Note: Descriptions are shown in the official language in which they were submitted.
CA 02477524 2004-08-26
METHOD FOR CONTROLLING THE POWER SUPPLY OF A MOBILE DATA
MEMORY, USE OF SAID METHOD IN AN IDENTIFICATION SYSTEM
HAVING AT LEAST ONE MOBILE DATA MEMORY
[001 J
FIELD AND BACKGROUND OF THE INVENTION
[002] The invention relates to a method for controlling the power supply of a
mobile
data memory with contactless data transfer, which has at least one energy
accumulator
and consumers. The invention further relates to a mobile data memory and an
identification system with at least one read/write device and a mobile data
memory.
[003] GB 2 284 728 discloses a data communication device for contactless data
transfer,
which has a control mechanism for the power supply of the data communication
device.
[004] In the prior art, identification systems are known, which have one or
more
stationary read/write devices, which contactlessly exchange data with mobile
data
memories via a data transfer link, which is usually radio-based. Such systems
are used in
technical installations where a plurality of objects or goods must be moved as
quickly and
freely as possible. These objects can be of a wide variety of types, e.g.,
packages in a
shipping installation, assembly parts in a production line, luggage in a
transport system,
etc.
[005] An example of such an identification system is described in the ISO/IEC
JTC
1/SC 31 WG4 Draft Standard entitled "Radio Frequency Identification Standard
for Item
Management - Air Interface, (WD 18000) dated August 15, 2001.
[006] This draft standard provides that the read/write device polls for the
presence of a
mobile data memory in the detection range. For this purpose, the read/write
device emits
an unmodulated first carrier signal with a predefinable backscatter frequency
of, for
example, 2.45 GHz. A mobile data memory located in the reception range can
passively
return this signal to the read/write device, e.g., by so-called
backscattering.
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[007] Independently thereof, the mobile data memory modulates the impedance of
an
integrated transmit/receive antenna in cyclic sequences with a significant
identification
sequence to identify the mobile data memory in a read/write device. In
addition, the
read/write device receives time information as to when the mobile data memory
will
switch on its data receiver. If the read/write device can receive the returned
modulated
backscatter frequency, the validity of the reply is checked. If valid, the
read-write device
in addition applies a communication frequency to the carrier signal at the
time when the
mobile data memory is expected to be ready for receiving. In the proposed
standard, the
communication frequency is shifted relative to the backscatter frequency by a
fixed
frequency amount, e.g., by approximately 10.6 MHz. By applying the
communication
frequency, the read/write device signals to the mobile data memory that a data
transfer
will follow. The second signal with the communication frequency is therefore
modulated
for data transfer. The transferred data can contain, for example, an
identification number
of the read/write device. The receiving signal received from the
transmit/receive antenna
of the mobile data memory is polled cyclically and at short intervals for the
presence of
the backscatter frequency and the communication frequency. If both frequencies
are
detected, the data receiver of the mobile data memory remains enabled to
receive data.
[008] The mobile data memory usually has an energy accumulator, particularly a
battery, for its power supply. To achieve the longest possible service life it
is therefore
necessary to minimize the power consumption. One known measure to reduce power
consumption, for example, is to select electronic components that have
particularly low
power requirements. Furthermore, a circuit design of a mobile data memory must
take
into account that a far greater amount of energy is required to receive data
than to
transmit it. In contrast to the very low power requirement of the initially
described
passive backscattering in which the antenna impedance is modulated only
momentarily,
several circuits must be connected for data reception. In addition, these
circuits, e.g., data
modulators, controllers and electronic memories, require a minimum period
until
transients have subsided and they are ready for operation. It must furthermore
be taken
into account that, in operational use, data is generally transferred between
the read/write
device and the mobile data memories only during a fraction of the total
operating period.
The above-cited draft standard has proposed, therefore, that the data receiver
of the
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mobile data memory be activated only cyclically to reduce energy consumption.
Typically, the pulse duty factor of ON to OFF time is approximately 0.3 to
0.4. During
the ON time, the validity of any date present is checked.
[009] Despite the above-described measures, it has heretofore not been
possible to
minimize the power consumption to the point where there is no need to replace
the
battery during the service life of the mobile data memory. This has the
drawback that the
data stored in the mobile data memory can be lost if the battery is exhausted.
[010] A further drawback is that the mobile data memory has to be withdrawn,
for
example, from the production process to change the battery in time. This can
cause delays
and can interfere with the process flow. Depending on the application, the
required life of
a mobile data carrier can be approximately 10 to 15 years.
