JP2008252374A - Circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration in signal waveform quality caused by an impedance discontinuous part that exists in the middle of a transmission path in a fast-speed signal transmission system for transmitting and receiving a synchronous high-speed pulse signal through one transmission path. <P>SOLUTION: In the signal transmission system for transmitting and receiving a synchronous high-speed pulse signal through one transmission path 13 between a transmitting side board 11, on which a transmitting side semiconductor device 112 is mounted, and a receiving side board 12, on which a receiving side semiconductor device 122 is mounted, In the transmitting side substrate 11, a connector 113 is mounted and a PCB wiring 114 is formed in a transmission path from the transmitting side semiconductor device 112 to the connector 113. The wiring length of the PCB wiring is set so as to make the round-trip transmission time of a signal propagating on the PCB wiring to be 1/4 or 1/4+n/2 (n is a positive integer) of a switching period of a pulse signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a circuit board, and more particularly to a circuit board on which a semiconductor device and a transmission line connector are mounted. For example, a synchronous pulse signal is transmitted between a personal computer and a peripheral device via a single USB cable. It is used for a signal transmission system for transmitting and receiving.

  In general, a signal transmission system for transmitting / receiving a signal via a wired transmission path between a transmission side substrate on which a transmission side semiconductor device is mounted and a reception side substrate on which a reception side semiconductor device is mounted, or a transmission / reception semiconductor device is mounted 2. Description of the Related Art A signal transmission system that transmits and receives high-speed signals between transmission / reception boards via a wired transmission path is used. In such a high-speed signal transmission system, when the impedance of the transmission line and the impedance of the terminating resistor are different, a reflected wave similar to the incident wave is generated.

  Patent Document 1 discloses a high-speed signal transmission wiring mounting structure in which a chip resistor is connected to a transmission path in order to suppress temporal fluctuation of a signal due to a reflected wave traveling back and forth in the transmission path and reduce jitter. In the structure of Patent Document 1, since the synthesis point of the input wave and the reflected wave in the output signal waveform is near the edge of the signal waveform, jitter (jitter), dip (dip), etc. with respect to the signal waveform near this edge This may cause a decrease in signal waveform quality.

  By the way, as one type of the high-speed signal transmission system as described above, there is a system that transmits and receives a synchronous high-speed pulse signal via a single transmission line. In this system, the printed wiring is formed on the transmission path from the transmission side semiconductor device to the connector on the transmission side substrate, and the printed wiring is formed on the transmission path from the connector to the reception side semiconductor device on the reception side substrate. There is a configuration one. In the above system, a printed wiring is formed in a transmission path from the semiconductor device to the transmission / reception connector on the transmission / reception substrate on which the semiconductor device incorporating the transmission side circuit and the reception side circuit is mounted. Is configured to be selectively connected to the printed wiring by a switching circuit.

In these transmission lines, there are a terminal connection portion of a semiconductor device package and a connector (for example, a USB standard connector) mounted on a substrate. In general, since it is difficult to obtain a connector that can control impedance, a connector mounted on a transmission line, a terminal connection portion of a semiconductor device package, and the like often have impedance discontinuities. Such impedance discontinuity causes signal reflection, affects the signal waveform such as jitter and dip, and causes signal waveform quality to deteriorate. For example, the connector has an effect of adding or reducing capacitance, and the waveform reflected by the connector includes many components obtained by differentiating the incident wave. This is different from the problem that a reflected wave is generated in the transmission line described in Patent Document 1 described above, and a measure different from that of Patent Document 1 is required.
JP 2001-111408 A

  The present invention has been made in view of the above-described circumstances. When a synchronous pulse signal is transmitted or received via a single transmission line, a signal caused by an impedance discontinuity existing in the middle of the transmission line. An object of the present invention is to provide a circuit board capable of suppressing a decrease in waveform quality.

  According to a first aspect of the circuit board of the present invention, a transmission-side semiconductor device including a transmission circuit that transmits a pulse signal is mounted, an output wiring connected to the transmission-side semiconductor device, and a connector connected to the output wiring The printed wiring is formed in the transmission path from the transmitting semiconductor device to the connector, and the length of the printed wiring is the length of the signal propagating on the printed wiring. The round-trip transmission time is set to be ¼ or ¼ + n / 2 (n is a positive integer) of the switching period of the pulse signal.

