PATENT DOCUMENT

Publication Number: US-11271600-B2
Application Number: US-201816976657-A
Country: US
Kind Code: B2

Title: Transmitters and methods for operating the same

Abstract:
A transmitter is provided. The transmitter includes an envelope tracking circuit, wherein the envelope tracking circuit includes an envelope circuit configured to generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope. Further, the envelope tracking circuit includes a bandwidth reduction circuit configured to generate a bandwidth reduced envelope signal based on the envelope signal, and a DC-to-DC converter configured to generate a supply voltage for a power amplifier of the transmitter based on the bandwidth reduced envelope signal. The transmitter additionally includes a predistortion circuit configured to generate a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration. The predistortion circuit is further configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal.

Claims:
What is claimed is: 
     
       1. A transmitter, comprising:
 a power amplifier configured to provide a radio frequency signal; and 
 an envelope tracking circuit configured to:
 generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope using discrete signal levels; 
 generate a bandwidth reduced envelope signal based on the envelope signal by modifying a transient between two consecutive discrete signal levels in the envelope signal; and 
 generate a supply voltage for the power amplifier based on the bandwidth reduced envelope signal. 
 
 
     
     
       2. The transmitter of  claim 1 , wherein the envelope tracking circuit is configured to modify the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal. 
     
     
       3. The transmitter of  claim 2 , wherein an absolute value of the linear interpolation&#39;s slope over time is smaller than an absolute value of the transient&#39;s slope over time. 
     
     
       4. The transmitter of  claim 1 , wherein the envelope tracking circuit is further configured to:
 generate an analog control voltage for the DC-to-DC converter based on the bandwidth reduced envelope signal. 
 
     
     
       5. The transmitter of  claim 1 , further comprising:
 a predistortion circuit configured to generate a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion circuit is further configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal. 
 
     
     
       6. The transmitter of  claim 5 , wherein the envelope tracking circuit is configured to modify the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal; and
 wherein the predistortion circuit is configured to generate the predistorted baseband signal using: 
 a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels; 
 a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and 
 a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       7. The transmitter of  claim 6 , wherein the predistortion circuit comprises:
 a first predistorter configured to generate a first auxiliary predistorted baseband signal based on the baseband signal and the first predistortion configuration; 
 a second predistorter configured to generate a second auxiliary predistorted baseband signal based on the baseband signal and the second predistortion configuration; and 
 a signal combiner configured to generate the predistorted baseband signal using linearly changing contributions of the first auxiliary predistorted baseband signal and the second auxiliary predistorted baseband signal while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       8. The transmitter of  claim 6 , wherein the predistortion circuit comprises:
 a predistorter configured to generate the predistorted baseband signal based on the baseband signal and a set of predistortion coefficients; and 
 a predistortion configuration circuit configured to linearly change the set of predistortion coefficients from a first set of predistortion coefficients related to the first predistortion configuration to a second set of predistortion coefficients related to the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       9. A mobile device comprising:
 an antenna element configured to radiate radio frequency signals; and 
 a transmitter communicatively coupled to the antenna element and configured to perform operations comprising:
 generating, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope using discrete signal levels; 
 generating a bandwidth reduced envelope signal based on the envelope signal by modifying a transient between two consecutive discrete signal levels in the envelope signal; and 
 generating a power supply voltage for a power amplifier of the mobile device based on the bandwidth reduced envelope signal. 
 
 
     
     
       10. The mobile device of  claim 9 , the operations further comprising:
 generating a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion configuration is adjusted based on the bandwidth reduced envelope signal. 
 
     
     
       11. The mobile device of  claim 10 , the operations further comprising modifying the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal;
 wherein generating the the predistorted baseband signal comprises using:
 a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels;
 a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and 
 
 a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
 
     
     
       12. The mobile device of  claim 1 , wherein generating the predistorted baseband signal comprises:
 generating a first auxiliary predistorted baseband signal based on the baseband signal and the first predistortion configuration; 
 generating a second auxiliary predistorted baseband signal based on the baseband signal and the second predistortion configuration; and 
 generating the predistorted baseband signal using linearly changing contributions of the first auxiliary predistorted baseband signal and the second auxiliary predistorted baseband signal while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       13. The mobile device of  claim 11 , wherein generating the predistorted baseband signal comprises:
 generating the predistorted baseband signal based on the baseband signal and a set of predistortion coefficients; and 
 linearly changing the set of predistortion coefficients from a first set of predistortion coefficients related to the first predistortion configuration to a second set of predistortion coefficients related to the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       14. An envelope tracking circuit comprising:
 an envelope circuit configured to generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope using discrete signal levels; 
 a bandwidth reduction circuit configured to generate a bandwidth reduced envelope signal based on the envelope signal by modifying a transient between two consecutive discrete signal levels in the envelope signal; and 
 a DC-to-DC converter configured to generate a supply voltage for a power amplifier based on the bandwidth reduced envelope signal. 
 
     
     
       15. The envelope tracking circuit of  claim 14 , wherein the bandwidth reduction circuit is configured to modify the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal. 
     
     
       16. The envelope tracking circuit of  claim 15 , wherein an absolute value of the linear interpolation&#39;s slope over time is smaller than an absolute value of the transient&#39;s slope over time. 
     
     
       17. The envelope tracking circuit of  claim 14 , wherein the bandwidth reduction circuit is configured to modify the transient by using a window function. 
     
     
       18. The envelope tracking circuit of  claim 17 , wherein the bandwidth reduction circuit is configured to modify the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal; and
 wherein the predistortion circuit is configured to generate the predistorted baseband signal using:
 a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels;
 a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and 
 a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
 
 
     
     
       19. The envelope tracking circuit of  claim 18 , wherein the predistortion circuit comprises:
 a first predistorter configured to generate a first auxiliary predistorted baseband signal based on the baseband signal and the first predistortion configuration; 
 a second predistorter configured to generate a second auxiliary predistorted baseband signal based on the baseband signal and the second predistortion configuration; and 
 a signal combiner configured to generate the predistorted baseband signal using linearly changing contributions of the first auxiliary predistorted baseband signal and the second auxiliary predistorted baseband signal while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
 
     
     
       20. The envelope tracking circuit of  claim 18 , wherein the predistortion circuit comprises:
 a predistorter configured to generate the predistorted baseband signal based on the baseband signal and a set of predistortion coefficients; and
 a predistortion configuration circuit configured to linearly change the set of predistortion coefficients from a first set of predistortion coefficients related to the first predistortion configuration to a second set of predistortion coefficients related to the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels.

