Abstract:
A signal transmission apparatus comprises a first signal transmission section configured to transmit a first signal for performing measurement of characteristics of a transmission line to the transmission line. A reflection characteristic measurement section is configured to measure a reflection characteristic of the transmission line. A pass characteristic measurement section is configured to measure a pass characteristic of the transmission line. A determination section is configured to determine a transmission clock frequency based upon the reflection characteristic. A second signal transmission section is configured to modulate information and to transmit a second signal obtained by the modulation to the transmission line. A second signal receiving section is configured to receive and to demodulate the second signal which has been transmitted by the second signal transmission section and has passed the transmission line.

Description:
CROSS-REFERENCE TO RELATED APPLICATION: 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-193700, filed on Jul. 28, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    This embodiment relates to a signal transmission apparatus which performs transmission of a signal via a transmission line and a signal transmission apparatus control method. 
         [0004]    2. Description of the Related Art 
         [0005]    Devices using the PCI (Peripheral Component Interconnect) standard and the PCI-X standards, which have been used for personal computers and servers have been transitioning to the PCI Express standard. ATA (Advanced Technology Attachment), which has been used for connection of a storage device such as a hard disk and a CD-ROM, has been transitioning to Serial ATA. Similarly, SCSI (Small Computer System Interface) has been transitioning to Serial Attached SCSI. 
         [0006]    Thus, the electrical interface for signal transmission rapidly transitions from a parallel interface to a serial interface. 
         [0007]    Since the serial interface uses a wider band than the parallel interface, there is a demand for a method for appropriately determining loss, jitter, noise, variation and the like in a transmission line, and also for obtaining a more stable transmission waveform. 
         [0008]    The serial interface has a transmission LSI (Large Scale Integration) device for sending out a signal waveform; a transmission line configured by a printed circuit board, a connector and a cable; and a receiving LSI device for receiving a signal waveform. 
         [0009]    Designing a high-speed transmission system with a GHz-order transmission speed is required to obtain an optimum transmission quality requires consideration of the capability of a transmitter and a receiver, variation of characteristics of elements and substrate materials, characteristics of each of elements constituting a transmission line, noise and the like. 
         [0010]    A conventional transmission system has a printed circuit board, a cable and a connector in addition to the transmission LSI device and the receiving LSI device. Examples of items to be considered in this case include: transmission and receiving performance; variation of LSI&#39;s, materials and characteristics; power source and crosstalk noise; reflection; loss of PCB (Printed Circuit Board) wire, VIA, cable, connector and transmission/receiving LSI package; and the like. 
         [0011]    In the related art, there are an equalizer for automating setting of an equalization parameter and a pre-emphasis adjustment method for shortening the time required for pre-emphasis adjustment (see Japanese Laid-open Patent Publication No. 2004-015622 and Japanese Laid-open Patent Publication No. 2006-246191, for example). 
         [0012]    In general high-speed transmission, receiving eye opening adjustment and EQ (equalizer) adjustment by the emphasis adjustment are performed. However, since the transmission clock frequency is specified in advance, an optimum transmission method is not necessarily realized. 
         [0013]    Recently, a high-speed transmission system is provided with a plurality ports, and a multi-port transmission/receiving circuit is included in an LSI device. Therefore, it is feared that the transmission quality may be deteriorated by open reflection in an open lane or noise by simultaneous operation of multiple lanes. Furthermore, though it is often assumed that the receiving margin is increased by increasing the receiving eye opening, noise inside the multi-port LSI is increased by receiving a large eye opening waveform. Similarly, deterioration of the transmission quality may be also caused. 
