US 20130090148A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2013/0090148 A1 KETTUNEN et al. (43) Pub. Date: Apr. 11, 2013

(54) CIRCUIT (52) US. Cl. USPC ...... 455/5521; 333/24 R; 333/24 C (75) Inventors: Arttu Aukusti KETTUNEN, Oulu (Fl); Marko Johannes VIITALA, Kontio (Fl) (57) ABSTRACT

(73) Asslgneei Renesas Moblle corporatlon An apparatus for coupling a baseband that _ uses a ?rst signalling standard to a radio frequency integrated (21) Appl' NO" 13/268,295 circuit that uses a second signalling standard includes a buffer (22) Filed: Oct 7’ 2011 coupled to the baseband integrated circuit and a net Work coupled between the buffer and the radio frequency Publication Classi?cation integrated circuit. The resistor network implements a voltage divider so as to convert a ?rst voltage used by the baseband (51) Int. Cl. integrated circuit to a second voltage used by the radio fre H04 W 88/06 (2009.01) quency integrated circuit. The apparatus may be used in a H03H 7/06 (2006.01) mobile telecommunications device.

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CIRCUIT COUPLING frequency integrated circuit, the resistor netWork implement ing a voltage divider so as to convert a ?rst voltage used by the TECHNICAL FIELD baseband integrated circuit to a second voltage used by the [0001] The present invention relates to a coupling for inte radio frequency integrated circuit, the resistor netWork com grated circuits. In particular, but not exclusively, the present prising a ?rst resistor coupled betWeen a voltage source and a invention relates to an apparatus and a method for coupling a ?rst node, the ?rst node being arranged to receive a signal baseband integrated circuit to a radio frequency integrated from the baseband integrated circuit, a second resistor circuit Wherein the tWo integrated circuits use different sig coupled betWeen the ?rst node and a second node, the second nalling standards. Apparatus according to the present inven node being coupled to an input of the second integrated circuit tion may be used in mobile telecommunications devices. and a third resistor coupled betWeen the second node and ground. A coupling is coupled betWeen the voltage BACKGROUND source and the ?rst resistor. [0002] Within mobile communications netWorks there is a [0008] In accordance With an exemplary embodiment, trend toWards ever faster over-the-air data rates. For example, there is provided a mobile communications device compris General Packet Radio Service (GPRS) offers data rates of ing a baseband integrated circuit for performing baseband around 56 to 114 kilobits per second over the Global System processing of a signal, the baseband integrated circuit using a for Mobile Communications (GSM), Whereas next genera ?rst signalling standard, a radio frequency integrated circuit tion mobile broadband technologies such as Long Term Evo for performing radio frequency processing of a signal, the lution (LTE) and Mobile WorldWide Interoperability for radio frequency integrated circuit using a second signalling MicroWave Access (WiMAX) and their descendants offer standard and an interface for coupling the baseband inte data rates of around 1 gigabit per second and higher. grated circuit and the radio frequency integrated circuit. The [0003] Typically, higher data rates are enabled by develop interface comprises a buffer and a resistor netWork coupled to ments in radio frequency signalling technology. For example, the output of the buffer, the resistor netWork implementing a these developments may be embodied in neW radio frequency voltage divider so as to convert a ?rst voltage used by one of integrated circuits that provide the necessary radio frequency the baseband integrated circuit and the radio frequency inte signal processing. These neW radio frequency integrated cir grated circuit to a second voltage used by the other of the cuits may use neWer physical interface standards, such as the baseband integrated circuit and the radio frequency integrated fourth revision of the DigRF standard adopted by the MIPI circuit. Alliance. This in turn requires integrated circuits that inter [0009] In accordance With an exemplary embodiment, face With the neW radio frequency integrated circuits to also there is provided a method for communicating a data signal be revised to use the neWer physical interface standards. betWeen a baseband integrated circuit that uses a ?rst signal These may include baseband integrated circuits. This requires ling standard and a radio frequency integrated circuit that uses revisions to the manufacturing of mobile device integrated a second signalling standard comprising receiving a data circuits and results in higher costs. signal produced by one of the baseband integrated circuit and [0004] “Implementing an SLVS Transceiver” as published the radio frequency integrated circuit, buffering the data sig in issue 10 of EDN Magazine on 26 May 201 1 describes Field nal, adjusting a voltage of the data signal from a ?rst voltage