GB2372184A

GB2372184A - Transmitter pre-distortion linearizer with a memory for correction coefficients controlled in dependence on transmitter output power and input signal power

Info

Publication number: GB2372184A
Application number: GB0211030A
Authority: GB
Inventors: Toshikazu Nakajima
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1999-10-13
Filing date: 2000-10-12
Publication date: 2002-08-14
Anticipated expiration: 2020-10-12
Also published as: GB0211030D0; GB2372184B

Abstract

A pre-distortion linearizer 2 for correcting non linearities introduced to a signal by a transmitter 3 (modulator and amplifier) has a first memory 7 which stores tables of amplitude and phase correction data. The instantaneous power of the I and Q base band signals is calculated 6 and the power of the RF signal for transmission is also detected 11. These two power signals are fed into an address generating portion 10 which determines an address in the first memory in dependence upon them. The correction data from that address is then fed into the linearizer which applies it to the base band signal. The system also includes a second memory 8 which stores further tables of correction data for different operating temperatures and frequencies. These may be transferred to the first memory by the CPU 9 as the temperature and frequency vary in a caching arrangement.

Description

TRANSMITTER AND DISTORTION COMPENSATION METHOD TO BE USED THEREFOR BACKGROUND OF THE INVENTION The present invention relates to a transmitter and a distortion compensation method to be used therefor. More particularly, the invention relates to a distortion compensating method in a transmitter having a pre-distortion type linearizer.

Conventionally, a transmitter of this type is constructed, as shown in Figure 7, with a transmission signal generating portion 21, a pre-distortion type linearizer 22, a transmitter 23, a directional coupler 24, an antenna 25, a power calculator 26, a compensation value calculating means 27, and a demodulation means 28.

Here, since the transmission signal is distorted due to the non-linear characteristics of the amplifier in the transmitter 23, the pre-distortion type linearizer 22 is provided between the output of the signal generating portion 21 and the input of the transmitter 23.

The pre-distortion type linearizer 22 performs pre-correction so as to cancel the distortion components generated in the transmitter 23 with correction data components. In this way, the distortion of the output waveform of the transmitter 23 can be improved (reduced).

The directional coupler 24 divides the RF signal. Most of the power is output through the antenna 25. However, part of the power is input to the demodulating means 28.

The power calculator 26 calculates the instantaneous power of the base-band signal from the transmission signal generating portion 21.

To generate the compensation data input for the pre-distortion type linearizer 22, part of the output of the transmitter 23 is returned to base band by the

demodulator 28, and the distortion component is arithmetically derived from this signal and the output of the power calculator 26 by the compensation value calculating means 27.

In the distortion compensation method in the known transmitter set forth above, since the distortion component is arithmetically derived by returning a part of the transmitter output to base band by the use of demodulation means, and calculating the distortion component from this signal and the result of the power calculated by the compensation value calculating means, the scale of the circuit becomes large, thus increasing current consumption. In particular, known methods using demodulators are described in International Patent Application W098/51005 and United States Patent 5,404, 375.

A transmitter with pre-distortion type linearizers is also described in United States Patent 5,524, 286. Such transmitter systems have look-up tables readily available, one of which is selected for the measured conditions, that is channel, battery level and measured temperature. This requires a large circuit size and corresponding power consumption.

SUMMARY OF THE INVENTION The invention in its various aspects is defined in the independent claims below, to which reference should now be made. Advantageous features are set forth in the appendant claims.

A preferred embodiment of the invention is described in more detail below with reference to the drawings. This preferred embodiment stores the distortion compensation data to be transmitted to the distortion type linearizer in a first memory and sequentially updates the data in the first memory with the appropriate table from a second memory, depending upon variations of the transmission frequency and the environmental temperature. In this way, a transmitter with good transmission waveform can be realized with restricting power consumption without causing increase in the circuit size.

Furthermore, the address for the first memory is derived by an address generating portion from the instantaneous value of the power of the base-band input to the linearizer and the power of the transmission output signal, this being provided by a power detection portion which replaces the demodulator of the known transmission system.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given hereinafter and from the accompanying drawings of the preferred embodiment of the present invention, which, however, should not be taken to be limitative to the invention, but are for explanation and understanding only.

