Abstract:
There is described an electronic device, the device comprising (a) a power supply terminal for connecting to a power supply ( 130, 330 ), (b) a first circuit ( 110, 310 ) coupled to be powered by the power supply, the first circuit ( 110, 310 ) being susceptible to power supply noise within a predetermined frequency range, and (c) a second circuit ( 120, 320 ) coupled to be powered by the power supply, the second circuit ( 120, 320 ) comprising an open-loop capacitive DC-DC converter ( 323 ) having a switching frequency outside of the predetermined frequency range. There is also described a system comprising an electronic device and a reader/writer device. Furthermore, there is described a method of manufacturing an electronic device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority under 35 U.S.C. §119 of European patent application no. 14156424.5, filed on Feb. 24, 2014, the contents of which are incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of electronic devices, in particular to integrated electronic devices comprising multiple circuits and a common power supply. 
       ART BACKGROUND 
       [0003]    Several integrated electronic devices exist, in which two or more circuits are built on a single chip and supplied by a single, i.e. common power supply. In some cases, ripple (or other input noise) caused by one of the circuits may have a negative impact on the operation of another circuit. This problem occurs e.g. when an NFC contactless frontend is implemented on the same chip as a contact-card frontend and both frontends are to be supplied by a single battery. More specifically, a contact-card frontend usually includes a capacitive boost DC-DC converter (e.g. a voltage doubler) for regulating the supply voltage according to the requirements of the contact-card frontend. As the switching frequency of such a capacitive boost DC-DC converter is directly proportional to the load current, the switching may generate ripple within a frequency that is problematic for the contactless front end and may even cause the latter to malfunction. Other examples may involve an audio processing circuit which may be negatively influenced by input noise or ripple caused by a DC-DC converter supply varying load within the audible frequency range. 
         [0004]    Attempts towards solving the above problems have been made, including reducing ripple by adding additional resistances in the input of the DC-DC voltage doubler with feedback loop. However, such techniques require a huge area for additional series switches, and moreover, they require sensing of the load current. This also introduces control loop delay in the system. In such a scenario, during this delay if the RF frontend is ON, then there are chances of high magnitude ripple disturbing the RF frontend operation. 
         [0005]    There may thus be a need for a simple and efficient way of overcoming the above drawbacks. 
       SUMMARY OF THE INVENTION 
       [0006]    This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are set forth in the dependent claims. 
         [0007]    According to a first aspect there is provided an electronic device, the device comprising (a) a power supply terminal for connecting to a power supply, (b) a first circuit coupled to be powered by the power supply, the first circuit being susceptible to power supply noise within a predetermined frequency range, and (c) a second circuit coupled to be powered by the power supply, the second circuit comprising an open-loop capacitive DC-DC converter having a switching frequency outside of the predetermined frequency range. 
         [0008]    This aspect is based on the idea that the amount of power supply noise within a predetermined frequency range to which the first circuit is susceptible, can be significantly reduced by implementing an open-loop capacitive DC-DC converter in the second circuit, the open-loop capacitive DC-DC converter having a switching frequency outside of the predetermined frequency range. The switching frequency of the open-loop capacitive DC-DC converter is fixed and independent of the load current and does therefore not cause power supply noise, such as ripple, within the predetermined frequency range. 
         [0009]    In the present context, the term “the first circuit being susceptible to power supply noise within a predetermined frequency range” may particularly denote that the operation of the first circuit may suffer severe impact or even be impossible in case of power supply noise occurring within the predetermined frequency range. In other words, the “predetermined frequency range” may be considered as a critical frequency range for the first circuit in the sense that noise within this frequency range may be problematic for the first circuit. 
         [0010]    In the present context, the term “open-loop capacitive DC-DC converter” may in particular denote a DC-DC converter relying on a capacitor to double an input voltage at a fixed switching frequency without a feedback loop or other regulation system. 
         [0011]    According to an embodiment, the second circuit further comprises a first low-dropout regulator coupled between the power supply terminal and an input of the open-loop capacitive DC-DC converter. 
         [0012]    By arranging the first low-dropout regulator (LDO) between the power supply terminal and the input of the open-loop capacitive DC-DC converter, the input voltage of the open-loop capacitive DC-DC converter is stabilized and relatively robust to changes in the voltage provided at the power supply terminal. Thereby, the open-loop capacitive DC-DC converter is assisted in providing a stable output voltage even without a feedback loop. 
