BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view illustrating a typical sensor pad RFID reader equipped with continuously variable input devices such as a knob or fader of the present invention.
FIG. 2 is a block diagram of the PN code modulated tag and processor of the present invention.
FIG. 3
a is a graphic representation of the data send protocol for each continuous input device using induction RFID tags of the present invention, and FIG. 3b is a graphic representation of the data send protocol for each continuous input device using active RFID tags of the present invention.
FIG. 4 is a block diagram of a wireless data input system with a processor-assisted reader of the present invention.
FIG. 5 is a table showing the multiple operation of devices that use PN codes for identification and modulation of digital data using RFID transponder tags of the present invention.
FIG. 6
a is a block diagram of a device process using a single switch with the sensor pad RFID reader and PN code of the present invention, and FIG. 6b is a block diagram of a device process using multiple switches with said sensor pad RFID reader and PN code of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention generally comprises a simple means to allow continuous data input from RFID tag devices to induction or active type RFID readers. With regard to FIG. 1, a typical proximity RFID reader unit 11 includes a reader housing 12 which surrounds and supports a sensor pad 13. In most cases such a design will consist of a stand-alone sensor pad with a limited number of user input devices that provide a continuous variable output reading and must be transmitted to the RFID reader as digital signals. The user input devices may include knobs 14, faders 16, trackballs 17, joysticks 18 and various types of switches that are physically operated by a user. The sensor pad area may also be used for other forms of continuous input but must rely on the tag for communication. The sensor pad surface and reader housing may also be placed over a LCD screen so that iconic representations 19 and 21 of the knob and fader inputs are displayed on the LCD screen. These iconic representations could include any type of graphic with any type of digital readout, like numerals that change as a knob is turned, a fader cap is moved, a joystick is adjusted or a switch is pushed. The housing 12 may be a small enclosure sized for convenient hand held operation. The reader unit 11 is connected to a controller and processor unit 22 by wire or wireless connections.
With regard to FIG. 2, in one embodiment of the invention each user input device (14, 16, 17, 18) includes the elements for passive remote transmission of data to the RFID reader 11. The analog input sensor of the user input device 31, such as the knob angular position sensor, fader linear position sensor, joystick XY position sensor, and trackball angular axis sensor, generates a sensor signal that is fed to an A/D converter 32, and the resulting digital signal is fed to a microprocessor 33. The digital input can also be the input from a switch and in this case a single bit representing the switching action is sent to the μP 33. A switch 34 is connected to the μP to activate the μP into operation thereby allowing the digital stream of data to be output to the RFID circuit 36. In addition, the PN code 38 is stored in a non-volatile memory and connected through an inverter 37 to the RFID circuit 36. The μP 33 is connected by a data line to the inverter 37 to selectively invert the PN code as it is fed therethrough to the RFID circuit 36. The resulting coded signal is fed to antenna 39, which interacts with the antenna of the RFID reader 11 as is well-known in the prior art.
For knobs, faders and joysticks, a preferred switch for this activation operation is a touch sensitive switch that will activate the device upon contact with a human hand or finger. For instance, grabbing a knob between the thumb and forefinger or using a finger to slide a fader cap or adjust a joystick. Of course, a mechanical switch can also be used. If the device is a switch, then it simply activates the RFID and turns it on.
The data transmission protocol for continuous devices using inductive RFIDs is shown in FIG. 3a. For induction type RFID tags the process of data reading and coding from a continuously operating variable input device uses an RFID that receives a data-ready input signal from a μP. When the reader powers up the induction RFID tag to respond (reader switch-on), the RFID very soon receives a RFID power-on signal as the tag receives the inductively transmitted power. The RFID then goes into a sleep state while data is prepared in the μP 33. A data-ready signal must reply from the μP within a delay time or wait-for-data period to indicate that there is data ready to transmit, otherwise there is no tag reply. Note that the delay or sleep period is specific or unique to the device, as each different device may have a different delay or sleep time the μP begins to transmit the PN code and inverted PN code to convey the device ID as well as the data from the analog input device 31. When the data-ready signal is active then the tag will respond by sending a PN code that is repeated M times. For example if an ASCII character is sent then the PN code is repeated 8 times (M=8). Also the PN code can be modulated in various ways. For example, the PN code can be sent as on-off PN code sequences using appropriate lead and trail bits, or using direct and inverted PN code sequences. Also by example, the RFID chip can send M code responses with a data-ready capability and an ability to invert the code as well. The first approach above is easier because it requires that an RFID chip have an ability to send M code responses with a data-ready capability. Each PN burst results in a binary one data bit accumulated in the reader, and each PN1 results in a binary zero bit. (Each PN1 word may comprise the inverted PN code.) When the PN word transmission in complete, the μP sends a end-of-data signal to the RFID circuit, indicating that the M-bit modulated data burst is complete.
