JP2008287387A - Contactless electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contactless electronic device capable of reducing current consumption. <P>SOLUTION: For example, there is provided a circuit, which can set an oscillation frequency of a reference clock CLK in proportion to the value of a frequency setting signal TR_OSC1. When a signal (TRcal) for controlling a transmission speed sent from a reader/writer is received, one cycle of this TRcal is counted by the reference clock CLK of which TR_OSC1 value is X, and the resulting TRcal counter value is acquired. Using this TRcal counter value and X, the TR_OSC1 value is converted in the case where the TRcal counter value is desired to be a predetermined setting value Y, and a reply is made to the reader/writer using the CLK reflecting the conversion value. By using a method by which to vary the oscillation frequency of the CLK according to the transmission speed, the precision of the transmission speed can be determined by the CLK frequency setting precision. Thereby, the CLK of the frequency lower than the conventional frequency can be used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-contact electronic device, and more particularly to a technique useful when applied to a non-contact electronic device such as an RFID tag capable of setting a communication speed.

  In recent years, contactless electronic devices that operate by receiving electric power from radio waves have increased. As an example of such a non-contact electronic device, an RFID chip (RFID tag) has received attention. The RFID tag is used, for example, to identify and manage people and things by radio. In general, a unique number is assigned to every tag in the RFID tag, and the number can be read out by wireless communication from a device called a reader / writer. Since the reader / writer side associates the number with the actual object, the RFID tag itself does not have a complicated function. For example, a function for reading a number assigned to a tag and a function for storing information and a security function are included in some products.

  There are several types of such RFID tags, and typical ones are those of the 13.56 MHz band using the electromagnetic induction method and the 900 MHz band using the radio wave method (UHF band: 860 to 960 MHz). Or the thing of a 2.4 GHz band (microwave band) is mentioned. In recent years, attention has been focused on the 900 MHz band due to the long communication distance. Various specifications regarding the 900 MHz band RFID tag are defined as standards. For example, a standard called “EPC Global Class 1 Generation 2 (abbreviated as EPC C1G2 or EPC Gen2)” is widely known.

  Although the RFID tag (RFID chip) as described above has a relatively simple function, it is required to be produced at a very low cost because it is used, for example, as a substitute for a barcode. In addition, since a so-called passive type that operates by receiving power from radio waves is usually used, it is also necessary to have low current consumption.

  Under such circumstances, for example, the RFID tag defined by the EPC Gen2 described above can communicate at a distance of about 3 m using a 900 MHz band radio wave. From this, several technical features arise. First, considering a long communication distance of 3 m, the power received by each chip also decreases with the communication distance, so that it becomes necessary to operate each chip with a low current. Specifically, each chip must be operated with a current of about 10 μA, for example.

  Further, since the radio wave is in the 900 MHz band, the reference clock needs to be generated inside the chip. For example, in an RFID tag using an electromagnetic induction system of 13.56 MHz band, a reference clock can be extracted from radio waves in addition to power and information. However, when a clock is extracted from a 900 MHz band radio wave, a large current is consumed for clock extraction and frequency division, which is not preferable. Therefore, an oscillation circuit that generates a reference clock for the chip is required.

  Here, consider the performance required for the reference clock. A problem that arises in this case is that the communication speed can be changed by the reader / writer in EPC Gen2. That is, when a signal defining the communication speed (specifically, a signal with a frequency (period) proportional to (inversely proportional to) the communication speed) is transmitted from the reader / writer, the RFID tag receives and measures this signal, It is necessary to send a reply using the communication speed specified by this signal.

  When a signal that defines a communication speed is measured and a reply is made according to the communication speed, a reference clock having a certain fixed oscillation frequency is generally used. That is, a reference clock having a fixed oscillation frequency is generated in the RFID tag, and the communication speed is recognized by the number of signals that define the communication speed using this reference clock. A reply clock timing is generated by reflecting the count number on the reference clock having the fixed oscillation frequency, and a reply is made based on this. The difference between the signal that defines the communication speed and the actual communication speed is defined by the standard.

  When using a reference clock with a fixed oscillation frequency, if the frequency is slow, the measurement accuracy of the communication speed and the accuracy of the response speed based on the measured speed will decrease, so depending on the required communication speed and accuracy. The minimum required reference clock frequency is determined. Also, if the reference clock frequency is different between when the communication speed is measured and when a reply is actually made, an error in the communication speed occurs. In order to prevent this, the stability of the reference clock frequency is also required.

