GB2505471A

GB2505471A - Time alignment of envelope and main signal paths in an envelope-tracking transmitter

Info

Publication number: GB2505471A
Application number: GB201215529A
Authority: GB
Inventors: Markus Nentwig; Christian Jung; Maarit Inka Susanna Melvasalo
Original assignee: Broadcom Corp
Current assignee: Broadcom International Ltd; Broadcom Corp
Priority date: 2012-08-31
Filing date: 2012-08-31
Publication date: 2014-03-05
Also published as: GB201215529D0; WO2014033661A1

Abstract

To achieve delay matching in an envelope-tracking transmitter, a two-tone test signal (figure 7A) is applied to the main signal path while a corresponding single-tone test signal (figure 7B) is applied to the envelope path. The amplitudes of the two test tones in the RF path are opposite and equal so that the respective modulation products generated by the power amplifier at a selected output measurement frequency cancel if the delays in the main and envelope paths are matched.Â An adjustable delay is varied to obtain a minimum in the output signal at the measurement frequency (figure 4).

Description

Delay Estimation

Technical Field

The present disclosure relates to delay estimation. Tn particular, but not exclusively, the present disclosure relates to measures for reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter.

Background

Figure 1 shows an envelope tracking wireless transmitter. The wireless transmitter comprises a power amplifier (PA) which generates an output signal. The wireless transmitter uscs a modulated PA supply voltage provided by a switched mode power supply (SMPS) to improve efficiency by reducing current consumption.

The SMPS may also comprise some non-switched circuitry, for example to improve wavefomi accuracy at high frequencies. The modulated PA supply voltage carries some modulation information. A radio frequency (RE) signal is provided to the PA via a radio frequency input of the PA. An envelope signal is provided to the PA via an envelope input of the PA. An envelope signal is provided via an envelope path (upper branch in Figure 1). An RE signal is provided via an RE path (lower branch in Figure 1) A delay mismatch between the RE path and the envelope path causes degradation of signal quality, for example distortion at frequencies outside the wanted bandwidth of the output signal. The delay mismatch depends on component and manufacturing tolerances, for example the accuracy of component placement in a soldering process for a printed wiring board of a wireless transmitter. The delay mismatch needs to be calibrated individually for each manufactured device.

For example, in an envelope tracking transmitter for LTE 20 MHz mode, the delay mismatch should be controlled with ns accuracy. This is a shorter time than a typical sampling period used for digital signal processing in a typical transmitter, for example a 100 MHz rate gives a 10 ns sample duration.

Since delay calibration is necessary, the delay between the envelope path and the radio frequency path should be estimated. However, in many cases, the modulated supply voltage of the power amplifier may not be directly accessible for measurement, as it may be confined inside a sealed module, so cannot be used for delay estimation.

One known approach involves direct time-domain analysis of the SMPS S output which involves measuring the waveform delay with an oscilloscope. This approach may be sufficient for a 200 kHz 2G signal, but becomes difficult in 3G and later systems that utilize a much higher bandwidth (for example LTE2O). Other disadvantages of this approach include the fact that that it requires a fast (and therefore expensive) oscilloscope or comparator to capture the PA output signal at RF, it requires access to the modulated PA supply vohage and is difficult to automate.

Another known approach involves measuring a distortion product of a test signal and calibrating a dclay clcmcnt to minimize thc mcasurcd distortion product.

The measurement could be carried out either using a spectrum analyser or with an RFIC's own receiver, using a high (envelope) bandwidth test signal. Any timing mismatch will increase the measured wideband noise level and the timing offset can be for example reduced by minimizing the noise in the received band. The approach has a low accuracy as the noise contribution should be approximately 10dB below the receiver's own noise floor in order not to impair sensitivity. Other disadvantages of this approach include the fact that the method requires widcband measurements and long-term averaging, making it expensive, slow and difficult to perform without test equipment external to the wireless transmitter.

It would therefore be desirable to provide robust measures for delay estimation of the envelope path of a wireless transmitter, including, for example, measures which do not rcquirc acccss to thc modulated supply voltage of the power amplificr.

Summary

In accordance with a first aspect of the present disclosure, there is provided a method for reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, the radio frequency path and the envelope path being combined into an output signal, the method comprising: applying a first test signal to the radio frequency path; applying a second test signal to the envelope path; detecting a magnitude associated with the output signal; and configuring at least one of the radio frequency path and the envelope path to reduce the detected magnitude.

S In accordance with a second aspect of the present disclosure, there is provided apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, the radio frequency path and the envelope path being combined into an output signal, the processing system being adapted to: apply a first test signal to the radio frequency path; apply a second test signal to the envelope path; detect a magnitude associated with the output signal; and configure at least one of the radio frequency path and the envelope path to reduce the detected magnitude.

In accordance with a third aspect of the present disclosure, there is provided apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, substantially in accordance with any of the examples as described herein with reference to and illustrated by the accompanying drawings.

In embodiments, the apparatus is comprised in an ASIC or an FPGA.

In accordance with a fourth aspect of the present disclosure, there is provided computer software adapted to perform the method of the first aspect of the present

disclosure.

Embodiments comprise a computer program product comprising a non-transitory computer-readable storage medium having computer readable instructions stored thereon, the computer readable instructions being executable by a computerized device to cause the computerized device to perform the method of the first aspect of

the present disclosure.

