Negative-resistance circuit and active filter for millimetre wave frequencies

An active filter which includes:

• a plurality of negative-resistance circuits;
• and
• a plurality of coupled resonators, wherein each negative-resistance circuit has an output terminal which is operatively connected in series to a one coupled resonator to form a silicon based microstrip bandpass filter configured for use in the millimetre wave frequency band ranging between 30 GHz and 300 GHz, and wherein each negative-resistance circuit includes:
• only one transistor having three terminals;
• an inductive element in the form a distributed constant transmission line which is connected to a first terminal of the transistor, the inductive element operatively serving as a Radio Frequency (RF) choke to connect a first power source to the first terminal of the transistor in order to bias the first terminal while suppressing Radio Frequency (RF);
• a first capacitive element which operatively bypasses a second power source, connected to a second terminal of the transistor, in order to shunt high frequencies;
• a second capacitive element which capacitively couples the output terminal to the first terminal of the transistor;
• and
• a capacitive feedback circuit which is configured to feed a signal from a third terminal of the transistor back to the first terminal.