Abstract:
A modulation method and modulator for an envelope tracking power supply. An output of a multi-level switching regulator ( 202 ) in the envelope tracking power supply modulator is in parallel connection with an output of a linear regulator ( 201 ) via an inductor ( 203 ) and supplies power to a load. The modulation method for the envelope tracking power supply includes: generating a first control signal ( 209 ) according to the current ( 211 ) obtained from inputting a first reference level signal ( 206 ); comparing the amplitude of a second reference level signal ( 2061 ) obtained according to the first reference level signal ( 206 ) with preset amplitudes of at least three levels, and outputting a second control signal ( 210 ) according to the comparison result and the first control signal ( 209 ); the multi-level switching regulator ( 202 ) outputting a level signal of corresponding amplitude according to the second control signal ( 210 ), and loading the amplitude of the level on the inductor ( 203 ) to output an inductive current ( 208 ′); and linearly regulating the first reference level signal ( 206 ) via a linear regulator ( 201 ) to obtain a voltage output ( 207 ) to the load. The present disclosure resolves the problem of fixed rate of change of current output by the switching regulator of the envelope tracking power supply regulator and cannot adjust to different load current change rates, thus the inductive current outputted by the multi-level switching regulator can better track the load current change.

Description:
TECHNICAL FIELD 
     The present disclosure relates to communication technology, in particular to a power supply modulation method and a power supply modulator. 
     BACKGROUND 
     In a power supply that supplies power to a Radio Frequency (RF) power amplifier, it is commonplace to employ a voltage modulation in the power supply. 
     Hereinafter, the voltage modulation will be described by taking the RF power amplifier as a load. To deal with the increasing user requirements for bandwidth, the modulation mode for the communication system becomes more and more complicated. One prominent problem is that the efficiency of the RF power amplifier is low, which is the bottleneck for improving the efficiency of whole communication system. As to the linear power amplifier, if a conventional DC power supply is used, to preserve linearity, it is required that the supply voltage be greater than the peak voltage of RF signals. When the peak of RF signals is relatively low, the power amplifier simultaneously withstands higher voltage and load current, and thus the efficiency of the power amplifier is relatively low. The average efficiency of the power amplifier depends on the Peak to Average Power Ratio (PAPR) of the RF signals. To maximize communication bandwidth within a limited frequency band, modern communication systems employ a modulation mode with a non-constant envelope (amplitude) and higher PAPR. For example, the PAPR is 6.5 db˜7.0 dB in the Wideband Code Division Multiple Access (WCDMA) system and the PAPR is 9.0 db˜9.5 dB in Orthogonal Frequency-Division Multiple Access (OFDMA) used in the Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMax), which causes a reduction of the efficiency of the power amplifier. A series of other problems appear, such as increase of the power amplifier&#39;s size and weight, and higher requirements to thermal environments for the air cooling, which results in increased application and maintenance costs. Therefore, it is significant to improve the efficiency of the power amplifier. 
     According to the existing literature and technologies, the manner for improving the power amplifier depending on the power supply technology mainly comprises the Envelope Elimination and Restoration (EER) power supply and the Envelope Tracking (ET) power supply. According to the EER power supply technology, a RF signal to be amplified is separated to an envelope and a phase modulation signal utilizing the feature i.e., a constant envelope signal may be effectively amplified by a nonlinear power amplifier, then the nonlinear power amplifier is powered by the ET power supply to restore the amplified RF signals. Since the amplified signal amplitude depends on the output voltage amplitude of the ET power supply, it requires higher tracking precision of the ET power supply, otherwise the linearity of the amplified signal will be affected. The ET power supply technology employs the linear power amplifier, and improves the efficiency of the linear power amplifier through dynamically adjusting the supply voltage of the ET signals. In the above two solutions, dynamically modulating the output voltage of the power supply is required. The power supply modulator must simultaneously keep a high efficiency to ensure that the two solutions may effectively improve the efficiency of the whole amplifier system. 