  Of course, the change over time is important for this stability, but the stability against the operating conditions of the chip is also important. Specifically, when the reader / writer transmits data, a system called 100% ASK (Amplitude Shift Keying) is used. This is a method of performing communication by turning on / off radio waves. When the radio wave is off, the internal power supply drops because no radio wave is supplied, and when the radio wave is turned on again, the internal power supply rises rapidly. It is necessary to realize a stable clock against the change in the internal power supply. However, since it is unlikely that the temperature changes from when a signal defining the communication speed is received under actual use conditions to when a reply is made, stability with respect to temperature is not so important.

  Considering satisfying these conditions, the frequency of the reference clock must be 3.5 MHz or more. At frequencies below that, the accuracy of the required transmission rate (reply rate) cannot be achieved because the sampling accuracy by the reference clock is too coarse. If voltage (and temperature) variations are taken into account under the condition that the minimum reference clock frequency is 3.5 MHz, an oscillation frequency of about 6 to 8 MHz at maximum may occur depending on the circuit configuration. This increase in clock frequency is mainly due to temperature changes. From the above conditions, it is difficult to cancel the temperature dependence of the oscillation frequency. When the oscillation frequency rises to about 8 MHz, the current consumption of the RFID tag also increases, so that it is difficult to realize a low current consumption.

  For this reason, there is a limit to the method of ensuring the accuracy of the transmission speed by finely sampling the reference clock, and another method needs to be considered. Accordingly, one of the objects of the present invention is to provide a non-contact electronic device capable of realizing a reduction in current consumption. The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  A non-contact electronic device according to an embodiment of the present invention receives a calibration signal or the like that defines a communication speed transmitted from an external device such as a reader / writer by radio, and transmits the calibration signal to the external device based on the communication speed. A reply is made to this. Here, the non-contact electronic device includes means for generating a reference clock having a frequency proportional or inversely proportional to the frequency setting value, and counts the calibration signal using a reference clock in which, for example, a trimming value is set as the frequency setting value. . Then, using this count number and the trimming value, the frequency set value when the count number becomes a predetermined set value is converted, and the reference clock that reflects this converted frequency set value is used for the external device. Reply. Specifically, the timing at the time of reply is generated by dividing the reference clock reflecting the converted frequency setting value.

  In this way, by using a method in which the oscillation frequency of the reference clock itself is made variable according to the communication speed designated by the reader / writer, the setting accuracy of the communication speed is determined by the frequency setting accuracy of the reference clock to be made variable. It becomes possible. Therefore, it is possible to use a reference clock having a lower frequency compared to a method that ensures accuracy by increasing the oscillation frequency of the reference clock as in the conventional method, and it is possible to reduce power consumption. .

  By using the non-contact electronic device according to one embodiment of the present invention, the communication speed can be increased with the accuracy of setting the oscillation frequency of the reference clock, so that power consumption can be reduced.

  In the following embodiments, when referring to the number of elements, etc. (including the number, numerical value, quantity, range, etc.), unless otherwise specified and in principle limited to a specific number in principle, It is not limited to the specific number, and it may be more or less than the specific number.

  Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  The contactless electronic device of the present embodiment has at least a wireless communication function for transmitting and receiving information to and from an external device using radio waves and the like, and a wireless communication speed from the contactless electronic device to the external device Can be set based on a speed command signal (calibration signal) from an external device. A typical example of such a non-contact electronic device is a UHF band RFID tag defined by EPC Gen2. Hereinafter, the RFID tag will be described in detail as an example. However, the RFID tag is not necessarily limited to the RFID tag, and the same is applicable to a non-contact electronic device having the wireless communication function and the communication speed setting function as described above. It is applicable to.

  Details of the RFID tag according to the present embodiment will be described with reference to FIG. 2 and the like. However, in the general method described above, a reply is not made using a reference clock having a fixed oscillation frequency regardless of the communication speed. One of the main features is that a reply is made using a reference clock having a variable oscillation frequency according to the communication speed. Hereinafter, description will be made in order from an example of the entire configuration of an RFID tag including such features.

