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Modulated supply stage with feedback to switched supply

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Modulated supply stage with feedback to switched supply


There is disclosed a voltage supply stage comprising: a selection means for selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; a combining means for combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; and an adjusting means adapted to generate the correction signal in dependence on the reference signal and the adjusted power supply voltage, wherein the selection means is arranged to select the one of the plurality of supply voltages further in dependence on a signal derived from one of the inputs to the combining means.
Related Terms: Modulate

Browse recent Nujira Limited patents - Cambourne, GB
USPTO Applicaton #: #20140203653 - Class: 307 80 (USPTO) -


Inventors: Martin Wilson

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The Patent Description & Claims data below is from USPTO Patent Application 20140203653, Modulated supply stage with feedback to switched supply.

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CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a Continuation of U.S. patent application Ser. No. 12/991,695, with a 371(c) date of Jun. 13, 2011, and is incorporated herein by reference.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to a modulated supply stage, and particularly to such a stage in which a feedback loop is connected to provide an input to control selection of a low frequency switched supply. The feedback may be provided from the output of the low frequency switched supply stage or from the output of a high frequency correction stage.

2. Description of the Related Prior Art

It is known by those skilled in the art that envelope tracking (ET) and envelope elimination and restoration (EER) can give large improvements in efficiencies of power amplifier operation, particularly with signals such as orthogonal frequency-division multiplexing (OFDM) which have large crest factors. However, it is also known that the application of these techniques presents considerable difficulties due to the large powers and bandwidths involved. These difficulties become particularly formidable when applied to portable wireless terminals where the number of discrete components must be minimised and large dimensioned magnetics must be avoided.

An apparently simple solution would be to make the modulator a fast responding linear regulator. However, this would simply change power wasted in the power amplifier with that wasted in the linear regulator, resulting in no net gain in efficiency.

In order to gain some efficiency, some prior art implementations have been known to follow the switched mode supply with a low drop-out (LDO) fast responding linear regulator. This removes the errors inherent in the switched mode operation. However a problem arises in that there must be sufficient range in the linear regulator to allow for the peaks in the switched mode error, which can be considerably larger than the root mean square (RMS) error. This results in a large standing dissipation in the LDO.

A significant improvement on this is provided by techniques disclosed in GB2398648. This implementation is shown in FIG. 1. FIG. 1 shows a diagram of a typical switched mode power supply used as an efficient power conversion means. It must be noted that this is given as an example; the invention is not restricted to topologies of this type.

A coarse DC-DC switched supply 102 provides an approximation to the required waveform, provided as a reference waveform on input line 118, after filtering with filter network 104. The filter comprises an inductor 106 for storage of magnetic energy, and a capacitor 108 for storage of electric energy. A transformer 110 is used which can give true summation, e.g. signals can be added and subtracted, so the mean correction from a correction amplifier 114 can be set to zero, eliminating large standing dissipation. The output of the transformer provides an output to a load 112. The output of the transformer 110 is fedback to provide an input to the correction amplifier 114, which receives as a further input a reference signal on line 116 (which may be the same as, or derived from the same source as, the reference signal on line 118). The transformer combines the switched supply voltage with the output of the correction amplifier to provide a corrected output voltage.

A potential problem with the architecture of FIG. 1 is that the transformer 110 has to have a high self-inductance to prevent shunting of the correction current through the unwanted inductance of the transformer. This means that large ferrite cores must typically be used. Whilst this is acceptable for wireless infrastructure implementations, this presents particular difficulties for portable handset implementations or any implementation where size restrictions may apply.

The supply stage of FIG. 1 is capable of very efficient operation, but the circuit can only be switched between two levels: intermediate levels can only be obtained by the filtering action of the energy storage elements 106 and 108. For low frequency outputs (frequencies much less than the switching frequencies), this arrangement will be able to perform tracking, but the circuit may provide poor tracking at high frequency. There will also be substantial breakthrough of switching related products at high frequencies. When the said power conversion circuit is used as a modulator, the energy storage elements form a parallel resonant tank which will present a high impedance to the load at some frequencies.

The effect of this can be seen in FIG. 2. The reaction of the energy storage elements to the rapidly changing current demand produces a waveform 204 at the power amplifier. This shows severe mistracking when compared with the wanted waveform 202. Also, the high output impedance may result in instability of the load.

Examples of prior art switched mode modulators can be found in U.S. Pat. Nos. 5,905,407, 6,054,914, 6,198,374, 6,300,826, 6,583,664, 6,661,210, 6,661,217, 6,710,646, 6,792,252, and in US Patent application No. 2002/0008574.

It is an aim of the invention to provide an improved modulated power supply stage.

SUMMARY

OF THE INVENTION

In one aspect the invention provides a voltage supply stage comprising: a selection means for selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; a combining means for combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; and an adjusting means adapted to generate the correction signal in dependence on the reference signal and the adjusted power supply voltage, wherein the selection means is arranged to select the one of the plurality of supply voltages further in dependence on a signal derived from one of the inputs to the combining means.

