Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2000-05-26
2001-11-27
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000, C370S282000
Reexamination Certificate
active
06323756
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a data transmission device for transmitting data from a driver to a receiver via a transmission line path.
BACKGROUND ART
FIG. 11
shows a configuration of a conventional data transmission device
200
. The data transmission device
200
includes a driver
210
for sending data, a receiver
220
for receiving the data sent from the driver
210
, and a transmission line path
230
for connecting between the driver
210
and the receiver
220
. Data is transmitted via the transmission line path
230
from the driver
210
to the receiver
220
.
The driver
210
includes an output buffer
212
for outputting data onto the transmission line path
230
. The output buffer
212
is connected via a pad
214
to the transmission line path
230
.
The receiver
220
includes an input buffer
222
for receiving data from the transmission line path
230
. One input terminal of the input buffer
222
is connected via a pad
224
and a stub resistor
232
to the transmission line path
230
.
An end of a terminator resistor
240
is connected to an end on the receiver
220
side of the transmission line path
230
. The other end of the terminator resistor
240
is connected to a terminator potential V
term
.
The amplitude of a data signal on the transmission line path
230
is determined by the resistance of the terminator resistor
240
and the output impedance of the driver
210
. Therefore, with an appropriate setting of the resistance of the terminator resistor
240
and the output impedance of the driver
210
, the amplitude of the data signal on the transmission line path
230
can be limited to a sufficiently small value.
The resistance of the terminator resistor
240
is typically set so as to be substantially equal to the characteristic impedance Z of the transmission line path
230
. This prevents data sent from the driver
210
from being reflected at the end on the receiver
220
side of the transmission line path
230
.
However, the use of the terminator resistor
240
for terminating the transmission line path
230
causes a problem such that there is power consumption in the absence of data transmission on the transmission line path
230
. This is because when data is held at a HIGH level, a direct current (I
sink
) flows from the terminator potential V
term
to the driver
210
via the terminator resistor
240
; and when data is held at a LOW level, a direct current (I
source
) flows from the driver
210
to the terminator potential V
term
via the terminator resistor
240
.
Also, in the presence of data transmission, since a direct current flows via the terminator resistor
240
, the slopes of a waveform showing the transition of the potential of the transmission line path
230
becomes mild as the potential difference between the potential of the transmission line path
230
and the terminal potential V
term
is increased (see FIG.
12
). This often causes skew.
Further, the output impedance of the driver
210
when the driver
210
outputs data of the HIGH level is not always in agreement with the output impedance of the driver
210
when the driver
210
outputs data of the LOW level. When these are not in agreement with each other, the absolute value of the direct current (I
source
) flowing from the driver
210
to the terminal potential V
term
is not identical to the absolute value of the direct current (I
sink
) flowing from the terminal potential V
term
to the driver
210
. Therefore, the value of the potential amplitude of the transmission line path
230
from the terminal potential V
term
when the driver
210
outputs the HIGH level data is different from the value of the potential amplitude of the transmission line path
230
from the terminal potential V
term
when the driver
210
outputs the LOW level data.
This means that the terminal potential V
term
is shifted from a middle value between a potential (Hi-potential) corresponding to the HIGH level data and a potential (Lo-potential) corresponding to the LOW level data. For instance, in an example shown in
FIG. 12
, the terminal potential V
term
is 1.1 V; the Hi-potential is 1.5 V; and the Lo-potential is 0.8 V.
The receiver
220
determines whether data on the transmission line path
230
has the HIGH level or the LOW level using the terminal potential V
term
as a reference potential. Therefore, when the terminal potential V
term
is shifted from the middle value of the Hi-potential and the Lo-potential, the time which it takes data to transit from the LOW level to the HIGH level is different from the time which it takes data to transit from the HIGH level to the LOW level. This is responsible for skew occurring when the receiver
220
latches data on the transmission line path
230
in synchronization with a predetermined clock signal.
An object of the present invention is to provide a data transmission device in which power consumption is reduced.
Another object of the present invention is to provide a data transmission device in which occurrence of skew is prevented.
DISCLOSURE OF THE INVENTION
A data transmission device according to the present invention includes a driver for sending data; a receiver for receiving data sent from the driver; a transmission line path for connecting between the driver and the receiver; and a variable impedance element having a controllably variable impedance. The variable impedance element is connected to the transmission line path.
According to this invention, by controlling the impedance value of the variable impedance element, a reduction in power consumption and prevention of skew occurrence can be optimized.
For example, when the data transmission device is operated at a low speed, skew is unlikely to occur. Therefore, in this case, the impedance value of the variable impedance element is controlled in such a manner as to decrease the impedance value of the variable impedance element. This prevents a direct current from flowing through the transmission line path. As a result, power consumed by the data transmission device can be reduced. When the data transmission device is operated at a high speed, skew is likely to occur. Therefore, in this case, the impedance value of the variable impedance element is controlled in such a manner as to agree with the impedance of the transmission line path. This prevents data from being reflected at an end of the transmission line path. As a result, occurrence of skew is prevented.
The impedance value of the variable impedance element may be changed according to a potential of the transmission line path.
For example, when the potential difference between the potential of the transmission line path and the terminal potential is less than a predetermined value, the impedance value of the variable impedance element may be controlled in such a manner as to increase the impedance value of the variable impedance element. This allows data to transit from a LOW-level to a HIGH-level (or the HIGH-level to the LOW-level) at a high speed. Further, when the potential difference between the potential of the transmission line path and the terminal potential is greater than a predetermined value, the impedance value of the variable impedance element may be controlled in such a manner as to decrease the impedance value of the variable impedance element. This restricts the amplitude of data and prevents data reflection.
The impedance value of the variable impedance element may be changed according to a control signal input from the outside of the variable impedance element.
For example, when data is transmitted data high speed, a control signal which demands that the impedance value of the variable impedance element is set to a low value is input to the variable impedance element. The variable impedance element decreases the impedance in response to the control signal. This prevents data from being reflected at an end of the transmission line path. As a result, occurrence of skew is prevented. Further, when data transmission is on standby or data is transmitted at a low speed, a control signal whi
Iwata Toru
Yamauchi Hiroyuki
Yoshikawa Takefumi
Hofsass Jeffery
Kelly Michael K.
La Anh
Matsushita Electric - Industrial Co., Ltd.
Snell and Wilmer
LandOfFree
Data transmitter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Data transmitter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Data transmitter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2587622