Description:
FIELD 
     The present disclosure relates to Envelope Tracking (ET). In particular, examples relate to transmitters using ET and methods for operating a transmitter. 
     BACKGROUND 
     Conventional ET has limited bandwidth capability due to high accuracy requirements for the time alignment between the ET-path and the main signal path. For example, a time misalignment of ±0.5 nsec may already lead to inacceptable high spectral degradation for a 60 MHz Radio Frequency (RF) signal. As a consequence, conventional transmit systems for high bandwidth signals use constant supply voltages for their Power Amplifiers (PA). Using a constant supply voltage, however, reduces system efficiency. Further, the higher the bandwidth of an envelope signal, the less efficient is the DC-DC tracker. 
     Hence, there may be a desire for an improved ET technique. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Some examples of apparatuses and/or methods will be described in the following by way of example only, and with reference to the accompanying figures, in which 
         FIG. 1  illustrates a first example of a transmitter; 
         FIG. 2  illustrates a second example of a transmitter; 
         FIG. 3  illustrates a third example of a transmitter; 
         FIG. 4  illustrates an exemplary temporal course of a supply voltage for a PA; 
         FIG. 5  illustrates an exemplary temporal course of a gain of a PA; 
         FIG. 6  illustrates reference temporal course of a supply voltage for a PA; 
         FIG. 7  illustrates a third example of a transmitter; 
         FIG. 8  illustrates an example of a mobile device comprising a transmitter; 
         FIG. 9  illustrates a flowchart of an example of a method for operating a transmitter; and 
         FIG. 10  illustrates a flowchart of an example of another method for operating a transmitter. 
     
    
    
