JP2013187674A - Radio transmitter and envelope tracking power control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem wherein digital modulation waves of CDMA, WCDMA, FDM and the like have a large difference between average power and peak power.SOLUTION: An envelope tracking power supply includes a plurality of variable voltage sources, and a power control section controls the plurality of variable voltage sources such that a supply voltage is divided finely in a frequent range on the basis of a voltage distribution of received transmission baseband signals to thereby implement maximum efficiency of a high frequency amplifier. The power control section has a threshold memory including a plurality of first intervals and a frequency memory including a plurality of second intervals, and changes thresholds held in the first intervals in such directions as cause the individual second intervals to approach an average value of the second intervals.

Description

  The present invention relates to a wireless transmitter and an envelope tracking power supply control method using an envelope tracking technique, and more particularly to a wireless transmitter and an envelope tracking power supply control method that improve efficiency by controlling a power supply.

  High-frequency amplifiers used in mobile communication base stations, etc., have become a challenge to improve their efficiency in order to reduce operating costs. Envelope tracking technology (hereinafter referred to as “high-efficiency technology”) ET: Envelope Tracking).

  Before describing ET, the characteristics of a transistor used in a general high-frequency amplifier will be described first. With reference to FIG. 1, characteristics of output power and efficiency with respect to input power of a transistor will be described. In FIG. 1, the horizontal axis represents the input power of the transistor, and the vertical axis represents the output power and efficiency. As input power increases, output power saturates. The efficiency near the saturated power is the highest.

  With reference to FIG. 2, output characteristics and efficiency characteristics when the transistor power supply voltage Vdd is varied by 5V from 50V to 10V will be described. In FIG. 2A, the saturation power of the transistor varies depending on the power supply voltage. In FIG. 2B, the efficiency is different in the input power value at which the maximum efficiency is obtained at each power supply voltage.

  Next, ET will be described. ET is a technology that achieves high efficiency by varying the power supply voltage of a transistor in a high-frequency amplifier in accordance with the envelope of an input signal. The principle of ET will be described with reference to FIG. In FIG. 3, the components required for ET are an envelope detector, an envelope tracking power supply (ET power supply), and a high-frequency amplifier.

  The envelope information of the input signal detected by the envelope detector is sent to the ET power source. The ET power supply outputs a voltage along the envelope information. In this way, the high-frequency amplifier (transistor) varies the power supply voltage so that it always operates in the most efficient state near the saturated power with respect to the input power. As a result, ET achieves high efficiency. FIG. 3 shows an example in which an envelope is detected from a transmission RF signal and an ET operation is performed. However, other control may be performed with a discrete voltage value using a signal amplitude obtained by digital calculation.

  Referring to FIG. 4, when the power supply voltage of the transistor is fixed, the efficiency when the ET operation is performed is compared. In FIG. 4, the horizontal axis represents the input voltage, and the vertical axis represents the efficiency. The efficiency when the power supply voltage is fixed is lower than the efficiency when the ET operation is performed. ET uses the characteristics of the transistor, and the power supply voltage is varied so that the transistor always operates in the most efficient state near the saturation power with respect to the input power. Compared to the fixed case, the efficiency is high.

  In particular, with respect to average power, such as digitally modulated waves using CDMA (Code Division Multiple Access), WCDMA (Wideband Code Division Multiple Access), FDM (Frequency Division Multiplexing), etc. used in recent mobile communications. For signals with high peak power, the ET feature of high efficiency in a wide input power range can be utilized.