Programmable Gate Array (FPGA) adaptations to provide an used by said one of the baseband integrated circuit and the SLVS-compatible interface. A bespoke FPGA generates a radio frequency integrated circuit to a second voltage used by modi?ed LoW-Voltage Differential Signalling (LVDS) signal the other of the baseband integrated circuit and the radio that can be received by a Scalable LoW-Voltage Signalling frequency integrated circuit, and pas sing the data signal to an (SLVS) peer device. input of said other of the baseband integrated circuit and the [0005] It is thus desirable to be able to support higher data radio frequency integrated circuit. rates in mobile communications devices Without complex components and at a loW cost. [0010] In accordance With an exemplary embodiment, there is provided an apparatus for coupling a baseband inte SUMMARY grated circuit that uses a ?rst signalling standard to a radio frequency integrated circuit that uses a second signalling [0006] In accordance With an exemplary embodiment, standard, the apparatus comprising a buffer coupled to the there is provided apparatus for coupling a baseband inte radio frequency integrated circuit, the buffer being arranged grated circuit that uses a ?rst signalling standard to a radio to adjust a voltage of the data signal from a ?rst voltage frequency integrated circuit that uses a second signalling speci?ed by the second signalling standard to a second volt standard, the apparatus comprising a buffer coupled to the age speci?ed by the ?rst signalling standard baseband integrated circuit and a resistor netWork coupled betWeen the buffer and the radio frequency integrated circuit, [0011] Further features and advantages of the invention the resistor netWork implementing a voltage divider so as to Will become apparent from the folloWing description of pre convert a ?rst voltage used by the baseband integrated circuit ferred embodiments of the invention, given by Way of to a second voltage used by the radio frequency integrated example only, Which is made With reference to the accompa circuit. nying draWings. [0007] In accordance With an exemplary embodiment, there is provided apparatus for coupling a baseband inte BRIEF DESCRIPTION OF THE DRAWINGS grated circuit that uses a ?rst signalling standard to a radio frequency integrated circuit that uses a second signalling [0012] FIG. 1A is a simpli?ed schematic diagram shoWing standard, the apparatus comprising a resistor netWork a baseband integrated circuit coupled to a radio frequency coupled betWeen the baseband integrated circuit and the radio integrated circuit; US 2013/0090148 A1 Apr. 11, 2013

[0013] FIG. 1B is a simpli?ed schematic diagram showing high data rates With loW poWer consumption making it espe an apparatus for coupling a baseband integrated circuit to a cially attractive for use in mobile devices. Certain embodi radio frequency integrated circuit according to an embodi ments thus offer a fast and cost-ef?cient physical DigRFv4 ment; interface betWeen radio frequency and baseband integrated [0014] FIG. 2A is a simpli?ed schematic diagram shoWing circuit that may be implemented With general components. a number of components that implement a single-ended cou Without the apparatus the radio frequency integrated circuit pling for the apparatus of FIG. 1B; cannot be connected to existing LVDS hardWare. This in turn [0015] FIG. 2B is a simpli?ed schematic diagram shoWing means that existing baseband processing hardWare can be an exemplary differential coupling for the apparatus of FIG. reused With neWer radio frequency signalling technologies, 1B; reducing Waste and costs. [0016] FIG. 3 is a simpli?ed schematic diagram shoWing an [0020] In certain embodiments, the resistor netWork com exemplary coupling for a receive direction; and prises a ?rst resistor coupled betWeen a voltage source and a [0017] FIG. 4 is a How diagram illustrating an exemplary ?rst node, the ?rst node being coupled to an output of the method for sending a signal from a baseband integrated cir buffer, a second resistor coupled betWeen the ?rst node and a cuit to a radio frequency integrated circuit according to an second node, the second node being coupled to an input of the embodiment. second integrated circuit and a third resistor coupled betWeen the second node and ground. This provides a simple imple DETAILED DESCRIPTION mentation using passive components. [0018] In certain embodiments an interface betWeen a base [0021] In certain embodiments the apparatus forms part of band integrated circuit that uses a ?rst signalling standard and one of tWo signalling lines in a differential signalling system, a radio frequency integrated circuit that uses a second signal the differential signalling system coupling the baseband inte ling standard is provided. The signalling standards may relate grated circuit to the radio frequency integrated circuit. A to signals to be sent from, or received at, a particular physical second apparatus, or an