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Dynamic Bandwidth Control

Dynamic Bandwidth Control refers to the use of feedback to control the communication bandwidth of a system. More specifically, in RFID a steady state powering field is required onto which a communication signal is modulated. The feedback allows the steady state signal to be supported by a highly efficient resonance, whereas the smaller modulation signals are controlled to give a fast response and high speed communication that would otherwise be prevented.

The picture shows an implementation together with the Self Adjusting Resonance, where a feedback path has been added between the resonance amplitude and the stimulus signal, Vs. This feedback path acts to keep the resonance amplitude constant over the timescale of the modulation. As such the circuit responds immediately to any load modulation, which is now registered through the level of power input into the system.

Dynamic Bandwidth Control breaks the link between the dynamics of the circuit at modulation frequencies and those for a slowly varying powering signal. This has particular application in full-duplex RFID, where communication and power functions are carried out simultaneously.

Some beneficial results are summarised below that are described in more detail in Applications.

Power Efficiency

This technology opens up the use of highly efficient antennae for RFID, which has a direct benefit on the power drain of the reading process. A natural application is the hand-held reader where battery life is an important consideration.


Range is improved in two ways. Firstly, increased efficiency means that the energising field may be increased for a given power budget. Secondly, the task of demodulating the small communication signal is made easier because the of the low steady state loss. The power required to sustain the energising field is reduced and the relative amplitude of the load modulation is increased.

Further information available on request and detailed in Applications.


Cambridge Resonant Technologies Ltd. 2007