Further features and advantages of embodiments will become apparent from the following description of preferred embodiments, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 shows an envelope tracking wireless transmitter according to the

prior art;

Figure 2 shows an envelope tracking amplifier according to embodiments; S Figure 3 depicts spectra of a fir st test signal, a second test signal and the resulting output signal according to embodiments; Figure 4 depicts the detected magnitude of one or more components in an example output signal plotted against the delay offset according to embodiments; Figure 5 depicts the detected magnitude of one or more components in an example output signal plotted against the delay offset according to embodiments; Figure 6 depicts a measurement receiver and associated detection apparatus according to embodiments; Figure 7 depicts spectrums of first and second test signals and resulting output signal components according to embodiments; Figure 8 shows a plot of a fast fourier transform (FFT) of a measured PA output signal according to embodiments.

Figure 9 shows a plot of detected magnitude in the output signal at a given target frequency against delay offset according to embodiments; Figure 10 shows a plot of two output signal detection results at different target frequencies where the first test signal applied to the RE path comprises two pairs of test tones according to embodiments; Figure 11 shows voltage-current characteristics of the PA of the wireless transmitted according to embodiments; and Figurc 12 shows a flow diagram according to cmbodiments.

Detailed Description

In general, the output signal of a PA in a wireless transmitter can be accessed and can therefore be used for the purposes of delay estimation. Embodiments of the present disclosure provide delay estimation of the envelope path of a wireless transmitter based on the radio frequency output signal of the PA.

Embodiments comprise measures, including methods, apparatus, computer software and computer program products, for reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter. The radio frequency path and the envelope path are combined into an output signal; in embodiments, the radio frequency path and the envelope path arc combincd into the output signal by a powcr amplifier. A first tcst signal is applied S to the radio frequency path and a second test signal is applied to the envelope path. A magnitude associated with the output signal is detected and at least one of the radio frequency path and the envelope path are configured to reduce the detected magnitude.

Embodiments optimize the delay using the full transmitter, taking also delays internal to the PA and the interconnects between into account. The detection is performed directly where the delay error manifests itself which would not the case for a measurement taking place on the cnvelopc signal; embodiments therefore provide more accurate delay estimation.

In embodimeilts, the configuring comprises adjusting a variable delay between the envelope path and the radio frequency path. The adjusting may for example comprise adjusting the variable delay to minimize the detected magnitude.

In embodiments, the configuring comprises configuring a signal processing unit in at least one of the radio frequency path and the envelope path which provides a differential delay between the radio frequency path and the envelope path.

Figure 2 shows an envelope tracking amplifier of a wireless transmitter according to embodiments. The wireless transmitter may for example comprise the wireless transmitter of Figure 1. The envelope tracking amplifier comprises a PA which is provided with a modulated power supply voltage by an enyelope modulator, for example a SMPS. A first tcst signal (denoted envelope input' in Figure 2) is applied to the SMPS of the envelope path and a second test signal (denoted radio frequency input' in Figure 2) is applied to the RF path. The output signal ofthe PA is used to cstimatc thc dclay mismatch bctwccn a radio frequency path and an cnvclopc path of the wireless transmitter. In embodiments, the magnitude comprises a power or a square root of a power, for example the absolute power of one or more FF1 bins of the output signal.

In embodiments, the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination. The at least one product component may for example comprise one or more nonlinear product components.

A simple, linearized model for the PA is: output = inputRF * (I -I-inputEnv) where output, inputRF and inputEnv may be voltages or currents, for example.

The output contains a combination product between inputkF and inputEnv, plus inputRE passing through directly. The multiplication between inputRE and inputEnv causes one or more product components (or mixing products') between spectral components of inputRF and inputEnv. In embodiments, the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination.

In embodiments, the tcst signals are constructed in such a way that two mixing products overlap on the test frequency and cancel, as long as there is no delay difference between the signals.

1 5 In embodiments, the magnitude of the at least one product component is detected in the output signal at a given target frequency.

In embodiments, the first test signal comprises a spectral null at the given target frequency.

In embodiments, the first test signal comprises a multi-tone signal, for example comprising a first test tone and a second test tone.

In embodiments, a first Fourier coefficient of the first test tone has the same magnitude and opposite sign of a second Fourier coefficient of the second test tone.

Such features mean that the resulting mixing products have opposite sign, so they cancel cach other out at the target frequency instead of adding up (i.e. they destructively interfere as opposed to constructively interfere).

In embodiments, at least one of the first test signal and the second test signal comprises a cyclic signal. In embodiments, both the first and second test signals comprise cyclic signals. The first and second Fourier coefficients may be defined by a Fourier transform performed over a cycle length that is common to first and second test tone.

Figure 3 depicts spectra of a first test signal, a second test signal and the resulting output signal according to embodiments.

Figure 3A depicts the spectrum of a first test signal which is applied to the radio frequency path according to embodiments. In these embodiments, the first test signal comprises a cyclic signal including a test tone (a) and a test tone (b). Both the amplitude and phase of test tone (a) and a test tone (b) can be chosen freely, for example complex-valued baseband signals modulated to a radio frequency carrier.

Figure 3B depicts the spectrum of a second test signal which is applied to the envelope path according to embodiments. In these embodiments, the second test signal comprises a cyclic signal including a test tone (c) and a test tone (d). In these embodiments, the second test signal is real-valued such that its spectrum is Hermitian symmetric around 0 Hz.

Figure 3C depicts the spectrum of the output signal produced when first and second tcst signals as per Figures 3A and 3B are applied to the radio frequency path and the envelope path respectively of a wireless transmitter according to embodiments. As can be seen, a product component (ac) is produced in the output 1 5 from test tone (a) and test tone (c). A further product component (bd) is produced in the output from test tone (b) and test tone (d). However, at a given target frequency (denoted test frequency' in Figure 3C), product component (ad) and product component (b) add on top of each other and cancel each other out.