  According to a second aspect of the circuit board of the present invention, a receiving-side semiconductor device including a receiving circuit that receives a pulse signal is mounted, an input wiring connected to the receiving-side semiconductor device, and a connector connected to the input wiring. And a printed wiring is formed in a transmission path from the receiving semiconductor device to the connector, and the length of the printed wiring is the length of the signal propagating on the printed wiring The round-trip transmission time is set to be ¼ or ¼ + n / 2 (n is a positive integer) of the switching period of the pulse signal.

  According to the circuit board of the present invention, when a synchronous pulse signal is transmitted or received via one transmission line, the signal waveform quality is reduced due to an impedance discontinuity existing in the middle of the transmission line. Can be suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this description, common parts are denoted by common reference numerals throughout the drawings.

<First Embodiment>
FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a signal transmission system to which a circuit board of the present invention is applied. This signal transmission system includes a transmission-side substrate 11 having a transmission-side semiconductor device 112 and a first connector 113 with a transmission circuit 111 built-in, and a reception-side semiconductor device 122 and a second connector 123 with a reception circuit 121 built-in. A synchronous high-speed pulse signal is transmitted / received to / from the receiving substrate 12 mounted via a single transmission line (for example, cable) 13. Here, the switching period of the high-speed pulse signal is, for example, about 2 nS.

In the transmission side substrate 11, printed wiring (PRINT CIRCUIT BOAD wiring, hereinafter referred to as PCB wiring) 114 is formed on the transmission path from the transmission side semiconductor device 112 to the first connector 113. The wiring length of the PCB wiring 114 is such that the round-trip transmission time of the signal propagating through the PCB wiring 114 is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the pulse signal. In addition, PCB wiring 124 is formed on the transmission path from the reception-side semiconductor device 122 to the second connector 123 on the reception-side substrate 12. The wiring length of the PCB wiring 124 is set such that the round-trip transmission time of the signal propagating through the PCB wiring 124 is an integral multiple of 1/4 or 1/4 + 1/2 of the switching period of the pulse signal. Yes.

  Next, an optimum wiring length is obtained for the PCB wiring 114 of the transmission side substrate 11 and the PCB wiring 124 of the reception side substrate 12 from the viewpoint of preventing deterioration of signal waveform quality.

  FIG. 2 schematically shows a waveform measurement circuit when the relationship between the PCB wiring length and the amount of jitter generated in the transmission signal is actually measured in the transmission side substrate 11 in FIG. Here, 115 is a wiring part (including the lead part of the package) in the transmission side semiconductor device 112, 21 is a termination circuit of the transmission line 13, 22 and 23 are digital oscilloscopes with a jitter measurement function and their measurement input probes. .

Now, if the distance that a high-speed pulse signal with a switching period of 2.083nS travels on the PCB wiring in 1nS is 140mm,
The distance that the signal travels in the half of the switching cycle is 2.083nS / 2 × 140mm = 145.81mm
The distance that the signal travels during a quarter of the switching cycle is 2.083nS / 4 × 140mm = 72.905mm
The distance the signal travels in the period of (1/4) + (1/2) x 1 of the switching cycle is 218.72mm
The distance that the signal travels in the period of (1/4) + (1/2) x 2 of the switching cycle is 364.53 mm
become.

  Therefore, when the PCB wiring length is set to 20, 30, 60, 90, 130, 200, 300, and 450 mm on the transmission side substrate 11 and the reception side substrate 12 in FIG. 1, and the same semiconductor device is mounted on each substrate Each jitter amount was actually measured.

  According to the actual measurement data shown in FIG. 3, the round trip transmission time of the signal propagating on the PCB wiring corresponds to 1/5, 1/4, 1/2, 3/4 of the switching period of the pulse signal, respectively. When the wiring length was set, the jitter amount was about 35 pS, about 20 pS, about 27 pS, and about 20 pS. From this measured data, we confirmed the phenomenon that the jitter amount is reduced when the round-trip transmission time of the signal propagating on the PCB wiring is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the pulse signal. can do. Here, in reality, n = 0 or n = 1 is desirable. The reason is that the signal attenuation occurs when the signal travels on the PCB wiring, and the signal attenuation amount has a frequency characteristic. Therefore, if the PCB wiring length is long, the frequency characteristic of the signal attenuation amount decreases and signal distortion occurs. This is because a shorter PCB wiring length is preferable.

