HK1213372B - Envelope tracking system with internal power amplifier characterization - Google Patents

Description

Envelope tracking system with internal power amplifier characterization

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No. 61/800,350, filed on 3/15/2013, which is incorporated herein by reference in its entirety.

Technical Field

The present application relates generally to envelope tracking power amplifier systems and, more particularly, to envelope tracking power amplifier systems having improved characteristics.

Background

The Envelope Tracking (ET) system can be found in the Radio Frequency (RF) transmitter part of radios where power efficiency is important, such as cellular radios used in mobile phones. A typical ET system includes a variable power supply that supplies a dynamically changing supply voltage to a Power Amplifier (PA), which tracks the modulation amplitude. The goal of such ET systems is to improve power efficiency by operating the PA with low headroom (headroom).

The supply voltage level may be determined using a look-up table that references the supply voltage value as a reference for the amplitude. Fig. 7 illustrates the nature of the selections that may be used for the look-up table. As an example, the lookup table may contain PA supply voltage values ranging from 1.2V to 5V for magnitudes corresponding to a PA output power of 22 dBm. The choice of this value can be set to provide a good balance between PA efficiency and linearity. If the PA supply voltage is set too low, the PA operates with lower headroom and thus higher efficiency, but with higher distortion. Conversely, if the PA supply voltage is set too high, the PA operates with higher headroom and thus lower efficiency, but the additional headroom allows for lower distortion levels.

The values of the look-up table are typically determined in the factory by characterizing (characterizing) a typical PA on a typical radio under typical conditions. The set of initial values is then copied to other ET systems. However, during actual operation of other ET systems, the PA may exhibit different characteristics than those during characterization of a typical PA, depending on factors such as PA processing and manufacturing tolerances, power supply circuit variations, environmental factors, temperature, operating frequency modulation formats, and antenna mismatch. Thus, the set of initial values may not operate the PA with a proper balance of power efficiency and distortion.

Disclosure of Invention

Embodiments of the present application include an RF PA system that generates its own local characterization information. The RF PA system then uses the characterization information to control the supply voltage to the PA. As a result, the RF PA system can control the supply voltage in a manner that more accurately achieves a desired balance between power efficiency and distortion.

In an embodiment, the RF PA system includes a PA that generates an RF output signal from an RF input signal, the PA being powered by a supply voltage. A characterization block generates characterization information corresponding to a relationship between the supply voltage and a performance of the RF PA system (e.g., gain, power efficiency, distortion, receive band noise) for a plurality of levels of one or more operating conditions of the RF PA system (e.g., temperature, operating frequency, modulation format, antenna mismatch, etc.). An amplitude estimator block estimates an amplitude of the RF input signal. The power supply control block generates a power supply voltage control signal based on the characterization information and the amplitude of the RF input signal, the power supply voltage control signal for controlling the power supply voltage.

In an embodiment, a method of operation in an RF PA system includes: generating characterization information in the RF PA system, the characterization information corresponding to a relationship between a supply voltage of a PA and a performance of the PA for a plurality of levels of operating conditions of the RF PA system, the PA generating an RF output signal based on an RF input signal; estimating an amplitude of the RF input signal in the RF PA system; and generating, in the RF PA system, a supply voltage control signal based on the characterization information and the amplitude of the RF input signal, the supply voltage control signal for controlling a supply voltage of the PA.

The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.

Drawings

The teachings of embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings.

Fig. 1 illustrates an RF PA system in accordance with an embodiment.

Fig. 2 shows a graph of the relationship between the RF input power of a PA and the supply voltage VCC according to an embodiment.

Fig. 3 illustrates a more detailed view of the RF PA system of fig. 1 in accordance with an embodiment.

Fig. 4 shows waveforms for adjusting the supply voltage VCC during characterization according to an embodiment.

Fig. 5 illustrates a method of operation in an RF PA system in accordance with an embodiment.

Fig. 6 shows the adjustment of the supply voltage VCC during characterization according to another embodiment.

Fig. 7 illustrates the nature of the selections that may be used for the look-up table.

Detailed Description

Reference will now be made in detail to several embodiments of the present application, examples of which are illustrated in the accompanying drawings. Note that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.