In embodiments, the sign of test tone (b) is chosen so that product component (ad) cancels out product component (be) at the given target frequency.

In embodiments, test tone (a) and test tone (b) are chosen so that they cancel each other out at optimum delay. The delay mismatch is thus minimized by measuring and minimizing the magnitude (for example power) of the output signal of the PA, in this case at the given target frequency.

Figure 4 depicts the detected magnitude (y-axis) of one or more product components in an example output signal plotted against the delay offset (x-axis) according to embodiments. In this case, the fhndamental frequency of the envelope signal has a length of 16 samples and the magnitude comprises a power in dBs. As shown by item 400, at the given target frequency, the detected power is approaches zero which means that the delay is aligned. Note that, as shown by items 402 and 404, there arc ambiguities at +1-n (=8 in this example) complete cycles where the detected power approaches zero, but the actual delay will be much smaller than this, so such ambiguities can be ignored.

FigureS depicts the detected magnitude (y-axis) of one or more components in an example output signal plotted against the delay offset (x-axis) according to embodiments. In this case, the fundamental frequency of the envelope signal has a length of 8 samples. In these embodiments, the sensitivity (for example defined by change in power divided by change in delay = S power / S delay) has been increased by using a higher-frequency second test signal applied to the envelope path. By doubling the fundamental frequency of the envelope test signal, the distance between adjacent minima of the detected product power as a function of delay mismatch is reduced by a factor of two, which means that the width of the target "notch" at zero dclay mismatch (i.c. zcro offsct) is half thc size than in the cmbodimcnts of Figurc 4.

In embodiments, the output signal of the PA is measured with a measurement receiver. The measurement receiver could for example employ the same subsystem 1 5 that is used for forward/reflected power measurements within the wireless transmitter.

In embodiments, the first test signal and the second test signal comprise cyclic signals having a common cycle length.

Figure 6 depicts a measurement receiver and associated detection apparatus according to embodiments. In these embodiments, the output of the measurement receiver is multiplied with a complex-valued rotating phasor signal, for example provided by an NCO, corresponding to the target frequency (of opposite sign). The signal produced by the multiplying is then integrated (by element sum' in Figure 6) over Ic fill periods. The delay is adjusted to minimize the magnitude (calculated by clcmcnt abs' = absolute valuc in Figure 6) of the integration rcsult.

Embodiments involve narrow-band power measurement around the target frequency. Such narrow-band measurement effectively rejects noise at any other frequency (note, when averaging k cycles of in samples each, the output is identical to one bin from a km-size FFT, and the effective measurement bandwidth is BWN = 1/(kinfl, with T being the cycle length. For example in = 52, T = 1 / 52 Msps, k = 100, results in BWN = 10 kFlz, centered around the test tone frequency (IMFIz, for example). The implementation of such a narrow bandpass filter by other means Figure 7 depicts spectrums of first and second test signals and resulting output signal product components according to embodiments.

Figure 7A depicts the spectrum of a first test signal which is applied to the radio frequency path according to embodiments. In this embodiment, the first test signal comprises a multi-tone cyclic signal comprising a test tone pair. The test tone pair comprises a first test tone (t) p) and a second test tone U In this embodiment, the first test tone and the second test tone are spaced 8MHz apart. The carrier channel centre frequency is an example 710 MHz. In embodiments, the given target frequency is located within a bandwidth of the first test signal. In these embodiments, the target frequency is located halfway (or centered') between the frequency of the first test tone and the second test tone of the first test signal.

Figure 7B dcpicts the spectrum of a second test signal which is applied to the envelope path according to embodiments. The second test signal comprises energy at +/-f11, i.e. at a minus' thndamental frequency (in this case -4MHz) and a plus' fundamental frequency (in this case +4MHz). In these embodiments, the second test signal is a real-valued signal at baseband so that its spectrum is Hermitian symmetric about zero Hz (i.e. DC) and has zero imaginary component. In embodiments, the tone spacing between the fir st and second test tones of the first test signal is twice the fundamental frequency of the second test signal.

In the embodiments of Figures 7A and 7B, both the fir st test signal and the second test signal are cyclic with the same cycle length which means that discrete line spectrums are produced in the output. No combination of tones gives a frequency spacing with an odd number of frequency "bins" (for example bin 1). This means that intermodulation products from the power amplifier cannot leak energy into the target bin, making the measurement robust towards unwanted distortion products caused by the PA.

Figure 7C depicts a partial spectrum containing some nonlinear components of the output signal produced when first and second test signals as per Figures 7A and 7B are applied to the radio frequency path and the envelope path respectively of a wireless transmitter according to embodiments. A product component (denoted mixing product A' in Figure 7C) can be seen in a target bin at a target frequency of 4MHz below the frequency of the second test tone. Mixing product A is a down-conversion product component defined -Jz RF:tEnv. Note that the first or second test tone tones do not contain any signal energy at the target frequency, only the mixing product A component appears there.

Figure 7D depicts a partial spectrum containing other nonlinear components of S the output signal produced when fir st and second test signals as per Figures 7A and 7B are applied to the radio frequency path and the envelope path respectively of a wireless transmitter according to embodiments. A product component (denoted mixing product B' in Figure 7D) can be seen in a target bin at a target frequency of 4MHz above the frequency of the first test tone. Mixing product B is an up-conversion product component defined byfj,yj =Jj tt. Again, note that the first or second test tone tones do not contain any signal energy at the target frequency, only thc mixing product B component appears there.

