Patent Publication Number: US-7902938-B2

Title: Data transmitter, data transmission line, and data transmission method

Description:
TECHNICAL FIELD 
     The present invention relates to a data transmitter, data transmission line, and data transmission method and, more particularly, to a data transmitter, data transmission line, and data transmission method between integrated circuits. 
     BACKGROUND ART 
     U.S. Pat. No. 5,319,755 (reference 1) discloses a conventional data transmission method between integrated circuits. According to this method, as shown in  FIG. 1 , a transmission line  1  serving as a data bus connects input/output circuits  3  present in respective integrated circuit chips  2 . The transmission line  1  transmits digital signals to transmit data between the integrated circuits  2 . 
     This method poses an upper limit on the data transmission speed between the integrated circuits  2 , and it is difficult to transmit a basic clock of several GHz or more. The problem is negligible when the basic clock frequency of a signal propagating through the transmission line  1  is equal to or smaller than several GHz. However, when the basic clock frequency becomes equal to or higher than several GHz, the signal exhibits the dispersion phenomenon owing to the property of the transmission line  1 , and the influence of the dispersion phenomenon is not negligible. The dispersion phenomenon is that the pulse transmission speed changes depending on the frequency component, so input and output pulses differ in shape or the pulse width increases, inhibiting high-speed pulse transmission. This problem becomes serious when a capacity  5  accessory to the input/output circuit  3  of the integrated circuit  2  has a larger value. 
     U.S. Pat. No. 5,023,574 (reference 2) discloses a technique of generating a high-speed pulse. According to this technique, many varactor diodes are arranged at proper intervals in a transmission line to generate a nonlinear wave. This technique is disadvantageously applicable to only a case where the structure of a transmission line is very special, i.e., the transmission line is formed on a board surface, like a microstrip line or coplanar line, because varactor diodes must be inserted midway along the transmission line. 
     Japanese Patent Laid-Open No. 2001-111408 (reference 3) discloses a structure for packaging a high-speed signal transmission wire. In this structure, the distance between an impedance mismatched portion on a transmitting board and that on a receiving board is set such that the signal transmission time becomes an integer multiple of the time half the signal switching cycle. This structure suppresses temporal fluctuations caused by a reflected wave, and reduces jitters. Japanese Patent Laid-Open No. 2001-251030 (reference 4) discloses a line system between integrated circuits that controls a signal transmission delay by arranging a capacitive load structure on a line connecting integrated circuits. 
     Japanese Patent Laid-Open No. 2003-198215 (reference 5) discloses an arrangement which unifies the signal transmission speed. According to this reference, a long transmission line is formed in a low-permittivity region, and a short transmission line is formed in a high-permittivity region on a transmission line board on which a plurality of circuit components are mounted on a dielectric board and many transmission lines for connecting the circuit components are formed on the dielectric substrate. Japanese Patent Laid-Open No. 5-63315 (reference 6) discloses a printed wiring board on which delay pads are arranged on part of a signal line on the printed wiring board, and delay pads corresponding in number to a change of the delay time so that the control signal and data signal become in phase. 
     Japanese Patent Laid-Open No. 5-283824 (reference 7) discloses a circuit board configured to prevent reflection between devices having different electrode pads by coating a circuit board having a specific permittivity with a material having a different permittivity and controlling the permittivity. 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     It is, therefore, an object of the present invention to implement a high data transmission speed of several Gbits/sec to 10 Gbits/sec or more in data transmission between integrated circuits. 
     It is another object of the present invention to achieve a high data transmission speed even by using transmission lines formed not only on a general printed wiring board but also in layers of a high-density multilayered printed wiring board. 
     Means of Solution to the Problems 
     In order to achieve the above objects, a data transmitter according to the present invention is characterized by comprising a plurality of integrated circuits each having at least one input/output circuit, and a transmission line which connects to the input/output circuits of the integrated circuits and has an element that changes an effective reactance per unit length depending on at least one of a signal voltage and a signal current. 