       SUMMARY  
       [0014]    According to one embodiment of the invention, a signal transmission apparatus comprises a first signal transmission section configured to transmit a first signal for performing measurement of characteristics of a transmission line to the transmission line. A reflection characteristic measurement section is configured to measure a reflection characteristic of the transmission line based upon a reflected signal transmitted by the first signal transmission section and reflected by the transmission line. A pass characteristic measurement section is configured to measure a pass characteristic of the transmission line based upon a passed signal that has been transmitted by the first signal transmission section and has passed the transmission line. A determination section is configured to determine a transmission clock frequency based upon the reflection characteristic measured by the reflection characteristic measurement section and the pass characteristic measured by the passed characteristics measurement section. A second signal transmission section is configured to modulate information using the transmission clock frequency determined by the determination section and to transmit a second signal obtained by the modulation to the transmission line. A second signal receiving section is configured to receive and to demodulate the second signal which has been transmitted by the second signal transmission section and has passed the transmission line. 
         [0015]    In another embodiment, a signal transmission method comprises transmitting a first signal performing measurement of the characteristics of a transmission line to the transmission line. A reflection characteristic of the transmission line is measured, based upon a reflected signal reflected by the transmission line. A pass characteristic of the transmission line is measured based upon a pass signal that has passed the transmission line. A transmission clock frequency is determined, based upon the measured reflection characteristic and the measured pass characteristic. Information is modulated using the determined transmission clock frequency, and a second signal obtained by the modulation is transmitted to the transmission line. The second signal is then received and demodulated. 
         [0016]    In another embodiment, the invention comprises a signal transmission apparatus comprising transmitting means for transmitting a first signal performing measurement of characteristics of a transmission line to the transmission line. This embodiment also includes measuring means for measuring a reflection characteristic of the transmission line based upon a reflected signal reflected by the transmission line, and for measuring a pass characteristic of the transmission line based upon a pass signal that has passed the transmission line. Determining means are provided, for determining a transmission clock frequency based upon the measured reflection characteristic and the measured pass characteristic. Modulating means are provided to modulate information using the determined clock frequency, and for transmitting a second signal obtained by the modulation to the transmission line. Demodulating means are provided for receiving and demodulating the second signal which has been transmitted and has passed the transmission line. 
         [0017]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a block diagram showing an example of the configuration of a signal transmission system of are embodiment of the invention; 
           [0019]      FIG. 2  is a block diagram showing an example of the configuration of software in a controller of an embodiment of the invention; 
           [0020]      FIG. 3  is a flowchart showing an example of the operation of the signal transmission system of an embodiment of the invention; 
           [0021]      FIG. 4  is a flowchart showing an example of set value candidate determination processing of an embodiment of the invention; 
           [0022]      FIG. 5  is a table showing an example of a judgment table of an embodiment of the invention; 
           [0023]      FIG. 6  is a graph showing an example of S parameter measurement values of an embodiment of the invention; and 
           [0024]      FIG. 7  is a waveform diagram showing an example of an eye pattern of a received signal of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Embodiments of the invention will be described with reference to drawings. 
         [0026]    A signal transmission system or apparatus according to an embodiment of the invention performs binary transmission. In the binary transmission, a transmission signal can take two kinds of levels at a data judgment timing. Furthermore, this signal transmission system determines a transmission clock frequency so that the transmission quality satisfies predetermined conditions and the transmission speed becomes the highest. In this embodiment, the transmission clock frequency determined in this way will be hereinafter referred to as an optimum frequency. 
         [0027]    The configuration of the signal transmission system according to this embodiment will be described below. 
         [0028]      FIG. 1  is a block diagram showing an example of the configuration of the signal transmission system according to the invention. This signal transmission system has a transmission LSI device  11 , a receiving LSI device  12 , printed circuit boards  13  and  14 , a connector  15 , a controller  16  and a memory  17 . The transmission LSI device  11  can have a transmission control section  21 , a modulation section  22 , an amplification section  23  (Amp), an emphasis section  24  (Emphasis) and a first network analyzer  28 . The receiving LSI device  12  can have an EQ  31 , a demodulation section  32 , a waveform storage section  33 , a BER (Bit Error Ratio) measurement section  34 , an eye opening measurement section  35 , a judgment table storage section  36 , a judgment section  37 , and a second network analyzer  38 . 
