Patent ID: 7257504

Claim:
In the production of an RF ID tag that receives and stores energy from an interrogator signal and sends a responsive signal on a transmit frequency back to the interrogator, a method for efficiently tuning and assuring accuracy of the tag's transmit frequency in responding to an interrogator, comprising: in manufacture of a series of tags on a wafer, only roughly setting the transmit frequency to a gross frequency range for all tags, by measuring a characteristic of a circuit component in the tag that affects transmit frequency and roughly tuning based on this characteristic in a testing phase of manufacture, at the point of application of the tags to products or product containers, fine tuning each tag's transmit frequency over the air by sending an interrogating signal within the gross frequency range to the tag and detecting a response from the tag, measuring the frequency of the response, determining a frequency adjustment amount for each tag, and sending a further signal within the gross frequency range to each tag to set bits in a non-volatile element of the tag circuitry to adjust the tag substantially to the desired tag transmit frequency, and applying a plurality of the tags to products or containers, at the point of application.