     In a modern communication system, an RF envelope signal has a wider bandwidth. For example, the bandwidth of WCDMA with a single carrier is 5 MHz, and the bandwidth of WCDMA with four carriers is 20 MHz. The ET power supply is required to provide a high modulation bandwidth and high efficiency. In the prior art, a switched-mode power supply regulator is able to provide a high conversion efficiency. However, extremely high switching speed is required in the application for 20 MHz bandwidth, which cannot be achieved through the conventional switch devices, which causes the reduction of the conversion efficiency of the regulator. In the prior art, the switched-mode power supply regulator always cooperates with the linear power supply regulator to utilize the high frequency feature of the linear power supply regulator and the efficiency of the switch-mode power supply regulator, so as to optimize the precision of modulation and efficiency. A typical structure is shown in  FIG. 1 , in which a linear regulator  201  employs a feedback control of an output voltage  207 , so as to ensure that the output voltage  207  of the linear regulator  201  tracks a reference input signal  206 . A switch regulator  102  is a current source structure which is a composed of a step-down switch circuit, i.e., a BUCK circuit. The control manner of the switch regulator  102  is that the linear regulator  201  outputs current  208  to a hysteresis controller  103 . That is, detecting the output current  208  of the linear regulator  201 , when the output current  208  of the linear regular  201  is high, a switch tube  104  turns on and the output current of a switch regulator  102  is increased; when the output current  208  of the linear regular  201  is low, a switch tube  105  turns on and the output current of the switch regulator  102  is reduced; thereby, controlling the amplitude of the output current  208  of the linear regulator  201  be in a low range and reducing the output power the linear regulator  201 . Since the efficiency of the linear regulator is relatively low, the reduction of the output power of the linear regulator  201  may help to improve the efficiency of the power supply modulator system. 
     However, in the prior art above mentioned, there are the following issues: the current change rate of the switch regulator  102  with the BUCK circuit is fixed, which cannot adapt to various load current change rates. Taking the RF power amplifier as an example, the current change rate of the RF envelope signals is relatively high, and the load current of the power supply regulator also changes therewith. The fixed output current change rate of the switched regulator may cause the tracking sometimes to fail under the current change rate of a higher load current; and may cause frequent switching under the current change rate of a lower load current, so that the switching frequency and the switching loss are increased and the system efficiency is reduced. 
     SUMMARY 
     To address the issue in the prior art that the current change rate of the switch regulator with the BUCK circuit is fixed and cannot adapt to current change rates for various load current, the disclosure provides a power supply modulation method and a power supply modulator. 
     An embodiment of the disclosure provides a modulation method for an envelope tracking power supply. An output of a multi-level switch regulator in the envelope tracking power supply is connected in parallel with an output of a linear regulator through an inductor. The method includes the following steps: 
     generating a first control signal according to a current obtained from an input first reference level signal; the first reference level signal controlling a change trend of an output current of the multi-level switch regulator; 
     comparing an amplitude of a second reference level signal obtained from the first reference level signal with preset amplitudes of at least three grades of levels, outputting a second control signal according to a result of the comparison and the first control signal; at least one of the preset amplitudes of at least three grades of levels is less than the amplitude of the second reference level signal, and at least one of the preset amplitudes of at least three grades of levels is greater than the amplitude of the second reference level signal; 
     outputting, by the multi-level switch regulator, a level signal with corresponding amplitude according to the second control signal, and applying a level with the corresponding amplitude on the inductor to output an inductive current; and 
     linearly adjusting, by a linear regulator, the first reference level signal to obtain a voltage output from the power supply to a load. 
     Another embodiment of the disclosure provides a modulator for an envelope tracking power supply. The modulator includes a linear regulator, a multi-level switch regulator, an inductor, a current controller and a level selection controller. 
     An output of the multi-level switch regulator is connected in parallel with an output of the linear regulator through the inductor; 
     the current controller, the level selection controller and the multi-level switch regulator are connected in series in turn; 
     the current controller is configured to generate a first control signal according to a current obtained from an input first reference level signal; the first reference level signal controls a change trend of an output current of the multi-level switch regulator, the current controller is connected with the level selection controller through a port for outputting the first control signal, and a second reference level signal obtained from the first reference level signal is input to the level selection controller; 
     the level selection controller is configured to compare an amplitude of the second reference level signal obtained from the first reference level signal with preset amplitudes of at least three grades of levels to output a second control signal; at least one of the preset amplitudes of at least three grades of levels is less than the amplitude of the second reference level signal, and at least one of the preset amplitudes of at least three grades of levels is greater than the amplitude of the second reference level signal, the level selection controller is configured to be connected with the multi-level switch regulator through a port for outputting the second control signal; 
     the multi-level switch regulator is configured to output a level signal with a corresponding amplitude according to the second control signal, and to apply a level with the corresponding amplitude on the inductor to output an inductive current; and 
     the linear regulator is configured to linearly adjust the first reference level signal to obtain a voltage output from the power supply to a load. 