The inputs to the combining means are the signals to be combined: the selected power supply voltage and the correction signal. The selected power supply voltage is the output of the selection means, which is preferably a switched voltage supply. The correction signal is the output of the adjustment means.

The signal derived from one of the inputs to the combining means may be the output of the selection means.

The signal derived from one of the inputs to the combining means may be the output of the adjusting means.

A feedback control stage may provide the signal derived from one of the inputs to the combining means to the selection means. The feedback control stage may be adapted to receive as a first input the reference signal and as a second input one of the inputs to the combining means, and further adapted to adjust the reference signal in dependence on the one of the inputs to the combining means to provide an adjusted reference signal for the selection means.

In an embodiment the feedback control stage may comprise: a subtractor for subtracting the output of the selection means from the reference signal; a proportional-integral, PI, controller for receiving the subtracted signal and generating a modified output, and a summer for adding the modified output of the PI controller to the reference signal, to form the output of the feedback control stage being the adjusted reference signal.

In an alternate embodiment the feedback control stage may comprise: a proportional-integral, PI, controller for receiving the output of the adjusting means and generating a modified output, and a summer for adding the modified output of the PI controller to the reference signal, to form the output of the feedback control stage being the adjusted reference signal.

The combining means preferably comprises an inductor, and the adjustment means preferably comprises a voltage-to-current converter, wherein a current representing the correction signal is injected at the second terminal of the inductor to adjust the current flowing in the inductor provided by the selected power supply voltage, a thus adjusted current flowing in a load connected to the second terminal of the inductor to thereby develop the adjusted supply voltage across said load.

The voltage supply stage preferably comprises a reference adjustment stage for adjusting the reference signal to provide a modified reference signal. The selection means may be adapted to select in dependence on the modified reference signal. The feedback control means may be adapted to provide the signal derive from one of the inputs to the combining means in dependence on the modified reference signal.

The reference adjustment stage may comprise a means for adjusting the amplitude of the reference signal in dependence upon a difference between the amplitude of the reference signal and the amplitude of the selected supply voltage. The means for adjusting the amplitude of the reference signal may include: a correlator for determining the amplitude error between the reference signal and the selected supply voltage; and an amplitude adjustment block for modifying the reference signal in dependence on said error. The reference adjustment stage may comprise a means for controlling a current flow in the combining means to maximize current slow in the combining means and thereby minimize current flow in the adjustment means. The means for controlling the current flow may include: a correlator for determining the current flow in the inductor and for providing a control signal to modify coefficients of a differentiator in dependence thereon, the differentiator being arranged to receive the reference signal and generate a differentiated version thereof. The differentiator may be arranged to receive as an input the amplitude adjusted reference signal generate a differentiated amplitude adjusted reference signal, the reference adjustment stage further comprising a summer for summing the amplitude adjusted reference signal with the differentiated amplitude adjusted reference signal to form the modified reference signal.

A tracking modulated power supply stage for a mobile wireless device preferably includes a voltage supply stage as defined.

In this aspect the invention also provide a method for generating a supply voltage comprising: selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; generating the correction signal in dependence on the reference signal and the adjusted power supply voltage; and providing as a feedback signal one of the input signals to the combining step, wherein the selecting step is further arranged to select the one of the plurality of supply voltages in dependence on the feedback signal.

The providing step may provide the output of the selection means as the feedback signal. The providing step may provide the output of the adjusting means as the feedback signal.

The method may further comprise the step of controlling the feedback signal for providing the signal derived from one of the inputs to the combining means to the selection means.

The step of controlling the feedback may comprise receiving as a first input the reference signal and as a second input one of the inputs to the combining step, and adjusting the reference signal in dependence on the one of the inputs to the combining step to provide an adjusted reference signal for the selecting step.

The step of controlling the feedback may comprise: subtracting the output of the selection means from the reference signal; receiving the subtracted signal and generating a proportional-integral, PI, modified output, and adding the modified output to the reference signal, to form the adjusted reference signal.

The step of controlling the feedback may comprise: receiving the output of the adjusting means and generating a proportional-integral, PI, modified output, and adding the modified output to the reference signal, to form the adjusted reference signal.

The combining means may comprise an inductor, and the adjustment means may comprise a voltage-to-current converter, the method further may comprise injecting a current representing the correction signal at the second terminal of the inductor to adjust the current flowing in the inductor provided by the selected power supply voltage, a thus adjusted current flowing in a load connected to the second terminal of the inductor to thereby develop the adjusted supply voltage across said load.

The method may further comprise the step of adjusting the reference signal to provide a modified reference signal.

The selecting step may be adapted to select in dependence on the modified reference signal.

