U.S. patent application number 09/891322 was filed with the patent office on 2001-11-01 for semiconductor memory.
Invention is credited to Kurihara, Ryoichi, Takekuma, Toshitsugu, Yamagiwa, Akira.
Application Number | 20010035769 09/891322 |
Document ID | / |
Family ID | 18279543 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035769 |
Kind Code |
A1 |
Takekuma, Toshitsugu ; et
al. |
November 1, 2001 |
Semiconductor memory
Abstract
A signal transmitting circuit includes a circuit block having a
driving circuit and an intra-block transmission line for
transmitting a signal from the driving circuit, a circuit block
having a receiving circuit and an intra-block transmission line for
transmitting the signal to said receiving circuit, and a main
interblock transmission line for propagating a signal between the
driving and receiving circuit blocks. The inter-block transmission
line is terminated by a resistor having substantially the same
impedance as the interblock transmission line. The intra-block
transmission lines are provided with a resistance element having a
resistance substantially equal to a value derived by subtracting
half of an impedance of the inter-block transmission line from an
impedance of the intra-block transmission line, to lower signal
amplitude and suppress reflections of a signal at branch points
along the main interblock transmission line, thereby enabling a
high-speed signal transfer.
Inventors: |
Takekuma, Toshitsugu;
(Ebina-shi, JP) ; Kurihara, Ryoichi; (Hadano-shi,
JP) ; Yamagiwa, Akira; (Hadano-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18279543 |
Appl. No.: |
09/891322 |
Filed: |
June 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09891322 |
Jun 27, 2001 |
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09716251 |
Nov 21, 2000 |
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09716251 |
Nov 21, 2000 |
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09084017 |
May 26, 1998 |
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6172517 |
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09084017 |
May 26, 1998 |
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08773753 |
Dec 24, 1996 |
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5818253 |
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08773753 |
Dec 24, 1996 |
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08476576 |
Jun 7, 1995 |
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5568063 |
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08476576 |
Jun 7, 1995 |
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08269352 |
Jun 30, 1994 |
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5548226 |
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Current U.S.
Class: |
326/30 |
Current CPC
Class: |
G06F 13/4072 20130101;
H04L 25/0278 20130101; G06F 13/4086 20130101; H04L 25/0292
20130101; H05K 1/0237 20130101; H05K 1/14 20130101; H04B 3/02
20130101; H04L 25/028 20130101; H04L 25/0298 20130101; H05K 1/0216
20130101 |
Class at
Publication: |
326/30 |
International
Class: |
H03K 019/003 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 1993 |
JP |
05-334631 |
Claims
We claim:
1. A signal transmitting device comprising: a main transmission
line terminated at one end or both ends thereof; a mother board on
which said main transmission line is formed; a receiving circuit
coupled to the main transmission line for receiving a first signal;
a driving circuit for driving a second signal; a first stub-line
circuit for transmitting the second signal output from said driving
circuit to said main transmission line; a first resistor inserted
between said main transmission line and said first stub-line; a
first daughter board connected to said mother board, said first
daughter board having the driving circuit, the first stub-line and
the first resistor; and a connector for connecting the mother board
and the first daughter board.
2. A signal transmitting device according to claim 1, wherein said
driving circuit includes an output circuit of a push-pull type for
driving said second signal.
3. A signal transmitting device according to claim 1, wherein said
first driving circuit is connected to a power supply and a ground
through an element having a switching function, and wherein the
minimum resistance of said element having said switching function
is 50 ohms or less.
4. A signal transmitting device according to claim 1, wherein the
impedance of said main transmission line is lower than the
impedance of said first stub-line.
5. A signal transmitting device according to claim 1, wherein the
first resistor suppresses reflections at a branch point between the
main transmission line and the first stub-line.
6. A signal transmitting device according to claim 5, wherein the
first resistor has a resistance value to provide impedance matching
between the main transmission line and the first stub-line.
7. A signal transmitting device according to claim 5, wherein said
first resistor has a resistance substantially equal to a value
derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line.
8. A signal transmitting device as claimed in claim 7, wherein said
first resistor has a resistance ranging from 0.5 times to 1.5 times
of said value.
9. A signal transmitting device as claimed in claim 1, wherein said
receiving circuit includes a differential input circuit for
receiving said first signal.
10. A signal transmitting device as claimed in claim 1, wherein a
reference voltage used in said receiving circuit is supplied from
the outside of said receiving circuit.
11. A signal transmitting device as claimed in claim 1, further
comprising: a second stub-line for transmitting the first signal
from said main transmission line to said receiving circuit; and a
second resistor inserted between said main transmission line and
said second stub-line.
12. A signal transmitting device according to claim 11, wherein the
impedance of said second stub-line is higher than the impedance of
said main transmission line.
13. A signal transmitting device according to claim 11, wherein the
second resistor suppresses reflections at a branch point between
the main transmission line and the second stub-line.
14. A signal transmitting device according to claim 13, wherein the
second resistor has a resistance value to provide impedance
matching between the main transmission line and the second
stub-line.
15. A signal transmitting device according to claim 11, wherein
said first resistor has a resistance substantially equal to a first
value derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line, and wherein said second resistor has a resistance
substantially equal to a second value derived by subtracting a half
of an impedance of said main transmission line from a predetermined
impedance of said second stub-line.
16. A signal transmitting device as claimed in claim 15, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said first value.
17. A signal transmitting device according to claim 11, further
comprising: a second daughter board connected to said mother board,
said second daughter board having the receiving circuit, the second
stub-line and the second resistor.
18. A signal transmitting device as claimed in claim 1, wherein the
amplitude of a signal on the main transmission line is lower than
that of the second signal outputted from said drive circuit.
19. A signal transmitting device according to claim 1, wherein a
value of a supply voltage supplied to said signal transmitting
device, an output characteristic value of said signal driving
circuit and an input characteristic value of said input circuit
used in the signal transmitting device have the following
relations: Vss.ltoreq.VoL.ltoreq.V-
iL.ltoreq.Vref.ltoreq.ViH.ltoreq.VoH.ltoreq.Vcc
Vss.ltoreq.VoL.ltoreq.ViL.-
ltoreq.Vtt.ltoreq.ViH.ltoreq.VoH.ltoreq.Vcc where Vcc: supply
voltage supplied to said output circuit, VoH: "high" level
prescribed value of said output circuit; ViH: "high" level
prescribed value of said input circuit; Vref: reference voltage of
said input circuit; Vtt: terminating voltage; ViL: "low" level
prescribed value of said input circuit; VoL: "low" level prescribed
value of said output circuit; and Vss: ground voltage.
20. A signal transmitting device comprising: a mother board; a main
transmission line formed on the mother board, the main transmission
line being terminated at one end or both ends thereof; a receiving
circuit coupled to the main transmission line for receiving a first
signal; and a connector for connecting a daughter board to the
mother board, wherein the daughter board comprises: a driving
circuit for driving a second signal, a first stub-line for
transmitting the second signal output from said driving circuit to
said main transmission line, and a first resistor disposed between
the connector and the driving circuit.
21. A signal transmitting device comprising: a mother board; a main
transmission line formed on the mother board, the main transmission
line being terminated at one end or both ends thereof; a receiving
circuit coupled to the main transmission line for receiving a first
signal; and a connector for connecting a daughter board to the
mother board, wherein the daughter board includes at least one of:
a driving circuit for driving a second signal, a first stub-line
for transmitting the second signal output from said driving circuit
to said main transmission line, and a first resistor disposed
between the connector and the driving circuit.
22. A signal transmitting device comprising: a mother board; a main
transmission line formed on the mother board, the main transmission
line being terminated at one end or both ends thereof; a receiving
circuit coupled to the main transmission line for receiving a first
signal; and a connector being capable of connecting a daughter
board with the mother board, wherein the daughter board comprises:
a driving circuit for driving a second signal, a first stub-line
for transmitting the second signal output from said driving circuit
to said main transmission line, and a first resistor disposed
between the connector and the driving circuit.
23. A signal transmitting device according to claim 20, wherein the
impedance of said main transmission line is lower than the
impedance of said first stub-line.
24. A signal transmitting device according to claim 20, wherein the
first resistor suppresses reflections at a branch point between the
main transmission line and the first stub-line.
25. A signal transmitting device according to claim 24, wherein the
first resistor has a resistance value to provide impedance matching
between the main transmission line and the first stub-line.
