The present application claims priority from Japanese patent application serial nos. 2011-125505 and 2012-050185, filed on Jun. 3, 2011, and Mar. 7, 2012, the contents of which are hereby incorporated by reference into this application.
The present invention relates to a radio transmitter and an envelope tracking power supply control method. More particularly, the present invention relates to a radio transmitter that improves the power added efficiency (PAE) by controlling a power supply, and to a method for controlling an envelope tracking power supply.
In power amplifiers used in base stations in mobile or wireless communications, the improvement in the power added efficiency (PAE) is required in order to reduce operational costs. One of the PAE improvement technologies that have recently attracted attention is envelope tracking (hereinafter referred to as ET). In an RF power amplifier, PAE is defined as the ratio of the difference of the output and input signal power to the DC power consumed.
Before describing ET, the characteristics of the transistor used in a common power amplifier will be described. The output power and PAE characteristics with respect to the input power of the transistor will be described with reference to
Referring to
Next, ET will be described. ET is a technology that improves the PAE by allowing the power supply voltage of the transistor within the power amplifier to vary according to the envelope of an input signal. The principle of ET will be described with reference to
The envelop information of the input signal that is detected by the envelope detection unit is transmitted to the ET power supply. The ET power supply outputs a voltage having a shape corresponding to the envelope information. In this way, the power amplifier (transistor) allows the power supply voltage to vary to be able to typically operate with the maximum PAE in the vicinity of the saturated power, with respect to the input power. Thus, the ET improves the PAE.
The PAE when the power supply voltage of the transistor is fixed and the PAE when the ET is operated will be compared with reference to
Particularly, it is possible to take advantage of the characteristics of ET that the PAE is high in a wide input power range with respect to signals with the peak power higher than the average power, as in the digitally modulated waves using modulation schemes such as Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), and Frequency Division Multiplexing (FDM) that are used in recent mobile communication.
However, when the ET is applied to the signal with the peak power higher than the average power, it is necessary to have an ET power supply with a wide dynamic range to be able to properly output any voltage.
Known examples of ET power supply are disclosed in JP-A No. 511065/2008 and JP-A No. 277806/1987. The background of the technology will be described with reference to
JP-A No. 136309/1998 discloses a technology called Peak Factor Reduction (hereinafter referred to as PFR) that reduces the difference between the average power and the peak power of a signal by reducing the peak power included in the signal. The PFR prevents the high power input itself. The PFR reduces the output dynamic range that is required for the power supply to allow the power supply voltage to precisely vary with respect to the input range of higher occurrence probability. Thus, the PFR improves the PAE. The PFR is the technology that allows the power amplifier operating at a fixed voltage to reduce the peak power included in the signal. This can reduce the difference between the average power and the peak power of the signal, allowing the power amplifier to operate at higher PAE. This technology is currently used by many mobile communication transmitters.
JP-A No. 198513/1991 discloses a power amplifier of a combination of ET and distortion compensation. Further, JP-A No. 336626/2004 discloses a power amplifier that makes the power supply voltage constant at low output power by changing the power supply voltage at higher output power.
A plurality of voltage supplies are prepared. Then, a voltage is selected and output from the plurality of voltage supplies so that the power amplifier can operate at the max PAE with respect to the input signal. In this case, being more precise selection of the power supply voltage is an important factor in the improvement of the PAE of the power amplifier. This is because, as described with reference to
As described above, the difference between the average power and the peak power is large in the digitally modulated waves such as CDMA, WCDMA, and FDM. However, not only the power difference but also the difference in the occurrence probability is large in these digitally modulated waves. More specifically, the occurrence probability is Rayleigh distribution that is shown in
The present invention provides a radio transmitter that allows ET to operate at higher PAE by controlling the ET power supply to output the voltage according to the signal power distribution.