Embodiments of the present application include an RF PA system that generates its own local characterization information using feedback from within the RF PA system itself. The RF PA system then uses the characterization information to control the supply voltage to the PA. As a result, the RF PA system can control the supply voltage in a manner that more accurately achieves a desired balance between power efficiency and distortion. In an embodiment, the RF PA system can perform characterization during normal transmit operation of the RF PA system without interrupting operation of the RF PA system. In another embodiment, the RF PA system may perform characterization during an offline calibration mode.

Fig. 1 illustrates an RF PA system according to an embodiment of the present application. The RF PA system includes a transmit modulator 10, an amplitude estimator 13, an RF up-converter 2, a Power Amplifier (PA)3, an antenna 4, a duplexer 5, a feedback receiver 24, a characterization block 102, a characterization information table 33, a power supply control block 104, and an Envelope Tracking (ET) power supply 8. Each block shown in the figures may be implemented as circuitry or a combination of circuitry and software. The RF PA system may be found in a cellular phone, a mobile hotspot, a tablet computer, or any other type of computing device that supports wireless communication. The RF PA system may support different wireless transmission standards, such as 3G, 4G, and Long Term Evolution (LTE), to transmit wireless signals to remote devices. To simplify the drawing, only the transmission path for transmitting outgoing signals is shown in fig. 1, while the reception path for receiving incoming signals is omitted in fig. 1.

The transmit modulator 10 generates a digital baseband signal 1 comprising the desired information to be transmitted as a radio signal to a remote device. An RF up-converter (up converter)2 up-converts the digital baseband signal 1 to generate an RF input signal 17 operating at a particular RF carrier frequency. The variable gain RF up-converter 2 may be implemented by a pair of up-conversion mixer (mixer) circuits followed by a variable gain driver. The transmit modulator 10 controls the gain of the variable gain RF up-converter 2 by means of a gain control signal 16. The gain of the variable gain RF up-converter 2 may be adjusted for various reasons, including transmit power control and noise optimization in the transmit path.

An optional predistortion block (not shown) may also predistort the baseband signal 1 before the baseband signal 1 reaches the variable gain RF up-converter 2. The predistortion block may receive a feedback signal 42 from the feedback receiver 15 and compare this signal 15 with the baseband signal 1 to update its predistortion parameters.

The PA3 receives and amplifies the RF input signal 17 to generate the RF output signal 12 at the output of the PA 3. The RF output signal 12 reaches the antenna 4 after passing through the duplex filter 5 and is transmitted wirelessly by the antenna 4 to a remote device. The duplex filter 5 provides isolation between the RF output signal 12 and a Receive (RX) signal 11 from the antenna 4, while passing the RF output signal 12 to the antenna 4. PA3 is powered by an envelope tracking supply voltage VCC that tracks the amplitude of the envelope of the RF input signal 17. The level of the supply voltage VCC is important because it affects the balance between PA3 power efficiency and linearity. In general, if the supply voltage is low, PA3 operates with lower headroom and thus higher efficiency but higher distortion. Conversely, if the supply voltage value is set higher, PA3 operates with higher headroom and thus lower efficiency, but the additional headroom allows for lower distortion levels.

The digital baseband transmit signal 1 is also fed to an amplitude estimator 13. The amplitude estimator 13 determines the envelope amplitude of the RF input signal 17 and generates an input amplitude signal 110 indicative of the amplitude of the RF input signal 17. The amplitude estimator 13 first uses the formula "amplitude ═ sqrt (I)²+Q²) "to estimate the amplitude of the digital transmission signal 1, where I and Q are the in-phase and quadrature components of the digital baseband transmission signal 1, respectively. The amplitude estimator 13 then adds the gain of the variable gain RF up-converter 2, as indicated by the gain control signal 16, to this result. Since the gain of the variable gain RF up-converter 2 is controlled by the transmit modulator 10, the gain control signal 16 is also fed to the amplitude estimator 13 so that the amplitude estimator 13 knows the gain of the variable gain RF up-converter 2.

