1987-10-07
1990-04-24
Hille, Rolf
357 75, 357 70, H01C 2302, H01C 2312
Patent
active
049204068
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a semiconductor device, more particularly to a semiconductor device wherein a large number of high-speed integrated circuits (high-speed ICs) comprising of high-speed digital signal logic circuits are mounted on a printed circuit board.
BACKGROUND ART
In general, in this kind of semiconductor device, when the integrated circuits mounted on the printed circuit board are high-speed ICs, it is necessary to consider impedance matching at various points on transmission lines printed on the printed circuit board so as to enable transmission of high-speed signals transmitted from drive side ICs (for example, signals changing from low level to high level at a high speed) to receiving side ICs in a manner such that the signal waveforms are not destroyed.
FIG. 1 shows the concept of an example of this kind of semiconductor device in the prior art, wherein a single drive side IC 6 mounted on a printed circuit board 10 drives two receiving side ICs 7 and 8 (that is, there are two fan-outs). The high-speed signal transmitted from a package lead 61 (one of the package leads of the drive side IC 6) for signal output in the drive side IC 6 passes through a transmission line formed by a microstrip line 91 printed on the printed circuit board 10 to transmit the signal data successively to the receiving side ICs 7 and 8, and, finally, is absorbed by the terminating resistor 95 connected between the end of the transmission line and the ground.
In the figure, reference numeral 62 is a drive side IC chip, 71 and 72 are package leads and a chip of the receiving side IC 7, and 81 and 82 are package leads and a chip of the receiving side IC 8. Note that, in the figure, for brevity's sake, an example is shown of the connection of two receiving side ICs 7 and 8 to a line for transmitting high-speed signals transmitted from a single drive side IC 6. But in actuality, a large number of receiving side ICs will be connected to the transmission line and these receiving side ICs will in turn function as drive side ICs for ICs connected successively in cascade on the printed circuit board.
As shown in the figure, further, in the semiconductor device of the example of the prior art, when connecting the receiving side ICs 7 and 8 to the microstrip line 91 which serves as the transmission line (so-called trunk line), the microstrip lines 92 and 93 (that is, branched transmission lines) branched (as so-called incoming lines) from the microstrip line 91 are formed by printed wiring on the printed circuit board 10 in the same way as the microstrip line 91. The ends of these microstrip lines 92 and 93 are connected to package leads of the receiving side ICs 7 and 8, respectively, each of which package leads is one of the plurality of package leads of the receiving side ICs which acts as an input pin.
In particular, when these ICs are high-speed ICs, as mentioned above, when forming the transmission line by printed wiring on the printed circuit board, special consideration is given to impedance matching in the layout of the transmission line. In the above structure, the characteristic impedances Z.sub.0 of each of the microstrip lines 91, 92, and 93 are all formed to be, for example, 50 ohms (the value of the characteristic impedance is determined based on the width of the printed wiring, the dielectric constant and the thickness of the insulator used for the printed circuit board, etc.) and the terminating resistor 95 is also formed to be 50 ohms.
In this construction, if the lengths of the microstrip lines 92 and 93, each branched from the microstrip line 91 and led into each of the receiving side ICs 7 and 8, are 1.sub.1 and 1.sub.2, respectively, when the degree of high speed of the signals transmitted through the same, as further clarified later, is within a range where the existence of the branched microstrip lines 92 and 93 each having the lengths of 1.sub.1 and 1.sub.2 are tolerable, there is no special problem in the transmission of the signals due to the construction of the above-menti
REFERENCES:
patent: 4534105 (1985-08-01), Reusch
patent: 4631572 (1986-12-01), Zimmerman
Emori Shinji
Watanabe Yoshio
Fujitsu Limited
Hille Rolf
Le Hoang-anh
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