On the other hand, when ET is applied to a signal whose peak power is higher than the average power, an ET power source that has a wide dynamic range and can accurately output an arbitrary voltage is required.
Known examples of the ET power supply include Patent Document 1 and Patent Document 2. The background art will be described with reference to FIG. Patent Documents 1 and 2 disclose a method of configuring an ET power source using a plurality of voltage sources in common. In FIG. 5A, the ET power source 1300 includes a plurality of constant voltage sources obtained by equally dividing the rated power source voltage Vdd of the high frequency amplifier, and outputs a voltage in accordance with the envelope signal from the envelope detector. Thus, the output voltage in the case of a configuration having a plurality of voltage sources is stepped as shown by the broken line in FIG. 5B.
Patent Document 3 discloses a peak factor reduction (hereinafter referred to as PFR) technique that reduces the difference between the average power and peak power of a signal by suppressing the peak power included in the signal. The PFR that limits the high power input itself narrows the output dynamic range required for the power supply, and realizes high efficiency by finely varying the power supply voltage for the input range having a higher probability of occurrence. PFR reduces the difference between the average power and peak power of a high-frequency amplifier that operates at a fixed voltage by suppressing the peak power contained in the signal, enabling the high-frequency amplifier to operate in a highly efficient state. This technology is still used in many mobile communication transmitters.

  Patent Document 4 discloses a high-frequency amplifier that combines ET and distortion compensation. Further, Patent Document 5 discloses a high-frequency amplifier that changes the power supply voltage when the output power is high and makes the power supply voltage constant when the output power is low.

Special table 2008-51065 gazette JP-A-62-277806 JP-A-10-136309 Japanese Patent Laid-Open No. 03-198513 JP 2004-336626 A

  When multiple voltage sources are prepared, and a voltage that allows the high-frequency amplifier to operate at maximum efficiency with respect to the input signal is selected and output, it is highly efficient how the power supply voltage can be selected. Is an important factor. This is because, as described with reference to FIG. 2, the power supply voltage at which the high-frequency amplifier operates at the maximum efficiency varies depending on the input power. When dealing with a digital modulation wave whose input power constantly changes, it is ideal for obtaining maximum efficiency to smoothly follow the envelope of the input signal. Therefore, in an ET power supply that outputs discrete voltages from a plurality of voltage sources, a power supply that follows the envelope of the input signal with higher accuracy, that is, the higher the selectable voltage, the higher the efficiency of the high-frequency amplifier. Increases efficiency by approaching voltage.

  As described above, digital modulation waves such as CDMA, WCDMA, and FDM have a large difference between average power and peak power. However, there is a large difference not only in the power difference but also in the appearance probability. Specifically, the appearance probability is the Rayleigh distribution shown in FIG. As can be seen from FIG. 6, in these digital modulated waves, the appearance probability near the average power is the highest, and the other appearance probabilities are low.

  The present invention provides a wireless transmitter capable of performing a more efficient ET operation by controlling the ET power supply to output a voltage corresponding to the signal power distribution.

  An object of the present invention is to provide an envelope tracking power supply that includes an envelope tracking power supply that supplies power to a high frequency amplifier, a high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power supply. Includes a plurality of variable voltage sources, and the power supply control unit wirelessly controls the plurality of variable voltage sources so as to finely divide the power supply voltage in a high frequency area based on the voltage distribution of the received transmission baseband signal. This can be achieved with a transmitter. .

  Further, in a wireless transmitter including an envelope tracking power source that supplies power to a high frequency amplifier, a high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power source, the envelope tracking power source includes a plurality of envelope tracking power sources. The power supply control unit holds the efficiency characteristics of the high frequency amplifier and the signal power distribution information for each modulation method in the internal memory, receives information on the modulation method of the transmission RF signal, and based on the information Reads the signal power distribution information of the corresponding modulation method from the memory and the efficiency characteristics of the high-frequency amplifier, and in the power range where the probability of occurrence in the transmission signal is low, the voltage is fixed and the selection range of the voltage is widened. This can be achieved by a wireless transmitter that generates a control function that increases the number of selectable voltages in the range and controls the envelope tracking power supply.

Further, in an envelope tracking power supply control method in a wireless transmitter including an envelope tracking power supply that supplies power to a high frequency amplifier, a high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power supply, Determining a class data interval; and
Storing the data section in the first memory; calculating the amplitude of the transmission baseband signal; storing the data section in the second memory; and storing the data section in the second memory And a step of comparing adjacent sections of the second memory and changing the data section recorded in the first memory based on the comparison result. Can be achieved.

  By controlling the ET power supply to output a voltage corresponding to the signal power distribution, a more efficient ET operation can be performed.