The power supply control block 104 receives the input amplitude signal 110 and generates the power supply control signal 18 as a function of changes in the amplitude of the RF input as indicated by the input amplitude signal 110. The power supply control block 104 takes into account the different operating conditions of the RF PA system when generating the power supply control signal 18. Examples of operating conditions include: the ambient temperature of the RF PA system, the operating frequency of the RF PA system (e.g., RF carrier frequency), the modulation format of the baseband signal 1 (e.g., orthogonal frequency division multiplexing, phase shift keying), the amount of antenna mismatch at the output of the PA3 (e.g., output impedance mismatch), and various environmental factors. The power supply control block 62 may generate the power supply control signal 18 using a look-up table that references the power supply voltage value of the power supply control signal 18 to the magnitude value of the input magnitude signal 110. Alternatively, the power supply control block 104 may use an equation that calculates the value of the power supply control signal 18 from the input amplitude signal 110.

The ET power supply 8 controls the level of the power supply voltage VCC according to the power supply control signal 18. Examples of the ET power supply 8 include a linear regulator, a switching power supply, and a hybrid power supply using both the linear regulator and the switching power supply. Referring briefly to fig. 2, a graph of the relationship between the RF input power of the PA3 and the supply voltage VCC (which corresponds to the supply control signal 118) is shown, according to an embodiment. The horizontal axis represents the RF input power to the PA, which corresponds to the amplitude of the RF input signal 17. The vertical axis represents the supply voltage VCC of PA 3. When the RF input power is greater than-5 dBm, the supply voltage VCC is controlled in an envelope tracking manner such that the supply voltage VCC substantially tracks the RF input power. Note that when the RF input power is less than-5 dBm, the supply voltage VCC remains substantially constant at a minimum level of 1.2V so that the PA3 can properly maintain the bias voltage.

Referring back to fig. 1, the decoupler 22 and the characterization block 102 form a feedback path that is used to characterize the RF PA system and generate the characterization table 33. The decoupler 22 provides a coupled version 23 of the RF output signal 12 to a feedback receiver 24. The feedback receiver 24 estimates the amplitude of the RF output signal 12 by: down converting the coupled output signal 23, demodulating the down converted signal, and using the formula "amplitude ═ sqrt (I)²+Q²) To estimate its amplitude. The feedback receiver 24 then generates an output amplitude signal 42 indicative of the amplitude of the RF output signal 12.

The characterization block 102 receives the output amplitude signal 42, the RX signal 11, and other information and uses these inputs to measure the performance characteristics of the RF PA system (e.g., gain, power efficiency, distortion, receive band noise). Examples of performance characteristics include gain, power efficiency, distortion, and receive band noise, among others.

Performance characteristics are measured across many different RF input levels and supply voltage values for different levels (e.g., different sizes or states) of operating conditions of the RF PA system. The characterization block 102 then generates one or more characterization tables 33 that include characterization information describing the relationship between the different RF input levels, supply voltage values, operating condition levels, RF output levels, and measured performance levels of the RF PA system. The characterization table 33 may be stored in a memory, such as a non-volatile memory.

The following table is an example of entries (entries) that can be seen in the characterization table.

TABLE 1

RF input

VCC value

Temperature of

Frequency of

RF output

Gain of

Efficiency of

5dBm

2.4

20℃

1700MHz

25dBm

20dBm

50％

5dBm

2.5

20℃

1700MHz

25.1dBm

20.1dBm

51％

5dBm

2.4

20℃

1720MHz

25dBm

20dBm

53％

5dBm

2.5

20℃

1720MHz

25.1dBm

20.1dBm

51％

0dBm

2.4

20℃

1700MHz

20dBm

20dBm

49％

0dBm

2.5

20℃

1700MHz

20dBm

20dBm

48％

The operating conditions in table 1 include temperature and frequency. The performance characteristics in table 1 include gain and power efficiency. Table 1 shows only a small portion of the characterization table 33. In practice, the characterization table 33 may have hundreds or more different entries distributed across one or more tables that capture different combinations of RF input amplitude, supply voltage values, operating condition levels, performance characteristics, and RF output amplitude. In one embodiment, the characterization table 33 may include equations that relate the RF input amplitude, the supply voltage value, to the RF output amplitude and the performance characteristic for a given operating condition. The equation can calculate the performance characteristics of the RF PA system from variations in different operating conditions, RF input amplitude, and supply voltage.