  FIG. 1 is a block diagram showing an example of the configuration of an RFID tag according to an embodiment of the present invention. In FIG. 1, an antenna ANT is connected to terminals LA and LB. The rectifier circuit RCT extracts power from the radio wave received by the antenna ANT. The RFID tag TG performs various operations using the extracted power. The reference level generation circuit REF generates a reference potential VREF and a reference current IREF that are circuit operation references. The clamp circuit CLP refers to the reference potential VREF from the reference level generation circuit REF and adjusts the voltage extracted by the rectifier circuit RCT to a constant voltage.

  The modem circuit ASK demodulates data received from the reader / writer via the antenna ANT, and modulates data transmitted from the RFID tag TG to the reader / writer. The oscillation unit OSC_BLK generates a stable reference clock CLK by using VREF and IREF generated by REF. Since EPC Gen2 uses a 900 MHz band radio wave, it is difficult to set the frequency of the radio wave as a reference clock. Therefore, a stable reference clock CLK is generated by OSC_BLK and used in the logic unit LOG and others.

  The logic unit LOG is a block that performs various information processing. For example, processing for transmission / reception data DAT_SR transmitted / received to / from the modulation / demodulation circuit ASK, processing for memory data DAT_M read / written from / to a memory unit (here, EEPROM (Electrically Erasable Programmable ROM)), and the like are performed. Furthermore, the logic unit LOG also controls communication speed, which is one of the main features of the present embodiment. More specifically, the communication speed that is a command from the reader / writer is measured, a frequency setting signal TR_OSC1 corresponding to the measurement result is generated, and the oscillation frequency of OSC_BLK is variably controlled by outputting this signal to OSC_BLK. . The memory unit (EEPROM here) is a block for storing information. In addition to the EPC code, various user information, trimming values of each circuit, and the like are stored here.

  FIG. 2 shows an operation outline of communication speed control performed by the oscillation unit and the logic unit in the RFID tag of FIG. 1, and (a) is a waveform diagram showing an example of various processing contents associated with communication speed control. (B) is a figure which shows the example of a characteristic of an oscillation part. FIG. 2A shows a signal demodulated by the modulation / demodulation circuit ASK (ASK demodulation), a reference clock CLK from the oscillation unit OSC_BLK, a count operation (TRcal counter) in the logic unit LOG, and LOG to OSC_BLK. The frequency setting signal TR_OSC1 to be set is shown.

  The ASK demodulation is a signal having a period TRcal, and this signal is obtained by demodulating a signal specifying a communication speed transmitted from the reader / writer RW to the RFID tag TG. In EPC Gen2, by changing the length of this TRcal, an arbitrary communication speed (response speed) LF (Link Frequency) such as 40 kHz to 640 kHz can be designated for the RFID tag TG. The relationship between TRcal and LF can be set depending on the mode. For example, mode A “LF = 3 / (TRcal × 64)” or mode B “LF = 1 / (TRcal × 8)” is selected. Can do.

  Here, mode A is selected, and LF = 640 kHz (1.56 μs) is set by TRcal = 33.3 μs (30 kHz). In this case, in the present embodiment, adjustment is performed as follows so that the reference clock CLK from the oscillation unit OSC_BLK is 1.92 MHz (0.52 μs).

  First, in an initial stage, the reference clock CLK from the oscillation unit OSC_BLK operates at an initial setting frequency based on an initial setting value (for example, a trimming value) of the frequency setting signal TR_OSC1, and TRcal is measured using this CLK. . At this time, if CLK is an oscillation frequency of 1.92 MHz, the value of the TRcal counter obtained by counting TRcal by CLK should indicate 64. Here, if the relationship between the oscillation frequency of the frequency setting signal TR_OSC1 and the CLK in the oscillation unit OSC_BLK is linear (proportional) as shown in FIG. 2B, the TRcal counter value is calculated from the measured TRcal counter value as 64. That is, the set value of TR_OSC1 for setting CLK to 1.92 MHz can be easily calculated.

  For example, if the TRcal counter indicates 40 when the initial setting value of the frequency setting signal TR_OSC1 is 32, from 32 × 64/40 = 51, if TR_OSC1 is set to 51, CLK is set to 1.92 MHz. It should be. If CLK can be set to 1.92 MHz, an LF of 640 kHz can be easily obtained by dividing this by 3, and a reply can be sent to the reader / writer using this LF.