The above aim is achieved by a radio transmitter including an envelope tracking power supply for supplying power to a power amplifier, the power amplifier for amplifying an analog high frequency signal, and a power supply controller for controlling the envelope tracking power supply. The envelope tracking power supply includes a plurality of variable voltage supplies. The power supply controller controls the plurality of variable voltage supplies so as to precisely divide the power supply voltage in a high frequency area, based on the voltage distribution of a received transmitted base band signal.
Further, there is also provided a radio transmitter including an envelope tracking power supply for supplying power to a power amplifier, the power amplifier for amplifying an analog high frequency signal, and a power supply controller for controlling the envelope tracking power supply. The envelope tracking power supply includes a plurality of variable voltage supplies. The power supply controller stores PAE characteristics of the power amplifier, as well as the signal power distribution information for each modulation method in an internal memory. The power supply controller receives information on the modulation method of the transmitted RF signal, reads the signal power distribution information of the corresponding modulation method, as well as the PAE characteristics of the power amplifier from the internal memory based on the received information, fixes the voltage and increase the number of voltage options in the power range of low occurrence probability in the transmitted signal, generates a control function for increasing the number of selectable voltages in the power range of high occurrence probability, and controls the envelope tracking power supply.
Still further, there is provided a method for controlling an envelope tracking power supply in a radio transmitter. The radio transmitter includes an envelope tracking power supply for supplying power to a power amplifier, the power amplifier for amplifying an analog high frequency signal, and a power supply controller for controlling the envelope tracking power supply. The envelope tracking power supply control method includes the steps of: determining data zones of class; storing the data zones in a first memory; calculating an amplitude of a transmitted base band signal to determine which of the data zones corresponds to the calculated amplitude; storing the corresponding data zone in a second memory; after the step of storing in the second memory has been executed for a predetermined number of times, comparing the adjacent zones of the second memory; and changing the data zone stored in the first memory based on the comparison result.
By controlling the ET power supply to output the voltage according to the signal power distribution, ET operation with higher PAE can be achieved.
Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which;
In the following, the present invention will be described using examples with reference to the accompanying drawings. Like elements or components in the drawings are designated by the same reference numerals and will not be redundantly described.
The configuration of a radio transmitter will be described with reference to
The digital unit 105 receives a transmitted base band (BB) signal that is transmitted from the upper device. The digital unit 105 sets the transmission power, the transmission frequency, the number of transmission carriers and the like, and transmits them to the analog unit 106. The analog unit 106 converts the BB signal received from the digital unit 105 into an analog high frequency signal. Then, the analog unit 106 outputs the analog high frequency signal to the power amplifier 104.
The memory 108 stores in advance the power distribution information for each of the modulation methods such as CDMA, WCDMA, and FDM. The memory 108 also stores in advance the PAE characteristics of the power amplifier 104. More specifically, the power distribution information of the digitally modulated wave is Rayleigh distribution shown in
The function generator 107 receives the information such as the modulation method of the transmitted signal from the upper device. Then, the function generator 107 controls so that the power supply voltage can be precisely changed to the voltage passing through the max PAE point in each input voltage, in the input range of high occurrence probability, based on the information in the memory 108.
The specific operation of the power supply controller 101 will be described. The function generator 107 reads necessary information from the memory 108. The function generator 107 first determines the minimum voltage at which the power amplifier 104 can operate as an amplifier in the PAE characteristics of the power amplifier 104. This voltage is the lower voltage of the ET power supply 103. The minimum voltage is denoted by V0.
The minimum voltage prevents that the power amplifier 104 does not operate as an amplifier with no gain when the power voltage is too low. Next, the function generator 107 extracts the power supply voltage at which the PAE is the maximum in each input signal voltage from the PAE characteristics of the power amplifier 104. The function generator 107 generates a function passing through all the points of the power supply voltages extracted from the PAE characteristics of the power amplifier 104.