     A data transmission line according to the present invention is characterized by comprising an element which changes an effective reactance per unit length depending on at least one of a signal voltage and a signal current. 
     A data transmission method according to the present invention is characterized by comprising the steps of preparing a transmission line whose effective reactance per unit length changes depending on at least one of a signal voltage and a signal current, and transmitting a signal between a plurality of integrated circuits via the transmission line. 
     Effects of the Invention 
     The present invention can change the effective reactance per unit length of a transmission line (data transmission line) in accordance with at least one of the signal voltage and signal current of a transmitted pulse signal. As a result, a nonlinear wave is generated in the transmission line, and a transmitted pulse signal can reach the receiving side without any influence of the dispersion phenomenon caused by the transmission line. Since the pulse waveform hardly changes and the pulse width hardly increases, high-speed data transmission can be achieved. 
     No varactor diode need be inserted in the transmission line, unlike the prior art. High-speed data transmission can be implemented even using transmission lines formed not only on a general printed wiring board but also in layers of a high-density multilayered printed wiring board. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a conventional data transmitter between a plurality of integrated circuits that transmits data between the integrated circuits via a transmission line; 
         FIG. 2  is a block diagram showing the arrangement of a data transmitter between integrated circuits according to the first embodiment of the present invention; 
         FIG. 3  is a plan view showing an example of a concrete structure for implementing the data transmitter between integrated circuits shown in  FIG. 2 ; 
         FIG. 4  is a sectional view taken along the line A-A′ in  FIG. 3 ; 
         FIG. 5  is a sectional view taken along the line B-B′ in  FIG. 3 ; 
         FIG. 6  is a graph showing the relationship between the electric field and dielectric polarization of a dielectric used for a transmission line; 
         FIG. 7  is a graph showing the relationship between the capacitance of the transmission line and the signal voltage in the use of a dielectric having the characteristic shown in  FIG. 6  for the transmission line; 
         FIG. 8  is a graph showing the relationship between the magnetic field and magnetization of a magnetic substance used for the transmission line; 
         FIG. 9  is a graph showing the relationship between the inductance of the transmission line and the signal current in the use of a magnetic substance having the characteristic shown in  FIG. 8  for the transmission line; 
         FIG. 10  is a block diagram showing the arrangement of a data transmitter between integrated circuits according to the second embodiment of the present invention; 
         FIG. 11  is a plan view showing an example of a concrete structure for implementing the data transmitter between integrated circuits shown in  FIG. 10 ; 
         FIG. 12  is a sectional view taken along the line C-C′ in  FIG. 11 ; 
         FIG. 13  is a sectional view taken along the line D-D′ in  FIG. 11 ; 
         FIG. 14  is a graph showing the circuit simulation results of data transmitters each between integrated circuits according to the embodiment and prior art; 
         FIG. 15  is a plan view showing the arrangement of a transmission line according to the third embodiment of the present invention; and 
         FIG. 16  is a sectional view taken along the line E-E′ in  FIG. 15 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     Outline of Embodiments 
     As shown in  FIGS. 2 and 10 , a data transmitter between integrated circuits according to embodiments of the present invention comprises a plurality of integrated circuits  102  and a transmission line (data transmission line between integrated circuits)  101  which connects the integrated circuits  102 . 
     One integrated circuit  102  comprises an internal circuit  104  having a proper arrangement and at least one appropriate input/output circuit  103 . The input/output circuit  103  connects to the transmission line  101 . These circuit arrangements are not particularly limited, and an integrated circuit  102  of a known arrangement is available. 
     The effective reactance component per unit length of the transmission line  101  changes depending on at least one of the signal voltage and signal current. More specifically, the transmission line  101  comprises an element which changes at least one of the effective capacitive component and effective inductance component per unit length depending on at least one of the signal voltage and signal current. 