The characterization information in characterization table 33 is used by power supply control block 104 to determine values of power supply control signal 18 that balance power efficiency and distortion for the current level of one or more operating conditions (e.g., temperature, frequency, modulation, impedance mismatch) of the RF PA system. Because the characterization table 33 is generated locally at the RF PA system during normal operation of the RF PA system, it allows the power supply control block 104 to control the supply voltage VCC in a manner that more accurately balances power efficiency and distortion to accommodate true operating conditions than would otherwise be possible.

In an embodiment, a delay alignment block (not shown) may also insert a time delay at the ET supply 8 or within the variable gain up-converter 2 to ensure proper time synchronization between the supply voltage VCC and the amplitude of the RF output signal 12.

Fig. 3 illustrates a more detailed view of the RF PA system of fig. 1 in accordance with an embodiment. The power supply control block 104 includes a look-up table (LUT) builder block 302, a LUT, a supply voltage adjustment block 314, and a digital-to-analog converter (DAC). The LUT references the digital supply voltage value as an amplitude level of the amplitude signal 110. For example, the LUT may have 32 entries for supply voltage values that correspond to RF input power levels of-21 dB to +10dBm spaced apart by 1 dB.

The initial supply voltage values in the LUT are typically determined in the factory by characterization of a typical PA on a typical radio under typical conditions. The LUT may be populated with this set of nominal supply voltage values, which are adapted to various values of the desired RF output 12 signal amplitude based on the desired gain of the PA under nominal conditions.

The LUT outputs a supply voltage value 312 that is adjusted by a supply voltage adjustment circuit 314 to an adjusted supply voltage value 316. The operation of the voltage adjustment circuit 114 will be described in more detail below with reference to the characterization block 102. The adjusted power supply voltage value 316 is converted to an analog power supply control signal 18 using a digital-to-analog converter DAC. The power supply control signal 18 controls the ET power supply 8 to output a specific power supply voltage VCC level for supplying power to the PA 3.

During actual operation of the radio, the PA3 may exhibit different characteristics than those during typical PA3 operation in the factory, depending on factors such as PA processing and manufacturing tolerances, power supply circuit variations, environmental factors, temperature, operating frequency, modulation format, antenna mismatch, to name a few. Due to these unpredictable characteristic variations, the default LUT entries may not be well suited for operating the RF PA system at the target power efficiency and distortion level. To account for these variations, the characterization block 102 characterizes the RF PA system by perturbing (perturbing) the system with small variations in the supply voltage VCC so as not to cause excessive distortion in the RF PA system, while also measuring performance characteristics of the RF PA system. The process is repeated for different operating condition levels and amplitudes of the RF input signal 17 to generate the characterization table 33. The LUT builder 302 then uses the characterization table 33 to change and refine (refine) the values in the LUT.

Alternatively, instead of perturbing the supply voltage VCC, other embodiments may introduce a perturbation to the RF input signal 17 and measure the performance characteristic while perturbing the RF input signal 17.

The characterization block 102 includes a table generation block 322, a distortion estimator 324, an efficiency estimator 326, and a noise estimator 352. Characterization generally occurs when the RF PA system is operating in normal transmit operation, without an offline calibration mode. In other words, the characterization occurs when the transmit modulator 10 is generating a baseband signal 1 comprising information to be transmitted to the remote device. The baseband signal 1 is converted to an RF input signal 17 and amplified to an RF output signal 12. The RF input amplitude is provided to the LUT, which outputs a supply voltage value 312 using the initial LUT value. At the same time, table generation block 322 also generates a voltage adjustment signal 318, the voltage adjustment signal 318 specifying a target adjustment level (e.g., a multiplication factor) for the supply voltage VCC. The supply voltage adjustment circuit 314 then adjusts the supply voltage value 312 to an adjusted supply voltage value 316, which is converted to the supply control signal 18.

Reference is briefly made to the waveforms illustrated in fig. 4, which illustrates the adjustment of the supply voltage VCC during characterization according to one embodiment. Fig. 4 includes a waveform of the RF output signal 12 and a waveform of the supply voltage VCC, which tracks the amplitude of the RF output signal 12. Prior to time T1, the power supply voltage VCC is generated using the default power supply voltage value 312 without any adjustment. At time T1, the brownout power supply voltage value 312 is adjusted by the voltage adjustment signal 318, which results in a discontinuity in the supply voltage VCC. The discontinuity is small enough that any distortion in the RF output signal 12 still falls below the threshold required to adjust the amplitude or phase error. After time T1, the generation of the supply voltage VCC continues by adjusting the default LUT values. This adjustment results in a slight increase in the supply voltage VCC after time T1. In other embodiments, the adjustment may result in a decrease in the supply voltage VCC instead of an increase in the supply voltage VCC.