It is a graph explaining the input / output and efficiency characteristics of a transistor. It is a graph explaining the input / output characteristic of a transistor when a power supply voltage is changed. It is a graph explaining the efficiency characteristic of a transistor when a power supply voltage is changed. It is a block diagram explaining the principle of ET. It is a graph explaining the efficiency comparison of ET and fixed voltage. It is a block diagram explaining ET. It is a graph explaining the output voltage of ET. It is a figure explaining the electric power distribution of a digital modulation wave signal. It is a block diagram explaining the structure of a transmitter. It is a circuit diagram explaining the structure of ET power supply. It is a figure explaining a control function. It is a graph explaining the output voltage of ET of a prior art. 6 is a graph for explaining an output voltage of the ET of Example 1. It is a graph explaining the difference of Example 1 and the ET power supply output of a prior art. It is a figure explaining the electric power distribution of the digital modulation wave signal of Example 2. FIG. 6 is a graph for explaining an output voltage of an ET of Example 2. It is a block diagram explaining the structure of a radio transmitter. It is a process flowchart of a wireless transmitter. It is a training flowchart. It is a figure explaining transition of the contents held in a threshold memory. It is a figure explaining transition of the contents held in a frequency memory. It is a figure explaining an input signal level distribution and a voltage division pattern.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

  The configuration of the wireless transmitter will be described with reference to FIG. Note that the operating principle of the ET power supply has already been described, and is therefore omitted. In FIG. 7, the wireless transmitter 110 includes a transmission signal processing unit 100, a power supply control unit 101, an ET power supply 103, a high frequency amplifier 104, and an envelope detection unit 109. The transmission signal processing unit 100 includes a digital unit 105 and an analog unit 106. The power supply control unit 101 includes a memory 108 and a function generation unit 107.

  The digital unit 105 receives a transmission BB (baseband) signal sent from the host device. The digital unit 105 sets transmission power, a transmission frequency, the number of transmission carriers, and the like, and sends 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 and outputs the analog high frequency signal to the high frequency amplifier 104.

  The memory 108 stores in advance power distribution information for each modulation method such as CDMA, WCDMA, FDM, and the like. In addition, the memory 108 stores efficiency characteristics of the high-frequency amplifier 104. Specifically, the power distribution information of the digital modulation wave is a Rayleigh distribution as shown in FIG. This probability density function is stored in the memory 108. The efficiency characteristic of the high-frequency amplifier 104 is data of input / output vs. efficiency characteristics due to a difference in power supply voltage as shown in FIG. 2B.

  The function generation unit 107 receives information such as the modulation scheme of the transmission signal from the host device. Thereafter, the function generation unit 107 performs control such that the power supply voltage can be finely varied in an input range that passes through the maximum efficiency point at each input voltage and has a high appearance probability based on information in the memory 108.

  A specific operation of the power control unit 101 will be described. The function generation unit 107 reads necessary information from the memory 108. The function generator 107 first determines the lowest voltage at which the high frequency amplifier 104 operates as an amplifier in the efficiency characteristics of the high frequency amplifier 104. This voltage is the lower limit voltage of the ET power source 103. The minimum voltage is V0. The minimum voltage prevents the power supply voltage from being too low and the high-frequency amplifier 104 does not have gain and does not operate as an amplifier. Next, the function generation unit 107 extracts the power supply voltage having the maximum efficiency at each input signal voltage from the efficiency characteristics of the high-frequency amplifier 104. The function generation unit 107 generates a function that passes through all these points.

  The configuration of the ET power source will be described with reference to FIG. Since the basic operation principle is the same as that of the prior art, detailed description is omitted. The difference from the prior art is that each voltage source is not a fixed voltage source but a variable voltage source that changes an output voltage according to a control signal from the power supply control unit 101. In FIG. 8, the output voltage of the first stage variable voltage source is V0. The number of stages of the variable voltage source is (n + 1) stages. Further, V0 + V1 + V2 +... + Vn = Vdd.

  With reference to FIG. 9, the function which a function production | generation part produces | generates is demonstrated. In FIG. 9, the lower part shows the probability density with respect to the input voltage. The upper stage is the output voltage of the ET power supply with respect to the input voltage. The lower part of FIG. 9 is the same as FIG.