  As another example, it is assumed that LF = 533 kHz (1.88 μs) is set by TRcal = 40 μs (25 kHz). In this case, in this embodiment, adjustment is performed so that the reference clock CLK from the oscillation unit OSC_BLK is 1.62 MHz (0.62 μs). That is, the TRcal counter value is adjusted to 1.62 MHz, which is an oscillation frequency at which the value is 64. First, when the reference clock CLK from the oscillating unit OSC_BLK is operating at the initial setting frequency based on the initial setting value “32” of TR_OSC1 as in the case of LF = 640 kHz, the measurement result of TRcal (= 40 μs). The value of the TRcal counter becomes 48. Therefore, from 32 × 64/48 = 43, if TR_OSC1 is set to 43, CLK should be set to 1.62 MHz. If CLK can be set to 1.62 MHz, an LF of 533 kHz can be easily obtained by dividing this by 3, and a reply can be sent to the reader / writer using this LF.

  Here, the case where mode A is used has been described, but the case where mode B is used can also be realized based on the same concept. In the case of mode B, in principle, the reference clock CLK may be set to an oscillation frequency such that the TRcal counter is 8. For example, when the initial setting value of TR_OSC1 is “32” and the TRcal counter under this condition is “X”, TR_OSC1 obtained by 32 × 8 / X is set, and the reference clock CLK by this setting is returned as it is. What is necessary is just to use as a clock timing for. However, under this condition, the value of the TRcal counter is too low and the frequency setting accuracy of the reference clock CLK may be insufficient. In this case, for example, the reference clock CLK may be set to an oscillation frequency such that the TRcal counter becomes 16, and the reference clock CLK may be divided by two to generate the clock timing for the reply operation. As described above, the combination of the value of the TRcal counter and the frequency division ratio can be changed as necessary.

  As described above, the RFID tag according to the present embodiment generates the reference clock CLK having a different oscillation frequency according to TRcal which is a designation signal of the communication speed LF from the reader / writer, and divides the CLK ( In some cases, the clock timing for reply is obtained (without frequency division). On the other hand, the RFID tag in the prior art sets a different counter value according to TRcal which is a designation signal of the communication speed LF from the reader / writer, and counts a reference clock with a fixed oscillation frequency based on this counter value. This is a method for obtaining a clock timing for reply. For example, the following effects can be obtained by using the RFID tag of the present embodiment due to the difference in the method.

  (1) Since the accuracy of the communication speed LF can be increased by increasing the number of bits of the frequency setting signal TR_OSC1 (that is, the frequency setting resolution), the accuracy can be improved with lower power consumption than in the conventional method. Is possible. That is, in the conventional method, since the accuracy is ensured by increasing the oscillation frequency, it is necessary to use a reference clock having a fixed frequency of, for example, 3.5 MHz or more, and power consumption increases accordingly. On the other hand, in the system of the present embodiment, the accuracy is essentially independent of the magnitude of the frequency, and the accuracy is determined depending on what frequency step size can be adjusted to, for example, 1.92 MHz or 1.62 MHz. Therefore, a frequency lower than that of the conventional method can be used, and power consumption can be reduced. Basically, the current consumption does not increase as the number of bits increases.

  (2) Since the return clock timing is obtained by using frequency division (in other words, the reference clock CLK is multiplied by the return clock timing), the circuit configuration is simplified. That is, in the conventional method, for example, a clock generation circuit that counts with a reference clock having a fixed oscillation frequency and outputs a signal when the count value reaches an arbitrary count value is required. In the example, a circuit corresponding to this can be realized by a divide-by-3 circuit.

  By the way, when the method described with reference to FIG. 2 is used, if a very low communication speed LF is set, the frequency of the reference clock CLK becomes very low, and the frequency setting accuracy of CLK is substantially reduced accordingly. It is expected that it will drop too much. That is, according to the oscillation characteristics as shown in FIG. 2B, the lower the frequency of the reference clock CLK, the greater the rate of change from the frequency corresponding to TR_OSC1 = Y to the frequency corresponding to TR_OSC1 = Y + 1. The accuracy of is reduced. In such a case, for example, the process shown in FIG. 3 may be performed. FIG. 3 is a flowchart showing an operation example of communication speed control performed by the logic unit in the RFID tag of FIG.