     As shown in  FIGS. 3 to 5 , the transmission line  101  may be formed in a proper printed wiring board  200 . In this case, the transmission line  101  comprises a ground conductor  305  formed on the printed wiring board  200 , an insulating material  3  arranged in the printed wiring board  200 , and a signal conductor  201  arranged in the insulating material  3 . Note that the ground conductor  305  may be formed in the printed wiring board  200 . 
     Alternatively, as shown in  FIGS. 11 to 13 , the transmission line  101  may be formed on the proper printed wiring board  200 . In this case, the transmission line  101  comprises a ground conductor  305  and signal conductor  501  formed apart from each other on the printed wiring board  200 , and an insulating material  3  which is sandwiched between the ground conductor  305  and the signal conductor  501  on the printed wiring board  200  and is joined to the ground conductor  305  and signal conductor  501 . 
     The ground conductor  305  is grounded, a signal voltage is applied between the signal conductor  201  and the ground conductor  305 , and the insulating material  3  insulates the signal conductor  201  and ground conductor  305  from each other. 
     The insulating material  3  contains, e.g., a dielectric  320  as an element which changes the effective reactance per unit length of the transmission line  101  depending on at least one of the signal voltage and signal current. As shown in  FIG. 6 , the dielectric  320  is a material exhibiting a nonlinear relationship between an electric field and dielectric polarization generated in the dielectric  320 . For example, at least one of lead zirconate titanate, bismuth strontium tantalate, ferroelectric, and liquid crystal is available as the dielectric  320 . 
     Instead of the dielectric  320 , a magnetic substance  330  is also available as the above-mentioned element. As shown in  FIG. 8 , the magnetic substance  330  is a material representing a nonlinear relationship between a magnetic field and magnetization generated in the magnetic substance  330 . For example, at least one of NiZn ferrite and sendust (Fe—Si—Al alloy) is available as the magnetic substance  330 . 
     Note that the maximum value of a change component in the effective reactance per unit length that changes depending on at least one of the signal voltage and signal current in the transmission line  101  is preferably equal to or larger than a fixed component independent of the signal voltage and signal current. 
     The above-mentioned integrated circuit  102  and transmission line  101  may be formed on the same printed wiring board  200 , as shown in  FIGS. 3 to 5 , or formed on different substrates. It is also possible to adopt an arrangement in which the transmission line  101  is formed singly and connected to the input/output circuit  103  of each integrated circuit  102 . 
     Embodiments of the present invention will be described in more detail. 
     First Embodiment 
     A data transmitter  1  between integrated circuits and a transmission line  101  according to the first embodiment of the present invention will be explained with reference to  FIGS. 2 to 5 . 
     As shown in  FIG. 2 , a plurality of integrated circuits  102  have input/output circuits  103 , which connect to the transmission line  101 . The integrated circuits  102  exchange data by transmitting/receiving digital pulses from/by the input/output circuits  103 . 
     In  FIGS. 3 to 5 , each integrated circuit  102  is formed from an integrated circuit chip  102 , and a plurality of integrated circuit chips  102  are arranged on a printed wiring board  200 . The integrated circuit  102  has an input/output terminal  103  as the input/output circuit  103 . 
     The printed wiring board  200  has the transmission line  101 . The transmission line  101  is a strip line formed from an insulating material  3 , a ground conductor  305  formed on the insulating material  3 , and a signal conductor  201  arranged in the insulating material  3 . The insulating material  3  has a through via hole  210 . The input/output terminal  103  of the integrated circuit chip  102  connects to the signal conductor  201  via the through via hole  210 . 
     The insulating material  3  uses a dielectric  320 . The dielectric  320  is a material such as ferroelectric or liquid crystal which exhibits a nonlinear relationship between the electric field E and dielectric polarization P in the dielectric, as shown in  FIG. 6 . In the example of  FIG. 6 , the dielectric  320  has a characteristic of gradually increasing the absolute value of the dielectric polarization P as the absolute value of the electric field E increases. 
     From this, as shown in  FIG. 7 , the capacitive component C (pF) per unit length of the strip line changes depending on the signal voltage V. In the example of  FIG. 7 , the capacitive component C decreases as the signal voltage V rises. 
     When the relation of equation (1) holds, a nonlinear wave having a pulse width T given by equation (2) is generated in response to input of an electrical pulse signal to the transmission line  101 :
 