additional part of the same apparatus, hardWare interface of a corresponding integrated circuit. The may supply similar components, eg a buffer and a resistor interface meets the required electrical speci?cation of each netWork, on the second of the tWo signalling lines. signalling standard. It enables physical data transmission [0022] In certain embodiments the resistance values of a betWeen the baseband integrated circuit and the radio fre plurality of in the resistor netWork are selected to quency integrated circuit. Voltage levels of the interface sig match a line impedance of the coupling betWeen the baseband nals are adjusted to meet a speci?ed range With passive com integrated circuit and the radio frequency integrated circuit. ponents and buffers. This simpli?es the interface and is more The resistance values may also be selected to match the cost-ef?cient than solutions that require separate, custom electrical speci?cation of the appropriate parts of both the made application-speci?c integrated circuits (ASIC). Certain ?rst and second signalling standards. embodiments thus enable voltage levels of interface signals to [0023] In certain embodiments a voltage source is coupled be controlled such that a serial data link betWeen a baseband to the resistor netWork via a coupling capacitor. The coupling integrated circuit and a radio frequency integrated circuit is capacitor prevents a drain current passing through the resistor functional in both transmit (TX) and receive (RX) directions. netWork and thus reduces the poWer consumption of the appa [0019] If the second signalling standard uses loWer voltage ratus. This is useful for mobile devices that have limited levels than the ?rst signalling standard then small changes in battery poWer. the output of the baseband integrated circuit have the poten [0024] FIG. 1A shoWs an exemplary mobile device 100 tial to cause any input received at the radio frequency inte comprising a baseband integrated circuit 110 and a radio grated circuit to be outside of the second signalling standard. frequency integrated circuit 120. The baseband integrated For example, What may be a small ?uctuation at the relatively circuit 110 may be con?gured to perform baseband process high voltage levels of the baseband integrated circuit may be ing; for example, on either a signal to be modulated and a large ?uctuation at the relatively loW voltage levels of the transmitted or on a signal that has been received and demodu radio frequency integrated circuit. Hence, in order for the lated. Baseband processing may comprise, amongst others, resistor netWork to accurately convert the voltage levels, encoding and decoding, error correction, data formatting, and baseband integrated circuits Would typically have to very bit manipulation. The radio frequency integrated circuit 120 closely match the ?rst signalling standard With little deviation may be con?gured to perform radio frequency processing; for from the standard. This Would restrict the baseband integrated example, to modulate a baseband signal received from the circuits that could be used, typically to more expensive or baseband integrated circuit for transmission using a carrier neWer circuits. HoWever, by using an apparatus With a buffer, Wave or to demodulate a received signal ready for baseband these strict requirements for the baseband integrated circuit processing and decoding. are relaxed, i.e. buffering reduces the requirements for a [0025] The interface betWeen a baseband integrated circuit baseband integrated circuit transceiver. Using one or more and a radio frequency integrated circuit forms a crucial part of buffers along With passive components makes certain any Wireless communication device. In FIG. 1A, the base embodiments easy to implement in various applications With band integrated circuit 110 comprises a transmitting compo out additional requirements for baseband integrated circuits. nent (TX) 132 for transmitting a signal over communication In certain variations the baseband integrated circuit uses a link 150 to a receiving component 144 of the radio frequency LoW-Voltage Differential Signalling (LVDS) standard and integrated circuit 120. In FIG. 1A, baseband integrated circuit the radio frequency integrated circuit uses a Scalable LoW 110 also comprises a receiving component 134 for receiving Voltage Signalling (SLVS) standard. For example, the radio a signal over communication link 160 from a transmitting frequency integrated circuit may have a physical interface component 142 of the radio frequency integrated circuit 120. con?gured according to the DigRFv4 standard, Which forms The transmitting component 132 and receiving component part of MIPI Alliance’s M-PHY standard. DigRFv4 supports 134 of the baseband integrated circuit 110 may collectively US 2013/0090148 A1 Apr. 11, 2013