26. A signal transmitting device according to claim 24, wherein
said first resistor has a resistance substantially equal to a value
derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line.
27. A signal transmitting device as claimed in claim 26, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said value.
28. A signal transmitting device as claimed in claim 20, wherein
said receiving circuit includes a differential input circuit for
receiving said first signal.
29. A signal transmitting device as claimed in claim 20, wherein a
reference voltage used in said receiving circuit is supplied from
the outside of said receiving circuit.
30. A signal transmitting device as claimed in claim 20, further
comprising: a second stub-line for transmitting the first signal
from said main transmission line to said receiving circuit; and a
second resistor inserted between said main transmission line and
said second stub-line.
31. A signal transmitting device according to claim 30, wherein the
impedance of said second stub-line is higher than the impedance of
said main transmission line.
32. A signal transmitting device according to claim 30, wherein the
second resistor suppresses reflections at a branch point between
the main transmission line and the second stub-line.
33. A signal transmitting device according to claim 32, wherein the
second resistor has a resistance value to provide impedance
matching between the main transmission line and the second
stub-line.
34. A signal transmitting device according to claim 30, wherein
said first resistor has a resistance substantially equal to a first
value derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line, and wherein said second resistor has a resistance
substantially equal to a second value derived by subtracting a half
of an impedance of said main transmission line from a predetermined
impedance of said second stub-line.
35. A signal transmitting device as claimed in claim 34, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said first value.
36. A signal transmitting device as claimed in claim 30, further
comprising: a second daughter board connected to said mother board,
said second daughter board having the receiving circuit, the second
stub-line and the second resistor.
37. A signal transmitting device as claimed in claim 20, wherein
the amplitude of a signal on the main transmission line is lower
than that of the second signal outputted from said drive
circuit.
38. A signal transmitting device according to claim 21, wherein the
impedance of said main transmission line is lower than the
impedance of said first stub-line.
39. A signal transmitting device according to claim 21, wherein the
first resistor suppresses reflections at a branch point between the
main transmission line and the first stubline.
40. A signal transmitting device according to claim 39, wherein the
first resistor has a resistance value to provide impedance matching
between the main transmission line and the first stub-line.
41. A signal transmitting device according to claim 39, wherein
said first resistor has a resistance substantially equal to a value
derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line.
42. A signal transmitting device as claimed in claim 41, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said value.
43. A signal transmitting device as claimed claim 21, wherein said
receiving circuit includes a differential input circuit for
receiving the first signal.
44. A signal transmitting device as claimed in claim 21, wherein a
reference voltage used in said receiving circuit is supplied from
the outside of said receiving circuit.
45. A signal transmitting device as claimed in claim 21, further
comprising: a second stub-line for transmitting the first signal
from said main transmission line to said receiving circuit; and a
second resistor inserted between said main transmission line and
said second stub-line.
46. A signal transmitting device according to claim 45, wherein the
impedance of said second stub-line is higher than the impedance of
said main transmission line.
47. A signal transmitting device according to claim 45, wherein the
second resistor suppresses reflections at a branch point between
the main transmission line and the second stub-line.
48. A signal transmitting device according to claim 47, wherein the
first resistor has a resistance value to provide impedance matching
between the main transmission line and the second stub-line.
49. A signal transmitting device according to claim 45, wherein
said first resistor has a resistance substantially equal to a first
value derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line, and wherein said second resistor has a resistance
substantially equal to a second value derived by subtracting a half
of an impedance of said main transmission line from a predetermined
impedance of said second stub-line.
50. A signal transmitting device as claimed in claim 49, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said first value.
51. A signal transmitting device according to claim 45, further
comprising: a second daughter board connected to said mother board,
said second daughter board having the receiving circuit, the second
stub-line and the second resistor.
52. A signal transmitting device according to claim 21, wherein the
amplitude of a signal on the main transmission line is lower than
that of the second signal outputted from said drive circuit.
53. A signal transmitting device according to claim 22, where in
the impedance of said main transmission line is lower than the
impedance of said first stub-line.
54. A signal transmitting device according to claim 22, wherein the
first resistor suppresses reflections at a branch point between the
main transmission line and the first stub-line.
55. A signal transmitting device according to claim 54, wherein the
first resistor has a resistance value to provide impedance matching
between the main transmission line and the first stub-line.
56. A signal transmitting device according to claim 54, wherein
said first resistor has a resistance substantially equal to a value
derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line.
57. A signal transmitting device as claimed in claim 56, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said value.
58. A signal transmitting device as claimed in claim 22, wherein
said receiving circuit includes a differential input circuit for
receiving the first signal.
59. A signal transmitting device as claimed in claim 22, wherein a
reference voltage used in said receiving circuit is supplied from
the outside of said receiving circuit.
60. A signal transmitting device as claimed in claim 22, further
comprising: a second stub-line for transmitting the first signal
from said main transmission line to said receiving circuit; and a
second resistor inserted between said main transmission line and
said second stub-line.
61. A signal transmitting device according to claim 60, wherein the
impedance of said second stub-line is higher than the impedance of
said main transmission line.
62. A signal transmitting device according to claim 60, wherein the
second resistor suppresses reflections at a branch point between
the main transmission line and the second stub-line.
63. A signal transmitting device according to claim 62, wherein the
second resistor has a resistance value to provide impedance
matching between the main transmission line and the second
stub-line.
64. A signal transmitting device according to claim 60, wherein
said first resistor has a resistance substantially equal to a first
value derived by subtracting a half of an impedance of said main
transmission line from a predetermined impedance of said first
stub-line, and wherein said second resistor has a resistance
substantially equal to a second value derived by subtracting a half
of an impedance of said main transmission line from a predetermined
impedance of said second stub-line.
65. A signal transmitting device as claimed in claim 64, wherein
said first resistor has a resistance ranging from 0.5 times to 1.5
times of said first value.
66. A signal transmitting device according to claim 60, further
comprising: a second daughter board connected to said mother board,
said second daughter board having the receiving circuit, the second
stub-line and the second resistor.
67. A signal transmitting device as claimed in claim 22, wherein
the amplitude of a signal on the main transmission line is lower
than that of the second signal outputted from said drive circuit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to technique of transmitting a
signal between elements such as a CPU and a memory device or memory
IC (for example, between digital circuits each composed of CMOS
elements or functional blocks of CMOS elements), and, more
particularly to techniques of quickly transmitting a signal through
one bus in which one main transmission line has plural elements
connected thereto.
[0002] As a technique of quickly transmitting a signal between
digital circuits each composed of a semiconductor integrated
circuit, there has been proposed a technique of a low-amplitude
interface for propagating a signal having a signal amplitude as low
as about 1 volt.
[0003] As a representative example of such a low-amplitude
interface, a GTL (Gunning Transceiver Logic) interface or a CTT
(Center Tapped Termination) interface has been heretofore proposed.
These low-amplitude interfaces are discussed in detail in pp 269 to
290 of Nikkei Electronics, Nov. 27, 1993.
[0004] FIG. 1 shows a prior art arrangement of such a low-amplitude
interface in which one main transmission line has plural branched
lines.
[0005] A numeral 100 denotes a transmission line terminated by
termination power supplies 60 and 61 and termination resistors 50
and 51. The transmission line 100 is connected to a driving circuit
block 1 and receiving circuit blocks 2, 3 and 4.
[0006] The transmission line 100 has an impedance of 50.OMEGA..
Each of branched lines 11 to 14 has an impedance of 50.OMEGA.. Each
of the terminating resistors 50 and 51 has an impedance of
50.OMEGA.. Each voltage of the terminating power supplies 60 and 61
is 0.5 volt. The sending or driving circuit 21 has an on resistance
of 10.OMEGA..
[0007] When the driving circuit 21 is at a logical "High" output,
the circuit 21 operates to connect the transmission line 11 to a
1-volt power supply (not shown). When the driving circuit 21 is at
a logical "Low" output, the circuit 21 operates to connect the
transmission line 11 to the ground, that is, a 0-volt power supply
(not shown). Numerals 32 to 34 denote receiving circuits included
in a receiving circuit block, respectively. These receiving
circuits compare received signals with the reference voltage
V.sub.ref to determine if the received signal is a Low or High
level. In this arrangement, V.sub.ref is set at 0.5V.
