Abstract:
A millimeter-wave radio frequency (RF) system, and method thereof for transferring multiple signals over a single transmission line connected between modules of a millimeter-wave RF system. The system comprises a single transmission line for connecting a first part of the RF system and a second part of the RF system, the single transmission line transfers a multiplexed signal between the first part and second part, wherein the multiplexed signal includes intermediate frequency (IF) signal, a local oscillator (LO) signal, a control signal, and a power signal; the first part includes a baseband module and a chip-to-line interface module for interfacing between the baseband module and the single transmission line; and the second part includes a RF module and a line-to-chip interface module for interfacing between the RF module and the single transmission line, wherein the first part and the second part are located away from each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/153,667 filed on Jun. 6, 2011, as U.S. Pat. No. 8,670,322. The contents of which are herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to radio frequency (RF) systems, and more particularly to enabling connectivity, and transmission of signals between RF modules of a RF system using a single transmission line. 
     BACKGROUND 
     The 60 GHz band is an unlicensed band which features a large amount of bandwidth and a large worldwide overlap. The large bandwidth means that a very high volume of information can be transmitted wirelessly. As a result, multiple applications, that require transmission of a large amount of data, can be developed to allow wireless communication around the 60 GHz band. Examples for such applications include, but are not limited to, wireless high definition TV (HDTV), wireless docking stations, wireless Gigabit Ethernet, and many others. 
     In order to facilitate such applications there is a need to develop integrated circuits (ICs), such as amplifiers, mixers, radio frequency (RF) analog circuits, and active antennas that operate in the 60 GHz frequency range. An RF system typically comprises active and passive modules. The active modules (e.g., a phase-array antenna) require, control and power signals for their operation, which are not required by passive modules (e.g., filters). The various modules are fabricated and packaged as RFICs that can be assembled on a printed circuit board (PCB). The size of the RFIC package may range from several to a few hundred square millimeters. 
     In the market of consumer electronics, the design of electronic devices, and thus RF modules integrated therein, should meet the constraints of minimum cost, size, and weight. The design of the RF modules should also take into consideration the current assembly of electronic devices, and particularly handheld devices, such as laptop and tablet computers in order to enable efficient transmission and reception of millimeter wave signals. 
     A schematic diagram illustrating the assembly of a laptop computer  100  that includes an RF system  110  for transmission and reception of millimeter wave signals is shown in  FIG. 1 . The form factor of the RF system  110  is spread between the base  102  and lid planes  105  of the laptop computer  100 . 
     The RF system  110  includes two parts: a baseband module  120  and RF module  130  respectively connected to the base plane  102  and lid plane  105 . The RF module  130  includes active transmit (TX) and receive (RX) antennas. When transmitting signals, the baseband module  120  typically provides the RF module  130  with control, local oscillator (LO), intermediate frequency (IF), and power (DC) signals. The control signal is utilized for functions, such as gain control, RX/TX switching, power level control, sensors, and detectors readouts. Specifically, beam-forming based RF systems require high frequency beam steering operations which are performed under the control of the baseband module  120 . The control typically originates at the baseband  120  of the system, and transfers between the baseband module  120  and RF module  130 . 
     The RF module  130  typically performs up-conversion, using a mixer (not shown) on the IF signal(s) to RF signals and then transmits the RF signals through the TX antenna according to the control of the control signals. The power signals are DC voltage signals that power the various components of the RF module  130 . 
     In the receive direction, the RF module  130  receives RF signals at the frequency band of 60 GHz, through the active RX antenna and performs down-conversion, using a mixer, to IF signals using the LO signals, and sends the IF signals to baseband module  120 . The operation of the RF module  130  is controlled by the control signal, but certain control information (e.g., feedback signal) is sent back to the baseband module  120 . An example for the assembly shown in  FIG. 1  can be found in US patent Application Publication 2010/0035561, which is assigned to the common assignee. 
     Current solutions require least two cables (transmission lines) are needed to transfer the IF, LO, power, and control signals between the baseband and RF modules  120  and  130 . 
     This drawback is critical in millimeter-wave RF systems, e.g., systems that operate in the 60 GHz frequency bands, as the RF module  130  must be located close to the active antennas to perform the functions described above in order to minimize the power loss of the received and transmit signals. Thus, the baseband module  120  is located apart from the RF module  130 . Further, because transferring high frequency signals over the cables significantly attenuates the signals, cables that provide low attenuation characteristics are utilized. However, such cables are relativity expensive, thus increasing the bill of material (BoM) of consumer electronics devices. 