     According the solutions of the disclosure, the multi-level switch regulator cooperates with the linear regulator and the multi-level switch regulator outputs voltages with at least three different amplitudes, so that the inductive current may better track the change of the load current, so as to address the issue in the prior art that the inductive current cannot efficiently track the load current change rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structure diagram of a power supply modulator in the prior art. 
         FIG. 2  is a diagram of a potential control principle for a current controller according to the disclosure. 
         FIG. 3  is a structure diagram of a power supply modulator according to the disclosure. 
         FIG. 4  is a structure diagram of a detailed power supply modulator according to the disclosure. 
         FIG. 5  is a waveform diagram obtained by a potential control method for the current controller according to the disclosure. 
         FIG. 6  is a detailed circuit structure diagram for a level selection controller according to the disclosure. 
         FIG. 7  is another detailed structure diagram of the power supply modulator according to the disclosure. 
         FIG. 8  is a diagram of a potential principle for realizing a controller according to an embodiment shown in  FIG. 7 . 
         FIG. 9  is a waveform diagram according to the embodiment shown in  FIG. 7 . 
         FIG. 10  is another structure diagram of the power supply modulator according to the disclosure. 
         FIG. 11  is a diagram of a potential control principle according to an embodiment shown in  FIG. 10 . 
         FIG. 12  is a waveform diagram according to the embodiment shown in  FIG. 10 . 
         FIG. 13  is an additional structure diagram of the power supply modulator according to the disclosure. 
         FIG. 14  is another additional structure diagram of the power supply modulator according to the disclosure. 
         FIGS. 15 and 16  are two structure diagrams of the power supply modulator according to the disclosure. 
         FIG. 17  is a potential structure diagram of a multi-level switch regulator according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the technical solution of the disclosure will be detailed in conjunction with the drawings. 
     To address the issue in the prior art, i.e., the current change rate of the switch regulator  102  with the BUCK circuit shown in  FIG. 1  is fixed and cannot adapt to current change rates for various load current values. The disclosure provides a power supply modulator shown in  FIG. 2  comprising a linear regulator  201 , a multi-level switch regulator  202 , an inductor  203 , a current controller  204  and a level selection controller  205 . An output of the multi-level switch regulator  202  is connected in parallel with the linear regulator  210  through the inductor  203 . The current controller  204 , the level selection controller  205 , the multi-level switch regulator  202  and the inductor  203  are connected in series in turn. The current controller  204  generates a first control signal  209  according to a current  211  obtained according to an input first reference level signal  206 . The current controller  204  is connected with the level selection controller  205  through a port for outputting the first control signal  209 . A second reference level signal  2061  is input to the level selection controller  205 . The level selection controller  205  compares the amplitude of the second reference level signal  2061  obtained according to the first reference level signal  206  with preset amplitudes of at least three grades of levels, and outputs a second control signal  210  according to a result of the comparison and the first control signal  209 . The level selection controller  205  is connected with the multi-level switch regulator  202  through a port for outputting the second control signal  210 . The multi-level switch regulator  202  outputs a level signal with a corresponding amplitude according to the second control signal  210 , and applies a level with the corresponding amplitude on the inductor  203  to output an inductive current  208 ′. The linear regulator  201  linearly adjusts the first reference level signal  206  to obtain a linearly adjusted output voltage  207 , i.e., a voltage output from the power supply to a load. The linear regulator  201  is connected in parallel with the multi-level switch regulator  202  through the inductor  203 . The linear regulator  201  adopts the voltage control and adjusts the voltage output to the load according to an envelope signal served as the first reference level signal  206 . When the change rate of the envelope signal has large fluctuation, the load current of the power supply modulator changes accordingly, the inductive current  208 ′ may better track the change of the load current. The output current of the linear regulator  201  may be better controlled through the multi-level switch regulator  202 , and may be limited to a smaller hysteresis loop, so as to limit power provided by the linear regulator  201  and reduce loss thereof to improve the efficiency of the whole power supply system. 
