Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1998-05-15
2003-05-27
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Interrogation response
C340S010340, C235S487000, C327S536000
Reexamination Certificate
active
06570490
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a contactless IC card which does not have a power supply, battery, or sources of signals such as a clock and a carrier. More particularly, the present invention relates to a contactless IC card which is characterized by a transmit/receive circuit adapted to recover a clock for operating signal processing circuits (such as logical circuits, memory, and so on), data, and electric power from a high frequency signal derived from an antenna or a coil arranged on the IC card, and to transmit a portion of data stored in the memory in accordance with the received data through the antenna or the coil as transmission data.
In “A Low-Power CMOS Integrated Circuit for Field-Powered Radio Frequency Identification Tags” by D. Friedman et al. published in 1997 IEEE ISSCC (International Solid-State Circuit Conference) p.294 and 295, SESSION 17/TD: LOW-POWER/LOW-VOLTAGE CIRCUITS/PAPER SA17.5, a RFID (Radio Frequency Identification) tag using a high frequency signal is described. This RFID tag is a passive tag which operates as follows. Upon reception, the tag recovers data and electric power from a 100% AM-modulated RF (Radio Frequency) signal from an antenna through a circuit composed of a Schottky diode (or a Schottky barrier diode) and a capacitor. Upon transmission, the tag changes the impedance of a circuit including the Schottky diode, the capacitor and the antenna to transmit data. Such a passive tag is advantageously manufactured at a low price and in a compact configuration.
FIG. 4
illustrates the configuration of a transmit/receive circuit for recovering electric power and data in the prior art.
(Data Reception and Power Recovery)
A first diode
71
connected between an antenna terminal
70
and the ground and having its anode terminal grounded, has its cathode terminal connected to anode terminals of second and third diodes
73
,
72
in parallel. Data and electric power are recovered from an output terminal
76
and a power terminal
77
, respectively, through capacitors
75
,
74
arranged between cathode terminals of the associated diodes
73
,
72
and the ground.
(Data Transmission)
Data is transmitted by opening or closing a switching element
78
arranged at the cathode terminal of the third diode
72
to change a load impedance of an antenna.
In the transmit/receive circuit of
FIG. 4
, the diodes
71
,
72
,
73
are mainly responsible for detection and rectification, and the capacitors
74
,
75
for accumulation of charge.
The conventional transmit/receive circuit has the second diode
73
for power recovery and the third diode
72
for data recovery connected in parallel to the cathode of the first diode
71
, so that a voltage detected and rectified by the first diode
71
is supplied commonly to the output terminal
76
and the power terminal
77
. With this configuration, a supply voltage outputted from the power terminal
77
is likely to exceed a data (clock) signal voltage outputted from the output terminal
76
, depending on the magnitude of a load connected to the power terminal
77
. In such a case, a logical circuit, which receives the supply voltage and data signal from the transmit/receive circuit, is highly susceptible to destruction.
In addition, when the switching element
78
is operated for data transmission, the power diode
73
is largely affected by a change in impedance, which would result in failing to recover a stable supply voltage.
SUMMARY OF THE INVENTION
The present invention is intended to individually optimize a rectifier circuit for data and clock and a rectifier circuit for electric power to facilitate adjustments of data, clock voltage, and supply voltage. For this purpose, a contactless IC card of the present invention comprises a transmit/receive circuit having a first rectifier circuit for outputting data and clock and a second rectifier circuit for outputting electric power, wherein the first rectifier circuit and the second rectifier circuit are provided with a carrier signal received by an antenna of the IC card.
These and other objects, features and advantages of the present invention will become more apparent in view of the following detailed description of the preferred embodiments in conjunction with accompanying drawings.
REFERENCES:
patent: 5387900 (1995-02-01), Plonsky et al.
patent: 5546031 (1996-08-01), Seesink
patent: 5649965 (1997-07-01), Pons et al.
patent: 5670772 (1997-09-01), Goto
patent: 5682032 (1997-10-01), Philipp
patent: 5798968 (1998-08-01), Lee et al.
patent: 5847662 (1998-12-01), Yokota et al.
IEEE 1997 International Solid-State Circuit Conference, “A Low-Power CMOS Integrated Circuit for Field-Powered Radio Frequency Identification Tags”, D. Friedman et al, pp. 294-295.
Ishifuji Tomoaki
Saitoh Takeshi
Shida Masaaki
Yang Clara
Zimmerman Brian
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