  In FIG. 9, the output of the first stage variable voltage source is a fixed value V0, and the input voltage is also a fixed value. The function generation unit 107 divides the difference between the input voltage distribution peak value Vp and the first-stage input voltage by n. Here, n division is performed so that the area surrounded by the vertical line of the divided input voltage, the probability density distribution, and y = 0 are all equal.

  The relationship between the input voltage divided in this way and the output voltage of the ET power supply is a broken line in the upper part of FIG. After generating the function, the function generation unit 107 determines the voltage V1 to Vn of each voltage source excluding the first stage shown in FIG. To do.

  The input signal to the high frequency amplifier 104 and the output voltage from the ET power source 103 will be described with reference to FIG. In FIG. 10, the vertical axis represents voltage, and the horizontal axis represents time. A solid line is an input signal, and a discrete broken line is an output voltage. As is apparent from the scale on the vertical axis, FIG. 10A shows the output of the ET power source of the fixed voltage source according to the prior art. On the other hand, FIG. 10B shows the output of the ET power source of the variable voltage source of this embodiment. In FIG. 10, the input signal is drawn so that the appearance probability of the signal voltage follows the probability density distribution of FIG. Compared to FIG. 10A, it can be seen that FIG. 10B can perform more accurate tracking in a voltage range with a high appearance probability.

  The comparison in FIG. 10 will be described in an easy-to-understand manner with reference to FIG. FIG. 11 is a diagram in which the output voltages of FIGS. 10A and 10B are overwritten. In FIG. 11, the hatched portion is where the tracking accuracy of the present embodiment is higher than that of the prior art. Since the efficiency of the high-frequency amplifier 104 is increased by increasing the tracking accuracy, the present embodiment can control the ET power source 103 with higher efficiency than the prior art.

  In the second embodiment, by combining PFR, the output dynamic range required for the ET power supply is narrowed to achieve higher efficiency. The configuration shown in FIGS. 7 and 8 is also used in the second embodiment. However, a PFR processing unit (not shown) is mounted on the digital unit 105 in the transmission signal processing unit 100. Other operations are the same as those in the first embodiment.

  With reference to FIG. 12, the probability density distribution when the PFR process is performed will be described. In FIG. 12, the vertical axis represents probability density and the horizontal axis represents signal power. As a result of the PFR processing, an upper limit of the signal power appears, and the probability density near the upper limit increases. By performing the PFR process, the maximum value of the signal input to the high frequency amplifier 104 is lowered. If it demonstrates using FIG. 9, Vp which is the maximum value of an input signal voltage will fall by PFR process. Therefore, since the maximum power value to be output from the ET power source 103 is reduced, it is possible to use more voltage sources in the power range with a high probability of occurrence. As a result, more accurate tracking can be performed.

With reference to FIG. 13, the input signal to the high frequency amplifier 104 and the output voltage from the ET power source 103 will be described. In FIG. 13, the vertical axis represents voltage, and the horizontal axis represents time. A solid line is an input signal, and a discrete broken line is an output voltage. According to FIG. 13, as is clear from the scale on the vertical axis, the peak voltage is lowered as compared with FIG. 10B.
According to the second embodiment, the efficiency of the high frequency amplifier 104 can be increased as compared with the case where the PFR is not applied.

  A wireless transmitter according to the third embodiment will be described with reference to FIGS. The wireless transmitters of the first and second embodiments are based on the Rayleigh distribution as the distribution of the transmission output. On the other hand, the wireless transmitter according to the third embodiment measures the distribution of the transmission output and controls the ET power source.

  The configuration of the wireless transmitter will be described with reference to FIG. In FIG. 14, the wireless transmitter 110A includes a transmission signal processing unit 100, a high frequency amplifier 104, an ET power source 103, an envelope detection unit 109, and a power source control unit 101A. The transmission signal processing unit 100 includes a digital unit 105 and an analog unit 106. The power supply control unit 101A includes a processing unit 110 and a memory 108. Further, the memory 108 includes a frequency memory 108a and a threshold memory 108b.