     The disclosure provides a modulation method for the power supply based on the above power supply modulator, which is shown in  FIG. 3 . The modulation method comprises the following steps: 
     Step  11 : The first control signal  209  is generated according to the current  211  obtained from the input first reference level signal  206 . The first control signal  209  controls the change of the inductive current output from the multi-level switch regulator  202 . 
     Step  12 : The amplitude of the second reference level signal  2061  obtained from the first reference level signal  206  is compared with the preset amplitudes of at least three grades of levels, and the second control signal  210  is output according to a result of the comparison and the first control signal  209 . 
     Step  13 : The multi-level switch regulator  202  outputs the level signal with a corresponding amplitude according to the second control signal  210 , and applies a level with the corresponding amplitude on the inductor  203  to output the inductive current  208 ′. 
     Step  14 : The first reference level signal  206  is linearly adjusted to obtain the linearly adjusted output voltage  207 . 
     As shown in  FIG. 4 , in Step  11 , the linearly adjusted output current  208  is served as the current  211  obtained from the first reference level signal  206 , which may be realized through the power supply modulator shown in  FIG. 4 , which differs from the power supply modulator shown in  FIG. 3  in that the current  208  (served as the current  211  obtained from the first reference level signal) output from the linear regulator  201  is sampled and input to the current controller  204 . 
     Taking the linearly adjusted output current  208  served as the current  211  obtained from the first reference level signal  206 , as an example, the waveform during the generation of the first control signal  209  is shown in  FIG. 5 . When the linearly adjusted output current  208  is greater than the preset upper limit threshold  402 , the generated first control signal  209  is a signal  4011  that controls the multi-level switch regulator  202  to increase the output inductive current; when the linearly adjusted output current  208  is less than the preset lower limit threshold  403 , the generated first control signal  209  is a signal  4012  that controls the multi-level switch regulator  202  to reduce the output inductive current. 
     An embodiment of the circuit of the current controller  204  and the level selection controller  205  is shown in  FIG. 6 . The inductive current control signal  209  is output after the current  208  output from the linear regulator passes the hysteresis comparison composed of a comparator  606  and a first multiplexer  605 , wherein, the input signals of the first multiplexer  605  are the preset upper limit threshold  402  and the preset lower limit threshold  403 . A location signal  609  is obtained by a accumulator  608  after the comparison between the first reference level signal  206  and each grade level  602 ,  603  and  604 . The location signal  609  is respectively input to a control end  615  of a second multiplexer  610  and a control end  616  of a third multiplexer  611 ; the second multiplexer  610  and the third multiplexer  611  respectively output upper grade level  612  and next grade level  613  of the current location. Input signals  601 ,  602 ,  603  and  604  of the second multiplexer  610  and the third multiplexer  611  respectively are respective levels from low to high of the multi-level switch regulator  202 . At last, a fourth multiplexer  614  outputs a second control signal  210  according to the current control signal  209 . 
     The linearly adjusted output current estimation obtained according to the first reference level signal  206  and circuit parameters may also serve as the current  211  obtained from the first reference signal  206 ; the difference is that the former is real current and the latter is a current estimation obtained from a predictive algorithm. 
     It may be realized using the power supply modulator shown in  FIG. 7  that the linearly adjusted output current estimation obtained serves as the current  211  obtained from the first reference signal  206 . The power supply modulator shown in  FIG. 7  differs from that shown in  FIG. 3  in that the first reference level signal  206  is input to an estimator  702 ; the estimator  702  obtains a linearly adjusted output current estimation  703  (serving as the current  211  obtained from the first reference signal) according to the first reference level signal  206  and the circuit parameters. A port of the estimator  702  for outputting current estimation is connected to the input of the current controller  204  for the current  211  obtained from the first reference level signal, and then obtains the second control signal  210  through the above methods for controlling current and controlling level selection. Since the second control signal  210  is not obtained from the output of the linear regulator  201 , the first reference level signal  206  of the linear regulator  201  may be input to a delayer to match a delay of the multi-level switch regulator  202  so as to output delayed first reference level signal  707 . The above circuits may be realized, but not limited to, by the digital control manner such as FPGA, CPLD and DSP. 
