Electronic digital logic circuitry – Multifunctional or programmable – Having details of setting or programming of interconnections...
Reexamination Certificate
2002-07-30
2004-05-18
Le, Don (Department: 2819)
Electronic digital logic circuitry
Multifunctional or programmable
Having details of setting or programming of interconnections...
C327S143000
Reexamination Certificate
active
06737884
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to power-on reset circuit which is utilized for an IC card that obtains electric power from the external electric power supply source without contacting, for example, through electromagnetic waves.
BACKGROUND OF THE INVENTION
In recent years, an IC card with a semiconductor integrated circuit device is becoming widespread. The IC card has a capability of exchanging information between an external reader/writer apparatus and a semiconductor integrated circuit device mounted in the IC card. This makes it possible to store necessary information in an internal nonvolatile memory of the semiconductor integrated circuit device, and conversely, to read information from the nonvolatile memory. By utilizing such an IC card, it is possible to realize a variety of functions that a magnetic card has carried out conventionally.
With a resent advance in the technology for large packing densities, the IC card has included a nonvolatile memory with a larger capacity. Accordingly, a multi-purpose card having a plurality of applications included in one IC card is also becoming widespread.
Further, non-contact type IC card system for the IC card has been studied in which the supply of electric power without contacting as well as data communication are carried out, utilizing electromagnetic waves with carrier frequencies of the order of several MHz to several tens of MHz. In case of non-contact type communication by using the IC card, no terminals for contacting is necessary, and no damages are caused in a contacting part of such terminals. Therefore, the IC card has advantages such as decrease in maintenance cost and easy handling.
One of the significant features of the non-contact type IC card system is that it is possible to arrange a system capable of a speedy and easily operable information exchange processing. For example, non-contact type IC card serving as a ticket for taking transport facilities such as a train and a bus allows a person to go through the ticket gate only by ways of holding the non-contact type IC card over the ticket gate (hereinafter referred to as “holding process”), or making the non-contact type IC card touch to the ticket gate in a moment (hereinafter referred to as “touch-and-go process”).
Thus, in such a non-contact type IC card system, considered are various manners for information exchange between an IC card and a reader/writer apparatus. Some examples are given as follows: (1) a way of holding the IC card over the reader/writer apparatus at a small distance within approximately several cm (holding process); (2) a way of inserting the IC card to a card holder set in the reader/writer apparatus (inserting process); and (3) a way of supplying voltage to the IC card at power-on in setting the IC card to the reader/writer apparatus.
These ways are different from each other in how to make the IC card close to the reader/writer apparatus. Accordingly, they are different from each other in a condition inside the IC card for producing a power supply voltage when supplying power by electromagnetic induction from the reader/writer apparatus to the IC card.
Further, electromagnetic induction makes it impossible to supply a large amount of electric power and causes variations in the amount of the power supply. Therefore, a power-on reset operation in starting the supply of power must be highly reliable.
The following will explain what kind of power-on reset or malfunction preventing circuit of a reset circuit is used in a conventional non-contact type IC card.
For example, Japanese Laid-Open Patent Publication No. 269327/1998 (Tokukaihei 10-269327) discloses a circuit configuration for carrying out the power-on reset with respect to the non-contact type IC card. In the technology described in the publication, the power of the logic circuit is shut off on the reset operation by detection of power supply voltage in an analog mode. This shut-off does not apply voltage to an input/output circuit to/from a microcomputer and a microcomputer circuit. The configuration will be described more specifically below.
FIG. 10
is a circuit diagram of an example of the circuit configuration. Voltage outputted from an antenna coil
51
is supplied to each circuits after supplied to REG-A
55
and REG-B
56
as regulator circuits, and VREF
57
as a reference voltage producing circuit. From the REG-A
55
, voltage is supplied to a microcomputer
64
and an interface section thereof. Further, from the REG-B
56
, voltage is supplied to a CLK reproducing circuit
53
, a reset producing circuit
54
, an MOD
66
as a modulation circuit, a DEMO
67
as a demodulation circuit, and (+) terminal of a comparator circuit
59
.
The output from the VREF
57
as a reference voltage producing circuit is for the voltage supply to the REG-A
55
and the REG-B
56
, and a switch
60
is provided on the path to the REG-A
55
to control a power rising sequence. Further, the output from the VREF
57
is connected to a (+) terminal of a comparator circuit
58
for controlling ON/OFF operation of the switch
60
.
The output voltages of the REG-A
55
and the REG-B
56
may be at the same potential or at a different potential. However, it is preferable that the REG-A
55
and the REG-B
56
have the same circuit configuration as a regulator.
Here, as a result of comparison in power rising rate among an analog detecting section including a resistor
61
and a diode
62
, the VREF
57
, the REG-A
55
, and the REG-B
56
, the REG-A
55
and the REG-B
56
rises in a most slow rate among them. The analog detecting section rises in a fastest rate, and the VREF
57
rises in a secondly fastest rate. By taking advantage of the difference in power rising rate, the power rising is controlled as follows.
First, the comparator circuit
59
determines which output voltages of the REG-B
56
and the VREF
57
is larger. In usual operation, the output voltage of the REG-B
56
is larger than that of the VREF
57
. However, the power rising rate of the REG-B
56
is relatively slow as described above. Therefore, at the moment when the non-contact type IC card is held over the reader/writer apparatus, the output voltage of the VREF
57
becomes larger than that of the REG-B
56
.
In such a situation, since the magnitude of the power supply voltage supplied to the microcomputer
64
is not sufficient for its stable operation, the microcomputer
64
must be in a reset state. Therefore, the reset producing circuit
54
produces a reset signal in accordance with the result of the comparison in the comparator circuit
59
. The reset signal is provided to the microcomputer
64
via a buffer circuit
69
D. Thus, the microcomputer
64
can operate, being released from a reset state, only when power supply voltage sufficient for a stable operation is supplied thereto.
However, the microcomputer
64
cannot always obtain intended signals from the outputs of buffer circuits
69
A to
69
D in unstable operations by the logic circuits such as the reset producing circuit
54
. In other words, a reset releasing signal may be outputted to the microcomputer
64
in a low power supply voltage before the output of the REG-A
55
is provided to the microcomputer
64
In such a case, the voltage of other terminals becomes higher than that of the microcomputer
64
, which results in damage and malfunction of elements in the microcomputer
64
. Also, the same event may occur in a terminal for clock and a terminal for data.
To prevent such disadvantages, it is arranged in the configuration shown in
FIG. 10
that the switch
60
is provided on the path over which reference voltage supplied to the REG-A
55
flows, and the switch
60
disconnects so as not to supply power to the microcomputer
64
during the period that an adequately large voltage for operation cannot be available. Further, the same power source as the microcomputer
64
is connected to the buffer circuits
69
A to
69
D so that the voltage larger than that of a power source terminal cannot be applied to other terminals
Nakao Yoshihiro
Shigemasa Haruhiko
Birch & Stewart Kolasch & Birch, LLP
Sharp Kabushiki Kaisha
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