OBJECTS OF THE INVENTION
[011] The object of the invention is to provide a method for controlling the
power
supply of a mobile data memory and a mobile data memory for transferring data
to at
least one read/write device, by means of which the service life of the mobile
data memory
can be increased.
SUMMARY OF THE INVENTION
[012] This object of the invention is attained by a method for controlling the
power
supply of a mobile data memory with the features of Claim 1.
[013] In this method, to control the power supply of a mobile data memory with
a
contactless data transfer, which includes at least one energy accumulator and
consumers,
the energy supply is lowered to a standby mode in such a way that the data
memory is
ready to receive data. A receiving signal can be evaluated, so that at least
one
predefinable backscatter frequency for a possible transmission mode and an
associated
communication frequency for receiving data can be detected. The energy supply
of the
data memory is then switched to a full operating mode. In the stand-by mode,
the energy
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CA 02477524 2004-08-26
supply can be lowered to an inactive sleep mode for a cyclic pause time, such
that the
ratio of the cyclic pause time to a higher-order cycle time can be at least
10:11 and less
than 1. Furthermore, in the full operating mode, the energy supply can be
switched to the
stand-by mode after receipt of the first data and a valid evaluation. In
addition, the
receiving signal can first be preamplified and/or intermediate frequency
demodulated.
The predefinable backscatter frequency contained in the receiving signal and
the
associated communication frequency can thus be intermediate frequency
demodulated,
such that an intermediate frequency signal can be generated and detected for a
possible
receipt of data.
[014] The method can be used in an identification system based on the ISO/IEC
18000
Standard for operation in an ISM frequency band of 2.45 GHz, 5.6 GHz or in the
UHF
frequency range.
[015] The object of the invention is further attained by a mobile data memory
for data
transfer to at least one read/write device with the features of Claim 12.
[016] To transfer data to at least one read/write device, the mobile data
memory is
equipped with an antenna, a data receiver connected therewith, and an energy
accumulator for the energy supply. The data receiver has at least one data
demodulator,
an electronic memory, a data processing unit connected therewith, and a level
detector
connected with the antenna for at least one predefinable backscatter frequency
and an
associated communication frequency. The level detector switches at least the
data
receiver to the energy supply when it detects the frequencies. The level
detector can have
a level detector unit, which controls at least one electronically controllable
switching
means to connect the at least one data receiver to the energy accumulator when
the
frequencies are detected. An intermediate frequency demodulator, which
generates an
intermediate frequency signal from the frequencies contained in a receiving
signal, can
furthermore be connected ahead of the level detector unit. In addition, the
level detector
can have a pulse generator, which switches the level detector unit off for a
cyclic pause
time within a cycle time. At least the level detector and the data demodulator
can be
integrated on a microchip.
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[017] The method can be used in an identification system based on the ISO/IEC
18000
Standard for operation in an ISM frequency band of 2.45 GHz, 5.6 GHz or in the
UHF
frequency range.
[018] The advantage connected therewith is that the battery no longer needs to
be
changed for the full life of the mobile data memory. This advantageously
eliminates the
associated logistic effort to search for and remove the mobile data memory,
e.g., from a
production or automation process. Any interference with the process flows can
thereby be
advantageously avoided.
[019] A further advantage is that no stored data can be lost as a result of an
exhausted
battery, e.g., because the battery failed to be replaced in time.
BRIEF DESCRIPTION OF THE DRAWINGS
[020] This will be explained with reference to the following figures, in which
FIG 1 shows an exemplary structure of a mobile data memory with a level
detector
according to the invention,
FIG 2 shows an advantageous exemplary variant of the embodiment of the level
detector according to the invention,
FIG 3 shows an exemplary signal shape of a receiving signal of a
transmit/receive
antenna of the mobile data memory,
FIG 4 shows an exemplary signal shape of a control signal for electronic
switching
means, which is generated by the level detector according to the invention,
FIG 5 shows an exemplary power consumption curve of a prior-art mobile data
memory,
FIG 6 shows an exemplary power consumption curve of the mobile data memory
according to the invention, and
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FIG 7 shows an exemplary power consumption curve of the embodiment of the
mobile data memory according to the invention as shown in FIG 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[021] FIG 1 shows an exemplary structure of a mobile data memory MDS with a
level
detector P1, P2 according to the invention. The mobile data memory MDS has an
exemplary integrated transmit/receive antenna A for data transmission with a
read/write
device SLG. A receiving signal ES coming from the antenna A is supplied to a
data
receiver DE via a signal line ZL. The data receiver DE furthermore has, for
example, a
data demodulator EMP to convert the data modulated onto the receiving signal
ES. These
data are forwarded for further digital processing to a data processing unit C,
e.g., a
controller C, connected via a data line DL. The data, possibly processed, are
then stored
in an electronic memory MEM, which is connected via a data bus DB.