         [0029]    The transmission LSI device  11  can be disposed on the printed circuit board  13 . The receiving LSI device  12  can be disposed on the printed circuit board  14 . 
         [0030]    In this example, transmission section  22  can have a port  1  and a port  2 . The receiving section  32  has a port  3  and a port  4 . The port  1  and the port  3  are connected via a transmission signal line on the printed circuit board  13 , the connector  15  and a transmission signal line on the printed circuit board  14 . A signal transmitted from the port  1  is received by the port  3 . Similarly, the port  2  and the port  4  are connected via a transmission signal line on the printed circuit board  13 , the connector  15  and a transmission signal line on the printed circuit board  14 . A signal transmitted from the port  2  is received by the port  4 . 
         [0031]    In this embodiment, the signal route constituted by the transmission signal line on the printed circuit board  13 , the connector  15  and the transmission signal line on the printed circuit board  14  will be hereinafter referred to as a transmission line or a lane. 
         [0032]    Each of the sections in the transmission LSI device  11  and the receiving LSI device  12  is provided for each lane. 
         [0033]    The controller  16 , the memory  17 , the transmission control section  21 , the transmission section  22 , the EQ  31  and the receiving section  32  are connected via a control signal line. 
         [0034]      FIG. 2  is a block diagram showing an example of the configuration of software in the controller. The controller  16  executes an S parameter measurement section  41 , a selection section  42  and a setting section  43 , which are software. Here, the controller  16  can be, for example, a CPU, and the S parameter measurement section  41 , the selection section  42  and the setting section  43  can be programs embodided as stored in memory  17 , which can be executed by controller  16 . 
         [0035]    The transmission control section  21  can perform judgment of an open lane in the transmission LSI device  11  or control of the amplification section  23 . The modulation section  22  can perform modulation of information to be transmitted by the transmission LSI device  11 . The emphasis section  24  amplifies a predetermined frequency in order to prevent deterioration of a waveform caused by the transmission line. The amplification section  23  can amplify a signal to be transmitted. 
         [0036]    The EQ  31  can equalize a waveform which has been deteriorated by the transmission line. The demodulation section  32  can demodulate a received signal. The waveform storage section  33  can store a received waveform. The BER measurement section  34  can measure the BER of the received signal. The eye opening measurement section  35  can measure the eye opening of the received signal. The judgment table storage section  36  stores a judgment table. 
         [0037]    The judgment table storage section  36  stores the judgment table for determining an optimum frequency in the transmission LSI device  11  or the receiving LSI device  12 . 
         [0038]    The judgment section  37  can determine the optimum frequency on the basis of the judgment table. 
         [0039]    The first network analyzer  28  can measure reflection characteristics such as reflection loss of the transmission line by transmitting a measurement signal (first signal) for measuring S parameters to the transmission line, and receiving the measurement signal reflected by the transmission line. The second network analyzer  38  can measure pass characteristics such as insertion loss of the transmission line, by receiving the measurement signal passing the transmission line. 
         [0040]    A first signal transmission section and a second signal transmission section correspond to the transmission control section  21 , the modulation section  22 , the amplification section  23  and the emphasis section  24 . A second signal receiving section corresponds to the EQ  31 , the demodulation section  32 , the waveform storage section  33 , the BER measurement section  34  and the eye opening measurement section  35 . 
         [0041]    A determination section corresponds to the judgment table storage section  36 , the judgment section  37 , the controller  16  and the memory  17 . 
         [0042]    The S parameter measurement section  41  can instruct the first network analyzer  28  and the second network analyzer  38  to perform measurement and to calculate the S parameter characteristic of the transmission line on the basis of the measurement. The S parameter is a parameter indicating the frequency characteristic of the transmission line. The selection section  42  can select multiple values as an amplification section set value, which is a set value for the amplification section  23 , an emphasis section set value, which is a set value for the emphasis section  24 , and an EQ set value, which is a set value for the EQ  31 , on the basis of the S parameter characteristic calculated by the S parameter measurement section  41 . 