Referring back to fig. 3, the efficiency estimator block 326 estimates the power efficiency of the PA3 associated with the adjusted supply voltage VCC and generates a power efficiency signal 334 indicative of the estimated power efficiency. In one embodiment, the efficiency estimator 40 estimates the power efficiency using the following equation:

(formula 1)

Pout is the power at the PA output. Pout is determined by squaring the RF output amplitude (indicated by output amplitude signal 42). Mismatch is a factor representing impedance Mismatch at the PA output. The Mismatch may be a fixed or variable value that is empirically determined based on an impedance Mismatch calculated from the power ratio and phase difference between forward and reverse power detected using forward and reverse connected directional couplers (not shown) coupled to the output of the PA 3. Pconsumed is the power consumed by PA 3. Pconsummed is determined by sampling the current and voltage supplied to PA3 via sampling signal 332 obtained from sampling circuit 340, and then multiplying the sampled current and sampled voltage. In another embodiment, sampling circuit 340 only samples the supply current, and not the supply voltage VCC, since the level of the supply voltage VCC is known at any given time.

The distortion estimator block 324 estimates the distortion of PA3 associated with the adjusted supply voltage VCC and generates one or more distortion signals 336 indicative of the estimated distortion level. In one embodiment, the distortion estimator block 324 receives a baseband signal 1 that includes desired transmit information. Distortion estimator block 324 compares the amplitude of baseband signal 1 with the RF output amplitude (indicated by output amplitude signal 42) to estimate the distortion of PA 3. A larger difference between the desired transmit signal and the RF output amplitude indicates a higher amount of distortion.

In another embodiment, the distortion estimator block 324 stores samples of the RF output magnitude over time and determines the AM-AM distortion (i.e., magnitude distortion) or AM-PM distortion (i.e., phase distortion) of the PA from the samples. The AM-AM distortion is calculated as the ratio of the RF output amplitude change to the supply voltage VCC change. The AM-PM distortion is calculated as the ratio of the measured RF output phase change to the supply voltage VCC change. Ideally, the AM-AM distortion and AM-PM distortion should be flat (flat). In another embodiment, the distortion estimator block 324 may measure distortion in the form of adjacent channel leakage power (ACP).

In some embodiments, the distortion may be represented by a polynomial that accounts for memory effects of the RF PA system. Memory effects refer to the fact that past conditions in an RF PA system may affect the current distortion level in the RF PA system.

Noise estimator block 352 receives RX signal 11 and estimates received band noise 352 in RX signal 11. Changing the supply voltage VCC 340 to PA3 may sometimes introduce noise into the RX signal 11. The noise estimator block estimates the noise and then generates a noise estimate signal indicative of the level of the receive band noise 352.

Table generation block 322 receives input amplitude signal 110, output amplitude signal 42, distortion signal 336, power efficiency signal 326, and noise estimate signal 353. The table generation block 322 generates entries in the characterization table 33 that correlate RF input amplitude, supply voltage value for the adjusted supply voltage VCC, RF output amplitude, operating condition level, and performance characteristic level (e.g., gain, power efficiency, distortion, noise). This process may be repeated multiple times for different RF input magnitudes, different power supply voltage values, and different operating condition levels to generate many different table entries. The result is a set of characterization information that describes the relationship between RF input amplitude, supply voltage value, RF output amplitude, operating conditions, and performance characteristics, for example, as shown in table 1.

In one embodiment, table generation block 322 estimates the gain of PA3 based on input amplitude signal 110 and output amplitude signal 42. In other embodiments, the table generation block 322 may obtain the magnitude information of the RF input signal directly from the LUT and use the magnitude information to estimate the gain.

Once the characterization table 33 is created, the LUT builder 302 utilizes the characterization table 33 to generate a new set of supply voltage values 312 for the LUT according to current operating conditions (e.g., temperature, frequency, modulation, mismatch) currently present in the system. For example, the LUT builder 302 may receive a signal indicating that the current operating conditions are a temperature of 25 degrees celsius, a carrier frequency of 1700MHz, a modulation type PSK, and a zero impedance mismatch. The LUT builder 302 then generates a supply voltage value 312 for the set of current operating conditions. In some embodiments, the LUT builder block 302 may generate a more complex LUT using one or more operating conditions as inputs to the LUT.