In the embodiments of Figure 7, the combination of RF and envelope paths via the PA causes a multiplication between the multi-tone RF path test signal and the envelope path test signal.

Frequencies for the test signals are selected so that mixing products A and B fall onto the same frequency: /,gcjpJ /) r ttinv tti ia:frnv In embodiments, the magnitude and!or phase of the first and second input tones are selected so that mixing products A and B cancel. Assuming an ideal multiplication in the PA, the magnitudes should be the same. For a real PA with memory effects (possibly magnified by the bias point), cancellation can be improved by scaling the RE tones relative to each other.

Two mixing products (in this case A and B) overlap and cancel each other out if the timing between the test signals is accurate. If the delay between the envelope and RE branches is balanced, mixing products A and B will cancel perfectly; if not, the detected magnitude (for example power) will increase.

In addition to the desired nonlinear mixing product components of the first test signal applied to the RE path and the second test signal applied to the envelope path, nonlinearitics of the power amplifier may also cause other spurious components at other frequencies. Using a common cycle length for both the first and second test signals means that the spurious components will also tend to be cyclic within the same common cycle length. Signal components that are cyclic within a common cycle length but located at different frequencies are orthogonal and can thus be measured without interference from other components.

In embodiments, the magnitude of one or more product component at the target frequency is determined by multiplying the output signal with a complex-valued rotating phasor at a negative frequency of the given target frequency over an integer number of cycles and integrating the product of the multiplication over time.

Figure 8 shows a plot of an FFT of a measured PA output signal according to embodiments. Figure 8 illustrates other mixing products which result from the PA nonlinearity, in this case intermodulation products between the test tones. However, such intermodulation products do not affect the detection result of embodiments as they are orthogonal to desired mixing products at the given target frequency.

In embodiments, the detecting comprises detecting the magnitude of a first product component and a second product component produced in the output signal by the combination and the adjusting comprises adjusting the variable delay to achieve a predetermined ratio between the first product component and the second product component.

In embodiments, the adjusting comprises successively selecting the variable delay at a plurality ofpredetermined delay offsets, for example [-3, -2, 0, 1, 0, 1, 2, 3] ns.

Figure 9 shows a plot of detected magnitude in the output signal at a given target frequency against delay offset (in ns) according to embodiments. In these embodiments, the adjusting comprises successively selecting the variable delay at a plurality of predetermined delay offsets (in this case the offsets, as shown by each plus' point on the curve, are approximately 0.Sns apart); the predetermined offset which produces the smallest detected magnitude (for example power) is then identified as the appropriate delay estimate.

Embodiments where the first test signal comprises a single test-tone pair provide good accuracy. The minimum detected magnitude could for example be found by varying the delay according to a binary search algorithm. However, embodiments where the first test signal consists of a single test-tone pair provide no direction information in terms of which direction the delay should be varied in (i.e. more delay or less delay) in order to reduce the detected magnitude in the output signal.

In embodiments, the first test signal applied to the RE path comprises a plurality of pairs of tcst tones. The pairs of tcst tones arc applied to the RF path at different "test tone" frequencies, resulting in mixing products at different target frequencies. In embodiments, the test tone pairs are delayed relative to each other (in time), so that each gives a minimum at a different delay offset.

The pairs of test tones in the plurality of pairs of test tones may for example be spaced at predetermined frequency separations relative to each other. Each pair of test tones in the plurality of pairs of test tones may for example comprise a tone spacing of twice the fundamental frequency of the second test signal.

In cmbodimcnts, thc dctccting compriscs dctccting a first magnitudc of a first nonlinear product component produced in the output signal by the combination at a first target frequency that is a centre frequency of a first test tone pair in the plurality of pairs of test tones and also detecting a second magnitude of a second nonlinear product component produced in the output signal by the combination at a second target frequency that is a centre frequency of a second test tone pair in the plurality of pairs of test tones. In such embodiments, the configuring is carried out at least on the basis of which of the first magnitude and the second magnitude is lower.

Figure 10 shows a plot of two output signal detection results at different target frequencies, measured simultaneously, where the first test signal applied to the RF path comprises two pairs of test tones according to embodiments. One of the test tone pairs results in the detection result shown in trace 1010, detected at a first target frcqucncy, and thc othcr tcst tonc pair rcsults in thc dctcction result shown in tracc 1020. By measuring two detection results simultaneously, a single measurement provides sign information on the delay mismatch. For example if the detection result of trace 1020 is higher than the detection result of trace 1010, the variable delay can be adjusted towards more positive values. When the detected magnitudes of the blue and black readings are equal, it can be concluded that the delay offset has been correctly estimated. Employing such embodiments can assist in finding the appropriate delay faster, i.e. with a smaller number of measurements. In such embodiments, the adjusting may comprise adjusting the variable delay to achieve a predetermined ratio between first and second product components produced in the output signal by the combination; in this case, the predetermined ratio is 1, but could differ in other embodiments.

Figure 11 shows voltage-current characteristics of a PA of a wireless transmitter according to embodiments. Delay measurement was repeated with different offsets to the PA supply voltage and corresponding delay offset results are plotted in the following table: voltage offset / V measured delay offset / ns o o 0.3 1.4 0.6 4 1 13 The "nominal" PA supply voltage is 0.5 V. As can be seen from Figure 11, the PA gets morc linear as the bias voltage increases. The morc linear the PA becomes, the less nonlinear mixing products are produced. Therefore, embodiments comprise applying a minimum supply voltage to the PA in order to provide a sufficiently nonlinear PA to create the mixing product(s) for delay estimation purposes according to embodiments.