     It would be therefore advantageous to provide a solution for connecting, using a single transmission line, radio frequency modules in an electronic device for use in at least the 60 GHz frequency band. 
     SUMMARY 
     Certain embodiments disclosed herein also include a millimeter-wave radio frequency (RF) system. The system comprises a single transmission line for connecting a first part of the RF system and a second part of the RF system, the single transmission line transfers a multiplexed signal between the first part and second part, wherein the single transmission line is a metal line fabricated on a multilayer substrate; wherein the multiplexed signal includes intermediate frequency (IF) signal, a local oscillator (LO) signal, a control signal, and a power signal; the first part includes a baseband module and a chip-to-line interface module for interfacing between the baseband module and the single transmission line; and the second part includes a RF module and a line-to-chip interface module for interfacing between the RF module and the single transmission line, wherein the first part and the second part are located away from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a diagram illustrating the assembly of a laptop computer having radio transmission capabilities in the 60 GHz band. 
         FIG. 2  is a diagram of a RF system constructed according to an embodiment of the invention. 
         FIG. 3  is a diagram of a multiplexer constructed according to an embodiment of the invention. 
         FIG. 4  is a diagram of a frequency plan utilized for multiplexing signals according to an embodiment of the invention. 
         FIGS. 5A and 5B  are diagrams of a bias-T unit designed according to an embodiment of the invention. 
         FIG. 6A  depicts graphs illustrating return loss varying with frequency measured for the LO and IF signals multiplexed by the proposed solution. 
         FIG. 6B  depicts graphs illustrating channel transmission loss measured for the LO and IF signals multiplexed by the proposed solution. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments disclosed by the invention are only examples of the many possible advantageous uses and implementations of the innovative teachings presented herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views. 
     Certain embodiments disclosed herein enable the connectivity of various RF modules using a single transmission line. In one embodiment, the connectivity is between a baseband module and a RF module, including active electrical elements in an electronic device having a distributed form factor of a motherboard and RF module. 
     A schematic diagram of an RF system  200  utilized to describe various embodiments of the invention is illustrated in  FIG. 2 . The RF system  200  includes a baseband module  210  coupled to a chip-to-line interface module  220 . In addition, the RF system  200  includes an RF module  230  coupled to a line-to-chip interface unit  240 . The RF module  230  comprises a RF circuitry  231  to perform up and down conversions of radio signals and to control the TX and RX active antennas  232  and  233 . In an embodiment of the invention, each of the antennas  232  and  233  is a phase array antenna. The RF system  200  enables the efficient transmission and reception of signals in at least the 60 GHz band. 
     The baseband module  210  and RF module  230  are apart from each other and are connected using a single transmission line  250  through the interfaces  220  and  240 . In one embodiment, the baseband and RF modules  210  and  230  are respectively located at the base and lid planes of a laptop computer. One of ordinary skill should appreciate that a connection between these planes is using, for example, a cable. Placing the baseband and RF modules  210  and  230  apart from each is required to locate the active antennas at such a location where optional reception/transmission of signals may be achieved. Such a location is typically not in proximity to the baseband module which is usually placed by the device&#39;s fan/ventilation. As another example, at a tablet computer, the baseband and RF modules  210  and  230  are located at opposite ends of the tablet. 
     At least four different signals are simultaneously transferred over the transmission line  250  including, but not limited to, power, control, intermediate frequency (IF), and local oscillator source (LO). It should be noted that the IF and control signals are transferred over the line  250  in both directions. The control signal controls, at least, the switching of the TX and RX active antennas, the direction of the antenna (beam forming), and gain control. The LO signals are required to synchronize the two modules and to perform up and down conversions of high frequency signals. 
     Each signal transferred over the transmission line  250  has a different frequency band. In an embodiment of the invention, a frequency plan is disclosed that enables the efficient transfer of the five signals over the transmission line  250 . In accordance with an embodiment of the invention, the transmission line  250  is a standard micro coaxial cable. In this embodiment, the connection between the PCS and the micro coaxial cable is using a micro connector. According to another embodiment, the transmission line  250  can be formed by fabricating a metal line on a multilayer substructure. 
     During the simultaneous transfer of the LO, IF, control and power signals over the transmission line  250 , the interface units  220  and  240  are utilized. The interface units  220  and  240  multiplex the various signals and impedance matches between the transmission line  250  and the PCBs to which the modules  210  and  230  are connected to. 