comprise a physical port or interface 130 of the baseband tWo transmission lines 162 and 164 are provided and these are integrated circuit 110. Likewise, the transmitting component terminated by a resistive load in the form of resistor 175. 142 and receiving component 144 of the radio frequency Apparatus 190 acts to convert a signal produced according to integrated circuit 120 may collectively comprise a physical the second signalling standard to a signal that may be received port or interface 140 of the radio frequency integrated circuit by a component that utilises the ?rst signalling standard. 120. [0026] In the present embodiment, the baseband integrated [0030] FIG. 2A shoWs the con?guration of the ?rst compo circuit 110 has a physical interface 130 that meets a ?rst nent 182 in more detail. A similar con?guration may also be signalling standard; in this case the LoW-Voltage Differential used for the second component 184. In FIG. 2A the tWo end Signalling (LVDS) standard, Which has a nominal peak-to integrated circuits are illustrated: baseband integrated circuit peak voltage of 700 mV. The radio frequency integrated cir 110 comprising a transmitting component and radio fre cuit 120 has a physical interface 140 that meets a second quency integrated circuit 120 comprising a receiving compo signalling standard; in this case the DigRFv4 standard as nent. Any resistive loads, such as resistor 170, are omitted for developed by the MIPI Alliance. The DigRFv4 standard in clarity. The baseband integrated circuit 110, Which may for turn uses Scalable LoW-Voltage Signalling (SLVS) standard example be a Field Programmable Gate Array (FPGA), has a With a nominal peak-to-peak voltage of 200 mV (i.e. SLVS LVDS interface that produces a signal according to this stan 200). Hence, the tWo integrated circuits have input/output dard. The radio frequency integrated circuit 120, Which may (I/O) interfaces de?ned by different I/O signalling standards. use a physical layer interface (PHY) according to the M-PHY In the present embodiment, the use of LVDS and SLVS-200 standard, has an SLVS interface arranged to receive a signal are provided as example, in other embodiments an alternative according to this standard. A buffer 210 is coupled to the ?rst and/or second signalling standard may be used. LVDS output of the baseband integrated circuit and a resistor [0027] FIG. 1B shoWs communication links 150 and 160 in netWork 220. The buffer may comprise a unity gain buffer more detail. In the example of FIG. 1B, the transmitting ampli?er or voltage folloWer. In this case the buffer acts to component 132 of the baseband integrated circuit 110 is isolate the impedance seen at the input to the buffer, e. g. from coupled to the receiving component 144 of the radio fre the LVDS output, from the impedance seen at the buffer quency integrated circuit 120 using a differential signalling output, eg that is presented to the resistor netWork 220. In system. In the differential signalling system tWo transmission certain embodiments the buffer need not be a unity gain lines 152 and 154 are provided. The transmission lines 152 ampli?er. The use of a buffer relaxes the requirements of the and 154 are terminated by a resistive load, provided in FIG. baseband integrated circuit interface, eg it enables existing 1B by resistor 170. In this example a 100 Ohm resistor is used. baseband integrated circuits With LVDS interfaces to be used This is chosen to match the characteristic impedance of the Without modi?cation. The buffer may be, for example, a transmission links, Which is typically 50 Ohms per link. In DS25BR100 as supplied by National Semiconductor Corpo some implementations the load resistor may be integrated in ration, used Without pre-emphasis and Without equalisation. the receiving component. The transmission lines 152, 154 and [0031] As described above, the buffer is connected in turn resistor 170 provide a Wire loop. As in this example, the to resistor netWork 220. Resistor netWork 220 comprises a baseband integrated circuit uses the LVDS standard and so number of resistors, in this example three, that are provided produces a voltage signal With a 700 mV nominal peak-to along the transmission line 152 in order to convert a voltage peak voltage. As a data signal to be transmitted over the level for the ?rst signalling standard to a voltage level for the communication link 150 changes state, eg a digital binary second signalling standard. In this case the resistor netWork signal toggling from 1 to 0 or vice versa, the polarity of a 220 converts a LVDS voltage to a SLVS-200 voltage. FIG. 2A differential voltage signal generated over the communication shoWs three resistors: a ?rst resistor 222 With a resistance R1, link 150 changes, Which may be detected by the receiving a second resistor 224 With a resistance R2, and a third resistor component 144. For example, the baseband integrated circuit 226 With a resistance R3. The ?rst resistor 222 is coupled to a may generate an LVDS voltage signal With a +/—350 mV voltage source 240 supplying a voltage VCC via a direct cur voltage sWing on top of a 1.25V common-mode voltage. rent (DC) coupling capacitor 230. The DC coupling capacitor [0028] FIG. 1B shoWs an apparatus 180 that may form part 230 prevents a DC current ?oW from the voltage source, thus of communication link 150 and that acts to convert a signal reducing the poWer consumption of the apparatus 180. This is produced according to the ?rst signalling standard to a signal especially important for mobile devices Where poWer con that may be received by a component that utilises the second sumption needs to be minimised so as to maximise the battery signalling standard. The apparatus 180 may comprise tWo life for mobile operation. The DC coupling capacitor 230 also components: a ?rst component 182 to be used in relation to has a bene?t that it does not add to the impedance of the the ?rst differential transmission link 152 and a second com transmission line. The ?rst resistor 222 is then coupled to a ponent 184 to be used in relation to the second differential ?rst nodeA of the transmission line 152. The second resistor transmission link 154. Alternate single-ended embodiments 224 is coupled betWeen the ?rst node A and a second node B. may also be implemented, in Which case only one of trans The third resistor 226 is coupled betWeen the second node B mission link 152 and ?rst component 182 or transmission link and ground 250. The second node B is then coupled to the 154 and second component 184 may be used. input of the radio frequency integrated circuit 120. [0029] FIG. 1B also shoWs an apparatus 190 that may form part of communication link 160. In the example of FIG. 1B, [0032] The resistor netWork 220 provides a voltage divider the transmitting component 142 of the radio frequency inte Wherein a ?rst alternating current (AC) or differential voltage grated circuit 120 is coupled to the receiving component 134 seen at the ?rst node A, VA_ AC, is related to a second altemat of the baseband integrated circuit 110 using a differential ing current or differential voltage seen at the second node B, signalling system. The differential signalling system is simi VB_AC, via the equation: lar to the system that implements communication link 150: US 2013/0090148 A1 Apr. 11, 2013

(wherein, in this example, VA_ AC and VBAC both represent a communications between the radio frequency integrated cir peak-to-peak voltage swing, e.g. +/—X mV). The resistance cuit 120 and the baseband integrated circuit 110. In FIG. 3, a values R1, R2 and R3 are selected to match the characteristic buffer 310 similar to buffer 210 is provided. The buffer 310 is line impedance ZO of the transmission line at the ?rst node A, con?gured to additionally amplify, i.e. provide a voltage gain for example according to the equation: for, a signal from the radio frequency integrated circuit 120. The buffer 310 is con?gured to amplify this signal meeting the second signalling standard to a voltage level that meets the wherein the ?rst resistor is seen to be in parallel with the ?rst signalling standard. Hence, the buffer output signal, for a resistor pairing of the second and third resistors. The DC signal originating from the radio frequency integrated circuit voltage at the ?rst node A is calculated using the equation: 120, is at a correct level for the baseband integrated circuit 110 and a resistor network is not needed. This embodiment for the baseband integrated circuit receive direction thus and the DC voltage at the second node B is calculated using reduces the component count and is more cost-ef?cient. In the equation: certain embodiments, apparatus 180 and apparatus 190 may be provided as a single integrated interface apparatus. The values of VA_ AC and VA are set by the ?rst signalling [0038] Embodiments of the present invention may be standard. The values of VB_AC and VB are set by the second implemented in mobile devices. As used herein mobile signalling standard. The value of ZO depends on the properties devices include mobile or cell phones (including so-called of the transmission line; often it is approximated to 50 or 60 “smart phones”), personal digital assistants, pagers, tablet Ohms. The values of R1, R2, R3 and VCC are then chosen such and laptop computers, content-consumption or generation that the above equations are satis?ed. When using commer devices (for music and/or video for example), etc. Embodi cial components values may be selected that provide the best ments of the present invention may also be implemented approximate match to the speci?cations set by the signalling within wireless devices. “Wireless devices” include in gen standards. eral any device capable of connecting wirelessly to a network, [0033] For one particular implementation environment and includes in particular mobile devices as described above using LVDS as the ?rst signalling standard and SLVS-200 as as well as ?xed or more static devices, such as personal the second signalling standard: VA_ ACI350 mV and VAIl .34 computers, game consoles and other generally static enter V; VB_AC:86 mV and VB:0.327 