         [0043]    Here, the amplification section set value indicates an amplification characteristic, which can be either the output amplitude value or the amplification factor of the amplification section  23 . The emphasis section set value indicates an emphasis characteristic, and in this example it is gain in the frequency to be emphasized. The set value for the EQ  31  indicates an equalization characteristic, and it is the central frequency in this example. The EQ  31  has a frequency characteristic in which the gain becomes the maximum at the central frequency. 
         [0044]    The signal transmission system of this embodiment may be a bidirectional interface having a common transmission line. In this example, the receiving LSI device  12  side is further provided with the modulation section  22 , the amplification section  23 , the emphasis section  24  and the first network analyzer  28  on, and the transmission LSI device  11  side is further provided with the EQ  31 , the demodulation section  32 , the waveform storage section  33 , the BER measurement section  34 , the eye opening measurement section  35 , the judgment table storage section  36 , the judgment section  37  and the second network analyzer  38 . This signal transmission system performs transmission from the receiving LSI  12  side to the transmission LSI  11  side, similarly to transmission from the transmission LSI  11  side to the receiving LSI  12  side. 
         [0045]    The operation of the signal transmission system according to this embodiment will be described below. 
         [0046]      FIG. 3  is a flowchart showing an example of the operation of the signal transmission system according to this embodiment. 
         [0047]    At  511 , the setting section  43  judges whether the judgment table exists in the memory or other appropriate location. If the judgment table exists (S 11 : Yes), the flowchart proceeds to processing S 25 . If the judgment table does not exist (S 11 : No), the setting section  43  performs judgment table creation processing for creating the judgment table (S 12 ), and the flowchart proceeds to processing S 25 . In the judgment table creation processing, the setting section  43  acquires information, for example, inputted by users, about the data sheet (LSI standard) of the transmission LSI  11  and the receiving LSI  12  and creates the judgment table on the basis of this information. 
         [0048]    The setting section  43  can acquire the created judgment table and sets it in the judgment table storage section  36  (S 25 ). 
         [0049]    The transmission control section  21  can judge whether there is an open lane or not (S 31 ). If there is not an open lane (S 31 : No), the flowchart proceeds to processing S 21 . If there is an open lane (S 31 : Yes), the transmission control section  21  turns off the open lane or sets the output level to 0 for the amplification section  23  (S 32 ), and the flowchart proceeds to processing S 21 . By judging an open lane which is unnecessary for transmission and stopping transmission/output, it is possible to suppress crosstalk due to open reflection and noise inside the LSI device, so that the BER can be advantageously reduced. 
         [0050]    The S parameter measurement section  41  turns off the EQ  31  (S 33 ), and performs S parameter measurement processing for measuring the S parameter by the first network analyzer  28  and the second network analyzer  38  (S 34 ). 
         [0051]    The judgment section  37  performs frequency determination processing for determining an optimum frequency on the basis of S parameter measurement values obtained by the S parameter measurement processing and the judgment table stored in the judgment table storage section  36  (S 35 ). 
         [0052]    The selection section  42  performs set value candidate determination processing for determining multiple set value candidates which are candidates for the set values for the amplification section  23 , the emphasis section  24  and the EQ  31  (S 40 ). 
         [0053]    The selection section  42  sequentially sets combinations of set value candidates and performs eye opening measurement processing by the eye opening measurement section  35  and BER measurement processing by the BER measurement section  34  (S 41 ). 
         [0054]    The selection section  42  selects appropriate set values which are a combination of set value candidates satisfying predetermined appropriateness condition, on the basis of the eye opening and the BER obtained for each combination of set value candidates (S 42 ). 
