1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device and an IC tag for transmitting/receiving data in radio communication with a reader/writer.
2. Description of the Related Art
Recently in physical distribution management at factories and in stock control at retail stores, RFID (Radio Frequency IDentification) technology is receiving attention. This is a technology for attaching a tag having an IC, in which the identification information on a product is written, to the product and reading the information by radio antenna.
For this technology, a reader/writer and a tag for RFID (hereafter called IC tag) are used. The reader/writer is for transmitting modulated radio signals including data and carrier to an IC tag, and receiving the radio signals transmitted from the IC tag. The IC tag demodulates the received radio signals, and executes processing based on the received data. The IC tag also transmits the reply to the received data to the reader/writer. Here the IC tag is an IC chip and an antenna which are integrated, for example.
Among IC tags, an IC tag called a passive type receives radio signals from the reader/writer and the power supply voltage is generated by these radio signals (see Udo Karthaus, et al, “Fully Integrated Passive UHF RFID Transponder IC with 16.7-μW Minimum RF Input Power”, IEEE Journal of Solid-State Circuits, Vol. 38, No. 10, October 2003, pp. 1602-1608). In other words, in the case of a passive type IC tag, the radio signals used for communication with the reader/writer are used for supplying power and transmitting/receiving data.
In this series of operations, the data transmitted from the IC tag to the reader/writer is data in which the identification information is binarized. When this data is transmitted to the reader/writer, a signal called a sub-carrier may be used to guarantee the demodulation of data at the reader/writer side. In other words, the radio signals which are transmitted from the IC tag to the reader/writer are not only the carrier and data, but may have a sub-carrier, that is signals of which frequency is lower than the carrier, superimposed.
Conventionally signals corresponding to the sub-carrier are generated by a divider installed in the IC tag. In other words, the carrier received from the reader/writer is divided, and signals having a frequency lower than that of the carrier are generated.
However as the frequency of the carrier increases, the size of the divider for generating the necessary frequency also increases, and it is becoming difficult to generate signals corresponding to the sub-carrier by dividing the carrier in the IC tag. Also an increase in size of the divider increases the power consumption by the divider, and this increases the power consumed in the IC tag.
According to a first aspect of the invention a semiconductor device, comprises a receive circuit for generating receive data from received radio signals, a power supply voltage generation circuit for generating power supply voltage based on the received radio signals, a control circuit for performing logical processing based on the received data, a transmission circuit for generating radio signals including transmission data and transmitting the radio signals via an antenna and an oscillation circuit, which is operated using the power supply voltage generated by the power supply voltage generation circuit, for generating a predetermined frequency of clocks.
The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:
The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed.
Embodiments of the present invention will now be described with reference to the drawings.
The reader/writer 2 is a device which transmits the modulated radio signals, including the data and carrier (2.45 GHz), to the IC tag 1, and receives the radio signals transmitted from the IC tag 1.
The IC tag 1 demodulates the received radio signals and executes processing based on the received data included therein. The IC tag 1 transmits a reply to the received data to the reader/writer 2. The IC tag 1 of the present embodiment is a passive type IC tag 1 which has no internal power supply, and where the IC chip 10 and the antenna are integrated.
As described above, the IC tag 1 transmits the radio signals, including the reply to the received data as data, to the reader/writer 2. According to this embodiment, signals called a sub-carrier are superimposed on the radio signals for transmitting the data from the IC tag 1 to the reader/writer 2. First the sub-carrier in the present embodiment will be described.
In the present embodiment, when data is transmitted from the IC tag 1 to the reader/writer 2, the signals acquired by modulating the carrier based on the ASK (Amplitude Shift Keying) are transmitted. This ASK modulation is a type of amplitude modulation. If the frequency of the carrier is fc and the frequency of the data is fd, the frequency spectrum of the amplitude-modulated signals have distribution of which the peaks are fc (carrier), fc−fd (lower side band) and fc+fd (upper side band). When data is acquired from the modulation signals having a frequency in this frequency spectrum, data is acquired from the frequency band with fc−fd (or fc+fd) as a center based on the data. Therefore normally only frequency components corresponding to the distribution with fc−fd (or fc+fd) as a center are passed using such filters as LPF (or HPF), and data is demodulated.
Here the case when the frequency fd of the data is extremely low will be considered. In the frequency spectrum of amplitude-modulated signals in this case, the space between fc−fd and fc+fd becomes smaller since fd is a small value. In other words, the space between the lower side band and the upper side band becomes smaller. If the space between the lower side band and the upper side band becomes smaller, LPF (or HPF), for passing the signals with frequency components with the fc−fd (or fc+fd) as the center, must have a sharp characteristic as a filter. As this space becomes smaller, demodulating data with appropriately separating the lower side band and the upper side band becomes difficult.
With the foregoing in view, a signal called a sub-carrier is used if the frequency fd of the data is extremely lower than the frequency fc of the carrier. This is a signal having a frequency fs that can separate the lower side band and the upper side band of the frequency of the carrier.