The data transmission protocol for continuous devices using active RFIDs is shown in FIG. 3b. The process is almost identical to the inductive device but one difference is that the reader must transmit a short activation signal (reader sync signal) to the RFID tag requiring the tag to reply within a specific delay or sleep time period to a data-ready signal from the μP with modulated data. Another distinction is that the RFID tag can reply with M responses or many more depending on how the tag device is programmed, since it does not rely on the uncertain reader signal to power the tag.
One advantage of using the above RFID powering and data transmission schemes shown in FIGS. 3a and 3b, is that they will operate with a reader that is sending a continuous or pulsed EM field. The reader can continuously send an EM field and simultaneously receive data, or the reader may pulse the EM field at predetermined time intervals long enough to power the RFID tag and μP circuits to allow the RFID to send a required return data signal within the power cycle.
FIG. 4 depicts the elements of the power circuit of each RFID device. This circuit requires few components and allows for the whole circuit to be powered directly from the reader depending on the RF signal strength. Reader 11 is provided with an antenna circuit comprised of an inductor 42 in parallel with capacitor 43, whereby the LCr factor determines the resonant frequency of the antenna circuit. Each RFID device includes a similar antenna circuit comprised of inductor 46 in parallel with capacitor 47 to produce an LCt factor that tunes the RFID antenna circuit to the reader antenna circuit. The RFID antenna circuit is connected to power regulator 48, which in turn delivers power to a charge regulator 49. The power from charge regulator 49 is fed to the μP 33, which powers the μP and causes it to deliver a control signal to the RFID circuit 36. If the combination of the μP and tag circuit cannot be powered as a single unit by the instantaneous power of the reader power signal, then an optional battery 51(typically a long life lithium, or the like) is connected to the charge regulator to allow for sufficient powering of the μP and analog input component. That is, the battery may be charged when the device is not transmitting, and may accumulate sufficient power to drive the RFID transmission protocol (described above) when necessary.
FIG. 5 illustrates the multiple device operation of the sensor pad. Devices D1 through Dn are normally placed down on the sensor pad in locations corresponding to respective multiple graphical representations (1 to N) displayed on a computer screen, such as the representations 19 and 21 of FIG. 1. In this case each graphical representation is a circle or graphical knob shown on a computer screen which is situated below the transparent sensor pad. The computer screen may be an LCD under the sensor pad surface, or a stand-alone computer screen separate from the sensor pad surface. The transponder (tag) circuits inside each of the knob, fader, joystick, trackball, or switch devices on the sensor pad surface are programmed so that each transmits a unique identification PN code when activated by the inductive sensing field of a proximity reader 61. The input of each tag circuit is connected to the output of the μP of each knob, fader, joystick or switch represented as D1-Dn, as described above. Changes caused by adjusting a device, e.g., turning a knob, moving a fader or joystick, are represented as digital data, which are transmitted to the antenna tank circuit of the tag. The operative tag will be powered up by energy inductively coupled from the reader to the antenna coil, and will transmit its unique tag PN code to the reader. The μP assigns a unique time delay (as shown in FIG. 3b) for each device called T1 to Tn. These unique times are important to prevent multiple PN codes from colliding with each other. Although code collision is allowed, it is desirable to minimize these effects as much as possible (to perhaps a maximum of two or three code collisions for each transmission of a data code word). The transponder tag circuit may comprise an IC with surface mount components such that the entire circuit of FIG. 2 can be easily implemented on a single circuit board, which can also carry the μP, analog input device, and antenna coil. Alternatively, this entire circuit could be reduced to an ASIC.