     As shown in  FIG. 2 , the chip-to-line interface unit  220  includes a multiplexer  222  and a Bias-T unit  224  and the line-to-chip interface unit  240  includes a demultiplexer  242  and a Bias-T unit  244 . The multiplexer  222  multiplexes the IF signal, LO signal, and control signal to be output on a single output provided to the input of the Bias-T unit  224 . The Bias-T unit  224  adds a DC voltage signal from a power source and outputs the signal to the transmission line  250 . The multiplexer  222  also performs a demultiplexing operation to produce the IF signal(s) and control signal transferred from the RF module  230 . 
     The demultiplexer  242  de-multiplexes the input received on the transmission line  250 , to generate the control signal, IF signal, and LO signal. Prior to that, the Bias-T unit  244  extracts the DC voltage signal to power the RF module  230 . It should be noted that the DC voltage signal is always provided to the RF module  230  to enable proper operation. The demultiplexer  242  also performs a multiplexing operation on the IF signal (results of a down conversion of the received RF signals) and control signal to be transferred to the baseband module  210 . 
     In the embodiment illustrated in  FIG. 2 , the multiplexer  222  and Bias-T unit  224  are integrated in the baseband module  210  which are embedded in an RFIC. In the same fashion, the demultiplexer  242  and Bias-T unit  244  are integrated in the RF module  230 , which is fabricated as an RFIC. In another embodiment, the multiplexer  222  and demultiplexer  242  are part of the baseband and RF modules respectively, thus are part of RFICs. The Bias-T units  224  and  244 , on the other hand, are part of PCBs  201  and  202 , thus the DC signal multiplexing/demultiplexing is performed over the PCBs. 
     In an embodiment of the invention the source of the LO signal is at the RF module  230 . Accordingly, the LO signal is multiplexed with the received IF signal (after down conversion) and transferred to the baseband module  210  over the transmission line  250 . 
     In the embodiment shown in  FIG. 2 , the baseband module  210  and RF module  230  are fabricated on different substrates and connected using a transmission line (e.g., a cable). According to another embodiment of the invention, the RF and baseband modules are fabricated on the same substrate and are connected using a coaxial cable. In this embodiment, the techniques disclosed herein for multiplexing the signals are also applied. 
       FIG. 3  shows a non-limiting block diagram of the multiplexer  222  constructed in accordance with an embodiment of the invention. The multiplexer  222  separates the frequency spectrum to three different frequency bands: f IF , f LO , and f CTRL  to multiplex the LO signal, IF signal, and control signal in these bands respectively. Specifically, the multiplexer  222  includes a high-pass filter (HPF)  310 , a base-pass filter (BPS)  320 , and a low-pass filter (LPF)  330 ; each passes signals in the f IF , f LO , and f CTRL  respectively. 
     In accordance with an embodiment, to ensure reliable transfer of signals over the transmission line  250 , the frequencies of f IF , f LO , and f CTRL  are set to 13-17.4 GHz, 7-8.2 GHz, 200 Mhz-1.5 GHz respectively. This frequency plan is also illustrated in  FIG. 4 . According to another embodiment, the frequency plan may be set as follows: the f IF  is 13 GHz to 17.4 GHz; the f LO  is below 1 GHz, and the f CTRL  is 200 MHz to 1.5 GHz. According to another embodiment of the invention, the f IF  is 5 GHz to 10 GHz, the f LO  band is below 100 MHz, and the f CTRL  is above 10 GHz. Yet in another embodiment, the frequency plan is: f IF  is 5 GHz to 10 GHz, the f LO  is above 15 GHz, and the f CTRL  of the control signal is 200 MHz to 1.5 GHz. 
     In another embodiment, when the control and IF signal never overlap during the operation, it is safe to use the same frequency band for control and IF signal, by sharing hardware elements, such as RX and TX circuitry, and matching networks, thereby reducing the complexity of multiplexing the signals. 
     The demultiplexer  242  has the same structure as the multiplexer  222  and also includes a high-pass filter (HPF), a base-pass filter (BPS), and a low-pass filter (LPF) that filter the multiplexed signal received on the line  250  to the IF signal, LO signal, and control signal respectively. 
       FIG. 5A  is an exemplary and non-limiting electrical diagram equivalent to the bias-T unit  224  implemented according to an embodiment of the invention. The unit  224  is connected to the metal line  501  between the output of the multiplexer  222  and a connector  502  of the transmission line  250 . The metal line  501  is printed on the PCB. 
