Patent Description:
RFID systems include, at least, an RFID reader and an antenna. The antenna is used by the reader to transmit interrogation signals to RFID tags and receive responses from the RFID tags. RFID systems can use multiple antennas connected to a single reader in order to spread the relatively high cost of the RFID reader electronics over a relatively large servicing area. Multiple antennas can be connected to a single RFID reader using an RFID antenna multiplexer (mux). Multiple muxes can be connected to a single RFID reader in various topologies.

In addition to a coaxial cable or other radio frequency (RF) connection between the reader and a mux, a data cable is also connected between the reader and a mux. As an example of a data cable, some systems use an Ethernet cable to pass control information between the reader and any muxes. A power supply cable can also be used. The power supply cable and a data cable can sometimes be combined, or power can be supplied over the RF coaxial cable. Alternatively, for example, in retail environments where AC power is distributed throughout a premises, power can be supplied to a mux locally. Power is needed for the electronics of the muxes and the data cables provide signaling so that the RFID reader can direct switching between or among antennas at appropriate times. <CIT> is directed to a system and method for multiplexing radio frequency signals.

Aspects and features of this disclosure include a radio frequency identification (RFID) antenna multiplexer.

According to an embodiment of the invention, a radio frequency identification (RFID) antenna multiplexer is defined in claim <NUM>.

According to an other embodiment of the invention, a radio frequency identification (RFID) system is defined in claim <NUM>.

According to an other embodiment of the invention, a method of operating a radio frequency identification (RFID) system is defined in claim <NUM>.

According to an other embodiment of the invention, a radio frequency identification (RFID) reader is defined in claim <NUM>.

Other embodiments of the invention are defined in the dependant claims.

Certain aspects and features of the present disclosure relate to a system that improves, and makes more efficient, the installation and operation of RFID systems that make use of an external RFID antenna multiplexer (mux) or multiple such muxes and an RFID reader. Certain aspects and features relate to a mux that only requires the radio frequency (RF) connection to operate, for example, the mux may only require an RF coaxial cable (RF coax) running between the reader and the multiplexer. A control signaling cable is not required.

In some aspects, no control signaling interface or cable is needed because a mux detects a reduction in RF power indicative of switch timing. In some aspects, no DC power need be supplied to the mux, either distributed through the RF coax or otherwise. The external mux in such an example derives power by harvesting a small amount of signal energy from the reader's RF signal, converting it to a DC voltage, and storing it between RF transmissions. In some aspects, neither a control signaling connection nor a power connection is needed. These aspects and features reduce the cost, complexity, and installation time for RFID systems that make use of multiple antennas.

In some examples, an RFID mux includes an RF switch connected, or communicatively coupled, to output ports and an input port. A logic circuit is connected to the RF switch. The logic circuit is configured to cause the RF switch to select an output port from among the multiple output ports to connect, or communicatively couple, to the input port based on a reduction in RF power from the reader as detected at the input port.

In some examples, an RFID mux includes an energy harvester connected, or communicatively coupled, to the input port to harvest signal energy from the RFID reader. The RFID mux in this example further includes a storage device connected to the energy harvester to store the signal energy and supply power for the operation of the RFID antenna multiplexer using the signal energy. In further examples, the RFID mux includes the logic circuit configured to cause the RF switch to select an output port based on a reduction in RF power as well as the energy harvester and the storage device.

In some examples, an RF detector circuit is connected to the logic circuit and the input port of the RFID antenna multiplexer to detect the reduction in RF power at the input port. In some examples, the RFID antenna multiplexer includes an input switch connected to the logic circuit to program a connection sequence for the plurality of output ports. In some examples, the RFID antenna multiplexer includes an RFID chip readable by the RFID reader to identify the RFID antenna multiplexer. In some examples, the RFID chip can also be used to store information from the reader and to provide connectivity status information to the reader.

These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative aspects but, like the illustrative aspects, should not be used to limit the present disclosure.

<FIG> is a system block diagram showing an example of an RFID system <NUM> in which a reader <NUM> according so some aspects of the present disclosure is connected to RFID antennas <NUM>. The RFID reader <NUM> has one or more antenna ports which are attached to antennas <NUM>. The reader <NUM> transmits radio signals to RFID tags <NUM> using one of the attached antennas <NUM>. The tags communicate back to the reader by modulating information in their radar cross section, thereby creating a modulated backscatter signal which the reader demodulates.

