Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Having specific delay in producing output waveform
Reexamination Certificate
2000-02-15
2002-03-12
Kim, Jung Ho (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Having specific delay in producing output waveform
C327S108000, C327S288000, C327S404000
Reexamination Certificate
active
06356133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present relates generally to bus driver circuit. More specifically, the invention relates to a bus driver circuit permitting adjustment of transition period of rising up and falling down of a transmitting data output and whereby realizing high speed transmission of the transmitting data.
2. Description of the Related Art
Conventional high speed bus driver for transmission of a transmitting data has different through rate (transition period in rising up of the transmitting data output) for efficiently performing high speed signal transmission depending upon the kind and nature of the data waveform to be transmitted, signal propagation speed and installation condition of other associated boards.
Accordingly, in order to perform signal transmission efficiency, it is necessary to select optimal through rate depending upon the kind and nature of the data waveform to be transmitted, signal propagation speed and installation condition of other associated boards.
However, the through rate of this type of bus driver is significantly depends on the performance of a transistor included therein. Therefore, the conventional bus driver circuit has no function for adjusting the through rate or has simple adjustment function discussed below.
One example of the conventional bus driver circuit which permits adjustment of the through rate, has been disclosed in Laid-Open application No. 2-122725. In this publication, there is a disclosure for the bus driver circuit, in which the through rate is adjusted by a control terminal and N-channel transistor and P-channel transistor. In concrete, when a voltage of high potential (H) is applied to the control terminal, the N-channel transistor and the P-channel transistor are turned ON. By this, the N-channel of an inverter is strengthened so that the gate of the P-channel transistor may turn into low potential (L) at high speed. As set forth above, in this prior art, the through rate of the output buffer is adjusted.
Thus, the conventional bus driver circuit does not have the through rate adjusting function or has only a simple adjusting function. Therefore, it is not possible to efficiently perform high speed transmission of the data waveform at an optimal through rate depending upon the kind and nature of the data waveform to be transmitted, signal propagation speed and installation condition of other associated boards. Also, the foregoing conventional bus driver circuit having the through rate adjusting function, adjustment of the through rate is permitted between two levels. Therefore, in order to obtain optimal through rate, the design has to be differentiated per the system to apply.
Therefore, it has been desired a bus driver circuit which permits multi-level adjustment of the through rates.
Next, discussion will be given for the prior art in a signal output circuit for outputting a signal to be input to the bus driver circuit.
At first, in advance of discussion for the prior art, the general construction of a bus transmission path will be discussed with reference to the drawing, particularly to FIG.
12
. As shown in
FIG. 12
, a plurality of bus transmission paths
303
are provided on a mother board
300
. Also, on the mother board
300
, a plurality of connectors
301
are mounted, To the connectors
301
, substrates
302
are connected. Thus, the internal circuit of the substrates
302
are connected to the bus transmission paths. Each of the substrates
302
receives and transmits signals via the bus transmission paths.
A characteristic impedance of the bus transmission paths may be varied depending upon the various factors. A major factor to cause variation in the number of substrates to be installed to the connector
301
is yield in fabrication. Amongst, discussion will be given for variation of the impedance with reference to the drawing, particularly to
FIG. 12
,
In the construction of the bus transmission path as illustrated in
FIG. 12
, the number of substrate
302
to be connected to the bus transmission path
303
is not constant. For example, in
FIG. 13
, only substrates
302
at both ends are connected to the connector
301
. Therefore, number of the substrate is two. On the other hand, in
FIG. 14
, the number of the substrate to be installed becomes seven.
By variation of the number of the installed substrates, the characteristic impedance of the bus transmission path
303
is varied. In order to show this, the approximated characteristic impedances of respective constructions of
FIGS. 13 and 14
are calculated.
In the bus transmission path of the construction shown in
FIG. 12
, it is assumed that the distance between the connectors
301
is 1 inch (2.54 cm), the characteristic impedance of the bus transmission path in the case where no substrate is installed is Z
0
:0.75&OHgr; and propagation delay period is t=7 ns/m. At this time, an inductance component L
0
and capacitance component C
0
are approximately calculated as 13.5 nH/inch and 2.36 Pf/inch.
Here, assuming that 25 pF of the capacitance component is increased per each substrate
302
, the characteristic impedance Z
1
of the bus transmission path
303
in the construction of
FIG. 13
can be calculated as 32.2&OHgr;. On the other hand, the characteristic impedance Z
2
of the bus transmission path
303
in the construction of
FIG. 14
becomes 20.5&OHgr;. Namely, when the construction of
FIG. 14
is constructed by adding five substrates
302
for the construction of
FIG. 13
, the characteristic impedance is lowered in the extent of 14.7&OHgr;.
In the discussion given hereabove, variation of the characteristic impedance is theoretically calculated with employing approximation for simplification. However, in practice, it is difficult to predict variation of the characteristic impedance in advance of actual installation of the substrate. For example, the characteristic impedance may be variable not only depending upon the number of substrate to be installed in the bus transmission path but also depending upon the position of installation of the substrate. Thus, the characteristic impedance of the bus transmission path is variable depending upon various factors. Then, associating with variation of the characteristic impedance, the signal waveform to be propagated on the bus transmission path may be differentiated.
For example, in case of a pulse wave, when the characteristic impedance of the bus transmission path is excessively large, the rising up period of the pulse becomes long. On the other hand, when the characteristic impedance is too small, ringing may be caused. Ringing is a transitional vibration of the waveform to be caused by abrupt rising up of the pulse and can be a cause of malfunction.
Beside, in order to propagate signal at high speed, signal has to be maintained at constant waveform. Therefore, the characteristic impedance of the bus transmission path has to be corrected to be a given constant value.
One example of the conventional signal output circuit having an adjusting function for the characteristic impedance of the bus transmission path is shown in FIG.
15
. With reference to
FIG. 15
, between the output portion
311
for outputting the signal and the bus transmission path
333
, a resistor
351
is connected. In this signal output circuit, by varying the resistance of the resistor
351
, the characteristic impedance is adjusted to shape the signal waveform into a desired shape. The resistance of the resistor
351
is determined depending upon the characteristic impedance of the bus transmission path
333
.
However, in the above-mentioned conventional signal output circuit, when the characteristic impedance is varied by modification of the installation condition of the substrates in the bus transmission path, it becomes necessary to exchange the resistor per se in order to vary the resistance value to make handling cumbersome.
Also, as set forth above, it is difficult to even theoretically predict the characteristic impedance of the bus transmission path. Therefore, the resis
Kim Jung Ho
NEC Corporation
Whitham Curtis & Christofferson, PC
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