In embodiments, the PA is biased to maximize the nonlinear mixing product(s) produced by the PA when combining the RF test signal(s) and the envelope test signal.

One embodiment uses the highest possible voltage swing that the envelope modulator can provide at the PA. For example a +1-1.5 V sine wave, around a DC voltage of 1.8 V produced an envelope signal that varies between 0.3 V and 3.3 V. Figure 12 shows a flow diagram according to embodiments. Figure 12 depicts measures for reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter. The radio frequency path and the envelope path are combined into an output signal. In item 1200, a first test signal is applied to the radio frequency path. In item 1202, a second test signal is applied to the envelope path. In item 1204, a magnitude associated with the output signal is detected. In item 1206, at least one of the radio frequency path and the envelope path is configured to reduce the detected magnitude.

Embodiments of the present disclosure may be implemented in a wireless transmitter at least in part by computer software stored in memory which is executable by a processor; or by a processing system; or by hardware, or by a combination of tangibly storcd software and hardware (and tangibly stored firmware). According to embodiments, all (or some) circuitries required for the aforementioned flmnctionalities may be embedded in the same circuitry, a system in package, a system on chip, a module, a LTCC (Low temperature co-fired ceramic) or the like. Embodiments may be executed in/by a processing unit in cooperation between a modenVtransceiver and a controller unit or iniby a controller unit of a wireless transmitter.

In embodiments, the wireless transmitter may be comprised in an electronic device or IJE ofa communication system. An electronic device implementing cmbodimcnts need not be the entire UE, but embodiments may be implemented by one or more components of same such as the above described tangibly stored software, hardware, firmware and digital processor (DP), or a system-on-a-chip (SOC) or an application specific integrated circuit ASIC or a digital signal processor (DSP) or a modem or a subscriber identity module (such as a SIM card).

In embodiments, the detection may be performed in a production calibration station for wireless mobile consumer products, for example implemented on an FPGA.

Various embodiments of a UE may include, but are not limited to: mobile (or cellular') telephones (including so-called "smart phones"), data cards, TJSB dongles, personal portable digital devices having wireless communication capabilities including but not limited to laptop/palmtop/tablet computers, digital cameras and music devices, sensor network components and Internet appliances. A liE may also be referred to as a user terminal or endpoint device.

Various embodiments of memories employed in embodiments include any data storage technology type which is suitable for the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like.

Various embodiments of processors employed in embodiments include but are not limited to microprocessors, DSPs, multi-core processors, general purpose computers, and special purpose computers.

It will be understood that any processors or processing system or circuitry referred to herein may in practice be provided by a single chip or integrated circuit or S plural chips or integrated circuits, optionally provided as a chipset, an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), etc. The chip or chips may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry, which are configurable so as to operate in accordance with embodiments. In this regard, embodiments may be implemented at least in part by computer software stored in (non-transitory) memory and executable by the processor, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware).

Although at least some aspects of the embodiments described herein with reference to the drawings comprise computer processes performed in processing systems or processors, embodiments also extend to computer software, computer programs, particularly computer programs on or in a carrier, adapted for putting embodiments into practice. The program may be in the form of non-transitory source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other non-transitory form suitable for use in the implementation of processes according to the invention. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a solid-state drive (SSD) or other semiconductor-based RAM; a ROM, for example a CD ROM or a semiconductor ROM; a magnetic recording medium, for example a floppy disk or hard disk; optical memory devices in general; etc. The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments.

Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

List of acronyms and abbrcviations:

S

2G 211d generation, i.e. GSM 3" generation, i.e. WCDMA ASIC application-specific integrated circuit DC direct current dB decibel EER enyelope elimination and restoration ET envelope tracking FFT fast fourier transform

FPGA field-programmable gate array

GSM Global system for mobile communications kHz kilohertz LTE long term evolution LTE2O 20 MHz mode of LTE MHz megahertz NCO numerically controlled oscillator ns nanosecoild PA power amplifier RF radio frequency RFIC radio frequency intcgratcd circuit SMPS switched mode power supply liE user equipment WCDMA Wideband codc division multiple access CmA

Claims

1. A method lbr reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter the radio frequency path and the envelope path being combined into an output signal, the method comprising: applying a first test signal to the radio frequency path applying a second test signal to the envelope path; detecting a magnitude associated with the output signal; and configuring at least one of the radio frequency path and the envelope path to reduce the detected magnitude.

2. A method according to claim 1, wherein the magnitude comprises a power or a square root of a power.

3. A method according to claim 1 or 2, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination.

4. A method according to claim 3, wherein the magnitude of the at least one product component is detected in the output signal at a given target frequency.

5. A method according to claim 3 or 4, wherein the at least one product component comprises one or more nonlinear product components.

6. A method according to any preceding claim, wherein at least one of the first test signal and the second test signal comprises a cyclic signal.

7. A method according to any of claims 4 to 6, wherein the first test signal comprises a spcctral null at the given target frequency.

8. A method according to any preceding claim, wherein the first test signal comprises a multi-tone signal.

9. A method according to claim 8, wherein the multi-tone fir st test signal comprises a first test tone and a second test tone.

10. A method according to claim 9, wherein the second test signal comprises energy at a fundamental frequency, and wherein the tone spacing between the first and second test tones is twice the fundamental frequency of the second test signal.