     A typical bias-T is a three-port network used for setting a DC bias point of an electronic element without disturbing other elements. The low frequency port is used to set the bias, a high frequency port passes the radio frequency signals but blocks the biasing levels, and a combined port connects to the device, which sees both the bias and RF. A conventional bias-T is based on a capacitor that allows AC through but blocks the DC bias and an ideal inductor that blocks AC, but allows DC. The conventional bias-T cannot be utilized in millimeter-wave frequency, as there are no explicit inductors available based on PCB traces and/or PCB mounted. Further, a conventional bias-T cannot be utilized in the proposed solution, as there are at least 3 different frequencies (i.e., AC) that should be passed or blocked by the bias-T module. 
     According to certain embodiments of the invention, the inductor is replaced by a resonance network that resonates at the frequency bands of the LO, IF and control signals. As illustrated in  FIG. 5A , the Bias-T unit  224  includes a capacitor  505  and a resonance network  510  for inserting DC voltage signal provided by a power source  520 , at a port  503 , to the high frequency multiplexed signal output by the multiplexer  222 . In certain embodiments of the invention, the capacitor  505  is part of the multiplexer  222 , i.e., fabricated in the RFIC containing the multiplexer  222 . The output at the connector  504  includes multiplexed LO, IF and control signals with a DC signal. The Bias-T unit  224  blocks the DC levels from returning to the input port  502  using the capacitor  505 . 
     The resonance network  510  introduces to the metal line  501  an open circuit for the f LO , f IF , and f CTRL  frequencies. Specifically, the resonance network  510  includes 3 sub-networks  511 ,  512 , and  513  designed to resonate in the f LO , f IF , and f CTRL  frequencies respectfully, thus blocking AC signals at these frequencies. This is achieved as each sub-network shorts the signal at the resonance frequency. The capacitor (C) and inductor (L) values are defined according to the resonance frequency. 
     In an embodiment of the invention, the resonance network  510  is implemented using a transmission line, to meet the constraints of millimeter-wave circuits. An exemplary and non-limiting diagram illustrating the implementing of one of the sub-networks, e.g., a sub-network  511  is shown in  FIG. 5B . 
     Each branch of an LC circuit is replaced by a transmission line having a length of a quarter of a wavelength (λ/4). The wavelength corresponds to the resonance frequency, i.e., one of the f LO , f IF , and f CONT  frequencies (λ=c/f, where c is the speed of light and f is the frequency). The transmission line  550  is connected to the power source  520 , while the transmission line  555  is connected to the ground. Thus, the structure shown in  FIG. 5B , opens (i.e., provides a very high impedance) signals at the resonance frequency and allows DC signal to pass to the connector  502 . 
       FIG. 6A  depicts graphs  601  and  602  of a return-loss varying with the frequency measured at the connection of the transmission line  250  to the PCB at the RF module  230 . The graph  601  and  602  respectively represent the LO signal and the IF signal of the multiplexed signal output by the multiplexer  222 . The return-loss is a measure of voltage standing wave ratio (VSWR), expressed in decibels (dB) and may be caused due to an impedance mismatch. A high value of return-loss denotes better quality of the electrical element under test. As can be noticed for frequency bands f LO  (7 GHz-8.2 GHz) and f IF  (13 GHz-17 GHz), the measured return-loss is well above +10 dB. A person with ordinary skill in the art should appreciate that such a result represents a low return-loss value, thus good performance of the signals transmitted to the RF module. 
       FIG. 6B  depicts graphs  603  and  604  representing the loss of the LO and IF signals measured from the path of a PCB point at the input of the transmission line ( 250 ) through the line ( 250 ), to a PCB point at the output of the transmission line ( 250 ) at the RF module. The measurement is for the frequency spectrum of the multiplexed signal, which is between DC and 20 GHz. As can be noticed, in the entire frequency band the loss of both signals is below +10 dB. A person with ordinary skill the art should appreciate that such a result represents good performance of the disclosed solution. 
     It is important to note that these embodiments are only examples of the many advantageous uses of the innovative teachings herein. Specifically, the innovative teachings disclosed herein can be adapted in any type of consumer electronic devices where reception and transmission of millimeter wave signals is needed. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, it is to be understood that singular elements may be in plural and vice versa with no loss of generality. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.