to the power amplifier 19
(This amplifier has a constant amplification gain.) After amplification, the signal is supplied to the antenna 20 for wireless transmission.

The transmission power control signal output from the transmission power controller 21 is transmitted from a terminal 22 to the transmission power controller 21.
Are generated based on the power control information bit supplied to the transmission power controller 21 from the terminal 23 and the power control information bit supplied to the transmission power controller 21 from the terminal 23. Here, the power control information bit is data of a power control information bit included in a signal transmitted and received from a partner with which the wireless telephone device communicates, and power control based on the power control information bit is referred to as closed-loop control. This is called control. The reception level information signal is information on a reception level of a signal transmitted and received from a partner with which the wireless telephone device communicates, and power control based on the reception level is referred to as open loop control.

Next, the configuration of the predistorter 30 of this embodiment is shown in FIG. I data input terminal 31 and Q data input terminal 32 are connected to FIR filters 82I and 82Q
A terminal to which data and Q data are supplied.
The I data and Q data obtained in 1 and 32 are supplied to the arithmetic circuit 33. Further, the transmission power control signal output from the transmission power controller 21 is supplied to the arithmetic circuit 33.
Then, the arithmetic circuit 33 obtains a variable x by performing the following equation.

[0027]

X = (I ² + Q ² ) · PC · IG where PC is a transmission power control signal, and IG is a constant corresponding to the conversion gain from the output of the predistorter 30 to the power amplifier 16.

Then, using the variable x calculated by the equation (6), the predistorter characteristics F1 (x),
Data is read from the memories 34 and 35 storing F2 (x). Here, the memory 34 is a memory for storing the predistorter characteristic F1 (x) of the real part, and the memory 35 is a memory for storing the predistorter characteristic F2 (x) of the imaginary part. In 35, a corresponding predistorter characteristic (a reverse distortion characteristic for the power amplifier 16) is calculated in advance and stored in each address. Then, using the variable x as a read address of the memories 34 and 35, the predistorter characteristic stored at that address is read.

The I data obtained at the input terminal 31 and the predistorter characteristic F1 (x) of the real part read from the F1 memory 34 are supplied to a multiplier 36 for multiplication, and the multiplied signal is obtained. Is supplied to the adder 40. Further, the Q data obtained at the input terminal 32 and the predistorter characteristic F2 (x) of the imaginary part read from the F2 memory 35 are supplied to a multiplier 37 for multiplication, and the multiplied signal is subtracted by a subtractor. 40. Then, the subtractor 40 subtracts the output of the multiplier 37 from the output of the multiplier 36 and supplies the subtracted signal from the I ′ data output terminal 42 to the digital / analog converter 13 side.

Further, the Q data obtained at the input terminal 32 and the predistorter characteristic F2 (x) of the imaginary part read out from the memory 35 for F2 are supplied to a multiplier 38 for multiplication. Is supplied to the adder 41. Further, the I data obtained at the input terminal 31 and the predistorter characteristic F1 (x) of the real part read from the F1 memory 34 are supplied to a multiplier 39 for multiplication, and the multiplied signal is added to an adder. 41. Then, the adder 41 adds the output of the multiplier 38 and the output of the multiplier 39, and supplies the added signal from the Q 'data output terminal 42 to the digital / analog converter 13 side.

Multipliers 36 to 3 in this predistorter
The arithmetic processing by 9, 9, the subtractor 40 and the adder 41 is an arithmetic processing by multiplication of the I and Q vectors and the predistorter function by a complex number.

The predistorter 3 configured as described above
0, the power amplifier 16 whose amplification gain changes is used. However, the inverse component of the nonlinear distortion generated with the change of the amplification gain is generated in the predistorter 30 and the inverse component is generated. Is multiplied by the I and Q data.
Therefore, even if the amplification gain is adjusted by the power amplifier 16,
The inverse component of the non-linear distortion caused by the amplification is always multiplied by the predistorter 30 to cancel the distortion, and as a result, a linear transmission signal is wirelessly transmitted from the antenna 20.
As described above, in the processing in the predistorter 30, the nonlinear distortion is compensated, so that a variable power amplifier 16 that generates nonlinear distortion can be used, and an amplifier with high power efficiency can be used as the amplifier 16. A good signal can be transmitted efficiently with low power.

In particular, in the case of this example, the present invention is applied to the transmission circuit of the CDMA wireless telephone system. In the case of the CDMA wireless telephone system, it is necessary to strictly manage the transmission power from each terminal. Yes, by applying the predistorter of the present example, good control of transmission power specified in a CDMA wireless telephone system can be realized by a transmission circuit having a simple configuration.

Here, an example of the characteristics of the nonlinear amplifier used as the variable power amplifier 16 is shown in FIG. 3 (a is an input-to-amplitude characteristic, and b is an input-to-phase characteristic). FIG. 4 shows an example of the corresponding characteristics of the predistorter 30 (c is an input versus amplitude characteristic, and d is an input versus phase characteristic). The characteristics shown in FIGS. 3 and 4 are characteristics when the frequency of the transmission signal is about 1880 MHz. As can be seen from a comparison between the two figures, the characteristics of the amplifier and the characteristics of the predistorter are substantially opposite to each other for both the amplitude and the phase.