  The threshold memory 108b stores a plurality of thresholds that are power supply voltages. Note that the number of thresholds is equal to the number of power supply stages. The frequency memory 108 </ b> Aa stores a plurality of appearance frequencies of the transmission BB signal for the voltage in the section sandwiched between the threshold and another threshold.

  The digital unit 105 receives a transmission BB (baseband) signal sent from the host device. The digital unit 105 sets transmission power, a transmission frequency, the number of transmission carriers, and the like, and sends 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 and outputs the analog high frequency signal to the high frequency amplifier 104.

  An envelope detection unit (envelope detector) 109 detects an envelope from an analog signal. The envelope detector 109 can also detect an envelope from a digital signal. However, in that case, the envelope detection unit is included in the digital unit 105. Therefore, the position of the envelope detector is not limited to FIG.

  The transmission baseband signal (transmission BB signal) is supplied to the power supply control unit 101A and the transmission signal processing unit 110. The high frequency amplifier 104 amplifies the transmission signal and transmits it from a transmission antenna (not shown).

  With reference to FIG. 15, the processing flow of the power supply control unit 101A will be described. This processing flow is started when the power is turned on. In FIG. 15, the power supply processing unit 101A determines a class data section (S210). The power processing unit 101A stores the threshold information in the threshold memory (S221). The power supply processing unit 101A allocates the frequency memory (S222). The power supply processing unit 101A simultaneously generates and outputs a control signal for the ET power supply (S223). After step 222, the power supply processing unit 101A calculates the amplitude (√ (I ^ 2 + Q ^ 2) of the transmission BB signal (S224) The power supply processing unit 101A compares the calculation result with a plurality of thresholds, and the corresponding frequency. (S226) The power supply processing unit 101A determines whether the specified number of times has been completed (S227) When YES, the power supply processing unit 101A determines that the frequency of its own section is the frequency of the adjacent section in the frequency memory. When the answer is YES, the power processing unit 101A transitions to step 224. When the result is NO in step 228, the power processing unit 101A moves the frequency to the higher frequency (S229). The process proceeds to step 221. When NO in step 227, the power supply processing unit 101A transitions to step 224.

  In addition, although one step 228 and step 229 have been described for the sake of simplicity of illustration, only step (number of power supply stages −1) is actually performed. Also, the transition to step 224 is when the frequencies of all the sections are equal.

  The training flow will be described with reference to FIG. 16, the power processing unit 101A calculates the amplitude (√ (I ^ 2 + Q ^ 2) of the transmission BB signal (S211) .The power processing unit 101A determines whether the amplitude is maximum or minimum (S212). At this time, the power processing unit 101A stores the maximum value / minimum value information in the memory (S213), and proceeds to Step 211. When NO in Step 212, the power processing unit 101A determines whether the specified number of times has been completed. When YES, the power supply processing unit 101A sets (maximum value−minimum value) / power supply stage number n as the data section X (S216) The power supply processing unit 101A sets the class An = nX (S21). When the answer is NO in step 214, the power supply processing unit 101A makes a transition to step 211.

  With reference to FIG. 17, a transition of values held in the threshold memory will be described. In FIG. 17, description will be made assuming that the number n of stages of the ET power supply is 10. (A) is an initial value. The threshold memory 108b is divided into 10 sections, and each holds 0. (B) is a threshold memory 108b during training. The leftmost section (referred to as section 1) holds 5 which is the minimum value of the power output, and section 2 holds 33 which is the maximum value of the power output, and sections 3 to 10 remain 0. .

(C) is a threshold memory 108b after the end of training. The section 1 holds 0 which is the minimum value of the power output, and the section 2 holds 40 which is the maximum value of the power output. (D) is the threshold value memory 108b after the threshold value calculation is completed.
(Maximum value−minimum value) / number of power supply stages n = (40−0) / 10
= 4
Therefore, the section width is 4, the section 1 is 4, the section 2 is 8, and the section 10 holds 40 similarly. (E) and (f) are values of the threshold memory 108b in the learning process. The threshold value memory 108b changes the threshold value by 1 so that the frequency of the section held by the frequency memory 108a is averaged. However, the maximum value 40 is fixed. In the state of FIG. 17 (f), the section widths of the thresholds from section 1 to section 10 are 8, 4, 3, 3, 3, 3, 3, 2, 3, 8 in order. Note that the amount of change in the threshold value may be changed greatly when the difference is large.