[0008] Next, a description will be given as to how a signal is
transmitted to each point in FIG. 1 on this bus when the driving
circuit 21 is switched from the Low output to the High output. At
first, a potential of the transmission bus 100 is derived when the
driving circuit 21 is at the Low output. The voltage at the point A
on the transmission line at this time corresponds to a voltage
given by dividing the terminating power source of 0.5 volt by the
terminating resistances 50 and 51 and the on resistance of the
sending circuit 21. That is, the voltage is derived by:
0.5V.times.10.OMEGA./(10.OMEGA.+50.OMEGA./2)=0.14(V)
[0009] Next, the potential will be derived of the transmission line
which occurs when the output of the sending circuit 21 is switched
from the Low output to the High output so that a signal is
transmitted to a point A of FIG. 1 as follows. Immediately after
the output of the sending circuit 21 is switched, the power supply
voltage is divided by the on-resistance of the sending circuit and
the impedance 50.OMEGA. of the transmission line 11. Hence, the
potential boost at the point A is derived by:
1V.times.50.OMEGA./(50.OMEGA.+10.OMEGA.)=0.83(V)
[0010] The addition of the initial voltage 0.14 V and the voltage
boost, that is, 0.97 V corresponds to the potential at the point
A.
[0011] The potential occurring when the waveform of the amplitude
of 0.83 V reaches the branch point B is derived as follows. If the
transmission line 100 is viewed from the transmission line 11,
since the transmission line 100 is divided into two, left and right
parts, the virtual impedance of the transmission line 100 if viewed
from the transmission line 11 becomes a half of an impedance
50.OMEGA. of the transmission line 100, that is, 25.OMEGA.. On the
other hand, since the impedance of the transmission line 11 is
50.OMEGA., the mismatch of the impedance results in bringing about
the reflection of a signal at the point B.
[0012] The reflective coefficient is derived as follows.
(50.OMEGA.-25.OMEGA.)/(50.OMEGA.+25.OMEGA.)=0.33
[0013] This means that a one-third part of the signal amplitude of
0.83 V transmitted to the point A, that is, a signal of the
amplitude 0.28 V is reflected and returned to the sending circuit
side. The signal of the left amplitude 0.55 V is transmitted to the
transmission line 100 as a first transmitted wave. Hence, the
potential of the transmitted signal corresponds to an addition of
0.55 V and the initial potential, that is, 0.69 V.
[0014] When the signal having the amplitude of 0.28 V returned to
the sending circuit reaches the sending circuit, the signal is
mirror-reflected and reaches the point B again. A two-third part of
the signal passes through the transmission line 100, while the
remaining one-third part of the signal is returned to the
transmission line 11. According to such an action, the signal
travels to and fro on the transmission line 11 again and again.
Each time the signal waveform reaches the point B, the two-third
part of each waveform is output to the transmission line 100. By
this operation, the amplitude of 0.83 V originally at the point A
is dividedly transmitted to the transmission line 100 bit by
bit.
[0015] The signal of 0.69 V which passed through the point B and
transmitted to the transmission line 100 reaches the point C. At
this point, two transmission lines are each made to have an
impedance of 50.OMEGA. before the passage of the signal. Hence, the
mismatch of the forward synthesized impedance 25.OMEGA. to the
impedance of 50.OMEGA. of the transmission line on which the signal
has passed results in bringing about the reflection of the
signal.
[0016] The reflective coefficient is as follows:
(50.OMEGA.-25.OMEGA.)/(50.OMEGA.+25.OMEGA.)=0.33
[0017] The potential of the waveform passed through the point C
corresponds to a potential derived by multiplying the signal
amplitude of 0.55 V at the point B by a transmittance 2/3(=1 -1/3)
and adding the initial potential to the multiplied value. That
is,
0.55V.times.{fraction (2/3)}+0.14V=0.50(V)
[0018] A similar reflection takes place at the point E or the point
G. The potential at the point E is 0.38 V and the potential at the
point G is 0.30 V.
[0019] These results are shown in FIGS. 2A to 2C. FIG. 2A shows
signals which come to and go out of the point C, that is, a signal
of the point B coming to the point C and signals of the point D and
the point E going out of the point C. For explaining them clearly,
the signal at the point A is shown as well. Likewise, FIG. 2B shows
signals which come to and go out of the point E. FIG. 2C shows
signals which come to and go out of the point G. In FIGS. 2A to 2C,
a numeral 201 denotes a signal waveform at the point A in FIG. 1. A
numeral 202 denotes a waveform at the point B. A numeral 203
denotes a waveform at the point C. A numeral 204 denotes a waveform
at the point D. A numeral 205 denotes a waveform at the point E. A
numeral 206 denotes a waveform at the point F. A numeral 207
denotes a waveform at the point G. A numeral 208 denotes a waveform
at the point H. When the signal drops, the same thing takes place.
The signal waveforms at the drop of the signal are as shown in
FIGS. 3A to 3C. In FIG. 3, numerals 201 to 208 denote signal
waveforms at the point A to the point H shown in FIG. 1,
respectively.
[0020] From the situation described above, it is understood that
the use of the conventional signal transmitting circuit makes it
impossible to allow the first signal at the point A indicating a
High level from the driving circuit 21 to exceed the reference
voltage Vref (0.5 V in the above condition) at all of the receiving
circuit blocks for establishing that the signal is at the High
level. In other words, due to the large degree of reflection at the
various points B, C, E and G, the original High level voltage at
the point A for the first signal is attenuated to very low levels
of voltage that will not exceed the reference voltage V.sub.ref at
the receivers. Therefore, even though the sending circuit 21 is
indicating a High level, the receivers 32, 33 and 34 will not be
able to recognize this for the first signal. Eventually, after
repeated signals, the level of voltage at points B, C and D will
increase to levels much closer to the level at point A, but, until
this occurs, the receivers will not be able to recognize the High
level.
[0021] The signal entering each branched line at the branch point
C, E or G, like the transmission line 11, is reflected over and
over inside of the branched line. When the reflected waveform
returns to the branch point, the two-third part of the signal goes
to the transmission line 100. This brings about a waveform
distortion on the transmission line 100.
[0022] As mentioned above, in the foregoing prior art, the
reflections take place at each branch point. The potential drops
resulting from the reflections are overlapped with each other.
Hence, the rise of the signal potential is delayed in a remote
place of the driving circuit. This results in disadvantageously
increasing the delay time, and thereby prevents quickly
transmitting the signal.
[0023] Further, the signal entered ilnto the receiving circuit
block is reflected in the receiving circuit part and then goes into
the transmission line 100. This also results in disadvantageously
distorting the signal waveform, thereby lowering the reliability of
the signal transmission.
[0024] To speed up the signal transmission and make the signal
amplitude on the line 100 smaller, the above prior art is arranged
so that the supply voltage is 1 V. In the circuit discussed in the
aforementioned paper, to achieve an amplitude of 1 V at the
normally used power supply of 3.3 V, the driving circuit is
arranged to give a special value of 100.OMEGA. to its on-resistance
for realizing a small amplitude.
[0025] The special value given to the on resistance as mentioned in
the paper, however, makes the widely available transistors having
an on resistance of about 10 W useless. In other words, specially
designed transistors are required.
[0026] Further, such a higher on resistance given to the sending
circuit 21 leads to increasing the power consumption of the driving
circuit, thereby disadvantageously increasing the overall power
consumption.
[0027] As another known prior art arrangement relevant to the
present invention, U.S. Pat. No. 4,922,449 to Donaldson et al may
be referred to. This U.S. Patent discloses a technique of providing
a resistor between a circuit block and an inter-block signal
transmission line in a circuit line structure having plural circuit
blocks containing a driving circuit and a receiving circuit and the
inter-block signal transmission line for propagating a signal
between the circuit blocks. The object of providing the resistor
therebetween is for reducing passage current appearing at the time
of signal collision by the source switching operation, that is,
reducing the amplitude of the signal on the inter-block signal
transmission bus. The resistance is set as 20 W to 40 W. This
resistance may bring about a signal reflection at a branch point
between the transmission line inside of the circuit block and the
inter-block transmission line. The signal reflection may
disadvantageously inhibit the realization of fast signal
transmission. That is, this technique does not define any
resistance based on a relation of an impedance between the
inter-block signal transmission line and the signal transmission
line inside of the block.