11. A method according to claim 4 and claim 9 or 10, wherein the given target frequency is located within a bandwidth of the first test signal.

12. A method according to claim 4 and any of claims 9 to 11, wherein the given target frequency comprises a frequency halfway between the frequency of the first test tone and the frequency of the second test tone.

13. A method according to any preceding claim, wherein the second test signal comprises a real-valued signal.

14. A method according to any preceding claim, wherein the configuring comprises adjusting a variable delay betwecn the cnvclope path and thc radio frequency signal branch.

15. A mcthod according to claim 14, whcrcin the adjusting compriscs adjusting the variable delay to minimize the detected magnitude.

16. A mcthod according to claim 14 or 15, whcrcin thc detccting compriscs dctccting thc magnitudc of a first product component and a sccond product component produced in the output signal by the combination, and wherein the adjusting comprises adjusting the variable delay to achieve a predetermined ratio between the first product component and the second product component.

17. A method according to any of claims 14 to 16, wherein the adjusting comprises successively selecting the variable delay at a plurality of predetermined delay offsets.

18. A method according to any preceding claim, wherein the configuring comprises configuring a signal processing unit in at least one of the radio frequency path and the envelope path, the signal processing unit providing a differential delay between the radio frequency path and thc envelope path.

19. A method according to any preceding claim, wherein the radio frequency path and the envelope path are combined into the output signal by a power amplifier.

20. A method according to any preceding claim, wherein the first test signal and the second test signal comprise cyclic signals having a common cycle length.

21. A method according to any of claims 9 to 20, wherein a first Fourier coefficient of the first test tone has the same magnitude and opposite sign ofa second Fourier coefficient of the second test tone.

22. A method according to any of claims 8 to 21, wherein the multi-tone first test signal comprises a plurality of pairs of test tones.

23. A method according to claim 22, wherein the pairs of test tones in the plurality of pairs of test tones are spaced at predetermined frequency separations relative to each other.

24. A method according to claim 22 or 23, wherein each pair oftest tones in the plurality of pairs of test tones comprises a tone spacing of twice the fundamental frequency of the second test signal.

25. A method according to any of claims 22 to 24, wherein the detecting comprises detecting: a first magnitude of a first nonlinear product component produced in the output signal by the combination at a first target frequency that is a centre frequency of a first test tone pair in the plurality of pairs of test tones; and a second magnitude of a second nonlinear product component produced in the output signal by the combination at a second target frequency that is a centre frcquency of a second test tone pair in the plurality of pairs of test tones; and the configuring is carried out at least on the basis of which of the first magnitude and the second magnitude is lower.

26. A method according to any of claims 4 to 25, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination at the given target frequency by multiplying the output signal with a complex-valued rotating phasor at a negative frequency of the given target frequency over an integer number of cycles and integrating the product of the muhiplication over time.

27. Apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, the radio frequency path and the envelope path being combined into an output signal, the processing system being adapted to: apply a first test signal to the radio frequency path; apply a second test signal to the envelope path; detect a magnitude associated with the output signal; and configure at least one of the radio frequency path and the envelope path to reduce the detected magnitude.

28. Apparatus according to claim 27, wherein the magnitude comprises a power or a square root of a power.

29. Apparatus according to claim 27 or 28, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination.

30. Apparatus according to claim 29, wherein the magnitude of the at least one product component is detected in the output signal at a given target frequency.

31. Apparatus according to claim 29 or 30, wherein the at least one product component coii.piises one or more nonlinear product components.

32. Apparatus according to any of claims 27 to 31, wherein at least one of the first test signal and the second test signal comprises a cyclic signal.

33. Apparatus according to any of claims 30 to 32, wherein the first test signal comprises a spectral null at the given target frequency.