       FIG. 8  shows a specific circuit for realizing the power supply modulator shown in  FIG. 7 . The specific circuit estimates real output amplitude of the multi-level switch regulator  202  using the second control signal  210  and estimates a real output voltage of the linear regulator  201  using the first reference level signal  206 . The second control signal  210  and the first reference level signal  206  are input to a first subtracter  7021  of the estimator  702 ; the first subtracter  7021  of the estimator  702  outputs a differential signal  801  that is a voltage estimation of two ends of the inductor and is input to a divider  7022  of the estimator  702  to divide an inductance, so as to obtain an inductive current change rate  802 ; the inductive current change rate  802  is input to an integrator  7023  of the estimator  702  to perform a time integration so as to obtain an estimated inductive current  803 . A load current estimation  804  may be obtained by a second divider  7024  of the estimator  702  through dividing the load value by the first reference level signal  206 . The load current estimation  804  and the estimated inductive current  803  are input to a second subtracter  7025  of the estimator  702 , and a difference output from the second subtracter is the linearly adjusted output current estimation  703 . 
     A potential waveform is shown in  FIG. 9  through using the power supply modulator with the estimator  702  shown in  FIG. 8 . A waveform  901  is a waveform diagram of the second control signal  210 , a waveform  902  is a waveform diagram of the first reference level signal  206 , and a waveform  903  is a waveform diagram of a product of the inductive current  208 ′ output from the multi-level switch regulator  202  and the load. 
     In  FIG. 9 , a phenomenon that the inductive current estimation (i.e., the estimation of the inductive current  208 ′ output from the multi-level switch regulator  202 ) cannot track the load current may still exist.  FIG. 10  shows an embodiment with added load current slope compensation based on the embodiment shown in  FIG. 7 , so as to further improve the tracking effect of the load current by the inductive current. A load current slope estimation circuit  1001  and a slope compensation control circuit  1003  are applied to the embodiment shown in  FIG. 10 . The first reference level signal  206  is input to the load current slope estimation circuit  1001 ; the load current slope estimation circuit  1001  estimates the load current slope according to the first reference level signal  206  and circuit parameters of the power supply, to obtain a predicted signal of the load current change rate; a port for outputting the predicted signal  1002  of the load current change rate is connected with the slope compensation control circuit  1003 ; the slope compensation control circuit  1003  performs slope compensation control on the predicted signal  1002  of the load current change rate to obtain a slope compensation control signal  1005 ; a port for outputting the slope compensation control signal  1005  is connected with the level selection controller  205 ; the level selection controller  205  further performs adjustments according to the slope compensation control signal  1005  through the second control signal  210  obtained according to the previously obtained location signal  609  (i.e., the result of comparison) of the first reference level signal  206  and the first control signal  209 , so that the inductive current may better track the load current. 
       FIG. 11  shows a potential logical circuit for realizing the solution of the load current slope estimation shown in  FIG. 10 . As shown in  FIG. 11 , the first reference level signal  206  is input to the divider of the load current slope estimation circuit  1001  to divide the load value, so as to obtain a load predicted current  804 ; the load predicted current  804  subtracts the delay signal  1101  thereof to obtain the predicted signal  1002  of the load current change rate; the predicted signal  1002  of the load current change rate and the preset upper limit threshold  1102  are input to the first comparator of the slope compensation control circuit  1003 . When the forward direction change rate is greater than the upper limit threshold  1102 , the slope compensation control signal  1005  is output, and the first summator of the slope compensation control circuit  1003  compensates the current location  609  by adding 1 according to the slope compensation control signal  1005  output at this moment, and outputs the compensated signal to the port  615  of the level selection controller shown in  FIG. 6 ; the multi-level switch regulator  202  forwardly outputs one grade higher level amplitude to accelerate the increase of the output inductive current. Similarly, when the backward direction change rate is over the lower limit threshold  1103 , the slope compensation control signal  1005  is output, and the second summator of the slope compensation control circuit  1003  compensates the current location  609  by subtracting 1 according to the slope compensation control signal  1005  output at this moment, and outputs the compensated signal to the port  616  of the level selection controller shown in  FIG. 6 ; the multi-level switch regulator  202  backwardly outputs one grade lower level amplitude to accelerate the reduction of the output inductive current. 