[0028] Moreover, another prior art arrangement which provides a
resistor between an inter-block signal transmission line and a
signal transmission line inside of the circuit block is disclosed
in JP-B-54-5929. In this prior art arrangement, a resistor is
provided only between the circuit block on the side of the
receiving circuit and the inter-block signal transmission line, but
no resistor is provided between the circuit block provided with a
sending circuit and the inter-block signal transmission bus. Like
U.S. Pat. No. 4,922,449, a signal reflection takes place when the
signal outputted from the sending circuit is transmitted onto the
inter-block signal transmission bus. As in the previously described
arrangement, this signal reflection may disadvantageously inhibit
realization of fast signal transmission.
SUMMARY OF THE INVENTION
[0029] It is an object of the present invention to provide a signal
transmitting device, a circuit block, and an integrated circuit
which are arranged to overcome the foregoing disadvantages,
suppress the drop of a signal potential on a transmission line
having branched lines, prevent repetitive reflections in each
branched line, and keep an amplitude of a signal small on the line,
for quickly transmitting a signal.
[0030] To achieve the object in a preferred mode, a signal
transmitting device comprises a first circuit block including a
driving circuit for driving a signal and an intra-block
transmission line for transmitting a signal from the driving
circuit to the outside of the circuit block, a second circuit block
including a receiving circuit for receiving a signal and an
intra-block transmission line for transmitting a signal to be
inputted to the receiving circuit, and an inter-block transmission
line for transmitting the signal between the circuit blocks,
wherein the inter-block transmission line is terminated by one or
two elements each having a resistance equal to or close to a
characteristic impedance value of the inter-block transmission
line. In addition, the resistance of each of resistors 80 to 83 is
provided with a resistance equal to or close to a value obtained by
subtracting a half of the impedance of the inter-block transmission
line from the impedance of the intra-block transmission line.
[0031] In a circuit device having plural blocks each having both of
a driving circuit and a receiving circuit, likewise, the
inter-block transmission line is terminated by one or two elements
each having a resistance equal to or close to a characteristic
impedance of the inter-block transmission line. Each intra-block
transmission line is provided to have a resistance equal to or
close to a value obtained by subtracting a half of the
characteristic impedance of the inter-block transmission line from
the impedance of the intra-block transmission line.
[0032] In the case where a package with a long lead frame such as
quad flat package (QFP) or a pin grid array (PGA) is used in an
integrated circuit having a driving or a receiving circuit
integrated thereon termination is made to the inter-block
transmission line, a resistor is provided for impedance matching
between the inter-block transmission line and the intra-block
transmission line, and the impedance of the lead frame and the
impedance of the intra-block transmission line are matched.
[0033] In accordance with the present invention, by inserting a
resistor having a resistance close to a value derived by reducing a
half of an impedance of the line from the impedance of the branched
line, it is possible to prevent repetition of reflections inside of
the branched line and attenuate the amplitude of the transmission
line by dividing the inserted resistance and the terminating
resistance, thereby enabling to quickly transmit the signal.
[0034] In the case where a large number of branch points exist on
the inter-block transfer line, the capacitance because of the
existence of the resistors, the inter-block transmission line is
not able to see the branched line directly (i.e., the total of the
transmission line load capacitance and the capacitance of the
driving and receiving circuits). This is effective in suppressing
the line impedance from being lowered. Further, the waveform
distortion due to live-insertion can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a diagram showing a conventional unidirectional
transmission line;
[0036] FIGS. 2A to 2C are charts showing signal waveforms (leading
waveforms) appearing in the case of using the conventional
transmission line;
[0037] FIGS. 3A to 3C are charts showing signal waveforms (tailing
waveforms) appearing in the case of using the conventional
transmission line;
[0038] FIG. 4 is a block diagram showing an embodiment 1 of the
present invention;
[0039] FIG. 5 is a circuit diagram showing an example of a driving
circuit;
[0040] FIG. 6 is a circuit diagram showing an example of a
differential receiving circuit;
[0041] FIGS. 7A to 7C are graphs showing signal waveforms (leading
waveforms) in the embodiment 1 of the present invention;
[0042] FIGS. 8A to 8C are graphs showing signal waveforms (tailing
waveforms) in the embodiment 1 of the present invention;
[0043] FIG. 9 is a graph showing a waveform distortion occurring
when live-insertion is executed in the case of using the
conventional transmission line;
[0044] FIG. 10 is a graph showing a waveform distortion due to
live-insertion in the case of using the circuit according to the
embodiment 1 of the present invention;
[0045] FIG. 11 is a block diagram showing an embodiment 2 of the
present invention;
[0046] FIGS. 12A to 12B are graphs showing waveforms occurring when
the sending circuit is switched by using the conventional
transmission line;
[0047] FIGS. 13A to 13B are diagrams showing waveforms of switching
operation by driving circuit of the embodiment 2;
[0048] FIG. 14 is a block diagram showing an embodiment 3 of the
invention;
[0049] FIG. 15 is a diagram showing a modification of the
embodiment 3;
[0050] FIGS. 16A to 16C are graphs showing signal waveforms
(leading waveforms) occurring in the case of the circuit according
to the embodiment 3 of the present invention;
[0051] FIGS. 17A to 17C are graphs showing signal waveforms
(tailing waveforms) occurring in the case of the circuit according
to the embodiment 3 of the present invention;
[0052] FIGS. 18A to 18C are graphs showing signal waveforms
(leading waveforms) occurring in the case of changing an impedance
on a transmission line in the circuit according to the embodiment 1
of the present invention;
[0053] FIGS. 19A to 19C are graphs showing signal waveforms
(tailing waveforms) occurring in the case of changing an impedance
on a transmission line in the circuit according to the embodiment 1
of the present invention;
[0054] FIG. 20 is a circuit diagram showing an arrangement of the
embodiment 3 of the present invention in which a capacitor is used
in place of the resistor;
[0055] FIG. 21 is a circuit showing another arrangement of the
embodiment 3 of the present invention in which a capacitor is used
in place of the resistor;
[0056] FIGS. 22A to 22C are graphs showing signal waveforms
(leading waveforms) occurring in the case of using the arrangement
shown in FIG. 20;
[0057] FIGS. 23A to 23C are graphs showing signal waveforms
(tailing waveforms) occurring in the case of using the arrangement
shown in FIG. 20;
[0058] FIG. 24 is a graph showing a signal waveform occurring in a
circuit arrangement shown in FIG. 4;
[0059] FIG. 25 is a graph showing a signal waveform occurring in a
case that resistors 80 to 83 have smaller values in the circuit
arrangement shown in FIG. 4;
[0060] FIG. 26 is a graph showing a signal waveform occurring in a
case that the resistors 80 to 83 have larger values in the circuit
arrangement shown in FIG. 4;
[0061] FIG. 27 is a block diagram showing an embodiment 4 of the
present invention;
[0062] FIG. 28 is a sectional view showing a QFP package;
[0063] FIG. 29 is a sectional view showing a PGA package; and
[0064] FIG. 30 is a diagram showing an example of a device on which
the QFP package is mounted.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0065] Embodiment of the present invention will be described in
detail with reference to the accompanying drawings.
[0066] FIG. 4 shows in fundamental block diagram, a first
embodiment of a unidirectional transmission line to which the
present invention is applied.
[0067] In FIG. 4, a numeral 1 denotes a driving circuit block
(unit) having a driving circuit 21. Numerals 2 to 4 denote
receiving circuit blocks provided with receiving circuits 32 to 34,
respectively. The circuit blocks include resistors 80 to 83 and
transmission lines 11 to 14, respectively. A transmission line 100
is connected to the circuit blocks 1 to 4, and both ends of the
transmission bus 100 are terminated by the resistors 50 and 51,
each having a resistance equal to or close to a characteristic
impedance value of the transmission line 100.
[0068] In FIG. 4, the transmission line 100 has an impedance of
5.OMEGA.. The branched lines 11 to 14 each have an impedance of
100.OMEGA.. Each of the termination resistors 50 and 51 has a
resistance of 50.OMEGA.. Terminating power supplies 60 and 61
operate to supply a voltage of 1.5 V. The driving circuit 21 has an
on resistance of 10.OMEGA..
[0069] The driving circuit 21 operates to connect a transmission
line to a 3V-power supply (such as 62 in FIG. 5) when the driving
circuit 21 holds the output high or connect the transmission line
to a ground potential (such as 63, in FIG. 5) when the driving
circuit 21 holds the output low. In FIG. 4, numerals 32 to 34
denote receiving circuits.