34. Apparatus according to any of claims 27 to 33, wherein the first test signal comprises a multi-tone signaL 35. Apparatus according to claim 34, wherein the multi-tone first test signal comprises a first test tonc and a second test tone.36. Apparatus according to claim 35, wherein the second test signal comprises energy at a fundamental frequency, and wherein the tone spacing bctwecn the first and second test tones is twice the fundamental frequency of the second test signal.37. Apparatus according to claim 30 and claim 35 or 36, wherein the given target frequency is located within a bandwidth of the first test signal.38. Apparatus according to claim 30 and any of claims 35 to 37, wherein the given target frequency comprises a frequency halfway between the frequency of the first test tone and the frequency of the second test tone.39. Apparatus according to any of claims 27 to 38, wherein the second test signal comprises a real-valued signal.40. Apparatus according to any of claims 27 to 39, wherein the configuring comprises adjusting a variable delay between the envelope path and the radio frequency signal branch.41. Apparatus according to claim 40, wherein the adjusting comprises adjusting the variable delay to minimize the detected magnitude.42. Apparatus according to claim 40 or 41, wherein the detecting comprises detecting the magnitude of a first product component and a second product component produced in the output signal by the combination, and wherein the adjusting comprises adjusting the variable delay to achieve a predetermined ratio between the first product component and the second product component.43. Apparatus according to any of claims 40 to 42, wherein the adjusting comprises successively selecting the variable delay at a plurality of predetermined delay offsets.44. Apparatus according to any of claims 27 to 43, comprising a signal processing unit in at least one of the radio frequency path and the envelope path, wherein the configuring comprises configuring the signal processing unit in at least one of the radio frequency path and the envelope path, the signal processing unit being adapted to provide a differential delay between the radio frequency path and the envelope path.45. Apparatus according to any of claims 27 to 44, comprising a power amplifier adapted to combine the radio frequency path and the envelope path into the output signal.46. Apparatus according to any of claims 27 to 45, wherein the first test signal and the second test signal comprise cyclic signals having a common cycle length.47. Apparatus according to any of claims 35 to 46, wherein a first Fourier coefficient of the fir st test tone has the same magnitude and opposite sign of a second Fourier coefficient of the second test tone.48. Apparatus according to any of claims 34 to 47, wherein the multi-tone first test signal comprises a plurality of pairs of test tones.49. Apparatus according to claim 48, wherein the pairs of test tones in the plurality of pairs of test tones are spaced at predetermined frequency separations relative to each other.50. Apparatus according to claim 48 or 49, whercin each pair of test tones in the plurality of pairs of test tones comprises a tone spacing of twice the fundamental frequency of the second test signal.51. Apparatus according to any of claims 48 to 50, wherein the detecting comprises detecting: a first magnitude of a first nonlinear product component produced in the output signal by the combination at a first target frequency that is a centre frequency of a first test tone pair in the plurality of pairs of test tones; and a second magnitude of a second nonlinear product component produced in the output signal by the combination at a second target frequency that is a centre frequency of a second test tone pair in the plurality of pairs of tcst toncs, and wherein the configuring is carried out at least on the basis of which of the first magnitude and the second magnitude is lower.52. Apparatus according to any of claims 30 to 51, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination at the given target frequency by multiplying the output signal with a complex-valued rotating phasor at a negative frequency of the givcn targct frcqucncy ovcr an intcgcr numbcr of cyclcs and intcgrating thc product of the multiplication over time.53. Apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, substantially in accordance with any of the examples as described herein with reference to and illustrated by the accompanying drawings.54. Apparatus according to any of claims 27 to 53, wherein the apparatus comprises an application-specific integrated circuit, ASIC, or a field-programmable gate array, FPGA.55. Computer software adapted to perform the method of any of claims 1 to 26.Amendments to the claims have been tiled as follows: Claims 1. A method for reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, the radio frequency path and the envelope path being combined into an output signal, the method comprising: applying a signal to the radio frequency path which provides a first test signal at radio frequency; applying a second test signal to the envelope path; detecting a magnitude associated with the output signal; and configuring at least one of the radio frequency path and the envelope path to reduce the detected magnitude, wherein the detecting comprises detecting the magnitude of a first product component and a second product component produced in the output signal by the combination, and o wherein the configuring comprises adjusting a variable delay between the LCD envelope path and the radio frequency signal branch to achieve a predetermined ratio C between the first product component and the second product component.2. A method according to claim 1, wherein the magnitude comprises a power or a square root of a power.3. A method according to claim 1 or 2, wherein the detccting comprises detecting the magnitude of at least one product component produced in the output signal by the combination.4. A method according to claim 3, wherein the magnitude of the at least one product component is detected in the output signal at a given target frequency.5. A method according to claim 3 or 4, wherein the at least one product component comprises one or more nonlinear product components.6. A method according to any preceding claim, wherein at least one of the first test signal and the second test signal comprises a cyclic signal.7. A method according to claim 4 and zero or more of claims 5 and 6, wherein the first test signal comprises a spectral null at the given target frequency.8. A method according to any preceding claim, wherein the first test signal comprises a multi-tone signal.9. A method according to claim 8, wherein the multi-tone first test signal comprises a first test tone and a second test tone.10. A method according to claim 9, wherein the second test signal C') comprises energy at a fundamental frequency, and wherein the tone spacing between the first and second test tones is twice the C) o fundamental frequency of the second test signal. U,o 11. A method according to claim 4 and claim 9 or 10, wherein the given target frequency is located within a bandwidth of the first test signal.12. A method according to claim 4 and any of claims 9 to 11, wherein the given target frequency comprises a frequency halfway between the frequency of the first test tone and the frequency of the second test tone.13. A method according to any preceding claim, wherein the second test signal comprises a real-valued signal.14. A method according to any preceding claim, wherein the adjusting comprises adjusting the variable delay to minimize the detected magnitude.15. A method according to any preceding claim, wherein the adjusting comprises successively selecting the variable delay at a plurality of predetermined delay offsets.16. A method according to any preceding claim, wherein the configuring comprises configuring a signal processing unit in at least one of the radio frequency path and the envelope path, the signal processing unit providing a differential delay between the radio frequency path and the envelope path.17. A method according to any preceding claim, wherein the radio frequency path and the envelope path arc combined into the output signal by a power amplificr.C') 18. A method according to any preceding claim, wherein the first test signal and the second test signal comprise cyclic signals having a common cycle o length.LU0 19. A method according to claim 9 and zero or more of claims 10 to 18, wherein a first Fourier coefficient of the first test tone has the same magnitude and opposite sign of a second Fourier coefficient of the second test tone.20. A method according to claim 8 and zero or more of claims 9 to 19, whcrcin the multi-tone first tcst signal comprises a plurality of pairs of test tones.21. A method according to claim 20, wherein the pairs of test tones in the plurality of pairs of test tones are spaced at predetermined frequency separations relative to each other.22. A method according to claim 20 or 21, wherein each pair of test tones in the plurality of pairs of test tones comprises a tone spacing of twice the fundamental frequency of the second test signal.23. A method according to any of claims 20 to 22, wherein the detecting comprises detecting: a first magnitude of a first nonlinear product component produced in the output signal by the combination at a first targct frequency that is a centre frequency of a first test tone pair in the plurality of pairs of test tones; and a second magnitude of a second nonlinear product component produced in the output signal by the combination at a second target frequency that is a centre frequency of a second test tone pair in the plurality of pairs of test tones; and the configuring is carried out at least on the basis of which of the first magnitude and the second magnitude is lower.24. A method according to any of claims 4 to 23, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination at the given target frequency by multiplying the o output signal with a complex-valued rotating phasor at a negative frequency of the LCD given target frequency over an integer number of cycles and integrating the product of C the multiplication over time.25. Apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, the radio frequency path and the envelope path being combined into an output signal, the processing system being adapted to: apply a signal to the radio frequency path which provides a first test signal at radio frequency; apply a second test signal to the envelope path; detect a magnitude associated with the output signal; and configure at least one of the radio frequency path and the envelope path to reduce the detected magnitude, wherein the detecting comprises detecting the magnitude of a first product component and a second product component produced in the output signal by the combination, and wherein the configuring comprises adjusting a variable delay between the envelope path and the radio frequency signal branch to achieve a predetermined ratio between the first product component and the second product component.26. Apparatus according to claim 25, wherein the magnitude comprises a power or a square root of a power.27. Apparatus according to claim 25 or 26, wherein thc detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination. C1)28. Apparatus according to claim 27, wherein the magnitude of the at least o one product component is detected in the output signal at a given target frequency. U,o 29. Apparatus according to claim 27 or 28, wherein the at least one product component comprises one or more nonlinear product components.30. Apparatus according to any of claims 25 to 29, wherein at least one of the first test signal and the second test signal comprises a cyclic signal.31. Apparatus according to claim 28 and zero or more of claims 29 and 30, wherein the first test signal comprises a spectral null at the given target frequency.32. Apparatus according to any of claims 25 to 31, wherein the first test signal comprises a multi-tone signal.33. Apparatus according to claim 32, wherein the multi-tone first test signal comprises a first test tone and a second test tone.34. Apparatus according to claim 33, wherein the second test signal comprises energy at a fundamental frequency, and wherein the tone spacing between the first and second test tones is twice the fundamental frequency of the second test signal.

