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Self Adjusting Resonance

The Self Adjusting Resonance is so called because the new resonant circuit naturally adjusts to any stimulus frequency over a designed band, independent of the efficiency level. An example is shown comprising a conventional resonant circuit with an additional MOSFET and a second capacitor.

When a waveform is stimulated in the resonance, the MOSFET is turned on for a fraction of the full duty cycle, depending on the amplitude of the resonance and the constant gate voltage Vg. Here the MOSFET is being used as an analogue element, charged through the inductance of the antenna - this  gives efficient operation without switching losses and high frequency noise. Any frequency within the following two limits will cause the circuit to 'resonate':



Once the circuit is adjusted to the stimulus frequency, the amplitude of the resonance is adjusted through Vg; for example, as Vg is reduced to negative voltage the amplitude of the resonance ramps up. Control can be either external or via feedback from the resonance amplitude. 

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

Resonance Alignment

The task of aligning two narrow resonances to transfer power or information is simplified. Now one or both may be made to operate over a fixed band, with overlapping bands the only necessity. 


Detuning of a conventional resonance by the environment (metal, temperature, etc) will shift the operating band of the resonance. However, provided the band still encompasses the target operating frequency, normal operation will still be possible.

Component tolerance

Similar to detuning, frequency shifts resulting from component variation at manufacture will have no detrimental effect on operation if the target operating frequency is still encompassed.

Multi-band operation

In some cases multiple frequencies of operation are required, for example when EMC licensing bands change across country borders. This may be accommodated by the width of the operating frequency band.

Phase Noise

The Self Adjusting Resonance tunes to the stimulus, Vs. This may be driven directly from a highly stable source, such as a crystal oscillator, with a very low phase noise. Excellent read range in RFID applications may be achieved with this arrangement.


All these properties come with no major cost overhead. In fact, savings are expected through the relaxation of component tolerance at manufacture.

In summary, the self adjusting resonance breaks the conventional limit between bandwidth and efficiency. Moving away from a classic linear resonator provides a whole host of attractive attributes that will improve the performance of many RF products.

Further information available on request and detailed in Applications.


Cambridge Resonant Technologies Ltd. 2007