  In FIG. 3, first, the logic unit LOG measures TRcal and calculates the TR_OSC1 value as described in FIG. 2 (S301, S302). Here, the logic unit LOG determines that the measured value of TRcal or the calculated value of TR_OSC1 is very small and smaller than a predetermined set value (that is, the transmission frequency (communication speed LF) is too low) (S303). ), The communication speed LF is set using the conventional method (S305). That is, for example, a trimming value is set in TR_OSC1, and the communication speed LF is set by reflecting the TRcal counter value measured in S301 in the reference clock CLK in this state. Conversely, if the transmission frequency is equal to or higher than the set value in S303, the communication speed LF is set using the method of the present embodiment shown in FIG. 2 (S304).

  In S305, when the conventional method is used, it is intended for the case where the communication speed LF is low, so that sufficient accuracy can be maintained even if the oscillation frequency using the trimming value is set to be somewhat low. Further, depending on the specification of the setting range of the communication speed LF, there is a case where switching between the method of the present embodiment and the conventional method may not be performed.

  FIG. 4 is a sequence diagram illustrating an example of part of communication processing performed between the reader / writer and the RFID tag. When starting communication, first, the reader / writer RW turns on the radio wave (RF). At this time, the RFID tag TG operates by converting this radio wave into electric power by the rectifier circuit RCT, and the logic unit LOG or the like starts a startup sequence and reads a trimming value from the memory unit (EEPROM). The oscillating unit OSC_BLK operates at a default frequency immediately after start-up, but oscillates at a frequency determined by the trimming value after the read trimming value is set via the logic unit LOG. As the trimming value, a value that reflects the correction of manufacturing variation and is convenient for data reception is selected.

  Next, the reader / writer RW performs a Select operation. This is an operation of selecting one TG from a plurality of RFID tags TG. EPC Gen2 can communicate with a plurality of TGs at a time. Therefore, it is necessary to select a TG to communicate with, and the operation is performed here. In practice, the RW confirms that there are a plurality of RNs 16 serving as responses to the later-described Query, and identifies the TG.

  Subsequently, the reader / writer RW transmits a signal called “Query”. The TRcal for defining the communication speed LF shown in FIG. 2 is a part of this Query, and the TRcal measurement and transmission setting value calculation (calculation of the frequency setting signal TR_OSC1) as described in FIG. 2 are performed at this time. To be done. TRcal can be set for each query, and the transmission setting value is recalculated for each query. Thereafter, the RFID tag TG returns a value of RN16, but changes the frequency immediately before transmission based on the transmission setting value calculated above. By this frequency change, transmission can be performed at an expected transmission frequency. When transmission is completed, the frequency is immediately returned to the trimming value.

  Thereafter, communication is performed by changing the frequency to the transmission setting value described above only at the time of transmission. In the example of FIG. 4, after the transmission of RN16, the RFID tag TG receives the ACK from the reader / writer RW by switching to the trimming value, switches to the transmission set value, transmits “PC + EPC + CRC16”, and switches to the trimming value again. Query Rep is received from the reader / writer RW. The RN 16 is a 16-bit random number generated by the RFID tag TG, and is used to identify a plurality of TGs. ACK is a signal for confirming that communication from the RFID tag TG has been normally received. PC is a signal defining the number of words, EPC is a number given by the EPC standard, and CRC16 is an error correction code. The Query Rep is a signal indicating that the Query is correctly terminated and actual processing is started.

  As described above, by setting the frequency based on the transmission set value only at the time of transmission and setting the frequency based on the trimming value at the time of reception, it becomes possible to perform transmission and reception stably. In other words, if the method described in FIG. 2 is used, the reference clock also becomes a very low value when the communication speed LF is set to a very low value, so that in some cases, the next received data can be received. There is a risk of disappearing. Since accuracy at the time of transmission is not required at the time of reception, such a situation can be surely prevented by using a trimming value at the time of reception as shown in FIG. Depending on the specification of the setting range of the communication speed LF, such switching may not be performed.

  FIG. 5 is a block diagram showing a detailed configuration example of a part of the logic unit and the oscillation unit in the RFID tag of FIG. The oscillation unit OSC_BLK includes a bias circuit BIAS, a frequency setting circuit FRQ_ST, and an oscillation circuit OSC1. The bias circuit BIAS generates reference currents IREF1 to IREF3. The frequency setting circuit FRQ_ST receives IREF1 and IREF2 and the frequency setting signal TR_OSC1 from the logic unit LOG, and outputs a frequency setting voltage PBIAS having a voltage value corresponding to the value of TR_OSC1. The oscillation circuit OSC1 receives the reference voltage BGR04 from the PBIAS and IREF3 and the reference level generation circuit REF of FIG. 1, performs an oscillation operation, and outputs a reference clock CLK.

