Communications: electrical – Systems – With specific power supply
Reexamination Certificate
2001-01-19
2002-10-15
Wu, Daniel J. (Department: 2632)
Communications: electrical
Systems
With specific power supply
C340S572100, C340S572700, C340S635000, C340S636210, C340S870030
Reexamination Certificate
active
06466126
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a portable data device efficiently utilizing its available power and method thereof, and in particular, to a portable data device efficiently utilizing its available power by adjusting its clock rate.
BACKGROUND OF THE INVENTION
Credit cards, typically provided with magnetic stripes, have been around for many years. These types of credit cards, however, have a design flaw. The mechanical interface between the credit card and the reader requires periodic cleaning. The poor reliability of the readers, due to the mechanical interface, causes down time for reader maintenance. Contactless smart cards have been developed which eliminate the mechanical interface between the card and the reader.
Standards are currently being created around the contactless smart card. The most widely accepted standard is the ISO-14443, which specifies the nature and characteristics of the fields to be provided for power and bi-directional communications between a portable data device (e.g., smart card) and an interface device (e.g., a reader). The system requires the presence of both the reader and the smart card. Together, the reader and the smart card comprise a loosely coupled transformer. A sinusoidal waveform, which is also the radio frequency (“RF”) carrier, is injected onto the reader coil (antenna) and is used to create a magnetic field. When the smart card is placed in the field, the energy that passes through a loop antenna residing on the smart card is received by an integrated circuit (“IC”) also residing on the smart card. The power for the smart card is extracted from the magnetic field. By changing the intensity of the magnetic field as a function of time, data can also be transferred between the smart card and the reader.
FIG. 1
illustrates a block diagram of a contactless smart card system having a reader
100
and a smart card
110
. The reader
100
comprises a signal source
102
and a resonant output circuit, which comprises capacitors
104
and
106
and an inductive antenna
108
. The resonant frequency of the resonant output circuit
104
,
106
,
108
is substantially equal to the frequency of signal source
102
. The inductive antenna
108
generates an electromagnetic field when a signal is applied to it.
The smart card
110
comprises an integrated circuit
114
and an inductive loop
112
. When the smart card
110
is brought into the proximity of the reader
100
, the inductive antenna
108
of the reader
100
and the inductive loop
112
of the smart card
110
form a loosely coupled transformer. A coupling coefficient M
115
for the loosely coupled transformer is a function of distance and orientation of the inductive antenna
108
and the inductive loop
112
. The electromagnetic field generated by the inductive antenna
108
is received by the inductive loop
112
and converted to a current. This received current can be used to power the integrated circuit
114
. The electromagnetic field can also be used for data transfer between the reader
100
and the smart card
110
.
The integrated circuit
114
can consist of several different components. A digital circuit
116
provides the “brains” and functionality for the smart card
110
. The other components contained within the integrated circuit
114
support the functionality of the digital circuit
116
.
The inductive loop
112
and a tuning capacitor
118
constitute a resonant tank. This resonant tank is tuned to the signal frequency of the signal source
102
of the reader
100
. The resonant tank facilitates efficient power coupling of the received field to the integrated circuit
114
.
A power rectifier
120
rectifies the alternating current (“AC”) signal received on the inductive loop
112
creating a signal with direct current (“DC”) content. The power rectifier
120
essentially performs an AC-to DC transformation. A power controller
12
operates on this DC signal and creates the required power supply signals required to power the digital circuit
116
.
A receiver
124
performs data detection and reconstruction. The receiver
124
detects and reconstructs the digital bit stream of any signal transmitted by the reader
100
to the smart card
110
. The receiver
124
supplies input data for the digital circuit
116
. A transmitter
126
creates a modulated signal for transmission via the electromagnetic field from the smart card
110
to the reader
100
. The transmitter
126
provides the output data path for the digital circuit
116
.
A timing reference is created by a clock generator
128
, which creates a clock signal from the received signal. The clock generator
128
provides the timing reference for the digital circuit
116
.
FIG. 2
illustrates how the power level at the smart card
110
changes as the distance between the reader
100
and the smart card
110
varies for the smart card system shown in FIG.
1
. Curve
201
shows the power available to the smart card
110
for varying distances between the inductive antenna
108
and the inductive loop
112
. As can be seen as the smart card
110
moves closer to the reader
100
, the power received is greater than what is available at further distances. As the distance between the inductive antenna
108
of the reader
100
and the inductive loop
112
of the smart card
110
increases, the power available to the digital circuit
116
decreases. Due to integrated circuit requirements, the excess power received at close coupling between the smart card
110
and reader
100
should be consumed. Currently, the excess power is wasted by dumping it to ground. To allow operation of the smart card
110
over a range of distances, the power levels are set so the operating power of the smart card
110
is obtained at the desired maximum distance between the reader
100
and the smart card
110
. Since there is no feedback between the smart card
110
and the reader
100
, the power level cannot be adjusted during a transaction.
As the complexity of the smart card system increases, so will the power required by the smart card
110
to support the increased card capabilities. Due to emission standards, which support the smart card system of
FIG. 1
, the amount of power delivered by the reader to the smart card
110
cannot be increased. So as can be expected, the operating range of the smart card
110
is reduced when additional system features/requirements are added to the smart card
110
. This reduction in operating range degrades system performance.
Further, it is generally accepted by the smart card industry that the transaction times must be less than 100 milliseconds. The overall transaction time is a function of the time required to transfer information between the reader
100
and the smart card
110
. As can be expected, additional features increase the time required to complete a transaction. ISO specifications dictate the nature and characteristics of the carrier frequency to be provided for power between the reader
100
and the smart card
110
. Since the frequency delivered to the smart card
110
is dictated by the ISO standards, and the clock rate is derived from the frequency, the number of clock cycles during a given time period is a constant. Additional commands, however, require more clock cycles, thus increasing transaction time.
Moreover, for prior art smart card designs, such as that shown in
FIG. 1
, there is a fixed amount of useful power dissipation. The integrated circuit
114
operates using a constant clock frequency independent of the distance between the reader
100
and the smart card
110
. Since power dissipation in a digital complementary metal oxide semiconductor (“CMOS”) circuit is directly proportional to the clock frequency, the amount of power dissipated by the CMOS digital circuit with a fixed clock frequency will also be fixed. If this fixed power dissipation requirement is met by the received power available in the RF field, then the smart card
110
will operate as desired. If the fixed power dissipation requirement is not met by the received powe
Collins Timothy James
Rakers Patrick Lee
Hughes Terri S.
Motorola Inc.
Nguyen Hung
Wu Daniel J.
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