The configuration of the ET power supply will be described with reference to
The function generated by the function generator 107 will be described with reference to
In
The broken line in the upper part of
The input signal to the power amplifier 104 as well as the output voltage from the ET power supply 103 will be described with reference to
The contrast between
A second embodiment is designed to improve the PAE by further reducing the output dynamic range required by the ET power supply by combining with PFR. Note that the configuration shown in
The probability density distribution in PFR process will be described with reference to
The input signal to the power amplifier 104 as well as the output voltage from the ET power supply 103 will be described with reference to
According to the second embodiment, the PAE of the power amplifier 104 is higher than the case without using PFR.
A radio transmitter according to a third embodiment will be described with reference to
The configuration of the radio transmitter will be described with reference to
The threshold memory 108b stores a plurality of thresholds which are power voltages. Note that the number of thresholds is equal to the number of power supply stages. The frequency memory 108a stores a plurality of occurrence frequencies of the transmitted BB signal with respect to the voltage in a zone between a threshold and the other threshold.
The digital unit 105 receives a transmitted base band (BB) signal that is transmitted from the upper device. The digital unit 105 sets the transmission power, the transmission frequency, the number of transmission carriers, and the like, and transmits them to the analog unit 106. The analog unit 106 converts the BB signal received from the digital unit 105 into an analog high frequency signal. Then, the analog unit 106 outputs the analog high frequency signal to the power amplifier 104.
The envelope detection unit (envelope detector) 109 detects the envelope from the analog signal. The envelope detector 109 can detect the envelope also from a digital signal. In this case, however, the envelope detector is included in the digital unit 105. For this reason, the position of the envelope detector is not limited to the position shown in
The transmitted base band signal (transmitted BB signal) is supplied to the power supply controller 101A and also to the transmission signal processor 110. The power amplifier 104 amplifies the transmission signal. Then, the power amplifier transmits the signal from a transmission antenna not shown.
The process flow of the power supply controller 101A will be described with reference to
Note that to simplify the drawing, it is shown that step 228 and step 229 are performed only once, but actually the steps 228 and 229 are performed for the number of times equal to the number of power supply stages minus one. The power supply controller 101A moves to step 224 when the frequencies of all the zones are equal.
The training flow will be described with reference to
If no in step 212, the power supply controller 101A determines whether the process has been executed for a predetermined number of times (S214). When the answer is yes, the power supply controller 101A sets the value of data zone X to (the maximum value−the minimum value)/the number of power supply stages n (S216). The power supply controller 101A sets the class An=nX (S217) and then returns. If no in step 214, the power supply controller 101A moves to step 211.
The transition of the values stored in the threshold memory will be described with reference to
The figure (c) shows the threshold memory 108b after the completion of the training. The zone 1 holds 0 which is the minimum value of the power supply output, and the zone 2 holds 40 which is the maximum value of the power supply output. The figure (d) shows the threshold memory 108b after the completion of the threshold calculation. Here,
(The maximum value−the minimum value)/the number of power supply stages n=(40−0)/10=4
Thus, the zone width is 4, and the zone 1 holds 4, the zone 2 holds 8, and then the zone 10 holds 40 in the same manner. The figures (e) and (f) show the values of the threshold memory 108b in the learning process. The threshold memory 108b changes each value of the threshold only by 1 so that the frequencies of the zones held in the frequency memory 108b are averaged. However, the maximum value 40 is fixed. In
The transition of the values held in the frequency memory 108a will be described with reference to
Note that the zone shown under each frequency includes 0 only when the particular zone includes 0, and the other zones do not include the lower limit. In other words, the zones 0 to 4 are 0 or more and 4 or less, and the zones 4 to 8 exceed 4 and are 8 or less.
The relationship between the input signal level distribution and the ET power supply voltage division pattern will be described with reference to
According to the third embodiment, whatever the distribution of the input signal is, it is possible to track the distribution and precisely divide the power supply voltage in the area of high occurrence frequency.
Number | Date | Country | Kind |
---|---|---|---|
2011-125505 | Jun 2011 | JP | national |
2012-050185 | Mar 2012 | JP | national |