[0070] The resistors 80 to 83 are each defined to have a resistance
of 75.OMEGA.. The method of defining the resistance will be
described later.
[0071] It is noted that in this embodiment, the transmission line
100 is terminated at both of the ends. However, it may be
terminated at one end by just one resistor, if preferred. Further,
this embodiment provides three receiving circuit blocks each having
a receiving circuit. However, the present invention is applicable
to a signal transmission device including at least one block having
the receiving circuit.
[0072] FIG. 5 shows an example of the sending or driving circuit 21
used in the arrangement of FIG. 4. This driving circuit 21 is a
push-pull driving circuit composed of a pull-up transistor 70 and a
pull-down transistor 71.
[0073] The pull-up transistor 70 shown in FIG. 5 is made of an
N-channel MOS field-effect transistor (NMOS). The material of the
transistor 70 is not limited to NMOS. For example, a P-channel MOS
field-effect transistor (PMOS) may be used for making the
transistor 70.
[0074] A low-amplitude driving circuit provided with the push-pull
driving circuit is discussed in detail in the Nikkei Electronics
paper referred to previously as a prior art arrangement. In this
paper, however, the driving circuit uses a transistor with as high
an on-resistor as about 100.OMEGA.. On the contrary, the present
invention uses a transistor with an on resistance of about
10.OMEGA. which is now widely available. The present invention may
use the conventional driving circuit, because the sum of
on-resistance of the resistors 80 to 83 added in this embodiment
and the transistor on resistance of about 10.OMEGA. is close to the
on resistance of 100.OMEGA. of the prior art device so that the
amplitude on the transmission bus 100 is approximately the same
magnitude as that of the prior art.
[0075] For example, assume that the impedance and the termination
resistor of the transmission line 100 is 50.OMEGA., the impedance
of the branched line is 100.OMEGA., the terminating power supply
feeds a voltage of 1.5 V, and the power supply for the driving
circuit feeds a voltage of 3 V. With these assumptions, the signal
amplitude becomes 0.6 V on the transmission line used in the
foregoing paper indicating the use of the transistor with the on
resistance of 100.OMEGA., and the amplitude is substantially equal
to the amplitude of 0.68 V of the transmission line 100 shown in
FIG. 4.
[0076] By lowering the on-resistance of the driving circuit 21 from
100.OMEGA. to 10.OMEGA., it is possible to reduce the power
consumed in the driving circuit. For example, in the above
condition, the prior art device arranged to use an on resistance of
100.OMEGA. consumes a power of 14.4 mW, while the present invention
may greatly reduce the power consumption down to 1.9 mW. Moreover,
the present embodiment may use a driving circuit having an
on-resistance of 10.OMEGA. or more, concretely, about 50.OMEGA..
Such a driving circuit may offer the same effect as above.
[0077] Next, an example of the receiving circuits of FIG. 4 is
shown in FIG. 6. This receiving circuit is a differential receiving
circuit for determining if an input signal is logically High or Low
based on whether or not an input voltage is higher or lower than
the reference voltage V.sub.ref. The reference voltage used herein
may be produced inside of an integrated circuit. However, if noises
appearing inside of the integrated circuit or noises which have
entered from the outside cause the power supply to fluctuate, the
reference voltage may fluctuate accordingly. Hence, it is better to
feed the reference voltage from the outside. Further, it is
preferable that the receiving circuit is an NMOS type differential
receiving circuit for receiving an input signal through the effect
of the NMOS. If this type receiving circuit is used as the
reference voltage, the voltage of the terminating power supply is
used. In this case, the reference voltage is equal to half of a
supply voltage. Hence, it is possible to receive a small amplitude
waveform of 1 V or less around the reference voltage.
[0078] For example, under the following condition, the amplitude at
receiving circuit is 0.68 V. Specifically, if each of the
resistances of terminating resistors 50, 51 is 50 ohms, each of the
resistances of matching resistors 80, 81, 82 and 83 is 75 ohms and
the on-resistance of driving circuit is 10 ohms, the supply voltage
for the driving circuit is 3 V, and the terminating supply voltage
is 1.5 V, when the driving circuit is at a low output, the voltage
at each receiving circuit is 1.16
V(=1.5V-(1.5V-0).times.(50.OMEGA./2)/(50.OMEGA./2+75.OMEGA.+10)=1.5-0.34)
and when the driving circuit is at a high output , the voltage at
each receiving circuit is
1.84V(=1.5V+(3-1.5).times.(50/2)/(50/2+75+10)=1.5+0.- 34). Thus,
the amplitude at each receiving circuit is 0.68V(=1.84-1.16).
[0079] In FIG. 4, just one receiving circuit 32 to 34 of each
circuit block is described by way of example. However, the present
invention is not limited by the number of the receiving
circuits.
[0080] In the signal transmission circuit arranged as described
above, the resistance of each of the resistors 80 to 83 is made
equal to a value derived by subtracting a half of an impedance of
the line 100 from an impedance of the intra-block transmission line
11. The impedance of the line 100 is required to be halved, because
the signal from the driving circuit block is branched into two ways
at a contact point B with the bus 100. That is, the following
expression is established:
Rm=Zs-ZO/2 (1)
[0081] where Zs denotes an impedance of the transmission line 11,
ZO denotes an impedance of the line 100, and Rm denotes a
resistance of the resistor 80.
[0082] As is understood from this expression, the total impedance
of the resistor 80 and the line 100 as viewed from the transmission
line 11 is made equal to the impedance of the transmission line 11
itself. This makes it possible to prevent repetitive reflections
inside of a branched line.
[0083] The resistors 81 to 83 may be defined by the similar method.
As such, another block may have the same effect as the foregoing
block 1.
[0084] Next, to describe the effect of the resistor derived by the
expression (1), the kind of waveform which is transmitted to each
point of FIG. 4 when the driving circuit 21 is switched from a Low
output to a High output will be discussed below with reference to
the circuit diagram of FIG. 4.
[0085] First, it is necessary to derive a potential of the
transmission line 100 occurring when the driving circuit 21 feeds a
Low output. The voltage of the transmission bus is made equal to
the voltage derived by dividing the terminating supply voltage of
1.5 V by the termination resistors 50 and 51, the resistor 80 and
the on resistance of the driving circuit 21. Concretely, the
voltage at the point B on the transmission line when the driving
circuit 21 provides a Low output is as follows:
1.5V.times.(75.OMEGA.+10.OMEGA.)/(10.OMEGA.+75.OMEGA.+25.OMEGA.)=1.16(V)
[0086] In the circuit of FIG. 4, the signal driven from the driving
circuit 21 is not reflected at the B point. Therefore, the overall
signal is transmitted to the transmission line 100. The potential
of the signal transmitted to the point B when the output of the
driving circuit is switched from Low to High is equal to the
voltage given by dividing the terminating supply voltage of 1.5 V
and the supply voltage of 3 V of the driving circuit 21 by the
terminating resistors 50 and 51, the resistor 80, and the on
resistance of the driving circuit 21. Hence, the signal potential
at the B point when the driving circuit 21 provides a High output
is derived as follows:
1.5V+(3V-1.5V).times.25.OMEGA./(10.OMEGA.+75.OMEGA.+25.OMEGA.)=1.84V
[0087] That is, the amplitude of the signal transmitted to the
point B is;
1.84V-1.16V=0.68V
[0088] When the signal of the amplitude of 0.68 V transmitted to
the transmission line 100 reaches the point C, though the
transmission line of 50.OMEGA., the resistor of 75.OMEGA. and the
transmission bus of 100.OMEGA. are viewed in the front, the
mismatch of the impedance brings about reflection, because the
total impedance of 38.9.OMEGA. of these two lines is different from
the impedance of 50.OMEGA. of the transmission line through which
the signal passes. The transmittance coefficient is: 1--the
reflection coefficient=1--1--(50-38.9)/(50+38.9)=0.875
[0089] The potential of the signal passing through the point C is
equal to the value derived by multiplying the signal amplitude of
0.68 V at the point B by the transmittance coefficient of 0.875 and
adding an initial potential to the multiplied value. That is, the
potential of the signal is:
0.68 V.times.0.875+1.16 V=1.76 V
[0090] Similar reflections take place at the point E or the point
G. The potential at the E or the G point are 1.68 V and 1.61 V,
respectively.