Without external antenna multiplexers, the number of antennas that can be connected to the reader <NUM> of <FIG> is limited by the number of antenna ports that reader has. Reader <NUM> includes a digital signal processor (DSP) <NUM> and memory <NUM>. The memory serves as a non-transitory computer readable medium to store software <NUM> (microcode, firmware, instructions, or the like) that is associated with the DSP and is executed on the DSP to operate RFID reader <NUM>. In this example, while no RFID antenna multiplexers are connected to reader <NUM>, software <NUM> includes instructions that can reduce RF power to signal RFID antenna multiplexers according to some aspects of this disclosure, and optionally that can detect external muxes, charge the external muxes to initialize them to be RF powered, and send and receive control information as stored in the external muxes.

<FIG> is a system block diagram showing an example of an RFID system with a RFID reader connected to antennas through RFID antenna multiplexers according to some aspects of the present disclosure. System <NUM> as illustrated in <FIG> uses external antenna multiplexers to expand the number of antennas the reader is connected to. This allows a single reader to cover more area and, provide more read points, or both. This design uses a separate control bus <NUM> to communicate with the external multiplexers <NUM>. However, external multiplexers <NUM> include energy storage devices <NUM> to eliminate the need to independently supply DC power to the muxes. The muxes also include an energy harvester and other power supply components (not shown) according to aspects of the present disclosure. Without the built-in components to supply power based on RF signal energy, DC power would need to be supplied to multiplexers <NUM> either through the control bus <NUM> or through the RF coaxial cable using bias tees.

<FIG> is a system block diagram showing an example of an RFID system with an RFID reader connected to antennas through RFID antenna multiplexers according to additional aspects of the present disclosure. The RFID reader <NUM> can optionally interface with client <NUM>. Client <NUM> can be a cloud-based client, a personal computer, an enterprise computer system or any other device or function that could be used obtain settings or input setup information via a network connection when needed. RFID system <NUM> uses the external RFID antenna multiplexers <NUM> to expand the number of antennas used by the reader. This allows a single reader to cover more area, provide more read points, or both. In this example, the muxes <NUM> include energy harvesting and storage. The muxes <NUM> also include a logic circuit configured to cause the RF switch in the multiplexer to select an output port from among the multiple output ports to connect to the input port based on a reduction in RF power of the interrogation signal from the reader. Examples of RFID antenna multiplexers with both of these features are discussed in detail with reference to the remaining figures of this disclosure. However, an RFID multiplexer with only the energy harvesting and storage feature or only the switching of outputs based on RF power reduction features described herein can be implemented with appropriate components from any of the examples shown.

The design in the example of <FIG> does not require a separate control bus to configure the external multiplexers <NUM> or cause the muxes to switch at appropriate times. The design also does not require DC power to be supplied to the muxes. This design provides substantial reduction in product and installation costs. Multiplexers <NUM> allow daisy chaining or nesting. In this example, external muxes <NUM> are identical but are illustrated with additional labels, namely, A, B, C, D, and E. These labels will be referred to later when describing initializing and charging the energy storage devices in the muxes.

Still referring to <FIG>, the number of levels of muxes which may be nested in a system like system <NUM> depends on the minimum activation power of the external multiplexer <NUM>. For example, if the reader <NUM> can generate <NUM> dBm of output power, and an external multiplexer <NUM> has a minimum activation power of <NUM> dBm, then the multiplexers can be nested until the final unit in the daisy chain receives <NUM> dBm of input power. The nesting depth will depend on insertion loss of the multiplexers and cable losses. In order to design a system, a loss budget based on the desired antenna network topology can be determined. The insertion loss of the external multiplexer <NUM> would typically be from <NUM> dB to <NUM> dB.

<FIG> is a schematic block diagram of an external RFID antenna multiplexer according to some aspects of the present disclosure. The reader RF connection of the mux <NUM> is connected to the reader's antenna port. Coupler <NUM> samples a portion of the reader's radio signal and passes the sample into a rectifier <NUM>, which performs alternating current to rectified current conversion such as full-wave rectification, half-wave rectification, or similar. The rectified signal is supplied to the energy harvester <NUM>. The energy harvester <NUM> is a device or circuit which extracts power from highly variable and high output impedance sources, such as radio signals, thermal energy, photodetectors, etc. Such energy harvesters are available in chip form. The energy harvester <NUM> provides a variable power input to a charger <NUM>. The charger <NUM> manages charging an energy storage device such as a battery or capacitor. In this example, charger <NUM> transfers power from the energy harvester <NUM> into the energy storage device <NUM> with high efficiency. Charger <NUM> also monitors the charge level to avoid overcharging, and in some cases to avoid undervoltage. Chargers are also available in chip implementations. Charger <NUM> uses the harvested power to charge the energy storage device <NUM>. In some examples, energy storage device <NUM> is a capacitor. Since the energy system can power the mux without a battery in such an example, the cost and maintenance time that would otherwise be required if a battery were used is avoided.