The reader 61 receives the raw PN code burst from all the devices D1-Dn, and produces a baseband signal 62 that is fed to a CDMA processor 63. The CDMA processor process compares the broadband signal to a filter bank of PN codes that contains all the codes of the devices D1-Dn. When code PN1 is fed to the filter bank having stored codes MF1 . . . MFn, it is compared with all the programmed codes until a match with MF1 is found, leading to device D1 being detected. The data content of D1, here termed S1 is derived from the burst. Likewise PN2 is matched against all codes until a match with MF2 is found leading to detection of D2 and derivation of data S2. This process is carried out until code PNn is matched with MFn, and the related data is read. The serial data D2S2 to DnSn is fed from the CDMA processor to the host computer, which typically also operates the electronic display associated with the sensor pad. Assuming that the data thus derived replicates at least some changes in the settings of the devices D1-Dn, the host computer may update the display appropriately to portray graphically the altered settings of the devices.
With regard to FIG. 6a, there is shown the implementation of a simple data RFID device, and the components that are similar to those of FIG. 2 are labelled with the same reference numerals having a prime (′) designation. The input device to the μP 33′ is a switch 66 that convey a single event bit to the RFID circuit 36′ (i.e. for M=1). Note that a device having a simple SPST switch will only send one PN code sequence and does not need to invert the code. This device design is programmed with a μP to allow the RFID to delay sending the PN code depending on the status of the RFID and timing of the switch event. It is the intention of this design to allow a switch as a standalone option for a user input device, or add it as an additional function to any existing device for an independent switching purpose. For example, a knob, fader or joystick can have a plurality of switches that may send single bit events for purposes that are independent of the continuous input of data. FIG. 6b shows another implementation that is similar to FIG. 6a, except that the device may employ multiple switches 66a-66n and may use the input data stream to identify the switch being activated (i.e. M>1 for two or more switches on one device).
The reader 61 (FIG. 5) consists of two significant parts: the RF front-end and the processor. The processor is required to recognize the unique tag PN codes of the transponder tags that are dedicated to a function of sending ordinary binary data from the user input devices to the reader. In particular, the reader will recognize the dedicated tag PN codes using a high-speed RF coupling decoder circuit followed by a combination of matched filters to recognize the PN codes from the decoder's base-band signal output. The base-band signal can be over-sampled by some facto N. For instance a factor of 5 or greater than the highest chipping frequency of the PN code transmitted from the tag. As an example, if a reader can decouple a tag signal chipping at 70 kHz then the reader's base-band signal shall be sampled at 350 kHz or better at 700 kHz to allow for a better quality PN code to be matched. The ultimate objective is to decode the modulation of the PN code to determine the digital read-out of the analog device inside each user input device. Over-sampling is useful not only for the quality of the decoding but mainly for the ability to operate multiple PN coded devices simultaneously.
Once the tag PN codes have been decoded the reader's processor will also arrange recognized data from the devices as a packet structure that includes the device ID, and the continuous digital reading of the analog input device (by example, this could be as a single 8-bit ASCII character) or a sequence of 8 bit or 16-bit representations of the signal. Depending on the number of devices operating simultaneously, the reader's processor must arrange the output data packets such that there is sufficient bandwidth to serially communicate to a computer program performing iconic representations of the devices.
A further embodiment of this invention permits a reader's processor to be programmed to allow a new device to be placed on the sensor pad and accept the unknown code to be programmed into the processor. A newly scanned PN code that is not matched with an existing code can be recognized and logged for further use. Similarly, with the aid of the host computer the processor can allow an administrative user to disable the device PN code from further operation on the sensor pad.
The number and functions of sensor pad user input devices that can be encoded and wirelessly linked to a reader in this fashion is virtually unlimited. As a practical matter, however, it may be found that this approach to passive remote devices representation'is best suited to a relatively small sensor pad with a simple square reader antenna surrounding the outside of the sensor pad area. RFID units requiring large and complex sensor pads are better implemented with a fractal antenna pattern surface etched on, for example, an ITO (Indium-Tin Oxide) conductive surface or its equivalent.
It should be understood that this invention is not restricted to any particular manufacturer's proximity system, and is generally useful with any induction type proximity reader, provided that the tags used in the remote programmer unit can be read by the target proximity reader. Generally there are many commercial reader front-end circuits available (from companies like MicroChip, Phillips, Tex. instruments, etc.) and may be linked to an FPGA or any other suitable DSP that can support high-speed matched filter implementations.
The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and many modifications and variations are possible in light of the above teaching without deviating from the spirit and the scope of the invention. The embodiment described is selected to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular purpose contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
Patent Application
20080084271