     DETAILED DESCRIPTION 
     Various examples will now be described more fully with reference to the accompanying drawings in which some examples are illustrated. In the figures, the thicknesses of lines, layers and/or regions may be exaggerated for clarity. 
     Accordingly, while further examples are capable of various modifications and alternative forms, some particular examples thereof are shown in the figures and will subsequently be described in detail. However, this detailed description does not limit further examples to the particular forms described. Further examples may cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Like numbers refer to like or similar elements throughout the description of the figures, which may be implemented identically or in modified form when compared to one another while providing for the same or a similar functionality. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, the elements may be directly connected or coupled or via one or more intervening elements. If two elements A and B are combined using an “or”, this is to be understood to disclose all possible combinations, i.e. only A, only B as well as A and B. An alternative wording for the same combinations is “at least one of A and B”. The same applies for combinations of more than 2 Elements. 
     The terminology used herein for the purpose of describing particular examples is not intended to be limiting for further examples. Whenever a singular form such as “a”, “an” and “the” is used and using only a single element is neither explicitly or implicitly defined as being mandatory, further examples may also use plural elements to implement the same functionality. Likewise, when a functionality is subsequently described as being implemented using multiple elements, further examples may implement the same functionality using a single element or processing entity. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including”, when used, specify the presence of the stated features, integers, steps, operations, processes, acts, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, acts, elements, components and/or any group thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) are used herein in their ordinary meaning of the art to which the examples belong. 
       FIG. 1  illustrates a transmitter  100 . The transmitter comprises an ET circuit  110  as well as a main signal path represented by predistortion circuit  150 , mixer  160 , and PA  170 . The ET circuit  110  generates a supply voltage  141  for PA  170 . 
     A baseband (transmit) signal  101  is provided to both the ET circuit  110  and the main signal path. For example, baseband signal  101  may be provided by a baseband processor. The baseband signal  101  may, e.g., be provided in Cartesian representation or in polar representation. 
     ET circuit  110  comprises an envelope circuit  120  configured to generate, based on the baseband signal  101 , an envelope signal  121  indicating a temporal course of the baseband signal  101 &#39;s envelope. The envelope of baseband signal  101  is a (smooth) curve outlining the extremes of baseband signal  101 . That is, envelope signal  121  indicates the temporal course of the baseband signal  101 &#39;s peak value. 
     The envelope signal  121  has a first bandwidth that is determined by the bandwidth of the baseband signal  101 . That is, the higher the bandwidth of the baseband signal  101 , the higher is the bandwidth of the envelope signal  121 . 
     The ET circuit  110  generates the supply voltage  141  for PA  170  by means of DC-to-DC converter  140 . The efficiency of the DC-to-DC converter  140  depends on the bandwidth of its control signal. A higher bandwidth of the control signal causes increased switching activity of the DC-to-DC converter  140  and, hence, higher switch losses (which corresponds to a reduced efficiency of the DC-to-DC converter  140 ). As indicated in  FIG. 1 , the DC-to-DC converter  140  is controlled based on the envelope signal  121 . Hence, a high bandwidth of envelope signal  121  might reduce the efficiency of DC-to-DC converter  140 . On the other hand, using ET for baseband signals with high bandwidth is desired. In order to enable ET for high bandwidths of baseband signal  101 , envelope tracking circuit  110  comprises a bandwidth reduction circuit  130  configured to generate a bandwidth reduced envelope signal  131  based on the envelope signal  121 . In other words, bandwidth reduction circuit  130  modifies the envelope signal  121  to reduce its bandwidth. As a result, the bandwidth reduced envelope signal  131  exhibits a second bandwidth that is lower than the first bandwidth of the envelope signal  121 . 
     Since DC-to-DC converter  140  generates the supply voltage  141  for the power amplifier  170  based on the bandwidth reduced envelope signal  131 , the analog DC-to-DC converter  140  can be operated at higher system efficiency. Further, the proposed bandwidth reduction may allow to use ET for baseband signals with increased bandwidth. For example, transmitter  100  may allow ET for bandwidths of more than 60 MHz, 80 MHz, 100 MHz, 120 MHz, 150 MHz etc. 
     The Main signal path comprises a predistortion circuit  150  to correct for gain/phase errors introduced by PA  170 . The modification of envelope signal  121  is taken into consideration by means of predistortion circuit  150 . Predistortion circuit  150  is configured to generate a predistorted baseband signal  151  based on baseband signal  101  and an adjustable predistortion configuration. That is, predistortion circuit  150  is configured to modify baseband signal  101  using the adjustable predistortion configuration. The adjustable predistortion configuration may, e.g., comprise a set of adjustable/variable predistortion coefficients and/or different adjustable sets of predistortion coefficients. The predistortion circuit  150  is configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal  131 . Accordingly, the predistortion of baseband signal  101  may be adapted (adjusted) to the modification of envelope signal  121  in ET circuit  110 . 
     As indicated in  FIG. 1 , an optional mixer  160  in the main signal path generates a RF (input) signal  161  for PA  170  based on the predistorted baseband signal  151 . PA  170  then amplifies the RF signal  161  using the ET based supply voltage  141  in order to generate the amplified RF signal  104  output by transmitter  100  to, e.g., a coupled antenna (not illustrated) or an intermediary filter (e.g. a duplexer or a triplexer). 
     While some basic principles of ET according to the proposed technique were described above in connection with  FIG. 1 , more detailed examples of transmitters using ET according to the proposed technique are described in the following with reference to  FIGS. 2 and 3 . 
       FIG. 2  illustrates a transmitter  200 . Similar to transmitter  100 , transmitter  200  comprises a main signal path  280  and an ET circuit  210 . Again, a baseband (transmit) signal  201  is provided to both the ET circuit  210  and the main signal path  280 . The ET circuit  210  generates the supply voltage  241  for PA  270  of the main signal path  280  by means of DC-to-DC converter  240 . 
     ET circuit  210  comprises an envelope circuit  220  configured to generate, based on the baseband signal  201 , an envelope signal  221  indicating a temporal course of the baseband signal  201 &#39;s envelope. Envelope circuit  220  comprises a magnitude determination circuit  222  configured to determine the continuous temporal course  223  of the baseband signal  201 &#39;s envelope. Further, envelope circuit  220  comprises a signal level selection circuit  224  configured to approximate the continuous temporal course  223  of the baseband signal  201 &#39;s envelope using a plurality of discrete signal levels. Accordingly, the envelope signal  221  indicates the temporal course of the baseband signal  201 &#39;s envelope using discrete signal levels. In other words, signal level selection circuit  224  translates the baseband signal  201 &#39;s envelope (RF envelope) to N discrete supply levels for PA  270 . Envelope signal  221  has high bandwidth. 
     The reduction of the envelope signal  221 &#39;s bandwidth is based on the modification of signal transients between consecutive discrete signal levels in the envelope signal  221 . That is, bandwidth reduction circuit  230  of ET circuit  210  is configured to generate the bandwidth reduced envelope signal  231  by modifying a transient  225  between two consecutive discrete signal levels in the envelope signal  221 . Transient  225  illustrates the sudden transition from the first one of the consecutive discrete signal levels in the envelope signal  221  to the second one of the consecutive discrete signal levels. The temporal duration T of transient  225  indicates the transition time from the first one of the consecutive discrete signal levels in the envelope signal  221  to the second one of the consecutive discrete signal levels. 
     As indicated in  FIG. 2 , the bandwidth reduction circuit  230  may be configured to modify the transient  225  by replacing the transient  225  with a linear interpolation  232  between the two consecutive discrete signal levels in the envelope signal  221 . An absolute value of the linear interpolation  232 &#39;s slope over time is smaller than an absolute value of the transient  225 &#39;s slope over time (assuming that both slopes are plotted in coordinate systems using the same scaling). The transient  225  illustrated in  FIG. 2  has an exemplary slope of substantially 90°, whereas the linear interpolation  232  has a slope of substantially 45°. 
     ET circuit  210  further comprise a Digital-to-Analog Converter (DAC)  290  configured to generate an analog control voltage  290  for the DC-to-DC converter  240  based on the bandwidth reduced envelope signal  231 . The DC-to-DC converter  240 , hence, generates the supply voltage  241  for PA  270  based on the bandwidth reduced envelope signal  231  and delivers the required load current to PA  270 . 
     As indicated above, the efficiency of DC-to-DC converter  240  depends on the bandwidth of its control signal, i.e. the bandwidth of the analog control voltage  291 . The bandwidth of the analog control voltage  291  depends on the transients in the input signal for DAC  290 . The shorter the temporal duration of a transient in the input signal for DAC  290 , the higher is the bandwidth of the input signal and, hence, the bandwidth of analog control voltage  290  for DC-to-DC converter  240 . Since the transient  225  in envelope signal  221  is replaced by linear interpolation  232  having a reduced slope, the transition time between the consecutive discrete signal levels is increased in the bandwidth reduced envelope signal  231  compared to envelope signal  221 . Accordingly, the bandwidth of bandwidth reduced envelope signal  231  is decreased compared to envelope signal  221 . Accordingly, DC-to-DC converter  240  may be operated at high system efficiency also for high bandwidths of baseband signal  201 . 
     Further, the reduced bandwidth transition may allow to predict transition effects with higher accuracy. When the analog control voltage  290  exceeds the analog bandwidth of PA  240 , the effect on the PA gain and phase changes may be unstable. The actual waveform that feeds the PA supply depends on the analog circuit designs (e.g. capacitance, resistance and magnetic induction) and in practice produces fluctuations that are difficult to predict and compensate. 
     Main signal path  280  comprises predistortion circuit  250  (e.g. using Digital PreDistortion, DPD) to correct for gain/phase errors introduced by PA  270  during transitions of supply voltage  241 . Mixer  260  in main signal path  280  generates a RF (input) signal  261  for PA  270  based on the predistorted baseband signal  251 . PA  270  then amplifies the RF signal  261  using the ET based supply voltage  241  in order to generate the amplified RF signal  204 . 
     Predistortion circuit  250  is configured to generate a predistorted baseband signal  251  based on the baseband signal  201  and an adjustable predistortion configuration. Predistortion circuit  250  is further configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal  231 . 
     Predistortion circuit  250  comprises a plurality of predistorters  252 - 1 ,  252 - 2 , . . . ,  252 - n . For example, predistortion circuit  250  may comprise a predistorter for each of the N discrete signal levels of envelope signal  221 . 
     Referring to the two consecutive discrete signal levels illustrated in  FIG. 2 , predistortion circuit  250  comprises a first predistorter  252 - 1  configured to generate a first auxiliary predistorted baseband signal  253 - 1  based on the baseband signal  201  and a first predistortion configuration. The first predistortion configuration is related to the first one of the two consecutive discrete signal levels. Further, predistortion circuit  250  comprises a second predistorter  252 - 2  configured to generate a second auxiliary predistorted baseband signal  253 - 2  based on the baseband signal  201  and a second predistortion configuration. The second predistortion configuration is related to the second one of the two consecutive discrete signal levels. N th  predistorter  252 - n  is configured to generate an n th  auxiliary predistorted baseband signal  253 - n  based on the baseband signal  201  and an n th  predistortion configuration. The n th  predistortion configuration is related to an n th  discrete signal levels. In other words, each of the N discrete signal levels may have a dedicated predistortion configuration. 
     Further, predistortion circuit  250  comprises a signal combiner  254  configured to combine the auxiliary predistorted baseband signals  253 - 1 ,  253 - 2 , . . .  253 - n  to the predistorted baseband signal  251 . For example, while the bandwidth reduced envelope signal  231  exhibits the first one of the two consecutive discrete signal levels, the predistorted baseband signal  251  may be the first auxiliary predistorted baseband signal  253 - 1 . While the bandwidth reduced envelope signal  231  exhibits the second one of the two consecutive discrete signal levels, the predistorted baseband signal  251  may be the second auxiliary predistorted baseband signal  253 - 2 . For the transition from the first one to the second one of the two consecutive discrete signal levels, signal combiner  254  may combine the first auxiliary predistorted baseband signal  253 - 1  and the second auxiliary predistorted baseband signal  253 - 2 . For example, the signal combiner  254  may be configured to generate the predistorted baseband signal  251  using linearly changing contributions of the first auxiliary predistorted baseband signal  253 - 1  and the second auxiliary predistorted baseband signal  253 - 2  while the bandwidth reduced envelope signal  231  exhibits the linear interpolation  232  between the two consecutive discrete signal levels. 
     An alternative implementation of the predistortion is illustrated in  FIG. 3  showing a transmitter  300 . Transmitter  300  is identical to transmitter  200  except for the implementation of the predistortion. 
     Predistortion circuit  350  comprises a (single) predistorter  352  configured to generate the predistorted baseband signal  351  based on the baseband signal  201  and a set of predistortion coefficients. Further, predistortion circuit  350  comprises a predistortion configuration circuit  353  configured to adjust the set of predistortion coefficients based on the bandwidth reduced envelope signal  231 . For example, predistortion configuration circuit  353  may use a dedicated set of predistortion coefficients for each of the N discrete signal levels of bandwidth reduced envelope signal  231 . Referring to the two discrete signal levels illustrated in  FIG. 2 , predistortion configuration circuit  353  may, e.g., be configured to adjust the set of predistortion coefficients to a first set of predistortion coefficients related to a first predistortion configuration, while the bandwidth reduced envelope signal  231  exhibits the first one of the two consecutive discrete signal levels. Predistortion configuration circuit  353  may further be configured to adjust the set of predistortion coefficients to a second set of predistortion coefficients related to a second predistortion configuration, while the bandwidth reduced envelope signal  231  exhibits the second one of the two consecutive discrete signal levels. 
     For the transition from the first one to the second one of the two consecutive discrete signal levels, predistortion configuration circuit  353  continuously changes the first set of predistortion coefficients to the second set of predistortion coefficients. For example, the predistortion configuration circuit  353  may be configured to linearly change the set of predistortion coefficients from the first set of predistortion coefficients to the second set of predistortion coefficients while the bandwidth reduced envelope signal  231  exhibits the linear interpolation  232  between the two consecutive discrete signal levels. 
     In other words, instead of using multiple DPD instances and combining the individual DPD results afterwards, the system may alternatively be implemented with only one DPD instance but with coefficients being changed during the transition. 
     In  FIGS. 2 and 3 , two exemplary implementations of predistortion circuits are illustrated. It is evident from the above description that the functionality of a predistortion circuit according to the proposed technique may implemented in different ways. To conclude, a predistortion circuit according to the proposed technique may be configured to generate the predistorted baseband signal using: 
     a) a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels; 
     b) a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and 
     c) a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
     The above described modification of signal transitions in the envelope signal together with the accordingly adapted predistortion is expressed below in terms of exemplary mathematical expressions. 
     The linear interpolation between two discrete signal levels may be described as follows: 
     a) rising transient (signal transition) in the envelope signal: 
     
