Reflecting modulator circuit comprising a negative impedance amplifier

A de-modulator circuit for de-modulating a binary phase shift keyed signal, comprising:

• a modulator circuit including a negative impedance amplifier operable for reflecting and amplifying a signal applied to the amplifier;
• and
• switching means for switching the amplifier between two reflecting states having impedances in the two reflecting states selected such that a phase of a reflected and amplified signal switches by substantially 180°.

A transponder tag, comprising:

• a modulator circuit including a negative impedance amplifier operable for reflecting and amplifying a signal applied to the amplifier;
• and
• switching means for switching the amplifier between two reflecting states having impedances in the two reflecting states selected such that a phase of a reflected and amplified signal switches by substantially 180°.

A transponder tag, comprising:

• a negative impedance amplifier configured to reflect a received signal;
• and
• a switchable biasing circuit configured to bias the amplifier in a first state wherein the amplifier reflects a first signal having a first phase, the biasing circuit further configured to bias the amplifier in a second state wherein the amplifier reflects a second signal having a second phase that differs substantially from the first phase.