 C ( V )=1/( aV+b )  (1)
 
 T=[LC ( V   0 ){( aV   0   +b )/ a}/A]   1/2   (2)
 
where A is the pulse amplitude and V 0  is the offset value of the signal voltage.
 
     The waveform (signal voltage) of the nonlinear wave is given by
 
 V ( x,t )= A sec h   2 ( kx−ωt )  (3)
 
In this case, k satisfies equation (4) and ω satisfies equation ( 5 ):
 
sin  hk=[A/F ( V   0 )] 1/2   (4)
 
ω=[ A/{LC ( V   0 ) F ( V   0 )] 1/2   (5)
 
where
 
 F ( V   0 )≡1 /{aC ( V   0 )}= a/b+V   0   (6)
 
where V 0  is the offset value of the signal voltage.
 
     In the first embodiment, as shown in  FIG. 2 , a nonlinear capacitor  820  is formed between the signal conductor  201  and ground conductor  305  of the transmission line  101 . 
     The data transmitter  1  between integrated circuits according to the first embodiment may adopt a dielectric which changes the effective inductance component per unit length (cm) of the transmission line  101  depending on at least one of the signal voltage and signal current. 
     Since a nonlinear wave generated in the transmission line  101  is a solitary wave free from any dispersion, the pulse width does not increase on the receiving side or the waveform does not change. Data transmission between the integrated circuits  102  can use short-width pulses, implementing high-speed data transmission at several Gbits/sec to 10 Gbits/sec or more. 
     An example of using the dielectric  320  as the insulating material  3  has been described, but a magnetic substance  330  is also available as the insulating material  3 . The magnetic substance  330  is a material representing a nonlinear relationship between the magnetic field H and magnetization M generated in the magnetic substance  330 , as shown in  FIG. 8 . In the example of  FIG. 8 , the magnetic substance  330  has a characteristic of gradually increasing the absolute value of the magnetization M as the absolute value of the magnetic field H increases. 
     By using the magnetic substance  330  as part of the insulating material  3 , a nonlinear wave can be generated in response to input of an electrical pulse signal to the transmission line  101 , similar to the use of the above-mentioned dielectric  320 . 
     For example, the effective inductance component per unit length (cm) of the transmission line  101  is set to change with, e.g., a state as shown in  FIG. 9  depending on the signal current (the effective inductance component decreases along with an increase in signal current). This arrangement can generate a nonlinear wave in response to input of an electrical pulse signal to the transmission line  101 . Data transmission between the integrated circuits  102  can use short-width pulses, achieving high-speed data transmission at several Gbits/sec to 10 Gbits/sec or more. 
     Second Embodiment 
     A data transmitter  1  between integrated circuits and a transmission line  101  according to the second embodiment of the present invention will be described with reference to  FIGS. 10 to 13 . 
     The second embodiment is different from the first embodiment in that a signal conductor  501  of the transmission line  101  is formed on the surface of a printed wiring board  200 . The transmission line  101  connects to input/output circuits  103  of a plurality of integrated circuits  102  arranged on the printed wiring board  200  to execute data transmission between the integrated circuits  102 . 
     In  FIGS. 11 to 13 , each integrated circuit  102  is formed from an integrated circuit chip  102 , and a plurality of integrated circuit chips  102  are arranged on the printed wiring board  200 . The integrated circuit  102  has an input/output terminal  103  as the input/output circuit  103 . 
     The printed wiring board  200  has the transmission line  101 . The transmission line  101  is a coplanar line formed from the signal line conductor  501 , ground conductors  305  arranged on the two sides of the signal line conductor  501  so as to be spaced apart from the signal line conductor  501 , and an insulating material  3  interposed between the signal line conductor  501  and the ground conductor  305 . 
     A dielectric  320  contained as at least part of the insulating material  3  is a material such as ferroelectric or liquid crystal which exhibits a nonlinear relationship between the electric field E and dielectric polarization P in the dielectric. The capacitive component C per unit length of the coplanar line changes depending on the signal voltage V. Since a nonlinear wave is generated in correspondence with an electrical pulse signal to be transmitted in the transmission line  101  in data transmission between a plurality of integrated circuits  102 , high-speed data transmission at several Gbits/sec to 10 Gbits/sec or more can be implemented. 
     Also in the second embodiment, a magnetic substance  330  can replace the dielectric  320  contained in the insulating material  3 . 
     The whole printed wiring board  200  shown in  FIGS. 12 and 13  may be made of the insulating material  3 , e.g., silicon, glass, or ceramics. 
     Alternatively, the printed wiring board  200  may be made of the insulating material  3  at least partially containing the dielectric  320  or magnetic substance  330 . In this case, the insulating material  3  interposed between the signal line conductor  501  and the ground conductor  305  on the surface of the printed wiring board  200  may contain neither the dielectric  320  nor magnetic substance  330 . 
     In the second embodiment, as shown in  FIG. 10 , the contact between the input/output circuit  103  of the integrated circuit  102  and a nonlinear capacitor  820  connects to the transmission line  101 . The nonlinear capacitor  820  has a characteristic of decreasing the capacitance as the signal voltage rises. The effective capacitance per unit length of the transmission line  101  changes depending on the signal voltage. The present invention can, therefore, be practiced by adjusting the circuit arrangement so as to generate a nonlinear wave in the transmission line  101 . 