       FIG. 12  shows a potential waveform diagram obtained from the solution of the load current slope compensation as shown in  FIG. 10 . A waveform  1201  is a waveform diagram of the second control signal  210  after adding the load current slope compensation, a waveform  1202  is a waveform diagram of the first reference level signal  206 , and a waveform  1203  is a waveform diagram of a product of the predicted inductive current and the load. It can be seen from  FIG. 12  that the effect of tracking the load current by the inductive current is obviously improved. 
     In the embodiments shown in  FIGS. 7 and 10 , the control of the multi-level switch regulator  202  does not employ the feedback signal output from the linear regulator  201 , therefore, the output level obtained from the predictive algorithm may cause a problem about the volt-second balance of the inductor. For a low-frequency signal, it presents for the inductor that a low resistance is connected with two voltage sources, which are the multi-level switch regulator and linear regulator.  FIG. 13  shows an additional embodiment for addressing the above issue. As shown in  FIG. 13 , the output of the linear regulator  201  is connected to a high-pass filter  1301 , so that the linearly adjusted output voltage is filtered by the high-pass filter and then the linear regulator  201  is connected in parallel with the multi-level switch regulator  202  through the inductor  203 , and thus the output voltage, which is obtained through linear adjustment performed on the first reference level signal  206  by the linear regulator  201 , is filtered by the high-pass filter, and the filtered voltage serves as a voltage of the load output from the power supply, which increases impedance of the low-frequency signal between the two voltage sources, i.e., the multi-level switch regulator  202  and linear regulator  201 , and addresses the problem about the volt-second balance of the inductive current through automatically adjusting the output voltage. 
       FIG. 14  shows another embodiment for addressing the problem about the volt-second balance according to the disclosure. As shown in  FIG. 14 , the output of the linear regulator  201  is sampled to be connected to a low-pass filter  1401 , so as to perform low-pass filtering on the linearly adjusted output sampled current signal to output low-frequency signal of the sampled current signal; a port of the low-pass filter  1401  for outputting low-frequency signal of the current is connected with the multi-level switch regulator  202 . The output DC component of the multi-level switch regulator  202  is controlled using filtered sampled current signal, so as to keep the inductive current in balance. 
     In Step  12 , respective level amplitudes to be compared are set according to respective level signal amplitudes output from the multi-level switch regulator  202  and match with the amplitude of the second reference level signal  2061 . 
     Given that preset amplitudes of three grades of levels respectively are 1V, 2V and 3V, the amplitude of the second reference level signal  2061  is 2.3V, which is compared with 1V, 2V and 3V. Since 2.3V is between 2V and 3V, it is determined that one grade upper level and one grade lower level of the second reference level signal  2061  respectively are the level with 2V and the level with 3V. The second reference level signal  2061  may be the first reference level signal  206 , and also may be the linearly adjusted output level signal  207  obtained by linearly adjusting the first reference level signal  206 . When realized by the hardware, the input of the level selection controller  205  for inputting the second reference level signal may input the first reference level signal  206 , as shown in  FIG. 15 ; or, the input of the level selection controller  205  for inputting the second reference level signal may input the signal obtained by linearly adjusting the first reference level signal  206 , as shown in  FIG. 16 . 
     Since respective amplitudes of the first reference level signal  206  and the output level signal  207  of the linear regulator are different, for example the amplitude of the first reference level signal  206  is 2.3V and the amplitude of the output level signal  207  of the linear regulator is 3.3V, if the output level signal  207  of the linear regulator serves as the second reference level signal  2061 , the preset amplitudes of respective grades of levels need to match with the amplitude of the output level signal  207  of the linear regulator, for example, the amplitudes of respective grades of levels are set as 2V, 3V and 4V, the preset amplitudes of 2V, 3V and 4V are equal to the amplitudes of respective grades of levels output from the multi-level switch regulator  202 . The 2V, 3V and 4V matching with the first reference level signal  206  and the 1V, 2V and 3V matching with the output level signal  207  of the linear regulator are set according to the amplitudes of respective grades of levels of 2V, 3V and 4V output from the multi-level switch regulator  202 . 