It should be noted that the predistorter 30 can also be realized by an arithmetic circuit composed of an integrated circuit called a digital signal processor (DSP). That is,
For example, as shown in FIG. 5, a predetermined number of bits of I data and Q data are supplied to the digital signal processor 51, and a predetermined number of bits of transmission power control data are supplied. And, in this digital signal processor 51,
The F1 memory 52 and the F2 memory 53 are connected, and the digital signal processor 51 and the memories 52 and 53 are connected to each other.
A clock having a predetermined frequency is supplied from a clock input terminal 54. Then, in the digital signal processor 51,
By performing the arithmetic processing based on the above [Equation 6], the corresponding data of the predistorter characteristic is read out from the memories 52 and 53, multiplied by the I data and Q data, and the I 'data and Q ′ The data is output from the digital signal processor 51 and supplied to the subsequent circuit (digital / analog converter).

By using the digital signal processor in this manner, the predistorter of this embodiment can be configured with a simple integrated circuit.

In the case of the predistorter in any of the configurations shown in FIGS. 2 and 5, the size of the memory for storing the predistorter characteristics must be determined in consideration of the required distortion compensation accuracy. That is, the variable x obtained by Expression 6
If the value of is calculated finely, the compensation accuracy in the predistorter improves, but the memory address also needs to be correspondingly large, so the memory capacity must be determined according to the required compensation accuracy. There is.

In the above-described embodiment, the power amplifier 19 at the last stage in the transmission circuit of FIG. 1 has a constant amplification gain. The compensation in the predistorter 30 may be performed.

The position where the predistorter is provided is as follows:
The present invention is not limited to the example of FIG. 1 and may be provided at another position as long as it is a stage preceding the power amplifier. However,
By processing with the predistorter at the stage of digital data, the processing inside the predistorter can be performed relatively easily and accurately by digital calculation, and stable distortion compensation where the compensation characteristics do not fluctuate due to factors such as environmental changes. it can.

Further, in the above embodiment, the present invention is applied to the transmission circuit of the radio telephone apparatus to which the CDMA system is applied, but the present invention can be applied to various radio transmission circuits for other transmission systems in which amplification is performed by a nonlinear amplifier. Of course.

[0041]

According to the present invention, the state of occurrence of nonlinear distortion in a power amplifier whose amplification gain changes can be accurately determined by a predistorter, and the inverse of the nonlinear distortion is determined based on the determined state of nonlinear distortion. A component can be generated, and the inverse component can effectively suppress nonlinear distortion in the power amplifier. Therefore, even when the amplification gain in the power amplifier in which nonlinear distortion occurs is changed, accurate distortion compensation corresponding to the amplification gain can always be performed, and a good signal without distortion with controlled transmission power can be transmitted. be able to.

In this case, the predistorter is provided with a signal processing operation means and a digital memory, and performs an operation using a complex number, thereby performing a nonlinear distortion compensation by adding an inverse component of the nonlinear distortion. Good nonlinear distortion compensation can be performed with simple arithmetic processing.

Further, in the above-described case, by handling the transmission signal wirelessly transmitted by CDMA modulation, the power of the CDMA modulation signal to be transmitted is controlled to a predetermined state, and the distortion of the transmission signal is reduced. It is possible to eliminate CD
Radio transmission by MA modulation can be performed favorably.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a predistorter according to one embodiment.

FIG. 3 is a characteristic diagram of the nonlinear amplifier according to the embodiment;

FIG. 4 is a characteristic diagram of a predistorter according to one embodiment.

FIG. 5 is a configuration diagram showing another example of a predistorter.

FIG. 6 is a configuration diagram illustrating an example of a transmission circuit using a conventional predistorter.

FIG. 7 is a characteristic diagram showing the principle of a predistorter.

[Explanation of symbols]

11I I data input terminal, 11Q Q data input terminal, 16 variable power amplifier, 21 transmission power controller, 2
2 power control information bit input terminal, 23 reception level information signal input terminal, 30 predistorter, 33 arithmetic circuit, 34 F1 memory, 35 F2 memory, 3
6, 37, 38, 39 Multiplier, 40 Subtractor, 41
Adder

Claims (3)

[Claims] A transmission power control means for generating a transmission power control signal for controlling transmission signal power; a variable gain amplifier having an amplification gain determined by the transmission power control signal and amplifying the transmission signal; A radio transmission circuit, comprising: a pre-distorter positioned before the amplifier and adding an inverse component of nonlinear distortion to a transmission signal in advance according to a value calculated from the transmission power control signal and the transmission signal. 2. The predistorter according to claim 1, wherein the predistorter includes a signal processing operation unit and a digital memory, and performs an operation using a complex number to perform a nonlinear distortion compensation by adding an inverse component of the nonlinear distortion. The wireless transmission circuit according to any one of the preceding claims. 3. The wireless transmission circuit according to claim 1, wherein a transmission signal wirelessly transmitted by CDMA modulation is handled.