Operational filter building block

A configurable operational filter comprising:

• a first voltage input terminal for coupling to a positive voltage supply;
• a second voltage input terminal for coupling to a negative voltage supply;
• a ground terminal for coupling to ground;
• and
• a plurality of 3-terminal operational filter circuits each coupled to said first and second voltage input terminals and to said ground terminal, each one of said plurality of filter circuits comprising:
• an input terminal for receiving an input signal from an input signal source,
• a first output terminal that provides a first frequency response in response to a first condition, said first condition comprising a resistor coupled in series between said input terminal and said input signal source, said first output terminal providing a second frequency response in response to a second condition, said second condition comprising a capacitor coupled in series between said input terminal and said input signal source,
• a second output terminal that provides said second frequency response in response to said first condition and that provides a third frequency response in response to said second condition,
• an operational amplifier circuit having an inverting input, a non-inverting input, and an amplifier output, said inverting input coupled to said input terminal, said non-inverting input coupled to ground, and said amplifier output coupled to said second output terminal,
• a capacitor coupled in series between said inverting input and said amplifier output, and
• a non-inverting integrator having an integrator input and an integrator output, said integrator input coupled to said amplifier output, and said integrator output coupled to said first output terminal;
• wherein:
• said first, second, and third frequency responses are each selected from the group consisting of low pass, band-pass, and high pass frequency responses.

A method of constructing a 3-terminal filter circuit to electrically filter an input signal from an input signal source, said filter circuit comprising an input terminal, a first output terminal, and a second output terminal, said method comprising:

• coupling an inverting input of an operational amplifier to said input terminal;
• coupling an output of said amplifier to said first output terminal;
• coupling a capacitor in series between said inverting input and said amplifier output;
• coupling an input of a non-inverting integrator to said amplifier output;
• and
• coupling an output of said integrator to said second output terminal;
• wherein said filter circuit provides:
• a first frequency response at said first output terminal and a second frequency response at said second output terminal in response to a first condition, said first condition comprising a resistor coupled in series between said input terminal and said input signal source;
• a third frequency response at said first output terminal and said first frequency response at said second output terminal in response to a second condition, said second condition comprising a capacitor coupled in series between said input terminal and said input signal source;
• and wherein
• said first, second, and third frequency responses are each selected from the group consisting of low pass, band-pass, and high pass frequency responses.

A method of configuring a 3-terminal filter circuit to provide one of first and second sets of filter responses, said first set of filter responses including low pass and band-pass responses and said second set of responses including high pass and band-pass responses, said filter circuit comprising an input terminal, a first output terminal, a second output terminal, an operational amplifier coupled between said input terminal and said second output terminal, and an integrator coupled between said second output terminal and said first output terminal, said method comprising:

• coupling a first resistor in series between said input terminal and said first output terminal;
• coupling a second resistor in series between said input terminal and said second output terminal;
• and
• coupling one of a third resistor and a capacitor in series between an input signal source and said input terminal, wherein coupling said third resistor provides said first set of filter responses and coupling said capacitor provides said second set of filter responses.