In the drawings: Figure 1 is a block diagram showing the construction of one embodiment of a transmitter according to the present invention; Figure 2 is an illustration showing the correspondence between V = (V1 + v2) and an address generated in an address generating portion of Figure 1; Figure 3 is an illustration showing the correspondence between the address and compensation data in a first memory; Figure 4 is an illustration showing the correspondence between temperature and frequency and a compensation table in a second memory of Figure 1 ;

Figure 5 is an illustration showing the gain and phase characteristics of the transmitter as such of Figure 1; Figure 6 is a flowchart showing a process operation of the CPU of Figure 1; and Figure 7 is a block diagram showing the construction of a known type of transmitter.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention will be discussed hereinafter in detail in terms of the preferred embodiment of the present invention with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be clear, however, to those skilled in the art, that the present invention may be practised without these specific details.

Well-know components are not shown in detail.

Figure 1 is a block diagram showing the construction of one embodiment of a transmitter according to the present invention. In Figure 1, one embodiment of a transmitter assembly according to the present invention is constructed with a transmission signal generating portion 1, a pre-distortion type linearizer 2, a transmitter 3, a directional coupler 4, an antenna 5, a power calculator 6, a first memory 7, a second memory 8, a CPU 9, an address generating portion 10, and a power detector portion 11, all connected as shown.

The transmission signal generating portion 1 generates a base-band signal consisting of an I signal and a Q signal. The transmitter 3 modulates and amplifies the base-band signal into an RF signal. Here, the transmission signal may be distorted due to non-linear characteristics of the amplifier and so forth in the

transmitter 3. Therefore, the pre-distortion type linearizer 2 is provided between the output of the transmission signal generating portion 1 and the input of the transmitter 3.

The pre-distortion type linearizer 2 corrects for distortion components generated by the transmitter 3 by multiplying correction data provided from the first memory 7 and the base-band signal with each other. In this way the output waveform of the transmitter 3 is improved with respect to distortion.

The directional coupler 4 divides the RF signal.

Most of the power divided by the directional coupler 4 is output to the antenna, and a part thereof is input to the power detector portion 11. The power detector portion 11 detects the RF signal and outputs a transmission (power) level to the address generating portion 10, as a direct current voltage value VI.

The power calculator 6 calculates the instantaneous power of the base-band signal which it outputs to the address generating portion 10 as a certain alternating voltage value v2.

The address generating portion 10 determines an address for data to be output by the first memory 7 from the direct current voltage value VI and the alternating current voltage value v2. The first memory 7 holds compensation data in a form of a table for outputting the data contained in the designated address to the pre-distortion type linearizer 2.

A given compensation data table in the first memory 7 is only established for a certain temperature and a certain frequency for the transmitter 3. Therefore, it becomes necessary to update the compensation data table depending whenever there is variation in the environmental temperature or the transmission frequency. In the second

memory 8, compensation data tables are stored for all cases, that is for different transmission frequencies and environmental temperatures. CPU 9 transfers the desired compensation data table from the second memory 8 to the first memory 7, in dependence upon the variation of the environmental temperature and the transmission frequency.

Figure 2 is an illustration showing the correspondence between V = (VI + v2) and the generated address in the address generating portion 10 of Figure 1.

In Figure 2, there is illustrated a compensation data table storing addresses with reference to the level of (VI + v2).

In the compensation table shown, "a" is stored as an address to be output when the level of (VI + v2) is " < AO","1"is stored as an address to be output when the level of (VI + v2) is"AO V < Alois stored as an address to be output when the level of (VI + v2) is "Al V < A2"and"3"is stored as an address to be output when the level of (VI + v2) is "A2 V < A3",...., and so on.

Figure 3 is an illustration showing the correspondence between the address and the compensation data in the first memory 7 of Figure 1. In Figure 3, there is shown an example in which compensation data table &num;1 storing the addresses and the corresponding compensation data is stored in the first memory 7.

In the compensation data table &num;1, compensation data "-#G10, -##10" is stored in an address "0", compensation

data"-AG11,-A611"is stored in an address"1", compensation data"-AG12,-A612"is stored in an address "2", compensation data"-AG13,-A913"is stored in an address"3",...., and so on.

Figure 4 is an illustration showing the correspondence between the temperature and frequency and

the compensation data table in the second memory 8 of Figure 1. In Figure 4, there is shown an example in which the compensation data tables"table &num;0","table &num;1", "table &num;2","table &num;3"are respectively stored with reference to temperature t ( < tO, tO t < tl, tl t < t2, t2 to < t3...) and frequency f (fO, fl, f2,...).

Figure 5 is an illustration showing the gain and the phase characteristics of the transmitter 3 alone of Figure 1. Figure 6 is a flowchart illustrating the operation of CPU 9 of Figure 1.

Referring to Figures 1 to 6, the operation of one embodiment of a distortion compensation circuit of the transmitter according to the present invention will now be described.

