Method and Device for Suppressing a Transmitting Signal in a Receiver of an RFID Write/Read Unit

• US 20070194887A1
• Filed: 04/05/2007
• Published: 08/23/2007
• Est. Priority Date: 10/08/2004
• Status: Active Grant

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: Elektrobit Wireless Communications OY (Bittium Oyj)
• Inventors: Kung, Roland
• Granted Patent: US 7,456,747 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• 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
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

A method and apparatus is disclosed for operating an RFID read/write unit with transmitting signal suppression. The RFID read/write unit comprises a radio frequency part including a transmitter and a receiver, and a baseband part based on digital signal processing. The method involves producing an amplitude and phase weighted copy of a transmitting signal, namely a compensation signal, with the baseband part. After linear modulation of the compensation signal, a resultant signal at an input of the receiver is subtracted in an addition stage from a spurious coupling signal. The transmitting signal has an auxiliary signal impressed upon a carrier signal from the RFID read/write unit with a frequency offset fd, for the purpose of processing without any DC voltage in the receiver downstream of an RX converter. The input of the receiver comprises a turn-on and turn-off attenuation element which protects the radio frequency part.

Claims

1. A method for operating an RFID read/write unit with transmitting signal suppression, the method comprising:

providing the RFID read/write unit, the RFID read/write unit comprising a radio frequency part including a transmitter and a receiver, and a baseband part based on digital signal processing;

producing an amplitude and phase weighted copy of a transmitting signal, namely a compensation signal, with the baseband part; and

after linear modulation of the compensation signal, subtracting in an addition stage a resultant signal at an input of the receiver from a spurious coupling signal between the transmitter and the receiver, the transmitting signal having an auxiliary signal impressed upon a carrier signal from the RFID read/write unit with a frequency offset fd, for the purpose of processing without any DC voltage in the receiver downstream of an RX converter;

wherein the input of the receiver comprises a turn-on and turn-off attenuation element which, when turned on, protects the radio frequency part against overdrive or against intermodulation in the RX converter so that weights can be ascertained for the copy of the transmitting signal and direct rejection of the coupling signal is achieved, the attenuation element subsequently being turned off and the RFID read/write unit changing to an operating mode and performing permanent readjustment of the transmitting signal suppression.

2. The method as claimed in claim 1, wherein the carrier signal is amplitude modulated with a small swing or a sideband signal added, wherein the transmitter produces the auxiliary signal at the frequency offset fd from the carrier signal and wherein the auxiliary signal appears in the receiver downstream of the direct RX converter as an AC signal at frequency fd and is detected in amplitude and phase relative to the auxiliary signal transmitted by the baseband part, with the aim of ascertaining the weights to reach transmitting signal suppression of the carrier signal.

3. The method as claimed in claim 1, wherein the RFID read/write unit shifts the frequency of the carrier signal by fd for a short time in order to measure the amplitude and phase of the auxiliary signal, such that the weights are ascertained for the purpose of rejecting the carrier signal on the actual transmission frequency, and when the weights have been ascertained the RFID read/write unit operates on its original frequency.

4. The method as claimed in claim 1, wherein the modulating auxiliary signal is implemented digitally in the baseband part and is then shifted to the radio frequency domain by means of a TX converter, and is amplified, and wherein the amplitude and phase weighted copy of the transmitting signal is likewise produced digitally in the baseband part and is shifted to the radio frequency domain by means of a linear modulator such that all the amplitude and phase relationships between the transmitting signal and the compensation signal are determined computationally by the signal processor and that the weighted copy of the transmitting signal can be turned on and off in order to be able to calculate direct rejection of the coupling signal.

5. The method as claimed in claim 1, wherein the auxiliary signal is modulated with a pseudo random sequence such that the spectrum of the auxiliary signal from the one, first RFID read/write unit for an electronic tag and a further, second RFID read/write unit appears as a weak noise signal and can be detected only by the one, first RFID read/write unit, which knows the sequence.

6. The method as claimed in claim 5, wherein correlation properties of pseudo random sequences are used in order also to isolate reflected and hence delayed signals from a coupling signal between a reception antenna and a transmission antenna and hence to allow them to be measured and compensated, for the purpose of increasing the sensitivity of the first RFID read/write unit.

7. The method as claimed in claim 1 wherein other forms of the auxiliary signal are also produced which are altered in frequency fd and are added as a single sideband signal to the carrier signal from the read unit in order to pick up a frequency response.

8. The method as claimed in claim 1, wherein when a frequency hopping method is applied the weights for each frequency are stored in a memory in a signal processor, in order to retrieve stored starting values for compensation upon repeat use of the same frequency.

9. An apparatus for transmitting signal suppression, the apparatus comprising:

an RFID read/write unit, the RFID read/write unit comprising a radio frequency part and baseband part;

wherein the radio frequency part includes a transmitter and a receiver;

wherein the baseband part is based on digital signal processing and is configured to produce an amplitude and phase weighted copy of a transmitting signal, namely a compensation signal;

wherein, after linear modulation of the compensation signal, the receiver is configured to subtract a resultant signal delivered to an input of the receiver from a spurious coupling signal between the transmitter and the receiver, the transmitting signal having an auxiliary signal impressed upon a carrier signal from the RFID read/write unit with a frequency offset fd, for the purpose of processing without any DC voltage in the receiver downstream of an RX converter;

a turn-on and turn-off attenuation element provided in the receiver, wherein the attenuation element, when turned on, is configured to protect the radio frequency part against overdrive or against intermodulation in the RX converter so that weights can be ascertained for the copy of the transmitting signal and direct rejection of the coupling signal is achieved, and wherein, when the attenuation element is subsequently turned off, the RFID read/write unit changes to an operating mode and performs permanent readjustment of the transmitting signal suppression.

10. The apparatus of claim 9 wherein the carrier signal, the auxiliary signal and the compensation signal are implemented in the baseband part, and wherein the radio frequency part is constructed from linear basic blocks.

11. The apparatus as claimed in claim 10, wherein compensation for a number of coupling paths is made through at least one multiple implementation in order to produce weighted copies of the transmiting signal in the baseband part.