  In the configuration of Patent Document 1 of the conventional example, if the length of the transmission line is set to 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the high-speed pulse signal as described above, The synthesis point of the input wave and the reflected wave in the output signal waveform affects the signal waveform, such as jitter and dip, leading to a decrease in signal waveform quality.

  FIG. 4 shows the transmission side substrate when the PCB wiring length is set so that the round-trip transmission time of the signal propagating on the PCB wiring becomes 1/4 of the switching period of the pulse signal in the signal transmission system of FIG. 11 shows a state in which the composite point of the input wave and the reflected wave is near the center of the signal waveform among the 11 output signal waveforms. In this way, the degree of influence of jitter, dip, etc. on the signal waveform is reduced, and deterioration in signal quality can be suppressed.

  As described above, according to the present embodiment, in the transmission side substrate 11, the round-trip transmission time of the signal propagating on the PCB wiring is 1/4 or 1/4 + n / 2 of the switching period of the high-speed pulse signal (n is positive) By setting the PCB wiring length to be an integer), impedance mismatch at the impedance discontinuity existing in the middle of the transmission path of the transmission side substrate 11 can be reduced, and the factor given to the signal waveform is reduced. Thus, the signal waveform quality can be optimally adjusted, and the deterioration of the signal waveform quality can be prevented. That is, the phase (time relationship) between the transmitted wave (traveling wave) and the reflected wave at the connector portion can be adjusted to the best (appropriate), and as a result, impedance mismatch at the first connector 113 can be reduced. Can do.

  Similarly, the PCB wiring so that the round-trip transmission time of the signal propagating on the PCB wiring is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the high-speed pulse signal in the receiving-side substrate 12. By setting the length, impedance mismatch at the impedance discontinuity existing in the middle of the transmission path of the receiving side substrate 12 can be reduced, the factor given to the signal waveform is reduced, and the signal waveform quality is optimized. It is possible to prevent the signal waveform quality from being degraded. That is, the time relationship between the received wave and the reflected wave at the receiving circuit input node unit can be adjusted appropriately, and as a result, impedance mismatch at the receiving circuit input node unit can be reduced.

  In this embodiment, a coupling capacitor may be inserted in series with the PCB wiring. Further, the transmission-side semiconductor device 112 does not have an output terminal for a synchronous clock signal for transmission signals, and the transmission-side substrate 11 also has no output terminal for a synchronous clock signal for transmission signals. Similarly, the receiving-side semiconductor device 122 does not have an input terminal for a synchronous clock signal for a transmission signal, and the receiving-side substrate 12 also does not have an input terminal for a synchronous clock signal for a transmission signal.

  Further, the transmission side semiconductor device 11 has a built-in termination resistor (not shown) that matches the impedance of the PCB wiring 114 between the output side of the transmission circuit 111 and a predetermined potential node. A termination resistor (not shown) that matches the impedance of the PCB wiring 124 is preferably built in between the input node side of the receiving circuit 121 and the predetermined potential node.

  In addition, since the chip resistance as in Patent Document 1 of the conventional example is not connected to the PCB wiring of the transmission side substrate 11 and the reception side substrate 12, impedance discontinuity such as soldering land and solder is not connected to the chip resistance connection portion. The problem that the element exists does not occur.

<One specific example of the first embodiment>
FIG. 5 shows a specific example of the first embodiment. The transmission side substrate 11 has a multilayer wiring structure, and is equipped with a transmission side semiconductor device (IC) 112 having a transmission circuit built therein and a first USB connector 113a. In this case, a first PCB wiring 114 is formed on the transmission side substrate 11 to connect the transmission side semiconductor device 112 and the first USB connector 113a. The PCB wiring length is set so that the round-trip transmission time of the signal propagating on the PCB wiring 114 is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the high-speed pulse signal. .

  The reception side substrate 12 has a multilayer wiring structure, and is mounted with a reception side semiconductor device (IC) 122 incorporating a reception circuit and a second USB connector 123a. In this case, a second PCB wiring 124 that connects the receiving-side semiconductor device 122 and the second USB connector 123 a is formed on the receiving-side substrate 12. The PCB wiring length is set so that the round-trip transmission time of the signal propagating on the PCB wiring 124 is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the high-speed pulse signal. .

  The first USB connector 113a and the second USB connector 123a are connected by a single USB cable 13 having USB connectors 13a attached to both ends.