With reference to FIG. 18, the transition of the value held in the frequency memory 108a will be described. In FIG. 18, description will be made assuming that the number n of stages of the ET power supply is 10 as in FIG. 17. (A) is an initial value. The threshold memory 108a is divided into 10 sections, and each holds 0. (B) is frequency data at the end of a certain number of times when the threshold width is equal. (C) and (d) are values of the frequency memory 108a in the learning process. FIGS. 18B, 18C, and 18D are frequency data at the end of a certain number of times in the threshold states of FIGS. 17D, 17E, and 17F, respectively. It can be understood that the frequency data is averaged in the order of FIGS. 18B, 18C, and 18D.
In addition, the section described under the frequency includes only the section including 0 and the exception section does not include the lower limit. In other words, 0 to 4 is 0 or more and 4 or less, and 4 to 8 is more than 4 and 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 FIG. Here, the horizontal axis represents voltage, and the vertical axis represents occurrence frequency. Further, (a) is a power supply voltage division pattern in an initial state, and (b) is a power supply voltage division pattern after learning. From the comparison of (a) and (b), it can be understood that the power supply voltage is finely divided in a region where the occurrence frequency is high.

  According to the third embodiment, regardless of the distribution of the input signal, the power supply voltage can be finely divided in a region having a high occurrence frequency following the distribution.

  DESCRIPTION OF SYMBOLS 100 ... Transmission signal processing part, 101 ... Power supply control part, 103 ... ET power supply, 104 ... High frequency amplifier, 105 ... Digital part, 106 ... Analog part, 107 ... Function generation part, 108 ... Memory, 109 ... Envelope detection means, 110: wireless transmitter, 1300: ET power supply.

Claims (5)

In a wireless transmitter including an envelope tracking power supply that supplies power to a high frequency amplifier, the high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power supply,
The envelope tracking power supply includes a plurality of variable voltage sources,
The wireless power transmitter, wherein the power supply control unit controls the plurality of variable voltage sources so as to divide the power supply voltage finely in a high frequency region based on the voltage distribution of the received transmission baseband signal. The wireless transmitter according to claim 1,
The power control unit includes a threshold memory including a plurality of first sections and a frequency memory including a plurality of second sections, and each of the second sections approaches a mean value of the second section. In addition, the wireless transmitter changes the threshold value held in the first section. In a wireless transmitter including an envelope tracking power supply that supplies power to a high frequency amplifier, the high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power supply,
The envelope tracking power supply includes a plurality of variable voltage sources,
The power supply control unit retains the efficiency characteristics of the high-frequency amplifier and the signal power distribution information for each modulation method in an internal memory, receives information on the modulation method of the transmission RF signal, and based on the information, modulates the corresponding modulation from the internal memory The signal power distribution information of the system and the efficiency characteristics of the high-frequency amplifier are read, and in the power range where the probability of occurrence in the transmission signal is low, the voltage is fixed and the selection range of the voltage is widened. A radio transmitter characterized by generating a control function for increasing the number and controlling the envelope tracking power source. The wireless transmitter according to claim 3, wherein
Furthermore, a transmission signal processing unit is provided,
The transmission signal processing unit performs a peak factor reduction process on a transmission signal to the high frequency amplifier circuit. In an envelope tracking power supply control method in a wireless transmitter including an envelope tracking power supply that supplies power to a high frequency amplifier, the high frequency amplifier that amplifies an analog high frequency signal, and a power supply control unit that controls the envelope tracking power supply,
Determining a class data interval; and
Storing the data section in a first memory;
Calculating the amplitude of the transmission baseband signal and storing in a second memory which one of the data sections corresponds;
After executing the step of storing in the second memory a prescribed number of times, the adjacent sections of the second memory are compared, and the data section recorded in the first memory is changed based on the comparison result And an envelope tracking power control method.

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