[0091] These results are shown in FIGS. 7A to 7C. FIG. 7A shows
signal waveforms which come to and go out of the point C, that is,
the signal waveform at the point B which comes to the point C and
the signal waveforms at the points D and E which go out of the
point C. Likewise, FIG. 7B shows signal waveforms which come to and
go out of the point E. FIG. 7C shows signal waveforms which come to
and go out of the point G. In FIGS. 7A-7C, a numeral 702 denotes a
signal waveform at the point B in FIG. 4. A numeral 703 denotes a
signal waveform at the point C. A numeral 704 denotes a signal
waveform at the point D. A numeral 705 denotes a signal waveform at
the point E. A numeral 706 denotes a signal waveform at the point
F. A numeral 707 denotes a signal waveform at the point G. A
numeral 708 denotes a signal waveform at the point H. When the
signal drops, the same thing occurs. The signal waveforms at this
time are shown in FIGS. 8A to 8C. In FIGS. 8A to 8C, numerals 702
to 708 denote the signal waveforms from the point B to the point H
as in FIG. 4.
[0092] In the case of using the signal transmitting circuit clearly
described in this embodiment, it is understood that it is possible
for any first signal indicating a High level from the driving
circuit 21 at each branch point to exceed the reference voltage
(1.5 V in the above condition). Therefore, each receiving circuit
will be able to recognize the High level being sent.
[0093] Such an effect of this invention is sufficiently brought
about by the resistance for resistors 80 to 83 derived by the
expression (1) as well as any value close to the resistance derived
by the expression (1).
[0094] This will be described with reference to FIGS. 24 to 26.
FIG. 24 shows the waveforms at the points A, C, D, G and H in FIG.
4 through the relation between a time and a voltage as the sending
circuit 21 continues to output a pulse waveform in the circuit
arrangement shown in FIG. 4 in which the inter-block transmission
line (main transmission line) 100 has an impedance of 50.OMEGA.each
of the intra-block transmission lines 11 to 14 has an impedance of
100.OMEGA., each of the terminating resistors 50 and 51 has a
resistance of 50 .OMEGA., the terminating supply voltage is 1.65 V
and each of the resistors 80 to 83 has a resistance of 75.OMEGA.
obtained by the expression (1).
[0095] In FIG. 24, a numeral 701 denotes a signal waveform at the
point A. A numeral 703 denotes a signal waveform at the point C. A
numeral 704 denotes a signal waveform at the point D. A numeral 707
denotes a signal waveform at the point G. A numeral 708 denotes a
signal waveform at the point H . It is difficult to visually
separate the curve indicated by 707 from the curve indicated by
708, because both of the curves are overlapped with each other.
[0096] On the other hand, the other condition is illustrated in
FIG. 25. FIG. 25 shows a waveform when each resistance of the
resistors 80 to 83 is changed to 50.OMEGA. for obtaining a larger
amplitude. As in FIG. 25, numerals 701, 703, 704, 707 and 708 show
the waveforms at the points A, C, D, G and H as in FIG. 4,
respectively. The resistance 50.OMEGA. used herein is only 66 % of
the resistance of 75.OMEGA. obtained by the expression (1). As can
be seen from FIG. 25, such resistance values may be used without
any trouble.
[0097] If the impedance of the intra-block line is 75.OMEGA., each
resistance of the resistors 80 to 83 may be fixed to 75.OMEGA. for
keeping the signal amplitude the same as the value of FIG. 24. The
waveform for this case is shown in FIG. 26. In this case, each
resistance of the resistors 80 to 83 is larger than the resistance
of 50.OMEGA. obtained by the expression (1) by a factor of 50 %.
With regard to this, it should be noted if each resistance of the
resistors 80 to 83 is shifted to and fro by about 50 % relative to
the value obtained by the expression (1), the effect of the present
application can still be achieved.
[0098] Further, to enhance the effect of the invention, it is
preferable to set the resistances of the resistors 80 to 83 to be a
higher value than the impedance of the main transmission line 100.
In addition, when the transmission line 100 has many branch lines,
the signal from the driving circuit 21 cannot exceed the reference
voltage even through the effect of the signal transmitting circuit
used in this embodiment. A method for coping with this shortcoming
will be clarified in the embodiment 3.
[0099] Each signal which enters into the transmission lines 12 to
14 at the points C, E and G is mirror-reflected on the
corresponding receiving circuit and then returns to the branch
point. Since this circuit keeps the impedances properly matched,
the overall signal is transmitted to the transmission line 100 at
one time without reflection of the signal on the branch point.
[0100] As is obvious from this figure, the resistors inserted in
the present invention make it possible to greatly reduce the
potential drop resulting from the reflection. Further, these
resistors make the signal potential drop in a remote receiving
circuit from the driving circuit negligible.
[0101] By inserting a resistor having a predetermined resistance
around a contact between the transmission line inside of the
circuit block and the inter-block transmission line, it is possible
to keep the signal amplitude on the transmission bus smaller and
transmit the signal at high speed. How much the amplitude is made
smaller is allowed to be freely designed by changing the impedances
of the transmission line 100 and each intra-block transmission
line. For example, if the sending circuit 21 has an on resistance
of 10.OMEGA., assuming that the intra-block transmission line has
an impedance of 100.OMEGA. and the transmission line 100 has an
impedance of 25.OMEGA., the signal amplitude of the transmission
bus is calculated as follows:
1.5V.times.12.5.OMEGA./(12.5.OMEGA.+87.5.OMEGA.+10-
).times.2=0.34(V) in which each of the resistors 80 to 83 has a
resistance of 87.5.OMEGA.. The waveforms at this case are shown in
FIGS. 18A to 18C and 19A to 19C. In these figures, numerals 702 to
708 denote the signal waveforms at the B to the H points as in FIG.
4. From this figure, it is understood that a waveform with a
smaller amplitude and a small drop is obtained.
[0102] Further, the resistors 80 to 83 have an effect of
suppressing lowering of the impedance of the transmission line 100
resulting from the load capacitance in the circuit block. That is,
by inserting a resistor between the transmission line 100 and each
of the circuit blocks 1 to 5, the inter-block transmission line is
not able to see the capacitance in the circuit block directly
(i.e., the total of the transmission line load capacitance and the
capacitance of the driving and receiving circuits). Hence, it is
possible to suppress the lowering of the impedance of the
transmission line.
[0103] Moreover, the signal transmitting system of the present
invention offers a further advantageous effect in a situation where
a new board is added to the transmission bus in operation or a
mounted broad is pulled out, that is, if a so-called live-insertion
is executed. For example, consider that a board charged up to the
High level is inserted to the transmission line to which the Low
signal is transmitted. In this case, since the potential of the
in-board capacitance is different from the potential of the
transmission line, current flows from the board to the transmission
line. The current flow is transmitted to the transmission line. The
flown current is further transmitted as a distorted waveform into
the receiving circuit inside of the branched line. If this waveform
distortion goes up to a higher potential than the reference
voltage, the receiving circuit recognizes that the High signal is
transmitted and thus malfunctions.
[0104] To describe the effect of the waveform distortion, FIG. 9
shows a waveform occurring when the live-insertion is done in the
conventional transmission line and FIG. 10 shows a waveform
occurring when the live-insertion is done by the transmitting
circuit offered by the invention. As shown in FIGS. 9 and 10, the
waveform distortion caused by the live-insertion is reduced by the
present invention.
[0105] Embodiment 2
[0106] The following description will be directed to embodiment 2
in which the present invention is applied to a bidirectional
transmission line.
[0107] FIG. 11 is a fundamental block diagram showing the second
embodiment. The circuit blocks 1 to 4 provide driving circuits 21
to 24, receiving circuits 31 to 34, resistors 80 to 83, and
transmission lines 11 to 14, respectively. A transmission line 100
is connected to the circuit blocks 1 to 4 and is terminated by the
resistors 50 and 51, each having a resistance equal to a
characteristic impedance value of the transmission line 100.
[0108] FIG. 11 shows the transmission line terminated at both ends
by the resistors. However, if desired, the transmission bus may be
terminated at one end by one resistor. Further, FIG. 11 shows four
blocks. In actuality, the present invention may apply to any
transmission line if it is connected to two or more blocks.