<Second Embodiment>
In the second embodiment, a synchronous high-speed pulse signal is transmitted / received between two transmission / reception boards equipped with a transmission / reception semiconductor device and a transmission / reception connector via a single transmission line. Each semiconductor device includes a transmission circuit, a reception circuit, and a switching circuit for switching and connecting the transmission circuit and the reception circuit to an external terminal that is used for both transmission and reception.

  On each transmission / reception board, PCB wiring is formed in the transmission path from the semiconductor device to the connector, and this PCB wiring is selectively connected to the transmission circuit and the reception circuit by the switching circuit. The wiring length of the PCB wiring is set so that the round-trip transmission time of the signal propagating on the PCB wiring is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the high-speed pulse signal. ing.

  In the second embodiment, during the period in which the PCB wiring is connected to the transmission circuit by the switching circuit, the impedance mismatch in the connector portion existing in the middle of the transmission path is caused as in the first embodiment described above. It is possible to reduce the factors that are given to the signal waveform, to optimally adjust the signal waveform quality, and to prevent the signal waveform quality from deteriorating. Further, during the period in which the PCB wiring is connected to the receiving circuit by the switching circuit, the impedance mismatch at the receiving circuit input node portion existing in the middle of the transmission path is reduced as in the first embodiment described above. Therefore, it is possible to reduce the factor given to the signal waveform, optimally adjust the signal waveform quality, and prevent the deterioration of the signal waveform quality.

1 is a circuit diagram showing a configuration of a first embodiment of a signal transmission system of the present invention. The circuit diagram of the waveform measurement circuit at the time of measuring the relationship between PCB wiring length and the amount of jitter which arises in a transmission signal in the transmission side board | substrate and reception side board | substrate in FIG. The figure which shows the result of having actually measured each jitter amount when PCB wiring length is set to various values in the transmission side board | substrate in FIG. 1, and a receiving side board | substrate, and the same IC is mounted in each board | substrate. In the signal transmission system of FIG. 1, when the round-trip transmission time of a signal propagating over the PCB wiring length is set to be ¼ of the pulse switching period, the input wave and the reflected wave in the output signal waveform are combined. The timing waveform figure which shows a mode that a point becomes the center vicinity of a signal waveform. FIG. 3 is a circuit diagram showing a specific example of the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Transmission side board | substrate, 111 ... Transmission circuit, 112 ... Transmission side semiconductor device, 113 ... 1st connector, 114 ... PCB wiring, 12 ... Reception side board | substrate, 121 ... Reception circuit, 122 ... Reception side semiconductor device, 123 ... Second connector, 124 ... PCB wiring, 13 ... transmission path.

Claims (4)

A transmission-side semiconductor device that includes a transmission circuit that transmits a pulse signal is mounted, has an output wiring connected to the transmission-side semiconductor device and a transmission-side substrate on which a connector connected to the output wiring is disposed,
Printed wiring is formed in the transmission path from the transmission-side semiconductor device to the connector,
The length of the printed wiring is set so that the round-trip transmission time of the signal propagating on the printed wiring is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the pulse signal. A circuit board characterized by the above.   Each of the transmission-side semiconductor device and the transmission-side substrate does not have a synchronous clock signal output terminal for a transmission signal, and the transmission-side semiconductor device is connected to a predetermined potential node on the output node side of the transmission circuit. The circuit board according to claim 1, further comprising a termination resistor that matches the impedance of the printed wiring. A receiving-side semiconductor device having a built-in receiving circuit that receives a pulse signal is mounted, and has a receiving-side substrate on which an input wiring connected to the receiving-side semiconductor device and a connector connected to the input wiring are arranged,
Printed wiring is formed in the transmission path from the receiving semiconductor device to the connector,
The length of the printed wiring is set so that the round-trip transmission time of the signal propagating on the printed wiring is 1/4 or 1/4 + n / 2 (n is a positive integer) of the switching period of the pulse signal. A circuit board characterized by the above.   The receiving-side semiconductor device and the receiving-side substrate each do not have a synchronous clock signal input terminal for a transmission signal, and the receiving-side semiconductor device is connected to a predetermined potential node on the input node side of the receiving circuit. 4. The circuit board according to claim 3, wherein a termination resistor matching the impedance of the printed wiring is incorporated in the circuit board.

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