V; and ZO:48.6Q. Hence, tainment devices, various other domestic and non-domestic values ofRl:l 209, R2:6l .89, R3I2OQ andVCC:3 .3 V may machines and devices, etc. The term “user equipment” is be used. These values are provided as an example based on often used to refer to wireless devices in general, and particu one optimiZed value set for a particular implementation envi larly mobile wireless devices, hence, embodiments may be ronment, different values may be used for different imple implemented with such “user equipment”. mentation environments and/ or different signaling standards. [0039] It will be understood that the circuitry referred to They demonstrate how different signaling standards may use herein may in practice be provided by a single chip or inte different AC and/ or DC voltage levels. grated circuit or plural chips or integrated circuits. The term [0034] FIG. 4 shows an exemplary method for physical data “coupled” is used to denote both a direct coupling, eg a transmission between a baseband integrated circuit that uses conductive trace between two components, and an indirect a ?rst signalling standard and a radio frequency integrated coupling, eg an electrical connection that may incorporate circuit that uses a second signalling standard. In this example, one or more intermediate electronic components. Likewise the ?rst signalling standard is LVDS and the second signal the term “coupled between” may denote a direct coupling, ling standard is SLVS-200 as set by M-PHY of the DigRFv4 e.g. conductive traces on either side of a component con standard. The method may be used with the apparatus of the nected to each of two other components, or an indirect cou preceding Figures. At step 410 an LVDS signal is received pling, eg the component may be coupled between the two from the baseband integrated circuit. At step 420 the signal is other components together with one or more additional elec buffered. At step 430 a voltage of the signal is converted, in tronic components. this case the voltage may be converted from a single line [0040] Although the present embodiments have been voltage of 350 mV to a line voltage of 200 mV. At step 440 the described in the context of a coupling between a baseband converted voltage is passed to the SLVS input of the radio integrated circuit and a radio frequency integrated circuit, frequency integrated circuit. A similar method may also be they may also be adapted for use in other M-PHY implemen provided for converting an SLVS output into an LVDS input, tations, for example for a ?rst and second integrated circuit in the voltage levels being accordingly adjusted. any one of display, camera, audio, video, and memory cou [0035] The above embodiments are to be understood as plings or power management systems. It is to be understood illustrative examples of the invention. Further embodiments that any feature described in relation to any one embodiment of the invention are envisaged. may be used alone, or in combination with other features [0036] For example, FIG. 2B shows one embodiment of described, and may also be used in combination with one or apparatus 180 wherein the second component 184 shares the more features of any other of the embodiments, or any com same con?guration as the ?rst component 182. bination of any other of the embodiments. Furthermore, [0037] As another example, FIG. 3 shows a variation for equivalents and modi?cations not described above may also apparatus 190. In certain embodiments, apparatus shares the be employed without departing from the scope of the inven same basic con?guration as apparatus 180, for example the tion, which is de?ned in the accompanying claims. con?gurations shown in FIG. 2A or FIG. 2B. This enables the 1. Apparatus for coupling a baseband integrated circuit that same basic con?guration to be used in both transmit and uses a ?rst signalling standard to a radio frequency integrated receive directions. In other embodiments, such as the embodi circuit that uses a second signalling standard, the apparatus ment shown in FIG. 3, an alternative con?guration is used for comprising: US 2013/0090148 A1 Apr. 11, 2013

a buffer coupled to the baseband integrated circuit; and 10. A mobile communications device comprising: a resistor network coupled betWeen the buffer and the radio a baseband integrated circuit for performing baseband pro frequency integrated circuit, the resistor netWork imple cessing of a signal, the baseband integrated circuit using menting a voltage divider so as to convert a ?rst voltage a ?rst signalling standard; used by the baseband integrated circuit to a second volt a radio frequency integrated circuit for performing radio age used by the radio frequency integrated circuit. frequency processing of a signal, the radio frequency 2. The apparatus of claim 1, Wherein the baseband inte integrated circuit using a second signalling standard; grated circuit uses a LoW-Voltage Differential Signalling and (LVDS) standard and the radio frequency