[0109] The arrangements of the driving circuits 21 to 24 and the
receiving circuits 31 to 34 included in the circuit blocks shown in
FIG. 11 are the same as those described with reference to FIGS. 5
and 6. The values of the resistors 80 to 83 are allowed to be
defined by the manner of the embodiment 1 indicated in FIG. 4.
Further, assuming that the circuit block 1 operates to issue a
signal, the signal waveforms at the points A to H are the same as
those of the embodiment 1.
[0110] In the arrangement having the driving circuit and the
receiving circuit in one circuit block indicated in the embodiment
2, by making the resistance equal to or close to the resistance
obtained by the previous expression (1), it is possible to reduce
the waiting time accompanied with switching of the driving circuit.
Later, in the circuit arrangement shown in FIG. 11, the change of
the signal waveform occurring when the driving circuit is switched
will be described below.
[0111] At first, the driving circuit is switched in accordance with
the following procedure.
[0112] (1) The driving circuit 21 outputs a High signal.
[0113] (2) 10 ns later than (1), the driving circuit 21 is switched
to a high impedance state. At this time, the driving circuit 24
outputs a High signal.
[0114] After the driving circuit 21 is switched, the terminating
potential drops the signal potential on the transmission line
located close to the driving circuit 21 until the High signal from
the driving circuit 24 reaches that part of the transmission line.
Hence, the dropped waveform is transmitted to each branched line
through the transmission line.
[0115] The dropped waveform at each point occurring in the case of
the conventional transmission line with no resistor is shown in
FIGS. 12A and 12B, while the dropped waveform at each point
estimated about the transmission line of the present invention is
shown in FIGS. 13A and 13B. The waveforms in these figures are
those at the input circuit block of the receiving circuit 32
included in a circuit block 2 adjacent to a circuit block 1 having
the driving circuit 21.
[0116] As is obvious from FIGS. 12A and 12B, in the conventional
transmission line, the overlapped adverse effects of repetitive
reflections in the branched line and the dropped signal caused by
switching the driving circuit result in delaying when the receiving
circuit reads an input signal, that is, 2Td later than when the
driving circuit is switched. Td indicated a time when a signal is
transmitted from one end to the other end of the transmission line.
Herein, Td is about 6 ns.
[0117] On the other hand, the transmission line according to the
present invention needs only a delay of Td after the driving
circuit is switched before the receiving circuit reads the input
signal. That is, the present invention provides a capability of
reducing a waiting time required to read the input signal after the
driving circuit is switched fron 2 Td to Td.
[0118] The foregoing embodiment has been described for High to High
switching. This operation holds true to all kinds of switchings
such as Low to Low, Low to High, and High to Low. Further, this
effect is active in any combination without depending on a driving
circuit to be switched.
[0119] Embodiment 3
[0120] The following description will be directed to a third
embodiment which is particularly effective in the case of providing
a large capacitance at the tip of each branched line in a situation
where there are many branched lines. FIG. 14 is a fundamental block
diagram for explaining a unidirectional transmission bus according
to this embodiment. FIG. 15 is a fundamental block diagram for
explaining a bidirectional transmission bus according to this
embodiment. In FIG. 14, a circuit block 1 includes a driving
circuit 21, and circuit blocks 2 to 4 include receiving circuits 32
to 34, respectively. Further, the blocks have resistors 80 to 83
and transmission lines 11 to 14, respectively. In FIG. 15, the
circuit blocks 1 to 4 provide sending circuits 21 to 24, receiving
circuits 31 to 34, resistors 80 to 83, and transmission lines 11 to
14, respectively. In FIGS. 14 and 15, the transmission line 100 is
connected to the circuit blocks 1 to 4, and is terminated by
resistors 50 and 51 each having a resistance equivalent to a
characteristic impedance value of the transmission line 100.
[0121] In FIGS. 14 and 15, the transmission line is terminated at
both ends by the resistors. However, if preferred, the transmission
line may be terminated at one end by one resistor. Further, in
FIGS. 14 and 15, the number of blocks is 4. In actuality, the
present invention is applicable only if two or more blocks are
provided.
[0122] Incidentally, in these figures numerals 90 to 93 denote
switches. Numerals 110 to 113 denote resistors.
[0123] In this embodiment, the operation and the effect of the
switches will be described with reference to the fundamental block
diagrams of FIGS. 14 and 15. The other parts of this third
embodiment are the same as those of the embodiments 1 and 2.
Therefore, description about such other parts is not provided here
to avoid redundancy.
[0124] If the capacitance at the tip of the branched line is great
or if a large number of branched lines are provided, the drop of
the signal potential at the branch point of the transmission line
is unacceptably large. Even the embodiments 1 and 2 are unable to
suppress such a large drop.
[0125] For example, consider the condition indicated in the
embodiment 1, that is, the circuit arranged so that in FIG. 4 the
transmission line 100 has an impedance of 50.OMEGA., each branched
line 11 to 14 has an impedance of 100.OMEGA., each of the
terminating resistors 50 and 51 has a resistance of 50.OMEGA., each
of the termination power supply has a voltage of 1.5 V, each of the
resistors 80 to 83 has a resistance of 75.OMEGA., the on resistance
of the sending circuit 21 is 10.OMEGA., the driving circuit 21
operates to connect the transmission bus to a 3-V power supply when
the circuit 21 feeds a High signal, and the driving circuit 21
operates to connect the transmission bus to the ground or 0-V
supply when the circuit feeds a Low signal. In such a time, if
seven or more branched lines are provided, the first signal from
the sending circuit 21 indicating a High level will not exceed the
reference voltage (Vref) after the sixth branch point.
[0126] To overcome this shortcoming, the third embodiment will be
described as a method of eliminating a delaying time caused by a
dropped signal potential. This is accomplished by passing more
current than an amount of current necessary for compensating the
drop of the signal potential at the branch point.
[0127] At first referring to FIG. 14, when the driving circuit 21
is operated, the switch 90 in the circuit 1 closes to lower the
resistance between the transmission line 100 and the intra-block
signal transmission line 11. This makes it possible to increase a
signal amplitude on the bus 100. The same holds true for the
operation of the driving circuits 21 to 24 and their corresponding
switches 90 to 93 in FIG. 15.
[0128] For example, on the condition that each of the terminating
resistors 50 and 51 has a value of 50.OMEGA., each of matching
resistors 80 to 83 has a value of 75.OMEGA., each of the sending
circuits 21 to 25 has an on resistance of 10.OMEGA., and each of
the switch resistors 80 to 83 has a value of 10.OMEGA., by closing
the switch 90, the resistance between the transmission line 100 and
the branched line 11 is decreased from 75.OMEGA. to 8.8.OMEGA. and
the amplitude on the transmission bus 100 is increased from 0.68 V
to 1.3 V. This results in eliminating the delay time caused by the
dropped signal potential at the branch point.
[0129] To transfer the signal at high speed if the signal is
reversed at the next cycle, the switch is enabled to open 0.3 cycle
later than the starting time for outputting a signal from the
driving circuit. By this, the signal amplitude is allowed to be
returned to the predetermined value, that is, a suitably small
amplitude for enabling the fast transfer. Of course, the delay
could be set to be different than 0.3 cycle, where appropriate.
[0130] FIGS. 16A to 16C and 17A to 17C are the drawings for
explaining the effect of this invention. The waveforms shown in
these figures are those occurring when the driving circuit 21 is
enabled by the circuits shown in FIGS. 14 and 15. FIGS. 16A to 16C
show the waveforms on the rise. FIGS. 17A to 17C show the waveforms
on the drop. For purposes of example, the resistance of resistors
110 through 113 was set at 20.OMEGA. each for arriving at these
waveforms.
[0131] FIGS. 16A and 17A show the signal waveforms which come to
and go out of the point C shown in FIG. 14, that is, the waveform
at the point B which comes to the point C and the waveforms at the
points B and E which go out of the point C. Likewise, FIG. 16B and
17B show the signal waveforms which come to and go out of the point
E. FIGS. 16C and 17C show the signal waveforms which come to and go
out of the point G. A numeral 1402 denotes the signal waveform at
the point B shown in FIG. 14. A numeral 1403 denotes the signal
waveform at the point C. A numeral 1404 denotes the signal waveform
at the point D. A numeral 1405 denotes the signal waveform at the
point E. A numeral 1406 denotes the signal waveform at the point G.
A numeral 1408 denotes the signal waveform at the point H.