  The logic unit LOG includes a counter unit CUNT_TRcal, a transmission set value calculation unit CALC, a selection unit SEL, and the like. These can be realized by a dedicated circuit, for example, or by program processing using a processor or the like. As described with reference to FIG. 2, the counter unit CUNT_TRcal counts the cycle of TRcal using the reference clock CLK from the oscillation circuit OSC1 when the setting signal TRcal for the communication speed LF is input. The transmission setting value calculation unit CALC uses the count value of CUNT_TRcal to calculate the value of TR_OSC1 according to the communication speed LF as described in FIG.

  The selection unit SEL selects one of the TR_OSC1 value calculated by CALC, the trimming value read from the memory unit (EEPROM), and the default value of TR_OSC1, and outputs the selected value to the frequency setting circuit FRQ_ST. In this selection, for example, a state machine realized by a dedicated circuit or program processing is used, and this state machine identifies the transmission or reception timing based on the communication protocol as shown in FIG. The selection unit SEL is controlled according to the above.

  FIG. 6 is a circuit diagram showing a detailed configuration example of the frequency setting circuit in the oscillation unit of FIG. The frequency setting circuit FRQ_ST shown in FIG. 6 has a source connected to the power supply voltage VDD, a PMOS transistor MP1 that outputs the frequency setting voltage PBIAS from the commonly connected gate and drain, and a drain between the drain of the MP1 and the ground voltage GND. The configuration includes a plurality of current sources IS0 to IS6 connected in parallel. Each of IS1 to IS6 can be individually controlled to be turned on / off by a frequency setting signal TR_OSC1, and IS0 is always on.

  Each of IS0 to IS6 includes, for example, an NMOS transistor that is biased based on IREF1 and sets a current value by a gate width W, and an NMOS transistor that is connected in series to the NMOS transistor and functions as a switch. The NMOS transistor functioning as this switch is controlled by TR_OSC1 (however, the NMOS transistor corresponding to IS0 is always on) and is configured to operate in a linear region using IREF2 or the like. As a result, the current source IS is strong against changes in the power supply voltage.

  The NMOS transistors for setting the current value correspond to IS0, IS1, IS2, IS3, IS4, IS5 and IS6, and the ratio of the gate width W is 1, 1, 2, 4, 8, 16, 32. Yes. Therefore, by combining connection / disconnection of IS1 to IS6, a variable current source capable of adjusting the current value in 64 steps can be realized, and accordingly, 64 steps of PBIAS can be set. In order to further increase the frequency setting accuracy, the TR_OSC1 bit is increased, and the current source IS may be added accordingly.

  FIG. 7 is a circuit diagram showing a detailed configuration example of the oscillation circuit in the oscillation unit of FIG. FIG. 8 is an explanatory diagram showing the operation of the oscillation circuit of FIG. Since the oscillation circuit OSC1 oscillates based on the PBIAS generated in FIG. 6, it is possible to maintain a stable frequency against fluctuations in the power supply voltage due to noise or the like. The oscillation circuit OSC1 illustrated in FIG. 7 includes a set / reset flip-flop circuit SRFF, a comparison circuit CMP_BLK, a time constant generation circuit TGEN, and the like. The SRFF outputs a reference clock CLK by alternately receiving a set input and a reset input from CMP_BLK. TGEN stores a variable current determined by PBIAS in a capacitor, and CMP_BLK outputs a set input and a reset input when the voltage of the capacitor reaches a certain level. Thus, CLK having a frequency proportional to the magnitude of the current set by PBIAS is generated. Since the current set by PBIAS is proportional to the set value of TR_OSC1 as shown in FIG. 6, the oscillation frequency of CLK is proportional to the set value of TR_OSC1.

  More specifically, as shown in FIG. 8, the function and operation of each circuit are as follows. First, due to PBIAS, a current having a magnitude set by PBIAS flows through the PMOS transistor MP2 in TGEN. When CLK is 'H', the PMOS transistor MP3 is turned on and the NMOS transistor MN1 is turned off. Therefore, the current of MP2 is stored in the capacitor C1 via MP3, and the voltage RAMP1 of C1 rises at a constant rate. When the voltage of RAMP1 exceeds a preset reference voltage BGR04, CMP_BLK operates and one output signal CMP1 falls. When CMP1 falls, SRFF is inverted and CLK becomes ‘L’. Along with this, MP3 is turned off and MN1 is turned on, and RAMP1 falls substantially to the ground voltage GND level.