       
         
           
             
               
                 
                   
                     
                       V 
                       ⁢ 
                       c 
                       ⁢ 
                       
                         c 
                         
                           y 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     = 
                     
                       
                         A 
                         ⁢ 
                         
                           M 
                           
                             x 
                             ⁢ 
                             1 
                           
                         
                       
                       + 
                       
                         
                           
                             ( 
                             
                               
                                 A 
                                 ⁢ 
                                 
                                   M 
                                   
                                     x 
                                     ⁢ 
                                     2 
                                   
                                 
                               
                               - 
                               
                                 A 
                                 ⁢ 
                                 
                                   M 
                                   
                                     x 
                                     ⁢ 
                                     1 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           t 
                         
                         T 
                       
                     
                   
                   ; 
                   
                     0 
                     &lt; 
                     t 
                     &lt; 
                     T 
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     b) falling transient (signal transition) in the envelope signal: 
     
       
         
           
             
               
                 
                   
                     
                       V 
                       ⁢ 
                       c 
                       ⁢ 
                       
                         c 
                         
                           y 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                     
                     = 
                     
                       
                         A 
                         ⁢ 
                         
                           M 
                           
                             x 
                             ⁢ 
                             2 
                           
                         
                       
                       - 
                       
                         
                           
                             ( 
                             
                               
                                 A 
                                 ⁢ 
                                 
                                   M 
                                   
                                     x 
                                     ⁢ 
                                     2 
                                   
                                 
                               
                               - 
                               
                                 A 
                                 ⁢ 
                                 
                                   M 
                                   
                                     x 
                                     ⁢ 
                                     1 
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           t 
                         
                         T 
                       
                     
                   
                   ; 
                   
                     0 
                     &lt; 
                     t 
                     &lt; 
                     T 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     In expressions (1) and (2), Vcc y(t)  denotes the bandwidth reduced envelope signal, AM x1  denotes the the first one of the two consecutive discrete signal levels, AM x2  denotes the secand one of the two consecutive discrete signal levels, and T denotes the duration of the signal transition between the two consecutive discrete signal levels in the bandwidth reduced envelope signal. 
     Corresponding DPD correction factors during the transition between the two consecutive discrete signal levels may be described as follows: 
     a) rising transient (signal transition) in the envelope signal: 
     
       
         
           
             
               
                 
                   
                     DPD 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   ⁢ 
                   
                     
                       = 
                       
                         
                           D 
                           ⁢ 
                           P 
                           ⁢ 
                           
                             D 
                             1 
                           
                         
                         + 
                         
                           
                             