         [0013]    According to a further embodiment, the second circuit further comprises a second low-dropout regulator coupled to an output of the open-loop capacitive DC-DC converter. 
         [0014]    By adding a second LDO at the output of the open-loop capacitive DC-DC converter, a very stable voltage may be provided. 
         [0015]    According to a further embodiment, the second circuit comprises a contact communication interface. 
         [0016]    The contact communication interface enables data communication with another device via an electric connection established between corresponding contact terminals of the devices. The other device may e.g. be a “contact card” compliant to ISO 7816 standard or EMVCo or NDS standards. 
         [0017]    According to a further embodiment, the second low-dropout regulator is coupled to provide the contact communication interface with a predetermined supply voltage. 
         [0018]    The predetermined supply voltage may depend on the specific type of contact communication interface. For a Class A contact communication interface, the predetermined supply voltage may be 5V, for a Class B contact communication interface, the predetermined supply voltage may be 3V, and for a Class C contact communication interface, the predetermined supply voltage may be 1.8V. 
         [0019]    According to a further embodiment, the first circuit comprises a contactless communication interface. 
         [0020]    The contactless communication interface enables data communication with another device via a wireless RF (Radio Frequency) connection, such as an NFC (Near Field Communication) connection. The other device may e.g. be a proximity coupling device (PCD), i.e. a reader/writer device or another NFC interface, such as a proximity integrated circuit card (PICC) or card installed in some other device, such as a mobile telephone. In other words, the electronic device may communicate with an NFC card as well as performing peer-to-peer communication with another (similar) device. 
         [0021]    According to a further embodiment, the first circuit comprises a low-dropout regulator coupled to the power supply terminal to provide a regulated voltage to the contactless communication interface. 
         [0022]    The LDO operates in by-pass mode or as a bypass switch when the difference between the input voltage provided to the LDO from the power supply terminal and the expected regulated output voltage of the LDO is insignificant, i.e. below 0.5V. In this mode of operation, the LDO provides no power supply rejection. Hence, any switching noise caused by the second circuit would pass through the LDO and potentially cause a negative influence on the operation of the first circuit. However, as the possible switching noise of the second circuit falls outside of the critical frequency band of the first circuit, the operation of the first circuit will not be disturbed, at least not significantly. 
         [0023]    According to a further embodiment, the predetermined frequency range is 100 kHz to 1 MHz, such as 150 kHz to 900 kHz, such as 200 kHz to 800 kHz, such as 300 kHz to 700 kHz, such as 400 kHz to 600 kHz, such as around 500 kHz. 
         [0024]    In particular when the first circuit comprises an NFC communication interface, operation of the first circuit will not be significantly disturbed by switching noise outside of the frequency range from about 100 kHz to about 1 MHz. 
         [0025]    According to a further embodiment, the switching frequency of the open-loop capacitive DC-DC converter is larger than 1 MHz. 
         [0026]    In particular when the first circuit comprises an NFC communication interface, operation of the first circuit will not be significantly disturbed by switching noise generated by the open-loop capacitive DC-DC when the latter uses a switching frequency larger than about 1 MHz. 
         [0027]    According to a second aspect, there is provided an electronic communication system, the system comprising (a) an electronic device according to the first aspect or any of the above embodiments, and (b) at least one reader/writer device adapted to perform contact and/or contactless communication with the electronic device. 
         [0028]    The reader/writer device may be a stationary device, such as a device for performing payment transactions at a store or a device for checking the validity of an electronic ticket for public transportation. Alternatively, the reader/writer device may be a mobile device, such as a mobile terminal for performing payment transactions or a mobile communication device, such as a mobile phone. 
         [0029]    According to a third aspect, there is provided a method of manufacturing an electronic device, the method comprising (a) providing a power supply terminal for connecting to a power supply, (b) providing a first circuit coupled to be powered by the power supply, the first circuit being susceptible to power supply noise within a predetermined frequency range, and (c) providing a second circuit coupled to be powered by the power supply, the second circuit comprising an open-loop capacitive DC-DC converter having a switching frequency outside of the predetermined frequency range. 
         [0030]    This aspect provides a method of manufacturing an electronic device according to the first aspect or any of the above embodiments. 