If a sub-carrier is used, a first modulation signal acquired by modulating the sub-carrier is generated based on the data. Then a second modulation signal for modulating the carrier by this first modulation signal for transmission is generated. By this, the lower side band and the upper side band can be separated for certain when the data is demodulated, and data can be demodulated accurately.
The radio signals to be output from the IC tag 1 to the reader/writer 2 in this embodiment is data of the ASK-modulated carrier, and are radio signals having the above described sub-carrier component. The IC tag 1 to be used in this embodiment will now be described. This IC tag 1 modulates the sub-carrier by the data to be transmitted to the reader/writer 2, as described above, and modulates the carrier by this modulated sub-carrier.
This IC chip 10 comprises a receive circuit 11, power supply voltage generation circuit 12, transmission circuit 13, control circuit 14, storage circuit 15, oscillation circuit 16 and output circuit 17.
The receive circuit 11 is a circuit for generating receive data by demodulating the radio signals received by the antenna 20. In the receive circuit 11, reference clocks CLK for the control circuit 14 to operate are generated from the radio signals, and are supplied to the control circuit 14. The power supply voltage generation circuit 12 is a circuit for generating the power supply voltage from the radio signals received by the antenna. The transmission circuit 13 is a circuit for modulating the transmission data as the radio signals to be sent to the reader/writer 2. The control circuit 14 is a circuit for performing writing and reading for the storage circuit 15 and other logical processing according to a command received from the reader/writer 2. This control circuit 14 also includes a charge pump circuit for receiving clocks generated in the oscillation circuit 16, and generating voltages for writing data in the storage circuit 15, although this is not illustrated. The storage circuit 15 is a circuit comprised of a non-volatile memory, such as an EEPROM, for holding identification information and data sent from the reader/writer 2. The oscillation circuit 16 is a circuit comprised of a ring oscillator, for example, for generating predetermined frequency clocks (hereafter called sampling clocks CLKSAM), which are different from the above mentioned reference clocks CLK. These sampling clocks CLKSAM are used as the above mentioned sub-carrier, and are also supplied to the charge pump circuit which generates high voltage for writing data to the storage circuit 15. The frequency fs of the sampling clocks CLKSAM is determined based on the frequency fc of the carrier and the frequency of the data. In the present embodiment, the carrier is 2.45 GHz and the frequency of the data is about 20 KHz, so the frequency fs of this sampling clock CLKSAM is set to 400 KHz. The output circuit 17 generates pulses for modulation from the transmission data to be sent from the IC tag 1 to the reader/writer 2 and the sampling clocks CLKSAM, and outputs them to the transmission circuit 13.
Now the operation of the IC tag 1 constructed like this will be described. This IC tag 1 receives radio signals from the reader/writer 2 by the antenna 20. The received radio signals are input to the IC chip 10. In the receive circuit 11, the receive data and the reference clock CLK are acquired from the carrier and data included in the radio signals, and are output to the control circuit 14. The control circuit 14 performs reading and writing for the storage circuit 15 based on the received data, and outputs the transmission data to the output circuit 17 if there is data to be transmitted to the reader/writer 2.
In the output circuit 17, the sampling clocks CLKSAM are converted into pulses for modulation based on the transmission data, and are output to the transmission circuit 13. In the transmission circuit 13, the carrier is modulated based on the pulses for modulation by the later mentioned modulation circuit, to generate the ASK-modulation signals where the carrier, sub-carrier and data are superimposed. This signal is sent to the reader/writer 2 as a radio signal via the antenna 20.
The above mentioned series of operations of the IC tag 1 are performed by the power supply voltage generated by the power supply voltage generation circuit 12. The above mentioned sampling clocks are clocks generated by a free-running oscillator created in the oscillation circuit 16.
Now details on the transmission data format and the radio signals to be transmitted from the IC tag 1 to the read/writer 2 will be described.
In IC tag 1, data on individual information, for example, may have to be transmitted to the reader/writer 2 based on a command from the reader/writer 2. In this case, necessary transmission data Ds is read from the storage circuit 15 by the control circuit 14.
The transmission data Ds read here is encoded by the control circuit 14, using a method called Manchester encoding, and becomes Manchester-encoded transmission data Dsm.
In this way, the Manchester-encoded transmission data Dsm is serial data, and is input to the output circuit 17.
The output circuit 17 outputs the pulse for modulation PM acquired by determining the AND of the Manchester-encoded transmission data Dsm, and the sampling clocks CLKSAM (see
Here it is assumed that the amplitude of the carrier is A, and the amplitude of the portion of the carrier modulated by the pulses for modulation is B (see
As the above description shows, according to the IC chip 10 of the present embodiment, the transmission data Ds is Manchester-encoded (Dsm), and the pulses for modulation PM are acquired by modulating the sampling clock using this data Dsm. The carrier is then modulated by these pulses for modulation PM, and is transmitted as an ASK modulation wave (radio signals) to be transmitted from the IC tag 1. Therefore the radio signals to be transmitted from the IC tag 1 to the reader/writer 2 are radio waves where the transmission data, carrier and sub-carrier are superimposed.