The feedback control step may be adapted to provide the signal derived from one of the inputs to the combining step in dependence on the modified reference signal.

The step of adjusting may include adjusting the amplitude of the reference signal in dependence upon a difference between the amplitude of the reference signal and the amplitude of the selected supply voltage.

The step of adjusting the amplitude of the reference signal may include: determining the amplitude error between the reference signal and the selected supply voltage; and modifying the reference signal in dependence on said error.

The step of adjusting may comprise controlling a current flow in the combining means to maximize current flow in the combining means and thereby minimize current flow in the adjustment means.

The step of controlling the current flow may include: determining the current flow in the inductor and for providing a control signal to modify coefficients of a differentiator in dependence thereon, the differentiator being arranged to receive the reference signal and generate a differentiated version thereof.

The method may further comprise the steps of: receiving at the differentiator as an input the amplitude adjusted reference signal; and generating a differentiated amplitude adjusted reference signal, the adjustment step further comprising summing the amplitude adjusted reference signal with the differentiated amplitude adjusted reference signal to form the modified reference signal.

In another aspect the invention provides a combiner for combining a first voltage signal with a second voltage signal to provide a combined voltage signal, comprising: an inductor having a first terminal connected to the first voltage signal; a load connected to the second voltage terminal; and a conversion means for receiving at an input the second voltage signal and generating at an output a current representing the second voltage signal, the output of the conversion means being connected to the second terminal of the inductor, wherein a current is generated in the load representing the combined first and second voltages, the combined voltage signal thus being developed across the load.

The combiner may further comprise a capacitor connected at the second terminal of the inductor, wherein in combination the inductor and the capacitor form an L-C filter for the combined signal.

The conversion means may be a voltage-to-current converter.

The load may be a power amplifier, and the combined voltage is a supply voltage for the power amplifier.

A modulated voltage supply may comprise a combiner as defined, and may further comprise: a selection means for selecting one of a plurality of power supply voltages in dependence on a reference signal, the selected supply being the first voltage signal, the conversion means being an adjusting means for generating a correction signal comprising the second voltage signal in dependence on the reference signal and the combined voltage signal.

In this aspect the invention also provides a method for combining a first voltage signal with a second voltage signal to provide a combined voltage signal, comprising: connected to the first voltage signal to a first terminal of an inductor; connecting a load to the second terminal of the inductor; converting the second voltage signal into a current representing the second voltage signal; providing the current representing the second voltage signal at the second terminal of the inductor, wherein a current is generated in the load representing the combined first and second voltages, the combined voltage signal thus being developed across the load.

The step of providing the current representing the second voltage signal at the second terminal of the inductor may comprise injecting current into the second terminal of the inductor.

In a further aspect the invention provides a voltage supply stage comprising: a selection means for selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; a combining means for combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; a correction means adapted to generate the correction signal in dependence on the reference signal and the adjusted power supply voltage; an adjustment means for adjusting the amplitude of the reference signal in dependence on a difference between the amplitude of the reference signal and the amplitude of the selected supply voltage; and differentiation means for controlling the current in the combining means to maximize the current flowing in the combining means and thereby minimize the current required to flow in the correction means.

The adjustment means may include: a correlator for determining an amplitude error between the reference signal and the selected supply voltage; and an amplitude adjustment block for modifying the reference signal in dependence on said error.

The means for controlling the current in the combining means to maximize the current flowing in the combining means and thereby minimize the current flowing in the correction means may include a correlator for determining the current flow in the inductor and for modifying coefficients of a differentiator in dependence thereon.

The amplitude adjustment block may receive the reference signal and generates the amplitude adjusted reference signal, the differentiator receives the amplitude adjusted reference signal and generates a differentiated version thereof at its output, and a summer sums the amplitude adjusted reference signal and the modified differentiated reference signal to provide the reference signal for use by the modulated power supply stage.

In this further aspect the invention also provides a method for a generating a modulated supply voltage, comprising: selecting one of a plurality of power supply voltages in dependence on a reference signal representing a desired power supply voltage; combining the selected power supply voltage with a correction signal to generate an adjusted power supply voltage; generating the correction signal in dependence on the reference signal and the adjusted power supply voltage; adjusting the amplitude of the reference signal in dependence on a difference between the amplitude of the reference signal and the amplitude of the selected supply voltage; and controlling the current in the combining means by differentiation to maximize the current flowing in the combining means and thereby minimize the current required to flow in the correction means.

The adjustment step may include: determining an amplitude error between the reference signal and the selected supply voltage; and modifying the reference signal in dependence on said error.



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Current detecing and switching apparatus
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Power supply system and control method thereof
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Electrical transmission or interconnection systems
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stats Patent Info
Application #
US 20140203653 A1
Publish Date
07/24/2014
Document #
14187743
File Date
02/24/2014
USPTO Class
307 80
Other USPTO Classes
International Class
02J4/00
Drawings
7


Modulate


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