         [0031]    It should be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise indicated, in addition to any combination of features belonging to one type of subject matter also any combination of features relating to different subject matters, in particular a combination of features of the method type claims and features of the apparatus type claims, is also disclosed with this document. 
         [0032]    The aspects defined above and further aspects of the present invention will be apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment to which the invention is, however, not limited. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0033]      FIG. 1  is a block diagram showing the general structure of an electronic device in accordance with an embodiment. 
           [0034]      FIG. 2  shows an exemplary closed-loop capacitive boost DC-DC converter. 
           [0035]      FIG. 3  shows a block diagram of an electronic device in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference signs or with reference signs, which differ only within the first digit. 
         [0037]      FIG. 1  is a block diagram showing the general structure of an electronic device  100  in accordance with an embodiment. More specifically, the electronic device  100  comprises a first circuit  110  and a second circuit  120  on a single chip. The first circuit  110  comprises an NFC contactless frontend  111  and antenna  116  for communicating with an NFC contactless card  119 . The second circuit  120  comprises a contact frontend  121  for communicating with a contact card  129 . Both the first circuit  110  and the second circuit  120  are connected to a common power supply  130 , such as a battery or any other type of power supply and have respective input decoupling capacitances  131  and  132 . To assure correct operation of the circuits  110  and  120 , some kind of voltage regulator has to be utilized to provide a useful supply voltage based on the voltage supplied by the battery  130 . To this end, capacitive DC-DC converters are key elements of today&#39;s ICs as they provide low footprint solutions with higher efficiency. The basic principle of capacitive DC-DC converters is based on charge transfer from input supply to the output decoupling capacitance. However, as explained further below, the switching occurring in such capacitive DC-DC converters may cause problematic noise. 
         [0038]      FIG. 2  shows an exemplary closed-loop capacitive boost DC-DC converter  201 . More specifically,  FIG. 2  shows a conventional DC-DC-converter  201  with feedback loop with clock gating implementation. The DC-DC converter  201  comprises a voltage doubler  240  connected to power supply  230 , and a feedback and control loop  250 . The voltage doubler  240  comprises controllable switches Ron 1 , Ron 2 , Ron 3 , and Ron 4 , capacitors Cfly and Cout, and resistors R 1  and R 2 , which form a voltage divider. The feedback and control loop  250  comprises a control block  252  comprising an AND gate receiving a clock signal  254  with a 50% duty cycle on one input. The feedback and control loop  250  further comprises a comparator  256  connected to voltage divider R 1 , R 2  and a reference voltage VREF. The output of comparator  256  is connected to the other input of AND gate  253 . The output signal from the control block  252  is applied as a control signal to the switches Ron 1  and Ron  2  of the voltage doubler  240 . The output signal from the control block  252  is further supplied to an inverter  258  and the output signal from the inverter  258 , i.e. the inverted output signal from the control block  252 , is applied as a control signal to the switches Ron 3  and Ron 4 . 
         [0039]    In operation, the architecture  201  shown in  FIG. 2  uses the voltage doubler  240  and feedback control loop  250  to provide a boosted and regulated output voltage VOUT. More specifically, in phase A of the clock signal  254 , the switches Ron 1  and Ron 2  are ON (i.e. closed) while Ron 3  and Ron 4  are OFF (i.e. open). Thereby, during phase A of the clock signal  254 , the capacitor Cfly is charged to the voltage VBAT of battery  230 . Then, in phase B of the clock signal  254 , the switches are all switched, i.e. Ron 1  and Ron 2  are now OFF and switches Ron 3  and Ron 4  are ON. Thereby, the bottom plate of the capacitor Cfly is connected to the positive terminal of battery  230 , i.e. to the voltage VBAT, whereas the top plate of the capacitor Cfly is connected to VOUT, which is also connected to the top plate of the capacitor Cout. Accordingly, on the onset of phase B of clock signal  254 , the voltage at terminal SAP bounces to 2*VBAT and the capacitor Cfly discharges to the capacitor Cout. 
         [0040]    The feedback and control loop  250  performs the function of regulating the boosted output voltage. More specifically, this control loop  250  varies the switching frequency of the DC-DC converter with load current in-order to provide the regulated output voltage. That is, the control signals provided to the switches Ron 1 , Ron 2 , Ron 3 , and Ron 4  are modified in accordance with the output from comparator  256 . 
         [0041]    Batteries have their own internal resistance. Due to this and the switching activity in the DC-DC loop (which is proportional to load current), a ripple with the same frequency as the switching frequency is generated on the VBAT supply  230 . More specifically, the output voltage VOUT can be written as: 
         [0000]    
       