         [0055]    An example of the appropriateness condition will be described. Under an appropriateness condition A, the selection section  42  can determine such set values that the BER is error free and the eye opening is the maximum, such set values that the BER is error free and the eye opening is the minimum, and such set values that the BER is error free and the eye opening is the closest to the central value, as the appropriate set values. Here, the central value is assumed to be an average value of the maximum value and the minimum value. Under an appropriate condition B, the selection section  42  can determine such set values that the BER is error free and the eye opening is within a range set in advance, as the appropriate set values. A user can select the appropriateness condition A or the appropriateness condition B as a predetermined appropriateness condition in advance. 
         [0056]    The selection section  42  can select an optimum set value, which is a set value satisfying a predetermined optimum condition, from among the appropriate set values and sets the value for the amplification section  22 , the emphasis section  24  and the EQ  31  (S 43 ). Here, the optimum condition is that the eye opening is closest to the central value. Thereby, it is possible to suppress noise caused by excess of the eye opening and the amplitude and improve the receiving sensitivity. 
         [0057]    The setting section  43  causes the transmission LSI device  11  and the receiving LSI device  12  to start normal transmission (S 44 ). The setting section  43  can also judge whether or not transmission is to be ended (S 45 ). 
         [0058]    If transmission is to be ended (S 45 : Yes), the flowchart ends. If transmission is not to be ended (S 45 : No), the setting section  43  judges whether or not transmission conditions have been changed (S 46 ). Here, the transmission conditions are, for example, transmission load, transmission distance and the like. 
         [0059]    If the transmission conditions have not been changed (S 46 : No), the flowchart proceeds to processing S 45 . If the transmission conditions have been changed (S 46 : Yes), the flowchart proceeds to processing S 31 . 
         [0060]    It is also possible to execute processing S 41  to S 42  for all the combinations of set value candidates and perform an operation with such set value candidates that the BER characteristic is in the best state. 
         [0061]    The operation of the signal transmission system according to this embodiment does not necessarily require use of the complete process illustrated by flowchart described above, and it is also possible to configure a specific flowchart to perform a specific operation. 
         [0062]    The frequency determination processing will be described below. 
         [0063]    The judgment table has at least one judgment pattern. The judgment pattern can have the range of transmission clock frequency to be set and S parameter conditions to be satisfied by the S parameter measurement values. The S parameter conditions include an insertion loss condition and a reflection loss condition. 
         [0064]    In the frequency determination processing, the judgment section  37  can acquire the frequency range of the judgment pattern within which the S parameter measurement values satisfy the S parameter conditions, and sets the highest frequency within the acquired frequency range as an optimum frequency. 
         [0065]    Any frequency that satisfies the judgment pattern may be selected as the optimum frequency even if it is not the highest frequency. For example, it is possible to select such a frequency that reflection is the least among frequencies satisfying the judgment pattern, as the optimum frequency. 
         [0066]    The details of the set value candidate determination processing will be described below. 
         [0067]    In the set value candidate determination processing, the selection section  42  can determine three kinds of set values as each of the set value for the amplification section  23 , the set value for the emphasis section  24  and the set value for the EQ  31 . 
         [0068]      FIG. 4  is a flowchart showing an example of the set value candidate determination processing according to this embodiment. As preprocessing, the selection section  42  can recognize the output amplitude value of each port of the transmission LSI device  11  and the eye opening value and the equalization characterization of each port of the receiving LSI device  12  and stores them into the memory  17  (S 51 ). Here, the eye opening value is the value in the amplitude direction. Next, the selection section  42  can acquire an upper-limit value of SDD  11  (SDD 11 _ 1 mt) which has little influence on transmission characteristics from an input performed in advance, and stores it into the memory  17  (S 52 ). 
         [0069]    The selection section  42  can select three kinds of output amplitude values which satisfy a predetermined setting condition from among all the output amplitude values, on the basis of the S parameter measurement values, the output amplitude value, and the eye opening value, and set them as amplification section set value candidates (S 61 ). The predetermined selection condition is that an input amplitude value of the receiving LSI device  12  obtained from the output amplitude value in consideration of transmission loss based on a result of measurement of the S parameters satisfies a condition specified in advance. 