                               ( 
                               
                                 
                                   D 
                                   ⁢ 
                                   P 
                                   ⁢ 
                                   
                                     D 
                                     2 
                                   
                                 
                                 - 
                                 
                                   D 
                                   ⁢ 
                                   P 
                                   ⁢ 
                                   
                                     D 
                                     1 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             t 
                           
                           T 
                         
                       
                     
                     ; 
                     
                       0 
                       &lt; 
                       t 
                       &lt; 
                       T 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     b) falling transient (signal transition) in the envelope signal: 
     
       
         
           
             
               
                 
                   
                     DPD 
                     ⁡ 
                     
                       ( 
                       t 
                       ) 
                     
                   
                   ⁢ 
                   
                     
                       = 
                       
                         
                           D 
                           ⁢ 
                           P 
                           ⁢ 
                           
                             D 
                             2 
                           
                         
                         - 
                         
                           
                             
                               ( 
                               
                                 
                                   D 
                                   ⁢ 
                                   P 
                                   ⁢ 
                                   
                                     D 
                                     2 
                                   
                                 
                                 - 
                                 
                                   D 
                                   ⁢ 
                                   P 
                                   ⁢ 
                                   
                                     D 
                                     1 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             t 
                           
                           T 
                         
                       
                     
                     ; 
                     