         
           
             VOUT 
             = 
             
               ( 
               
                 
                   2 
                   * 
                   VBAT 
                 
                 - 
                 
                   Iload 
                   * 
                   
                     ( 
                     
                       
                         ( 
                         
                           1 
                           
                             Fs 
                             * 
                             Cfly 
                           
                         
                         ) 
                       
                       + 
                       
                         ( 
                         
                           8 
                           * 
                           Ron 
                         
                         ) 
                       
                     
                     ) 
                   
                 
               
               ) 
             
           
         
       
     
         [0042]    Where: 
         [0043]    Iload=Load current of DC-DC, 
         [0044]    Fs=Switching frequency of DC-DC, 
         [0045]    Cfly=Fly capacitance of DC-DC, 
         [0046]    Ron=Ron 1 =Ron 2 =Ron 3 =Ron 4 =Switch resistance of DC-DC, 
         [0047]    VBAT=Input voltage of the DC-DC, and 
         [0048]    VOUT=Output voltage of the DC-DC. 
         [0049]    The above equation shows that for higher load current, the switching frequency will be higher, and for lower load current, the switching frequency will be lower. Furthermore, the equations also points to the fact that if Fs is fixed, then as Iload increases the VOUT will vary from a minimum value VOUT min =2*VBAT−Iload*8*Ron (under loaded condition) to a maximum value VOUT max =2*VBAT for Iload=0. 
         [0050]    As can be seen from the above, if a closed-loop capacitive boost DC-DC converter  201  as shown in  FIG. 2  is used in the second circuit  120  of  FIG. 1  to boost the battery voltage, e.g. 2.7V, to a supply voltage of 3V for a Class B contact card, then considerable switching noise will be introduced on the supply pin of the chip. The NFC critical frequency band is 100 KHz to 1 MHz. Hence, any switching noise generated by the DC-DC converter  201  within this frequency range will be disastrous for the functionality of the NFC contactless frontend  111 . 
         [0051]      FIG. 3  shows a block diagram of an electronic device  300  in accordance with an embodiment. More specifically, the electronic device  300  comprises a first circuit  310  and a second circuit  320  on a single chip. The first circuit  310  comprises a low-dropout regulator (TXLDO)  312 , an NFC contactless interface  314  and an antenna  316  for communicating with an NFC contactless card (not shown). The input of TXLDO  312  is connected to common power supply  330 , e.g. a 3V battery, over the input capacitance  331  of the first circuit  310 . The second circuit  320  comprises a first low-dropout regulator (SCLDO)  322 , an open-loop capacitive DC-DC converter  323 , a second low-dropout regulator (VCCLDO)  324 , a contact interface  326 , and a set of terminals  328  for connecting to a contact card (not shown). The input of SCLDO  322  is connected to the common power supply  330  over the input capacitance  332  of the second circuit  320  and provides a regulated voltage SCVDD as an input to the open-loop capacitive DC-DC converter  323 . The DC-DC converter  323  provides a voltage VOUT, e.g. in the range 4.8V to 4.3V as an input to VCCLDO  324 , which provides the contact interface  326  with a stable supply voltage VCC, e.g. 3V. The contact interface  326  is connected with the set of terminals  328  in order to communication with an external contact card. 
         [0052]    The open-loop capacitive DC-DC converter  323  essentially corresponds to the converter  201  shown in  FIG. 2  without the feedback loop provided by comparator  256  and AND gate  253 . Accordingly, the switching frequency of the open-loop capacitive DC-DC converter  323  is constant, i.e. equal to the frequency of the clock signal corresponding to  254  in  FIG. 2 . This frequency is preferably larger than 1 MHz, such as larger than 1.1 MHz, such as larger than 1.2 MHz, such as larger than 1.5 MHz, such as larger than 2 MHz. Thereby, ripple caused by the switching in DC-DC converter  323  is outside of the critical range of the NFC contactless interface  314 . Furthermore, the amount (i.e. amplitude) of ripple is significantly reduced in comparison to the DC-DC converter  201  of  FIG. 2  due to the inclusion of the first LDO, i.e. SCLDO  322 , which provides a well regulated input voltage to DC-DC converter  323 . 
         [0053]    The present invention is generally applicable to devices comprising an NFC contactless frontend and Contact-card frontend on a single chip, wherein both communication channels are supplied from a single battery with battery voltage as low as 2.3V. Even lower power supply voltages (battery voltages) may be implemented by using DC-DC Tripler configurations in place of DC-DC converter  323 . 
         [0054]    Generally, there are 3 different classes for contact-cards, i.e. Class C cards with a supply voltage of 1.8V, Class B cards with a supply voltage of 3V, and Class A cards with a supply voltage of 5V. The technology trend seems to point to a hugely increased use of in particular Class B and Class C cards. As discussed above, in particular in conjunction with  FIG. 3 , the present invention is capable of supplying a Class B card with 3V from a 2.3V utilizing a DC-DC converter  323  to boost the supply voltage without, however, causing switching noise, in particular ripple, within the critical frequency range of an NFC contactless frontend residing on the same chip and power by the same battery. 
         [0055]    It is noted that, unless otherwise indicated, the use of terms such as “upper”, “lower”, “left”, and “right” refers solely to the orientation of the corresponding drawing. 
         [0056]    It is noted that the term “comprising” does not exclude other elements or steps and that the use of the articles “a” or “an” does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.