Registers – Records – Conductive
Reexamination Certificate
2000-05-31
2003-12-09
Pitts, Harold I. (Department: 2876)
Registers
Records
Conductive
C235S487000
Reexamination Certificate
active
06659352
ABSTRACT:
This application is based on an application No. 2000-53785 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a semiconductor integrated circuit, a contactless information medium having the semiconductor integrated circuit, and a method for driving the semiconductor integrated circuit.
(2) Description of Related Art
Recently, contactless information mediums such as IC cards have been in practical use, where in the contactless information mediums, the mutual induction of the coil is used for data transfer and the power supply in the form of a radio wave having a certain wave length. The IC cards are classified broadly into the proximity type, the vicinity type and the like according to the distance between the IC card and a reader/writer with which they can communicate with each other. The standards are currently prepared for each type.
The proximity IC cards, which can be used at a distance from the reader/writers of approximately 1 cm to 20 cm, especially have a possibility of having a very broad range of uses. For example, people having an IC card as a season ticket can pass through the ticket collecting gate without taking out the card from the card case since the gate is opened or closed by communication between the IC card and the reader/writer in a contactless state.
However, for the IC cards to have a broad range of uses, it is important that the IC cards are compact and lightweight. In addition, it is expected that the wider range of uses the IC cards have, the more roughly the cards are handled. Therefore, taking into consideration the protection from such rough handling, it is a general rule that the contactless information mediums such as IC cards have a semiconductor integrated circuit containing a complicated circuit.
Now, the construction of a typical contactless IC card having a semiconductor integrated circuit will be described.
FIG. 1
is a block diagram showing the construction of a typical contactless IC card. Note that
FIG. 1
shows a reader/writer
990
which transmits/receives radio waves to/from an IC card
900
, as well as the IC card
900
. The following are description of the construction and operation of the IC card
900
.
The IC card
900
includes an antenna coil
981
which is used to transmit/receive radio waves to/from an antenna coil
991
connected to the reader/writer
990
. An alternating voltage is generated at both ends of the antenna coil
981
when the antenna coil
981
receives a radio wave from the antenna coil
991
, and the generated alternating voltage is input into a semiconductor integrated circuit
910
contained in the IC card
900
.
982
in the drawing indicates a capacitor for tuning.
The antenna coil
981
for reception is typically connected to the semiconductor integrated circuit
910
of the IC card
900
. The capacitor
982
for tuning is often connected to the semiconductor integrated circuit
910
of the IC card
900
, but in some cases it is placed in the semiconductor integrated circuit
910
.
The IC card
900
receives ASK(Amplitude Shift Keying)-modulated signals from the reader/writer
990
and obtains power for driving the semiconductor integrated circuit
910
from the received signals, and also obtains data transferred from the reader/writer
990
.
FIG. 2
shows a specific example of the construction of the carrier wave transmitted from the reader/writer
990
. As shown in the drawing, the parts having small amplitude in the ASK-modulated carrier represent data
0
, and the parts having large amplitude data
1
.
The semiconductor integrated circuit
910
includes a power supply circuit
911
, a first regulator circuit
912
, a modulation/demodulation circuit
913
, a logic circuit
914
, a nonvolatile memory
915
, a step-down circuit
916
, and a second regulator circuit
917
. Note that the step-down circuit
916
may be replaced with a step-up circuit for a reason to be described later.
FIG. 3
shows the internal construction of the power supply circuit
911
. As shown in the drawings, in the conventional IC card
900
, a general all-wave rectifier circuit
9111
and a capacitor
9112
for smoothing constitute the power supply circuit
911
. With this construction, an alternating voltage generated at both ends of the antenna coil
981
is rectified to become a direct voltage VCC. The rectified current is then regulated by the first regulator circuit
912
not to exceed a certain voltage value, and the regulated current is used as a voltage to drive the modulation/demodulation circuit
913
or the memory
915
. The rectified current is also stepped down by the step-down circuit
916
and regulated by the second regulator circuit
917
not to exceed a certain voltage value, and the regulated current is used as a voltage to drive the logic circuit
914
.
Though not shown in
FIG. 1
, the current having passed through the first regulator circuit
912
supplies a driving power to analog circuits such as a clock generator circuit. Here, the clock generator circuit generates a clock signal from the alternating voltage generated at both ends of the antenna coil
981
, the clock signal being used for operating the logic circuit
914
and the nonvolatile memory
915
.
Generally, digital circuits such as the logic circuit
914
are driven by a relatively low voltage (approximately 2V to 3V), while a voltage higher than this need to be supplied to the nonvolatile memory
915
. For example, FeRAM requires approximately 3V to 7V of voltage, and EEPROM requires approximately 10V of voltage (for writing or erasing). To deal with this, in the conventional contactless IC card
900
, the voltage generated by the power supply circuit
911
is stepped down by the step-down circuit
916
then supplied to the logic circuit
914
. Alternatively, a low voltage for driving the logic circuit
914
may be generated by the power supply circuit
911
, then the generated voltage may be stepped up by a step-up circuit to be used for driving analog circuits (such as the modulation/ demodulation circuit
913
and the clock generator circuit) and the nonvolatile memory
915
.
As shown in
FIG. 2
, the data transferred between the IC card
900
and the reader/writer
990
is piggybacked onto the carrier wave. The data received by the contactless IC card
900
from the reader/writer
990
is demodulated by the modulation/ demodulation circuit
913
; and the data to be transmitted from the contactless IC card
900
to the reader/writer
990
is modulated by the modulation/demodulation circuit
913
. The data transferred between the contactless IC card
900
and the reader/writer
990
is controlled by the logic circuit
914
and stored in the nonvolatile memory
915
.
Meanwhile, in the contactless IC card
900
in which the mutual induction of the coil is used to supply power and transmit/receive data, the power supply voltage generated by the power supply circuit
911
changes depending on the distance between the reader/writer
990
(power supply source) and the contactless IC card
900
. A very short distance between them in particular may generate an overvoltage and destroy the internal circuits of the contactless IC card
900
. To prevent such a failure, the first and second regulator circuits
912
and
917
are provided to regulate the power supply voltage generated by the power supply circuit
911
not to exceed a certain voltage value.
FIG. 4
shows the construction of a circuit conventionally used as the first regulator circuit
912
. First and second P-channel MOS transistors (hereinafter referred to as PchMOS transistors)
931
and
932
are connected in series between the output from the power supply circuit
911
(represented as “VCC” in the drawing) and the ground. The gate and the drain of the first PchMOS transistor
931
are directly connected to each other, and the source of the first PchMOS transistor
931
is connected to VCC.
The drain of the first PchMOS transistor
931
is connected to the source of the seco
Asada Hiroaki
Inoue Atsuo
Matsuura Taketoshi
Nakane Joji
Sumi Tatsumi
Matsushita Electric - Industrial Co., Ltd.
Pitts Harold I.
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