integrated circuit an interface for coupling the baseband integrated circuit uses a Scalable LoW-Voltage Signalling (SLVS) standard. and the radio frequency integrated circuit, the interface 3. The apparatus of claim 1, Wherein the resistor netWork comprising: comprises: a buffer; and a ?rst resistor coupled betWeen a voltage source and a ?rst a resistor netWork coupled to the output of the buffer, the node, the ?rst node being coupled to an output of the resistor netWork implementing a voltage divider so as buffer; to convert a ?rst voltage used by one of the baseband a second resistor coupled betWeen the ?rst node and a integrated circuit and the radio frequency integrated second node, the second node being coupled to an input circuit to a second voltage used by the other of the of the radio frequency integrated circuit; and baseband integrated circuit and the radio frequency a third resistor coupled betWeen the second node and integrated circuit. ground. 11. The mobile communications device of claim 10, com 4. The apparatus of claim 3, comprising a coupling capaci prising a voltage source coupled to the resistor netWork via a tor coupled betWeen the voltage source and the ?rst resistor. coupling capacitor. 5. The apparatus of claim 1, Wherein the apparatus forms 12. The mobile communications device of claim 10, part of one of tWo signalling lines in a differential signalling Wherein the buffer and resistor netWork form part of a ?rst system, the differential signalling system coupling the base differential transmission line, a second differential transmis band integrated circuit to the radio frequency integrated cir sion line comprising a further buffer and a further resistor cuit. netWork. 6. The apparatus of claim 1, Wherein resistance values of a 13. The mobile communications device of claim 10, plurality of resistors in the resistor netWork are selected to Wherein the baseband integrated circuit uses a LoW-Voltage match a line impedance of the coupling betWeen the baseband Differential Signalling (LVDS) standard and the radio fre integrated circuit and the radio frequency integrated circuit. quency integrated circuit uses a Scalable LoW-Voltage Sig 7. Apparatus for coupling a baseband integrated circuit that nalling (SLVS) standard. uses a ?rst signalling standard to a radio frequency integrated 14. A method for communicating a data signal betWeen a circuit that uses a second signalling standard, the apparatus baseband integrated circuit that uses a ?rst signalling stan comprising: dard and a radio frequency integrated circuit that uses a sec a resistor netWork coupled betWeen the baseband inte ond signalling standard comprising: grated circuit and the radio frequency integrated circuit, receiving a data signal produced by one of the baseband the resistor netWork implementing a voltage divider so integrated circuit and the radio frequency integrated cir as to convert a ?rst voltage used by the baseband inte cuit; grated circuit to a second voltage used by the radio buffering the data signal; frequency integrated circuit, the resistor netWork com adjusting a voltage of the data signal from a ?rst voltage prising: used by said one of the baseband integrated circuit and a ?rst resistor coupled betWeen a voltage source and a the radio frequency integrated circuit to a second voltage ?rst node, the ?rst node being arranged to receive a used by the other of the baseband integrated circuit and signal from the baseband integrated circuit; the radio frequency integrated circuit; and a second resistor coupled betWeen the ?rst node and a passing the data signal to an input of said other of the second node, the second node being coupled to an baseband integrated circuit and the radio frequency inte input of the second integrated circuit; and grated circuit. a third resistor coupled betWeen the second node and 15. The method of claim 14, comprising: ground; and applying a voltage source to the resistor netWork via a a coupling capacitor coupled betWeen the voltage source coupling capacitor. and the ?rst resistor. 16. Apparatus for coupling a baseband integrated circuit 8. The apparatus of claim 7, Wherein the baseband inte that uses a ?rst signalling standard to a radio frequency inte grated circuit uses a LoW-Voltage Differential Signalling grated circuit that uses a second signalling standard, the appa (LVDS) standard and the radio frequency integrated circuit ratus comprising: uses a Scalable LoW-Voltage Signalling (SLVS) standard. a buffer coupled to the radio frequency integrated circuit, the buffer being arranged to adjust a voltage of the data 9. The apparatus of claim 7, Wherein the apparatus forms signal from a ?rst voltage speci?ed by the second sig part of one of tWo signalling lines in a differential signalling nalling standard to a second voltage speci?ed by the ?rst system, the differential signalling system coupling the base band integrated circuit to the radio frequency integrated cir signalling standard. cuit. * * * * *