Still referring to <FIG>, the energy storage device <NUM> provides input power to the power regulation subsystem <NUM>. The power regulation subsystem <NUM>, in turn, provides regulated power to the entire mux. The power regulation subsystem in this example includes one or more buck regulators, one or more low drop out linear regulators, or both. Buck regulators provide higher efficiency but are typically noisier than linear regulators. For example, a linear regulator output would typically be used to power the RF switch <NUM>. The RF off detector <NUM> must detect when the input radio signal from the reader is shut off, or reduced to such a low level that it can be presumed to be logically off for purposes of controlling the switching of the mux. In the example of <FIG>, the RF detector includes fast peak detector <NUM> and a slow peak detector <NUM>. The two detector outputs are input to a comparator <NUM>, which determines when the fast peak detector output has fallen below the slow peak detector output. The time constants or bandwidth of the fast and slow peak detectors are set such that the detectors are slow enough to ignore or not respond to RFID command modulation but are fast enough to detect an RF off event (when the reader shuts off its RF output to the multiplexer <NUM> to cause the multiplexer to switch or advance in its switching sequence). The RF detector circuit <NUM> determines when the RF signal has powered off and passes that information to the logic circuit <NUM>. RF detector circuit <NUM> may be referred to as a radio off detector.

Continuing with <FIG>, the logic circuit <NUM> changes the switch control output <NUM> to the RF switch <NUM>. The logic circuit <NUM> in this example also provides a power control signal <NUM> to the power regulation subsystem <NUM> so that the power to other subsystems within multiplexer <NUM> can be disabled. Normally the logic circuit <NUM> would sequence through a specific sequence of ports, for example, Port <NUM>, Port <NUM>,. , Port N, then repeat. Optionally, the logic circuit <NUM> can include timing detection such that some predetermined pattern of reader RF off events signals to logic circuit <NUM> to alter the sequence in some way. For example, two RF off events <NUM> milliseconds apart would not occur in normal operation of a RAIN-based RFID system (RAIN-based RFID is also known as RFID based on the Gen2, ISOC, ISO-<NUM>, or ISO <NUM>-<NUM> standards). Such a sequence of two or more RF off events may be used to control or preset the port sequence in the logic circuit <NUM>. In some examples, the port selection sequence can be determined by the logic circuit. However, the port selection sequence can also be externally programmed, as discussed below.

<FIG> is a schematic block diagram of an external RFID antenna multiplexer according to further aspects of the present disclosure. The example of <FIG> includes a mechanical input switch <NUM>. In this example, input switch <NUM> is used to specify the order of the ports connected to the input port of the multiplexer, which is used for the reader RF connection. Examples of a mechanical switch include a rotary switch, and a DIP switch. The same switch or additional switches can also be used specify the initial port to connect in response to an initialization sequence. While the example shown in <FIG> includes a mechanical switch to program a connection sequence, an input switch can also take the form of an electronic switch, or can be implemented in software (firmware) that is used to implement the RFID antenna multiplexer.

By default, an external multiplexer can sequence through the connected output ports in some predetermined order or a circular fashion (e.g. <NUM>, <NUM>,. , N-<NUM>, N, <NUM>,. In some applications it may be desirable to daisy chain or nest the external multiplexer as shown in <FIG> with multiplexers labeled A, B, and C. In such circumstances it may be desirable to program an alternative mux sequence.

<FIG> is a schematic block diagram of an external RFID antenna multiplexer according to additional aspects of the present disclosure. External RFID antenna multiplexer <NUM> includes an RFID chip <NUM> for enhanced logic control. An RFID chip with a backend serial interface communication channel (e.g. I2C or SPI) can be used. In this example, the logic circuit <NUM> can obtain port sequencing control from the RFID chip interface. This allows the RFID reader full control of the port sequencing. The inclusion of such an RFID chip configures the RFID antenna multiplexer to read the control information from the RFID chip and the RFID reader <NUM> is configured by its software to write the control information to the RFID chip. The control information can provide port sequencing as well as any other desired function such as startup management, power management, etc..

