News Column

Researchers Submit Patent Application, "DCM and PFM Management", for Approval

August 27, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Branca, Xavier (Grenoble, FR); Chesneau, David (Saint Jean de Moirans, FR), filed on August 14, 2012, was made available online on August 14, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "The present invention generally relates to reduction of power supply in mobile communication devices.

"It finds applications, in particular, while not exclusively, in mobile communication devices such as mobile phones, Smartphones or Personal Digital Assistant (PDAs).

"The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

"Current mobile phones have turned into mobile platforms. Thanks to broadband networks and to the huge increase of the number of software applications, mobile phones are actually inescapable in the daily life. Mobile phones are used for social networking, TV watching, web surfing, as gaming console, for steering and tracking, etc. The limit of their usefulness is now only given by the human imagination to invent new applications.

"However, mobile platforms are battery-operated systems and possess finite quantity of embedded energy. The efficiency of all the integrated circuits is challenged in order to ensure the longest autonomy. In addition, very high performance level is required to provide the most comfortable experience to the final consumer and the circuits complexity have increased in an exponential manner. Nevertheless, mobile platforms such as consumer electronic devices have to stand affordable prices with the handiest size.

"Audio amplifiers, as an interface with users, are key parts of mobile phones. They are required to achieve very good audio performances, in terms of Signal to Noise Ratio (SNR) and of Total Harmonic Distortion (THD) for example, and to meet High-Fidelity (Hi-Fi) sounds expectations. In this case, AB-class amplifiers are used but they suffer from a poor efficiency, e.g. less than 78%, linked to their voltage supply. One strategy to maximize the efficiency of such amplifiers is to minimize their voltage supply level as much as possible. Amplifiers are then of G or H class. Audio signal transmitted to the speakers is ground centred due to the jack connectors of headphones. Until recently, external high pass filters were used to cut-off the common mode at the output of audio amplifiers. Such filters, made of external capacitors of a few hundred of microfarads, were huge and expensive (8 mm.sup.2 each). Then capacitor-less AB-class amplifiers have been designed to get rid of these bulky capacitors. Such amplifiers are supplied by a symmetrical positive and negative voltage which enables to avoid the use of any output common-mode filter.

"Thus, audio amplifiers need a symmetrical positive and negative voltage supply to amplify audio signals without common mode.

"Formerly, two separated converters were employed to generate one positive and one negative voltage. Using two separated converters requires numerous bulky and expensive external components.

"Single Inductor Double Output (SIDO) DC-DC converter providing both a positive and a negative output voltage has been introduced in the document 'Single-Inductor Multiple-Output Switching Converters with Bipolar Outputs', D. Ma, W.-H. Ki, C. Y. Tsui, and P. K. T. Mok, IEEE International Symposium on Circuits and Systems, pp 301-304, vol. 2, 2001.

"Such a converter benefits from the high efficiency of inductive DC-DC converters with a minimized number of external components and power switches. An implementation of this Single Inductor Double Output Bipolar converter is described in the document 'Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD', MAXIM IC, 2003. Shottky diodes are used to simplify the overall control with detrimental impact on efficiency and transient responses.

"Single Inductor Multiple Output (SIMO) converters that generate both symmetrical outputs are commonly employed for imaging devices like AMOLED, LCD or CCD. Output voltage levels for such applications are higher than for audio applications. This leads to different power stage architectures such as described in the previous document 'Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD' and in the document Texas Instrument Inc., TPS65136 'POSITIVE AND NEGATIVE OUTPUT DC-DC CONVERTER', 2008. In this document, the power stage and the conduction scheme do not permit to supply two outputs with non-symmetrical loads like in an audio amplifier. In the previously introduced document 'Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD', time multiplexing is employed to avoid cross regulation at the cost of an impacted efficiency.

"However, it is mandatory for the headphone application to afford high efficiency for low output current too. This is not compatible with a converter working only in CCM.

"Thus, there is a need to develop a power supply that is able to afford high efficiency for low output current, while using a minimum of external components."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "A first aspect of the invention concerns a voltage regulating device comprising a power stage comprising an inductor between a first node and a second node; a first switch between the first node and a power supply node for which the potential is non-zero and of constant polarity; a first capacitor between a node at a reference potential and a second switch coupled to the first node; a second capacitor between a node at the reference potential and a third switch coupled to the second node; a fourth switch between the second node and a node at the reference potential; a fifth switch between the first node and a node at the reference potential; a first output for delivering a first voltage corresponding to the voltage at the terminals of the first capacitor; a second output for delivering a second voltage corresponding to the voltage at the terminals of the second capacitor.