[022] For transmission, data can be forwarded in the opposite direction, as
illustrated by
a dashed line in the figure, e.g., from the exemplary controller C to a data
modulator
SEND. The send unit SEND, which is connected to the exemplary common
transmit/receive antenna A, can be configured to operate actively or
passively. The
passive embodiment based on the above-described backscattering method has
particularly
low power consumption.
[023] According to the invention, the receiving signal ES coming from the
transmit/receive antenna A is supplied to a level detector P1, P2 for
detecting the
backscatter frequency fl for a possible transmission mode and the
communication
frequency fz for receiving data. Prior to that, the receiving signal ES can be
amplified
and subsequently intermediate frequency demodulated ZFD as illustrated in the
example
of the figure. The two frequencies fl, fZ are mixed in the receiving signal
ES. Both the
frequency sum fl + f2 and the frequency difference fl - f2, the so-called
intermediate
frequency ZF is then present in the mixed signal. The low-frequency signal
component,
the so-called intermediate frequency signal ZFS together with the associated
intermediate
frequency ZF is far below the two frequencies fl, f2, so that further signal
processing is
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simple. In the example of the figure, the advantageous intermediate frequency
signal ZFS
is subsequently supplied to a level detector unit PE and the data demodulator
EMP.
Alternatively, the receiving signal ES can also be supplied directly to the
data
demodulator EMP, as indicated by the dashed line.
[024] If, according to the invention, a minimum level MP for each of the
frequencies fl,
fZ, or a minimum level MP of the intermediate frequency signal ZFS is
exceeded,
switching means S, e.g., a switching transistor, can be operated by the
exemplary control
line AS. The switching means S then connect the corresponding components EMP,
C,
MEM of the data receiver DE to the battery BAT for a full operating mode. In
the closed
state, this results in the currents identified in FIG 1 by the reference
symbols IE, IC, IM.
IR denotes a minimum current, which is necessary for a sleep mode of the
mobile data
memory MDS, e.g., to maintain the memory content of the electronic memory MEM.
The
current identified as IP denotes the operating current of the level detector
P1, P2.
Typically, the zero signal current IR of the entire mobile data memory MDS is
a few pA.
In contrast, the current consumption IP of the level detector P1, P2 is
greater by a factor
of 100. If, in addition, all the components of the data receiver DE are
switched on to
receive data, the total power consumption may be increased by another factor
of 10 to 20.
To clarify, the associated power consumption IV 1 of the entire mobile data
memory
MDS is depicted in the example of FIG 6. Because the current values for the
zero signal
current IR, the level detector current IP and the current of the data receiver
IE+IC+IM
differ widely, only a qualitative representation is possible.
[025] According to the invention, the exemplary components EMP, C, MEM of the
data
receiver DE, or only parts thereof, are electrically added only if there is a
prompt to
transmit data from a read/write device SLG. Only then is the data demodulated
signal
analyzed and the validity of the data it contains checked.
[026] This has the advantage that compared to, e.g., the 100-fold power
requirement of
the prior-art data receiver, the 0.3 pulse duty factor of ON to OFF time makes
it possible
to reduce the power consumption by a factor of approximately 30. As a result,
a
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significant increase in the operating period of the mobile data memory MDS is
advantageously possible.
[027] FIG 2 shows an advantageous exemplary variant of the level detector P2
according to the invention. The level detector P2 has a level detector unit PE
for detecting
the two frequencies fl, f2, or the intermediate frequency ZF, and a pulse
generator TIME.
[028] According to the invention, the pulse generator TIME switches the level
detector
unit PE and the intermediate frequency demodulator ZFD to an inactive standby
mode
IR, IT for a cyclic pause time TP within a cycle time TZ by means of an
exemplary
control line ASP. In this operating mode, the two frequencies fl, fZ, or the
intermediate
frequency ZF, cannot be detected. IT is the mean power requirement of the
pulse
generator TIME. It corresponds approximately to that of the zero signal
current IR.