For example, considering the case that the transmission frequency is fo and the temperature is tl to t2, the contents of the compensation data table &num;2 corresponding to this condition is stored in the first memory 7. The base-band signal generated by the transmission signal generating portion 1 is applied to the transmitter 3 via the pre-distortion type linearizer 2.

In the transmitter it is modulated into an RF signal and amplified.

It is assumed that distortion of AG in amplitude of the transmission signal and AO in phase is caused in comparison with the ideal case where no internal distortion is present in the transmitter 3 (see Figure 5).

The RF signal output from the transmitter 3 is divided by the directional coupler 4 so as to input part of the divided power to the power detector portion 11.

The power detector portion 11 detects the power of this signal and outputs the result of the detection to an address generating portion 10 as the direct current voltage value VI. The address generating portion 10

combines the direct current voltage value V1 and an instantaneous power value v2 derived by the power calculator 6 to determine an address for the data to be output by the first memory 7 from VI + v2. In Figure 2, assuming, for example Al VI + v2 < A2, the address becomes"2". Therefore, in Figure 3, the first memory 7 outputs data (-AG12,-A612) from the address"2"to the pre-distortion type linearizer 2.

Now it is assumed that the temperature varies from t2 to t3. In Figure 4, CPU 9 transfers the content of the compensation data table &num;3 corresponding to this condition from the second memory 8 to the first memory 7, to update the data content of the first memory 7. For example, data of the address"2"of the first memory 7 now becomes (-AG22,-A922) taking the temperature characteristics of the transmitter 3 into account.

That is, when the transmission frequency is varied (step Sl of Figure 6) or when the environmental temperature is varied (step S2 of Figure 6), CPU 9 updates the stored content of the first memory 7, corresponding to the content of the compensation data table in the second memory 8 (step S3 of Figure 6).

Once updating of CPU 9 is completed, CPU 9 effects control for transmitting a value from the compensation data table in the first memory 7 corresponding to the address transmitted to the first memory 7 from the address generating portion 10 to the pre-distortion type linearizer 2 (step S4 of Figure 6).

When the transmission frequency or the environmental temperature does not vary, CPU 9 effects control by transmitting a value of the compensation data table in the first memory 7 without updating, the value corresponding to the address transmitted to the first memory 7 from the

address generating portion 10 to the pre-distortion type linearizer 2 (step S4 of Figure 6).

As set forth above, by storing the distortion correction data to be transmitted to the pre-distortion type linearizer in the first memory 7 and sequentially updating data in the first memory 7 with the storage content of the second memory 8 depending upon variation of the transmission frequency and the environmental temperature, a transmitter assembly with good transmission waveform can be realized without causing increasing of circuit size and power consumption.

As set forth above, according to the present system, in the transmitter assembly including the pre-distortion type linearizer which effects correction by pre-cancelling the distortion component caused in the transmission signal, by inputting a value dependent upon the instantaneous power of the transmission signal and the transmission power level of the transmission output signal from the first memory means preliminarily storing the correction data to the pre-distortion type linearizer, current consumption can be restricted without causing increasing of circuit scale.

Although the present invention has been illustrated and described with respect to an exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the scope of the present invention.

Therefore, the present invention should not be understood as limited to the specific embodiment set out above but to include all possible embodiments which can be embodied within the scope encompassed and equivalent thereof with respect to the features set out in the appended claims.