"The power stage further comprises at least one comparator arranged to detect an inversion of the current in the inductor and the power stage is further arranged to close the fourth and fifth switches and to open the first, second and third switches upon detection of an inversion of the current in the inductor

"This enables to implement a Discontinuous Conduction Mode (DCM) in a Single Inductor Double Output Bipolar Buck-Boost (SIDOBBB) converter, thus increasing the efficiency of the voltage regulation. Indeed, when low output currents are required, the current flowing through the inductor can be lower than its ripple; thus resulting in an inversion of the current in the inductor during discharge configurations. The inversion of the current results in energy losses in the voltage regulating device. The proposed solution addresses this problem by detecting the inversion of the current and by short-circuiting the inductor upon detection of the inversion of the current.

"According to some embodiments, the power stage comprises a first comparator and a second comparator, the first comparator being arranged to measure a potential difference between a negative input connected to the first output and a positive input connected to the first node and to detect an inversion of the current in the inductor when a positive potential difference is measured between the positive and negative inputs while the second switch is closed, and the second comparator being arranged to measure a potential difference between a positive input connected to the first node and a negative input connected to the node at the reference potential and to detect an inversion of the current in the inductor when a positive potential difference different is measured between the positive and negative inputs while the fifth switch is closed.

"Thus, such embodiments enable to detect the inversion of the current in the inductor in every configuration during which a current inversion is likely to happen. Indeed, the current inversion can only happen when the second switch is closed or when the fifth switch is closed.

"According to some embodiments, the voltage regulating device further comprises a control circuit for synchronizing and controlling the switches, the control circuit being coupled to the power stage and being arranged to generate control signals and the power stage is arranged to adopt one of the following configurations as a function of the control signals: a first configuration in which only the first and the third switches are closed; a second configuration in which only the first and the fourth switches are closed; a third configuration in which only the second and the fourth switches are closed; a fourth configuration in which only the third and the fifth switches are closed and a fifth configuration in which only the fourth and the fifth switches are closed.

"The power stage is further arranged to transmit an inversion signal to the control circuit upon detection of an inversion of the current in the inductor; and the control circuit is arranged to generate control signals to force the power stage to adopt the fifth configuration upon reception of the inversion signal from the comparison unit.

"Such embodiments enable to implement in a control circuit a control strategy to minimize the energy accumulated in the inductor.

"In complement, upon detection of an inversion of the current by the first comparator, the first comparator can be arranged to transmit a first inversion signal to the control circuit and upon detection of an inversion of the current by the second comparator, the second comparator can be arranged to transmit a second inversion signal to the control circuit.

"In some embodiments, the control circuit is arranged to produce error signals as a function of the difference between the reference potential and the first and second voltages and is configured to generate the control signals by comparing the first error signal and the second error signal to a periodic signal.

"This enables to implement a dynamic strategy to minimize the energy accumulated in the inductor by taking into account error signals.

"In variants or in supplement, the control circuit may be arranged to generate the control signals to produce one of the following configuration sequences during a clock cycle, the periodic signal having a period being equal to the clock cycle: the first configuration, followed by the second configuration, then the third configuration, if the second error signal is the first of the error signals to be less than the periodic signal during the clock cycle; the first configuration, followed by the fourth configuration, followed by the third configuration, if the first error signal is the first of the error signals to be less than the periodic signal during the clock cycle. the first configuration, followed by the fourth configuration, if it is necessary to provide energy to modify or maintain the value of the second voltage only; the second configuration, followed by the third configuration, if it is necessary to provide energy to modify or maintain the value of the first voltage only; and the first configuration, followed by the third configuration, if it is necessary to provide sufficient energy to adjust the first voltage and the second voltage.

"If an inversion signal is received by the control circuit during the clock cycle, each sequence of configurations further comprises the fifth configuration, which extends over a period beginning upon reception of the inversion signal and ending at an end of the clock cycle.

"These embodiments enable to implement a dynamic strategy that can be interrupted in case of detection of an inversion of the current, so that the efficiency of the voltage regulating device is increased.

"In some embodiments, if no inversion signal is received during a clock cycle: the first configuration extends over a period of time during which both the first error signal and the second error signal are greater than the periodic signal; the second configuration extends over a period beginning at the moment when the second error signal becomes less than the periodic signal, and ending at the moment when the first error signal becomes less than the periodic signal; the third configuration extends over a period during which both the first error signal and the second error signal are less than the periodic signal; the fourth configuration extends over a period of time beginning at the time when the first error signal becomes less than the periodic signal, and ending at the time when the second error signal becomes less than the periodic signal.

"According to some embodiments, if during a given clock cycle the first error signal becomes less than the periodic signal before a predetermined duration from the beginning of the given clock cycle expires, the control circuit is arranged to generate control signals to force the power stage to adopt the fifth configuration during a next clock cycle after the given clock cycle.