As an additional benefit, the integrated RFID chip <NUM> in <FIG> allows the reader <NUM> to determine if an external mux is attached to one of its antenna ports and identify the specifics of the mux. The RFID tag function of the chip is readable by the RFID reader to identify the RFID antenna multiplexer. The RFID chip <NUM> may uniquely identify itself as an external switch with its unique serial number. This feature allows the reader to determine if any external multiplexers are present on any of its antenna ports and, furthermore, allows the reader to identify the connection topology of the external multiplexers to efficiently control the antenna sequencing.

<FIG> shows a sequence control input <NUM> passing from the RFID chip <NUM> to the logic circuit <NUM>. In some examples, logic circuit <NUM> also passes connectivity status information to the RFID chip for feedback to the reader <NUM> via status output <NUM>. This status information can be used or stored by the reader. Additionally, this or other information can be displayed on display <NUM> for evaluation by a user or technician. The RFID reader <NUM> identifies any external mux connected by reading the product code and serial number stored in the embedded RFID chip <NUM>. The reader <NUM> sends commands to the mux logic circuit <NUM> and receives responses from the logic circuit <NUM> through the RFID chip <NUM>. This arrangement gives the reader complete, programmatic control over the external multiplexer(s) <NUM> without requiring any data cable connections.

The coupler <NUM> shown in the examples herein can be a <NUM> dB or <NUM> dB coupler. For RFID readers transmitting one watt, or <NUM> dBm, this means that the RF power applied to the rectifier <NUM> is on the order of one milliwatt, or <NUM> dBm. Thus, initial charging of the energy storage device <NUM> could take some time, for example, several seconds to several minutes, depending on the RF power input and how much capacitance is used in the energy storage device <NUM>. The reader <NUM> will need to manage the initial charging of the energy storage device(s) <NUM> on startup. <FIG> is a flowchart illustrating an example of processor-controlled operations of an RFID system according to some aspects of the present disclosure. Process <NUM> illustrated in <FIG> includes the startup sequence.

Process <NUM> in this example begins at block <NUM> from a reset or reboot. At block <NUM>, the reader determines if any external muxes are present, and goes directly into steady state, stand-alone operation at block <NUM> if not. To determine if any external mux is present, the reader may have configuration variables or files set through a user interface. Alternatively, if an RFID chip <NUM> is used in the muxes, then the reader can directly query for external multiplexers via the RAIN RFID interface. If there are external muxes, control passes to block <NUM>, where the first external mux is charged by sending an RF signal to the input port of the first mux for an appropriate amount of time in order to charge the mux. If a no-feedback system design is used, the reader may wait some predetermined time. Alternatively, if the logic circuit <NUM> can provide feedback, as may be the case when using an RFID chip <NUM>, then the reader <NUM> can query the logic circuit <NUM> to report the charge state. At block <NUM> of process <NUM>, the reader determines if there are additional external muxes present. If not, then control passes to steady state operation beginning with block <NUM>. Otherwise, the reader starts charging an additional RFID antenna multiplexer at block <NUM> using the stored refresh time and stored guard time.

In some examples, with optimized algorithms, the subprocess of block <NUM> may run for a limited amount of time due to the requirement to refresh the energy storage level for previously charged muxes. The reader <NUM> may identify and store a connection topology for the RFID antenna multiplexers. In some examples, the topology is stored by creating a data structure representation of the topological map of nested external RFID antenna multiplexers connected in the system. The RFID reader can be configured to energize some of the RFID antenna multiplexers more frequently than other of the plurality of RFID multiplexers. The reader <NUM> may keep track of the charge state of the various leaf multiplexers in the antenna network. A leaf multiplexer is any multiplexer which does not have another multiplexer attached to any of its outputs. In <FIG>, for example, external multiplexers B, C, D, and E are all leaf multiplexers. External multiplexer A is not a leaf multiplexer. The reader <NUM> may maintain an inventory schedule such that leaf multiplexers are energized often enough to remain ready continuously. This technique will be further discussed below with respect to <FIG>.

Still referring to <FIG>, after charging an additional mux at block <NUM> until previously charged muxes must be refreshed, the reader proceeds in block <NUM> to loop the RF charging signal back through all previously charged muxes. At block <NUM>, the reader determines if the currently charging mux has been fully charged. If not, control passes back to block <NUM> to continue charging. If so, control returns to block <NUM> to check for additional external multiplexers. Once charging is complete, connection sequences are determined within the system at block <NUM>, either at the muxes themselves or by the reader accessing previously stored control information and sending the control information to the muxes. The reader transmits interrogation signals through the muxes at block <NUM>. Each mux monitors for a reduction in the RF power of the interrogation signal at block <NUM>, and switches to the next output in its sequence at block <NUM> when the reduction in RF power is detected. This, transmitting, monitoring and switching continues until the system is shut down, reset or rebooted.