     A circuit simulation (SPICE) was done to confirm one of conditions under which a nonlinear wave is generated in the insulating material  3  containing the dielectric  320  or magnetic substance  330  in the transmission line  101  according to the second embodiment. 
     A circuit used for this simulation is identical to that shown in  FIG. 10 , and a plurality of nonlinear capacitors  820  and a plurality of integrated circuits  102  connect to a transmission line  101  having an overall length of 90 cm at an interval of 1 cm. As parameters of the transmission line  101 , the capacitance C per unit length (1 cm)=1.1 pF, the inductance L=2.9 nH, and the resistance R=4.8 mΩ. The nonlinear capacitor  820  was a varicap diode (variable-capacitance diode). The nonlinear capacitor  820  had a characteristic shown in  FIG. 7 , and decreased the capacitance value when the signal voltage rose. 
     As a comparison with the simulation, an arrangement was used and examined in which a conventional data transmitter between integrated circuits shown in  FIG. 1  was adopted and a fixed capacitor  840  in each integrated circuit  102  had a capacitance of a predetermined value (2 pF) regardless of the signal value. 
       FIG. 14  shows a waveform which appears on the other end (receiving side) of the transmission line  101  when supplying a 0.3-ns wide rectangular pulse  1101  as an input pulse to one end (transmitting side) of the transmission line  101 . When the capacitance value is constant, like the prior art, a waveform  1103  appearing on the receiving side increases its pulse width and decreases its amplitude owing to the dispersion phenomenon. To the contrary, in the use of the nonlinear capacitor  820 , like the second embodiment, a waveform  1102  appearing on the receiving side hardly increases its pulse width and rarely decreases its amplitude. 
     In the present invention, it is one of preferable conditions that, for example, the capacitance value of the nonlinear capacitor  820  shown in  FIG. 10  changes depending on the signal voltage. 
     It is another preferable condition that the maximum value of the nonlinear capacitor  820  is equal to or larger than the capacitance value (fixed value independent of the signal voltage) per unit length of the transmission line  101  in  FIG. 10 . By satisfying this condition, the influence of the nonlinear capacitor  820  becomes prominent to facilitate generation of a nonlinear wave in the transmission line  101 . 
     The transmission lines  101  are desirably formed on the surface of the printed wiring board  200 , but may be formed in the printed wiring board  200 . When the transmission lines  101  are formed on the surface of the printed wiring board  200 , i.e., the surface of the circuit board, they can be formed by only a limit number depending on the area of the circuit board. In contrast, when the transmission lines  101  are formed in the circuit board, they can be formed and stacked in the circuit board or multilayered board. By increasing the number of layers, the number of transmission lines  101  can be increased. When the number of transmission lines  101  is determined, the circuit board is multilayered to reduce the area, achieving significant downsizing and implementing a high-density packaged circuit. 
     Third Embodiment 
     A transmission line  101  according to the third embodiment of the present invention will be explained with reference to  FIGS. 15 and 16 . 
     Unlike the first and second embodiments, the transmission line  101  according to the third embodiment is formed separately from a printed wiring board  200 . A plurality of transmission lines  101  are parallel-arrayed to form a flexible multicore cable  700  covered with a proper outer insulator  600 . 
     In the flexible multicore cable  700 , a ground conductor  305  forms a plurality of parallel-arrayed closed conduits  800 . The closed conduit  800  is a cylindrical conduit having upper, lower, right, and left wall surfaces. Each closed conduit  800  is filled with an insulating material  3  at least partially containing a dielectric  320  or magnetic substance  330 . The insulating material  3  contains a signal conductor  201 . 
     Even with this arrangement, the capacitive component C per unit length changes depending on the signal voltage V. Similar to the first embodiment, a nonlinear wave can be generated in the transmission line  101  to achieve high-speed data transmission at several Gbits/sec to 10 Gbits/sec or more. 
     In the above embodiments, the transmission line  101  is formed on the printed wiring board  200 , and the effective reactance per unit length changes depending on at least one of the signal voltage and signal current. In data transmission between a plurality of integrated circuits  102 , a nonlinear wave is generated in the transmission line  101  in correspondence with an electrical pulse signal to be transmitted. As a result, the electrical pulse signal reaches the receiving side without any influence of the dispersion phenomenon caused by the transmission line  101 . The pulse waveform of the electrical pulse signal hardly changes, its pulse width hardly increases, and high-speed data transmission can be executed. 
     The above-described embodiments can implement high-speed data transmission by the printed wiring board  200 , and can greatly reduce the cost in comparison with the use of expensive optical communication or a coaxial cable. Many channels can fall within one printed wiring board  200 , which contributes to high-density data transmission. That is, low-cost, high-speed, high-density data transmission can be achieved between integrated circuits.