Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-02-04
2002-12-24
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S078000, C327S080000
Reexamination Certificate
active
06498519
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a voltage control circuit having the function of detecting which one of a reference voltage and an external supply voltage, such as a power source voltage supplied via a cable by the function of cable power status (CPS) conforming to, e.g., IEEE 1394 standard, is higher.
With the wide proliferation of multimedia centering around personal computers, the function of processing enormous amounts of data such as image data at a high speed has been required of each information device. Concurrently, technology for increasing a rate at which data is transferred between devices has been becoming important. Under such circumstances, the IEEE 1394 standard has been proposed as technology which enables high-speed data transfer, based on which development has been pursued. The IEEE 1394 standard suggests a serial transfer method whereby a transfer rate is increased by unprecedentedly reducing the number of buses, while increasing an operational frequency for transfer.
FIG. 8
shows a part of a configuration of an IEEE 1394 network system. In
FIG. 8
, individual network devices are connected to each other via cables. Each of the cables is composed of four data lines (a pair of data lines and a pair of strobe lines), a power source line, and a ground line. Depending on the type of a cable, only four lines compose the cable without using the power source line and the ground line.
An LSI compliant with the IEEE 1394 standard can be divided into a PHY section for primarily controlling data input and data output and a LINK section for controlling a transfer protocol. During data reception, a signal is transferred from a transfer cable to the PHY section and then from the PHY section to the LINK section. During data transmission, the signal is transferred in the opposite direction.
Besides high-speed data transfer, the IEEE 1394 standard also supports the CPS function for supplying power from a power source via the data transfer cable. The IEEE 1394 standard includes a plurality of standards such as IEEE 1394_
1995
, IEEE 1394. A, and IEEE 1394. B and the CPS function is defined in each of the standards.
That is, in an LSI compliant with the IEEE 1394 standard, the CPS function should be operated when the power-source voltage supplied via the cable is within a specified range. Since the CPS function is the standard for the PHY section for controlling data input and data output, it is necessary for the PHY section to have the function of detecting whether or not the power source voltage supplied via the cable is within the specified range.
In the IEEE 1394_
1995
, e.g., the voltage supplied from the outside by the CPS function is defined to be 8 to 40 V. This means that the CPS function should be operated when the voltage is at least in the range of 8 to 40 V. To develop an LSI compliant with the standard, therefore, it is necessary to provide the function of detecting whether or not the voltage supplied from the cable is within the range of 8 to 40 V.
PROBLEMS TO BE SOLVED
However, the application of a high voltage of 8 to 40 V directly to an LSI leads to the breakdown of the LSI and is not preferred. For this reason, the standard proposes reducing a supply voltage via a 400-k &OHgr; voltage dropping resistor and applying a reduced voltage to the PHY section. Consequently, the PHY section is so configured as to estimate the supply voltage by detecting the reduced voltage so that the accuracy of voltage drop as well as the accuracy of voltage detection are important factors in observing the standard.
As far as the present inventors have investigated, however, there has been proposed no circuit configuration which conforms to the standard.
FIG. 10
shows a circuit configuration of a voltage determining unit
15
conforming to the standard, which has been devised by the present inventors. In
FIG. 10
, a cable
12
is connected to an input terminal
51
of a voltage control circuit
50
via a voltage dropping resistor
11
(having a resistance value R
0
). In the voltage control circuit
50
, a resistor element
52
(having a resistance value R
1
) is connected to the input terminal
51
to be disposed in series to the resistor
11
. A current Icps flows from the cable
12
to the ground Vss and an external voltage VDD_ext is converted to a voltage Va in the voltage control circuit
50
. A comparator
53
compares the converted voltage Va with a comparison voltage Vb and outputs a signal Vcps indicative of the result of comparison. The signal Vcps becomes HIGH when the converted voltage Va is higher than the comparison voltage Vb, which enables the detection of the supply of a voltage that can be supplied via the cable as the external voltage VDD_ext.
FIG. 11
is a graph showing the relationship between the external voltage VDD_ext and the converted voltage Va in the circuit configuration of FIG.
10
. In
FIG. 11
, a power-source voltage VDD_int to the voltage control circuit
50
is assumed to be 3.3 V and a maximum withstand voltage Vmax is assumed to be 3.6 V. As shown in
FIG. 11
, the external voltage VDD_ext and the converted voltage Va are constantly in a proportional relationship in the circuit configuration of FIG.
10
. The resistance value R
1
is adjusted to such a value that the converted voltage Va does not exceed the maximum withstand voltage Vmax of 3.6 V even when 40 V is given as the external voltage VDD_ext. Hence,
R
1
=3.6·R
0
/(40−3.6)=0.0989·400 k=39.56 k&OHgr;
is derived from
3.6/R
1
=40/(R
0
+R
1
).
If the maximum value of the converted voltage Va is set to 3.3 V by allowing a margin,
R
1
=3.3·R
0
/(40−3.3)=
0.0899·R0=39.95
k&OHgr;
is satisfied. Therefore, the resistance value R
1
of the resistor element
52
is preferably adjusted to be in the range of 35 k&OHgr; to 40 k&OHgr;. It will easily be appreciated that the resistance value R
1
of the resistor element
52
varies depending on the voltage supplied via the cable, the maximum withstand voltage, or the resistance value of the voltage dropping resistor.
Although the reference voltage serving as the standard for determining the external voltage VDD_ext is 8 V, the reference voltage has been set to 7 V and the comparison voltage Vb has been set to 0.63 V, since it is common to set the reference voltage to the order of 5 V to 7.5 V by allowing a margin. The comparison voltage Vb is set appropriately based on the reference voltage and on the ratio between the respective resistance values of the voltage dropping resistor
11
and the resistor element
52
.
In a circuit configuration as shown in
FIG. 10
, however, the external voltage VDD_ext and the converted voltage Va are in the proportional relationship and the converted voltage Va is about {fraction (1/10)} of the external voltage VDD_ext. If the external voltage VDD_ext varies greatly, therefore, the converted voltage Va changes only by about {fraction (1/10)} of the variation of the external voltage VDD_ext. Conversely, variations in comparison voltage Vb and variations in the detection accuracy of the comparator
53
are magnified ten times to affect the detection of the external voltage VDD_ext. Variations in the resistance of the resistor
52
also greatly affect the accuracy with which the external voltage VDD_ext is detected.
On the other hand, it is considered that an input to the comparator is preferably set to about ½ of the power-source voltage in terms of sensitivity. In the circuit configuration of
FIG. 10
, the level of the input to the comparator
53
is close to the ground potential Vss, which is not preferred in terms of detection accuracy.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to perform a high-accuracy comparison between an external voltage and a reference voltage in a voltage control circuit for implementing, e.g., the CPS function. To attain the object, the present invention has widened the range of a converted voltage in a region in which the external voltage is close
Akamatsu Hironori
Arima Yukio
Hirata Takashi
Komatsu Yoshihide
Takahashi Satoshi
Lam Tuan T.
McDermott & Will & Emery
Nguyen Hiep
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