The supply voltage values 312 may be interpolated (interpolated) or extrapolated (interpolated) according to the information in the characterization table 33. Alternatively, the new supply voltage values 312 for the LUT may be generated using the formulas in the characterization table 33.

In an embodiment, LUT builder 302 generates a LUT that keeps the RF PA system operating within a range of target performance levels under current operating conditions. For example, the LUT may be generated such that PA3 produces distortion within an acceptable target range and also has power efficiency within the acceptable target range. The LUT builder 302 may also generate LUTs that keep the RF PA system operating at a particular target performance level. For example, the LUT may be generated such that PA3 has a constant gain. As another example, the LUT may be generated such that PA3 has constant AM-AM distortion.

Fig. 5 illustrates a method of operation in an RF PA system in accordance with an embodiment. In step 502, the LUT is populated with an initial set of supply voltage values 312. The initial value is generally a generic value suitable for a typical radio under typical operating conditions. In step 504, the RF PA system operates in normal transmit operation by generating a baseband signal 1 to be transmitted to the remote device through the antenna 4 using the desired transmit information. The RF PA system also uses the initial set of supply voltage values 312 in controlling the supply voltage VCC.

In step 506, the characterization block 102 characterizes the RF PA system during an initial period of time in which the RF PA system is operating in normal transmit operation without interrupting operation of the RF PA system. The characterization block 102 adjusts the supply voltage value 312 in order to adjust the supply voltage VCC. The characterization block 102 evaluates the resulting performance (e.g., power efficiency, distortion, and receive band noise) associated with the adjusted supply voltage VCC. The characterization block 102 then generates a new entry for the characterization table 33.

In step 508, once characterization is complete, the power control block 104 uses the characterization table 33 to generate a new power supply voltage value 312 for the LUT. In step 510, the new supply voltage value 312 for the LUT is then used to control the supply voltage control signal 18, and thus also the supply voltage VCC, during a later time period. Steps 506, 508 and 510 may also be repeated at periodic intervals to capture any changes in the RF PA system characteristics that may occur over time and further refine the LUT.

Fig. 6 shows the adjustment of the supply voltage VCC during characterization according to another embodiment. Fig. 6 includes waveforms for the supply voltage VCC, the amplitude of the RF input signal 17, and the supply current to PA 3. The baseband signal 1 is generated with a randomized (e.g. random or pseudo-random) pattern (pattern), which results in the RF input signal 17 also having the same randomized pattern in amplitude. The randomized pattern of the baseband signal 1 is such that the amplitude of the RF input signal 17 alternates between a reset position with a fixed amplitude and a randomized position with a random amplitude. The supply voltage VCC has different randomized patterns. The randomized pattern of the supply voltage VCC also alternates between a reset position with a fixed voltage level and a randomized position with a random voltage level. Each new amplitude of the RF input signal 17 corresponds to a different level of the supply voltage VCC. The randomized pattern speeds up the construction of the characterization table 33 and can be generated in a specialized offline characterization mode. As previously described, the characterization block 102 estimates the power efficiency and distortion level for different RF input magnitudes and supply voltage VCC levels to generate new entries for the characterization table 33.

Further additional alternative structural and functional designs of RF PA systems according to the present application will be appreciated by those skilled in the art upon review of the present application. Thus, while particular embodiments and applications of the present application have been illustrated and described, it is to be understood that the embodiments are not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations which will be apparent to those skilled in the art may be made in the arrangement, operation, and details of the method and apparatus of the present application without departing from the spirit and scope of the present disclosure as defined in the appended claims.

Claims (18)

1. A radio frequency power amplifier system, comprising:

a power amplifier for generating a radio frequency output signal from a radio frequency input signal, the power amplifier being powered by a supply voltage;

a characterization block to generate an adjustment signal to adjust the supply voltage during a first time period, and to generate characterization information as the supply voltage is adjusted during the first time period, the characterization information corresponding to a plurality of levels for one or more operating conditions of the radio frequency power amplifier system, a relationship between the supply voltage and a performance of the radio frequency power amplifier system;

an amplitude estimator block for estimating an amplitude of the radio frequency input signal; and

a power supply control block to generate a supply voltage control signal to control the supply voltage to the power amplifier based on initial supply voltage values in a lookup table and the amplitude of the radio frequency input signal during the first time period and to generate the supply voltage control signal based on the characterization information and the amplitude of the radio frequency input signal during a second time period.