     In the concrete implementation, when the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes larger, the second control signal  210  may be a control signal instructing the multi-level switch regulator  202  to output a level with an amplitude one grade higher than that of the reference level signal; when the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes smaller, the second control signal  210  may be a control signal instructing the multi-level switch regulator  202  to output a level with an amplitude one grade lower than that of the reference level signal. For example, the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes larger, the second control signal  210  is a control signal instructing the multi-level switch regulator  202  to output a 3V level (the amplitude thereof is one grade higher than that of the reference level signal with 2.3V), vice versa. Regardless of corresponding to the first reference level signal  206  or the level signal  207  output from the linear regulator, the principle for setting amplitudes of respective grades of levels is that: at least one of the amplitudes of respective grades of levels to be compared is less than the first reference level signal  206  (or the level signal  207  output from the linear regulator), and at least one of the amplitudes of respective grades of levels to be compared is greater than the first reference level signal  206  (or the level signal  207  output from the linear regulator). Certainly, when the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes larger, the second control signal  210  may be a control signal instructing the multi-level switch regulator  202  to output a level with an amplitude two grades higher than that of the reference level signal. The general principle is that the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes larger or smaller, and the second control signal  210 , obtained according to the comparison between the amplitude of the second reference level signal  2061  and preset the amplitudes of respective grades of levels, is a control signal instructing the multi-level switch regulator  202  to output a level with an amplitude higher (corresponding to increase of the inductive current) or lower (corresponding to reduction of the inductive current) than that of the reference level signal. 
     If the current estimation is adopted, the solution estimates the load current slope according to the first level signal  206  and circuit parameters of the power supply to obtain the predicted signal  1002  of the load current change rate, then performs slope compensation control on the predicted signal  1002  of the load current change rate to obtain the slope compensation control signal  1005 , so as to output the second control signal according to the result of comparison, the first control signal and the slope compensation control signal. For example, the result of comparison is that the amplitude of the second reference level signal  2061  is 2.3V and between 2V and 3V, the first control signal  209  requires that the inductive current output from the multi-level switch regulator  202  becomes larger, and the location of the amplitude of the second reference level signal  2061  at amplitudes of respective grades of levels is added 1 according to the slope compensation control signal, i.e., the location between 2V and 3V is changed to between 3V and 5V (a location with one grade higher than the location between 2V and 3V), the second control signal is a control signal instructing the multi-level switch regulator to output a level with an amplitude two grades higher than that of the reference level signal. 
     Specifically, the multi-level switch regulator  202  may have a switch structure as shown in  FIG. 17 . Voltages at various times of the second control signal  210  serve as the second control signal  210 . For example, it is realized that the output amplitude of the multi-level switch regulator is the output voltage  307  of V 1 /V 2 /V 3  through controlling conduction choice of switch tubes  304 / 305 / 306  by the input voltage  301 / 302 / 303 , and V 1 /V 2 /V 3  respectively are amplitudes of the input voltage  301 / 302 / 303 . 
     Obviously, it should be understood that various modifications and changes may be made to the disclosure without departing from the spirit and scope of the disclosure. When these modifications and changes are within the scope of the appended claims and their equivalent technology, these modifications and changes are also included within the scope of protection of the disclosure. 
     INDUSTRIAL APPLICABILITY 
     The disclosure provides a power supply modulation method and a power supply modulator. The output of the multi-level switch regulator in the envelope tracking power supply is connected with the output of the linear regulator through the inductor, the first control signal is generated according to the current obtained from the input first reference level signal, which controls the variation trend of the current output from the multi-level switch regulator. The amplitude of the second reference level signal obtained according to the first reference level signal is compare with at least three grades of level amplitudes, so as to output the second control signal according to the result of comparison and the first control signal. At least one of the amplitudes of respective grades of levels to be compared is less than the amplitude of the second reference level signal, and at least one of amplitudes of respective grades of levels to be compared is greater than the amplitude of the second reference level signal. The multi-level switch regulator outputs a level signal with a corresponding amplitude according to the second control signal, and applies a level with the amplitude on the inductor to output the inductive current. The first reference signal is linearly adjusted by the linear regulator to obtain the voltage output from the power supply to the load. The multi-level switch regulator cooperates with the linear regulator and the multi-level switch regulator outputs voltages with at least three different amplitudes, so that the inductive current may better track the change of the load current, so as to address the issue in the prior art that the inductive current cannot efficiently track the load current change rate.