                       0 
                       &lt; 
                       t 
                       &lt; 
                       T 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In expressions (3) and (4), DPD(t) denotes the resulting predistortion configuration, DPD 1  denotes the first predistortion configuration, DPD 2  denotes the second predistortion configuration, and T denotes the duration of the signal transition between the two consecutive discrete signal levels in the bandwidth reduced envelope signal. 
     Effects of the proposed bandwidth reduction on the supply voltage for the PA, and the PA behavior are illustrated in  FIGS. 4 to 6 . 
       FIG. 4  illustrates an exemplary temporal course of the supply voltage  410  for the PA (in arbitrary units) during a signal transition between the two consecutive discrete signal levels in the envelope signal. Bandwidth reduction and predistortion based on above expressions 1 to 4 is used. It is evident from  FIG. 4  that the supply voltage  410  smoothly changes during the transition of the envelope signal. The resulting gain  510  of the PA (in arbitrary units) is illustrated in  FIG. 5 . It is evident from  FIG. 5  that the temporal course of the gain  510  is substantially flat, i.e. substantially no PA gain change occurs. 
     As a comparison,  FIG. 6  illustrates a reference temporal course of the supply voltage  610  for the PA (in arbitrary units) without using the proposed bandwidth reduction and predistortion. It is evident from  FIG. 6  that the resulting amplitude changes during the transition and contains fluctuations that are difficult to compensate by means of predistortion. 
     By using the above linear method of predistortion combination, a Root Mean Square (RMS) Error Vector Magnitude (EVM) of −40 dB may, e.g., be obtained for a 20 MHz WLAN signal with significantly improved power consumption compared to a constant supply usage. The amount of efficiency improvement is depending on the transition time T. The faster the transient (the smaller T), the higher the overall efficiency (but also the higher the required envelope bandwidth). 
     In the foregoing, modifying the transient between consecutive discrete signal levels in the envelope signal by linear interpolation is described. Alternatively, any digital filter or digital windowing in time domain or any other method of bandwidth reduction may be used for generating the bandwidth reduced envelop signal. For example, bandwidth reduction circuit  230  illustrated in  FIGS. 2 and 3  may alternatively comprise a digital filter configured to modify the transient  225 , or be configured to modify the transient  225  using a window function. If the ET transient manipulation is more complex than the above linear interpolation, the adjustment of the predistortion configuration may follow similar complexity. 
     The above described ET technique may enables ET for signal bandwidths of more than 60 MHz. Furthermore, controlling the envelope supply transient and using forward path predistortion may (significantly) improve the noise and the EVM. Also, the design of the analog envelope tracker may be done with a higher system efficiency, when reducing the bandwidth of the envelope signal as proposed. 
     The above described examples use an analog DC-DC tracker in the ET circuit. Alternatively, a discrete multi-level DCDC supply may be used. This is exemplarily illustrated in  FIG. 7 .  FIG. 7  illustrates a transmitter  700 . Similar to the above described transmitters, transmitter  700  comprises an ET circuit  710  and a main signal path represented by predistortion circuit  760 , mixer  770 , and PA  780 . Again, a baseband (transmit) signal  701  is provided to both the ET circuit  710  and the main signal path. The ET circuit  710  generates the supply voltage  751  for PA  780  of the main signal path. 
     ET circuit  710  comprises an envelope circuit  720  configured to generate, based on the baseband signal  701 , an envelope signal  721  indicating a temporal course of the baseband signal  701 &#39;s envelope. As indicated in  FIG. 7 , envelope circuit  720  may comprises a magnitude determination circuit  722  configured to determine the continuous temporal course  723  of the baseband signal  701 &#39;s envelope. Further, envelope circuit  720  may comprises a signal level selection circuit  724  configured to approximate the continuous temporal course  723  of the baseband signal  701 &#39;s envelope using a plurality of discrete signal levels. Accordingly, the envelope signal  721  may indicates the temporal course of the baseband signal  701 &#39;s envelope using discrete signal levels. For example, signal level selection circuit  724  may translate the baseband signal  701 &#39;s envelope to N discrete signal levels. 
     Further, ET circuit  710  comprises a sigma-delta encoder  730  configured to generate a pulse modulated signal  731  based on the envelope signal  721  (using sigma-delta modulation). For example, the pulse modulated signal  731  may be a pulse-width modulated signal or a pulse-frequency modulated signal. For example, sigma-delta encoder  730  may follow the N discrete signal levels of envelope signal  721  and encode it to pulse modulated signal  731  toggling between N levels. 
     ET circuit  710  further comprises (multi-level) DC-to-DC converter  740  following the encoded pulse modulated signal  731 . That is, DC-to-DC converter  740  is configured to generate, based on the pulse modulated signal  731 , a supply voltage signal  741  having predefined voltage levels. For example, DC-to-DC converter  740  may internally generates a plurality of predefined voltage levels in parallel, wherein one of the plurality of predefined voltage levels is selected by an internal multiplexer based on the discrete signal level that is encoded in the pulse modulated signal  731 . DC-to-DC converter  740  may output the selected predefined voltage level as supply voltage signal  741 . Compared to analog DC-DC trackers, DC-to-DC converter  740  may achieve a higher system efficiency. 
     An analog filter  750  is configured generate a filtered supply voltage signal  751  for PA  780  based on the supply voltage signal  741 . In other words, analog filter  750  smoothens the supply voltage signal  741 . 
     Since a sigma-delta encoder  730  is used, the noise in pulse modulated signal  731  may be shaped. The sigma-delta encoder  730  is configured to oversample envelope signal  721  (i.e. sample it with a frequency much higher than the Nyquist rate) so that noise in a band of interest at low frequencies may be reduced, while the noise at higher frequencies is increased. For example, a sample frequency of the sigma-delta encoder  730  may be selected such that shaped noise in the pulse modulated signal  731  is at frequencies of at least six, eight, ten, or twelve times a bandwidth of the baseband signal  701 . The analog filter  750  is configured to remove signal components from the supply voltage signal  741  related to shaped noise in the pulse modulated signal  731 . In other words, choosing a higher sampling rate (Fs) of the sigma delta encoder  730  may allow to shape the switching noise towards higher frequency offsets, where it can be filtered by relative simple and small size analog filter  750 . 
     Further, the sampling frequency (Fs) may be chosen different from used frequency bands or transmission/reception modes in order to avoid shaped noise falling onto the critical frequency bands. Accordingly, disturbances of the own receiver or in other co-existing systems (e.g. a WLAN+cellular co-existence) may be avoided. That is, the sample frequency of the sigma-delta encoder  730  may be different from other frequencies used within transmitter  700  (or a transceiver comprising transmitter  700 ). 
     The main signal path comprises predistortion circuit  760  (e.g. DPD) to correct for gain/phase errors introduced by PA  780  during transitions of filtered supply voltage signal  751 . Mixer  770  in the main signal path generates a RF (input) signal  771  for PA  780  based on the predistorted baseband signal  761 . PA  780  then amplifies the RF signal  771  using the ET based supply voltage  751  in order to generate the amplified RF signal  704 . 
     Predistortion circuit  760  is configured to generate the predistorted baseband signal  761  based on the baseband signal  701  and an adjustable predistortion configuration. Predistortion circuit  760  is further configured to adjust the predistortion configuration based on a control signal  791  related to the pulse modulated signal  731 . 
     A digital filter  790  is configured to generate the control signal  791  based on the pulse modulated signal  731  and a filter model. The filter model represents the signal processing behavior of the DC-to-DC converter  740  and the analog filter  750 . That is, the digital filter  790  reproduces substantially the waveform of the filtered supply voltage signal  751  and controls predistortion circuit  760 . As a consequence, the predistortion circuit  760  is controlled based on the actual waveform of the filtered supply voltage signal  751  so that gain/phase errors introduced by PA  780  during transitions of filtered supply voltage signal  751  may be precompensated. 
     As indicated in  FIG. 7 , predistortion circuit  760  may, e.g., comprise a plurality of predistorters  762 - 1 ,  762 - 2 , . . . ,  762 - n  configured to generate auxiliary predistorted baseband signals  763 - 1 ,  763 - 2 , . . . ,  763 - n  based on the baseband signal  701  and respective predistortion configurations. A signal combiner  764  of predistortion circuit  760  may then be configured to generate the predistorted baseband signal  761  based on adjustable contributions of the auxiliary predistorted baseband signals  763 - 1 ,  763 - 2 , . . . ,  763 - n . The contributions of the auxiliary predistorted baseband signals  763 - 1 ,  763 - 2 , . . . ,  763 - n  are adjusted based on the control signal  791 . That is, a combination of auxiliary predistorted baseband signals similar to what is described in connection with  FIG. 2  may be used. 
