Radio frequency (wireless) communications systems are known in the art. Radio frequency communications systems typically include a transmitter and a receiver. Other communications systems are bidirectional and include a first transponder that can send or receive a radio frequency communication, and a second transponder that can receive the radio frequency communications from the first transponder and transmit signals, via radio frequency, back to the first transponder.
Radio frequency identification devices define another form of bidirectional communications systems. As large numbers of objects are moved in inventory, product manufacturing, and merchandising operations, there is a continuous challenge to accurately monitor the location and flow of objects. Additionally, there is a continuing goal to interrogate the location of objects in an inexpensive and streamlined manner. One way of tracking objects is with an electronic identification system.
One electronic identification system utilizes an RF transponder device affixed to an object to be monitored. An interrogator is provided to transmit an interrogation signal to the device. The device receives the signal, then generates and transmits a responsive signal which may identify the device. The interrogation signal and the responsive signal are typically radio-frequency (RF) signals produced by an RF transmitter circuit. Since RF signals can be transmitted over greater distances than magnetic fields, RF-based transponder devices tend to be more suitable for applications requiring tracking of a tagged device that may not be in close proximity to an interrogator. For example, radio frequency based transponder devices tend to be more suitable for inventory control or tracking.
Synchronization of a particular receiving device (e.g., the interrogator) of a communication system to the data signal being received is necessary to achieve optimal sampling of the received data signal. Optimized sampling of the received data signal minimizes error rates. In prior art analog communication systems, phase lock loops including loop filters and voltage controlled oscillators are typically used to align a clock with phasing of incoming data.
Some wireless communication systems communicate via digital data transmissions. Communicating via a digital format provides numerous advantages including encoding, various modulation techniques, etc. Optimal sampling of the received signal provides reliable reception of the data at the receive side of such digital systems.
Problems often experienced in this art include the monitoring of error such as separation of the sampling signal from the received data signal. Further problems include maintaining proper alignment of the sampling signal with the received data signal during reception of the entire data signal.
Therefore, it is desirable to provide a communication system which achieves the benefits of digital communication while overcoming the problems associated therewith.