2. The radio frequency power amplifier system of claim 1 further comprising a feedback block for estimating a magnitude of the radio frequency output signal, the characterization block configured to generate the characterization information based on the magnitude of the radio frequency output signal.

3. The radio frequency power amplifier system of claim 1 wherein the characterization block estimates performance of the radio frequency power amplifier system across multiple levels of the supply voltage and generates the characterization information based on the estimated performance of the radio frequency power amplifier system.

4. The radio frequency power amplifier system of claim 1 wherein the characterization block generates the characterization information during normal transmit operation of the radio frequency power amplifier system.

5. The radio frequency power amplifier system of claim 1 wherein the characterization block generates the characterization information when the supply voltage and radio frequency input signal are provided with a randomized pattern.

6. The radio frequency power amplifier system of claim 1 wherein the power supply control block generates the lookup table based on the characterization information and generates the supply voltage control signal based on a value in the lookup table that corresponds to a magnitude of the radio frequency input signal.

7. The radio frequency power amplifier system of claim 1 wherein the power supply control block generates the supply voltage control signal based on a current level of an operating condition of the radio frequency power amplifier system.

8. The radio frequency power amplifier system of claim 1 wherein the characterization information corresponds to a relationship between the supply voltage and a gain of the power amplifier for a plurality of levels of one or more operating conditions of the radio frequency power amplifier system.

9. The radio frequency power amplifier system of claim 1 wherein the characterization information corresponds to a relationship between the supply voltage and a power efficiency of the radio frequency power amplifier system for a plurality of levels of one or more operating conditions of the radio frequency power amplifier system.

10. The radio frequency power amplifier system of claim 1 wherein the characterization information corresponds to a relationship between the supply voltage and distortion of the radio frequency power amplifier system for a plurality of levels of one or more operating conditions of the radio frequency power amplifier system.

11. The radio frequency power amplifier system of claim 1 wherein the characterization information corresponds to a relationship between the supply voltage and receive band noise in the radio frequency power amplifier system for a plurality of levels of one or more operating conditions of the radio frequency power amplifier system.

12. The radio frequency power amplifier system of claim 1 wherein the operating condition of the radio frequency power amplifier system is at least one of temperature, operating frequency, modulation format, and antenna mismatch.

13. A method of operation in a radio frequency power amplifier system, the method comprising:

generating, by a power amplifier, a radio frequency output signal based on a radio frequency input signal;

generating an adjustment signal for adjusting a supply voltage to the power amplifier during a first time period;

generating characterization information as the supply voltage is adjusted during the first time period, the characterization information corresponding to a relationship between the supply voltage to the power amplifier and a performance of the power amplifier for a plurality of levels of operating conditions of the radio frequency power amplifier system;

estimating the amplitude of the radio frequency input signal;

generating a supply voltage control signal based on an initial supply voltage value in a lookup table and a magnitude of the radio frequency input signal during the first time period, the supply voltage control signal to control the supply voltage to the power amplifier; and

generating the supply voltage control signal based on the characterization information and an amplitude of the radio frequency input signal during a second time period.

14. The method of claim 13, further comprising estimating an amplitude of the radio frequency output signal, the characterization information being generated based on the amplitude of the radio frequency output signal.

15. The method of claim 13, further comprising estimating performance of the radio frequency power amplifier system across multiple levels of the supply voltage, the characterization information generated based on the estimated performance of the radio frequency power amplifier system.

16. The method of claim 13, wherein the characterization information is generated during normal transmit operation of the radio frequency power amplifier system.

17. The method of claim 13, wherein the characterization information is generated when the supply voltage and radio frequency input signal are provided with a randomized pattern.

18. The method of claim 13, wherein generating a power supply control signal comprises: generating the lookup table based on the characterization information; and generating the supply voltage control signal based on a value in the look-up table corresponding to the amplitude of the radio frequency input signal.