     Although not explicitly illustrated in  FIG. 7 , the predistortion circuit  760  may alternatively comprise a predistorter configured to generate the predistorted baseband signal  760  based on the baseband signal  701  and predistortion coefficients. Further, predistortion circuit  760  may comprise a predistortion configuration circuit configured to adjust the predistortion coefficients based on the control signal  791 . That is, an adjustment of predistortion coefficients similar to what is described in connection with  FIG. 3  may be used. 
     However, the predistortion circuit  760  is not limited to the above exemplary implementations. 
     ET according to the technique described in connection with transmitter  700  may enable usage of a more efficient discrete multi-level DCDC for envelope tracking, further improving overall system efficiency. 
     An example of an implementation using ET according to one or more aspects of the proposed technique or one or more examples described above is illustrated in  FIG. 8 .  FIG. 8  schematically illustrates an example of a mobile device  800  (e.g. mobile phone, smartphone, tablet-computer, or laptop) comprising at least one transmitter  810  for RF signal generation according to an example described herein. For example, transmitter  810  may be part of a RF transceiver (not illustrated). Transmitter  810  is coupled to at least one antenna element  820  for radiating the RF signal to the environment. 
     The mobile device  800  may comprise further elements such as, e.g., an application processor, a baseband processor, memory, an audio driver, a camera driver, a touch screen, a display driver, sensors, removable memory, a power management integrated circuit or a smart battery. 
     To this end, a mobile device enabling ET for high bandwidth RF signals and, hence, enabling, increased efficiency may be provided. 
     The above wireless communication circuits using ET or transmitters according to the proposed technique or one or more of the examples described above may be configured to operate according to one of the 3 rd  Generation Partnership Project (3GPP)-standardized mobile communication networks or systems. The mobile or wireless communication system may correspond to, for example, a 5 th  Generation New Radio (5G NR), a Long-Term Evolution (LTE), an LTE-Advanced (LTE-A), High Speed Packet Access (HSPA), a Universal Mobile Telecommunication System (UMTS) or a UMTS Terrestrial Radio Access Network (UTRAN), an evolved-UTRAN (e-UTRAN), a Global System for Mobile communication (GSM), an Enhanced Data rates for GSM Evolution (EDGE) network, or a GSM/EDGE Radio Access Network (GERAN). Alternatively, the wireless communication circuits may be configured to operate according to mobile communication networks with different standards, for example, a Worldwide Inter-operability for Microwave Access (WIMAX) network IEEE 802.16 or Wireless Local Area Network (WLAN) IEEE 802.11, generally an Orthogonal Frequency Division Multiple Access (OFDMA) network, a Time Division Multiple Access (TDMA) network, a Code Division Multiple Access (CDMA) network, a Wideband-CDMA (WCDMA) network, a Frequency Division Multiple Access (FDMA) network, a Spatial Division Multiple Access (SDMA) network, etc. 
     An example of a method  900  for operating a transmitter is illustrated by means of a flowchart in  FIG. 9 . Method  900  comprises generating  902 , based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope. Further, method  900  comprises generating  904  a bandwidth reduced envelope signal based on the envelope signal, and generating  906  a power supply voltage for a power amplifier of the transmitter based on the bandwidth reduced envelope signal. Method  900  additionally comprises generating  908  a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion configuration is adjusted based on the bandwidth reduced envelope signal. 
     More details and aspects of the method are mentioned in connection with the proposed technique or one or more examples described above (e.g.  FIGS. 1 to 6 ). The method may comprise one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above. 
     An example of another method  1000  for operating a transmitter is illustrated by means of a flowchart in  FIG. 10 . Method  1000  comprises generating  002 , based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope. Further, method  1000  comprises generating  1004 , using a sigma-delta encoder, a pulse modulated signal based on the envelope signal. Additionally, method  1000  comprises generating  1006 , based on the pulse modulated signals, a supply voltage signal having predefined voltage levels, and generating  1008  a filtered supply voltage signal for a power amplifier of the transmitter based on the supply voltage signal. Method  1000  further comprises generating  1010  a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion configuration is adjusted based on a control signal related to the pulse modulated signal. 
     More details and aspects of the method are mentioned in connection with the proposed technique or one or more examples described above (e.g.  FIG. 7 ). The method may comprise one or more additional optional features corresponding to one or more aspects of the proposed technique or one or more examples described above. 
     The proposed technique may allow to extend usage of the well-established envelope tracking techniques for power consumption reduction for higher bandwidth systems (e.g. LTE, 5G NR, WLAN, etc.). 
     The examples as described herein may be summarized as follows: 
     Example 1 is a transmitter, comprising: an envelope tracking circuit, wherein the envelope tracking circuit comprises: an envelope circuit configured to generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope; a bandwidth reduction circuit configured to generate a bandwidth reduced envelope signal based on the envelope signal; and a DC-to-DC converter configured to generate a supply voltage for a power amplifier of the transmitter based on the bandwidth reduced envelope signal, and a predistortion circuit configured to generate a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion circuit is further configured to adjust the predistortion configuration based on the bandwidth reduced envelope signal. 
     Example 2 is the transmitter of example 1, wherein the envelope signal indicates the temporal course of the baseband signal&#39;s envelope using discrete signal levels, and wherein the bandwidth reduction circuit is configured to generate the bandwidth reduced envelope signal by modifying a transient between two consecutive discrete signal levels in the envelope signal. 
     Example 3 is the transmitter of example 2, wherein the bandwidth reduction circuit is configured to modify the transient by replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal. 
     Example 4 is the transmitter of example 3, wherein an absolute value of the linear interpolation&#39;s slope over time is smaller than an absolute value of the transient&#39;s slope over time. 
     Example 5 is the transmitter of example 3 or example 4, wherein the predistortion circuit is configured to generate the predistorted baseband signal using: a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels; a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
     Example 6 is the transmitter of example 5, wherein the predistortion circuit comprises: a first predistorter configured to generate a first auxiliary predistorted baseband signal based on the baseband signal and the first predistortion configuration; a second predistorter configured to generate a second auxiliary predistorted baseband signal based on the baseband signal and the second predistortion configuration; and a signal combiner configured to generate the predistorted baseband signal using linearly changing contributions of the first auxiliary predistorted baseband signal and the second auxiliary predistorted baseband signal while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
     Example 7 is the transmitter of example 5, wherein the predistortion circuit comprises: a predistorter configured to generate the predistorted baseband signal based on the baseband signal and a set of predistortion coefficients; and a predistortion configuration circuit configured to linearly change the set of predistortion coefficients from a first set of predistortion coefficients related to the first predistortion configuration to a second set of predistortion coefficients related to the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
     Example 8 is the transmitter of example 2, wherein the bandwidth reduction circuit comprises a digital filter configured to modify the transient. 
     Example 9 is the transmitter of example 2, wherein the bandwidth reduction circuit is configured to modify the transient using a window function. 
     Example 10 is the transmitter of any of examples 1 to 9, wherein the envelope tracking circuit further comprises: a digital-to-analog converter configured to generate an analog control voltage for the DC-to-DC converter based on the bandwidth reduced envelope signal. 
     Example 11 is the transmitter of any of examples 1 to 10, further comprising: a mixer configured to generate a radio frequency signal for the power amplifier based on the predistorted baseband signal. 
     Example 12 is a transmitter, comprising: an envelope tracking circuit, wherein the envelope tracking circuit comprises: an envelope circuit configured to generate, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope; a sigma-delta encoder configured to generate a pulse modulated signal based on the envelope signal; a DC-to-DC converter configured to generate, based on the pulse modulated signal, a supply voltage signal having predefined voltage levels; and an analog filter configured generate a filtered supply voltage signal for a power amplifier of the transmitter based on the supply voltage signal, and a predistortion circuit configured to generate a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion circuit is further configured to adjust the predistortion configuration based on a control signal related to the pulse modulated signal. 