35. Apparatus according to claim 28 and claim 33 or 34, wherein the given target frequency is located within a bandwidth of the first test signal.

36. Apparatus according to claim 28 and any of claims 33 to 35, wherein 1 0 the given target frequency comprises a frequency halfway between the frequency of the first test tone and the frequency of the second test tone.

37. Apparatus according to any of claims 25 to 36, wherein the second test signal comprises a real-valued signal.

38. Apparatus according to any of claims 25 to 37, wherein the adjusting LCD comprises adjusting the variable delay to minimize the detected magnitude.

39. Apparatus according to any of claims 25 to 38, wherein the adjusting comprises successively selecting the variable delay at a plurality of predetermined delay offsets.

40. Apparatus according to any of claims 25 to 39, comprising a signal processing unit in at least one of the radio frequency path and the envelope path, wherein the configuring comprises configuring the signal processing unit in at least one of the radio frequency path and the envelope path, the signal processing unit being adapted to provide a differential delay between the radio frequency path and the envelope path.

41. Apparatus according to any of claims 25 to 40, comprising a power amplifier adapted to combine the radio frequency path and the envelope path into the output signal.

42. Apparatus according to any of claims 25 to 41, wherein the first test signal and the second test signal comprise cyclic signals having a common cycle length.S43. Apparatus according to claim 33 and zero or more of claims 34 to 42, wherein a first Fourier coefficient of the first test tone has the samc magnitude and opposite sign of a second Fourier coefficient of the second test tone.44. Apparatus according to claim 32 and zero or more of claims 33 to 43, wherein the multi-tonc first test signal comprises a plurality of pairs of test tones.45. Apparatus according to claim 44, wherein the pairs of test tones in the C') plurality of pairs of test tones are spaced at predetermined frequency separations rclative to each othcr. a,LtD 46. Apparatus according to claim 44 or 45, wherein each pair of test tones 0 in the plurality of pairs of test tones comprises a tone spacing of twice the fundamental frequency of the second test signal.47. Apparatus according to any of claims 44 to 46, wherein the detecting comprises detecting: a first magnitudc of a first nonlincar product component produced in thc output signal by thc combinatioll at a first target frequency that is a centre frequency of a first test tone pair in the plurality of pairs of test tones; and a sccond magnitudc of a second nonlincar product componcnt produced in the output signal by the combination at a second target frequency that is a centre frequency of a second test tone pair in the plurality of pairs of test tones, and wherein the configuring is carried out at least on the basis of which of the first magnitude and the second magnitude is lower.48. Apparatus according to any of claims 32 to 47, wherein the detecting comprises detecting the magnitude of at least one product component produced in the output signal by the combination at the given target frequency by multiplying the output signal with a complex-valued rotating phasor at a negative frequency of the given target frequency over an integer number of cycles and integrating the product of the multiplication over time.49. Apparatus comprising a processing system for use in reducing degradation of signal quality caused by a delay mismatch between a radio frequency path and an envelope path in a wireless transmitter, substantially in accordance with any of the cxamplcs as dcscribcd hcrcin with rcfcrcncc to and illustratcd by the accompanying drawings.CO 50. Appatatus according to any of claims 25 to 49, wherein the apparatus 0) 15 comprises an application-specific integrated circuit, ASIC, or a fleld-progranunable o gate array, FPGA. U-,o 51. Computer software adapted to perform the method of any of claims I to 24.