Monolithic HBT active tuneable band-pass filter

An active band-pass filter which compensates for resistive losses that may exist with passive circuit components, said filter comprising:

• a passive filter circuit having an input and an output;
• and
• a negative resistance circuit coupled to the band-pass filter for generating a negative resistance so as to compensate for undesired resistive losses, said negative resistance circuit including;
• a three terminal device having a first terminal connected to the passive filter circuit for providing the negative resistance to the filter circuit;
• a coarse tuning circuit having a diode and a voltage input that is selectable for coarse tuning the negative resistance applied to the passive filter circuit;
• and
• a fine tuning circuit having a voltage input that is selectable for fine tuning the negative resistance applied to the passive filter circuit.

A tuneable negative resistance circuit for producing a negative resistance, said negative resistance circuit comprising:

• a bipolar transistor having a base, a collector and an emitter;
• an inductive shunt coupled to the collector of the bipolar transistor;
• an output coupled to the base of the bipolar transistor for outputting a tuneable amount of negative resistance;
• a coarse tuning circuit coupled to the emitter of the bipolar transistor, said coarse tuning circuit having a diode and a selectable voltage input for providing coarse tuning of the negative resistance;
• and
• a fine tuning circuit coupled to the emitter of the bipolar transistor, said fine tuning circuit having a selectable voltage input for providing fine tuning of the negative resistance.

A method of generating a tuneable negative resistance for a band-pass filter to compensate for resistive losses, said method comprising the steps of:

• providing a passive filter circuit having an input and an output;
• providing a negative resistance circuit having a transistor with a base, a collector and an emitter;
• generating a negative resistance at the base of the transistor;
• adjusting current flow through a diode which is coupled to the emitter of the transistor so as to provide coarse adjustment of the negative resistance;
• and
• adjusting current flow into the collector of the transistor to provide for fine tuning of the negative resistance.