"The predetermined duration can be equal to a half of the given clock cycle.

"These embodiments enable to implement Pulse Frequency Modulation (PFM) in DCM by skipping pulses (stopping conduction during one or several clock cycles), when a sufficient amount of energy has been accumulated in the output capacitors. This avoids losing the energy required to switch the switches, during clock cycles in which the output capacitors have a sufficient load.

"A second aspect concerns a power supply comprising a device coupled to a voltage source, the device comprising a power stage comprising an inductor between a first node and a second node; a first switch between the first node and a power supply node for which the potential is non-zero and of constant polarity; a first capacitor between a node at a reference potential and a second switch coupled to the first node; a second capacitor between a node at the reference potential and a third switch coupled to the second node; a fourth switch between the second node and a node at the reference potential; a fifth switch between the first node and a node at the reference potential; a first output for delivering a first voltage corresponding to the voltage at the terminals of the first capacitor; a second output for delivering a second voltage corresponding to the voltage at the terminals of the second capacitor;

"The power stage further comprises at least one comparator arranged to detect an inversion of the current in the inductor and the power stage is further arranged to close the fourth and fifth switches and to open the first, second and third switches upon detection of an inversion of the current in the inductor.

"In some embodiments, the power stage comprises a first comparator and a second comparator, the first comparator being arranged to measure a potential difference between a negative input connected to the first output and a positive input connected to the first node and to detect an inversion of the current in the inductor when a positive potential difference is measured between the positive and negative inputs while the second switch is closed, and the second comparator being arranged to measure a potential difference between a positive input connected to the first node and a negative input connected to the node at the reference potential and to detect an inversion of the current in the inductor when a positive potential difference different is measured between the positive and negative inputs while the fifth switch is closed.

"In some embodiments, the device further comprises a control circuit for synchronizing and controlling the switches, the control circuit being coupled to the power stage and being arranged to generate control signals; the power stage is arranged to adopt one of the following configurations as a function of the control signals: a first configuration in which only the first and the third switches are closed; a second configuration in which only the first and the fourth switches are closed; a third configuration in which only the second and the fourth switches are closed; a fourth configuration in which only the third and the fifth switches are closed and a fifth configuration in which only the fourth and the fifth switches are closed; and the power stage is further arranged to transmit an inversion signal to the control circuit upon detection of an inversion of the current in the inductor. The control circuit is arranged to generate control signals to force the power stage to adopt the fifth configuration upon reception of the inversion signal from the comparison unit.

"In addition, upon detection of an inversion of the current by the first comparator, the first comparator is arranged to transmit a first inversion signal to the control circuit and upon detection of an inversion of the current by the second comparator, the second comparator is arranged to transmit a second inversion signal to the control circuit.

"A third aspect concerns a mobile device having a power supply according anyone of the embodiments of the second aspect. The mobile device further comprises an audio amplifier supplied by the power supply.

"In some embodiments, the mobile device comprises a processor, an audio amplifier, a digital-to-analog converter, and a digital audio data processing unit arranged to deliver a digital audio data stream to the digital-to-analog converter, with the digital-to-analog converter being arranged to convert the digital audio data stream into an analog signal, the audio amplifier being coupled to the digital-to-analog converter so as to amplify the analog audio signal.

"The power supply may be coupled to the digital-to-analog converter in order to provide power to the digital-to-analog converter.

BRIEF DESCRIPTION OF THE DRAWINGS

"The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which:

"FIG. 1 illustrates a mobile device according to some embodiments of the invention;

"FIG. 2 represents a functional diagram of a power supply according to some embodiments of the invention;

"FIG. 3 illustrates a power stage according to some embodiments of the invention;

"FIGS. 4.a and 4.b are diagrams representing current in an inductor versus time, respectively in Continuous and Discontinuous Conduction Mode (CCM and DCM), according to some embodiments of the invention;

"FIGS. 5.a and 5.b represent an example of configuration sequences during several clock cycles according to some embodiments of the invention;

"FIG. 6 is a three-dimensional diagram representing efficiency of the power supply in CCM, DCM and Pulse Frequency Modulation (PFM), according to the invention, versus output current in a positive output of the power supply and output current in a negative output of the power supply."

For additional information on this patent application, see: Branca, Xavier; Chesneau, David. DCM and PFM Management. Filed August 14, 2012 and posted August 14, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5509&p=111&f=G&l=50&d=PG01&S1=20140807.PD.&OS=PD/20140807&RS=PD/20140807

Keywords for this news article include: Patents, Electronics, Digital To Analog.

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Source: Electronics Newsweekly


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