In some examples, the RFID reader includes a stored value for a configuration variable that enables the reader to work with the muxes described herein. With this function enabled in the reader, the reader will automatically discover any muxes connected, even if they are not charged or even if a charged mux gets moved to a new location. In some examples, the reader always maintains a stored connection topology of the attached antenna network. In some examples, the reader can be made to override and control the port switching connection sequence of muxes, for example, based on manual input using client <NUM>.

<FIG> is a schematic block diagram of an external RFID antenna multiplexer according to further aspects of the present disclosure. In <FIG>, one of the switch ports is connected to the energy harvester through the rectifier to supply additional energy to the energy harvester. Mux <NUM> includes internally terminated port <NUM> which routes essentially all the RF power available at the RF switch <NUM> back into the rectifier <NUM>, the energy harvester <NUM> and the charger <NUM> for faster charging of the energy storage device <NUM>. Internal port <NUM> can be selected by the logic circuit <NUM>, or port <NUM> can be set as the default port when the logic circuit <NUM> is powered down, such that all the available RF power is routed to the rectifier <NUM>. Rectifier <NUM> may include a combiner to sum or switch the coupled RF power from coupler <NUM> and the internal port <NUM> into the rectifier <NUM>. The output of the rectifier passes to the energy harvester <NUM>, charger <NUM>, and into the energy storage device <NUM>. The internal port, the rectifier with the combiner, or both, may be used in any of the examples of an RFID antenna multiplexer shown herein, including multiplexers <NUM>, <NUM>, or <NUM>.

To keep an external mux from depleting its energy storage device, the reader can regularly provide RF power to the external mux. The maximum time allowable between RF power applications at the reader RF input of the external mux is the maximum refresh time. The reader must ensure that all external muxes are refreshed at least as often as this maximum refresh time. The maximum refresh time may be reduced by a guard time to allow for switching. There are many ways to accomplish this. For example, the reader can be programmed to establish a maximum dwell time per mux and a guard time per mux based on the number of muxes and topology and to store these times for use during steady state operation.

The RFID reader can be configured to energize some of the connected RFID antenna multiplexers more frequently than others. For example, when external muxes according to aspects of this disclosure are daisy chained or nested, only muxes at the end of the daisy chain or nesting topology need to be considered for the energy storage refresh period. As previously mentioned, these muxes can be referred to as leaf muxes, meaning these muxes are at the tip of a mux tree topology. The non-leaf muxes always get refreshed whenever a leaf in that tree gets refreshed. For example, in <FIG>, muxes B, C, D, and E are leaves, while A is not. Mux A gets refreshed whenever B or C does, or whenever any of the antennas connected to mux A are used. Therefore, with respect to charge refresh interval management by the reader <NUM>, only the leaf multiplexers matter.

<FIG> is a state transition diagram <NUM> showing an example of the operating states of an external RFID antenna multiplexer according to some aspects of the present disclosure. The mux starts in state <NUM>, the discharged state. When an RF input signal with a level above the activation threshold is provided, the mux transitions to the charging state, <NUM>. If the RF input signal is removed prior to the mux being sufficiently charged to operate, the mux returns to discharged state <NUM>. If the charging produces sufficient operating voltage then the mux transitions to state <NUM>, the initialize state. In this state, the logic resets the mux components for operation. After this initialization is complete, the state transitions to waiting at <NUM>, where the mux waits for the RF signal to be removed, or optionally for a command from the reader <NUM> if the mux is designed to accept and respond to commands. Commands are handled in process command state <NUM>. When the RF signal is turned off, the mux transitions to programming state <NUM>, where it directs the RF switch <NUM> to change to the next port in the designed or commanded port connection sequence. After the switching, the mux transitions to wait state <NUM>, where it waits for the RF signal to be tumed back on. If the RF signal is not detected within some configured timeout interval, for example, <NUM> milliseconds, then the mux transitions to a low power standby state <NUM>. In this mode, the mux is charged and ready to operate, but waits for the RF signal to come back up before enabling the RF switch and possibly other subsystems. Alternatively, from within state <NUM>, if the RF signal is returned to an on state within the allowed amount of time, the mux transitions back to wait state <NUM>. In this example, if the mux enters standby state <NUM>, the mux leaves the standby state when the RF signal is detected. The RF signal detection can be accomplished with a circuit similar to the RF signal off detector <NUM> shown in detail in the example of <FIG>.