         [0070]    The selection section  42  can select all such frequencies that the SDD  11  is equal to or below SDD 11 _ 1 mt on the basis of the S parameter measurement result and sets them as an EQ set value group (S 62 ). Next, the selection section  42  selects the central value of the EQ set value group, a value immediately above the central value and a value immediately below the central value as EQ set value candidates (S 63 ). The selection section  42  acquires the range of gain in the emphasis characteristic from an input performed in advance (S 64 ). Next, the selection section  42  sets the central value, the maximum value and the minimum value within the acquired range as emphasis section set value candidates (S 65 ), and the flowchart ends. 
         [0071]    By the operation of the signal transmission system described above, it is possible to perform stable transmission with a preferable waveform and preferable receiving sensitivity at an optimum frequency. 
         [0072]    Furthermore, it is possible to perform stable transmission under optimum settings in all mass-produced apparatuses without being influenced by various variation factors. Thus, by using the signal transmission system according to this embodiment, it is possible to construct a high-capacity signal transmission system which easily realizes high reliability. Furthermore, by performing optimization again when changing the load or changing the transmission line, it is possible to construct a signal transmission system which is always stable. 
         [0073]    A specific example of the operation of the signal transmission system according to this embodiment will be described below. 
         [0074]      FIG. 5  is a table showing an example of the judgment table according to this embodiment. This judgment table is created on the basis of the data sheet of the transmission LSI device  11  and the receiving LSI device  12  and shows one judgment pattern. The judgment pattern has a judgment pattern number, a range of frequency, and an insertion loss (IL) condition and a reflection loss (RL) condition which are the S parameter conditions. The transmission clock frequency which can be used by the transmission LSI  11  and the receiving LSI  12  in this specific example is 1 GHz to 5 GHz (the transmission rate is 2 Gbps to 10 Gbps). 
         [0075]    In the S parameter measurement processing, SDD  21  (insertion loss between differential motion and differential motion) and the SDD  11  (reflection loss between differential motion and differential motion) are measured and set as S parameter measurement values.  FIG. 6  is a graph showing an example of the S parameter measurement values according to this embodiment. In this figure, the horizontal axis indicates frequency [MHz], and the vertical axis indicates the SDD  21  or the SDD  11  [dB]. The measurement values by a solid line indicate the SDD  11 , and the measurement values by a broken line indicate the SDD  21 . 
         [0076]    SDD 21 _ 0  indicates the range of the SDD  21  which satisfies the insertion loss condition. SDD 11 _ 0  indicates the range of the SDD  11  which satisfies the reflection loss condition. 
         [0077]    According to the judgment table and the S parameter characteristic described above, the highest frequency that satisfies the insertion loss condition and the reflection loss condition is 3.83 GHz (the transmission rate is 7.66 Gbps). Therefore, the optimum frequency is determined to be 3.83 GHz by optimum frequency determination processing. 
         [0078]      FIG. 7  is a waveform diagram showing an example of the eye pattern of a received signal according to this embodiment. In this figure, the horizontal axis indicates time, and the vertical axis indicates received voltage [V]. Here, T denotes a transmission clock cycle (1/transmission clock frequency). In this example, T=1/3.83 [GHz]=262 [psec]. 1 UI (Unit Interval) is a 1-symbol time interval (transmission clock cycle/2). In this example, 1 UI=1/3.83 [GHz]/2=131 [psec]. E denotes the eye opening (in the voltage direction). 
         [0079]    According to the various embodiments of the invention, it is possible to make the maximum use of the transmission line characteristics and the transmission/receiving LSI device characteristics and perform stable transmission with the maximum performance. In addition, since it is possible to easily and automatically make optimum transmission settings even when various variation factors occur, it is possible to always perform a stable operation even in a mass-produced apparatus. Furthermore, as a whole, the signal transmission system of the various embodiments makes it possible to improve the transmission quality, suppress transmission failures and considerably reduce man-hours for development, evaluation, examination and repair.