  When RAMP1 falls, the PMOS transistor MP4 in the TGEN is turned on and the NMOS transistor MN2 is turned off. As a result, the current of MP2 is stored in the capacitor C2, and this time the voltage RAMP2 of C2 is changed. It rises at a certain rate. As in the case of RAMP1, when RAMP2 exceeds BGR04, CMP_BLK operates and the other output signal CMP2 falls. When CMP2 falls, SRFF is inverted and CLK becomes ‘H’. In this way, CLK1 having a constant frequency is obtained by CMP1 and CMP2 falling alternately.

  FIG. 9 is a circuit diagram showing a configuration example in which the frequency setting circuit of FIG. 6 and the oscillation circuit of FIG. 7 are modified. 6 and FIG. 7 described above, the configuration example in which the setting value of the frequency setting signal TR_OSC1 and the oscillation frequency of the reference clock CLK have a proportional relationship is shown, but in FIG. 9, the setting value of TR_OSC1 and the oscillation period of CLK Shows a configuration example in which is proportional.

  9, in addition to the comparison circuit CMP_BLK and the set / reset flip-flop circuit SRFF similar to those in FIG. 7, the oscillation unit OSC_BLK2 has the same functions as the time constant generation circuit TGEN in FIG. 7 and the frequency setting circuit FRQ_ST in FIG. A time constant generation circuit TGEN2 is provided. In TGEN2, the current flowing through the PMOS transistor MP2a is set by the current source ISr, and this current is stored in a plurality of capacitors via the PMOS transistor MP3a or MP4a. Then, which of the plurality of capacitors is connected to the MP3a or MP4a can be set by the frequency setting signal TR_OSC1.

  In the example of FIG. 9, four capacitors C11a to C14a and C11b to C14b are provided for each of MP3a and MP4a, and the capacitance ratios of C11, C12, C13, and C14 are 1, 2, 4, and 8, respectively. The connection / disconnection of these four capacitors can be individually set by the frequency setting signals TR_OSC1_0 to TR_OSC1_3. Although omitted in FIG. 9, if a default capacity is provided when all four capacitors are not connected, the capacitance value can be adjusted in 16 steps by the combination of connection / disconnection of the four capacitors. Variable capacity can be realized.

When such a configuration is used, the rise time of the voltage RAMP1a of the capacitors C11a to C14a and the voltage RAMP2a of the capacitors C11b to C14b becomes longer each time the number of capacitors to be connected is increased, and the oscillation frequency of the reference clock CLK is accordingly increased. Become slow. When the configuration examples of FIG. 6 and FIG. 7 described above are used, TR_OSC1 after adjustment becomes TR_OSC1 initial value × 64 / TRcal counter. TR_OSC1 = TR_OSC1 initial value × TRcal counter / 64 (however, in the example of FIG. 9, 16 instead of 64). As described above, the ²ⁿ number of 64 is included in the numerator, but the current consumption of the oscillation unit may increase, but the circuit can be further simplified. Further, high accuracy can be easily realized because the number of capacitors need only be increased.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

  The contactless electronic device according to the present invention is a technology that is particularly useful when applied to an RFID tag in the UHF band capable of setting a communication speed, and is not limited to this, and is widely applicable to RFID tags in general and contactless electronic devices in general. Applicable.

1 is a block diagram showing an example of the configuration of an RFID tag according to an embodiment of the present invention. In the RFID tag of FIG. 1, the operation | movement outline | summary of the communication speed control which the oscillation part and a logic part perform is shown, (a) is a wave form diagram which shows an example of the various processing content accompanying communication speed control, (b) is It is a figure which shows the example of a characteristic of an oscillation part. FIG. 2 is a flowchart showing an operation example of communication speed control performed by the logic unit in the RFID tag of FIG. 1. It is a sequence diagram which shows an example of a part of communication process performed between a reader / writer and an RFID tag. FIG. 2 is a block diagram illustrating a detailed configuration example of a part of the logic unit and an oscillation unit in the RFID tag of FIG. 1. FIG. 6 is a circuit diagram illustrating a detailed configuration example of the frequency setting circuit in the oscillation unit of FIG. 5. FIG. 6 is a circuit diagram illustrating a detailed configuration example of the oscillation circuit in the oscillation unit of FIG. 5. It is explanatory drawing which shows operation | movement of the oscillation circuit of FIG. FIG. 8 is a circuit diagram illustrating a configuration example in which the frequency setting circuit of FIG. 6 and the oscillation circuit of FIG. 7 are modified.