Detection is possible only during a short cyclic sampling time TA for the
standby mode.
The sum of the cyclic sampling time TA and the cyclic pause time TP
corresponds to the
cycle time TZ. This is not depicted in the example of FIG 2 for reasons of
clarity. If,
according to the invention, the two frequencies fl, f2, or the intermediate
frequency ZF,
are detected within the short cyclic sampling time TA, the mobile data memory
MDS is
switched to the standby mode for receiving data.
[029] This has the advantage that the operating period of the mobile data
memory MDS
can be clearly extended by further lowering the power consumption. For
example, the
power consumption can be reduced by another factor of approximately TA/TZ
during a
cycle time TZ, i.e., by a factor of approximately 10 to 20.
[030] According to the invention, the ratio of the cyclic pause time TP to a
higher-order
cycle time TZ can be at least 10:11 and less than 1. The selection of the
suitable ratio can
advantageously be adjusted such that, for the time during which the mobile
data memory
MDS resides within the detection range of the read/write device SLG, data can
be
reliably read from and possibly written to the mobile data memory. This
residence time
may differ from application to application.
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[031] According to the invention, after receipt of the first data DAT of the
read/write
device SLG and after a valid identification ID of the data DAT, the energy
supply can be
switched from the full operating mode to the stand-by mode. Advantageously,
this makes
it possible to further reduce the current consumption. For clarification, the
associated
current consumption curve IV2 of the entire mobile data memory MDS is
qualitatively
illustrated in the example of FIG 7.
[032] FIG 3 shows an exemplary signal shape of a receiving signal ES from a
transmit/receive antenna A of the mobile data memory MDS. Parallel to the time
axis t,
an exemplary minimum level MP for the frequencies fl, fZ or the intermediate
frequency
ZF is indicated by a dashed line.
[033] FIG 4 shows an exemplary signal shape of a control signal AS with the
exemplary
logic levels ' 1' and '0' generated by the level detector P 1. If the level p
of the receiving
signal ES exceeds the minimum level MP, the control signal AS for the
switching means
S changes its logic level, for example, from '0' to '1'. The read/write device
SLG applies
the two frequencies fl, f2 with a lead time TV, such that the frequencies can
be detected
at the cyclic sampling points ZA of the mobile data memory MDS.
[034] FIG 5 shows an exemplary current consumption curve IVO of a mobile data
memory of the prior art in which all the components of the data receiver are
switched on
at cyclic intervals TZ for a full operating mode. In the inactive sleep mode,
the zero
signal current IR+IT results.
[035] FIG 6 shows an exemplary current consumption curve IV 1 for a mobile
data
memory MDS based on the method according to the invention. Here, the current
consumption IP of the level detector P1, P2 is indicated in addition to the
zero signal
current IR. According to the invention, the two frequencies fl, fZ, or the
intermediate
frequency ZF for receiving data can be detected at an advantageously low total
power
consumption. According to the invention, all of the components EMP, C, MEM of
the
data receiver DE are added only when the level detector P1, P2, upon
detection, emits a
control signal AS for the switching means S.
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[036] FIG 7 shows an exemplary current consumption curve IV2 of the variant of
the
mobile data memory MDS depicted in FIG 2. According to the invention, the
current
consumption IP of the level detector P2 is lowered during a cyclic pause time
TP to the
zero signal current IR and the current IT necessary for the pulse generator
TIME. The
mean current IT is comparable in amount to that of the zero signal current IR.
In the
example of FIG 7, the two current values IR, IT are therefore combined in one
figure to
simplify the representation. Furthermore, for a cyclic sampling time TA, which
starts at
the cyclic sampling instant ZA, there is a change from the inactive sleep mode
to the
standby mode. The two frequencies fl, fZ can be detected during the sampling
time TA.
The sampling time TA can be dimensioned such that, taking into account
transient effects
and processing times in the level detector P2, a reliable control signal AS
can be
generated at the end of the sampling time TA. In the example of FIG 7, the
result of the
detection is available at the branching point VP. Upon detection, the current
consumption
curve IV2a is established; otherwise the mobile data memory returns to the
inactive sleep
mode with the current consumption IT+IT according to the current consumption
curve
IV2b.
[037] Compared to the example illustrated in FIG 6, a substantial further
reduction in
the current consumption is thus advantageously possible.
la