<FIG> is a schematic block diagram of an external RFID antenna multiplexer according to additional aspects of the present disclosure. RFID antenna multiplexer <NUM> includes an RFID chip <NUM> with an RF on detection output. Using RF on detection, the mux state transitions to wait state <NUM> described above, where it waits for the RF signal to turn off, since the RF switch <NUM> cannot be powered on and change outputs while the RF signal is on. Switching while the RF signal is on can cause spurious RF emissions exceeding regulatory limits. In wait state <NUM>, when RF off is detected, the mux transitions to programming state <NUM>. If the energy storage device <NUM> becomes depleted so that its output voltage falls below the required operating voltage for the mux at any time, such as during long periods of standby or when the RF input drops below the minimum activation power threshold for prolonged periods, then the mux will automatically return to the discharged state <NUM>.

Still referring to <FIG>, the RFID chip <NUM> features a bidirectional SPI interface <NUM> for control and status information as well as a RF detection output (VAUX) <NUM>. The <NUM> and <NUM> signals connect to the logic circuit <NUM>. In this example, the energy harvester <NUM>, charger <NUM>, and a buck regulator <NUM> are all integrated into a single chip package <NUM>. The charger <NUM> has a VBAT_OK output <NUM> which signals to the logic circuit <NUM> that the system is charged sufficiently to enable the buck regulator <NUM> and the linear regulator <NUM>, which supplies the RF switch <NUM> with clean power. The single chip package shown here as well as discrete implementations with an energy harvester, charger, and buck converter can be used with any of the examples of RFID antenna multiplexers shown herein, including multiplexers <NUM>, <NUM>, <NUM>, and <NUM>. The internal port charging illustrated with respect to multiplexer <NUM> can also be used with multiplexer <NUM> of <FIG>.

Continuing with <FIG>, the VAUX signal <NUM> converts an amplitude modulated RF signal at the reader RF connection into a digital custom RF command <NUM> at the logic circuit input. Decoding the amplitude modulated RF signal into a baseband digital signal can be accomplished in any number of ways. The RFID chip provides this function together with the RAIN RFID functionality and the SPI interface <NUM>. The value of the custom RF command <NUM> is that the reader <NUM> and external RFID antenna multiplexer <NUM> may implement a fully custom command set that bypasses the need to singulate the RFID chip and put the RFID chip into access mode. Implementing custom RF commands <NUM> allows the reader <NUM> to control the external multiplexer <NUM> much more quickly than by using the SPI interface <NUM> through a RAIN RFID access sequence.

In order to implement the functions of the devices described herein, a general-purpose processor such as a DSP, microcontroller embedded controller, or microprocessor can be used and firmware, software, or microcode can be stored in a tangible or non-transitory storage medium that is associated with a processor. Such a storage medium may be a memory integrated into the processor, or may be a memory chip that is addressed by the processor to perform control functions. Such firmware, software or microcode is executable by the processor and when executed, causes the processor to perform its control functions. Such firmware or software could also be stored in or on a tangible medium such as an optical disk or traditional removable or fixed magnetic medium such as a disk drive used to load the firmware or software into an RFID device. An RFID device in this context can refer to a reader, a mux, some other device, or any combination of the foregoing.

The reader described as an example in this disclosure may also be implemented using a discrete component RFID reader design, such as one based on physically separate chips for DACs, ADCs, mixers, amplifiers, couplers, and the like. A processing function for a reader, the logic circuit for an RFID antenna multiplexer, as well as additional functional bocks or circuits in the reader or multiplexer can be implemented on a field programmable gate array (FPGA), or on an application specific integrated circuit (ASIC). A reader or mux may also be implemented as a system-on-a-chip (SoC), wherein many of the subsystems are integrated together on a chip. Sometimes multichip SoC solutions can be used to ease manufacturability given the variations in process which may be required based on frequency, power, and the like.

Claim 1:
A radio frequency identification (RFID) antenna multiplexer (<NUM>) comprising:
a plurality of output ports, at least some of the output ports connectable to an antenna (<NUM>);
an input port connectable to an RFID reader (<NUM>);
a radio frequency (RF) switch (<NUM>) communicatively coupled to the plurality of output ports and the input port; and
a logic circuit (<NUM>) communicatively coupled to the RF switch,
characterised by the logic circuit being configured to cause the RF switch to switch output ports, according to a programmable connection sequence, when a reduction in RF power is detected at the input port.