RFID INTERROGATOR DEVICE

• US 20080024280A1
• Filed: 07/24/2007
• Published: 01/31/2008
• Est. Priority Date: 07/28/2006
• Status: Active Grant

• Current Assignee: Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Kato, Masakazu
• Granted Patent: US 8,077,010 B2
• Time in Patent Office: Days
• US Class Current: 340/10.3
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

RFID interrogator device carries out an automatic gain control when an RF signal from RFID tag with a backscatter radio-communication is received. To carry out the automatic gain control, amplitude of the reception signal is measured within a prescribed time corresponding to a length of preamble added to the head of data of the RF signal. An AGC value is determined based on the measured amplitude value.

Claims

1. An RFID interrogator device, having a reader function, which conducts a backscatter radio-communications with an RFID tag, utilizing absorption and reflection of radio wave, comprising:

a transmission section configured to transmit a command to the RFID tag, the transmission section also transmitting a continuous radio wave with no modulation to the RFID tag to enable the RFID tag to carry out the backscatter radio-communications;

a reception section configured to receive an RF signal from the RFID tag with the backscatter radio-communications to obtain a reception signal, the reception section having a variable gain amplifying function;

an automatic gain control section configured to measure an amplitude of the reception signal within a prescribed time after a predetermined time Ta has passed from the completion of the transmission of the command to the RFID tag; and

a control section configured to make the reception section execute the variable gain amplitude function based on the measured amplitude value to modify the amplitude of the reception signal to a desired level.

2. The device according to claim 1, wherein the predetermined time Ta is less than a time period T1 from the completion of the reception of the command by the RFID tag to the commencement of the transmission of the RF signal by the RFID tag.

3. The device according to claim 2 further including a table indicating a relationship between an amplitude value of the reception signal measured by the automatic gain control section and a desired level to be used in the variable gain amplifying function by the reception section to determine the desired level from the table based on a maximum amplitude value that the automatic gain control section has measured.

4. The device according to claim 2, wherein the RF signal from the RFID tag includes a preamble and, the prescribed time that the automatic gain control section carries out the measurement corresponds to the length of the preamble of the RF signal.

5. The device according to claim 4, wherein the automatic gain control section sets a predetermined first AGC value when the automatic gain control section carries out its measurement and determines a second AGC value based on the measured amplitude value of the reception signal.

6. The device according to claim 5, wherein the automatic gain control section includes a determining function for determining whether the measured amplitude value exceeds a target value and changes the predetermined first AGC value to the second AGC value when the measured amplitude value exceeds the target value to carry out further measurement whereby making the reception section execute the variable gain amplifying function based on the further measured amplitude value.

7. The device according to claim 6, wherein the automatic gain control section includes a determining function for determining whether the measured amplitude value exceeds a target value, the automatic gain control section changing the predetermined first AGC value to the second AGC value less than the first AGC value when the measured amplitude value exceeds the target value.

8. The device according to claim 7 further including a table indicating a relationship between an amplitude value of the reception signal measured by the automatic gain control section and a desired level to be used in the variable gain amplifying function by the reception section to determine the desired level from the table based on a maximum amplitude value that the automatic gain control section has measured.

9. The device according to claim 5, wherein the automatic gain control section includes a determining function for determining whether the measured amplitude value exceeds a target value and changes the predetermined first AGC value to the second AGC value less than the first AGC value when the measured amplitude value exceeds the target value.

10. The device according to claim 1, wherein the RF signal from the RFID tag includes a preamble which is used when the automatic gain control section measures an amplitude of the reception signal.

11. The device according to claim 10, wherein the command from the transmission section includes one of a write operation related command and a read operation related command and the device further includes a discriminating section configured to discriminate the write operation related command or the read operation related command when transmitting the command to the RFID tag.

12. The device according to claim 11 further including:

a write function configured to transmit the write operation related command to the RFID tag through the transmission section; and

a memory configured to store therein an AGC value that is determined based on the measured amplitude value and is set in the reception section when the reception section receives the reception signal from the RFID tag responding to the read operation related command from the transmission section,

wherein the AGC value, that is stored in the memory just before the write operation related command is transmitted, is read out from the memory and is set in the reception section when the reception section receives the RF signal from the RFID tag responding to the write operation related command from the transmission section.

13. The device according to claim 1, wherein the automatic gain control section includes a determining function for determining whether the measured amplitude value exceeds a target value, the automatic control section changing a predetermined AGC value when the measured amplitude value exceeds the target value to execute further measurement of the amplitude of the reception signal for the predetermined time and controlling the variable gain amplifying function of the reception section based on the measured amplitude value of the further measurement.

14. An RFID interrogator device which conducts a backscatter radio-communication with an RFID tag, utilizing absorption and reflection of radio wave, comprising:

a transmission section configured to transmit a command to the RFID tag;

a quardrature demodulator configured to demodulate the RF signal from the RFID tag to obtain a base band signal;

a variable gain amplifier configured to amplify the base band signal from the demodulator to a desired level; and

a controller configured to control the operation of the variable gain amplifier and to measure an amplitude of the base band signal within a prescribed time after a predetermined time Ta has passed from the completion of the transmission of the command to the RFID tag to automatically control the operation of the variable gain amplifier based on the result of the measurement.

15. The device according to claim 14, wherein the predetermined time Ta is less than a time period T1 from the completion of reception of the command by the RFID tag to the commencement of transmission of the RF signal by the RFID tag.

16. The device according to claim 14, wherein the controller changes a predetermined AGC value to execute further measurement of amplitude of the base band signal for the predetermined time when the measured amplitude value exceeds a target value and controls the operation of the variable gain amplifier based on the measured amplitude value of the further measurement.

17. The device according to claim 16, wherein the controller changes the predetermined AGC value to an AGC value less than the predetermined AGC value when the measured amplitude value exceeds the target value.

18. The device according to claim 16, wherein the RF signal from the RFID tag includes a preamble which is used when the controller measures amplitude of the base band signal demodulated from the RF signal.

19. The device according to claim 14, wherein the command from the transmission section includes one of a write operation related command and a read operation related command, and the device further includes:

a write function configured to transmit the write operation related command to the RFID tag through the transmission section; and

a memory configured to store therein an AGC value that is determined based on the measured amplitude value and is set in the variable gain amplifier when the variable amplifier amplifies the base band signal obtained from the RF signal that is transmitted from the RFID tag responding to the read operation related command from the transmission section,

wherein the AGC value, that is stored in the memory just before the write operation related command is transmitted, is read out of the memory and is set in the variable gain amplifier when the variable amplifier amplifies the base band signal obtained from the RF signal that is transmitted from the RFID tag responding to the write operation related command from the transmission section.