Canonical lowpass filter with digitally programmable cutoff frequency settings using current followers

A method for assembling a second order low-pass canonical filter, comprising:

• forming a first stage by:
• connecting a current source (Ii) in series with an input terminal of a first programmable current division network;
• connecting a first single output terminal current follower in series with the first programmable current division network;
• connecting a first three output terminal current follower circuit in series with the first single output terminal current follower;
• forming a second stage by:
• connecting a second programmable current division network in series with a negative output terminal of the first three output terminal current follower circuit;
• connecting a second single output terminal current follower in series with the second programmable current division network;
• connecting a second three output terminal current follower circuit in series with the second single output terminal current follower;
• and
• generating a low pass filtered output current (I0) at the negative output terminal of the second three output terminal current follower circuit,
• configuring the three output terminals of each of the three output terminals of the three output terminal current follower circuits to have a positive feedback terminal, a negative feedback terminal and a negative output terminal,
• forming the positive feedback terminal by connecting a slewing node of a first op amp to a positive input terminal of a second op amp, wherein the positive feedback terminal is a slewing node of the second op amp;
• forming the negative output terminal by connecting the slewing node of the first op amp to a positive input terminal of a third op amp and connecting a slewing node of the third op amp to a positive input terminal of a fourth op amp, wherein the negative output terminal is a slewing node of the fourth op amp;
• and
• forming the negative feedback terminal by connecting the slewing node of the first op amp to a positive input terminal of a fifth op amp and connecting a slewing node of the fifth op amp to a positive input terminal of a sixth op amp, wherein the negative feedback terminal is a slewing node of the sixth op amp.

A method for low pass filtering a current signal, comprising:

• injecting, by a current source, an input current (Ii) into a first stage circuit including an input terminal of a first programmable current division network having a first digital control input (β1);
• generating, by the first programmable current division network, a fractional output (β1Ii) of the input current (Ii);
• transmitting the fractional output (β1Ii) to an input terminal of a first single output terminal current follower;
• generating, by the first single output terminal current follower, a first buffered fractional output current;
• transmitting the first buffered fractional output current to a first three output terminal current follower circuit in series with the first single output terminal current follower;
• generating, by the first three output terminal current follower circuit, a first stage output current (Ii);
• transmitting the first stage output current (Ii) to a second stage circuit including an input terminal of a second programmable current division network in series with a negative output terminal of the first three output terminal current follower circuit;
• generating, by the second programmable current division network, a fractional output current (β2Ii) of the first stage output current (Ii);
• transmitting the fractional output current (β2Ii) to an input terminal of a second single output terminal current follower;
• generating, by the second single output terminal current follower, a second buffered fractional output current;
• transmitting the second buffered fractional output current to an input terminal of a second three output terminal current follower circuit in series with the second single output terminal current follower;
• and generating, by the second three output terminal current follower circuit, a low pass filtered output current (Io) from a negative output terminal of the second three output terminal current follower circuit.