Claims

CLAIMS 1. A transmitter assembly comprising : transmission signal generating means for generating a base-band signal; transmission means for modulating and amplifying said base-band signal into an RF signal; a pre-distortion type linearizer coupled between the output of the transmission signal generating means and the input of the transmission means; directional coupling means for dividing said RF signal; and control means having inputs coupled to an output of the directional coupling means and the output of the transmission signal generating means and an output coupled to a control input of the linearizer and including means for storing correction data, the control means generating a control signal for the linearizer dependent upon the power of the RF transmission output signal.
2. A transmitter assembly as set forth in claim 1, wherein the control means generates a control signal for the linearizer dependent upon (i) the instantaneous power of the base-band signal and (ii) the power of the transmission output signal.
3. A transmitter assembly as set forth in claim 1 or 2, wherein the control means generates a control signal for the linearizer dependent upon a direct current voltage corresponding to the power of the transmission output signal.
4. A transmitter assembly as set forth in claim 2, wherein the control means generates a control signal for the linearizer dependent upon an alternating current voltage value corresponding to the instantaneous power of the base-band signal.
5. A transmitter assembly as set forth in claim 1, wherein the control means generates a control signal for the linearizer which is dependent upon the sum of (i) an alternating current voltage value corresponding to the instantaneous power of a transmission signal and (ii) a direct current voltage corresponding to the power of the transmission output signal.
6. A distortion compensation method, for a transmitter assembly including a pre-distortion type linearizer, the method comprising the steps of: generating a base-band signal; modulating and amplifying the base-band signal into an RF signal; coupling a pre-distortion linearizer in the signal path of the base-band signal prior to modulation and amplification into the RF signal; dividing the RF signal; and generating a control signal for the linearizer dependent upon the power of the RF transmission output signal, the control signal being dependent upon stored correction data.
7. A distortion compensation method as set forth in claim 6, wherein the control signal is dependent upon (i) the instantaneous power of the base-band signal and (ii) the power of the transmission output signal.
8. A distortion compensation method as set forth in claim 6 or 7, wherein the control signal is dependent upon a direct current voltage corresponding to the power of the transmission output signal.
9. A distortion compensation method as set forth in claim 7, wherein the control signal is dependent upon an alternating current voltage value corresponding to the instantaneous power of the base-band signal.
10. A distortion compensation method as set forth in claim 6, wherein the control signal is dependent upon the sum of (i) an alternating current voltage value corresponding to the instantaneous power of a transmission signal and (ii) a direct current voltage corresponding to the power of the transmission output signal.
11. A transmitter assembly including a pre-distortion type linearizer, comprising: transmission signal generating means for generating a base-band signal consisting of an I signal and a Q signal; transmission means for modulating and amplifying said base-band signal into an RF signal; said pre-distortion type linearizer being provided between the output of said transmission signal generating means and the input of said transmission means; first storage means for preliminarily storing correcting data; directional coupling means for dividing RF signal; power detecting means for detecting the power of said RF signal and outputting a transmission level; power calculating means for calculating the instantaneous power of said base-band signal; and

address generating means connected to the power detecting means and the power calculating means for determining an address for data to be output by said first storage means from said transmission level and said instantaneous power of said base-band signal; wherein said first storage means contains correction data as a table with reference to a signal level; and further comprising: second storage means having a plurality of tables of correction data for different transmission frequencies and environmental temperatures; and means for updating the content of said first storage means with the corresponding table from said second storage means when the transmission frequency and/or the environmental temperature varies.
12. A transmitter assembly as set forth in claim 11, wherein an address corresponding to said signal level and correction data corresponding to said address are stored in said first storage means.
13. A transmitter assembly as set forth in claim 11 or 12, wherein said address is dependent upon the sum of an alternating current voltage value corresponding to the instantaneous power of a transmission signal and a direct current voltage corresponding to the power of transmission output signal.
14. A transmitter assembly as set forth in claim 11,12 or 13, wherein said correction data consists of a predetermined amplitude value and a predetermined phase value of the transmission signal.
15. A distortion compensation method for a transmitter assembly including a pre-distortion type linearizer, the method comprising the steps of : providing said pre-distortion type linearizer between a base-band output of transmission signal generating means and an input of transmission means; providing first storage means for preliminary storing correcting data; dividing an RF signal from said transmission means by directional coupling means; detecting the power of said RF signal and outputting a transmission level; calculating the instantaneous power of said base-band output of said transmission means; determining an address for data to be output by the first storage means from said transmission level and said instantaneous power of said base-band signal; reading out a value corresponding to said address from first storage means preliminarily storing said correction data, and inputting the read out value to said pre-distortion type linearizer ; wherein said first storage means contain correction data in a form of table with reference to a signal level; and wherein the content of said first storage means is updated with a corresponding table from second storage means storing a plurality of tables storing correction data for different transmission frequencies and environmental temperatures when the transmission frequency and/or environmental temperature varies.
16. A distortion compensation method as set forth in claim 15, wherein the address corresponding to the signal level and correction data corresponding to said address are stored in said first storage means.
17. A distortion compensation method as set forth in claim 15 or 16, wherein said address is dependent upon the sum of an alternating current voltage value corresponding to the instantaneous power of a transmission signal and a direct current voltage corresponding to the power of transmission output signal.
18. A distortion compensation method as set forth in claim 15,16 or 17, wherein said correction data consists of a predetermined amplitude value and a predetermined phase value of the transmission signal.
19. A transmitter assembly substantially as herein described with reference to Figs. 1-6 of the drawings.
20. A distortion compensation method substantially as herein described with reference to Figs. 1-6 of the drawings.