[0132] The use of the switch makes it possible to increase the
signal amplitude on the transmission line 100 and to eliminate the
delay time caused by the dropped signal potential at the branch
point. As described above, the switch control makes it possible to
transfer a signal of a small amplitude at fast speed even in a
transmission line having large load capacitance or a large number
of branched lines. Though the switch control is not shown, the
switch is controlled by a control unit included in the circuit
block having the driving circuit in accordance with conventional
switching techniques.
[0133] In place of the resistors 110 to 113, similar effects can be
offered by using capacitors. Embodiments arranged to use such
capacitors are shown in FIGS. 20 and 21. FIG. 20 shows the same
arrangement as that shown in FIG. 14 in which a capacitor 120 is
used in place of the resistor 110. FIG. 21 shows the same
arrangement as that shown in FIG. 15 in which capacitors 120 to 123
are used in place of resistors 110 to 113. It is preferable that
the capacitance, in general, is about several tens of
pico-farads.
[0134] If the potential on the capacitor driving side is changed on
the signal from the sending circuit, the potential of the capacitor
on the transmission line 100 will also rise according to the charge
conservation law. Hence, a larger amplitude can be obtained
relative to the amplitude changed only through the resistors 80 to
83.
[0135] With regard to the switches, it is preferable to close the
switch contained in the unit for operating the driving circuit and
open the other switches. Further, the signal amplitude on the
transmission bus 100 is increased through the effect of the
capacitor line and is returned to the initial amplitude through the
effect of the terminals 50 and 51 in about several nano seconds.
Hence, while the driving circuit is in operation, the switches may
be kept closed.
[0136] FIGS. 22A to 22C and 23A to 23C show the rising waveform and
the dropping waveform at each point when the driving circuit 21 is
operated in the circuit diagram of FIG. 20. In FIGS. 22A to 22C and
23A to 23c, FIGS. 22A and 23A show the signal waveforms which come
to and go out of the point C of FIG. 20, that is, the signal
waveform on the point B which comes to the point C and the signal
waveforms on the points D and E which go out of the point C.
Likewise, FIGS. 22B and 23B show the signal waveforms which come to
and go out of the point E. FIGS. 22C and 23C show the signal
waveforms which come to and go out of the point G. In these
figures, a numeral 2002 denotes the signal waveform at the point B
of FIG. 20. A numeral 2003 denotes the signal waveform at the point
C. A numeral 2004 denotes the signal waveform at the point D. A
numeral 2005 denotes the signal waveform at the point E. A numeral
2006 denotes the signal waveform at the point F. A numeral 2007
denotes the signal waveform at the point G. A numeral 2008 denotes
the signal waveform at the point H.
[0137] As described above, the signal amplitude on the transmission
line 100 is allowed to be increased through the effect of the
capacitors, thereby eliminating the delay time caused by the
dropped signal potential at a branch point.
[0138] Embodiment 4
[0139] FIG. 27 shows an embodiment in which the driving circuit and
the receiving circuit are integrated so that an inter-circuit block
transmission line is connected to an intra-circuit block
transmission line through an transmission bus like a lead of an
integrated circuit.
[0140] In FIG. 27, a numeral 5 denotes an inner circuit block (an
inner unit, for example, an integrated circuit) which is mounted on
a circuit block 1 (for example, a board having an integrated
circuit mounted thereon). Numerals 6 to 8 denote inner circuit
blocks having receiving circuits 32 to 34, respectively, which
inner circuit blocks are mounted inside of the circuit blocks 2 to
4, respectively. The circuit blocks 1 to 4 have resistors 80 to 83
and transmission lines 11 to 14 and 41 to 44, respectively. The
transmission lines 11 to 14 are designed to have the same or almost
the same characteristic impedance as that of the transmission lines
41 to 44. Further, the transmission line 100 has the circuit blocks
1 to 4 connected thereto and is terminated at both ends by the
resistors 50 and 51 having a resistance equal to or close to the
same characteristic impedance as that of the transmission line
100.
[0141] Also in this embodiment, the transmission line may be
terminated at one end by one resistor. The necessary number of the
receiving circuit blocks is one or more.
[0142] FIG. 28 shows a section of a QFP (Quad Flat Package)
package. FIG. 29 shows a section of a PGA (Pin Grid Array) package.
In FIG. 28, when a driving signal is to be provided, a chip 130
serving as a driving circuit operates to output a signal by way of
bonding wires 140, 141 and lead frames 120, 121, in sequence. When
receiving the signal, the chip 130 receives the signal by way of
the lead frames 120, 121 and the bonding wires 140, 141, in
sequence. In FIG. 29, when a driving signal is provided, the chip
131 operates to output a signal by way of bonding wires 142, 143,
in-package wire patterns 170, 171, and I/O pins 160, 161 in
sequence. When receiving a signal, the chip 131 receives a signal
in a way of the I/O pins 160, 161, the in-package wire patterns
170, 171, and the bonding wires 142, 143 in sequence. In FIGS. 28
and 29, the lead frames 120, 121, the in-package wire patterns 170,
171 and the I/O pins 160, 161 need to have the characteristic
impedance matching described in the present invention.
[0143] In general, the characteristic impedance of the board often
takes a value of 60 to 100.OMEGA.. Hence, the most preferable
method is that the lead frames 120, 121 and the in-package wire
patterns 170, 171 are designed to each have a characteristic
impedance value in the range of 60 to 100.OMEGA..
[0144] To describe how the above components correspond to the
portions shown in FIG. 27, the sending circuit 21 and the receiving
circuits 32 to 34 correspond to the chips 130 and 131. The
transmission lines 41 to 44 correspond to the lead frames 120, 121,
the in-package wire patterns 170, 171 and the I/O pins 160, 161.
The inner circuit blocks 5 to 8 correspond to the QFP package and
the PGA package itself. In addition to the package form shown in
FIGS. 28 and 29, any package form may be taken only if the
substantially similar components are integrated.
[0145] FIG. 30 shows a model on which the QFP package of FIG. 28 is
mounted. The model of FIG. 30 is arranged so that four boards 190
to 193 are mounted on a mother board 180 through connectors 200 to
203. As the corresponding portions to those shown in FIG. 27, the
transmission lines 11 to 14 correspond to transmission lines 230 to
233, the matching resistors 80 to 83 correspond to matching
resistors 210 to 213. The inter-circuit block transmission line 100
corresponds to a data bus 240. The terminating resistors 50, 51
correspond to terminating resistors 220, 221. In addition, in FIG.
30, the transmission lines 230 to 233 run on the outer layer of the
board. On the other hand, those lines may be formed on the inner
layer. In the arrangement shown in FIG. 30, the number of boards to
be mounted is not limited. Further, a similar circuit may be
composed on just one board without the mother board.
[0146] According to the present embodiment, for matching the
impedances with each other, the components having larger packaging
capacitance and inductance such as a logic LSI are more
effective.
[0147] In this embodiment, each inner circuit block has just one
driving circuit or receiving circuit. Like the embodiment 2, on the
other hand, one inner circuit block may have both of the driving
circuit and the receiving circuit.
[0148] The present invention offers new ideas in light of the
method of designing or manufacturing an integrated circuit such as
an IC or an LSI or a module such as a memory. Previously, the
process of designing or manufacturing such devices, the impedance
of a transmission line on the board to be mounted has not been
considered at all. According to the present invention, in the
process of designing or manufacturing such devices, the following
new designing and manufacturing process is taken:
[0149] (1) Define an impedance of a transmission line of a board to
be mounted.
[0150] (2) Define an impedance of a transmission line on a board on
which a transmission line such as a lead frame for an integrated
circuit to be designed is to be connected. (Define an impedance on
each lead frame. If the transmission line on the board is constant,
follow it.)
[0151] (3) The transmission bus is manufactured according to the
impedance of the designed transmission and then is connected to an
integrated circuit chip by using a wire-bonding technique, for
example.
[0152] (4) Mount the transmission line on the right place of the
board.
[0153] Based on this manufacturing method, it is possible to
manufacture an integrated circuit or a signal transmitting circuit
which is suitable to fast transmission.
[0154] It is to be understood that the above-described arrangements
are simply illustrative of the application of the principles of the
present invention. Numerous other arrangements may be readily
devised by those skilled in the art which will embody the
principles of the invention and fall within its spirit and
scope.
* * * * *