     Example 13 is the transmitter of example 12, further comprising: a digital filter configured to generate the control signal based on the pulse modulated signal and a filter model, wherein the filter model represents the signal processing behavior of the DC-to-DC converter and the analog filter. 
     Example 14 is the transmitter of example 12 or example 13, wherein a sample frequency of the sigma-delta encoder is selected such that shaped noise in the pulse modulated signal is at frequencies of at least six times a bandwidth of the baseband signal. 
     Example 15 is the transmitter of example 14, wherein the analog filter is configured to remove signal components from the supply voltage signal related to the shaped noise in the pulse modulated signal. 
     Example 16 is the transmitter of example 14 or example 15, wherein the sample frequency is different from other frequencies used within the transmitter. 
     Example 17 is the transmitter of any of examples 12 to 16, wherein the pulse modulated signal is a pulse-width modulated signal or a pulse-frequency modulated signal. 
     Example 18 is the transmitter of any of examples 12 to 17, further comprising: a mixer configured to generate a radio frequency signal for the power amplifier based on the predistorted baseband signal. 
     Example 19 is the transmitter of any of examples 12 to 18, wherein the predistortion circuit comprises: a plurality of predistorters configured to generate auxiliary predistorted baseband signals based on the baseband signal and respective predistortion configurations; and a signal combiner configured to generate the predistorted baseband signal based on adjustable contributions of the auxiliary predistorted baseband signals, wherein the contributions of the auxiliary predistorted baseband signals are adjusted based on the control signal. 
     Example 20 is the transmitter of any of examples 12 to 18, wherein the predistortion circuit comprises: a predistorter configured to generate the predistorted baseband signal based on the baseband signal and predistortion coefficients; and a predistortion configuration circuit configured to adjust the predistortion coefficients based on the control signal. 
     Example 21 is a mobile device comprising a transmitter according to any of examples 1 to 20. 
     Example 22 is the mobile device of example 21, further comprising at least one antenna element coupled to the transmitter. 
     Example 23 is a method for operating a transmitter, comprising: generating, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope; generating a bandwidth reduced envelope signal based on the envelope signal; generating a power supply voltage for a power amplifier of the transmitter based on the bandwidth reduced envelope signal; and generating a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion configuration is adjusted based on the bandwidth reduced envelope signal. 
     Example 24 is the method of example 23, wherein the envelope signal indicates the temporal course of the baseband signal&#39;s envelope using discrete signal levels, and wherein generating the bandwidth reduced envelope signal comprises: modifying a transient between two consecutive discrete signal levels in the envelope signal. 
     Example 25 is the method of example 24, wherein modifying the transient comprises: replacing the transient with a linear interpolation between the two consecutive discrete signal levels in the envelope signal. 
     Example 26 is the method of example 25, wherein an absolute value of the linear interpolation&#39;s slope over time is smaller than an absolute value of the transient&#39;s slope over time. 
     Example 27 is the method of example 25 or example 26, wherein the predistorted baseband signal is generated using: a first predistortion configuration while the bandwidth reduced envelope signal exhibits the first one of the two consecutive discrete signal levels; a second predistortion configuration while the bandwidth reduced envelope signal exhibits the second one of the two consecutive discrete signal levels; and a linearly changing combination of the first predistortion configuration and the second predistortion configuration while the bandwidth reduced envelope signal exhibits the linear interpolation between the two consecutive discrete signal levels. 
     Example 28 is the method of example 24, wherein a digital filter is used for modifying the transient. 
     Example 29 is the method of example 24, wherein a window function is used for modifying the transient. 
     Example 30 is the method of any of examples 23 to 29, further comprising: generating an analog control voltage for the DC-to-DC converter based on the bandwidth reduced envelope signal. 
     Example 31 is the method of any of examples 23 to 30, further comprising: generating a radio frequency signal for the power amplifier based on the predistorted baseband signal. 
     Example 32 is a method for operating a transmitter, comprising: generating, based on a baseband signal, an envelope signal indicating a temporal course of the baseband signal&#39;s envelope; generating, using a sigma-delta encoder, a pulse modulated signal based on the envelope signal; generating, based on the pulse modulated signals, a supply voltage signal having predefined voltage levels; generating a filtered supply voltage signal for a power amplifier of the transmitter based on the supply voltage signal; and generating a predistorted baseband signal based on the baseband signal and an adjustable predistortion configuration, wherein the predistortion configuration is adjusted based on a control signal related to the pulse modulated signal. 
     Example 33 is the method of example 32, further comprising: generating the control signal based on the pulse modulated signal and a filter model, wherein the filter model represents the generation of the filtered supply voltage signal. 
     Example 34 is the method of example 32 or example 33, wherein a sample frequency of the sigma-delta encoder is selected such that shaped noise in the pulse modulated signal is at frequencies of at least six times a bandwidth of the baseband signal. 
     Example 35 is the method of example 34, wherein generating the filtered supply voltage signal comprises: removing signal components from the supply voltage signal related to the shaped noise in the pulse modulated signal. 
     Example 36 is the method of example 34 or example 35, wherein the sample frequency is different from other frequencies used within the transmitter. 
     Example 37 is the method of any of examples 32 to 36, wherein the pulse modulated signal is a pulse-width modulated signal or a pulse-frequency modulated signal. 
     Example 38 is the method of any of examples 32 to 37, further comprising: generating a radio frequency signal for the power amplifier based on the predistorted baseband signal. 
     The aspects and features mentioned and described together with one or more of the previously detailed examples and figures, may as well be combined with one or more of the other examples in order to replace a like feature of the other example or in order to additionally introduce the feature to the other example. 
     The description and drawings merely illustrate the principles of the disclosure. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to furthering the art. All statements herein reciting principles, aspects, and examples of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof. 
     A block diagram may, for instance, illustrate a high-level circuit diagram implementing the principles of the disclosure. Similarly, a flow chart, a flow diagram, a state transition diagram, a pseudo code, and the like may represent various processes, operations or steps, which may, for instance, be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. Methods disclosed in the specification or in the claims may be implemented by a device having means for performing each of the respective acts of these methods. 
     It is to be understood that the disclosure of multiple acts, processes, operations, steps or functions disclosed in the specification or claims may not be construed as to be within the specific order, unless explicitly or implicitly stated otherwise, for instance for technical reasons. Therefore, the disclosure of multiple acts or functions will not limit these to a particular order unless such acts or functions are not interchangeable for technical reasons. Furthermore, in some examples a single act, function, process, operation or step may include or may be broken into multiple sub-acts, -functions, -processes, -operations or -steps, respectively. Such sub acts may be included and part of the disclosure of this single act unless explicitly excluded. 
     Furthermore, the following claims are hereby incorporated into the detailed description, where each claim may stand on its own as a separate example. While each claim may stand on its own as a separate example, it is to be noted that—although a dependent claim may refer in the claims to a specific combination with one or more other claims—other examples may also include a combination of the dependent claim with the subject matter of each other dependent or independent claim. Such combinations are explicitly proposed herein unless it is stated that a specific combination is not intended. Furthermore, it is intended to include also features of a claim to any other independent claim even if this claim is not directly made dependent to the independent claim.

Metadata:
Filing Date: 20180327
Publication Date: 20220308
Grant Date: 20220308
Priority Date: 20180327
Inventors: BELITZER, ALEXANDER
YOFFE, Yaron
COHEN, YANIV
KERNER, Michael
Assignee: APPLE INC
CPC Classifications: [{"code": "H04B1/62", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04B2001/0425", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/3241", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/3241", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B2001/0425", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/0227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/451", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/24", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F1/3241", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B1/0475", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 68058424