Explanation of symbols

TG RFID tag ANT antenna LA, LB terminal RCT rectifier circuit CLP clamp circuit ASK modulation / demodulation circuit REF reference level generation circuit OSC_BLK oscillation unit LOG logic unit CLK reference clock TR_OSC frequency setting signal DAT data VREF reference potential IREF reference current ST Circuit OSC oscillation circuit CUNT_TRcal counter unit CALC transmission set value calculation unit SEL selection unit PBIAS frequency setting voltage BGR04 reference voltage IS current source MP PMOS transistor MN NMOS transistor C capacitance TGEN time constant generation circuit CMP_BLK comparison circuit SRFF set reset flip-flop circuit

Claims (11)

A non-contact electronic device that receives a first signal transmitted from an external device by radio and sends a reply to the external device at a communication speed specified by the first signal,
The first signal has a frequency proportional to or inversely proportional to the communication speed,
The non-contact electronic device generates a reference clock having a frequency proportional to or inversely proportional to a frequency setting value, and the frequency setting value such that a value obtained by counting the first signal with the reference clock becomes a predetermined setting value. And a reply to the external device using a reference clock reflecting the calculated frequency setting value. The contactless electronic device according to claim 1.
When receiving various signals from the external device, the frequency setting value is set to a fixed value set in advance, and reception is performed using a reference clock reflecting the fixed value. The contactless electronic device according to claim 1.
If the communication speed when sending a reply to the external device is slower than a preset communication speed, the frequency setting value is set as a fixed value, and a reference clock that reflects this fixed value is used. A non-contact electronic device characterized by performing a reply. The contactless electronic device according to any one of claims 1 to 3,
The non-contact electronic device is an RFID tag using a UHF band. A non-contact electronic device that receives a first signal transmitted from an external device by radio and sends a reply to the external device at a communication speed specified by the first signal,
The first signal has a frequency proportional to or inversely proportional to the communication speed,
The non-contact electronic device is:
An oscillation unit that generates a reference clock having a frequency proportional to or inversely proportional to the frequency setting value;
A control unit for controlling the oscillation unit,
The controller is
First means for counting the first signal using a reference clock in a state where a first value is set to the frequency setting value;
Using the count number obtained by the first means and the first value, a frequency setting value for converting the count number to a second value set in advance is calculated by conversion, and a third result which is the calculation result A second means for setting a value in the oscillating unit;
And a third means for generating a timing when a reply is made to the external device using a reference clock in which the third value is reflected. The contactless electronic device according to claim 5.
The non-contact electronic device according to claim 3, wherein the third means generates a timing when a reply is made to the external device by dividing the reference clock reflecting the third value. The contactless electronic device according to claim 5.
The non-contact electronic device according to claim 1, wherein the control unit further includes fourth means for setting the frequency setting value to a preset trimming value when receiving various signals from the external device. The contactless electronic device according to claim 5.
The control unit further includes:
A fifth means for determining whether the communication speed identified by the count number obtained by the first means or the third value obtained by the second means is faster or slower than a preset communication speed;
In the fifth means, when the communication speed is slower than a preset communication speed, the frequency setting value is set as a preset trimming value, and the reference clock reflecting the trimming value and the first means are obtained. And a sixth means for generating a timing for sending a reply to the external device using the count number. The contactless electronic device according to claim 5.
The oscillation unit is
A frequency setting circuit that generates a current that is variable according to the frequency setting value;
A non-contact electronic device comprising: an oscillation circuit that charges a capacitor with the current generated by the frequency setting circuit and oscillates at a frequency corresponding to a charging time of the capacitor. The contactless electronic device according to claim 5.
The oscillation unit is
A constant current source;
A variable capacitor whose capacitance value is variable according to the frequency setting value;
A non-contact electronic apparatus comprising: an oscillation circuit that charges the variable capacitor with a current of the constant current source and oscillates at a frequency corresponding to a charging time of the variable capacitor. The contactless electronic device according to any one of claims 5 to 10,
The non-contact electronic device is an RFID tag using a UHF band.

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