Therefore if the transmission data Ds is demodulated from the radio signals transmitted from the IC tags 1 by the reader/writer 2, the data transmitted from the IC tag 1 has the frequency spectrum shown in
As described above, according to the present embodiment, the self-oscillating oscillation circuit 16 created in the IC chip 10 generates the sampling clocks CLKSAM corresponding to the sub-carrier. These sampling clocks CLKSAM are superimposed by the output circuit 17, and become the pulses for modulation PM. Also by transmitting the radio signals, where the carrier, sub-carrier and transmission data are superimposed, from the IC tag 1 by the modulation circuit, appropriate demodulation can be performed by the reader/writer 2 side.
Now the circuit for generating the sampling clocks CLKSAM corresponding to the sub-carrier according to the present embodiment will be described.
If a signal indicating “1” is input to the trimming terminal S1 here, the transistor T1 turns ON. Therefore the capacitor C1 is connected to the output node of the inverter I1. If a signal indicating “0” is input to the trimming terminal S1, on the other hand, the transistor T1 turns OFF. Therefore the capacitor C1 is not connected to the output node of the inverter I1. For the trimming terminals S2-S4 as well, the connection/disconnection of the capacitors C2-C4 is determined depending on the signal to be input to the trimming terminals S2-S4 respectively.
The ring oscillator shown in
Now the method thereof will be described. To make understanding easier, the case of S1=1, S2=0, S3=0, S4=0 is represented with “1000”, then in the case of the circuit shown in
This IC chip 10 has a memory address register in the storage circuit 15, and in the initial status, the address of the EEPROM which provides the combination of “1000”, for example, is stored in the trimming terminals S1-S4. At testing when the IC chip 10 is created, the oscillation frequency of the oscillation circuit 16 is measured with which the address shown in this memory address register is overwritten, then the oscillation frequency can be adjusted with an arbitrary combination for the trimming terminals S1-S4.
In the stage when the trimming started, the default address (e.g. address indicating “1000”) has been written in the memory address register (step S1). When trimming starts, the oscillation circuit starts oscillation and the oscillation frequency thereof is measured by the tester (step S2). The tester judges whether the measured oscillation frequency is in the tolerable range to be used as the sub-carrier (step S3).
If the measured frequency is in the tolerable range, it is regarded that the free-running oscillator in the IC chip 10 is oscillating at an accurate frequency, and the test is ended (step S4).
When the measured frequency is outside the tolerable range, the tester judges whether the measured frequency is higher or lower than the expected oscillation frequency in the tolerable range (step S5).
When the measured frequency is higher than the expected oscillation frequency, the tester decrements the address written in the memory address register by one, for example (step S6). The combination of S1-S4 written in the decremented address is a combination for decreasing the oscillation frequency of the oscillation circuit 16 one stage lower than the current oscillation frequency.
When the measured frequency is lower than the expected oscillation frequency, the tester increments the address written in the memory address register by one (step S7). The combination of signals S1-S4 written in the incremented address is a combination of increasing the oscillation frequency of the oscillation circuit 16 one stage higher than the current oscillation frequency.
By changing the address written in the memory address register, the oscillation circuit reads signals based on the data written in the new address of the storage circuit 15. Signals based on this data are supplied to the trimming terminals S1-S4 (step S7).
After the signals supplied to the trimming terminals S1-S4 change, the processing returns to step S2, and the tester measures the frequency oscillated by the oscillation circuit again.
Then this process is sequentially repeated, and when the measured frequency comes within the tolerable range, overwriting the content of the memory address register is ended, and trimming is completed.
Since overwriting of the register is ended when the oscillation frequency of the oscillation circuit comes into a range to be applied as the sub-carrier, the oscillation circuit 16 created in the IC chip 10 can operate as a circuit which has a stable oscillation frequency.
f=1/(2π61/2CR)
In other words, the oscillation frequency f is set by the capacitance value C and the resistance value R. So in the CR oscillation circuit of the present embodiment, the phase shift circuit of each stage is created to be the phase shift circuit shown in
As
In other words, the connection/disconnection of each capacitor C11-C13 and the resistors R21-R23 is determined by the potential applied to the trimming terminals S1-S6.
Just like the case of the ring oscillator shown in
Here the method for determining the signals to be supplied to the trimming terminals S1-S6 is very similar to the method in the ring oscillator shown in
As described above, according to this embodiment, the oscillation circuit 16 is installed inside the IC chip 10 of the IC tag 1, and the clock to be output by this oscillation circuit 16 is used as the sub-carrier, so transmission radio waves, that can be stably demodulated by the reader/writer, can be generated without installing a divider inside the IC chip 10.
In the above embodiment, using clocks generated by the oscillation circuit as the sub-carrier was described, but the clocks generated by the oscillation circuit can also be used as the clocks for the charge pump circuit which is used for writing the storage circuit.
The control circuit 14 does not operate the oscillation circuit based on the receive data unless data is written to the storage circuit or unless data is transmitted to the reader/writer, so that the power for the IC tag 1 to consume can be decreased.
It is apparent that the present invention is not limited to the above embodiment and it may be modified and changed without departing from the scope and spirit of the invention.
Number | Date | Country | Kind |
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2004-222599 | Jul 2004 | JP | national |