TUNED RESONANT CIRCUITS

摘要

We describe a circuit block for a resonant circuit, the circuit block having a pair of connections for connection of the circuit into the resonant circuit as a capacitor, the circuit block comprising: a first, non-linear capacitor, said first, non-linear capacitor having two different values of capacitance dependent on a value of a voltage of a resonant signal on the non-linear capacitor; a power supply circuit coupled to said non- linear capacitor to provide a power supply for the circuit block; a plurality of second capacitors each coupled to a respective second capacitor switch to enable a said second capacitor to be switched in or out of parallel connection with said first, non-linear capacitor; and a tuning control circuit powered by said power supply, coupled to said second capacitor switches, and having an input to sense an amplitude of said resonant signal; and wherein said tuning control circuit is configured to control said second capacitor switches to successively switch said second capacitors in or out of said parallel connection with said first, non-linear capacitor dependent on said amplitude of said resonant signal until said first, non-linear capacitor has substantially a single one of said two different values such that in said resonant circuit said circuit block then appears to behave substantially as a fixed value capacitor. Embodiments of the invention are particularly useful in RFID tags.